May 2024
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Recent studies have explored the ecological relationship between native urban forests and self-sown non-native forests in large cities and metropolises but further research efforts dedicated to analyzing this relationship in small cities are still needed. To improve our understanding of the ecology of urban native and alien woods in Mediterranean small cities, we analyzed the woody species richness, the community weight mean of moisture and nitrogen ecological indicators, and soil disturbance indicators in the main urban wood types in Campobasso city (Italy), as well as their spatial distribution pattern across a gradient of cover and aggregation of green areas. The study showed that both native oak woods and Robinia pseudoacacia wood contributed to the maintenance of woody species richness. If we exclude the riparian environment along streams, urban alien woods dominated by R. pseudoacacia occupied marginal areas, tolerating soil disturbance and a high disturbance frequency, thus occupying habitats where the native oak forests could not grow. Native oak woods were only found in large and medium-large patches while urban alien woods filled up the vacant lots, even in small patches, showing therefore a context-dependent distribution. The situation was different for the riparian habitat, where R. pseudoacacia wood shared the ecological niche with the native woods with Populus alba and Salix alba, which calls for action to prevent the spread of this alien species along river banks. Our results highlighted that urban remnant woods should be considered important assets for the planning and upkeep of urban green areas.