Responses to invasion and invader removal differ between native and exotic plant groups in a coastal dune

Abstract

The spread of exotic, invasive species is a global phenomenon that is recognized as a major source of environmental change. Although many studies have addressed the effects of exotic plants on the communities they invade, few have quantified the effects of invader removal on plant communities, or considered the degree to which different plant groups vary in response to invasion and invader removal. We evaluated the effects of an exotic succulent, iceplant (Carpobrotus edulis), on a coastal dune plant community in northern California, as well as the community responses to its removal. To assess possible mechanisms by which iceplant affects other plants, we also evaluated its above- and belowground influences on the germination and growth of a dominant exotic annual grass, Bromus diandrus. We found that iceplant invasion was associated with reduced native plant cover as well as increased cover and density of some exotic plants-especially exotic annual grasses. However, iceplant removal did not necessarily lead to a reversal of these effects: removal increased the cover and density of both native and exotic species. We also found that B. diandrus grown in iceplant patches, or in soil where iceplant had been removed, had poorer germination and growth than B. diandrus grown in soil not influenced by iceplant. This suggests that the influence of iceplant on this dune plant community occurs, at least in part, due to belowground effects, and that these effects remain after iceplant has been removed. Our study demonstrates the importance of considering how exotic invasive plants affect not only native species, but also co-occurring exotic taxa. It also shows that combining observational studies with removal experiments can lead to important insights into the influence of invaders and the mechanisms of their effects.

Invasive legume management strategies differentially impact mutualist abundance and benefit to native and invasive hosts

“…The legacy of plant invasion can persist long after a plant has disappeared from the landscape (Grman & Suding ; Reynolds & Cooper ; Magnoli et al ), and abiotic legacies produced by legumes are well documented (McLauchlan ; Grman & Suding ; Corbin & D'Antonio ; González‐Muñoz et al ; Magnoli et al ; Novoa et al ; Nsikani et al ). Our results add to a growing literature that documents similarly important biotic legacies.…”

Secondary invasion: The bane of weed management

“…For example, using broadleaf herbicides to control invasive forbs can suppress native forbs (Crone et al, 2009;Ortega and Pearson, 2011;Pokorney et al, 2010;Rinella et al, 2009). Second, ecosystem recovery may be deterred by legacy effects that persist following invader suppression, such as when an invader has altered soil properties, disturbance regimes, or reduced native propagule sources (D'Antonio and Vitousek, 1992;Magnoli et al, 2013;Seabloom et al, 2003). Third, provenance effects may favor invader over native recovery due to introduction filters that select for disturbance-adapted traits or release from natural enemies (Buckley and Catford, 2016;Liu and Stiling, 2006).…”

Plant community response following the removal of the invasive Lupinus arboreus in a coastal dune system

“…Many target species which, similar to lupin, favor the establishment of other non‐native species over the native dune flora through changes in microclimate, soil nutrient cycles, or increases in dune stability (e.g. Ens & French ; Marchante et al ; Emery et al ; Magnoli et al ). Our study has implications for such projects in dune systems worldwide.…”

“…Cushion species such as R. australis and S. uniflorus are naturally found only in areas of low total plant cover and may not be able to colonize the well-vegetated, nutrient-rich, deflation surface of the managed Kaitorete dunes. Similar changes in the soil related to other invasive plants prevent the reestablishment of native dune plants in parts of Spain (Novoa et al 2013) and California (Magnoli et al 2013). The lack of recovery of native plant species in the deflation environment is likely to be due to some combination of both these mechanisms.…”