In (re)afforestation work we usually talk about the planting of trees. Lots of 'em. But there's a fundamental limitation in this ethic that planting trees is what we need to save the planet. We should be rather talking about planting forests. Until our planting site has in it the components of the Mother of all plantations - the climax forest system - the "trees" we plant will always be weak and prone to exposure, disease and drought. Could this be why in America the U.S. Department of Agriculture accepts an 85% mortality rate in its plantations on clear fell sites over 100 Ha?

Guilds and Diversity

This is illustrated by a tale of connections in the North American Pacific Coast Forests, between Douglas fir (Pseudotsuga mensezii), soil mycorrhizae and a certain Red Tree Vole. The vole was found to transport spores of the mycorrhizae, needed by the fir for its uptake of soil nutrients within the soil of these forests. On clearfell sites, the habitat of the vole was destroyed and thus it would disappear. As a result, survival of fir seedlings was severely reduced. These components survive together and benefit each other in a symbiotic association known in Permaculture circles as guilds. In design, we work to create guilds, or rather to place the right species in such a way that they can create themselves. This illustrates the importance of diversity in our plantations.

Soil life

Thus we are not just looking at planting trees, but accommodating the soil life which is the foundation of healthy biological systems, be they forests, wetlands or prairie grasslands. In one gramme of undisturbed forest soil there may be 1000 million bacteria. These are the life, the very creators of the soil and thus everything that grows upon it. They give the "productive capacity" of our soil. Roots of plants growing in undisturbed soils form associations with the soil microorganisms - the latter make nutrients available for the former, and the microorganisms gain carbon in particular. Up to 80% of Carbon fixed in photosynthesis goes into below ground processes. While this carbon is "lost" to the plant, it is not lost to the system, of which the plant is only a part. The soil organisms improve plant growth through effects on nutrient cycling, pathogens, soil aeration and water holding capacity. Giving priority to feeding and supporting the life in the soil makes caring for plants growing there a much easier task.

Succession

A further lesson from Nature we would be wise to apply is the principle of succession - the redevelopment of the climax system following disturbance. In forests, this may occur naturally in landslides or the toppling of aged trees, creating clearings in the forests. The human causes are well known - clearfell, livestock pressure, etc. In either situation, if allowed, Nature will re-colonise sites using biological systems specifically adapted to the situation. If soil is poor and soil moisture low, She will establish plants which can survive. These can be called "pioneer" ground covers, followed by pioneer shrubs and trees. Often they are nitrogen-fixing legumes, able to synthesize nutrients from the air when they're not available in the soil. Such plants have the chief purpose of preparing the ground for the next stage - covering and protecting the soil, giving natural water and nutrient cycles a jump-start, and thus giving species which would not otherwise have survived a suitable niche in which to thrive. This process continues, each stage leading to a more fertile one, where the ability for a greater range and diversity of species to thrive increases until the climax state is reached once more. Throughout this process the annidated nature of the system becomes evident, with multi-storey "stacking" producing crops and system yields in a vertical plane as well as the "conventional" horizontal system (as with mono-crops).

Limiting Factors

For vital growth of biological systems, such processes and conditions are dependent on a few crucial factors mainly in the soil surface areas - moisture, air (oxygen), organic matter, temperature, the presence of symbiotic relationships (Friends), etc. When any one of these factors is sub-optimal or missing, growth is impaired even if other needs are in abundance. All the irrigation in the world will not produce an orchard if there is no fertility in the soil, and vice-versa.

Total Yield

Medicinal herbs, spices, dyes, fibre plants, bee forage plants, root crops and wildlife habitat are all part of the total yield. In forestry often these "Non-Timber Forest Products" (NTFPs - thankfully they're not called "minor forest products" anymore) are ignored - especially when we're not treating our planting site as a complete ecological system.

Implication for design - in imitation of nature

So the simple planting of trees is thus changed to creating, or allowing, complex interactions based on what happens naturally. We design to imitate this because it's efficient - nature does it using only sunlight - and successful. Design is also about reducing the limiting factors for optimum productivity.

"Permaculture" is the direct application of the principles of ecology.

(Nature) in the design of sustainable human habitats.

