Invasive plants as drivers of regime shifts: identifying high‐priority invaders that alter feedback relationships

Abstract

Aim A major challenge for invasion ecology is to identify high-impact invaders to guide prioritization of management interventions. We argue that species with the potential to cause regime shifts (altered states of ecosystem structure and function that are difficult or impossible to reverse) should be prioritized. These are species that modify ecosystems in ways that enhance their own persistence and suppress that of native species through reinforcing feedback processes.Methods Using both systems analysis and meta-analysis approaches, we synthesized changes to ecosystems caused by 173 invasive plant species. For the systems analysis, we examined published studies of impacts of invasive plants to determine which presented evidence consistent with a reinforcement of feedback processes. For the meta-analysis, we calculated the effect size ratio between standardized changes in recipient ecosystem and in the status of introduced species as an indication of a reinforcing feedback in particular speciesenvironment combinations. The systems analysis approach allowed us to conceptualize regime shifts in invader-dominated landscapes and to estimate the likelihood of such changes occurring. The meta-analysis allowed us to quantitatively verify the conceptual model and the key invader-context feedbacks and to detect the strength and direction of feedbacks.Results Most reinforcing feedbacks involve impacts on soil-nutrient cycling by shrub and tree invaders in forests and herbaceous invaders in wetlands. Feedbacks resulting in regime shifts were most likely related to processes associated with seed banks, fire and nutrient cycling. Results were used to derive a key for identifying high-impact invaders.Main conclusions Identifying combinations of plant life-forms and ecosystems most likely to result in regime shifts is a robust approach for predicting highimpact invasions and therefore for prioritizing management interventions. The meta-analysis revealed the need for more quantitative studies, including manipulative experiments, on ecosystem feedbacks.

Invasion legacy effects versus sediment deposition as drivers of riparian vegetation

“…Therefore, interannual changes in environmental conditions may either constrain the growth and thereafter the impact of IAPs locally, aid their establishment via enhanced propagule supply to newly created patches, or, once dense monocultures are established, have no further measurable effect (Bellard et al 2013). Dominance by IAPs may subsequently lead to less resilient and diverse plant communities over the short term, if certain species are filtered out through competition or other changes in the environment that accompany invasion (Gaertner et al 2014). This impact may, however, be reversed if sediment deposition during flood events lowers competitive ability of IAPs by reducing their cover and favours recruitment of native species, whether from the in situ propagule bank or recent deposition .…”

Direct and Indirect Interactions between Landscape Structure and Invasive or Overabundant Species

“…A recent review of 173 invasive plant species found that reinforcing feedbacks that caused regime shifts typically occurred in situations where seed banks, fire, or nutrient cycling had been altered by the invasive species [89]. For example, regime-shifts can be initiated when invasive grasses affect fire frequency or intensity in ways that further promote invasion.…”

A multi-scale modelling framework to guide management of plant invasions in a transboundary context

“…Invasion by H. sericea in fynbos causes major changes to the fuel characteristics of this fire-prone shrubland vegetation (van Wilgen and Richardson 1985). Due to the capacity to sustain and promote fire, invasion by H. sericea can lead to severe ecological and socioeconomic regime shifts (Gaertner et al 2014). Although such major impacts have yet to be quantified outside South African fynbos, H. sericea has the potential to become more widespread and abundant in Southern Europe and other areas with Mediterranean-type climate, as suggested by its aggressive invasiveness in South Africa.…”

“…Many invasive species cause substantial changes to ecosystem structure and functioning (Vilà et al 2011), provision of ecosystem services (Vilà et al 2010) and the broader economy (Pimentel et al 2005;Vilà et al 2010). Some invasive species potentially promote irreversible regime shifts (Gaertner et al 2014), and cause biotic homogenization synergistically with other drivers of global change (Thuiller 2007). Therefore, biological invasions as a global change process, and a worldwide problem, must be managed through international cooperation.…”