Dinâmica da serapilheira em um trecho de floresta atlântica secundária em área urbana do Rio de Janeiro

Abstract

Many studies on litter production and decompositon have been conducted throughout the Atlantic Rain Forest ecosystem with different use history and currently protected by conservation units. The present study was carried out in a section of secondary Atlantic Rain Forest known as the Camorim Forest, in the city of Rio de Janeiro. During the 1940s and 50s, the area was clear-cut for wood extraction, coal production and agriculture. To determine climate and human influence on the litter dynamic, 24 litterfall collectors were distributed over two plots; one located at the bottom of valley and the other located on the hill ridge. Temperature and rainfall data were also collected from two climate stations near the area under observation. Over a three year period, litterfall samples were collected every two weeks while the standing litter crop was collected every four months. Litterfall production collected from the bottom of the valley registered 9,5 Mg.ha-1.year-1, 9,7 Mg.ha-1.year-1 and 10,5 Mg.ha-1.year-1 over a three year study period. On the hill ridge position, litterfall production was 11,3 Mg.ha-1.year-1, 10,4 Mg.ha-1. year-1 and 12,9 Mg.ha-1.year-1. During the third year, the hill ridge position registered the greatest litter production among studies conducted on the Atlantic Rain Forest ecosystem. No statistical differences were observed in total litter production between the two positons over the three year study period. The production of leaf litterfall and reproductive structures in the hill ridge position were considered statistically higher during the three years of study. The highest production for reprodutive structures was registered during the first year, and the lowest during the second year. The litterfall composition percentages from the bottom of the valley were: leaves (62%), wood (30%), reproductive structures (5%) and others (3%). On the hill ridge position the percentages were: leaves (69%), wood (20%), reproductive structures (7%) and others (3%). Statistical differences were not detected for the standing litter crop between the two positions. The site at bottom of the valley registered 4,3 Mg.ha-1 while the position on the hill ridge was 4,6 Mg.ha-1. The average coefficient of decomposition (k) was 2,33 at the bottom of the valley and 2,53 on the hill ridge. The high litterfall production registered in the present study was considered a result of the natural regrowth of the Camorim Forest. The extremely high litterfall production, as well as the high rates of decomposition observed in the hill ridge position were the results of many interacting factors, not all of which were covered by this study. One such factor, the high rainfall registered in the first and third years, can be highlighted. Litterfall production, litterfall decompositon, Atlantic Rain Forest.