Negative per capita effects of purple loosestrife and reed canary grass on plant diversity of wetland communities

Abstract

Invasive plants can simplify plant community structure, alter ecosystem processes and undermine the ecosystem services that we derive from biotic diversity. Two invasive plants, purple loosestrife ( Lythrum salicaria ) and reed canary grass ( Phalaris arundinacea ), are becoming the dominant species in many wetlands across temperate North America. We used a horizontal, observational study to estimate per capita effects (PCEs) of purple loosestrife and reed canary grass on plant diversity in 24 wetland communities in the Pacific Northwest, USA. Four measures of diversity were used: the number of species (S), evenness of relative abundance (J), the Shannon-Wiener index (H ′ ) and Simpson's index (D). We show that (1) the PCEs on biotic diversity were similar for both invasive species among the four measures of diversity we examined; (2) the relationship between plant diversity and invasive plant abundance ranges from linear (constant slope) to negative exponential (variable slope), the latter signifying that the PCEs are density-dependent; (3) the PCEs were density-dependent for measures of diversity sensitive to the number of species (S, H ′ , D) but not for the measure that relied solely upon relative abundance (J); and (4) invader abundance was not correlated with other potential influences on biodiversity (hydrology, soils, topography). These results indicate that both species are capable of reducing plant community diversity, and management strategies need to consider the simultaneous control of multiple species if the goal is to maintain diverse plant communities.

Impact of land use on vegetation composition, diversity and potentially invasive, nitrophilous clonal species in a wetland region in Flanders

“…These species are able to outcompete less competitive and rare species in wetland communities as shown by, e.g. Galatowitsch et al (2000) and Schooler et al (2006) for P. arundinacea, Grace et al (2001) for E. repens, and Stachion and Zimdahl (1980) and Nuzzo (1997) for C. arvense. The threat of these species results from both their nitrophilous status as well as from their clonal growth.…”

Impacts of Biological Invasions on Freshwater Ecosystems

“…Similar cascading effects were observed after the invasion of the Potomac River estuary by the Asiatic clam Corbicula fl uminea . Water clarity in the estuary tripled within a few years of the clam ' s discovery, and coincided with the development of submerged Burrows 2005 ) and reduced diversity (Boylen et al 1999 ;Schooler et al 2006 ). The replacement of natives by non -indigenous plants, even those that appear to be ecologically equivalent to the native, can have subtle negative effects on associated communities and food webs (Brown et al 2006 ;Wilson & Ricciardi 2009 ).…”

Plant community structure mediates potential methane production and potential iron reduction in wetland mesocosms

“…Freshwater wetland ecosystems provide a number of valuable services, including biodiversity support, water quality maintenance and improvement, flood control, and carbon storage (Zedler and Kercher 2005). While there are a number of studies documenting changes in wetland biodiversity as a consequence of human activities (Findlay and Houlahan 1997, Findlay and Bourdages 2000, Houlahan and Findlay 2004, Rosas et al 2006, Schooler et al 2006, there have been fewer studies on links between changes in biodiversity and functions that support wetland services (Engelhardt and Ritchie 2001, Mahaney et al 2006, Bouchard et al 2007, Schultz et al 2011.…”