Assembly through invasion and restoration: effects on biodiversity and ecosystem function

Abstract

It is well established that human activities have damaged many natural systems. Two critical aspects of mitigating this damage are identifying pathways to impacts and identifying the characteristics of successful interventions. We address both topics with a pair of independent studies linked by their focus on plant conservation. First, we investigated the ecological impacts of an invasive warm season grass on plant populations and communities in a temperate mixed-grass prairie ecosystem. Invasive plants are a well-known threat to native plant and animal communities and understanding their impacts is critical to developing management strategies. We investigated how impacts vary across a gradient of invasion and examined the impact of the invader on the intra- and inter-specific diversity of native plants. We found that most (but not all) impacts scale linearly as invader abundance increases. Increasing invasion reduced the height and abundance of the dominant native grass and shifted its functional trait composition (within-species effects). Increasing invasion also decreased total plant cover as well as the abundance of specific plant functional groups (inter-specific effects). We show that the direct ecological impacts of invasive species may be compounded by shifts in the functional traits of dominant native species. Second, we studied whether deterministic (initial seed mix of prairie restoration) or stochastic (establishment year precipitation) processes exert stronger influence on community function. It is critical to planning effective restoration actions to understand whether stochastic climate variation can influence the trajectory of restored communities. We calculated abundance-based community-weighted means (CWMs) of four functional traits across nine years post-restoration in two communities. We found that while climate differences led to dissimilar species compositions among restored communities, the CWMs of three of the four functional traits converged over time. This suggests that the function of restored communities is robust to variation in climate variables. The results of both studies provide valuable information for conservation practitioners.