Our designs need to incorporate as many as possible of the above principles when looking at forest plantations. We have a series of design options, for which we need to understand factors such as:

• natural characteristics of the plant species
• niches in time & space the plant occupies - is it a pioneer, shade loving, drought tolerant, fast to establish, light demanding, frost tolerant, etc
• size of the plant above and below ground (wide canopy, deep tap root, etc)
• companions to the plant - birds, insects, other plants, etc.
• human-used products of the plant

When we have an idea of such criteria, we select and place the elements to work together, satisfying human and ecological needs of the site.

Plants that integrate into complete forest systems:

We can then fit additional functions in and around our plantation with the following examples:

The conventional method of mono-crop planting at 2.5m spacing ignores all the opportunities of working with the diversity, succession and stacking principles of natural systems. Similarly, to plant climax-type trees at such spacing can be a waste when they'll need selecting anyway. The above design template allows for diversity, succession, stacking, rapid covering of the ground and quick production too. The latter is important for example when farmers are foregoing grazing needs by protecting the site - but within three to six months fodder can be harvested from the developing understorey. We certainly don't need to be afraid of over planting. Research shows that Gliricidia sepium can reach densities of up to forty thousand trees per Hectare (i.e. 50cm distance between plants) before biomass production is reduced.

Practical Planting

Experiments in Britain, North America and Nepal have illustrated the principle of needing to plant the system, not just the tree. Plantations where a couple of handfuls of forest soil (especially when from a mature tree of the same species) were placed in the pit in the root zone have showed over 50% better survival than those with no inoculant.

Options

This design is only used to illustrate the principles, however. There are countless ways of adapting the design according to needs of the site and user group.

Where sites are very poor or if the right planting materials, time, or labour is in short supply, then the establishment does not have to happen at the same time. We can start by broadcasting the pioneers, such as Artemisia, Sesbania, Crotolaria, Cassia, etc. and next year, following cut-and-mulching of these, establish the next layer. Eventually, the most valuable, long lasting climax species (which you've been growing yourselves in a local nursery in the meantime, of course) can be added.

Any tree species planted as seedlings will benefit from a nurse crop of pioneer/green manure/legume-type plants sown close around. We have used Sesbania, Crotolaria, and Cassia to do this - they grow quick (and will self-seed), so providing shelter on exposed sites (or a sun trap if planted in an arc open to the sun-side where sunlight is in short supply), as well as fixing nitrogen, and bump-starting the soil life processes.

The design can vary in terms of products over horizontal and vertical planes, for example layers of fruit at all levels (vertically), or clumps of fruit at mid-canopy level, fodder at ground level, timber trees at upper canopy level, etc. We can play with succession by cutting (thinning) to maintain clearings at ground level, thus a high degree of edge diversity around the clearing. So design varies as succession continues.

Agroforestry

Contour planting on bunds within cultivated fields (e.g. LEISA - low external input sustainable agriculture ; SALT - sloping agricultural land technology) are not excluded from such applications. The design is rather squashed into contour lines, horizontal planting distances can be reduced to leave up/down slope space for annual cropping systems.

Complexity, not Complications

So if you think this is getting complicated, imagine varying all these dimensions (horizontal, vertical, time and relationships) at once! This is the traditional way of forest farming - the Cavite (Philippines), Chagga (Tanzania), the Western Ghats (Goa, India) are living examples. In Western Nepal, the Raute (meaning "Lords of the jungle"), nomadic hunter-gatherers on the verge of extinction take it a step further - they just wander through natural forests, gathering what they need and not returning for up to nine years. They don't even have to plant!

Which just leaves one option, to merely protect a site and allow nature to do the rest. However, the above design principles allow us to create intensely productive systems for humans, thus taking the pressure off damaged forest areas, allowing them to exist for their own intrinsic value, and for the health of the Earth.

Teaching method

The principles and variations of plantation and agroforestry design are limited when taught in two dimensions. A fun way is to use an earth pile, and sticks of different length and thickness, from tall, thick sticks (climax trees) to short pieces of straw (ground cover layer). Students can mould landscapes according to their own situations.

