Protected areas cover only about 10% of the earth’s land cover. That percentage is unlikely to increase much. Moreover, many parks are in places that are hard to protect or will be in the future.

Most wild plants and animals live outside protected areas. People use many of those plants and animals to meet their basic needs and efforts to conserve endangered species must take into account the plants and animals outside parks.

That is why there is growing interest in using agroforests to conserve biodiversity. Agroforests include land uses such as shaded coffee, cocoa, and rubber, windbreaks, live fences, and trees in pastures, and shifting cultivation with long rotations.

"Agroforestry and Biodiversity Conservation in Tropical Landscapes – a Synthesis" by Götz Schroth and nineteen other leading scientists examines to what extent such agroforests favor biodiversity. It is the synthesis chapter of a book with a similar title that Island Press will publish next year.

The authors conclude that agroforests provide valuable natural habitats for a wide variety of wild plants and animals, including some endangered ones. That may help stop species from going extinct, particularly in regions with little remaining natural forest. Farmers also grow plants in agroforests that might otherwise become scarce. Still, not every species can survive in agroforests, so they are not a perfect substitute for natural forests.

Agroforests also provide corridors that make it easier for birds, mammals, and other animals to travel between patches of forest. That can make the patches less genetically isolated and allow animals that disperse seeds and pollinate plants to move across the landscape. Moreover, agroforests can shield forest patches from wind and light. Not everything is positive though. Some plants become invasive species and agroforests may attract animals that damage crops or threaten livestock and people.

Agroforestry systems with more natural shade, older fallows, and fewer inputs are better for biodiversity, but they may not be the most profitable for farmers. To keep farmers from abandoning these traditional systems will often require specific policies and incentives.

Depending on the context, agroforests can either increase or decrease pressure on natural forests. Compared with cattle ranching or shifting cultivation, tree crops sometimes allow farmers to focus their resources on smaller areas and thus clear less forest. Similarly, some farmers that have their own agroforests harvest fewer forest products from natural forests. But there are also many cases where coffee, cocoa, and rubber have themselves been major causes of deforestation.

So agroforests won’t solve all of the world’s biodiversity problems. They may even create a few here and there. But getting more birds and bees and trees on farms is generally a step in the right direction.