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 #256 - Biochar

IMG 3188CElevitchBiochar is the carbon-rich product of heating organic biomass under certain controlled conditions. This piece of biochar was produced from the wood of Grevillea robusta, and clearly shows this species' characteristic intricate wood grain "lattice."

What is biochar?

Simply put, biochar is the carbon-rich product obtained when biomass, such as wood, manure or leaves, is heated in a closed container with little or no available air. In more technical terms, biochar is produced by so-called thermal decomposition of organic material under limited supply of oxygen (O2), and at relatively low temperatures (<700°C). This process often mirrors the production of charcoal, which is one of the most ancient industrial technologies developed by mankind – if not the oldest (Harris, 1999). However, it distinguishes itself from charcoal and similar materials that are discussed below by the fact that biochar is produced with the intent to be applied to soil as a means of improving soil productivity, carbon (C) storage, or filtration of percolating soil water. The production process, together with the intended use, typically forms the basis for its classification and naming convention.

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Overstory #255 - Climate Change Adaptation

North American Agroforestry landscapeAgroforestry practices that are most common in North America include riparian forest buffers, windbreaks, silvopasture, alley cropping, and forest farming.

Adaptation by Agroforestry

Agroforestry can add a high level of diversity within agricultural lands and, with it, an increased capacity for supporting numerous ecological and production services that impart resiliency to climate change (CC) impacts (see figure below) (Verchot et al. 2007). From a landowner’s perspective, the most valued services would be those that can dampen the negative effects of CC and weather extremes while augmenting the positive benefits provided by tree-based systems.

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Overstory #254 - The contribution of forests to sustainable development

Forests are unique in their capacity to address diverse social, ecological, and economic needs.Forests are unique in their capacity to address diverse social, ecological, and economic needs.

In many countries, development is needed to increase employment and raise the standard of living (Dasgupta, 2011). To be sustainable, however, development activities must balance economic, social and ecological factors. Forests are a unique resource for accomplishing this balance because of their capacity to respond to multiple economic, social and ecological needs and challenges, and because of their renewability.

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Overstory #253 - The value of biodiversity and ecosystem services

Coastal erosion in Hawai'i due to overgrazing by ungulates.Coastal erosion in Hawai'i due to overgrazing by ungulates, which impacts the near-shore environment negatively including silting in reef ecosystems.

Biodiversity and ecosystems deliver crucial services to humankind – from food security to keeping our waters clean, buffering against extreme weather, providing medicines to recreation and adding to the foundation of human culture. Together these services have been estimated to be worth over 21–72 trillion USD every year – comparable to the World Gross National Income of 58 trillion USD in 2008.

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Overstory #252 - Conservation of tree species by botanic gardens

Protected remnant native dryland forest between Mauna Kea and Mauna Loa, Hawai'i.

Importance of tree species

Trees are of exceptionally high ecological, socioeconomic and cultural importance. As the principal biomass component of forest ecosystems, they provide habitat for at least half of Earth’s terrestrial biodiversity (Millennium Ecosystem Assessment, 2005), supporting 80% of amphibian, 75% of bird and 68% of mammal species (Vié et al., 2009). Forest ecosystems play a major role in the Earth’s biogeochemical processes, and contain about 50% of the world’s terrestrial carbon stocks (FAO, 2010; Millennium Ecosystem Assessment, 2005), highlighting their importance for moderating human induced climate change. Trees and forest ecosystems provide a wide range of benefits to people including production of timber, fuelwood and fibre, and ecosystem services such as clean water, flood protection and prevention of soil erosion from watersheds, as well as being of high cultural and spiritual value (Millennium Ecosystem Assessment, 2005; UNEP, 2009). The total value of such services has been estimated at US$4.7 trillion per year (Costanza et al., 1997). Some 1.6 billion people depend directly on trees for their livelihoods (World Bank, 2004), and forest industries contribute around $468 billion annually to the global economy (FAO, 2011). Recent research has confirmed that high plant diversity is needed to maintain provision of many ecosystem services (Isbell et al., 2011).

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Overstory #251 - The importance of policy for agroforestry

The OverstoryThere are many key policy-related constraints to agroforestry, such as agricultural subsidies that exclude agroforestry cropping systems.

The increasing importance of agroforestry as a major land use practice

There is now general agreement about the magnitude and scale of the integration of trees into agricultural lands and their active management by farmers and pastoralists. Zomer et al. (2009) conducted a global assessment of tree cover on agricultural land and found that 48% of all agricultural land had at least 10% tree cover. A high percentage of tree cover is found in nearly all continents of the world, highest being in Central America and southeast Asia. Although Africa shows a smaller percentage of tree cover at continental level, the most widespread farming system in Africa is the so-called agroforestry parkland (scattered trees in cropland), making Africa a typically “treed continent” in agricultural areas (Boffa, 1999). The FAO Forest Resources Assessment Report has integrated since 2000 the assessment of trees outside forests, which consist mainly in agroforestry systems as well as tree systems in urban areas.

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