| Popis: |
We compare temporal variations in leaf fall among three sites of evergreen Atlantic Forest and analyze how climatic variables influence it. Sites were located at Serra dos Orgaos National Park at different altitudes. Litter was collected monthly, from September 1997 to September 2005. Leaves were separated from other litter elements, oven-dried and weighted. Differences in leaf fall mass among grids and how they correlated with temporal variations were analyzed. Climatic variables were obtained from a nearby station and deviations from climatological normals were analyzed. We grouped climatic variables using Principal Component Analyses (PCA) and the highest scores of the two main factors were selected to construct regression models for different time lags. Leaf fall represented 50.5-70 percent of the total litter fall and mean leaf fall differed significantly among grids. However, leaf fall seasonality in the three areas were correlated. Leaf fall increased at the end of dry periods, when temperature and precipitation started to increase. Climatic variables were classified into two groups: seasonal and anomaly. Models constructed with lag variation from 0 and 6 months show that leaf fall was best explained by an anomaly in the maximum mean temperature, with lag 0, and by precipitation, with a six-month lag. We conclude that plant species respond immediately to drastic deviations from climatic factors, while regular climatic conditions are responsible for the seasonality of leaf fall, most likely as a late response to water shortage at the end of the dry season. . |
