Víctor Gutiérrez spots a thick column of smoke rising from an overgrown field outside Pucallpa city in Peru’s Amazon region, stops his pickup truck, disembarks and hikes over charred hummocks toward the blaze.
Large flames dart through dry underbrush and massive ash flakes drift around his head. Unfazed by the ferocity of the blaze, Gutiérrez keeps one eye on the fire and the other on the forest edge several hundred feet away, where he anticipates it will stop.
“This is a typical escaped fire, but the forest will probably act as a firebreak, in part because the closed tree canopy keeps the humidity level higher there,” he said.
As forest conversion to agriculture and pasture lands are intensified in the Peruvian Amazon, so is the intentional use of fire. Because fields become overgrown quickly in the tropics, oil palm planters, farmers and cattle ranchers burn fields to clear weeds and set fires in pastures to eliminate ticks that annoy livestock. Problems arise when the wind whips a fire out of control and endangers the surrounding forest.
Although humidity generally stops fire from spreading beyond the edge of a field or pasture and into the forest, scientists fear that repeated burning could dry the understory vegetation (underbrush), making the forest more susceptible to burning in the future. Combined with climate change, survival of the forest could be at stake.
Gutiérrez, a Colombian-born research scientist at Columbia University’s Earth Institute in New York, is working with scientists with the Center for International Forestry Research(CIFOR) to study the relationships among humans, fires and forests in Peru’s Ucayali region.
“We want to see how climate, land-cover changes and social processes influence the occurrence and spread of fire. We also want to understand how the management of different types of vegetation in the landscape could be used to control or reduce fires while increasing the ability of secondary forests to grow and provide ecosystem services, such as wildlife habitat, carbon storage and water regulation.”
Human impact
Unlike temperate forests, where lightning can spark a wildfire, a damp tropical forest will typically burn only if someone lighting a match ignites it.
“Fire is becoming more pervasive in the Amazon, but the ecosystem is not adapted to fire conditions,” Gutiérrez said. “Fire harms human health, damages crops, and it also has important impacts on ecosystem processes. If we can keep fire out of areas where the forest would otherwise regenerate, then those areas could develop enough to reduce the likelihood of fires and to provide those ecosystem services.”
Much of Gutiérrez’s research is done at the forest’s edge, which is bordered by a pasture or field of cassava plants on one side and tall trees and thick undergrowth on the other.
When trees are cut down to make way for crop fields or animal pastures, the forest becomes fragmented, exposing more border edges to heat and sunlight, drying the undergrowth and making it easier for wildfire to spread into the forest. Such conditions will worsen if climate change causes an increase in drought-like conditions.
In the Amazon, cropped fields are often reverted into forest in a cyclical manner. Once a farmer abandons a field, allowing it to fall fallow, initally grass begins to grow taller, becoming more readily flammable and posing a fire hazard. But if trees begin to grow, they eventually will form a secondary forest that improves conditions for resisting fire.
“There’s a relationship between forest recovery and fire,” Gutiérrez says. “There’s a transition period during which the vegetation goes from promoting to prohibiting fire. We want to learn at what point that happens, how variations in drought conditions influence that relationship, and ultimately how people can manage the landscape so forest regrowth can be promoted in a way that it can reduce fire risk and at the same time accumulate carbon and provide other ecosystem services.”
Secondary terrain
A few miles away, Naomi Schwartz shades her eyes and scans the canopy of trees that have grown up, forming a secondary forest in a place that was a farmer’s field just 15 years ago.
Once the field was abandoned, various species began growing in succession – first the light-loving ones, then others that thrive in a cooler, darker environment under the canopy. Although the area is covered with small trees and a range of species that differ from those found in mature forests, they are still identifiable as forests due to their dense, tall vegetation and closed canopy.
Within a few years this new-growth forest will be valued for its conservation and ecosystem services, Schwartz said.
Armed with calipers and a measuring tape, Schwartz records the species and size of the trees. She also compares the species composition at the edge of the forest, where there is more light and environmental conditions may differ, to that in the interior.
“We want to see if resilience to fire is different when the vegetation is at different ages,” said Schwartz, a doctoral student in ecology, evolution and environmental biology at Columbia University working with the CIFOR scientists.
“Our hypothesis is that as the forest becomes more mature, it will be less vulnerable to fire that may escape from burning fields or pastures.”
Secondary forests are expanding around the world, but researchers and policy makers often overlook their importance, Schwartz says. They can improve local livelihoods by providing food, building materials and habitats for animals. They also provide ecosystem services, regulating the hydrological cycle and storing carbon as they grow and mature.
However, the potential for providing those services depends on how the secondary forest recovers.
“Tropical secondary forests can provide an array of ecosystem services as they mature,” Schwartz said. “But we don’t yet know how fire affects these forests’ recovery and their provision of ecosystem services.”
The data she and Gutiérrez are gathering will fill in important gaps in scientists’ understanding of the relationship between farmland and forests.
“For a long time, there was a general attitude that secondary forests weren’t worth much, but secondary forests are the forests of the future,” Schwartz said.
