Causes and Consequences of Invasive Plants in Wetlands: Opportunities, Opportunists, and Outcomes

Abstract

Wetlands seem to be especially vulnerable to invasions. Even though ≤6% of the earth's land mass is wetland, 24% (8 of 33) of the world's most invasive plants are wetland species. Furthermore, many wetland invaders form monotypes, which alter habitat structure, lower biodiversity (both number and "quality" of species), change nutrient cycling and productivity (often increasing it), and modify food webs. Wetlands are landscape sinks, which accumulate debris, sediments, water, and nutrients, all of which facilitate invasions by creating canopy gaps or accelerating the growth of opportunistic plant species. These and other disturbances to wetlands, such as propagule influx, salt influx, and hydroperiod alteration, create opportunities that are well matched by wetland opportunists. No single hypothesis or plant attribute explains all wetland invasions, but the propensity for wetlands to become dominated by invasive monotypes is arguably an effect of the cumulative impacts associated with landscape sinks, including import of hydrophytes that exhibit efficient growth (high plant volume per unit biomass).

Conceptual Frameworks and Methods for Advancing Invasion Ecology

“…Domain A: Difficulties arising from society and its relationship to biological invasions, measures that can be taken to overcome them and consequences for the scientific approach of invasion ecology; letters and numbers in parentheses refer to Perrings et al (2010b); c Bremner and Park (2007), Burt et al (2007), Byron (2008); d Mack et al (2000), Moore et al (2010); e Fischer and van der Wal (2007); f Andreu et al (2009); g Bodey et al (2010) to analyze, explain, and predict. Invasion processes are complex (Lodge 1993;Hayes and Barry 2008;B1 in Table 2) and context-dependent (Zedler and Kercher 2004;Gurevitch et al 2008;Blackburn et al 2009) (B2 in Table 2). This creates the need for methods that are able to explain and predict multiple interacting influences (Heger and Trepl 2003), and to take into account the history of current invasions for their explanation (Cassey et al 2005) (see right column in Table 2).…”

Effects of the herbicide imazapyr on juvenile Oregon spotted frogs

“…The introduction and spread of invasive species can lead to extinctions of native species [2]. Wetlands may be particularly vulnerable to invasion by nonnative plant species, especially when surrounding landscape changes alter wetland hydrology and nutrient levels [3]. Invasive plants can alter habitats, reduce the abundance and diversity of animal species, alter nutrient cycles, and potentially change food-web dynamics (reviewed in Zedler and Kercher [3]).…”

“…Wetlands may be particularly vulnerable to invasion by nonnative plant species, especially when surrounding landscape changes alter wetland hydrology and nutrient levels [3]. Invasive plants can alter habitats, reduce the abundance and diversity of animal species, alter nutrient cycles, and potentially change food-web dynamics (reviewed in Zedler and Kercher [3]). Many invasive wetland plants form monocultures, establishing and maintaining dominance in wetlands through a combination of factors including tolerance to variable hydrologic conditions, high seed production or viability in wet conditions, and ability to spread vegetatively by rhizome expansion or movement of stem or root fragments [3].…”

“…Invasive plants can alter habitats, reduce the abundance and diversity of animal species, alter nutrient cycles, and potentially change food-web dynamics (reviewed in Zedler and Kercher [3]). Many invasive wetland plants form monocultures, establishing and maintaining dominance in wetlands through a combination of factors including tolerance to variable hydrologic conditions, high seed production or viability in wet conditions, and ability to spread vegetatively by rhizome expansion or movement of stem or root fragments [3]. The ability of these plants to dominate wetlands coupled with increasing restrictions on chemical control complicates habitat restoration for native species, including amphibians.…”

A five year study of floristic succession in a restored urban wetland

“…Bauer (2012) introduced the concept of back-seat driver model, where species possess qualities of both (hitchhiking) passenger and (steering) driver as pathways to dominance, to explain the continuous widespread infestation of such species as Microstegium vimineum (Japanese stilt grass). Zedler and Kercher (2004) in a review noted that wetlands are especially vulnerable to invasions and that 8 of 33 of the world's most invasive plants are wetland species.…”