Effects of the Center-Edge Gradient and Habitat Type on the Spatial Distribution of Plant Species Richness in Santiago, Chile

Cities host a heterogeneous composition of native and exotic plants, yet the spatial distribution of plant richness and its drivers remain poorly understood. We evaluated the influence of the center-edge gradient, along the environmental gradient from the historic city center to the urban edge, and habitat type, reflecting local conditions, on plant richness in Santiago, Chile. Sidewalks, parks, and vacant lots (<i>n</i> = 234 per habitat type) were randomly sampled across varying distances from the historic center and urban edge, recording neighborhood socioeconomic level and municipality. Four richness metrics were analyzed using generalized linear mixed models (GLMMs): total richness, richness by origin (native or exotic), and richness by life form (trees, shrubs, or herbs), considering habitat type, socioeconomic level, and distances as fixed effects and municipality as a random effect. We recorded 699 species (13% native and 87% exotic; 23% trees, 20% shrubs, and 56% herbs). Distances to the city center and urban edge had no significant effect, whereas habitat type emerged as the primary determinant: sidewalks exhibited higher total, native, and exotic richness with more trees and shrubs, whereas vacant lots were dominated by herbs. These patterns indicate that floristic richness is distributed in a mosaic, independent of urban gradients. Given the importance of Santiago's Mediterranean region as a biodiversity hotspot, the low representation of native species is concerning. Increasing their presence and associated ecosystem services requires tailored interventions for each habitat type.