Determinantes da variação geográfica da biomassa flo restal no sul do Brasil: a contribuição de Floresta com Araucária

Abstract

A variety of environmental and biotic factors affect forest productivity and determines biomass accumulation. In forest ecosystems, the increase in primary productivity results in an increase in plant biomass and consequently elevates storage of organic carbon. Among the factors that influence biomass production, we should mention temperature, rainfall, soil type, floristic composition and disturbance regimes. It is widely accepted among researchers that increasing temperature, rainfall homogeneity and fertile soils increase productivity and enable higher biomass accumulation. Moreover, many authors indicate that species richness and diversity have a positive effect on biomass, because of the higher efficiency on resource use. The objectives of the study were to evaluate the variables affecting live aboveground forest biomass (AGB) in Subtropical Southern Brazil and analyze the spatial distribution of biomass estimates. The study was performed in Subtropical Moist Forests of Southern Brazil, classified as Broadleaf Forests (BF) and Mixed Coniferous-Broadleaf Forests (MF). A total of 38 1-ha plots were selected and all trees with DBH ≥ 9.5 cm were included for biomass estimation. Values for AGB were obtained using published alometric equations. Environmental variables (elevation, rainfall, temperature and soils) were obtained from the literature and biotic variables (density and diversity) were calculated from the data set. For the total number of plots, mean AGB was 194.3 ± 116.8 Mg ha-1 (mean ± SD) and mean carbon density 97.2 ± 58.4 MgC ha-1. Estimates differed between forest types (t= -4.598; p<0.001): mean AGB was lower in BF (AGBBF = 118.0 ± 58.4 Mg ha-1) when compared to MF (AGBMF = 249.8 ± 118.1 Mg ha-1). Principal component analysis performed well in summarizing climate and soil data sets. The explanatory multiple regression explained 49.8% of the variation in AGB (Ylog biomass = 0.03(0.49)xsqroot density + 0.11(0.36)x latitudinal axis - 0.22(-0.85)xelevation axis ? 0.03(-0.36)xdiversity - 0.09(-0.35)xorganic matter axis + 1.66; F5,32=8.34, p<0.001; r2=0.498). Elevation contributed more to the model than any other variable. There was no spatial dependency found between plots. The results from our study showed a negative relationship between aboveground biomass and elevation. Therefore, higher values of AGB are located at higher altitudes and subjected to cooler temperatures and frequent monthly rainfall. There seems to be an important contribution of the coniferous species Araucaria angustifolia in MF plots, since large trees of this species were found in many of the samples. Subtropical forests appear to be of great interest for carbon sequestration, especially in areas of Mixed Coniferous-Broadleaf Forests. In Brazil, the endangered coniferous species A. angustifolia is part of a high diversity forest (Araucaria Forest), with great potential for biomass accumulation and carbon sequestration, emphasizing the importance in conserving this ecosystem.