The phenological response of European vegetation to urbanisation is mediated by macrobioclimatic factors

Abstract

Plant phenology is a crucial component of ecosystem functioning and is affected by multiple elements of global change; we therefore need to quantify the current phenological changes associated to human activities and understand their impacts on ecosystems. Urbanisation and the intensification of anthropogenic activities alter meteorological conditions and cause phenological changes in urban vegetation worldwide. We used remote sensing data to evaluate the phenological response (start of season date SOS, length of season LOS and end of season date EOS) to urbanisation in the 69 most populated pan-European metropolitan areas (i.e., those that include cities with a population over 450,000 inhabitants) for the period 2002-2021, taking into account the main vegetation types (evergreen forests, deciduous forests, mixed forests, sparse woody vegetation and grasslands). While our findings support previously reported general phenological patterns in response to urbanisation, we found that macrobioclimatic factors strongly determined the strength and direction of the phenological response to urbanisation intensity. In general, SOS advanced and LOS increased with urbanisation intensity across Europe. However, the greatest advances in SOS were registered in metropolitan areas in the Mediterranean region, where there was also more uncertainty in the relationship between SOS and urbanisation. The EOS advanced with urbanisation in metropolitan areas in the Mediterranean macrobioclimate (except for deciduous forests), whereas the opposite trend was observed in metropolitan areas from the Temperate macrobioclimate. Our results suggest that macrobioclimatic constraints operating at the continental scale mediate the relationship between urbanisation intensity and plant phenology.