Edge effect on the spatial distribution of trees in an Araucaria Rainforest fragment in Brazil

Abstract The objective of this research was to evaluate which species in the Brazilian Araucaria forest have its spatial distribution influenced by edge effects. We performed annual forest inventories inside two one-hectare plots, divided in 10 rectangular subplots, delimited by every 10 meters of edge distance. Each tree with at least 10 cm at DBH was identified to species level, and their allometric measurements and geographical coordinates were recorded considering the categories living, recruitment and mortality. We analyzed the correlation between the abundance of each species in each subplot and its distance by the Spearman's Correlation Coefficient and a Generalized Additive Model (GAM) with a Poisson distribution. We analyzed the distribution of some species and the ecological groups using a Kernel density model. We observed numerous pioneers and early secondary species with relationship with the edge distance, usually concentrated close to the edges. The late secondary/climax species are more evenly distributed in the plots, despite of some species, as Eugenia uniflora, are negatively affected by the edge. From these results, it is observed that some light demanding species can be favored to live close to the edges, even if some shadow tolerant species can inhabit this region as well.

摘要 本研究旨在探究巴西南洋杉林中哪些物种的空间分布受边缘效应影响。本研究于两块1公顷样地内开展年度森林调查，将每块样地划分为10个矩形子样地，子样地以距林缘每10米为基准进行界定。对所有胸径（Diameter at Breast Height，DBH）≥10厘米的林木开展物种鉴定，并记录其异速生长测量数据与地理坐标，同时按存活、更新补充与死亡三类进行分类登记。本研究采用斯皮尔曼相关系数（Spearman's Correlation Coefficient）以及服从泊松分布（Poisson distribution）的广义加性模型（Generalized Additive Model，GAM），分析各子样地中各物种的多度与其距林缘距离的相关性；并借助核密度模型（Kernel density model）对部分物种及生态类群的分布格局展开分析。研究发现，众多先锋物种与早期次生演替物种的分布与林缘距离存在显著关联，通常集中分布于林缘附近区域。晚期次生演替/顶极群落物种则在样地内分布更为均匀，尽管部分物种如红果仔（Eugenia uniflora）会受到林缘的负面影响。综合上述结果可知，部分喜光物种更适宜在林缘附近存活，即便部分耐阴物种同样可在此区域栖息。