References:

• Hart, Robert (1991) "Forest Gardening" Green Books
• Perry, D.A., & Amaranthus, M.P. (1987) "The Use of Mycorrhizal Fungi and Associated Organisms in Forest Restoration" In "Restoring the Earth"

Author Contact:

Chris Evans, Technical Advisor,
Jajarkot Permaculture Programme
c/o P.O.Box 10908,
Kathmandu, NEPAL
Fax +977 1 259833
email jpp@mos.com.np

Copyright 1998 All Rights Reserved

If You Can't Eat Them, Succeed Them!

How to get started in this thick mat of weedy trees? What to do about all the huge clumping grasses in the pineapple patch? How to manage this morning glory vine strangling the orchard? I have had a lot of questions come up in the course of working in permaculture in Hawai'i, for myself on my own projects and from people I meet who are working toward sustainability. Whenever I get myself into a muddle about how to handle weeds, I remember my weed motto: If You Can't Eat Them, Succeed Them!

The function of weeds on the farm

First of all, I have to keep in mind that if I am starting to worry about weeds, it is usually because the weeds are outrunning me, or running me over, on the road to farm improvement. After all, weeds take farm land in the same direction I want it to go: towards more diversity, resilience, and abundance. For example:

Weeds support diverse soil microlife

Soil microlife feeds off plants. The diversity of plants on the surface is directly related to the diversity of microflora in the soil. Weeds can contribute greatly to that diversity. Removal of weeds to bare the soil reduces diversity. It is very likely that there is important soil life or function being supported by some family of weed that has yet to be documented.

Weeds control erosion and conserve water

Bare ground loses moisture to the air on sunny days, and soil to erosion when it rains. A healthy groundcover of living plants will conserve moisture and prevent erosion, and weeds can be part of that groundcover.

Weeds provide insect habitat, and encourage birds

Butterflies, spiders, bees, dragonflies, praying mantis, ladybugs, and other insects need food and habitat to thrive. A variety of insects will also support birds. A healthy mix of insects encourages balance and reduces the chance of insect "problems."

Weeds are a source of food and medicine for people

Many plants that I used to think of as weeds are prized as nutrient-rich vegetables or medicinals all over the tropics. A few examples in Hawai'i (all escaped introduced species) include amaranth, portulaca, bitter melon, chayote, Spanish needle and gotu kola. Many of these tolerate drought or other harsh conditions far better than cultivated vegetables, and can be quite delicious.

Weeds provide food for crop plants

In the tropics, nutrients essential to crop plant health are primarily in organic matter, not bound up in the soil. Organic matter needs to cycle through the soil for nutrients to get to plants. Cutting weeds back and mulching plantings with them is a common practice with tropical farmers, and increases crop plant health. It is best to cut the weeds before they seed to keep the seeds from sprouting right next to the crop. Weeds also can be soaked in water in a covered container for about a week then fed to plants in a (smelly!) nutrient-rich liquid fertilizer tea.

Weeds are a source of food for animals

Animals can be integrated in the farm to do most of the weed resource management. For example, ducks are used for selective weed control, because they can often be trained as ducklings to develop a taste for some weeds, and will eat those first when allowed to range freely.

Succeed the weeds

So, having reminded myself that weeds are useful, particularly as food for soil life, people, animals, and plants, I can use them as a resource. But, what about when it looks like the weeds are eating the crop plants, and not the other way around? If I have a particularly vigorous weed enthusiastically encroaching on a plant I desire (for example, a bunch grass surrounding a young citrus tree and suppressing its growth), there is one thing I can do, short of abandoning my planting: play the weed's game. The name of the game is succession. I have to be more appropriate than the weed, and make the weed's job obsolete. In short, I succeed the weed.

The weeds are taking the land the same direction I want it to go, towards more diversity, stability, and abundance. It is counterproductive to focus on fighting weeds, since after all they have the land's best interest at heart. Besides, I can't win. They have been excelling in the process of succession for many more generations than I have.

In the natural process of succession, weeds establish where they find a place, usually in open or partially open conditions, especially on bare soil. They modify the environment, eventually making the area inhospitable (too shady, etc.) to more of their kind. Other plants come in who thrive in the modified conditions, and the process of succession continues until the ecosystem is more or less stable, usually culminating in a closed-canopy forest. Most of the plants that I call weeds are involved in the primary stages of natural succession. They are medicine for the soil, repairing it and revitalizing life.

