Agrodiversity is the genetic diversity of cultivated plants and animals, whose use is vital in traditional smallholder farming worldwide. It refers to cultivated diversity that is both interspecific – among different species – and intraspecific – among multiple varieties of the same species. As different species and varieties have different properties and can tolerate or flourish in different conditions, access to agrodiversity allows farmers to adapt to changing conditions by focussing on whatever grows well, and maintain a genetic reservoir for adaptation to future change. Agrodiversity is a key component of agroecology: among other things it allows cultivation of polycultures, combinations of plants and animals that support each other's growth and exhibit high collective or systemic resilience to change.
Both traditional small-scale farmers and permaculturists are adapting to climate change by cultivating plants better suited to new conditions. In Southern Ghana, farmers cope with declining rainfall and rising temperatures by growing drought-tolerant and early-maturing varieties of staples, and increasing the range of secondary crops. In North America, the Central Rocky Mountains Permaculture Institute experiments with a wide range of exotic species and varieties to find plants capable of producing food under changing climatic conditions. It has established many of these as reliable domestic and commercial producers. Plants for a Future has compiled a database of over 7,000 edible and otherwise useful perennial plants, growing around 1,500 of these on its site in Cornwall. Also in Southwest England, the Agroforestry Research Trust in Devon has an ongoing programme to identify and test exotic perennial plants for their performance in agroecology systems.
Traditional polycultures have demonstrated benefits in addressing direct and indirect impacts of climate change, including water stress and disease. Experimental polycultures of sorghum, peanut and millet consistently yielded higher than the equivalent monocultures over a range of watering regimes; the differences in yield increased as water became more scarce. Replacing monocultures of commercial rice hybrids with polycultures of hybrid and traditional varieties dramatically reduced incidences of fungal infection, eliminating needs for fungicide application, and almost doubled overall yields.
Permaculture polycultures are less well-studied, with limited empirical data available. Preliminary field trials conducted by the UK Permaculture Association indicated slight increases in overall yields compared to monocultures, with a greater variety of edible produce available over a longer period of time. Yields varied greatly from site to site, suggesting that planting conditions and growing techniques were also significant.
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- Van der Velden, N., 2011. Mixed Vegetable Polycultures: Research Report. Leeds: Permaculture Association.