Exploring the distribution pattern of native and alien forests and their woody species diversity in a small Mediterranean city

Recent studies have explored the ecological relationship between native urban forests and self-sownnon-native forests in large cities and metropolises but further research efforts dedicated to analyzingthis relationship in small cities are still needed. To improve our understanding of the ecology of urbannative and alien forests in Mediterranean small cities, we analyzed the woody species richness, thecommunity-weight mean of moisture and nitrogen ecological indicators, and soil disturbance indicatorsin the main urban wood types of the city of Campobasso (Italy), as well as their spatial distributionpattern across a gradient of cover and aggregation of green areas. The study showed that both nativeoak forests and Robinia pseudoacacia forests contributed to the maintenance of woody species richness.If we exclude the riparian environment, R. pseudoacacia forests occupied small marginal patches,tolerating soil disturbance and a high disturbance frequency, thus occupying habitats where the nativeoak forests could not grow. Conversely, R. pseudoacacia forests shared the ecological niche with thenative riparian forests, which calls for action to prevent the spread of this alien species along riverbanks. Our results highlighted that urban remnant forests should be considered important assets for theplanning and upkeep of urban green areas.