If a tree species is to survive, its population must be large enough to allow for genetic diversity.

LIMA, Peru (25 March 2014) — When deforestation or the effects of climate change threaten natural forests, the best hope for the survival of certain tropical tree species may be to include them in agroforestry plots managed by smallholder farmers, according to a recent review.

Tree species can be conserved in three ways: They can continue to grow in their native, natural habitat, which is known as conservation in situ; they may be transplanted by farmers to nearby agroforestry plots — a technique known as conservation circa situm — if they are valued for their timber, fruit or for other uses; or they may be conserved in seed banks or gene banks, known as conservation ex situ, or outside their original habitat.

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The three types of conservation are interrelated, and smallholders play a role in all of them, but scientists actually know very little about the extent and the limitations of those connections and how effective they are, said Manuel Guariguata, a principal scientist with the Center for International Forestry Research (CIFOR) and co-author of the review paper.

“We know that agroforests can be very diverse, but we don’t really know the dynamics of the links between farms and natural ecosystems,” he said. “For example, we don’t know exactly what happens with timber and other species when smallholders domesticate them by planting them outside their natural habitat.”

Tropical forests are home to a great diversity of species. When small farmers find trees that are particularly valuable for timber, fuel, fruit, nuts, medicine or some other purpose, they transplant them or sow the seeds in their own agroforestry plots.

If a species is to survive, its population must be large enough to allow for genetic diversity, but more research is needed to determine how well small farms that combine agriculture and forestry contribute to conservation, according to the research, which appeared in the journal “Biodiversity and Conservation”.

INTERCONNECTED LANDSCAPES

“Conventional wisdom is that if you plant trees in plantation or agroforestry systems, they will contribute to the conservation of natural stands of trees,” said Ian Dawson of the World Agroforestry Centre, lead author of the review paper titled “What is the relevance of smallholders’ agroforestry systems for conserving tropical tree species and genetic diversity in circa situm, in situ and ex situ settings?”

That belief exists because it is assumed that people will harvest trees from the plantations or agroforestry plots, leaving the natural forest intact, but there is little research to support that assumption, Dawson said.

Farmers who combine agriculture and forestry can contribute to conservation in a several ways, Guariguata said, but it is important to look at how the different approaches work together to ensure the greatest benefit with the fewest unintended consequences.

As forests become fragmented, agroforestry plots may serve as connecting corridors or “stepping stones” between forest patches, allowing pollinators, animals and seed-dispersing birds to move from patch to patch so trees in the remaining natural forests can reproduce. Forest trees pollinate trees in smallholders’ agroforestry plots.

In places where certain species in natural forests cannot adapt to the pace of climate change, conservation on agroforestry plots may offer the only chance for survival, Dawson said.

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Situating smallholders at the fore

Many questions remain about how agroforestry can contribute to conservation.

Scientists must learn more about plantations or policies such as certification that really help conserve species in the wild — research that will involve studying both ecology and genetics, Guariguata said.

Because small farmers are constantly domesticating wild species that are useful to them, researchers can learn a lot from studying how farmers manage both the wild and domesticated trees and how the wild and domesticated populations interact, he said.

One crucial question is how a warming climate will affect tropical forests, Dawson said.

“A key concern is whether climate change will affect pollinator populations and what that could mean for tree species,” he said. “That’s especially important in farm landscapes, where conservation also depends on how valuable a species is to farmers.”

For more information on this review, contact Manuel Guariguata at m.guariguata@cgiar.org

CIFOR’s research on biofuels and biodiversity is part of the CGIAR Program on Forests, Trees and Agroforestry.