Spatial-temporal variation in litterfall in seasonally dry tropical forests in Northeastern Brazil

Abstract The production of litterfall is essential for nutrient cycling in terrestrial ecosystems. From November 2009 to October 2011, analyzed the monthly litterfall production in two areas of Caatinga, a type of Seasonally Dry Tropical Forest located in the Cariri Paraibano, in the semiarid region of the Paraíba, Northeastern Brazil. One of the areas, Private Natural Heritage Reserve (RPPN) Fazenda Almas, is legally protected, and the other, Fazenda Moreiras, does not. The aims were to evaluate the effects of precipitation, evapotranspiration and vegetation structure on the temporal and spatial dynamics of litterfall production. Eight sampling points were randomly chosen at each site, and two 1 m2 collectors were installed 50 m apart from each other. The collected material was sorted, dried and weighed. Additionally, the characteristics (density, species richness, height and mean basal area) of the tree-shrub stratum in plots with a 10 m radius surrounding each collector. Total litterfall production was 4,500 kg ha-1 yr-1 for Fazenda Almas and 3,300 kg ha-1 yr-1 for Fazenda Moreiras; these values were within the expected range for Seasonally Dry Tropical Forests. The inter- and intra-annual variation in litterfall production was positively correlated with precipitation and evapotranspiration rates, and four months after the highest precipitation rates, there was a marked decrease in litterfall occurred during the dry season. Furthermore, the contributions of the material fractions were distinct with the leaf fraction representing for more than 60% of the litterfall, and the vegetation structure explained 75% of the variation in litterfall production. Therefore, climatic factors and vegetation structure affect the temporal and spatial dynamics of litterfall production and consequently influence nutrient dynamics in the semiarid region of Brazil.

摘要 陆地生态系统中，枯落物生产对于养分循环至关重要。2009年11月至2011年10月，本研究针对巴西东北部帕拉伊巴州半干旱地区卡里里帕拉伊巴诺（Cariri Paraibano）境内的卡廷加（Caatinga）——一种季热带干旱林（Seasonally Dry Tropical Forest）——的两个区域，开展了枯落物产量的月度监测。其中一处为私有自然遗产保护区（RPPN）法曾达阿尔马斯（Fazenda Almas），已获得法律保护；另一处为法曾达莫雷拉斯（Fazenda Moreiras），未受法律保护。本研究旨在评估降水、蒸散量及植被结构对枯落物产量时空动态的影响。每个样地随机选取8个采样点，在相互间距50米处各布设2个面积为1 m²的收集器。收集得到的枯落物经分拣、烘干后称重。此外，在每个收集器周边10米半径的样地内，调查乔灌层的特征指标，包括密度、物种丰富度、平均高度与平均基面积。法曾达阿尔马斯的总枯落物产量为4500 kg·ha⁻¹·yr⁻¹，法曾达莫雷拉斯为3300 kg·ha⁻¹·yr⁻¹，该数值处于季热带干旱林的预期范围之内。枯落物产量的年际与年内变化与降水及蒸散速率呈正相关；在最高降水速率出现的4个月后，枯落物产量出现显著下降，且该下降发生于旱季。此外，枯落物各组分的占比存在显著差异：叶片组分占枯落物总量的60%以上，而植被结构可解释75%的枯落物产量变异。综上，气候因子与植被结构共同影响枯落物产量的时空动态，进而对巴西半干旱地区的养分循环过程产生影响。