• 5055CElevitch
  • Designing homegarden agroforest, Hawaii
  • Picking shade-grown coffee.
  • CI0A1404CElevitch
  • DSC00618CElevitch
  • DSC00793CElevitch

  • DSCN4706CElevitch

  • IMG 0040CElevitch
  • IMG 0250CElevitch
  • IMG 4104CElevitch
  • MG 48032CElevitch
  • S7B8240CElevitch

Subscribe to The Overstory

Much of the emphasis for a planting project is placed at the beginning with seed selection, nursery development, and outplanting. Unfortunately, the project manager often reduces his efforts after the seedlings are in the ground. Given the high risks during this period of establishment, such reduced efforts could prove disastrous to the stand.

Once planted in the field, seedlings no longer have the safe nursery environment. Instead, they are subject to several natural and human-caused hazards. Establishment thus becomes a period of protecting and tending the tree crop. In addition, establishment also determines how the tree develops for the remainder of the stand's life. Stands that have a vigorous, hazard-free start are more likely to develop into vigorous, healthy plantations. Those stands that have to compete with vegetation and other factors will have a slower start and may even fail.

This bulletin, the fourth in the World Bank "Forests and Forestry" series, describes management techniques used to reach plantation establishment, or when trees begin to dominate the site. Developed specifically for anyone involved with forest tree planting in the field, this bulletin gives a broad overview of preferred methods to ensure a rapid start and survival of the plants during the first few years after planting. It also includes preliminary silvicultural techniques to ensure stand quality.

Bulletins one through three in this series deal with seed supplies, planting stock and site preparation, respectively.

Sustainability is the goal

Newly planted stands can be damaged by many factors including adverse weather conditions, insect pests, disease, fire, wild and domestic animals, and people. The amount of risk from each cause varies with environment and location.

One of the more difficult situations to assess occurs when exotic species are planted untested in new environments. There is the chance that native insects or diseases may readily adapt to and destroy the exotic host. In such instances, the planter should prepare a small trial of the species before committing to a large-scale operation.

Other potential causes of damage can be identified early on through a site assessment (See Bulletin No.3, Site Analysis and Outplanting.) With this knowledge the operations manager can prepare remedial measures to reduce or prevent these occurrences.

Aside form identifying the hazards, the manager must also assess the cost-benefit ratio in identifying solutions. Total protection against all risks will prove too costly. Any potential profits from the stand would be eliminated by excessively high investment in protection. Also, in some cases physical protection measures cause social antagonism, such as impeding migratory routes. In this instance, other approaches are needed.

Thus, plantation managers must weigh the compromises and accept some degree of risk. In some cases, it may prove infeasible to establish a plantation at a given site.

Protection Is Essential

Tending the trees after planting creates favorable conditions for both the plants' survival and to stimulate a healthy, vigorous growth. Tending operations keep the plants from being suppressed by natural vegetation and protect them from other potential sources of harm such as animals, insects and disease. Generally these operations include a wide range of treatments including access control, soil and nutrient management, pest management, and so forth.

Animal control takes various forms

Animal damage can be caused by smaller animals, such as rodents, and larger animals, like cows, deer and elephants. Left unprotected, seedlings may be subject to browsing and trampling by both wild and domestic herds. Domestic animals, such as goats, pose an especially severe problem.

However, several means are commonly used to protect the plants. Control may be done by physical barriers, or by removal of the offending animals. Physical barriers include fences, walls, thorn hedges and ditches or a combination of any two or three of these. Fencing is often the easier means to install, but is an expensive option.

When protection against smaller species is desired, a wire-mesh enclosure can be used. The lower part of this type of fencing should be buried to prevent animals from burrowing underneath. Experience in many countries, however, has shown that wire fencing is often stolen and is therefore useless for long-term protection.

Plantation managers should also note that when fences are used, they can restrict community access to other areas otherwise available for free-range grazing. Migratory patterns, too, may be interrupted.

There are many instances where land appears to be severely degraded and therefore ideal for forest plantation establishment; yet in certain seasons these degraded sites are critical grazing areas for domestic or sometimes wild animals. Such factors must be taken into account as alternative arrangements will need to be made.

In areas prone to animal browse, a chemical repellent can be applied to young plants to discourage grazing animals. In the U.S., such products as Deer Away™ or Plant Pro-Tec have been effectively used to discourage large and small animals from browsing small trees.

The treatments typically have a strong repellent odor or taste and provide a quick, effective deterrent. However, the compounds last for only a short period and must be reapplied frequently if the problem continues. The method is best suited to smaller plantations as it is usually applied by manual rather than mechanical means. But one drawback is that such products are rarely available in developing countries.

For individual stems, protective staking or cut thorn bushes can help discourage goats or other animals from eating the seedlings during the first few years. Some companies market "stem guards" of various materials. These devices are favored for urban planting, particularly to protect trees planted along new roads.

In extreme cases, poison baits can be effective in controlling some incursions of specific animals. Various poisons can be used next to the seedlings or directly in the animal burrows. These compounds are usually applied in the form of poison-soaked grains such as wheat or oats. In the U.S., ORCO brand Gopher Grain Baits and Field Mouse Plus are examples. In developing countries, many local products have been used by farmers to protect their agricultural crops.

Extreme care must be used when using poisons to prevent harm to humans and non-target animals. Poisoned grains especially must be kept distinctly separate from food storage areas.

Controlling unwanted vegetation

Unwanted vegetation or weeds interfere with the development or survival of young plants by competing with them for sunlight, water, space and nutrients. In addition, a thick ground cover such as grass not only hinders nutrient uptake, but may also harbor harmful animal pests, which can girdle and destroy the small plants. Grass swards lose water very quickly at the onset of dry seasons or dry spells, significantly affecting the soil moisture of the upper soil layer, which will affect tree growth.

The objective is to reduce or remove this vegetation to promote better growth and development of the planted trees. In general, the intensity of the weeding operation should be done at a level that effectively encourages establishment at a reasonable cost. Also, the types of treatment should not be so severe that it degrades the site through soil or nutrient loss.

The intensity and type of treatments will vary according to four main factors: labor costs, tree species, spacing and vegetative density. Typically, species less tolerant of competing vegetation will require a more intensive weeding. However, some shade-tolerant species can withstand the shading effects of weed growth. In such cases it may not be necessary to do an intensive weeding, thus saving time, costs, and labor. Also, a limited weeding may benefit some specific plants by allowing the vegetative cover to protect them from drought, sun scorch, or desiccating winds. Vegetative cover can also reduce erosion and improve moisture infiltration.

Furthermore, as a general rule the smaller the tree, the more frequently weeding is necessary. Treatments are typically done for the first two to three years after planting, depending on how long it takes for the trees to be competitive on the site.

This timeframe also highlights the importance of planting stock quality (see "Forests and Forestry" Bulletin No. 2. Often, small, good quality plants raised in root trainers will outgrow larger poly-bag plants, thereby reducing weeding costs.

Foresters use thinning practices, described later in this bulletin, to manipulate stocking levels for weed control. Increased stocking per hectare at the time of planting will promote early crown closure and reduce weeding frequency; but there is a caution as a greater stocking may lead to increased competition among trees.

If a narrow spacing (2 square meters or less) is used, early thinning will be needed to permit tree growth while maintaining site control.

Care must be taken because not all species respond in the same way. For example, most eucalypts will not recover from early competition. This characteristic had a serious effect in Haryan State in north India. Farmers planted at one-meter spacings, which resulted in massive production of small-sized trees flooding the market and significantly lowering the selling price.

Had better spacing been used, the farmers would have had a greater chance to market different sized products.

Narrowing spacing can also cause a permanent reduction in growth rates where sites are deficient in some nutrients such as phosphate.

In terms of the third factor, vegetation density, planters can expect heavier weed growth on the more fertile sites. On sites with a light vegetative cover the goal is to keep the vegetation down to allow a more homogenous growth permitting a quicker establishment of the site. Conversely, a dense vegetative cover can suppress and kill newly planted trees. In this case, the goal is to reduce or eliminate the cover to increase plant survival and maintain an adequate number of trees for establishment.

Weed suppression methods include trampling or beating down the vegetation, or cutting it back either manually or by using machinery. When warranted, weed removal can be done by cultivation or by the use of herbicides.

Manual cultivation, done with hand implements such as a hoe, is quite effective, but is very labor intensive. Mechanical cultivation, when possible, calls for equipment like that used in agriculture.

Aside from eliminating weeds, cultivation can increase rainfall infiltration in the short term and reduce soil moisture losses. Cultivation can, if properly timed, also make a considerable growth difference in areas with a significant dry season.

Depending on the need and required intensity, weeding may be total or partial. Partial methods include spot weeding around the plants or line weeding, which follows the planting rows. Whenever possible, partial weeding is preferable as it minimizes site disturbance.

When weeding in especially heavy vegetation, it is common practice to stake seedlings that are hard to see to prevent accidental cutting of the plants.

Herbicides are also used as a removal method. These compounds are typically applied as a granular mix or liquid application. But note, the planter must carefully follow instructions for any required mixing and for proper application. Strict adherence to recommended usage is absolutely necessary to prevent harm to nontarget plants and especially to humans and animals.

One preventative measure in weed control is the use of cover crops. The type of crop selected, however, should not interfere with the growth of or access to the tree crop. A more thorough discussion and example of cover cropping is provided in Forestry Technology #3 , Site Analysis and Outplanting, available from The World Bank.

Closely spaced Acacia mangium outpaces imperata grass

A fast-growing South Pacific acacia is showing promise of breaking the hold of unyielding imperata grass. The tough, spreading grass has claimed many hectares of former forested areas, turning them into wastelands.

The tree, acacia mangium, "seems to be shaping up as a potential new tool for tropical reforestation," said Noel Vietmeyer in a recent concept paper. "Seedlings planted directly into this pernicious weed (imperata) shade it out and create a forest within three to five years." This is because imperata has a weak link--it cannot tolerate shade.

