ALTHOUGH agriculture, particularly in the developing world, is often associated with massive deforestation, scientists from the World Agroforestry Centre have demonstrated in a study using detailed satellite imagery that almost half of all farmed landscapes worldwide include significant tree cover.
The findings were announced at the second World Congress of Agroforestry, held last month in Nairobi, Kenya.
The World Agroforestry Centre is one of 15 centres supported by the Consultative Group on International Agricultural Research.
This is the first study to quantify the extent to which trees are a vital part of agricultural production in all regions of the world. It reveals that on more than 1 billion hectares - which make up 46 per cent of the world's farmlands and are home to more than a half-billion people - tree cover exceeds 10pc.
"The area revealed in this study is twice the size of the Amazon and shows that farmers are protecting and planting trees spontaneously," said Dennis Garrity, director general of the center.
"The problem is that policy-makers and planners have been slow to recognise this phenomenon and take advantage of the beneficial effect of planting trees on farms.
"Trees are providing farmers with everything from carbon sequestration to nuts and fruits, to windbreaks and erosion control, to fuel for heating and timber for housing.
"Unless such practices are brought to scale in farming communities worldwide, we will not benefit from the full value trees can bring to livelihoods and landscapes."
From the data presented in the study, the researchers said it is not possible, in all cases, to discern precisely the products and services trees provide.
However, a great deal of previous agroforestry research has documented a wide range of uses for trees on farms, including: fertiliser trees for improving crop yields and enhancing soil health, fruit trees for nutrition, fodder trees to feed livestock, timber and fuel-wood trees to provide shelter and energy, medicinal trees and trees that provide global commodities such as coffee, rubber, nuts, gums and resins.
As equally important on the service side are uses such as erosion control, water quality and biodiversity.
"If planted systematically on farms, trees could improve the resiliency of farmers by providing them with food and income," said Tony Simons, deputy director general at the World Agroforestry Centre.
"For example, when crops and livestock fail, trees often withstand drought conditions and allow people to hold over until the next season."
Previous estimates for the amount of farmland devoted to agroforestry have ranged from as low as 50,000 hectares to as high as 307 million hectares.
However, these estimates were not derived from detailed remote sensing data like in this assessment.
In this study, scientists were able to measure the amount of tree cover on each square kilometre of the world's 22.2 million sq. km. of farmland.
The scientists - who included researchers from the International Center for Integrated Mountain Development and the Katholieke Universiteit Leuven in Belgium - found that about 10 million sq. km of agricultural land have at least 10pc tree cover. That includes 3.2 million sq. km in South America, 1.9 million in sub-Saharan Africa and 1.3 million in Southeast Asia.
According to the report, "Trees are an integral part of the agricultural landscape in all regions, except north Africa and west Asia."
The data also show that people live with trees in farmed landscapes in virtually all of Central America and in about 80pc of such landscapes in Southeast Asia and South America. The proportion was lower but still large in sub-Saharan Africa, Europe and North America, where trees are a significant feature on about 40pc of agricultural land.
The study found that the extent of trees in farmland in North America and Europe is especially impressive, given the large commercial agricultural sectors of these regions.
"This study offers convincing evidence that farms and forests are in no way mutually exclusive but that trees are, in fact, critical to agricultural production everywhere," said professor Wangari Maathai, founder of the Green Belt Movement.
Most notably, the researchers found that globally, there is no consistent trade-off "between people and trees".
There are areas with low population and little tree cover and areas with lots of people and lots of trees. The amount of tree cover - low or high - could not be explained solely by climate conditions, they said.
The authors also pointed to "documented cases" in which forests are initially cleared for agriculture development but then tree cover later returns, at least partially, as farmers seek to enhance production by planting useful trees that can generate income or provide other services, such as protecting watersheds.
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