Impacts of spatiotemporal urban expansion on the species richness and functional traits of adults and sapling woody trees and shrubs of urban remnant forest patches

Abstract

Remnant urban forests, or scattered patches of forest within urban areas, serve as crucial biodiversity reservoirs. Investigating how urban environments influence biodiversity within these forests is essential for enhancing conservation strategies. This study examined data from 15 remnant forest patches in Guiyang, China, to assess the impacts of spatiotemporal urban expansion on species richness and functional traits across different life forms and ontogenetic stages in both interior and edge habitats of these patches. Employing generalized linear regression models, we examined variables including the intensity of urban expansion, road density, type of expansion, compound terrain complexity, and the interplay between urbanization levels and the timeframe of urban development. Our results indicated that increased urban expansion intensity positively affected the species richness of shrubs, yet negatively influenced tree richness. Furthermore, high urbanization levels were associated with lower species richness in adult trees and the species in the sapling and shrub layers with high seed mass traits when the duration of urbanization was prolonged. Additionally, we observed that edge-expansion type urban growth notably increased the risk of losing species with resource-conservation traits compared to leapfrog growth patterns. These outcomes highlight the detrimental effects of intensive urban expansion and edge-expansion growth on the conservation of woody plants, especially those characterized by resource conservation traits. They also draw attention to the delayed impacts of urbanization on plant diversity. In response, we advocate for the reduction of urban expansion intensity and control over edge-expansion growth patterns to protect plant diversity in remnant forests. It is also critical to prioritize the conservation of remnant forest patches located in areas that have undergone extensive urbanization for prolonged periods, as these are particularly vulnerable to biodiversity loss.