Beyond this exciting discovery, Vietmeyer goes further, explaining that the tree can eventually transform an imperata site back into its original productive condition. For instance, on former mangium lands in Sabah, a mangium forest now has native vines, shrubs, and ground covers growing under the shade and protection of its canopy.

Furthermore, "The soil is improving with the leaf litter," says Vietmeyer. This improvement includes the nutrient exchange created by mycorrhizal fungi and nitrogen-fixing bacteria.

Insect and disease prevention and control

Trees in natural stands are generally in balance with native insects and diseases. Problems occur when the natural balance is upset. One example is the introduction of an exotic tree species that is not adapted to endemic pests and diseases.

In another case, monoculture plantations can be vulnerable to widespread damage if a virulent pathogen is introduced and remains unchecked. For example, American southern pines planted in some provinces of China are being severely infested by an accidentally imported mealy bug which has no significant parasites in China.

The pathogen in such cases can easily move among the host trees uninterrupted and, if the organism's life cycle is short, its population may quickly attain epidemic proportions.

Despite this natural balance, healthy trees are sometimes attacked, especially in years of heavy infestation. Like the trees, both insects and fungi have their own pathogens with which they are usually in balance. If this balance is upset, the tree pathogens can cause a great deal of damage. Furthermore, few practical controls are available for most fungal and viral diseases of forest plantations.

To counter potential hazards, preventative measures are the first line of defense. The best precaution is to plant species that are resistant to, or tolerant of, the prevailing insects and diseases and are suited to the site's climate and soils. Afterward, proper tending operations that promote a healthy, vigorous growth of the plants are a must. Otherwise, the risk of damage by pathogens increases if the trees are weakened.

Plantations of mixed species also will help prevent widespread infestations. Typically, insects and diseases are specific to their host species and are not likely to switch species. Mixed plantations may be either composite stands or alternating sections of trees, which act to block the spread of pests or pathogens.

Even with the best prevention, attacks will occur. In this case, plantation managers must promptly investigate the cause and identify its origin. The life cycle is studied to determine at what stage in development the pest is most vulnerable. Once the pest is known and located, mechanical, chemical, or biological control measures can be taken, targeting the weakest link in its development chain. Good managers set up systems to monitor levels of pests and are ready for immediate action should any imbalances appear.

In newly planted sites, prompt removal and destruction of affected trees may be enough to stem the pathogen's spread. Preferably, the infected plants should be piled and burned to ensure a thorough eradication. Burning may pose a problem, however, if it is a viral or fungal pathogen. In this case, burning can aerially disseminate the spores or resting bodies.

Mechanical control is also an option. This involves the physical removal of the pest, which is possible if the insect is large enough and is caught early in the infestation. Use of traps may also be a possibility. Or, if alternate hosts are present, their removal will assist in stopping the spread. And, where the invading insect resides in the topsoil or leaf litter, these areas can be raked or tilled to interrupt the development cycle.

A chemical insecticide or fungicide also can be applied to check the advance of damaging pathogens. These compounds are applied as liquids, dusting powders, or mists. They may be applied using portable sprayers, blowers, or even squirt bottles for limited applications. In Asia, products from the ubiquitous neem tree (Azadirachta indica) are extensively used against pathogens.

However, any chemical applied should be used in strict accordance to the directions to prevent misapplication that could cause further damage to the stand, upset the pathogens' own equilibrium or, worse, pose a threat to human health.

Biological methods include the use of insect predators, parasites, or diseases of insects. It also includes the option of releasing sterile populations, which hinders reproduction of the organism. The advantage of biological controls over chemicals is a reduced risk of toxicity to nontarget plants and animals. However, biological controls are highly species specific and may cost more than chemical controls depending on the location of the stand and type of pest that is to be controlled. Management should liaise with the nearest research laboratory dealing with forest or agriculture pests to check on biological control possibilities.

The threat of fire

Fire is a particular threat during the dry season, but should be of concern in all but the wettest months. Farmers often burn areas to promote new growth for their cattle, while in many Indian states forest is burned to encourage development of young "tendu" leaves, which are used locally for making cigarettes (beedis).

However, simple measures can be taken by plantation managers to assess, prevent and control fires when they occur and there will be no serious damage if burning is properly controlled.

Assessing the degree of fire hazard involves a simple check of four factors: air temperature, relative humidity, wind speed, and fuel buildup. Dry conditions and strong winds expose the site to its greatest fire risk. Fires started during these periods can quickly burn out of control.

Many villages and communities periodically burn vegetation as a common practice. Fire prevention for plantations should be a main consideration in such areas. Methods to reduce the chance of fire include reduction of the ground level vegetative fuel source, controlled burns, and firebreaks. Reducing the fuel source can be done through either cultivation of the soil or cutting and chopping the grass and weeds. Burnable materials can be removed between rows or around each plant.

Firebreaks provide a direct barrier to ground fires and allow access to the plantation for maintenance or in case fire does occur. Main firebreaks are kept entirely free of vegetation. They should be laid at right angles to the prevailing winds.

Plantation managers must also consider the fire threat from both within and outside of the plantation. A full perimeter break will reduce the risk of outside fires, while intermittent breaks will stem the spread of fire from within the stand.

In addition, firebreaks should be engineered to allow proper drainage, thus preventing undue soil erosion. Also, the design and layout of access roads is important for protection as mentioned in Site Analysis and Outplanting.

Greenbelts, too, can be planted as a fire retardant border to the plantation. The use of vetiver grass is one example. Historically, in some areas of the United States, large stands of old timber were protected for centuries by small patches of shrubs and small trees, which acted as barriers to fires frequently set by Native Americans.

When feasible, periodic controlled burning can be used to reduce the vegetative fuel source. Controlled burns require appropriate weather conditions including light winds, some ground moisture, and mild temperatures and most of all careful planning and supervision. Otherwise, there is potential the fire will spread beyond the designated area. In the case of dense vegetation, complete removal should be done by successive burning. Removal in a single operation might cause too intense a burn, creating a hazardous condition which may burn out of control.

In areas prone to frequent fires, plantation planners should consider planting fire-tolerant species.

Even with the best preventative efforts, fires will occur. Fire needs heat, fuel, and oxygen to continue. Take away any of these three ingredients and the fire will stop. This means that during hazardous periods, a team of fire fighters will be needed on some form of standby to take rapid action on any identified fire.

When fires ignite, fire fighting is often limited to whatever materials can be found on hand. It is therefore best to be prepared by having appropriate handtools stored nearby. For instance, small ground fires can be extinguished by beating the lead of the fire with branches, wet blankets, or by throwing dirt on it with shovels in a fan-like motion. These actions cut off the oxygen supply.

Also, firelines can be made rapidly by a team of workers who, working in a single line, use handtools to scrape the earth. The fireline, which is cleared to bare mineral soil in the approaching path of the fire, contains the fire's spread. For small ground fires, the line only needs to be about 50 cm wide. Wider lines should be dug for hotter fires or where wind is a consideration.

When the fire is contained within the fireline, it can then be extinguished. The area must be watched until the fire is absolutely out. Many fires thought to be dead have restarted after being left too early.

Human-caused hazards

Hazards created by humans on newly planted sites can take many forms. However, these risks are often due to careless rather than purposeful action. Increased fire hazard from traditional field burning, noted above, is one example. Other factors might include unlawful trespass or unknowingly herding animals across the site.

Plantation managers might avoid these potential problems through good communications and involvement of local communities; foresters sometimes face problems with this because of their earlier policing role. If villagers are made partners in the potential benefits of a stand, they will more likely take an interest in the stand's protection.

To encourage long-term care of the plantation, some type of incentive program can be established to encourage villagers to care for the trees. A food for work program is one example. Participants in the planting program are compensated with food for work given during each stage of the planting and tending operations.

Possibly the most effective method, however, is to ensure that those involved have direct benefits from the plantation they are protecting in terms of the intermediate and final yields. For instance, forest village programs in Thailand provide community services, product marketing, profit incentives and transportation as a means to create agroforestry programs.

In each of these approaches consistent support is required throughout the project, both to ensure the project's success and demonstrate the potential of reforestation or afforestation efforts.

A checklist for safe pesticide applications

Used properly, pesticides--including herbicides, insecticides and fungicides--can effectively control unwanted vegetation, insects and fungi. Misapplication or inappropriate use, however, can endanger the crop, or worse, human and animal health.

Specific recommendations for local treatments are beyond the scope of this bulletin. The types of chemicals to use and specific circumstances under which they should be used are too numerous to list. However, if the forester determines that chemical control is an appropriate response to unwanted vegetation, insects, or disease, then he should seek appropriate guidance from either a manufacturer's representative or other qualified applicator.

The compounds should not be selected and used based on advice from third parties, or from sources only vaguely familiar with their usage.

The forester should follow basic precautions when using these chemicals:

  • Know the chemicals you are using and read the container labels thoroughly before application. Additional information should be available for most materials. Be certain the chemical is appropriate for the target species, type of site and desired result. Never use unlabeled or leftover compounds as this practice may prove disastrous or even fatal;
  • Use safe application methods. Be sure that conditions such as wind and ground moisture are favorable to application. Wear appropriate protective clothing, such as coveralls and impermeable, unlined gloves and boots. Nitrile gloves are best; latex gloves are useless. Also avoid wearing leather gloves and boots as these will absorb the compounds. Use soap and water to wash any exposed skin areas thoroughly after application;
  • Rinse and dispose of the chemical containers properly. Never wash equipment or containers near freshwater sources such as lakes, wells or streams. Also, dispose the rinse water properly, away from freshwater sources. Puncture or crush the containers to ensure they are not reused for food or fodder storage, or other purposes. Make sure they are emptied thoroughly. Also, triple rinse tanks and spray equipment;
  • Keep good records of the application noting location, date, time of day, wind speed and direction, temperature, and type of chemical used;
  • Prior to application, properly store the chemicals by keeping the containers upright in a cool, dry, protected shelter. Make sure they are well away from food sources and inaccessible to children and animals. Never store the chemicals in empty food or beverage containers.

