Print PageThe impacts of non-native invasive species on communities and ecosystem processes have received growing attention, but impacts are largely understood using correlative approaches. Surprisingly little attention has focussed on the use of removal experiments, which are a powerful tool for quantifying the effects of species in ecosystems, and are also the primary management technique used to control invasive species. Similarly, comparative approaches of plant functional traits between native and non-native species have studied floras rather than co-occurring species, or linked trait differences to ecological processes. In both cases, understanding soil-plant interactions during invasion is needed to evaluate the magnitude, importance and temporal dynamics of invader impacts. We develop a general framework for better understanding the impacts of invasive plants derived from removal experiments that are designed to quantify the per-unit-abundance impacts of species in ecosystems. We test these ideas using data from field experiments and comparative analyses of plant functional traits for several systems in New Zealand, and discuss the relative importance of these findings with respect to climate change.
Results/Conclusions
Three key findings from our work include: 1) a 4-yr exclusion experiment revealed that seemingly inconsequential low-biomass (i.e., 3% of total mass) weeds can have the largest effects early in primary succession; this is due to low-biomass weeds having relatively nutrient-replete tissues and rapid tissue turnover compared to dominant species. 2) Removal experiments along invasion fronts of invasive pines (Pinus contorta, P. nigra) demonstrate rapid, non-linear effects of increasing weed abundance on both soil properties and community composition. These non-linear effects are not congruent, but differ among ecological processes or taxa considered. 3) Comparative analyses of functional traits between co-occurring native and non-native species reveal consistent differences in N-based defence chemistry (i.e., non-natives have more foliar tannins and phenolics), which in turn drives ecological processes including decomposition and herbivory. Together, these findings demonstrate that: 1) there are consistent differences in functional traits between non-native plants and co-occurring native species, 2) trait differences are related to ecological processes, many of which involve feedbacks with soil communities, and 3) these effects will be magnified over time irrespective of climate change effects. A better understanding of the temporal changes in plant-soil interactions during invasion will shed light on the importance of mechanisms underlying weed impacts, but an explicit consideration of climate change is not essential for understanding these processes at the local level.