Succeeding weeds is about stepping-up the process of succession. I don't try to stop or arrest the process the weed is involved in; I speed it up. For example, introducing fast-growing trees like nitrogen fixing trees can alter the environment, making groundlayer weed growth slow or even stop with shade. Filling the space with the trees and plants I want will leave less room for weeds. Some of the most aggressive weeds need full sun and low fertility to thrive; by increasing shade, organic matter and soil health they will disappear.

As a last resort, or in areas where the weeds are just too overwhelming, I may need to take a step back in the succession process. This may involve sheet mulching with a thick weed barrier once, baring the soil once, or even spraying herbicide to kill grasses one time. But I have to remember that this is a step back from the natural process of things, and the next step is the weed's turn. Unless I want to be involved in a tedious two-step (I remove weeds, they come back, I remove weeds, they come back) for the rest of my farming career, I need to take two steps forward immediately after taking the one step back. This means mulching and filling the space with appropriate plants (groundcovers, crop trees and other vegetation), creating a healthy system with no room and no need for voracious weeds to modify it. Using this approach in the case of the citrus tree, I hand-pull, smother, or herbicide the bunch grass once, mulch the tree, then introduce a living groundcover vine to fill the area where the grass was encroaching. I could at the same time interplant with shade trees, as citrus like a little shade and grass does not. Farming in the tropics does not need to be a routine; it can be an evolution, an upward spiral. That is how I know I'm doing it right; when it is easier for me with each passing season.

Take the weed's lead

When choosing plants and methods to succeed the weeds, I take my cues of what is needed and wanted on the land from the weeds themselves. Weeds are experts in the process of succession, and great soil indicators as well, so I always look to them to learn what is appropriate. By imitating and accelerating what the weeds are doing, everyone succeeds.

References and further reading:

• Pfeiffer, Ehrenfried E. Weeds and What They Tell. Bio-Dynamic Farming and Gardening Association, Inc. P.O. Box 550, Kimberton, PA 19442 USA.
• Facciola, Stephen. Cornucopia: A Source Book of Edible Plants. 1990. Kampong Publications, 1870 Sunrise Drive, Vista, CA 92084 USA.

Author Contact:

Kim Wilkinson and Craig Elevitch
AgroForester
PO Box 428, Holualoa, HI 96725 USA
Tel: 808-324-4427, Fax: 808-324-4129
www.agroforestry.net

Copyright 1998

Nitrogen Fixing Trees for Agroforestry

Nitrogen fixation is a pattern of nutrient cycling which has successfully been used in perennial agriculture for millennia. This article focuses on legumes, which are nitrogen fixers of particular importance in agriculture. Specifically, tree legumes (nitrogen fixing trees, hereafter called NFTs) are especially valuable in subtropical and tropical agroforestry. They can be integrated into an agroforestery system to restore nutrient cycling and fertility self-reliance.

On unvegetated sites, "pioneer" plants (plants which grow and thrive in harsh, low-fertility conditions) begin the cycling of nutrients by mining and accumulating available nutrients. As more nutrients enter the biological system and vegetative cover is established, conditions for other non-pioneering species become favorable. Pioneers like nitrogen fixing trees tend to benefit other forms of life by boosting fertility and moderating harsh conditions.

NFTs are often deep rooted, which allows them to gain access to nutrients in subsoil layers. Their constant leaf drop nourishes soil life, which in turn can support more plant life. The extensive root system stabilizes soil, while constantly growing and atrophying, adding organic matter to the soil while creating channels for aeration. There are many species of NFTs that can also provide numerous useful products and functions, including food, wind protection, shade, animal fodder, fuel wood, living fence, and timber, (see chart for specific species yields) in addition to providing nitrogen to the system.

Nitrogen: From the Air to the Plants

Nitrogen is often referred to as a primary limiting nutrient in plant growth. Simply put, when nitrogen is not available plants stop growing. Although lack of nitrogen is often viewed as a problem, nature has an immense reserve of nitrogen everywhere plants grow--in the air. Air consists of approximately 80% nitrogen gas (N2), representing about 6400 kg of N above every hectare of land. However, N2 is a stable gas, normally unavailable to plants. Nitrogen fixation, a process by which certain plants "fix" or gather atmospheric N2 and make it biologically available, is an underlying pattern in nature. (See box below for details on how nitrogen fixation works).

