- Of the more than 60,000 known tree species only 1% is represented in specific agroforestry databases
- Trees become part of agroforestry practices by three routes: selective retention, as volunteers and by deliberate planting (or direct seeding)
- On-farm tree diversity profiles differ between use categories and AF practices, with 1-10, 10-100 or 100-1,000 tree species depending on context
- Tree diversity transitions imply a loss of retained and volunteer trees and increase in actively managed ones
- Domesticating forest aligns with domesticating trees, with winners and losers in both
Trees and forest relate to each other like eggs and chicken, and it is not possible to say which came first. Trees wouldn’t grow as tall as they do without forest neighbours, and forests without trees exist only on paper and in a policy sense. From an agricultural perspective the trees are the most distinctive aspect of agroforestry, and similarity with forests is a secondary concept, however (Box 2.1).
In reviewing four decades of agroforestry research Chapter 1 described three ‘nested’ agroforestry concepts, with AF1 focused on ‘trees on farm’ at field and farm level, the technologies used and value chains supported, AF2 focussed on the agriculture/forest interface at landscape and livelihoods scale, and AF3 at the governance and policy aspects of the way agriculture plus forestry interact as continuum with the full spectrum of sustainable development goals. There is a logical sequence1 of description and stock taking (‘Theory of Place’), understanding of transitions, their drivers and consequences (‘Theory of Change’) and transformations and leverage on drivers (‘Theory of Induced Change’). This applies at each of the three AF concepts, but effectiveness of ToIC’s at AF1 level may well depend on relationships included in the AF2 and AF3 concepts.
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