A free email agroforestry journal for practitioners, extension agents, researchers, professionals, students, and enthusiasts. One edition is sent each month focusing on a concept related to designing, developing, and learning more about trees and agroforestry systems. Focuses on trees and their roles in agriculture, natural ecosystems, human culture and economy.

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Overstory #161 - Forest fire and biological diversity


Fire is a vital and natural part of the functioning of numerous forest ecosystems. Humans have used fire for thousands of years as a land management tool. Fire is one of the natural forces that has influenced plant communities over time and as a natural process it serves an important function in maintaining the health of certain ecosystems. However, in the latter part of the twentieth century, changes in the human-fire dynamic and an increase in El Niño frequency have led to a situation where fires are now a major threat to many forests and the biodiversity therein. Tropical rain forests and cloud forests, which typically do not burn on a large scale, were devastated by wildfires during the 1980s and 1990s (FAO, 2001).

Although the ecological impact of fires on forest ecosystems has been investigated across boreal, temperate and tropical biomes, comparatively little attention has been paid to the impact of fires on forest biodiversity, especially for the tropics. For example, of the 36 donor-assisted fire projects carried out or ongoing in Indonesia, a megadiversity country, between 1983 and 1998, only one specifically addressed the impact on biodiversity.

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Overstory #160 - Women's Indigenous Knowledge


Women in most societies of the world, as mothers, grandmothers, wives, sisters, or daughters, often represent the first line of health care, prepare meals for the family, convey values, and provide the first role models for behavior. In many rural societies of developing countries, women carry the burden of farm labor and on-farm transport; they arrange for household energy (mostly firewood) and water. During periods of hunger, women know which plants can provide emergency meals to help keep their families alive.

Beyond the provision of livelihoods for local communities in the areas of family health, growing of staple crops, conflict management, and bio-diversity conservation, women have also found local answers to broader issues such as trade, tourism, education, health, and employment.

Despite the essential contributions to the lives of their families and communities, women still face many constraints in exercising more influence over their living conditions. These constraints include an excessive workload, the difficulties of accessing or controlling the key factors of production, and a lack of training opportunities and appropriate information, extension and advisory services (1).

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Overstory #144 - How Trees Stand Up


There is no doubt that trees are magnificent structures; a mature coastal redwood tree would overshadow most church steeples. Like all engineering structures, trees combine two elements to do this: they use good materials and they arrange the materials so that they are used to their best advantage. Trees have only one main structural material - wood - but as we shall see this is superbly engineered. Trees are also ingeniously designed structures that combine strength and flexibility. They can even respond to their environment and change their design accordingly. This allows them to support their canopy of leaves using a bare minimum of wood.

The mechanical design of wood

Wood needs to combine many useful properties to allow it to support the leaves of trees. It has to be stiff, so that trees do not droop under their own weight; it has to be strong, so that the sheer force of the wind does not snap the trunk and branches; it has to be tough, so that when the tree gets damaged it does not shatter; finally it has to be light, so that it does not buckle under its own weight. No manufactured material could do all of these things: plastics are not stiff enough; bricks are too weak; glass is too brittle; steel is too heavy. Weight for weight, wood has probably the best engineering properties of any material, so it is not surprising that we still use more wood than any other material to make our own structures! Its superb properties result from the arrangement of the cells and the microscopic structure of the cell walls.

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Overstory #159 - Collection of Botanical Specimens

Necessity of collecting botanical specimens

In the identification of an unknown tree, a specimen is worth more than many words or notes. It is difficult to identify a tree solely from the notes written in the forest.

From time to time foresters need to collect some botanical specimens of the trees with which they work. If they do not know the trees in the forest, then they should preserve specimens for identification later or for shipment to a large herbarium or to a specialist for determination.

For example, on making an inventory of the forest resources of a region, numbers or common names can be used for the unknown trees. Then, specimens should be collected for later identification.

Systematic botanists have various methods of collecting specimens. However, foresters generally collect only a few specimens and can employ the simple methods. In an emergency a twig can be broken from a tree and pressed in a notebook, in the pocket, or in a book. But it is worth the trouble to collect good specimens and in the end the identifications will be better.

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Overstory #158 - Forest Culture

Does smallholder forest culture exist?

Forest culture refers to the art and practice of cultivating forests. Forest culture is widespread in the tropics but constitutes what could be called "the invisible face of forest management". It is practiced within farmlands and follows various patterns and models. Most of the existing examples exhibit general patterns typical of natural forest ecosystems. As a consequence, locally cultivated forests, even though usually established outside the boundaries of natural forests, are easily confused with either primary or secondary forests. Smallholder cultivated forests range from occasional forest culture occurring within in a matrix of undisturbed natural forest ("interspersed forest culture") to planted forests maintained or restored on farmlands ("integral forest culture") (Michon et al. 1998).

1. Interspersed forest culture involves local, though rather large-scale modification of the natural forest for the benefit of introduced individuals planted and protected in specific places or periods in time. This kind of "enrichment planting" is integrated within existing forest structures, without totally destroying or replacing them. The interaction between human production efforts and natural forest cycles varies in intensity, time and space, from the planting of a few rattan clusters under a thinned forest canopy in some rattan gardens in East and Central Kalimantan, to cyclic benzoin cultivation in the Toba highlands, Sumatra (see further in this volume). In the latter case, the silvicultural pattern integrates an intensive but temporary phase of forest production into a matrix of unmanaged old-growth forest.

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Overstory #157 - Soil Erosion and Water Infiltration


Soil erosion is caused by rainwater that does not infiltrate into the soil, but instead runs off the soil surface. It is essential that the interconnected processes of soil erosion and water infiltration be well understood by farmers, extension workers, and scientists.

The consequence of conventional cultivation methods can be the gradual loss of soil and fertility until the land becomes unproductive. Erosion, as well as intensive weathering under hot, humid conditions, has brought about widespread, poor, badly eroded, and infertile soils throughout the tropics and subtropics (Ochse, et al., 1961). The same process has also taken place in temperate climates (e.g. the United States and Russia). Eroded, unproductive and abandoned lands, as well as advanced signs of desertification are a silent testimony to this phenomenon worldwide.

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