Boab tree and crops in Burkina Faso
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Treeless fields of wheat haven’t always been the common image of agriculture. For most of human history, agriculture took place amidst trees. It’s time to put the trees back, say Meine van Noordwijk, Dennis Garrity and Delia Catacutan
The trouble started when a tree-less, tillage-addicted form of agriculture became the norm and the image worldwide as what agriculture is, and should be, and was extended to parts of the world with less benign climates than where it originated.
Long before this concept took hold, agricultural practices in many parts of the world included the retention of valuable trees in cropped fields. This kind of agriculture employed only superficial soil tillage, usually in combination with a controlled fire that cleared the land but did not kill the larger trees.
In temperate zones with relatively mild climates, however, a different approach to growing crops emerged—‘non-conservation agriculture without trees’—which was successful because it was readily expanded: horse-drawn ploughs replaced human tillage then tractors replaced horses, drawing on much more horsepower to drag ever-deeper ploughs through soils that responded by mineralizing a substantial part of their organic matter, thereby providing nutrients for the crops.
This yield benefit, however, was not sustainable because it depleted the resource base: chemical fertilizer had to become the basis of plant nutrition. Because excessive tillage had killed many of the worms and other minute soil engineers, it became ‘necessary’ to create a structure compatible with crop roots.
By the mid-1970s, it had become clear that the ‘green revolution’ approach of intensifying crop production in the manner described above had worked well in some (particularly irrigated) environments, but not elsewhere.
A parallel approach to large-scale forestry had success in some limited areas but it ran into major social conflicts and issues over land rights elsewhere.
Out of this polarisation, a new—but also very old—concept emerged: ‘agroforestry’, which was most simply described as ‘agriculture with trees’.
However, the idea that crops and trees were compatible was dangerously revolutionary for academically trained agronomists and at the same time their colleagues, the trained foresters, had a hard time in seeing local people as partners, not as their major problem.
Yet in many parts of the tropics, the compatibility of crops and trees and people and forests appeared to be self-evident, if only one opened one’s eyes. Trees and crops, farmers and forests could work together.
And so the advances of agroforestry in understanding the biophysical, ecological, social and economic aspects of tree–soil–crop interactions were slow to be accepted in the world of ‘development’ and ‘modernization’.
But after some time and much work, new forms of agroforestry, compatible with mechanization and focussed on trees of high value, finally emerged in Europe, North America and Australia, which challenged the rules and regulations that had been formed around the concept of segregating trees and crops.
Agroforestry and its close relative, ‘conservation agriculture with trees’, has demonstrated the ability to adapt crop productivity to climate variability and change, and provide greater yield buffering under increasing temperatures and more frequent and severe droughts.
Depending upon which woody species are used, and how they are managed, their incorporation into crop fields and agricultural landscapes can contribute to maintaining vegetative soil cover year-round; bolstering nutrient supply through nitrogen fixation and nutrient cycling; enhancing suppression of insect pests and weeds; improving soil structure and water infiltration; increasing direct production of food, fuel, fibre and income from products from the intercropped trees; enhancing carbon storage, both above- and belowground; increasing quantities of organic matter in soil surface residues; and more effectively conserving above- and belowground biodiversity.
There are still many critical research issues to be explored. These include the choice of appropriate tree species for varied agroecologies, higher quality tree germplasm, better tree seed dissemination systems, and further improvements in tree propagation and establishment methods. The optimum tree densities for different systems have yet to be fully understood, and the best practices in exploiting the soil fertility synergies between organic and inorganic nutrient sources need to be elucidated.
Integrated systems pose a pioneering research agenda with enormous implications for so-called ‘climate smart’ agriculture.
The World Agroforestry Centre is working on this ecologically sustainable agriculture with a number of key partners from national research institutes, universities and NGOs in projects across the developing world so that we can all enjoy the fruits of trees in agricultural landscapes for a long time to come.
Edited by Robert Finlayson
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