Plantation Surveys

The post-planting period is an ideal time to establish sample test plots in the stand to monitor stand development. Monitoring preferably should continue through the entire rotation. Ongoing surveys help chart the stand's progress and assist in making early detections of potential problems. For example, remedies can be more effective in the early stages of an insect or disease attack, as opposed to battling the problem after the pests have become established. Of course, the main purpose is to be continually aware of the condition of the tree crop.

Through the survey, or stand exam, foresters have developed techniques to review tree and non-tree characteristics. Tree factors include growth, distribution, species, and survival rate. Other items might include signs of insect or disease damage, vegetative growth, and animal damage. These technologies should become part of any planting project, whether large or small.

In carrying out a survey, it is unnecessary to examine each tree in the entire stand as this would be cost prohibitive. Instead, a properly prepared sample survey of the site will accurately reflect the condition of the stand.

In designing his survey and choosing sample plots, the manager must keep potential bias to a minimum. For example, just sampling the edges of a stand, which are more accessible, will not give a true picture of the stand as a whole.

To get an accurate reading, the distribution of sample plots must be uniform throughout the stand. However, if the stand has variable conditions, such as flat ground, streams, hills, or other distinct site characteristics, then each section should be sampled separately, or stratified. Separate tally sheets should be kept for each stratified section so that separate estimates can be made if so desired.

Systematic sampling using circular sample plots is preferred in areas that are familiar to the forester and for which maps are available. Circular plots are easy to measure because a single measurement, the radius, is used to locate each plot's perimeter.

If a map is unavailable or the total size of the area is unknown, then a systematic strip inventory would be appropriate. This method divides the area into strips of equal widths. In most countries, the common width of a strip is 20 m (sometimes one chain). Strip lengths will usually vary because of irregularly shaped borders of the stand. Also, the strips should be layed at right angles to the drainage pattern.

Field tallies

For his field work, the manager can design a standard form that lists the desired survey traits. The form can have boxes to check off the various factors, making compilation easier once the survey is complete.

Typical factors include:

  • number and species of trees, heights, diameters;
  • notes on gaps in the stocking levels;
  • tree mortality and apparent causes;
  • amount and type of vegetation present including brush and grasses;
  • signs of animal presence and animal damage;
  • signs of natural site disturbance such as flooding, wind damage, or erosion.

In addition, if permanently marked sample plots are used, the plantation manager can gauge the quality of various seed sources. He can monitor such factors as growth, form, and vigor, given that other factors are constant among the seed lots.

Such records can help reduce the amount of experimentation from one rotation to the next.

Siting sample plots in a stand

Basic measures must be followed when preparing a survey to ensure the sample plots adequately reflect the true condition of the stand. Otherwise, the readings will be inaccurate, which could lead to inappropriate or wasteful management decisions.

The inventory design depends on several factors including topography, composition and variability of the stand, skill of the survey personnel, and the time and funds available for the work.

Simple systematic random sampling using fixed circular plots is a commonly employed method that is also easy to use. Circular plots have the advantage because a constant radius can be used to measure the plot area. Typical plot sizes used in the United States and Scandinavia range from .01 ha. to .1 ha. The smaller plots are suited to stands with small-sized trees.

A map of the area should be drawn and fixed spacing between plot centers is chosen, for instance 20 m. Using this interval, the forester can then select a starting point in one corner of the stand and lay out a grid using columns and rows. Preferably, the sample lines should run diagonally to the planting lines to provide a better cross section of the stand. In this manner, the plots are systematically distributed resulting in a homogenous sampling.

The number of plots selected will depend on the size of the area and the starting point location. Typically, a five percent inventory is used, though a lower intensity survey may be used if the stand appears homogenous in its makeup.

On this basis, the forester can make the requisite calculations:

Ap = PA

n = Ap/a

P = a/BL


A = total stand area

Ap = area of the stand that will be measured

P = equals intensity of inventory as a decimal %

a = area per plot in square units of B and L

n = number of plots

B = spacing between plots on a line in a given unit

L = spacing between lines in same units as B

For example a 5 percent inventory on a 50 ha. site using .1 ha. plots would require 25 sample plots (n = Ap/a).

Young Plantation Management

With proper tending and protection, trees should dominate the site within at least the first five years after planting and even earlier in the tropics. At this point, the trees have essentially become established and are ready for the preliminary phases of silvicultural treatments. These include thinning and pruning. Fertilization is another option, but should be applied before crown closure (See box).

Precommercial thinning

Thinning essentially reduces the number of trees on site to allow more growing space for those remaining. The goal is to reach the optimum spacing for mature trees to maximize the desired products or end use.

For most species the sale value of wood increases significantly with tree size and a suitable thinning regime will guarantee the largest number of the biggest trees possible.

Thinning also results is a more uniform distribution of the crop trees throughout the stand. If stand is not thinned, trees will become crowded, restricting their development and growth.

Some species, notably eucalypts as mentioned earlier, will not respond to thinning if left in competition too long. For pulpwood production, such species are established at their final stocking, which eliminates the need for thinning.

The operation is also an opportunity to remove undesirable plants including weed trees and trees that are diseased, infested, misshapen, or in poor health. Removal reduces the risk of spreading disease or insect infestations. Climbing vines and other threatening vegetation might also be eliminated at this time.

There is no general set age during which thinning should take place. Timing the activity will vary according to species, spacing of the plants, and the quality of the site. As a general rule, thinning is timely when tree branches touch or nearly touch, almost creating a thicket.

Plantation managers should consider three factors for a thinning operation: thinning intensity, cycle, and type. Intensity is the amount and frequency of tree removal. In some cases, thinning may be done in more than one operation over a short period. This temporarily retains some trees to maintain the protection of the crop trees and helps avoid the risk of wind damage.

The thinning cycle is the number of years between each thinning operation. In addition, the type of thinning has two strategies. Low thinning removes the slower growing and suppressed trees and is often referred to a "hygienic thinning." Conversely, crown thinning keeps the more dominant trees, thus favoring the better individuals. In all cases thinning cycles must relate to the crop growth for its most valued end-product.

Initial pruning

Pruning is the removal of branches to a height as far as can be reached. It is generally done when the stand is a decade old. Again, correct timing depends on the species and growth rate.

Pruning benefits the stand by adding value to timber crops by creating more clear, knot-free wood. The operation also reduces fire hazard by eliminating a fuel source and improves access through the stand.

The forester must ensure that workers cut branches as close to the stem as possible. Cutting can be done either manually with hand saws or by using power saws. Special long-handled pruning saws are available for higher pruning without climbing. Moreover, the activity should take place during a dormant season or slow growth period.

Furthermore, not all trees need to be pruned, or need to be pruned to the same general height. Decisions on what to prune should be made based on the type of species or the desired products. Some species may rapidly self-prune after crown closure, thus saving the effort and associated costs.

Other species may not respond well to pruning as they may require a larger percent of live crown. In any case, trees that are pruned must have an adequate percentage of live crown remaining to support the tree. Trimming too much can weaken the tree, thus slowing growth and making it vulnerable to disease or insect attack.

Fertilization quickens growth, corrects deficiencies

Fertilization can be used to either enhance the stand's growth or to amend the soil to correct any detected nutrient deficiencies. Treatments should be done early in the establishment phase, soon after planting. This is the point at which young plants can most use a growth spurt. Also, crown closure in a developing stand could inhibit proper application if the treatment is put off for several years.

Trees require an adequate dose of essential elements for proper growth and development. Lack of these may cause stunted, slow and less than optimal development.

Suspected deficiencies will likely show in the foliage as discoloration, deformation, or dieback. Field tests and lab analysis should be used to support initial suspicions. Elements most often in short supply are nitrogen and phosphorous. In addition, micro-nutrients are often overlooked, but can be extremely important, especially on degraded sites.

Before deciding to fertilize, the forester should complete a cost-benefit review. Benefits of fertilization include: allowing normal tree growth on marginal sites; increasing growth rates, which give the plants a better chance at survival; and permitting a quicker establishment. Costs include labor, materials, and transportation of materials to the site. Also, the forester should consider the presence of nitrogen-fixing species, which could negate the need to fertilize or reduce the application levels.

Application can be done manually by hand, by machinery such as tractors, or, in sufficiently large projects, by aerial spreading. Also, timing of application is important. For example, application without adequate rainfall may result in leaf burn or damage to the plants because of high salt concentrations in the soil.

This bulletin was originally published by The World Bank/AGRNR.

Author Contact:

by Norman Jones
1 Bradfield Avenue, BRIDGEND, Mid-Glam CF31 4HL, United Kingdom
Tel [44 16560] 656726; Fax [44 1656] 768369;
e-mail: njones18@compuserve.com

More than ever, reforestation and afforestation projects worldwide are expanding at a tremendous rate. FAO surveys indicate an increase in planted area from 18 million ha. in 1980 to 44 million ha. in 1990. Much planting takes place in areas that exhibit a broad range of site qualities. However, many sites are have been degraded by inappropriate agriculture, exploitation and, particularly, excessive grazing. Forests are rarely planted on top-quality sites as these are typically reserved for agriculture. As a result, forested sites range from serviceable to severely degraded. They may be characterized by poor drainage, thin soils, steep slopes, salinity, or previous heavy use.

Usually, there is little that can be done to alter or improve a given project site; but nonetheless, the forester can be aware of potential problems -- and opportunities. The forester must learn to differentiate sites that can be worked with from those that are marginal and others that must be avoided entirely. By recognizing a site's limitations, the forester can better direct his limited resources toward optimal site preparation to ensure both desired production and long-term plant survival.