How to Use NFTs in a System

In the tropics, most of the available nutrients (over 75%) are not in the soil but in the organic matter. In subtropical and tropical forests, nutrients are constantly cycling through the ecosystem. Aside from enhancing overall fertility by accumulating nitrogen and other nutrients, NFTs establish readily, grow rapidly, and regrow easily from pruning. They are perfectly suited to jump-start organic matter production on a site, creating an abundant source of nutrient-rich mulch for other plants. Many fast-growing NFTs can be cut back regularly over several years for mulch production.

The NFTs may be integrated into a system in many different ways including clump plantings, alley cropping, contour hedgerows, shelter belts, or single distribution plantings. (See figure below). As part of a productive system, they can serve many functions: microclimate for shade-loving crops like coffee or citrus (cut back seasonally to encourage fruiting); trellis for vine crops like vanilla, pepper, and yam; mulch banks for home gardens; and living fence and fodder sources around animal fields.

Ways to integrate nitrogen fixing trees in your plantings

Planting Nitrogen Fixing Trees

Species Selection

A survey of your area will be helpful in determining the habit and vigor of local NFTs. Some are small and produce edible shoots and pods, ideal for home garden use; others are large and fast growing for fuel wood or poles. Decide on what yields you want from your NFTs, and choose a diversity of species. For some characteristics of many nitrogen fixing trees, this chart may be of use.

Seed Pregermination Treatment (Scarification)

In many NFTs, the hard seed coat must be scarified in order to allow absorption of water, hence germination. There are several methods: hot water is the most common. Water temperature should be approximately 70-90 C° (160°F). The volume ratio should be 5-10 parts water to one part seeds. Seeds are placed in hot water for 1-3 minutes, then rinsed. Seeds may be soaked overnight at room temperature. A useful chart is given on the FACT Net website.

Seed Inoculation

After scarification, a sticking agent such as vegetable oil or plain water is applied sparingly to seeds, and inoculum dusted into the mix. Seeds should be sown immediately. Do not expose inoculated seed to extremes in temperature or direct sunlight.

Planting

Plant material in the form of bare root seedlings, stump cuttings and branch cuttings should be kept moist and protected until planting. Punch a small hole in the ground with the same diameter as the plant material. Seedlings should be placed in the hole with the root/shoot collar of the tree at soil level. Stump cuttings are handled likewise. Branch cuttings should be scarified in several places with a sharp knife to promote rooting and put in the ground about one third of their length.

Establishment

Initially NFTs require moisture and adequate nutrients, as well as protection from weed competition. The best way to achieve these conditions is to amend the soil and sheet mulch at the time of planting.

A Caution

As the goal in agroforestry is to foster a productive and stable ecosystem, rather than simply to add nitrogen to the system, NFTs should be used with due care and oversight. Too many nitrogen fixing plants can overnitrify the soil and pollute ground and surface waters. NFTs are not a panacea. Most will not thrive in shade or fertile conditions. Because of their ability to thrive under poor conditions, they can easily become weedy. Therefore, if possible, use only NFTs which are already established in your area, or that have a history of not becoming weeds. NFTs can also become competitive for available soil nutrients, especially in arid areas-careful and informed management practices are advised.

Also, be aware that there are many other significant avenues for nitrogen fixation in nature, such as free-living nitrogen fixing bacteria, which should also be incorporated into a design.

How Biological Nitrogen Fixation Works in Legumes

Working with a group of bacteria called rhizobia, legumes are able to pull nitrogen out of the air and accumulate it biologically. The bacteria, which are normally free-living in the soil in the native range of a particular legume, infect (inoculate) the root hairs of the plant and are housed in small root structures called nodules. Energy is provided by the plant to feed the bacteria and fuel the nitrogen fixation process. In return, the plant receives nitrogen for growth.

There are thousands of strains of rhizobia. Certain of these will infect many hosts, certain hosts will accept many different strains of rhizobia. Certain hosts may be nodulated by several strains of rhizobia, but growth may be enhanced only by particular strains. Therefore, when introducing hosts to a new area it is extremely important to also introduce a known effective symbiotic rhizobia strain. Such effective strains have been identified for thousands of the important nitrogen fixing legumes, and can be purchased at low cost for the value returned. The best method for ensuring effective nitrogen fixation is introduce a known effective strain of Rhizobium to the potting medium at the time of sowing. Large, healthy nodules may also be used to inoculate seeds. To determine if the nodule is effective, it may be cut open. Effective nodules will have a pink to dark red pigment inside.

