Pteridophytes as indicators of urban forest integrity

Abstract In this study we evaluated whether pteridophytes are reliable indicators of urban forest integrity. We inventoried the total pteridophyte diversity in 82 forest patches of the Hochelaga Archipelago (Montreal area, Quebec, Canada), and evaluated their level of integrity using landscape metrics (e.g., area, connectivity, matrix composition) calculated from satellite imagery and land use maps. To obtain information at microhabitat scale, we sampled pteridophyte diversity, as well as biotic and abiotic data, in 225 sample plots within these 82 patches. Relationships of pteridophyte richness to landscape metrics and to microhabitat variables were analyzed with parsimonious regression models. Variation partitioning was used to isolate the effects of each group of variables (forest area, land use, biotic/abiotic and edge effect). To enhance the interpretation of models involving richness, distance-based redundancy analyses of species composition data were performed. Indicator species of low and high levels of urban influence were then identified using the IndVal method. Results showed a strong species–area relationship that was influenced by surrounding land use. Pteridophyte richness decreased with increasing proportions of residential areas, urban heat islands (UHI) and water bodies in a 500 m-buffer zone around patches. Greater richness at the microhabitat scale was associated to greater distance from internal and external edges. Out of 38 species, 19 were significant indicators of low levels of urban influence. We conclude that pteridophytes are positive indicator of forest integrity, since they demonstrate typical plant responses to adverse urban-generated ecological conditions. Green-spored species are of particular interest, since their presence indicates low levels of UHIs. Impact of global climate changes on biodiversity can be predicted by studying UHIs, and we suggest using pteridophytes in this broader context.