An Oxford University study has measured the rate at which trees in the Amazon basin in Brazil, Peru and Bolivia inhale carbon from the atmosphere during severe drought . The research has focused on the growth rates and photosynthesis of trees in 13 rainforest areas and has compared the sectors that were most affected by the severe drought in 2010 with the areas that were not affected.
According to the scientists involved, the growth rates of the drought-stricken trees did not decline , but the rate of photosynthesis – the process by which plants convert carbon into energy to fuel their activity – slowed by 10% for more six months. This assumes that the decrease in carbon sequestration did not lower the growth rates of perennials but did increase the mortality of the trees , according to Christopher Doughty of the Oxford School of Geography and Environment and lead author of the study. In his view, “when trees die and decompose, carbon dioxide concentrations in the atmosphere rise, which could accelerate climate change during droughts.” Computer simulations of the biosphere have predicted these kinds of responses to drought, but these are the first direct observations of this effect in tropical forests.
Each of the plots studied, representative of the various climatic and soil conditions of the Amazon basin, measures one hectare and is home to between 400 and 500 trees . On the research, the University of Oxford has collaborated with the Global Ecosystem Monitoring Network (GEM), which closely tracks forest activity around the world.
The fieldwork lasted three years, during which the experts spent several weeks at each site to measure the rate of woody growth of each tree and the number of roots that had emerged. They also weighed the monthly leaf drop to calculate the number of leaves that each tree produces and calibrated the release of carbon dioxide from which wood, roots and leaves live to estimate the metabolic activity of the forest using infrared gas analyzers .
The 2010 Amazon drought coincided with the scientists’ work, but only affected parts of the Amazon. Taken together, the research data suggest that droughts in the Amazon basin are affecting CO2 levels in the atmosphere globally , both in the short term, by decreasing photosynthesis, and in the long term, through increased tree mortality.
