Over the past two decades hundreds of studies have documented effects of non-native plants on ecological patterns and processes in 'natural' ecosystems or mesocosms. Yet most studies offer only snap shot views of invaders impacts thus limiting our understanding of how impacts will change over long time scales. To prioritize species for management (control, or removal), it is important to know if they are likely to remain dominant and change the trajectory of an ecosystem or whether their dominance will fade and on decadal times scales they will become part of succession. A way to cast this dichotomy is to try to determine whether invaded systems are in an alternative stable state, or whether invaders are part of succession over decadal time scales. In this talk we review what is known about the duration of studies of plant invader impacts, and present a framework for predicting whether invaders will remain dominant in a site for decades, or more rapidly become part of longer term succession.
Results/Conclusions
A recent published survey demonstrated that >50% of all plant invader studies lasted less than one year, and more than half were also done in mesocosms instead of natural ecosystems. Thus a gaping hole in our knowledge is how invaders behave over long time spans in natural ecosystems. An understanding of whether invaded states are alternative stable states versus successional states thus cannot be made on the basis of accumulated empirical observations since few long term studies exist of invader dominance. Here we propose that whether invaders persist as dominants depends on environmental harshness, the species pool of potential colonists that could co-exist with or displace the invader, and the system distruption that promoted the intial rise of the invader. Specifically, abiotically harsh environments with a limited native species pool, should be those where successful invaders are likely to maintain their dominance for the longest time particularly if disturbances to or disruptions of the sytsem that are correlated with initial invasion, tended to make those systems more harsh than they already were. also We discuss the role of feedbacks in maintaining invader dominance and how these too are likely to vary with environmental stress.