Relationship of litter fall with diameter increment in an old growth forest in central Amazon region

Abstract

During the last decades, meteorological extreme events were frequent in the Amazon region. Floods followed by severe droughts can affect the dynamics of carbon in the forest, which is closely linked to environmental conditions of humidity. The litter and the growth of the trees are the main components of above ground net primary production. The objective of this study was to quantify the litter production and the diameter growth of trees, investigating their correlation with the seasonal rains in central Amazonian. The study was developed at the Experimental Station of the National Institute for Research in the Amazon (INPA), ZF2, Manaus-AM, Brazil, in two transects with dimensions of (20×2500m). The litter samples were collected with 120 litter traps and the growth of the trees was obtained through dendrometric bands installed on 250 trees. Precipitation was obtained by automated equipment (gauges) installed in the study area. The litter production for the period was 7.1 ± 0.23 Mg ha-1.year-1 on the plateau, 6.3 ± 0.15 Mg ha-1.yea-1 in the low land (confidence interval (CI) = 95%). The litter production was different per topographical classes (n=120, p=0.008). The correlation of litter and rain for the plateau was r=-0.83 (p=0.001) and r =-0.70 (p=0.011) for the low land. The average diameter increment of 250 trees was 1.43 ± 0.18 mm.year-1 (95% CI). The increment on the plateau was 1.46 ± 0.18 mm.year-1 and 1.35 ± 0.26 mm.year-1 (95% CI) in the low land, with weak evidence (n=250 and p=0.23) that the increments between topographic classes were not different. The correlation between rainfall and the mean increment of trees for the period studied was r=0.55 (p=0.063). The correlation between the production of litter and the increment in diameter of the trees was r =-0.60 (p=0.06). The correlation for topographical classes plateau is r=-0.51 (p=0.087) and low land is r=-0.57 (p=0.055). When the forest has a positive increase, this indicates that the trees are absorbing carbon from the atmosphere; while in the high litter production period, the trees show smaller increments and the carbon balance may be negative. All these relationships have an important and strongly correlated variable factor: rain.