In conventional cropping systems it is estimated that 50-800 kg of nitrogen per hectare per year are accumulated by nitrogen fixing plants, depending on species, soil and climate, Rhizobium efficiency, and management. Equivalent quantities of manufactured nitrogen is produced using an energy intensive process, and the end product is high-priced nitrogen in a form which can be detrimental to soil ecology.

References and further reading:

FAO, 1984. Legume Inoculants and Their Use, FAO of the United Nations, Rome. Excellent practical handbook for inoculation.

MacDicken, Kenneth G. 1994. Selection and Management of Nitrogen-Fixing Trees. Winrock International Institute for Agricultural Development, Morrilton, Arkansas, USA.

National Academy of Sciences. 1979. Tropical Legumes: Resources for the Future, National Academy Press, Washington, D.C..

Nitrogen Fixing Tree Association (Currently the FACT Net). 1989-1994. NFT Highlights. Nitrogen Fixing Tree Association, Morrilton, Arkansas, USA.

Author Contact:

Craig Elevitch and Kim Wilkinson
P.O. Box 428, Holualoa, HI 96725 USA
agroforestry.net

© 1995,1998

(Printed originally in the Permaculture International Journal, Issue No. 56)

Agroforestry Guides for Pacific Islands

An essential user-friendly resource for conserving and expanding the use of trees

Agroforestry Guides for Pacific Islands can be downloaded below in PDF format.  Download the FREE Adobe Acrobat Reader.

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1. Information Resources for Pacific Island Agroforestry

Provides an introduction to agroforestry, followed by descriptions and contact information for books, guides, periodicals, organizations, and web sites useful to practitioners of agroforestry in Pacific Islands.
(22-page PDF)

2. Multipurpose Trees for Agroforestry in the Pacific Islands

Introduces traditional Pacific Island agroforestry systems and species. Provides a species table with over 130 multipurpose trees used in Pacific Island agroforestry, detailing information on uses (food, fodder, timber, etc.) and tree characteristics such as height, growth rates, and habitat requirements. 
(48-page PDF)

3. Nontimber Forest Products for Pacific Islands: An Introductory Guide for Producers

Discusses the environmental, economic, and cultural role of nontimber forest products. Provides planning suggestions for those starting a nontimber product enterprise. Includes a species table of over seventy traditional Pacific Island nontimber forest products.
(30-page PDF)

4. Integrating Understory Crops with Tree Crops: An Introductory Guide for Pacific Islands

Introduces planning considerations for planting crops with forestry, orchard, or other tree-based systems. Examples of understory intercropping systems in the tropics are included, as well as a species list of over 75 trees, shrubs, and vines used as understory crops in the region. 
(22-page PDF)

5. Introduction to Integrating Trees into Pacific Island Farm Systems

Presents eight Pacific Island agroforestry practices that integrate trees into farm systems. Includes silvopasture (trees and livestock), windbreaks, contour hedgerows, live fences, improved fallow, woodlots, sequential cropping systems, and understory cropping.
(29-page PDF)

6. Choosing Timber Species for Pacific Island Agroforestry

Discusses seven steps for choosing timber species that meet the project goals, product requirements, and environmental conditions for a farm forestry or agroforestry project. Includes a species table of over 50 Pacific Island agroforestry species that provide quality wood products, detailing environmental tolerances and multiple uses. 
(25-page PDF)

7. Economics of Farm Forestry: Financial Evaluation for Landowners

Introduces strategies for determining the financial returns of small-scale forestry and farm forestry projects. Includes a discussion of the advantages and disadvantages of investing in farm forestry, and the steps in determining the costs involved, estimating returns, and comparing farm forestry with other land uses.
(31-page PDF)

8. Multipurpose Windbreaks: Design and Species for Pacific Islands

Covers information on windbreak design, followed by a discussion of planning considerations for multiple-use windbreaks for timber, fruit/nut production, mulch/fodder, or wildlife habitat. Includes species table of over 90 windbreak species for Pacific Islands, detailing environmental requirements and uses/products. 
(31-page PDF)

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