From soil to bird community: A Partial Least Squares approach to investigate a natural wooded area surrounded by urban patchwork (Astroni crater, southern Italy)

Forests are among the most important land ecosystems both in term of their contribution to the global carbon cycle and for their prominence in hosting large biodiversity. Under a changing world, both in terms of land use and climate scenarios, it is pivotal to understand the matter and energy flows in complex ecosystems such as forests, in order to infer potential relationships at different levels, i.e. from soil to bird community within the forest stands. In this context, soil organic matter is main source of carbon and energy for heterotrophic soil organisms, which are a main component of the whole food web all the way up to bird communities. Even though many studies have investigated factors affecting C cycle and bird communities in forest ecosystems separately, an integrated approach that links soil to bird community was never attempted. Accordingly, we have used an innovative Two-block Partial Least Squares analysis to investigate patterns of covariance between soil and nesting bird communities in a relatively small wooded area surrounded by the urban area of Naples (southern Italy). Our research revealed that, in spite of the small extent and the surrounding urban context, the area of the Astroni hosts a substantial C stock and has a diversified bird nesting community. The abundance of species such as blue tit, jay, green woodpecker and great tit had a direct covariance with C stock in litter, while sampling sites that were characterized by greater C stocks in the soil and higher microbial activity were correlated with abundance of other bird species, most noticeably short-toed treecreeper and blackbird. Despite the limited extent of our research area, our study showed, for the first time, patterns of covariance between some forest species and different soil variables, linking forest ecological compartments whose connections are not immediately detectable and that could open new perspectives in land use management, both in terms of C stock and biodiversity evaluations.