This bulletin, the third in the forestry series, addresses the specific needs of the field forester. It provides some basic measures to guide the forester in analyzing and preparing a site for outplanting. In addition, it outlines the requisite steps for developing a successful outplanting operation.

(Bulletins Nos. 1 and 2 describe how to collect good seed and methods for growing quality nursery stock).

Site Analysis

The forester must understand the site's capabilities and limitations both to ensure proper establishment and because of the long-term investment in tree growth. He can gain this understanding through an analysis of the site's properties. The analysis is best completed prior to collection of the nursery tree seeds in order to confirm the selection of species. In addition, the analysis must be as thorough as possible. Otherwise, decisions based on incomplete information or guesswork will greatly increase the chances of error. A thorough analysis examines four main site properties: soils; site biology; climate; and physical characteristics.

Soil is a key element

Soil is the main indicator of a site's tree growth potential. The soil's physical properties determine the flow and retention of ground moisture and either enhance or hinder proper root development.

The forester should examine the primary soil properties including texture, depth, organic matter content, and pH. He can chart these properties on a soil map of the area as each is explored. Texture is determined by varying combinations of sand, silt and clay and influences the rate at which water and oxygen move through the ground. Optimum texture is essential for root growth enabling trees to take up nutrients and water. A high clay content in the soil inhibits moisture retention and proper root development. Such soils are subject to sealing and surface crusting when exposed to raindrop impacts. Light, sandy soils tend to lose moisture quickly, yet permit rapid root development. Sandy clay loams provide the superior medium for moisture and root growth, but are only found on the best sites.

Texture and depth together determine how much ground moisture can be stored for tree survival through the dry seasons and growth during the wet seasons. Depth alone also affects a tree's ability to anchor itself and influences the total amount of available nutrients. Furthermore, areas with shallow soils should be carefully noted as root development will be hindered on these sites. Simple test holes can be dug with an auger to discover any heavy clay layers or compacted layers or "pans" near the surface. Such layers will restrict rooting and infiltration of rainwater. Soil profiles can also be viewed at nearby road cuts or from ant mounds because ants bring up the subsoil. Other soil properties that are important, but more difficult to measure, include organic matter content and soil pH.

Determining soil texture by hand

A simple test can be used to identify soils in the field. Take a small, damp soil sample and rub it gently between the thumb and forefinger. The feel of the soil will indicate its texture and type.

Individual sand grains can be felt and seen in sandy clay loams. When squeezed the sample will form a fragile cast that breaks easily. These are the preferred soils. A loam soil will feel somewhat gritty, yet fairly smooth. It will form a more durable cast when the sample is squeezed. Clay soils are entirely smooth and can be squeezed into long, flexible ribbons that will not readily break. These soils must be avoided as they will inhibit proper root development.

Possibly one of the easier methods of soil texture analysis is to take a sample and place it in a cylindrical glass container (a measuring cylinder is ideal but tall jam jar or wide mouth bottle can be used) and fill the container with water. Vigorously shake the container and place it to stand upright on a horizontal surface. Heavy material such as gravel will sink to the bottom, next sand, then clay and finally silt. Organic matter will probably float on the surface of the water. The layers can be measured and expressed as percentages.

Acting as a sponge, organic matter promotes better moisture retention and reduces surface evaporation. Because of this, the top organic layer is an important zone for initial growth of small outplanted trees. Unfortunately, in many sites, the topsoil which contains most of the organic matter is lost and residual organic matter is low. Testing for the presence of organic matter is simple; estimating the organic matter volume is more complex, requiring a laboratory analysis. To test for the presence of organic matter, put a few drops of hydrogen peroxide on a small amount of soil in a narrow container. Organic matter is present if the hydrogen peroxide bubbles and foams. In addition, the strength of the reaction relates to the amount of organic matter present.

Soil pH is a measure of the soil's acidity. Although it is not always necessary to test pH, the forester must be aware of certain species' sensitivity to the pH level. For example, many leguminous trees are pH sensitive. Some simple methods such as litmus paper are available for measuring pH in the field. However, these results should be checked against a laboratory analysis to ensure accuracy. With the above soil information, the forester can rank the suitability of sites for planting.

Ideal sites will:

  • have a sandy loam textured soil that is deeper than 50 cm;
  • have an organic matter content;
  • be neutral or slightly acidic;
  • not form surface seals or crusts;
  • not have restrictive layers in the top 50 cm.

Conversely, some sites will have soils that are unsuitable for tree planting. These areas must be avoided as efforts will be better spent on sites with greater potential.

Vegetation, typography provide clues

Typography and vegetation also indicate site quality.

In terms of typography, extreme slopes and shallow depressions may present undesirable moisture conditions. Typically, as slope increases the soil becomes thinner and poorer, which is an inadequate planting medium. Shallow depressions may have standing water most of the year. As for vegetation, indicator plant species provide clues to soil type, pH, and past use. For example, Tristania spp. and Ericaceae are indicators of acidic soil conditions.

In other instances, some vegetation will grow only on sites that have been heavily degraded by intensive agriculture. Imperata grass is a case in point. This fire climax species thrives on nutrient-deficient soils and renders vast areas of land unproductive. Furthermore, barren sites must be examined to explain the absence of plant growth. Such an absence may be due to harvesting, overgrazing leading to soil compaction, or lack of seed. Or, the soil may be totally devoid of organic matter, which means the essential soil flora and fauna have been lost.

In any case, the factors that have hindered establishment of natural vegetation must be corrected prior to tree planting and establishment. Also, an inventory of current vegetation must be completed as native and non-native vegetation can pose a threat to tree establishment.

Site structure and use

The area's available space and current use are an integral part of the analysis. Available space is defined by designated boundaries, soil limitations, and typography. Drainage patterns, too, are a critical component of this analysis. Activities on adjoining lands should also be noted. In addition, if the proposed area is already in use under agriculture or rangeland, the question must be raised, "Will the forestry project improve, disrupt or displace the existing activity?"

In consulting with local users, the foresters must plan to either sustain the existing goods and services (fuel, fodder, food, medicine, etc.) or provide for acceptable substitutes (e.g., tree fodder for grass; cash income for food, and so forth). Also note, future earnings from plantation products are only attractive to those farmers and villagers whose immediate needs are met. Even industrial plantations may need to provide other products and services. For example, in China local people will collect all fallen leaves, needles and branches, leaving the site bare and disturbing the nutrient cycle unless their fuel needs are otherwise met.

Small projects have potential

Aside from the main project, the forester should consider opportunities to use small sites, such as those around the home, school areas, along farm borders, riverbanks, along streets or roadsides. Such sites can be planted easily and quickly. And such plantings often fit very well with the farming system.

Small-site projects might include small orchards, streamside gully buffers, intermittent field trees, wind and water erosion breaks around farmlands, or shade trees. The "four-a-side" tree planting in China provides an excellent example of success in this field.

Planting Dates, Timing

As in agriculture, weather is either the handmaiden of success or messenger of failure. Favorable weather conditions during planting season are often extremely short, which demands adequate planning and an uninterrupted work schedule.

Timing and duration of the planting period is critical to the project's success. Growth and preparation of nursery stock must be completed when favorable planting conditions near their peak. If seedlings are not ready on time, the duration of this favorable period is shortened, which jeopardizes the seedlings' proper establishment or survival. Conversely, delays in field preparation can have an adverse affect as a seedling's vitality is significantly reduced when kept too long in the nursery.

Soil moisture is a key

One key indicator used to determine the optimum planting period is available soil moisture. Good planters monitor soil moisture and only plant when it reaches an adequate level. In areas where soils are severely compacted, planting during the season's first rainfall may not be the best choice as these sites may have to absorb the first several rains before enough soil moisture is available. In fact, early rain on compacted sites is often lost due to surface run-off. This loss can be overcome with suitable site preparation such as plowing along contours, deep ripping, hole digging, etc., to reduce the speed of run-off and increase water percolation into the soil. Planting dates may also be influenced by several other factors, such as soil condition or species requirements. In another instance, the selected species might be better planted in a dry season planting with limited irrigation. For some areas, a dual rainy season permits an initial planting, with a follow-up planting during the second rainy season. The second season can also be used as an in-fill for areas where the primary planting failed to establish.

Determining these seasons can be done through consulting existing records or knowledge of the local people. Although dates will not be exactly the same from season to season, enough of a range can be determined to prepare a planting schedule of readiness. The dependability of rain can be estimated if records over a number of consecutive years are available. The information should be grouped into five-day periods and the mean and standard deviation calculated for each period over the years of records. Calculation of the variation (standard deviation divided by mean expressed as a percentage) will indicate the most reliable periods to target for planting (the higher the percentage the more the variation).

In preparing a planting schedule, the forester can devise a simple chart outlining the requisite tasks and projected completion dates. Aside from the physical requirements of the seedling stock, the forester must also account for the supportive materials and resources. For instance, the start of the rainy season is typically the more active time for field laborers. In this case, the manager or forester must be aware of local labor priorities and schedule accordingly.

Migration times and patterns of domestic herds must also be taken into account as animal hooves, and appetites, will quickly destroy a newly planted site.

Planting Site Preparation

All preparation at the planting site must be completed prior to the first rains or the prescribed planting dates. If preparation is delayed, the chances for seedling survival rapidly decrease.

Survival depends a great deal on gaining the maximum from optimum weather conditions, which may occur for only a short period. The forester must also project beyond his immediate tasks and be prepared for emergencies, mishaps, and unexpected delays. It is best to have a back-up system for the mandatory functions, such as transportation and labor, or for delays due to weather.

In addition, project success is further assured when the project scale is kept within the limits of available resources and materials. Small, lasting successes are preferable to large-scale operations that may be ill-equipped to handle high tree volumes that cover extensive areas.

