Although it has been reduced to about 10% of its original area after 500 years of deforestation, the Atlantic Forest has enormous capacity to store carbon in its soil and trees. “Each hectare of Atlantic Forest can store up to 500 metric tons of carbon, whereas that same figure in Amazonia comes to less than 300 metric tons,” said agronomist Simone Vieira of the University of Campinas (Unicamp), in a lecture she gave as part of the Biota-FAPESP Education Conference Cycle in São Paulo on June 25, 2014. Although it stores carbon more efficiently, the Atlantic Forest occupies just 130,000 square kilometers—nearly one-fourth the size of the Amazon Forest.
According to Vieira, the soil of the Atlantic Forest stores proportionately more carbon than that of Amazonia, possibly because of the lower temperatures in southeastern Brazil. Owing to its variety of landscapes—the vegetation includes dunes, restinga forests, mangroves, Brazilian pine forests and dense moist forests—the Atlantic Forest exhibits variations in soil type, water availability and duration of drought periods—all factors that affect the ecosystem’s ability to store carbon.
Vieira and her colleagues are seeking to understand how the temperature variations expected for the coming decades could influence carbon storage in the Atlantic Forest. In research conducted under the Biota-FAPESP Program, they are investigating that effect by collecting soil samples at different altitudes to try to understand how the amount of stored carbon varies as a function of temperature. “Preliminary findings suggest that the higher the temperature, the lower the capacity to store carbon,” Vieira said. If the findings are confirmed, an increase of a few degrees in the Earth’s temperature could turn the Atlantic Forest—presently a carbon dioxide (CO2) absorber—into a source of the compound, which is the principal greenhouse gas.
Changes in soil use and management also affect gas emissions in Amazonia. A recent study published in Global Change Biology showed that environmental disturbances such as selective logging and the use of fire to maintain pastures emitted 54 million metric tons of CO2 in 2010 (40% of the carbon emitted as a result of deforestation in the region that year).
Another study published this year, coordinated by chemist Luciana Gatti of the Nuclear and Energy Research Institute, described a more worrisome scenario. She calculated the carbon balance in Amazonia in 2010 and 2011, which were the warmest years in three decades and featured significant variations in rainfall. In 2011, a very wet year, the forest absorbed 250 million metric tons of carbon, and burnoffs to clear land sent 300 million metric tons into the atmosphere. In 2010, a much drier year, the forest emitted more than it absorbed because of lack of rain and an increase in burnoffs (see Pesquisa FAPESP Issue No. 217). These findings suggest that, if higher temperatures do become a reality, the region could become a CO2 source and thereby step up global warming.
Burnoffs in Amazonia to clear pastureland, harvesting of timber, and agriculture are also changing the cycle of nutrients such as nitrogen, according to biologist Gabriela Nardoto of the University of Brasilia (UnB), who also participated in the conference cycle.
The replacement of forests by pastures and other agricultural activities have reduced the absorption of nutrients in these tropical ecosystems. “Nutrient cycling is one of the most important functions in ecosystem regulation,” Nardoto said. This is because the availability of nutrients determines the distribution of plants in different environments.
Low availability of nitrogen and phosphorous could also limit the growth of secondary forests (areas converted into pastures and later abandoned) in Amazonia. At the same time, she pointed out, burnoffs alter the cycle of nitrogen, an essential element for plant growth. “Nitrogen in the gaseous state makes up 78% of the atmosphere,” she said. “But in order for plants to utilize it, the bacteria in their roots must capture and convert it into other compounds, which will then be converted into ammonium and nitrate in the soil.”
Nitrogen stored in the form of ammonium and nitrate is one of the parameters used by agronomist Plínio Barbosa de Camargo to assess the water quality in the municipality of Extrema, in the state of Minas Gerais. Camargo, who also took part in the most recent edition of Biota-FAPESP, is looking for indicators to assess water quality in reforested areas in the Posses River Basin. “The idea is to compare reforested areas of different planting ages with agricultural areas and see if there has been any improvement in water quality and quantity.”
This was the final meeting of the Biota-FAPESP Education Conference Cycle begun in 2013. According to Carlos Joly, coordinator of Biota-FAPESP, in 2015 the program plans to issue a call for projects that will help improve the quality of environmental and science education for high school teachers and students.Republish