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 枯落物生产对于陆地生态系统的养分循环至关重要。2009年11月至2011年10月，研究人员针对位于巴西东北部帕拉伊巴州半干旱区域帕拉伊巴卡里里的卡廷加（Caatinga，一种季节干燥热带林（Seasonally Dry Tropical Forest））的两个区域，开展了月度枯落物生产量监测与分析。其中一处区域为阿尔马斯农场私人自然遗产保护区（Private Natural Heritage Reserve，缩写RPPN），受法律保护；另一处为莫雷拉斯农场（Fazenda Moreiras），未受法律保护。本研究旨在评估降水、蒸散量与植被结构对枯落物生产时空动态的影响。每个样地随机选取8个采样点，在每个采样点处设置2个间距50米的1平方米枯落物收集器。收集到的枯落物经分拣、干燥后称重。此外，在每个收集器周边10米半径的样地内，调查乔灌层的相关特征，包括密度、物种丰富度、平均高度与平均基面积。阿尔马斯农场的总枯落物生产量为4500千克·公顷⁻¹·年⁻¹，莫雷拉斯农场为3300千克·公顷⁻¹·年⁻¹，该数值处于季节干燥热带林的预期范围内。枯落物生产的年际与年内变化与降水量和蒸散速率呈正相关，且在最高降水事件发生4个月后，旱季的枯落物生产量出现显著下降。此外，枯落物各组分的贡献占比存在显著差异：叶片组分占枯落物总量的60%以上，而植被结构可解释75%的枯落物生产变异。因此，气候因子与植被结构共同影响枯落物生产的时空动态，进而对巴西半干旱区域的养分循环动态产生调控作用。