Nonnative plant response to silvicultural treatments: a model based on disturbance, propagule pressure, and competitive abilities.

Invasion by nonnative plants can result in substantial adverse effects on the functions of native forest ecosystems, including nutrient cycling and fire regimes. Thus, forest managers need to be aware of the potential impacts of management activities, including silvicultural treatments, on nonnative vegetation. To aid in that effort, we created a conceptual model of potential responses of nonnative plants to silvicultural treatments, used the model to make a general set of predictions, and tested our predictions against observed responses published in the scientific literature. Of a total of 42 studies that addressed the effects of silvicultural treatments on nonnative plants, 90% found a posttreatment increase in at least one nonnative plant species. All of the studies that assessed the effect of disturbance intensity on nonnative plants found that invasion success increased with increasing disturbance intensity or number of management entries. As predicted by the model, there was substantial among-species and among-site variation in nonnative plant responses to silvicultural treatments; variation in responses were probably driven by local conditions including propagule pressure, condition of the forest community, or characteristics of the local flora (native and nonnative species). Because species- and location-specific changes in nonnative plants are dependent on local conditions, local knowledge is important for predicting invasion potential. In addition, monitoring is essential for early detection of postharvest invasions and/or expansions of nonnative plants.