Community Attributes Predict the Relationship between Habitat Invasibility and Land Use Types in an Agricultural and Forest Landscape

Finding ecosystem or community level indicators for habitat invasibility may provide natural resource managers with environmentally friendly measures to control alien plant invasion; yet, ecosystem invasibility remains understudied. Here, we investigated alien plant invasion into various ecosystems representing different land use types in a subtropical peri-urban area of south China. Four invasive alien species were found from five out of the six ecosystems. Lower plant diversity in both the overstory and understory was consistently associated with more severe alien plant invasion to the ecosystems. The highest total abundance and plot occurrence of the invasive plants were found in the agroforestry ecosystem representing the highest disturbance. At plot scale, an increase in invasion severity was associated with a significant decrease in overstory stem density, species richness, and diversity, but with a significant increase in overstory plant dominance. The understory community attributes in response to the increase in invasion severity followed similar patterns, except that the stem density increased with invasion severity. Higher canopy openness and thus lower leaf area index and greater understory radiation were associated with higher invasion severity of invasive plants to the understory habitat. For predicting total abundance of the invasive species, the most important variable is land use type, while for the abundance of Lantana camara and Mikania micrantha, the most important predictor variable is overstory Berger–Parker index and canopy openness, respectively. Canopy structure and understory gap light regimes were among the most important factors determining the abundance of the worst invasive plant Mikania micrantha. Our results demonstrate that land use types with varying disturbance regimes determine the spatial heterogeneity in plant diversity and community structure, which predicts alien plant invasion and habitat invasibility; and that the severity of alien plant invasion in turn is a good indicator of habitat disturbance across the ecosystems.

Impacts of Nonnative Species on the Health of Natural and Planted Forests

Despite conservation efforts, most forest ecosystems worldwide are affected by biotic invasions; however, the specific impacts vary across different geographic regions and forest types. The relative contributions of the main drivers such as propagule pressure (e.g., due to human population, travel, and trade), climate, land use, and habitat invasibility remain uncertain. The special issue “Impacts of Nonnative Species on the Health of Natural and Planted Forests” was organized to facilitate timely communications among scientists and managers in different regions and to assist in attempts to improve forest health and maintain long-term sustainability. The special issue addresses broad issues related to forest invasions, including the impacts of nonnative species in various forest ecosystems (e.g., natural vs. urban) and the contributions of land use (e.g., fragmentation), human activity, and climate change to invasion. The new findings include identifying hotspots of potential invasion impacts and their causes, which can help inform policy makers as they develop effective strategies for prevention, early detection or eradication, and forest management.