COS 92-1 - Horticulture facilitates range infilling and climate-driven range expansion of invasive plants

Background/Question/Methods

Over half of U.S. invasive plants are sold through horticultural trade despite well-known negative impacts on ecosystems. Most states have regulations which reduce the sale of some species within their borders. But major inconsistencies across state regulations make it likely that horticulture practices facilitate ongoing invasions. Furthermore, the location of suitable habitat for many invasive species is likely to change with climate change, such that plant trade may be seeding future invasions. Here, we asked how horticultural sales might contribute to 1) the spread of invasive plants within their current invaded ranges and 2) the climate-driven range expansion of invasive plants. Using a dataset of 1069 nursery locations selling 535 invasive plant species, we estimated the distance between each nursery selling that species and its nearest population (based on several sources of occurrence records). We then used spatial climate data and habitat suitability maps under current and future conditions to identify how many nurseries sell species within their current invaded ranges or within areas that will become more suitable for invasion under future climate change.

Results/Conclusions

Invasive plant populations ranged from 70 meters to 4000 kilometers away from the nearest source of nursery propagules. The median distance was 250 km, suggesting many nurseries are regionally proximate to invasive populations but may not be a propagule source at the local scale. We found that 89% of nurseries were located within invasive plants’ current suitable range. For 298 species, the mean annual temperature of nursery locations was warmer than the mean annual temperature across existing populations. This suggests that nurseries expand many species’ climatic niche into warmer areas, supporting the hypothesis that nurseries select for species that will have an advantage as the climate changes. We also found that 335 nurseries were not located within a species’ current range but were located in areas that will become highly suitable for the species to expand into by 2050. These results suggest that current horticultural practices facilitate invasive species range infilling as well as climate-driven range shifts. Like most sectors, horticulture must adapt to a warming climate, but this will come at an ecological cost if horticultural practices continue to include invasive plants. More proactive government regulations are needed to limit the current and future spread of ornamental invasions.