UF Researcher: There In Help — But Little Hope — For Deforested Tropics

June 4, 1997

GAINESVILLE —The natural recovery of tropical forests leveled for agricultural use will be slow, but humans can encourage natural forest growth with such things as tree plantations, says a University of Florida researcher.

However, such recovery programs are unlikely to happen any time soon because most tropical forests are in poor, developing countries and reforestation programs are expensive, said Scot Duncan, a zoology master’s student researching tropical reforestation.

“In some areas where reforestation is very slow, tree plantations could be used to encourage forest regrowth,” Duncan said. “Unfortunately, there is little or no funding for such large-scale projects in most developing countries.”

Duncan spent six months studying seed dispersal patterns by animals in abandoned croplands near the Kibale National Forest in Uganda. He identified which animal dropped the seeds, the species of seeds and where the seeds fell. Most of the seeds were found around isolated trees that attracted birds and bats.

Many seeds dropped under these solitary trees may find an environment suited to their germination and growth. The area directly below solitary trees is cooler and more humid, and it has less competition among plants than open areas. If the seeds grow to be trees, these islands of vegetation could expand to reforest abandoned farmland.

Although the study was done in Africa, the findings can be applied to other depleted tropical forest ecosystems around the world.

While natural forces also cause loss of forested areas, the forest generally can repair itself. Human agricultural use, however, takes larger land areas and usually is more severe, depleting the soil and making it difficult and slow for natural processes to generate new growth.

“There is increasing interest among biologists about land-use practices and conservation strategies in the tropics,” Duncan said. “The soil in these areas is usually very poor and can only support agriculture for a short time. After a few years, the land is often abandoned. Once humans have made these changes, the areas are slow to grow back. As a result, seeds for new trees have to come in from off the site, usually through bird or animal droppings.”

Duncan said planting rows of fast-growing trees would mimic the natural reforestation pattern he observed and attract animals that would drop seeds and, in turn, speed up the recovery of the forest.

“Birds and bats are attracted to these solitary trees and use them to look for food and as perch sites,” he said. “Furthermore, when crossing open areas, birds go to these trees to look for predators, and bats bring fruit to eat from fruit trees in nearby areas, dropping seeds around the trees.

“The canopy provided by the taller trees will also encourage other growth,” Duncan said. “Plantations seem to be facilitating forest recovery at Kibale, where abandoned croplands had not recovered after many decades.”

However, even after these seeds are dispersed to a certain area, there’s no guarantee the plants will survive.

“There are many things that can affect seed survival. Rodents can eat seeds, mold and fungus can kill seeds and there is also competition between other plants for water and nutrients,” Duncan said. “Furthermore, in my study area, one-third of the seeds were shrub species, and only one-sixth of seeds were tree species. This suggests that colonizing vegetation will be predominately shrubs, vines and bushes, not trees.”

Because most of these seeds are not trees, it would take many decades for sizeable reforestation to occur using only natural processes. So managers may want to encourage forest growth by planting trees.

“This would work in any place where forest is regenerating after use for agriculture,” said Francis Putz, a UF botany professor. “The presence of these tree islands increases the rate of natural regeneration. Planting even a few trees, particularly those that are attractive to animals that disperse other seeds, will enhance forest regeneration.”