Mechanisms Underlying Nonindigenous Plant Impacts: A Review of Recent Experimental Research

Abstract

Nonindigenous plant species (NIS) can affect individuals, communities, and ecosystems through numerous direct and indirect mechanisms. To synthesize the current understanding of how NIS cause impacts, we reviewed experimental research from the past decade. We found alteration of the microenvironment, such as incident light and air and soil temperature, was much more often a mechanism underlying NIS impacts than competition for soil water and nutrients. NIS litter frequently caused the alteration of microenvironments, and litter effects were often of greater consequence than the effects of live NIS plants. Results supported altered soil microbial communities and mycorrhizal associations as mechanisms underlying NIS impacts on native plant growth, community structure, and nutrient cycling. Impacts often could not be attributed to a single mechanism, highlighting the need for multi-factor studies that identify and distinguish between multiple, concurrently operating mechanisms. Overall, our synthesis indicates that effective management will require attention to legacy effects of NIS, that removing live NIS may not ameliorate impacts, and that removal of dead NIS biomass may be necessary for native species' survival. Furthermore, rehabilitating soil microbial and mycorrhizal communities may be crucial for successful post-NIS management revegetation.

No consistent pollinator‐mediated impacts of alien plants on natives

“…; Morales & Traveset ; Skurski et al . ). Our results, a meta‐analysis of 76 studies, directly contradict this assertion.…”

“…Indeed, over the past decade, the invasion literature has increasingly focused on the pollinator‐mediated impacts of aliens – more so than any other mechanism (Skurski et al . ). Furthermore, evidence is mounting that the density and composition of species in a plant community have the potential to influence the size and diversity of the pollinator community (Westphal et al .…”

“…; Skurski et al . ; Goodell & Parker ), the potential for release from natural enemies to promote the evolution of greater investment in floral display (Blossey & Notzold ) and the fact that many are introduced as ornamental plants, which are typically specifically bred/selected for their floral display (e.g. Chittka & Schurkens ).…”

Do impacts of an invasive nitrogen‐fixing shrub on Douglas‐fir and its ectomycorrhizal mutualism change over time following invasion?

“…; Vila et al . ; Skurski, Rew & Maxwell ). Studies that are snapshots in time cannot reveal how impacts change over time.…”

Metacognitive learning in the ecology classroom: A tool for preparing problem solvers in a time of rapid change?

“…Invasive plants are defined as non-native plants that spread rapidly and negatively impact ecosystems, the economy, or human health (US Executive Order 13112, 1999). Invasive plants can alter ecosystem properties such as nutrient cycling, hydrology, and soil properties (reviewed in Skurski et al 2014), affect the ecosystem services that sustain human well-being (e.g., water filtration, food production; Pejchar and Mooney 2009), and impact the economy through high management costs (over $35 billion annually in the United States as of 2005; Pimentel et al 2005). The spread of invasive plants in Alaska has rapidly accelerated in recent decades (Carlson and Shephard 2007).…”