ATBC 2012 49th Annual Meeting Bonito-MS, Brasil
S11.OC.07 Amazonian secondary forests respond to climatic variation: biomass dynamics Mesquita RCG1, TV Bentos1, Jakovac AC1,2, Massoca P1, Williamson GB3 - 1Biological Dynamics of Forest Fragments Project, Instituto Nacional de Pesquisas da Amazônia (INPA) and Smithsonian Tropical Research Institute, PO Box 478, 69011-970, Manaus, AM, Brazil, 2Forest Ecology and Forest Management Group, Wageningen University and Research Centre, PO Box 47, 6700AA, Wageningen, The Netherlands., 3Dept. of Biological Sciences, Louisiana State University, Baton Rouge, La 70808, USA The study relates biomass dynamics and climatic events in secondary forest chronosequences of Central Amazonia. Trees with DBH ≥ 3 cm were measured annually between 1999 and 2011 in areas with different use histories: 9 transects on areas clearcut and maintained as pasture with prescribed fires until abandonment, and 8 transects on areas clearcut and abandoned without further use. For each transect we determined above ground live biomass (ABGB), annual mortality (MR) and recruitment (RR) rates. Climate data, obtained from a meteorological tower 50 km from the study area, were related to interannual biomass variations (IBV). Four drought events occurred during the study period, and the El Nino of 2009/2010 caused strong local droughts with 7.2 and 20.4 mm rainfall in September and November of 2009, respectively (6 and 14% of the expected average). For clearcut-abandoned areas, IBV was significant only twice: an increase in 1999/2000 (10.4% ±2.9%) following the 1998 El Nino drought and a decrease in 2009/2010 (12.9±7.2%) during an EL Nino drought. On these transects, larger dominant pioneer individuals died disproportionately. Higher rainfall deficit during the dry season caused higher MR (F1,9=5.04, R2=0.36, p=0.05) and lower biomass accumulation (F1,9=6.17, R2=0.41, p=0.03) in the subsequent year for clearcut-abandoned areas. In abandoned pastures, IBV were constant throughout the period, (pG-G = 0.394, F10,80 = 0.815), pointing to a possible higher resilience to droughts. RR was constant through time, being higher only in 1999/2000 on clearcut-abandoned areas. Biomass accumulation rates approached zero during drier years, and in 2009/2010 were only moderately negative (-2.1 ±6.6%). Use history affects floristic composition, with some species more resilient than others, with a differential ability to support extreme climate events. Drought can be an important agent, affecting species turnover and influencing secondary forest succession in the Amazon.
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