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 #215 - Agroforestry benefits for tropical organic farming

An agroforestry system approach

Conventional farming focuses on maximizing yields of a specific crop. It is based on a simple presumption: crop yields are increased by nutrient inputs and by controlling pests, diseases and weeds. Organic agriculture is a holistic way of farming: besides production of goods of high quality, an important aim is the conservation of natural resources such as fertile soil, clean water and rich biodiversity. The art of organic farming is to make the best use of ecological principles and processes. Organic farmers can learn a great deal from studying the interactions in natural ecosystems such as forests.

Trees and other plants take up nutrients from the soil and incorporate them in their biomass. The nutrients return to the soil when leaves or branches fall or plants die. Part of the biomass is consumed by various animals (including insects), and their excrement returns the nutrients to the soil. In the soil, a huge number of soil organisms are involved in the decomposition of organic material which makes nutrients available to plant roots again. The dense root system of forest plants collects the released nutrients almost completely. Forests host a high diversity of plant varieties of different size, root systems and requirements. Animals are also part of the system. In a healthy, diverse system, if one organism drops out, it is immediately replaced by another that fills the gap. Thus space, light, water and nutrients are used near-optimally. The result is a very stable system.

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Overstory #214 - Indicators and guidelines for landscape assessment and planning for agroforestry

Assessments and plans

Agroforestry practices can produce numerous environmental benefits that become significant only through multiple installations over a large area, including greater diversity of wildlife, healthier aquatic ecosystems, and cleaner stream water. Through landscape-level assessment and planning, a limited number of agroforestry installations can deliver significant improvements if designed and placed in critical locations.

Indicators and guidelines

Agroforestry produces environmental benefits by altering landscape structure and modifying the flow of resources across the landscape. Since you normally can't see these processes, you need to look for indicators of them in the patterns of land cover and land form that comprise landscape structure. An assessment of existing patterns can reveal potential resource problems. Guidelines, then, can be used to select locations and designs for agroforestry that will modify existing patterns and produce desired environmental benefits. The following sections provide some useful indicators and guidelines.

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Overstory #213 - Urban Forestry for Multifunctional Urban Land Use


The contributions of forests, trees and other urban green areas to the quality of urban life and the environment can be significant. When existing good practices are built upon, urban forestry has shown significant contributions to the quality of urban life and the environment, together with other types of comprehensive green-space planning and management concepts. Through agroforestry systems, for example, urban forestry and urban agriculture join forces in supporting livelihoods. Urban forestry has been developed in response to the call for innovative, comprehensive concepts that promote the multiple benefits of urban green space. Sometimes named urban and peri-urban forestry, the concept encompasses the planning and management of forests and other tree resources in and close to urban areas and thus integrates different parts of urban green structures.


World-wide urbanisation brings with it a wide range of challenges. The demand for land increases, and the energy, resource, water and waste disposal needs of urban populations need to be met. Especially in the developing world, where most mega-cities are located and urbanisation is particularly rapid and not necessarily controlled, providing good living conditions to urban populations is one of the main challenges of our time (UN Habitat, 2004). Policymakers are facing tremendous pressures to develop city management strategies that strive for sustainable cities where all inhabitants can enjoy at least a fair quality of life and a reasonably healthy environment.

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Overstory #212 - Forests on sites with high landslip risk

Forests on sites with high landslip risk

With their undergrowth, leaf litter, forest debris and uncompacted soils, forests are almost without question the best and safest land cover for minimizing surface erosion of all kinds (Wiersum, 1985; Kellman, 1969). On sloping lands within any climatic regime, the earlier FAO land suitability classes for lands that might safely be cleared and used for crops or grazing were predicated on this function of minimizing erosion under various uses (FAO, 1976). With their stronger, deeper root systems, forests are also the best land cover for minimizing the hazard of shallow landslips (Rapp, 1997; O'Loughlin, 1974; Ziemer, 1981). Such landslips are often catastrophic, and this section presents the case for keeping slip-prone lands in forest cover. Short-duration, intense storm events generally create shallow landslips, while prolonged, low-intensity events produce the deeper, larger landslides for which forests may be ineffectual - witness the estimated 20 000 landslips and landslides that occurred in a single day in the Sikkim-Darjeeling area in a 1968 event (Ives, 1970).

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Overstory #211 - Improving forage for native bee crop pollinators


Agroforestry practices can provide essential habitat for bees, our most important crop pollinators. The European honey bee receives most of the credit for crop pollination, but the number of managed honey bee hives is half of what it was in the 1950s; and this number continues to decline because of disease and the immigration of aggressive races of honey bees. Native bees, however, significantly contribute to crop pollination – and, in some cases, provide all of the pollination.

In order to support the native bee community, a wealth of flowers is necessary. Unfortunately, heavily managed farm landscapes often lack the diversity and abundance of flowers that native bees require. By providing abundant and diverse pollen and nectar sources, a diverse community of native bee species will increase, adjacent crops may yield more, growers could rely less on imported European honey bees, and farm biodiversity and other wildlife species will benefit.

This article discusses how to maximize the ability of an agroforestry practice to support crop-pollinating bees, including a step-by-step method for planning forage enhancements.

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Overstory #210 - Underutilised plant species and biodiversity

What is biodiversity and why is it important?

The term 'biodiversity' encompasses all variation found in living organisms, both between and within ecosystems, and includes species diversity and intra-specific genetic variation. Biodiversity is at the foundation of human society, because we survive on the range of products and services that it provides. Biodiversity is vital for the food security, proper nutrition, income and self-reliance of human communities, and also sustains the environment. In addition, through sometimes complex linkages with food habits, languages, traditional medicine, and religious and other practices, biodiversity sustains cultural richness and community identity, encourages organisation and communication, maintains social cohesion, and fulfils the aesthetic needs that allow societies to flourish (Brush, 2004).

Biodiversity is also essential for providing an adaptive capability in a world that is continually undergoing change - change that may be positive, such as general improvements in human health and increases in purchasing power - or pose challenges, such as global warming. In agricultural systems, adaptive pressures include the changing requirements of farmers and the markets they serve, which require adjustments over time in the types of crops cultivated and products offered.

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