Arrangements made on site

Landowners need to be aware far in advance of the desired planting schedule and required tools and materials that must be ready. At the site, boundaries must be clearly marked with posts or other types of suitable markers at frequent intervals. Fencing or animal barriers, completed beforehand, may be essential and can also serve as a border. Planting lines should also be established and marked. Typical plantations are designed in a straight-line grid. However, varying uses may require an alternate pattern, such as contour line spacing for terracing or land reclamation and staggered alternate line planting (on triangle).

Clearing planting spots for each tree to a 50 cm radius will save time and will mark individual tree planting spots. Clearing protects the tree from subsequent field burning and reduces competition from neighboring plants. Removal of undesirable plants also eliminates cover for potentially harmful pests, such as insects and small animals.

The unwanted vegetation can be slashed, chopped or burned. However, recent research suggests that it would be better to chip or at least scatter the vegetative debris on site because burning will cause an immediate loss of some nutrients and subsequent loss of others after the rains begin.

The planting holes themselves should not be pre-dug as this will dry out the mircrosite or, in the case of heavy rains, the holes may fill with water. Neither condition provides a suitable site for newly planted roots. In some countries the tradition is to dig fairly large holes as a means of site preparation then refill them, sometimes adding farm yard manure or topsoil from valley bottoms. These should be refilled and well consolidated before the day of planting.

Requirements for planting crews include transportation to the site, adequate shade for both workers and plants, ready access to clean drinking water, and proper tools. Tools include planting shovels or dibble bars and mattocks for clearing grass.

Access roads to the site must be well marked and deemed passable and in good repair. Designated alternate routes will provide an option should the primary route become impassable, a particular concern in rainy season weather.

Holding areas to receive the seedlings must be located and identified. Though temporary, these areas must still adequately shade the seedlings and protect them from roaming animals and desiccating winds.

One to two weeks prior to outplanting, a last site survey will help spot any problems or changes since the site was last inventoried. Final preparations can then be adjusted to accommodate any new conditions.

A final check of planting maps and records will ensure that the correct tree species will be delivered to the designated site.

Soil Corrective Measures

Rarely will the chosen site have the desired or adequate soil conditions necessary for a plantation program to reach its optimum production and survival. Soils often lack in nutrient content, ability to hold moisture, are too compacted, or are subject to rapid desiccation. In many cases, simple corrective measures will help counter such shortcomings.Several means can improve water holding capacity including use of windbreaks to slow evaporation and shading to reduce soil surface temperatures. The addition of surface organic matter, such as animal manure or leaf litter will further stem soil moisture loss.

Subsoiling, a deep breakup of the soil, at the planting spot is a highly effective practice that will encourage water infiltration and improve root development. Loosening the upper crust is also helpful. Note, however, that crust formation is caused by slaking and will re-occur unless the soil surface is kept moist, is protected, or is amended with lime or gypsum. Addition of compost is beneficial on many sites, particularly in the tropics and subtropics. However, in these countries compost is either difficult to obtain or is expensive due to its use in agriculture. In these cases, the compost must first be developed, maintained, and then transported to the planting site in large volumes. An abundant source of organic matter must also be close at hand for developing the compost mixture. The Berkeley method of composting is highly recommended. Cover crops, too, will act to stabilize the site, adding nutrients, organic matter and enhancing the water storage capacity of the soil. Depending on the selection, the crop may provide a cash income or short-term food source for humans or animals.

Nursery Preparation, Transporting

As preparations in the field are being made, equal emphasis must be given to the preparation of nursery stock. The nursery manager's goal is to have an adequate supply of seedlings ready to be outplanted when favorable conditions occur. (See Forests and Forestry Bulletin No. 2, Essentials of Good Planting Stock, for ideal nursery operations.)

Outplanting is a time of critical care for nursery stock because it is exposed to various conditions, transport and handling. Each step of the process, if not monitored carefully, can potentially damage the seedlings or allow desiccation of the plants. For both bareroot and container stock, adequate root-to-crown ratios must be maintained. Inattention to this detail will invite problems such as stems that are too large for their root structure, or the development of large root masses that will be subject to damage during outplanting. The root-to-crown ratio can be periodically monitored by exposing the roots of sample seedlings throughout the nursery. Proper ratios will vary by species. For containerized plants it is critical that a fibrous root system develops firmly, binding the potting mixture into a plug.

However, bareroot stock requires extra precautions. Root pruning is needed during development and growth, and so nursery operations must include undercutting. Roots that grow too deeply will be severely damaged during lifting. Although growing bareroot stock is an option, it is advisable to consider using root trainers, a system that uses rigid or semi-rigid containers with internal vertical ribs. The ribs direct root growth downward, which prevents spiraling, and the containers permit air-pruning of the roots, which controls root length. In effect, root trainers provide superior root systems that are ideally suited to the rigors of outplanting and stand establishment. This relatively new technology has proven highly effective wherever it has been applied.

Hardening off mimics field conditions

Hardening off is a measured reduction in watering just before outplanting takes place. Typically done over a four- to six-week period, the process readies the seedlings for the lower moisture conditions that can be expected in the field.

Watering can be limited to once daily, followed by watering every second day in the final weeks. However, care must be taken not to proceed too quickly as this might induce wilting or plant stress. If wilting occurs, water the plants immediately.

Just before removal and outplanting, the seedlings should undergo a final culling. Remove individual trees that are misshapen, poorly formed, diseased, too small, or of poor vigor. Also take out trees that are oversized. Culling must be taken seriously and based on measurements of seedling variation. The objective is to send to the field seedlings that are all of the same size and quality.

Again, care must be taken with bareroot stock. Use a shovel or other tool to ease the undesired tree from the ground. Pulling the tree out may damage the roots of neighboring seedlings.

Conversely, root trainers separate individual seedlings and separation is easy once the root plug has properly formed. This simplifies culling with little or no damage. If the planting site has adequate water supplies, the forester might consider lifting the plants out early and placing them in a temporary mini-nursery. The early move saves time and is helpful in areas where seasonal rains make roads impassable. Of course, the mini-nurseries have to be managed with great care.

In moving bareroot stock, the seedlings must be dug carefully to avoid unnecessary root damage. Once lifted, the seedlings are bundled in groups with the roots packed and wrapped in a water-saturated compost. In temperate countries, these bundles are often stored at low temperatures over winter prior to spring planting. Moving root trainer stock is much simpler. An adequate means of transportation is needed to keep the containers level and neatly stacked. Also, containers must be handled carefully to prevent crushing or damage to the seedlings.

How To Plant, Microsite Selection

Although the work must be done quickly during tree planting there is no reason for slackened quality. Subquality work at this point will negate all previous efforts, resulting in high plant mortality. Through whatever means possible, the forester must ensure that workers follow proper planting techniques and handling.

Proper spacing gives adequate coverage

Tree spacing, or trees per hectare, depends on the severity of the site, mature tree size, projected survival rate, available soil moisture, desired result, cover crops, intercropping, and so forth. For example, a plantation established on severe, dry sites calls for wide spacings, whereas windbreaks or live fencing demand a tight spacing.

Experiments over many years in the tropics and subtropics indicate that trees need between four square meters and nine square meters of space at the time of planting depending on their growth rate (faster means wider).

Early crown closure reduces weeding costs but care must be taken not to plant trees too closely as this leads to competition among trees for nutrients and water. This is particularly important with eucalyptus. Conversely, spacing trees too far apart may leave gaps in the crown. In addition, spacing requirements must be determined well in advance to ensure that an ample supply of seedlings is planned for.

During planting, workers will space the trees accordingly by following the pre-marked planting spots. To prevent error along the planting line, a pole of the proper length can be used as a measure between plants.

Microsite selection, clearing, moisture concerns

Workers must be able to judge the exact planting spot, or microsite, within the designated spacing. For example, a suitable distance should be kept from pathways to prevent damage by foot traffic. Also, extremely rocky spots, minor ground depressions, and shallow soils must be rejected. This may lead to plantation gaps, but cannot be avoided.

As noted previously, competing vegetation should be cleared away from each seedling for a distance of 50 cm. Other competing vegetation can be cut low to the ground and piled on the contour. This practice promotes improved soil and moisture conservation versus total site clearance, which causes increased runoff and erosion.

Rainwater catchment basins may be necessary in particularly dry areas to ensure seedling survival during the first years of establishment. These basins, built around each tree, divert the surface rainflow from a large area to irrigate the tree. But note, these may only be used in areas that have well-drained soils.

Soil between the tree rows should be cultivated to encourage water infiltration. Also, cultivation with dust mulching around individual seedlings will help lower surface evaporation.

The planting hole must be dug deep enough to allow straight root placement. Curling or bunching the roots is unacceptable; this practice will destroy the tree. Seedlings must also be planted to the root collar and the roots must not be exposed nor should they be planted too deeply. Backfilling the hole and tamping the soil against the lower roots will remove any air pockets. Water should not be applied before the tree is planted as this will also create air pockets around the roots. If the holes are too large, roots take too long to anchor in undisturbed soil, resulting in deformation of the butt-log.

When using bareroot stock, handle only a few seedlings at a time keeping exposure to sun and wind to a minimum. Seedlings not used immediately must be kept moist and under cover. When using poly-bag plants the bags should not be squeezed too tightly and should be cut cleanly from the entire root plug before planting.

Also, as they plant, workers will have a final chance to cull any seedlings that exhibit disease, poor form, or other signs of substandard quality.

A Case Study: Crops Keep Soil Problems Under Cover

Research is showing hopeful signs that legume cover crops can infuse renewed vigor into Thailand's weary forest soils. Long subjected to intensive use, the region's soils are exhibiting dramatic declines in crop yields and productivity. "Like most tropical soils, our Thai soils suffer severe degradation as a plant growing medium after cutting of the natural forest," said Tom Brummer, managing director of Thai Stora Agroforestry Co., Ltd. in Bangkok.

