Deeply-rooted, perennial woody plants have greater and very different positive impacts on soil properties, compared with shallow-rooted annual crops.

The perennial habit of trees, shrubs and vines reduces soil erosion by providing cover from heavy rain and reducing wind speed. Their integration into farming systems also creates a cool, shady microclimate, with increased humidity and lower soil temperatures (Ong and Huxley, 1996; Ong et al., 1996; van Noordwijk et al., 2004). The deep and widespread roots both provide permanent physical support to the soil, and aid in deep nutrient pumping, decreasing nutrient losses from leaching and erosion (Young, 1997; Huxley, 1999). Trees also improve soils by nutrient recycling, increasing organic matter inputs from leaf litter and the rapid turnover of fine roots. This improves soil structure and creates ecological niches in the soil for beneficial soil microflora and symbionts (Lapeyrie and Högberg, 1994; Mason and Wilson, 1994; Sprent, 1994). Additionally, leguminous trees improve nutrient inputs through symbiotic nitrogen fixation. These tree attributes have been a dominant focus of agroforestry systems (Young, 1997). Most of the benefits from trees come at the expense of competition for light, water and nutrients (Ong et al., 1996). Consequently a net benefit only occurs when the tradeoffs (ecological, social and economic) are positive.

Harnessing the symbiotic associations between almost all plants and the soil fungi (mycorrhizas) on their roots is beneficial to crop growth and soil nutrient management.

TMany agricultural practices (land clearance, cultivation, fertilizer and fungicide application) have negative impacts on mycorrhizal populations, affecting the species diversity, inoculum potential, and the fungal succession. Techniques to harness the appropriate fungi, ectomycorrhizas on gymnosperms and some legumes (Mason and Wilson, 1994), and endomycorrhizas on most other plants (Lapeyrie and Högberg, 1994), include the conservation of natural soil inoculum and the inoculation of nursery stock prior to planting (Mason and Wilson, 1994). These techniques are critical for sustainable production as mycorrhizal associations are essential to plant establishment and survival, especially in degraded environments. It is now recognized that the soil inoculum of these fungal species is an important component of the soil biodiversity that enhances the sustainable function of natural ecosystems and agroecosystems (Waliyar et al., 2003).

Extensive herding, the most widespread land use on earth, is more sustainable than commonly portrayed.

Pastoralism is a widespread, ancient and sustainable form of land use. Mobile and extensive herding is highly compat

ible with plant and animal diversity (Maestas et al., 2003). When returns to livestock are sufficient, herding can compete well economically with other forms of farming, allowing land to remain open and lightly used (Norton-Griffiths et al., 2007). Land degradation by overgrazing has been overstated with livestock playing a much smaller negative role than climate in constraining productivity in drier rangelands (Ellis and Swift, 1988; Oba et al., 2000), particularly in Africa. However, in wetter rangelands, feedbacks between livestock and vegetation can be strong and sometimes negative (Vetter, 2005). Degradation most commonly occurs when crop farming extends into marginal lands, displacing herders (Geist and Lambin, 2004) (See 3.2.2.1.9).

3.2.2.1.5 Integrated crop and livestock systems Worldwide, livestock have traditionally been part of farming systems for millennia. Integrated systems provide synergy between crops and livestock, with animals producing manure for use as fertilizer and improvement of soil structure (as well as a source of fuel), while crop by-products are a useful source of animal and fish food. In addition, fodder strips of grasses or fodder shrubs/trees grown on contours protect soil from erosion. The production of meat, milk, eggs and fish within small-scale farms generates income and enriches the diet with consequent benefits for health. On small farms, a few livestock can be stall-fed, hence reducing the negative impacts of grazing and soil compaction.

Integrated crop and livestock production is an ancient and common production system.

Close linking of crops and livestock in integrated systems can create a win-win with greater productivity and increased soil fertility (McIntire et al., 1992; Tarawali et al., 2001). Without this linkage, soil fertility can fall in cereal-based systems and surplus livestock manure is wasted (Liang et al., 2005). Linking crops and livestock forms a "closed" nutrient system that is highly efficient. Crop-livestock systems are usually horizontally and vertically diverse, providing small habitat patches for wild plants and animals (Altieri, 1999) and greater environmental sustainability than crop monocultures (Russelle et al., 2007).

In small-scale crop-livestock systems, fodder is often a limiting resource, which can be supplemented by tree/ shrub fodder banks.

In Kenya, tree-fodder from Calliandra calothyrsus grown in hedgerows and neglected niches has overcome the constraint of inadequate and low-quality feed resources and improved milk production and increasing income of around 1000 farmers by US$98-124 per year (Franzel et al., 2003). Three kg of C. calothyrsus fodder equals 1 kg of concentrate giving a yield of >10kg milk d-1 with a buttermilk content of 4.5%. Likewise, in the Sahel Pterocarpus erinaceus and Gliricidia sepium are grown in fodder banks as a dry season resource for cattle and goats and this fodder is also traded