Community structure of ferns in riparian forest: evaluation in anthropization gradient

Abstract Riparian forests are essential to the maintenance of biodiversity and foster the development of ferns that are indicators of environmental quality. However, these forests have been degraded due mainly to high population density, pattern of urban settlement and agricultural expansion in rural areas. This study evaluated the environmental quality of riparian vegetation of the Cadeia River in Southern Brazil, using phytosociological parameters of the understory's fern community and a Rapid Assessment Protocol of Habitat Quality (RAPQH). One hundred and twenty plots of 25 m2 were equally distributed among three fragments (FI, FII, FIII). All species of herbaceous ferns were inventoried in each sample unit. We calculated parameters of density, frequency, relative dominance and importance value (IV) of species for the analysis of community structure. The lowest species richness was recorded at FIII (seven species). The floristic composition is more heterogeneous and richness is higher in FI, where the parcels had greater plant cover and RAPQH scores. The RAPQH score decreased with increasing degree of urbanization in the surrounding matrix and FI and FII were classified as "natural," while FIII was classified as "impacted." Considering the four species with the highest IV in the three fragments (totaling 69.11% of IV in the FI, 78.36% and 91.06% in FII and FIII respectively), it can be affirmed that the fern community structure is degraded with increasing anthropization.

摘要：河岸森林 (Riparian forests) 是维持生物多样性的核心生态系统，同时孕育着可作为环境质量指示物的蕨类植物。然而，这类森林因区域人口密度过高、城镇定居模式以及乡村农业扩张等因素持续退化。本研究以巴西南部凯德亚河 (Cadeia River) 河岸植被为研究对象，通过林下蕨类群落 (understory's fern community) 的植物社会学参数 (phytosociological parameters) 与生境质量快速评估规程 (Rapid Assessment Protocol of Habitat Quality, RAPQH) 开展环境质量评价。
研究共设置120个25㎡的样地，均匀分布于3个河岸片段（FI、FII、FIII）中。对每个样地内的草本蕨类 (herbaceous ferns) 开展全面调查，计算物种的密度、频度、相对优势度及重要值 (importance value, IV) 等参数，以解析群落结构特征。
结果显示，FIII的物种丰富度 (species richness) 最低，仅记录7个物种。FI的植物盖度 (plant cover) 与RAPQH评分均较高，其植物区系组成 (floristic composition) 异质性更强、物种丰富度更高。研究发现，生境周边基质的城市化程度越高，RAPQH评分越低；其中FI与FII被归类为"自然状态"，而FIII则被判定为"受干扰状态"。
针对3个片段中重要值排名前四的物种（分别占FI总重要值的69.11%、FII的78.36%与FIII的91.06%）进行分析后可证实，随着人类活动干扰 (anthropization) 程度的加剧，该区域蕨类群落结构呈现退化趋势。