The effects of urbanization on species richness and floristic diversity in residential gardens

Abstract

Urbanization is recognized as a major driver reshaping plant diversity patterns globally; however, ecological responses to urbanization are highly site-specific and often diverge from generalized assumptions. This study investigates how urbanization influences plant species richness and Shannon diversity within residential gardens across an urban-to-rural gradient in Rize, Turkey—a rapidly urbanizing region along the Black Sea coast—thereby addressing a critical knowledge gap and challenging generalized assumptions commonly held in urban ecology. Field surveys across 150 residential gardens documented 603 plant taxa from 120 families, revealing critical patterns of biodiversity change under varying urbanization levels. Non-native species comprised 57% of the total taxa, highlighting their dominance in residential gardens across different urbanization intensities. Herbaceous species richness declined significantly in highly urbanized zones (F (2,27) = 10.35, p < 0.001), whereas non-native species richness exhibited a pronounced increase (+ 57%), particularly in areas with urbanization levels exceeding 55%. Woody species richness, however, remained relatively stable across urbanization gradients. Interestingly, moderately urbanized areas displayed the highest diversity indices (Shannon_H: 4.32), reflecting a transitional ecological dynamic consistent with the intermediate disturbance hypothesis. By contrast, areas with low urbanization (4.16) and high urbanization (4.26) exhibited reduced biodiversity, with native species showing the steepest declines in highly urbanized zones. Although urbanization is often associated with biodiversity loss, this paradigm warrants reevaluation in light of the observed increase in overall Shannon diversity driven by adaptable non-native species. Therefore, urban biodiversity management strategies should transcend generalized assumptions, addressing the complex interplay of native and non-native species dynamics across varying urbanization gradients.