Problems are readily apparent. The soils become compacted and reduce water infiltration by as much as 60 percent. Organic matter and mineral content declines and erodibility increases. The overall effect has resulted in crop yield reductions of up to 40 percent over several years, with further reductions projected. Alarmed at the rate of soil degradation, Brummer's company took action. "It was decided that the best soil improvement and protection method may be by planting a legume soil 'cover crop' under the trees," Brummer said.

To be successful, however, the crop would have to satisfy several criteria. Brummer's team devised the following:

  • No climbing and strangling of plantation trees;
  • No negative competition for the trees;
  • No barrier to foot access;
  • No fire danger during the dry season;
  • Be able to suppress weed growth;
  • Be able to tolerate some shading;
  • Grow fast to occupy the site;
  • Be able to survive the dry season and regenerate afterward.

In searching for candidate species, the team procured legume seed both commercially and from naturally occurring sources within their own plantation. The goal was to discover those species best suited as a cover crop, rather than testing for dry matter production or soil nitrogen enrichment.

In all, nine species were tested. The first year's efforts were limited to small plots under two-year-old plantation stock. Building on these preliminary results, the team selected four crop species and planted these in larger "operation sized" areas across a wide range of tree age classes. Species not chosen were deemed too large or not vigorous enough in growth.

First-year results of the second elimination trial showed good survival during the dry season. Drawbacks of species not selected in the second trial included inability to resist weed invasion, slow initial growth, lack of commercially available seed, and attractiveness of the plant to grazing animals. The chosen likely candidate species, Centrosema pubescens, closely matched the given criteria, with the added advantage of readily available seed. From the tests, Brummer's team further concluded that although one species proved preferable, a species mix would be more effective in the long run. For future studies, the team hopes to expand its tests to include more potential species.

This bulletin was originally published by The World Bank/AGRNR.

Author Contact:

by Norman Jones
1 Bradfield Avenue, BRIDGEND, Mid-Glam CF31 4HL, United Kingdom
Tel [44 16560] 656726; Fax [44 1656] 768369;
e-mail: njones18@compuserve.com

The extent of the world land base that is being reforested or afforested is significant and is growing still. Unfortunately, several of these efforts are wasted in planting poor quality trees. While some problems are beyond the forester's control--poor weather, insect attacks, disease outbreaks, animal browse, and the like--others fall within the forester's influence. Two such areas are seed collection (which was dealt with in Forestry Technology #1 -- the previous issue of this Bulletin) and planting stock preparation and selection. Measures outlined in this bulletin provide basic guidelines that will help the forester ensure a cost-effective means of producing high quality seedlings.

A Measure of Quality

The basic goal of having quality seedlings is to achieve the best growth possible and have the highest amount of desired outputs. Outputs can be timber, food, fuel, fodder or other uses such as site improvement. Seedling quality is gauged by two factors: one, by the genetic make-up of the parent stock and secondly by the physical growth, which is influenced by the seedling's immediate environment (i.e., nursery conditions and practices).

Selection for desirable genetic traits takes place in the field at seed collection sites. When done properly, field selection will provide the best possible seeds, containing the desired inherent traits seen in the parent stock. Care in seed selection and collection will also reduce the amount of undesirable stock coming from physically poor or damaged seed. Aside from genetic traits, a seedling also displays physical traits including sturdiness, good form, health and vigor. Many of these traits, which are affected by nursery practices, are within the forester's control.

Benefits Outweigh Extra Cost, Effort

Nursery-grown stock requires investment in infrastructure, staff training and skilled management. The level of these costs relate to the type of nursery stock produced, species growth responses and the number of trees produced. But, the potential benefits of good nursery practices far outweigh their costs. For instance, properly developed seedlings stand a better chance of survival both in the nursery and when replanted in the field.

In the long term, quality stock will also produce a faster, higher return for the desired outputs. These outputs may include products such as fuelwood, building materials, industrial cellulose, animal fodder, erosion control, and soil and microclimate improvement. Given these benefits, seedling costs are a small portion of the end-product value of plantations. Conversely, slackened efforts at ensuring stock quality will result in lost opportunity throughout the life of the plantation. Low-quality seedlings will experience slow growth after transplanting and add to weeding and maintenance costs. In addition, the trees will be less able to resist disease and insects and will have smaller product yields.

Poor plant quality will result in uneven development throughout the nursery and increase costs through excessive culling needs. In addition, suboptimal quality will increase the risk of losing the seedlings, requiring a renewed effort or, at worse, cancel the project due to lack of adequate seedlings.

Common Principles

Regardless of the size of the tree planting effort, several common techniques can be applied to ensure the best planting stock quality possible. The techniques are applicable across a wide range of climate and soil variations.

The application of good practices must begin when the project, large or small, is planned and must continue through to outplanting in the field. In all cases, everything that can be done, should be done, within reasonable limits of time and capital constraints.

Seeking Optimum Growth

To ensure quality stock, a series of steps must be followed beginning with the planning stages and carrying through to outplanting in the field. Oftentimes foresters or nursery managers focus their efforts on only a few steps of the process. Under such circumstances, nursery stock may still grow. But the omission of any steps will slow the seedlings' progress and produce stock of suboptimum quality.

Such marginal results are unacceptable in light of the time and costs required to produce a forest crop. In fact, the best nursery managers take the trouble to visit field plantations and take pride in the way their plants have responded to the harshness of the real world. To ensure quality stock, a series of steps must be followed, beginning with the planning stages and carrying through to outplanting in the field.

Identifying Weaknesses

Lack of knowledge may be the greatest hindrance to producing consistent quality in growing stock. Indeed, due to the rapidly expanding planting programs, many foresters have never seen a truly high-quality seedling population. Small-scale projects that have minimal resources are particularly vulnerable to lack of proper information for nursery planning, management, operations, and problem solving. Such information voids may be further compounded by inexperienced labor or lack of supervisory skills. Again, because of the lengthy time frame involved between field planting and harvesting, there is little room for error or omission in nurseries.

Producing the Best Possible Plants

The forester must keep the primary objective in mind: to grow the best possible uniform seedlings, for the highest plantation outputs, for the least possible cost. Of course, cost and seedling quality must be carefully balanced. The best plants are derived from consistent nursery practices that produce uniform growth throughout the seedling crop. Such practices include all the elements involved in nursery operations--watering, soil mixes, root pruning, weeding, and the like. The demands of planting schedules alone leave little room for inconsistencies. For example, if seedling growth is not carefully monitored, so that abnormalities can be detected and corrected, seedling development may vary widely.

As a result, some stock may be underdeveloped when planting season arrives and the opportunity for using the stock will be lost. Moreover, it is a fallacy to believe increased watering or fertilization schedules can correct the inadequacies of genetically poor stock that appears underdeveloped. A nursery manager can compound the problem if he keeps these underdeveloped seedlings for later use when "they are big enough." This is wrong. Never plant seedlings which have been held back for extra time.

What does good planting stock look like?
The prime targets are plant uniformity and health. Uniformity means there are few differences from plant to plant in height, stem thickness, the number and relative size of leaves. Health refers to both color and damage. Leaf and stem colors are often characteristic for a species and damage should be easily identified because parts may be eaten by insects or discolored by fungi.

Careful Planning is Crucial

To be successful, nursery establishment and operations must be well coordinated efforts that flow smoothly from one step to the next. Each step relates to the plants' needs in order for them to produce the best possible growth when outplanted. Proper planning and plant monitoring are vital to that effort. Without a clear plan to guide him, the forester can quickly fall behind schedule if unforeseen factors demand his immediate attention.

The following sections detail a three-part planning guide to raising quality seedling stock. The sections review container types, planning the nursery, and organizing its operations.

A case for root trainers

For decades tree nursery managers and organizations worldwide have relied heavily on plastic pots or poly-bags because of their low cost, apparent simplicity and convenience. However, this simplicity can be deceiving because management of poly-bag plants requires intensive supervision and care. Such containers have inherent problems, which may not appear in out-planted trees until several years after a plantation has been established. Most notably, poly-bags hinder proper root development, including lateral roots, and tend to produce spiraled roots. The result is restricted growth, poor resistance to stress and windthrow and, in some cases, early demise due to ensnarled root masses or pathogens. Poor management practices, such as improper potting mediums, uneven watering and lack of root pruning, further stress the plants.

One corrective measure is the use of root trainer systems. These systems use rigid or semi-rigid containers with internal vertical ribs, which direct root growth straight down rather than permitting spiral growth. The containerized plants are set on frames above the ground resulting in air-pruning of roots as they emerge from the containers. Equally important, the latest containers are designed to encourage lateral root development. The lateral roots exit the container and are controlled either by air or chemical pruning.

Studies have shown that root trainer-grown seedlings have more vigorous and rapid root growth than seedlings grown in poly-bags. Outplanting survival is greatly increased and, more important, long-term survival is ensured. Root trainer systems produce further benefits in simplifying nursery operations such as disease and insect control, transportation and handling, and monitoring and sampling. Also, the reusability of root trainer containers offsets their initial higher costs when compared to poly-bags. But note, when considering the root trainer system, the nursery manager should recognize that all nursery practices may need to be redeveloped to meet the container's use requirements. Root trainers are not simply a different type of container, but an entire cultural system that must be adhered to for success.

Nursery site selection, preparation

Depending on the type and duration of the project, tree nurseries may be either temporary or permanent. Temporary sites are preferred for small, short-term projects, such as establishing erosion control in a limited area or planting windbreaks for a set of fields. In this case, nursery construction can be done on a small scale using such disposable materials as cut thorn bushes for protective fencing. However, the same level of attention is required for the plants' needs regardless of nursery size.

