A fundamental question in invasive plant ecology is whether invasive and native plants have different ecological roles. Differences in functional traits have been explored, but we lack a comparison of the factors affecting the spread of co-occurring natives and invasives. Some have proposed that to succeed, invasives would colonize a wider variety of sites, would disperse farther, or would be better at colonizing sites with more available light and soil nutrients than natives. Others have argued that natives and invasives are more similar than we typically perceive. We examined patterns of spread over 70 years in a regenerating forest in Connecticut where both native and invasive species acted as colonizers. For seven invasive and 19 native species, we compared the characteristics of colonized plots, variation in characteristics of colonized plots, and the importance of site variables for colonization. We found little support for the hypotheses that invasive plants succeed by dispersing farther than native plants or by having a broader range of site tolerances. Colonization by invasives was not more affected by forest density than colonization by natives, and forest density had relatively low impact on colonization success for most species. Like native understory species, invasive plants spread into closed canopy forest and species-rich communities despite earlier predictions that these communities would resist invasion. The biggest differences were that soil nitrate and the forest being younger increased the odds of colonization for most invasives but only for some natives. The narrower range of spread patterns for invasives is consistent with a known bias in the selection of nonnative plants for introduction. In large part, the spread of native and invasive plants was affected by similar factors.
Yamamoto, Matthew, "Comparing Long-term Patterns of Spread of Native and Invasive Plants in a Successional Forest" (2023). Botany Honors Papers. 8.
The views expressed in this paper are solely those of the author.
Winner of the 2023 Oakes and Louise Ames Prize for most outstanding honors thesis.