Changes in community functional structure and ecosystem properties along an invasion gradient of Ligustrum lucidum

Abstract

Questions: It is well documented that invasive alien plants can reduce species richness and diversity and modify the composition of invaded communities. However, our knowledge on the impacts of invasive alien plants on the community functional structure and ecosystem properties and the mechanisms underlying these changes is more limited. We evaluated how the community functional structure and ecosystem properties change along a gradient of Ligustrum lucidum abundance. Location: Subtropical mountain forest in NW Argentina. Methods: We conducted tree vegetation sampling in 164 plots distributed along a gradient of L. lucidum abundance. For L. lucidum and for the most abundant tree species in these plots we estimated six functional traits (specific leaf area, leaf tensile strength, leaf nitrogen concentration, leaf water potential, wood density and maximum plant height), as well as their relative growth rates. Then, we calculated indices of community functional structure (community-weighted means for each trait; richness, evenness, divergence and dispersion). We explored the extent to which the invasive success of L. lucidum and its impact may be attributed to niche differentiation or to fitness superiority. Finally, we explored how L. lucidum abundance alters ecosystem properties. Results: Some indicators of community functional structure changed linearly while others tended to saturate along the invasion gradient. L. lucidum has a higher growth rate than resident species and it lays close to the periphery, but within the limits of the functional space defined by resident trees. L. lucidum tends to displace more functionally similar resident species. Soil moisture and N content declined, while soil C:N increased with L. lucidum abundance. Conclusions: Our findings suggest that both niche differentiation and fitness superiority contribute to explain the invasion success of L. lucidum and the changes in functional structure of the community along the gradient of L. lucidum abundance with evident impacts on ecosystem properties.