Permanent nurseries supply seedlings for ongoing programs like area reforestation, commercial plantations, village shade trees, fuelwood plantations, or agroforestry. In either case, the forester or nursery manager must consider where the nursery will be located in relation to the total planting area. Ideally, the nursery should be built in a central location with easy access to the desired project sites. Other factors include access to roads for transportation of seedlings, people and supplies. An ample, reliable and consistent water source must be located nearby. And, if possible, the site should be near a settled area to have a source of workers, materials and for security.

The area should be level, or have a slight slope for water drainage. Basins or other low areas should be avoided as these will collect water at the low points and inhibit proper growth. Low areas also tend to have more insect and disease problems.

Site selection varies by nursery type

Different types of nurseries require different site selection factors. Bare-root nurseries need to be carefully located in suitable soils to provide for optimum root development and growth. Loose, deep sandy clay loam soils are preferred. Also, a system for proper drainage is essential in preventing root growth stagnation due to standing water. When faced with growing bare-root stock in poor soil areas, some measures can be taken. Poor soils may be too hard for water to penetrate, too sandy to retain water, or are nutrient poor.

Soil improvement includes loosening the soil either manually or mechanically to allow for better water penetration and absorption. Additionally, compost materials made from decaying vegetation and animal manure will provide nutrients and help keep the soil loose and aerated.

In comparison, containerized nurseries are easier to locate because the potting medium can be brought in from a number of sources. It can be either mixed on or off-site with the required ingredients.

A simple test for hand texturing soils

To identify soils, a simple test can be done using just a small soil sample that is squeezed between the thumb and forefinger.

A sandy loam soil contains much sand, but has enough silt and clay to make it somewhat cohesive. Individual sand grains can be felt and seen. Squeezed when dry, the sample will form a cast that readily falls apart. Squeezed when moist, a cast can be formed that will bear careful handling without breaking.

A loam soil contains a relatively even mixture of different grades of sand, silt and clay. It is somewhat gritty yet fairly smooth to the feel. Squeezed when dry, it will form a cast that can be handled quite freely without breaking.

When moist, clay soils can be squeezed into ribbons that are long and flexible. Such soils must be avoided as they will inhibit proper root development and moisture absorption.

Good nursery design improves workflow, production

Essential parts of the nursery layout include a water storage source and location with siltation facilities if needed, shade for young seedlings (and nursery workers), adequate space for nursery beds and pathways, driveways and turnaround areas, storage areas for tools and equipment, soil mix stockpiles, fencing, gates, fire buffers and clear areas.

When planning any nursery it is important to have a "materials-flow-chart" or plan indicating how materials enter the nursery, how they move within the nursery and how they leave the nursery. Basic materials are: water, tools, seed, containers, potting mixture ingredients, etc. In addition, the site should also have additional areas set aside for expansion if demand increases and for cutting orchards if vegetatively propagated planting stock is to be raised. For containerized nurseries, pots are best arranged on raised beds with side supports for the plants. However, if ground-level beds are chosen they should be of gravel or some free-draining material. Pots can be placed in rows of 12 to 15 pots wide, depending on pot diameter, or an easy arm's reach to the center of the bed to facilitate weeding and other operations.

However, as discussed in the previous section, the use of plastic pots, or poly-bags, is highly discouraged as several serious problems may arise. Such problems could place any project in jeopardy at the nursery stage or even a much later date. For best results, root trainers are the preferred method. Root trainers are more than just a simple container, but include an entire system that promotes proper root development and growth. When root trainers are used the beds can be raised well above the ground to facilitate aerial root pruning and easier growth monitoring.

This bulletin was originally published by The World Bank/AGRNR.


Author Contact:

by Norman Jones
1 Bradfield Avenue, BRIDGEND, Mid-Glam CF31 4HL, United Kingdom
Tel [44 16560] 656726; Fax [44 1656] 768369;
e-mail: njones18@compuserve.com

forest 400Why work hard to collect good seed?

In agriculture, collecting seed from superior parent stock has been practiced for thousands of years. This technique results in higher yields and environmentally durable plants. This concept, however, has yet to gain widespread acceptance in forestry practice. To maximize yields and quality of trees for plantations, agroforestry, and other uses, the following principles for collecting seed should be observed.

One program, two benefits

In forestry, as in agriculture, the quality of offspring plants improved populations will result if the seed used to produce them was collected from superior individuals, stands or orchards. Seed quality is measured in two ways. One, by the physical quality of the seed and secondly by the desired physical traits of the resultant mature tree. The benefits of using quality seeds, chosen from selected parent trees, are twofold: improved survival and greater economic returns.

Improved Survival

Seeds from healthy, well-formed trees provide greater assurance that resulting stock will have good form, survive and better resist stressed conditions due to marginal sites, frequent cutting, or harsh climates. These adverse conditions typically weaken all but the strongest trees, making them vulnerable to insects, fungi, parasitic plants, and diseases. More important, because of the long-term resource investment and land and labor commitment in forestry, high survival rates of good quality trees is a must. In agriculture, farmers can recoup their loses after a poor season, or even two. Trees, however, occupy a site for years. Therefore, any reduction in growth or quality from planting inferior stock represents a lost opportunity, which can be measured in time and capital, for as long as a tree occupies a particular site.

Higher product yields

For the second benefit, economic return, the investment in selection will be more than compensated for by higher product yields over shorter rotations. Better yields result in more building materials, higher fruit production and quality, faster fuelwood growth, and quicker and more prolific regrowth after lopping.

Simple measures are most effective

Effective seed selection can create success, even though sophisticated techniques may not be used. Any attention given to seed source will be a measured improvement over current practices. In addition, careful seed handling practices must be included as part of the seed collection program. Such practices include transport, seed preparation, handling, cleaning, grading, and seed testing. Disregarding these practices will result in damaged seed or allow the inclusion of unwanted or excessive amounts of foreign materials, which may hinder germination and plant production.

The following sections in this bulletin describe how to develop a system of proper seed collection and handling practices.

Where to get started

Planning the seed collection strategy

Too often in large planting programs the task of seed collection is an afterthought, typically left until the last minute and done hurriedly by unskilled or untrained labor while final nursery preparations are being made. Small-scale planters usually have access to left-over seeds from large programs. In either case, little consideration is given to seed quality, form, or location of the parent stock. Sometimes, to satisfy the requisite seed volume, nursery managers purchase bulked seed from villagers. However, villagers tend to collect from the nearest trees or stands, which generally include immature, diseased, distressed and otherwise inferior seed. And, if seeds need to be collected from the crown, villagers will choose the easy-to-climb trees, which are typically small and misshapen. Such trees would not normally be chosen as prime seed source candidates. Also, in some species a single tree will produce a large amount of seed in some years. Such a harvest may satisfy the bulk requirement, but would be genetically dangerous because only one phenotype is represented. This technique causes problems for both large- and small-scale planters.

Careful planning avoids wasted time, effort

Either approach, using untrained labor or collecting seed from a single tree, can be a critical mistake. Such practices often result in low survival, substandard trees, and a poor economic return for the time and work invested, for example, nursery and site preparation costs. Instead of an impromptu search or purchase from unknown sources, any seed collection, both large-scale and small-scale, should be a developed program of scheduled activities overseen by knowledgeable individuals. This is especially true for those involved in large-scale planting programs. Those involved in small-scale plantings can often request advice from nearby large-scale planters. These essential activities include selection of preferable parent trees; preparation of equipment including provisions for handling, transport, extraction, testing, grading, and storage; recruitment and training of workers and; seed sampling and quality monitoring. A timeline and workplan for the collection itself must be developed in conjunction with overall nursery operations. More important of these is the selection of preferable parent stock. This can be accomplished by an able person who can distinguish between desired and inferior seed sources. This person, in turn, can supervise field collection crews during harvest. Incorporating many of these activities often requires the level of funding available to large-scale operations. Nevertheless, even the small-scale planter should apply the principles as best possible whenever collecting seed.

"The choice of seed source is one of the most important decisions faced by the forest manager. An error in judgment can lead to crops with poor stem and branch form or prone to pests and diseases. Within the genetic constitution of the seed is the potential for either good or poor tree growth, and since even small increases in growth rate or improved timber quality can lead to a much enhanced return on investment, the advantages of using the best available seed from which to grow the planting stock are considerable." Hibberd, P.G. (Forestry Commission Handbook 6: Forestry Practice) HMSO London, 1991.

Genetics provides the basis for seed selection

Why is it necessary to collect only from certain preferable trees?

Tree improvement programs worldwide have shown that seed collected from trees with particular traits tends to produce trees with similar traits. One can correctly assume that if good parent trees are selected, then most of the resultant offspring will be of desirable quality. Yet despite this concept's proven value and wide understanding, it is seldom applied in the field. To correct this shortcoming, simple parent tree selection guidelines should be developed. These would identify the desired traits and specify the parent trees that reflect those traits. Such traits might include straight trunks, fast growth, and better form. These guidelines are normally met in national or company research programs, but following them will benefit all planters who are careful about the source of their seeds. The traits in turn are chosen to reflect the ultimate desired use of the tree, including building materials, windbreaks, shade, fuelwood, or erosion control. At the same time, these guidelines should not be made cumbersome. For the benefit of those individuals collecting seeds, the guidelines could be a condensed set of simple criteria. Indeed, immediate benefits can be derived from using even the most basic concepts, such as selecting trees of good form and vigor and avoiding trees that are poorly developed, diseased, dying, or are isolated from others of the same species. These simple methods should be applied to large and small programs.

Collection strategy includes area, number, and spacing.

While it is important to collect seed from the best parent trees it is also important to gather seed from several parent trees. Collecting seed from several parent trees assures a diversity among seedlings being planted. Whether the program is large or small, maintaining diversity is important and will help guard against pest epidemics. To obtain adequate diversity, seedlots should be collected from a number of trees within a species' range. Researchers have yet to determine an ideal number of trees per seedlot.

