Produção de serapilheira e incremento diamétrico em uma Floresta de Terra Firme na Amazônia Central

Abstract

The above ground production in tropical forest has the litter and trunk increment of trees the main components of net primary production. The growth in the trunk is the way to capture carbon from the atmosphere and allocate in woody tissues. The litter fall is like as loss of carbon in the system, but is essential for the recycling of nutrients, which keeps the Amazon forest with high biomass in poor soils. The different types of soils and rainfall seasonality in central Amazon require adaptive differences of vegetation, and thus, the growth and yield of trees variable depending on their position. Therefore, the study objects to quantify litter fall production and the trunk increment of trees in two topographic classes (plateau and “baixio”), with different soils and their relations with precipitation and soil moisture in an old growth forest in central Amazon. This study was carried out in the ZF-2 Experimental Station of the National Institute for Research in the Amazon (INPA), some 90 km North of Manaus, Brazil. Litter production and diameter increment in two transects with (20x2500m) were monitored. The collection was performed with 120 litter traps (60 plateau, 60 “baixio”) with dimensions of 0.5 x 0.5 meters, with an area of 0.25 m2 were systematically arranged in two equidistant lines at 40 meters. The material was collected in the period 15-30 days, dried 65°C until constant weight, and separated into leaves, twigs (diameter < 2cm) and miscellaneous for weight. The collection of diametric increment was performed in 250 trees with “dendrometer” bands, with 125 in each topographic class (plateau and valley), randomly distributed among individual trees of different diameters. The data accumulated rainfall and soil water potential were collected with the aid of automatic equipment installed in the study area. Litter production and diameter increment were analyzed with a factorial analysis of variance with repeated measures. Pearson correlations with Bonferroni probability were performed to verify the tightness of the relationships analyzed in the study. Sampling was conducted between September 2012 and October 2013. Litter production on the plateau was 7.1 ± 0.2 Mg. ha- 1.yr - 1 (CI=95%) and was significantly higher than in the valley 6.3 ± 0.1 Mg. ha- 1.yr - 1 (n = 120 p = 0.008). Litter production for the period was variable during the year, with peak production in the dry season (June to October), with a correlation with rainfall (r = -0.77, p = 0.0029 ). Litter production had leaf production with approximately 70% of the total, with most of the production. The increase in mean diameter was 1.43 ± 0.18 millimeters.yr-1 did not differ between the topographies. However, the increments were slightly higher on the plateau. Rates increase followed trends in rainfall, where diameter growth was higher in the rainy season than in the dry season (r=0.56, p = 0.005). Trees with a diameter greater than 30 cm showed higher increments. The increment and litter fall showed no correlation with soil water potential. The correlation between litter production and the increment was (r=-0.60, p=0.06) where as the highest values for litter fall with to the smallest increment values. These results suggest that trees in the study site invest in growth propitious moments, especially with the presence of abundant water. When there is less water available, the plant decreases the cambial activity and is intended to maintain the minimum investment in your physiology, senile dispersing equipment and preparing to new phenology event.