Proportion of non-native plants in urban parks correlates with climate, socioeconomic factors and plant traits

Urban parks and gardens provide cultural and aesthetic services critical for human well-being. Yet, they represent one of the main reasons for the intentional introduction of ornamental species, some of which can escape and establish in natural ecosystems. Besides aesthetic reasons, climate and socioeconomic factors can also modulate which species are planted in urban parks. Here, we evaluate the relationship between traits of 486 ornamental woody species from 46 Spanish urban parks and climatic and socioeconomic variables. We specifically assessed how plant traits, climatic, and socioeconomic factors are related to the proportion of non-native species and, among them, to the proportion of established non-native species in Spain. Overall, we found clear associations between species traits and climatic variables. Most notably, parks with warmer winters have more plant species with conspicuous flowers, whereas parks with colder winters and a more continental climate have more species with higher tolerances to cold and shade. Most of the species recorded in our study are non-native (82 %). Higher proportions of non-native species in urban parks were positively associated with towns with large size homes and inhabitants with higher median age but negatively related to parks with species with a higher hardiness-zone range. Moreover, a greater proportion of non-native species that can establish in the natural ecosystems was found in parks with lower continentality conditions. Our results show that Spanish urban parks have an overwhelming proportion of non-native woody species, some of which have the potential to establish, and that the variation in their proportions can be explained by climatic, and socioeconomic factors.