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：河岸林（riparian forests）对生物多样性维持具有关键作用，同时孕育着作为环境质量指示物的蕨类植物。然而，受农村地区高人口密度、城市定居模式及农业扩张等因素影响，这类森林已出现不同程度的退化。本研究以巴西南部卡代亚河（Cadeia River）的河岸植被为研究对象，采用林下蕨类群落的植物社会学参数（phytosociological parameters）与生境质量快速评估方案（Rapid Assessment Protocol of Habitat Quality，RAPQH），对其环境质量开展评价。本研究共设置120个面积为25㎡的样地（plots），将其均等地分配至三个片段生境（FI、FII、FIII）中。对每个样地内的所有草本蕨类（herbaceous ferns）物种进行全面调查记录。研究计算了各物种的密度（density）、频度（frequency）、相对优势度（relative dominance）及重要值（Importance Value，IV），以此开展群落结构分析。FIII的物种丰富度（species richness）最低，仅记录到7个物种。FI的植物区系组成（floristic composition）异质性更强，物种丰富度更高，其样地的植被盖度（plant cover）与RAPQH评分均处于较高水平。RAPQH评分随周边基质（surrounding matrix）的城市化程度提升而呈下降趋势，其中FI与FII被归类为"自然状态"，而FIII则被归类为"受干扰状态"。针对三个片段中重要值最高的4个物种，其分别占据FI总重要值的69.11%、FII的78.36%以及FIII的91.06%，可以得出结论：随着人为扰动（anthropization）程度加剧，蕨类群落结构发生退化。