Local and global patterns of urban soil biodiversity
Urban soils provide many of the same ecosystem services as “natural” or agricultural soils e.g. decomposition and nutrient cycling, water purification and regulation, medium for plant growth, and habitat for organisms. Soils in cities are disturbed, transported, heavily managed and even created. Urbanization is portrayed as one of the leading causes of biodiversity loss and ample evidence from large organisms supports this claim. Due to the well known challenges to study soil biota, e.g. their cryptic nature and huge spatio-temporal heterogeneity, and taxonomical difficulties, urban soil biodiversity has not been sufficiently explored. Much less is known about the mechanisms driving soil invertebrate assemblages in cities. Urban land use can be viewed as a natural experiment, in which central questions in general ecology, such as disturbance responses, resilience, metacommunity dynamics, species invasion and biotic homogenization can be addressed. In this presentation I will summarize the current knowledge on urban soil biodiversity focusing on selected invertebrate groups such as earthworms, isopods, springtails, millipedes, and beetles. I present local diversity data from the Baltimore Ecosystem Study LTER, Budapest, Hungary, and Warsaw, Poland. I will compare soil fauna across cities on a large, biogeographical scale.
Urban soil is not just sterile, lifeless dirt. Rather, there is a surprisingly rich soil community playing fundamental roles in nutrient cycling, altering soil habitat being food supply to larger organisms that people value in cities. Species new to science have been described. Whether urban soil biodiversity is lower or higher than the previous habitat depends on the nature of that historical habitat. Replacement of large scale agricultural fields by suburbs, with their more diverse plantings and finer scale spatial heterogeneity, can actually increase soil biodiversity. The degree of biotic homogeneity among soil fauna is not uniform and varies by taxa. For instance, international comparisons of urban carabid beetle assemblages have shown a large degree of local differences. Other taxa, such as carrion beetles (Silphidae) have more specialized natural histories, and their species composition is largely determined by the regional species pool and the size and quality of urban forest fragments. By contrast, earthworm species show a high degree of similarity among cities in the USA and Europe due to a high proportion of synanthropic, peregrine species. The diverse urban landscape can still harbor a large percentage of the regional species pool, but the proportion of species surviving in cities is negatively correlated with that pool.