Invasion by exotic plant species has led to concerns of homogenization of biotic communities. Where plant invasion occurs, heterogeneity of plant communities can decrease, even when other diversity responses are minimal. Homogenization of soil communities may also result from exotic plant invasion, though responses of soil communities to plant invasion are relatively understudied. In a long-term study underway since 2007, we examined effects of invasion and subsequent management of Gypsophila paniculata, a large invasive forb on Lake Michigan sand dunes, on aboveground plant community diversity and heterogeneity and belowground nematode community diversity and heterogeneity. Experimental plots were either currently ‘invaded’ with G. paniculata, actively ‘managed’ to remove G. paniculata, or were uninvaded ‘reference’ plots. Heterogeneity was measured using Bray-Curtis and Jaccard dissimilarity measures, and at two spatial scales – the local plot scale and the larger landscape scale. Specifically, we ask (1) Do invasion and management alter plant community diversity and heterogeneity? (2) Do invasion and management alter soil nematode community diversity and heterogeneity? (3) Do any effects on community heterogeneity depend on spatial scale?
Results/Conclusions
While invasion and management had only minor effects on plant and nematode richness and Shannon diversity, we found that invasion reduced plant and nematode community heterogeneity in both Jaccard and Bray-Curtis dissimilarity measures at smaller spatial scales. For plants, invasion reduced Bray-Curtis dissimilarity by 25% and Jaccard dissimilarity by 14%. For nematodes, invasion reduced Bray-Curtis dissimilarity by 33% and Jaccard dissimilarity by 25%. At smaller spatial scales, management of the invasive species increased nematode heterogeneity to intermediate levels and returned plant heterogeneity to reference levels. However, at larger spatial scales, neither invasion nor management had any effect on plant or nematode community heterogeneity. Overall this indicates that this invasion had the effect of homogenizing plant and soil nematode communities at local scales, while landscape-level heterogeneity of these groups was unaffected. Reduced heterogeneity, particularly belowground, could have effects on plant community dynamics, since plant-soil interactions can contribute to continued invasion. Inclusion of the soil community will enhance our understanding of broader community responses during invasion and management.