Nectar resource provision in urban designed plant communities : the contribution of native and non-native plant species, invasion risk and ecological trade-offs

Sammanfattning

Urban areas are expanding rapidly worldwide, fundamentally altering ecosystem functions and posing major challenges for biodiversity conservation. Among the most critical consequences is the decline in pollinators, driven primarily by the loss of floral resources. Although urbanization profoundly impacts the natural environment, well-managed urban areas can play a surprisingly important role in conservation, as their unique mosaic of habitats harbors greater floral diversity and density than surrounding rural areas. Designed plant communities are deliberately composed combinations of plant species that represent a promising approach to improving the urban environment by integrating ecological principles and biodiversity values. The identity of each plant species is considered decisive for the ecological output of such communities, yet empirical evidence regarding the input of plant origin remains limited. This thesis uses a quantitative, secondary-data-based research design to empirically quantify nectar resource provision across 12 Designed plant communities in Sweden, comparing differences in nectar production, seasonal dynamics, invasion risk, and broader ecological value between native and non-native plant species. The results showed that non-native plant species dominated nectar production across the majority of sites, contributing a mean of 74.8 %, despite representing a smaller share of plant species richness. Non-native plant species contribution was particularly pronounced in June and August, while native plant species dominated in May and July. Nectar productivity and invasion risk proved to be independent traits, yet targeted removal of invasive non-native plant species would still result in a nectar loss of 47 % across all sites. Native plant species, however, demonstrated significantly greater ecological value beyond nectar productivity in attracting greater number of pollinators and supporting broader range of organisms, compared to non-native plant species, confirming that biodiversity contribution extends well beyond nectar productivity. These findings call for a fundamental shift away from origin-based plant selection toward individual, functionbased evaluations that simultaneously consider broader ecological values beyond nectar productivity, in order to achieve both pollinator support and biodiversity conservation goals.