Functional trait overlap does not predict the impact of invasive English Holly (Ilex aquifolium) on individual native species and the community

Invasive species can result in biodiversity loss and extinction. English Holly, Ilex aquifolium, is an invasive species that poses a significant threat to native plant biodiversity and community composition in British Columbia. Little is known about how functional trait overlap between native species and Ilex aquifolium affects competitive outcomes that result in changes in species abundance and biodiversity. This study aims to understand how native understory species respond to the presence of I. aquifolium individually and as a community in an urban park in a temperate forest system. We categorized common understory species observed in temperate rainforest into low, medium, and high functional trait overlap with I. aquifolium. In randomized quadrats, percent cover was taken for each plant species and quadrats were analyzed for changes in coverage, biodiversity, and community composition. Results found insignificant relationships between functional group cover, individual native species percent cover, and Shannon diversity in response to Ilex aquifolium percent cover. This could be attributed to limitations such as sample size, covariate interactions, and geographic range. However, further exploration found that community composition did change between quadrats with low and high I. aquifolium abundance. This suggests that there are some associations between certain species and I. aquifolium, and their abundance could be changing in response to I. aquifolium in more subtle ways. Future studies could look into functional traits other than primary reproductive strategy and growth plan to indicate niche overlap, and instead can use leaf size or root depth. Understanding how functional traits change native species' response to invasive species is important when creating conservation schemes, since it may indicate which native species may be most affected by invasion.