Effect of selective logging on floristic and structural composition in a forest fragment from Amazon Biome

ABSTRACT. This study was conducted in one region of a Seasonal Semideciduous Forest located in Tapurah (Mato Grosso State, Brazil) with the aim of studying its floristic and structural composition. The fixed area method was applied to 10 × 250 m clusters, allocating and measuring five clusters with five subunits of 500 m² each. Species with a diameter at breast height greater than or equal to 10 cm were considered, and the sample sufficiency of the floristic survey was verified by a species accumulation curve. The similarities between the sample subunits were calculated by the Jaccard Similarity Index, and the species diversity with the Shannon Diversity Index and Pielou Evenness Index. The horizontal vegetation structure was characterized by density, frequency, dominance and the values of ecological importance, and diametric distribution were assessed by the Spiegel procedure. The families Vochysiaceae, Fabaceae and Sapindaceae were highly represented, and Qualea paraensis, Aspidosperma discolor and Matayba arborescens were the most important species. A high diversity and low ecological dominance were found, and the diametric structure of the trees presented a negative exponential distribution. In general, the structure, floristic composition and richness of vegetation correspond to a forest with stable and autoregenerative community after selective logging.

摘要：本研究于巴西马托格罗索州塔普拉（Tapurah）的一处季节性半落叶林（Seasonal Semideciduous Forest）区域开展，旨在探究该林分的区系组成与结构特征。研究采用固定面积样地法（fixed area method），布设10×250米的样区，共设置5个样区，每个样区划分为5个面积为500平方米的亚单元。本研究将胸径（diameter at breast height）≥10厘米的木本物种纳入统计范畴，通过物种累积曲线（species accumulation curve）验证了区系调查的样本充分性。采用雅卡尔相似性指数（Jaccard Similarity Index）计算各样亚单元间的物种相似性，利用香农多样性指数（Shannon Diversity Index）与皮卢均匀度指数（Pielou Evenness Index）评估物种多样性水平。植被水平结构通过密度、频度、优势度及生态重要值进行表征，林木直径级分布则采用施皮格尔法（Spiegel procedure）进行分析。研究区内弯子木科（Vochysiaceae）、豆科（Fabaceae）与无患子科（Sapindaceae）物种丰富度极高，帕拉弯子木（Qualea paraensis）、异色白坚木（Aspidosperma discolor）与乔木麦塔巴（Matayba arborescens）为群落中重要性最高的物种。研究结果显示，该林分具有较高的物种多样性与较低的生态优势度，林木直径级分布呈负指数分布。总体而言，该植被的结构特征、区系组成与物种丰富度均符合经选择性采伐后仍保持稳定且具备自然更新能力的森林群落特征。