Drought effects on carbon dynamics of trees in a secondary Atlantic Forest.

• Extreme droughts negatively affect tree mortality in the Atlantic Forest. • The drought index, ARID, provides an assessment of the forest response to drought events. • Growth in net and gross carbon are related to drought events. The increase in the frequency of extreme weather events, such as drought, can negatively affect forest dynamics. Understanding this process in the Atlantic Forest and how global climate change affects its ecosystem, can be important for developing conservation and preservation strategies. Therefore, the main goal of this study, was to understand the effects of drought on tree mortality and carbon dynamics in a secondary Atlantic Forest. The study was conducted on a 17 ha secondary Atlantic Forest fragment. Data from 10 permanent plots, with 0.1 ha (20mx50m) each, randomly situated within the area were used. In the monitoring years (1994, 1997, 2000, 2004, 2008, 2010, 2013 and 2016), all individuals with DBH (Diameter at Breast Height; 1.3 m from the ground) greater than or equal to 5.0 cm were inventoried and identified. Carbon dynamics were evaluated. Historical weather data were obtained from the weather station of the National Institute of Meteorology (INMET) and used to calculate the Agricultural Reference Index for Drought (ARID). The correlation between ARID and tree dynamics was evaluated using the Sperman correlation coefficient. We adjusted a logistic regression to assess which factors were important in the risk of tree death. The gross increment was 43.21 MgC ha−1, including the carbon present in the recruitment. Net growth was 25.52 MgC ha−1, higher than the mortality rate, which was 17.70 MgC ha−1. The net periodic annual increment in carbon was 1.16 Mg ha−1 year−1. The highest mortality rates were concentrated in pioneer species and smaller trees. The drought index ARID is the important predictor of mortality risk. We found that the drought four years before the measurements affected carbon dynamics through reductions in growth and survival. The pioneer species showed high mortality in years with extreme drought events. Thus, the proposed drought index, ARID, provided an assessment of the response of forests to drought events, which affects their structure and dynamics. [ABSTRACT FROM AUTHOR]