From rural-urban gradients to patch – matrix frameworks: Plant diversity patterns in urban landscapes

Studies have attempted to disentangle the relationships between urban properties and species richness patterns by studying them within the urban-rural gradient context, the Island Biogeography framework, or the patch-matrix approach. We compared and contrasted these frameworks, to highlight their attributes. We assessed the role of patch properties and matrix characteristics, in light of these approaches, to identify the relative roles of different drivers in dictating urban plant species richness patterns. Vegetation surveys were conducted in 41 open space patches within the city boundaries of Haifa, Israel. Plants were classified into three categories: rare, native and non-native. Patch properties, distance to nearest neighboring patch, distance to city boundary, within patch heterogeneity and percentage of sealed surface buffering the patch were evaluated in relation to species richness. Non-linear regressions indicated that total, rare and native species richness were best explained by a combination of patch area, sealed surface and patch habitat heterogeneity. Non-native species richness was best explained indirectly by the proportion of sealed surface. No clear cut distinctions between the three frameworks were observed. The results point to the existence of non-linear interactive relationships between the drivers and species richness, which depend on patch and urban matrix properties, particularly on degree of urbanization. We conclude that patch-matrix mechanisms interact with the urban-rural gradient approach to determine plant richness patterns in urban landscapes. Additionally, the degree of urbanization is differentially associated with richness patterns, where rare and native species are negatively associated with it, and non-native species are positively associated with urbanization.