In plantations and along roads more emphasis should be placed on collecting from the best trees. In all cases care should be taken to collect seed from several trees representative of the best parent stock. Researchers have yet to determine an ideal number of trees per seedlot, i.e., those seeds that will be used in one planting. However, most agree that collection should not rely on only one or two individual trees. According to some sources, a minimum of 15 to 25 mother trees per bulked seed source is preferred. Furthermore, collection should cover a broad geography, including the environmental extremes at the edge of the range. Seed selected from a narrow sampling of trees should be avoided as this will limit genetic diversity. Keeping a proper distance between selected parent trees is also vital. During natural regeneration of some species, seeds fall near the parent stock. In time, inbreeding may occur, which will result in lower quality individuals. To reduce the chance of collecting a seedlot predominated by half-siblings, a 100-meter distance between collection trees of the same species is recommended. This practice is especially critical to species that are lopped or coppiced as a method of harvest and regeneration. The temptation to forego a minimum number and spacing strategy is perhaps greatest during years of abundant seed production. Here, a large seed quantities are available from relatively few trees. At such times, an even greater effort should be made to ensure genetic variety. Even better, abundant seed years can be opportune. When properly cleaned and prepared, seeds can be stored for several years. Stored volumes of good seed will help ensure supplies during leaner production cycles. Where possible, all large-scale planting programs should have at least two years' seed supply in storage. Conversely, leaner seed years present other challenges. During such years shortfalls will occur and the urge will be to collect for quantity, without regard to quality. If at all possible, seed collection during lean production years should be minimized.

Proper scheduling is vital to quality

Aside from genetic and site qualities, other considerations must be factored into the collection strategy. For instance, only mature seed from ripened fruits should be gathered. Harvest schedules must account for the different times at which fruits from various species ripen. Depending on species, maturation can last between two to six months. To help determine ripening, periodic surveys of the selected stands is suggested. Surveys should begin after flowering, as is the practice with cocoa. To prevent any false readings, specific sample trees should be marked and used throughout the process. The surveys will also serve as an early indication of the season's expected seed volume and quality. In addition, field surveyors can detect early infestations of insects, disease, or other seed predators. With such information, the harvesting strategy and schedules can be adjusted to accommodate any foreseen hindrances.

Take note of growing sites

Aside from desired end-use traits, the tree must adapt to its growing site. In particular, it must withstand periodic harsh conditions, such as drought, and be able to grow in poor soils. Physical traits alone may yield few clues as to site adaptability. Here, environmental distinctions may help.

The collection staff should note even the slightest variation throughout a species' range. Topography, soils, microclimate, associated vegetation, and man-caused factors such as perennial grazing may all influence how a species conforms to its surroundings. In overall location, a species typically grows best in the middle of its range and fares less well at the edges. However, seedlots should reflect all site variations, thus assuring that no one habitat is relied on too heavily. But some cautions are needed when sampling for habitat. When associated plants are used as site indicator species, one must discern between natural conditions and man-made alterations. For example, continual grazing can heavily degrade a site, even to the point where it changes the vegetative makeup. In addition, extreme dry or wet areas should be excluded if not within the normal bounds of a species' requirements. During collection of particular stands, efforts should concentrate on trees that comprise the stand's perimeter. These individuals produce better quality seed. Aside from natural areas, man-made stands should be reviewed carefully before selection as a seed source. For example, early reforestation efforts may have given little thought to seed collection, thus producing inferior parent trees to those found in natural stands. Or, the species planted on the site may not be well suited for the area. Whenever possible, historical data or records should be referred to for such stands.

A short list of collection tactics

    • Collect seedlots from between 15 and 25 individuals that are spaced at least 100 meters distance from any other collection tree of the same species.
    • Choose trees in vigorous health and avoid any that are diseased, suppressed, deformed, environmentally stressed, or in otherwise poor health.
    • Collect from trees that are well formed and either dominant or co-dominant in the canopy.
    • Avoid individuals that are isolated from others of the same species.
    • Harvest only mature seed from ripened fruits.
    • To ensure genetic variation, collect fruits equally from all parts of the crown--top, sides, and bottom--as these parts may have been pollinated at varying times from different sources.
    • Collect throughout a species' normal habitat, noting variations in site.
    • Man-made stands, including live fencing, plantations, or windbreaks, should be carefully reviewed as to their establishment before being selected as a seed source.

A field strategy. How to select good trees

Parent tree selection in the field is best done as a planned team effort coordinated by a trained person. This selection of preferred trees serves to eliminate errors that would otherwise be produced by last-minute collection efforts. In addition, a planned, timely program allows for the full use of available people and resources. Development of the collection strategy includes a series routine screenings of potential parent stock. The series is broken into three progressive phases.

Phase one is done well before the onset of flowering. Given simple guidelines for site selection and appearance, general laborers search for appropriate stands. Locations of such are recorded, along with general descriptive information.

Phase two involves technical staff. Here, the identified stands are reviewed for their potential as a seed source. The review includes analysis of the site makeup including soils and topography, species composition, volume and spacing, and age, size and health of the trees. Initial selections are made as to potential parent stock. These trees are marked for further study in phase three.

In phase three, trained professionals examine the marked individuals for a final selection. The trees are analyzed for their physical characteristics, including their form, branching, growth rate, dominance, crown cover, health, and any clues as to their seed productive capabilities. Before the final candidates are chosen, additional criteria are again considered. This includes the previous mentioned spacing preference of at least 100 meters between individuals of the same species. And, preference will be given to those trees located in the stand's perimeter. Finally, selected trees are marked and their location noted. Monitoring will increase as flowering begins and continue through the seed harvest period. Monitoring includes volume and quality of the seed as it matures, in addition to any indications of pest infestations including insects and disease.

Seed handling and preparation

Seeds are rarely taken directly from the collection site for immediate planting in the nursery.

Instead, they must first undergo a preparation that will ensure proper germination and help eliminate bad or damaged seed. Preparation includes all activities from collection to sowing. These activities cover transport, sorting, extracting, cleaning, testing, and grading. In addition, seed harvesting and sowing periods are often months apart, which requires adequate storage facilities. The facilities must protect the seed stock from the weather and intrusive pests such as animals, insects or molds. In some instances, proper temperature control may also be required. This is especially true if seed is to be kept over a number of years.

Handling in the field

Once the fruits are picked or collected, they must be transported directly for seed processing. Any lag time in the field could cause desiccation or predation by various seed pests. The seeds must also be well-protected from the weather to prevent excessive contact with moisture, which may prompt early germination. In addition, because of the variation in harvested fruits, handling techniques must flexible. Those in charge of collection must have adequate knowledge as to each species' requirements and limitations during transport. For example, while the hard coated seeds of most leguminous species travel well, other seeds are more fragile and require greater handling care.

Proper conditioning limits seed degradation

The nursery manager must have facilities readied for seed preparation at the time of collection. Such facilities should be located at the nursery site, thus eliminating the need for further transport before sowing. Seed extraction should occur as the fruits arrive from the field. Again, any lag between collection and preparation will cause the seed to degrade or spoil. Depending on species, equipment for both dry and moist extraction may be needed. Dry extraction requires appropriate sorting and drying areas, tumblers, and screens for sieving. Moist extraction calls for a method of macerating the fleshy fruits, followed by drying and cleaning of any remaining foreign materials.

In either case, all inert materials must be removed as these can result in poor germination or hamper storage ability. Also, the rate of drying and moisture content must be carefully monitored during the drying process. Seeds dried too quickly may become damaged. While small-scale planters may not have access to sophisticated equipment for drying and cleaning seeds, they should aim to remove as much foreign material as possible. After extraction, the pure seed is then graded. Grading helps ensure a more homogenous seed set, which in turn will produce more uniform growth in the nursery. Grading is done either by seed size, weight, or a combination of both. Actual seed size within the same species will vary due to a number of factors. The goal is to eliminate undersized, immature, or deformed seed. This usually can be done by hand if great quantities are not required. However, graders must be provided samples of the desired well-graded product to use as a guide. In addition to grading, seeds are tested for germination rates, and are examined for phytosanitary concerns and species purity. Using these factors, the forester must develop criteria for consistent seed certification. No matter how carefully done, collection efforts in the field will be nullified if inconsistent methods of grading and testing are used from one seed lot to the next.

Proper storage is essential

If the prepared seed is not used within a reasonable amount of time, adequate storage must be provided. As noted, most leguminous seeds store well in normal conditions, provided they are properly cleaned, dried, and protected. Such prepared, intact seed can be handled and stored without fear of damage. However, if storage is required for several years, special facilities, such as cold storage, may be needed for some species. On the other hand, if germination begins, different measures must be taken. Here, the seed ceases dormancy and begins to use stored nutrients for survival. At this point, its shelf life is drastically reduced. Thus, it is important to closely observe the condition of the stored seed and monitor it periodically to ensure the storage environment remains intact.

Why collect seed from several provinces?

Differences in how trees adapt to environments is often more important with a species than among species. There can be important differences in growth between seed sources from different geographical areas and environments. The areas and environments in which stands have developed through natural selection are call provenances. The growth, measured in height, in tropical hardwoods of the most vigorous provenances can be 30 to 50 percent greater than the growth in the least vigorous provenances. Unfortunately, there are very few tree species that have been adequately explored in their center of origin and studied in provenance and progeny tests on multiple sites, leaving much uncertainty about provenances which are intended to represent an entire species. Perhaps the most striking example of this comes form the use of Acacia mangium in Sabah, Malaysia, where ultimately thousands of hectares were planted from seed collected from one tree. As a result, growth rates of third generation were one-half those of the first generation.

This bulletin was originally published by The World Bank/AGRNR.

Author Contact:

by Norman Jones
1 Bradfield Avenue, BRIDGEND, Mid-Glam CF31 4HL, United Kingdom
Tel [44 16560] 656726; Fax [44 1656] 768369;
e-mail: njones18@compuserve.com