Revelando as causas e a distribuição temporal da mortalidade arbórea em uma floresta de terra-firme na Amazônia Central

Abstract

We analyzed the causes and temporal distribution of tree mortality in 10 ha of an old growth forest located in E.E.S.T / INPA, Manaus, Amazonas. The study aimed to 1) reveal the main causes of tree death and 2) describe the variation in mortality over the year and also correlates it with climatic variables. The study was conducted in two transects of 20 x 2,500 m (5 ha each) and all individuals with DBH ≥ 10 cm were sampled, totaling 5,808 trees. The transects were monitored every month, alternately, for a year. The sanitary condition of living trees was observed in each monitoring. The dead individuals were classified according to their mode of death (standing, broken or uprooted). The pre and post-death of the trees were analyzed in order to identify the cause of the death. During one year of monitoring, 67 individuals died or 6.7 trees / ha and the mortality rate was 1.15%. year-1. Of the 67 dead trees, 24 died uprooted, 23 broken and 20 standing dead. Mortality was highly correlated with the rates of monthly rainfall (r = 0.85). Therefore, the events of death are more frequent in the rainy season. The correlation between mortality and wind speed was not as strong as expected (r = - 0.29) and the direction of the individuals fall was random. Altogether were distinguished six categories of cause of tree death. Storms (rain + wind) was the main cause, accounting for 45% of deaths. Close behind was stress and biotic factors, killing 20 of the 67 dead individuals. Of these 20 trees, at least one was killed by liana Apuí and 3 died from infestation by pathogenic fungi. The results indicate that from the small intervals between monitoring is possible to determine the cause of trees death in tropical forests and elucidate the effect of seasonal variations on mortality. The work has generated new information to the Amazon and it is suggested that these studies are included in the projects of forest dynamics.