Experimental Fire in Brazilian Amazon Furthers Understanding of Impact on Ecosystem
To better understand the impacts of fire on the forest, scientists from Woods Hole Research Center (WHRC) and the Amazon Environmental Research Institute (IPAM) conducted an experimental fire from August 17 to 20th. This burn – part of a multi-year, large-scale research project – encompassed 100 hectares of forest in the transition zone between savanna and forest, in the state of Mato Grosso, Brazil. The region is known for high rates of deforestation and frequent occurrence of large fires of human origin.
According to Michael T. Coe, a WHRC scientist leading part of the project, “We have found that the forest is resilient, we see a lot of mortality but there is rapid regrowth of many of the core species and grasses are slow to invade. We have also found that fire frequency is extremely important. If the forest burns every few years, there is a lot of fuel build-up between fires that causes very intense fires compared to forest that burns every year.”
The first experimental fire was held in 2004, and has been the largest experiment with controlled fire in tropical areas of the world. The total area for experimental fire has been 150 hectares, or approximately 371 acres. The experimental area was divided into three plots of 50 hectares each. In one, the scientists control the area so no kind of burning happens. This "control area" serves as a parameter for future comparisons. Another 50 hectares were burned only once every three years. The remaining 50 hectares were burned annually to obtain data for research.
Before burning, researchers from both WHRC and IPAM collected many types of ecological information such as tree species, size and abundance, forest structure (canopy openness), number of seedlings, measurements of combustible material in the ground (stems and leaves) and also on groups of animals (insects and small mammals). After the fire, all this information is collected again for comparison on how the environment reacts to fire. The local temperature and humidity are also monitored before and after the fire to detect changes in the microclimate of the forest. The soil moisture is measured to see how these changes affect the availability of water.
According to Oswaldo de Carvalho, Jr., a researcher with IPAM, "To understand how fire affects the Amazon forest, we needed to burn forest areas with different intensity and frequency." He adds that the lack of scientific data in this area is because it is rarely possible to have systematic information before the occurrence of fire, disabling the knowledge of fire behavior and its effects on the structure and dynamics of forests.
In this project, researchers built a complex technological infrastructure for data collection. This included various types of sensors to measure temperature, humidity in the area, and the flow of water in the soil. Some of these sensors are installed in pits up to 10 meters deep. Equipment is also used to measure coverage of the forest canopy. Special collectors of leaves and seeds are used to check the productivity of the forest.
In the experimental area over 10,000 trees were surveyed. Besides the monitoring of regeneration and tree mortality, the parameters of canopy openness, tree growth and microclimate are measured over the years.
According to Jennifer Balch, a researcher at the National Center for Ecological Analysis and Sinthesys (NCEAS), University of California, preliminary results show that the transition forests are extremely vulnerable to recurring fires. The mortality of trees and vines increased between 80% and 120% respectively in comparison to the controlled area, as scientific observations show. Moreover, they concluded that forest fires diminish the number of species by 50% compared to forests not affected by fire. These areas, according to Balch, become more susceptible to invasion by non-native grasses, hindering the natural regeneration of vegetation. In addition, a third of all living biomass of the forest is lost after the first fire, making a major threat to the stock of carbon stored in these forests.
The results also reveal that the transition forest may be relatively resistant to forest fires of low intensity, but not to the recurrent fires of greater intensity. In a few years of experiment, the fires have transformed the forest into highly degraded due to the increased tree mortality. Most surprising was the manner in which this transformation occurred in a nonlinear manner. "We've seen dramatic increases in mortality of large trees just after the fires conducted during the drought of 2007," says IPAM researcher Paulo Brando. This indicates that more intense and more frequent droughts possible in the region will have serious consequences on the dynamics of these forests.
The location of the experiment
The farm where the experiment is conducted belongs to André Maggi, a supporter of the project. The farm has 82,000 hectares and is mainly for the cultivation of soybeans. The experiment is bordered by a country road and a crop field. To perform the controlled burning, scientists surround themselves with great care to ensure the safety of researchers and their teams and also for the fire to not escape to adjacent areas. The experiment has a license from the appropriate Brazilian environmental agencies.
In addition to WHRC and IPAM, other research partners include the State University of Mato Grosso, ESALQ / USP, Museu Paraense Emilio Goeldi, Universidade Federal do Pará, University of Florida, Yale University and RAINFOR - Oxford University.