Temporal Variation of Ecological Factors Affecting Bird Species Richness in Urban and Peri-Urban Forests in a Changing Environment: A Case Study from Milan (Northern Italy)

Urban and peri-urban forests determine different habitat services for biodiversity according to their characteristics. In this study, we relate ecological characteristics of urban and peri-urban forests to forest bird species richness and we assess whether their effect changed over time due to the urban sprawl within the urban region of Milan, Italy. We analyse two periods (1998–2002 and 2010–2014) using weighted generalized linear models that considered urban and peri-urban forests collectively and urban and peri-urban forests separately. Patch area, proximity to source areas and number of surrounding urban and peri-urban forests were the main factors predicting species richness within urban and peri-urban forests in both periods. While there were no differences in factors affecting bird richness in peri-urban forests between the two periods, the negative effect of urban matrix density was statistically significant for birds inhabiting urban forests in the second period. Moreover, protected areas within urban and peri-urban forests and urban forests in the second period were important determinants in providing suitable habitat for birds at the regional scale. This study offered important insights regarding urban and peri-urban forests characteristics that should be maintained to ensure biodiversity conservation across changing urban landscapes.