Dinâmica da serapilheira em uma cronossequencia de florestas no município de Capitão Poço-PA

Abstract

This study was conducted in the municipality of Capitão Poço, mesoregion of the northeast of Pará, microregion of Guamá, with the objective of studying the dynamics of litter in a chronosequence of forests with emphasis on the evaluation of litter stock, production and decomposition. For this purpose, different types of forests were selected: four secondary forests of 6, 10, 20 and 40 years of age, and a primary forest. For the analyses of the litter stocked on the soil, an iron mold of 0,25 m2 was used, in which the whole litter material contained inside was collected. For the litter production, 30 traps also measuring 0,25 m2 were used for bi-weekly collection over 12 months . For the analysis of the litter decomposition it was the litterbag method. Twenty bags (20 x30 cm) were filled with 10 g of mixture of dry leaves recently shed, who were placed on the soil and retrieved after 30, 60, 120, 180 and 270 days. The largest litter accumulation on the soil was found in the six year-old youngest secondary forests (6,70 Mg.ha-1), of 10 years (5,63 Mg.ha-1) and of 20 years (5,65 Mg.ha-1) in relation to the 40 year-old secondary forest (3,73 Mg.ha-1) and the primary forest (3,57 Mg.ha-1), due to smaller litter decomposition rate in the youngest forests that are in the first stages of forest succession. N and Mg of the stocked litter were also larger in the 40 year-old secondary forest and in the primary forest, unlike Ca, that had smaller amount in these forests. However, only P and K did not present statistical differences among all of the analyzed forests. The largest annual production of litter was found at the primary forest (9,81 Mg.ha- 1.ano-1), which differed from the secondary forests of 6 years (7,37 Mg.ha-1.ano-1), 10 years (8,39 Mg.ha-1.ano-1), 20 years (7,88 Mg.ha-1.ano-1) and 40 years (8,06 Mg.ha-1.ano-1), which did not present statistical difference amongst themselves, at the level of 5%. Litter monthly production was continuous in all of the forests, and the largest rates occurred during the driest period of the year, and during the beginning of the rainy season. Likewise, there was negative correlation between the litter production and rainfall in all of the forests, and the largest correlations were detected in secondary forest of 6 and 10 years, presenting both, larger sensitivity to the regime of rains. The largest decomposition rate was found at the oldgrowth forest (2.89), following by the 40 year-old secondary forests (2,33), 10 years (1,52), 20 years (1,43) and 6 years (1,15). These results indicate that as the forest ages, its decomposition rate increases and, consequently, the stock of litter on the soil decreases. This is related to higher activity of the organisms that participate in the breakdown, decomposition and removal of organic matter in more mature forests, needing less time for the renewal of the stocked litter.