Land use change and invasions by exotic species are widely recognized as the primary drivers of biodiversity loss. However, few studies have focused on how landscape structure of rapidly urbanizing regions is impacting the spread of exotic plant species and persistence of native plant diversity. Using the rapidly growing metropolitan region of Charlotte, North Carolina as a case study, we examine the hypothesis that landscape structure of the built and natural environment are linked to patterns of native and exotic plant diversity in forests along the urban to rural gradient. We posed the following three questions: 1) does urbanization positively influence exotic richness, 2) do urban forests have lower native species richness that is not explained by patch size or age of forest and 3) what is the relationship between exotic and native diversity along an land use gradient? We sampled 105 randomly located plots for woody species presence and abundance at 25 forested sites stratified across three land use types (urban, suburban and rural). We used building density and road density to serve as metrics of urbanization to define our land use types.
Results/Conclusions
Significant differences were detected for native richness among land use types using ANCOVA (F =7.8, P < .001). Native richness and diversity are highest in rural areas and decrease with increasing urbanization. Linear regression analyses indicated that native richness is negatively influenced by road density. Exotic richness is positively correlated with urbanization and is best explained by slope, mean year built of buildings located with 1 km, distance to forest edge, distance to roads and distance to central business district (adj. r2 = 0.495, P <. 001). No relationship has been detected between exotic and native diversity, rather our results suggest that urbanization positively influences exotic diversity and negatively influences native diversity. Overall, native richness and diversity significantly decrease along a rural to urban gradient supporting our hypothesis that the landscape factors associated with urbanization negatively impact the persistence of native biodiversity.
