Print PageThe reassembly of native communities for restoration purposes provides us the opportunity to explore underlying processes of biological resistance to invasion. We assessed through experiments the effectiveness of restoring wetland plant communities to suppress early invasion of Phragmites australis, a notorious invader in North America, focusing on life history traits and community assembly. We hypothesized that (1) certain emergent functional group of wetland species resist early invasion better than others; (2) vegetative traits such as plant size and growth rate will be correlated with invasion resistance; (3) a diverse community resists invasion better than a monospecific plant cover. We categorized eleven wetland plant species into three emergent functional groups based on life history traits and vegetative traits. We used pot experiments to simulate a situation where seeds of P. australis arrive on a waterlogged clay soil soon after a biological disturbance. In each pot, we sowed equal number of pure live seeds of one of eleven wetland plants, alone or in mixtures, together with seeds of P. australis. We measured cover, biomass, and height of wetland plants, and the number of shoots and aboveground biomass of P. australis as the response variables, for two years.
Results/Conclusions
Lolium multiflorum and Bidens cernua in group 1 were most effective, with 92% and 88% reduction of aboveground biomass of P. australis compared with control. Scirpus cyperinus, Penthorum sedoides, and Mimulus ringens in group 2 also significantly affected P. australis, but they were less effective (53 %, 47 %, and 40 % respectively). There was no significant competitive effect of all other wetland species in group 3. Our result supports that inhibitory priority effect leads to strong resistance of the ruderal species in group 1 to invasion. Vegetative traits such as biomass, early height increase, and plant cover were negatively correlated with establishment of P. australis and may be better predictor of resistance than life history trait. As these plant traits relate to amount of resource uptake, our results suggest the relevance of fluctuating resource availability theory to invasion process and restoration. Plant mixtures inhibited invasion of P. australis more than monospecific plant cover. In partitioning diversity effect, selection effect rather than complementarity effect increased overall invasion resistance of those mixtures. In conclusion, our research implies that communities with fast growing species forming a dense plant cover will resist early invasion of common reed best.
