The Intersection of Ecological Risk Assessment and Plant Communities: an Analysis of Agrostis and Panicum Species in the Northeastern U.S
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Plant Ecol (2011) 212:1629–1642 DOI 10.1007/s11258-011-9936-9 The intersection of ecological risk assessment and plant communities: an analysis of Agrostis and Panicum species in the northeastern U.S. Collin Ahrens • Geoffrey Ecker • Carol Auer Received: 22 December 2010 / Accepted: 20 May 2011 / Published online: 3 June 2011 Ó Springer Science+Business Media B.V. 2011 Abstract Ecological risk assessments for grass roadside and wasteland habitats, but was distributed species with novel traits are advisable, or required, equally in the three coastal habitats. Co-occurrence in order to identify potential environmental harms between P. virgatum and congenerics was infrequent, prior to large-scale cultivation. Credible risk assess- although one transect had both P. virgatum and the ments are built upon knowledge of the communities state-listed coastal species Panicum amarum. This is that could be negatively affected by crop-to-wild the first study to characterize Agrostis and Panicum gene flow, new weeds, or invasive plants. This study plant communities and distribution providing the focused on two cultivated grasses with different life basis for ecological risk assessments, coexistence- histories: the exotic, weedy Agrostis stolonifera strategies, and geographic exclusion zones. (creeping bentgrass) and the native Panicum virga- tum (switchgrass). Vascular plant communities were Keywords Habitat Plant community Agrostis Á Á Á analyzed in 190 transects (50 m) in ten habitat types Creeping bentgrass Panicum Switchgrass Á Á Á across two ecoregions (inland and coastal) in the Ecological risk assessment northeastern U.S. Ordination plots and dendrogram analysis showed clustering of inland plant community Abbreviations assemblages within habitat types, while coastal plant GE Genetically-engineered communities were similar across the habitats studied. CHP Lower New England Ecoregion subecoregion Agrostis and Panicum species had unequal distribu- Southern New England Coastal Hills and Plains tion across the habitat types and ecoregions. Agrostis CL North Atlantic Coast Ecoregion, subecoregion species were more common in the inland ecoregion Southern New England Coastal Lowland and habitats receiving moderate management or ERA Ecological risk assessment disturbance events. In both ecoregions, A. stolonifera had high co-occurrence values with other exotic Agrostis species, suggesting potential for interspecific gene flow. P. virgatum was most common in inland Introduction Grasses provide much of the world’s food, but they C. Ahrens (&) G. Ecker C. Auer also act as weeds and invasive species in diverse Department of PlantÁ Science,Á University of Connecticut, U-4163, Storrs, CT 06269, USA agricultural, natural, and cultural settings. In the U.S., e-mail: [email protected] a national energy initiative has identified a number of 123 1630 Plant Ecol (2011) 212:1629–1642 C4 grasses as potential biofuel feedstocks, but some incomplete, out-of-date, or they do not include of these species are considered weedy or invasive information about cultural or agricultural landscapes plants (Raghu et al. 2006). Thus, the large-scale (Barkworth et al. 2007; Magee and Ahles 2007; production of these plants could lead to management Gleason and Cronquist 1963). In addition, botanical or ecological problems. The development of genet- references typically have no information about the ically engineered (GE) grasses has raised concerns co-occurrence of closely related species that could about the downstream harm from crop-to-wild or favor interspecific gene flow. This information is crop-to-weed gene flow, especially if the novel critical for the design of geographic exclusion zones, phenotype increases stress resistance, fecundity, or regions where specific GE crops are not permitted overall fitness (Andow and Zwahlen 2006; Stewart because of potential for crop-to-wild gene flow et al. 2003; Wilkinson and Tepfer 2009). In addition, (McGinnis et al. 2010). Our project was designed to preventing gene flow in wind-pollinated grasses provide information about the distribution, habitat poses a challenge, and the containment problem types, and plant communities for two grass species increases when sexually compatible species (receiv- that have been modified through traditional breeding ing populations) exist in natural, agricultural, or and biotechnology to create novel traits for the U.S. cultural landscapes (defined as properties represent- market: A. stolonifera (creeping bentgrass) and Pan- ing the combined work of nature and man UNESCO icum virgatum (switchgrass). 2010). The escape of glyphosate-resistant Agrostis Agrostis stolonifera is a cool-season, perennial stolonifera (creeping bentgrass) in the western U.S. grass planted in golf courses and other cultural provides an example of the challenges involved in landscapes in the U.S. (Beard 2002). Most references biocontainment (Reichman et al. 2006; Watrud et al. treat A. stolonifera as an introduced species in the 2004; Zapiola et al. 2008). U.S., but some sources cite specific ecotypes (or The harmonization of policy for GE crops across populations) as native (Barkworth et al. 2007). many countries has resulted in a regulatory process Experimental field trial permits have been issued for that requires the construction of predictive ecological GE A. stolonifera (2002–2008) tolerant to herbicides, risk assessments (ERA) prior to commercialization insects, drought, salt, heat, disease, and shade (USDA (Andow and Zwahlen 2006; Auer 2008; Craig et al. 2010). Male sterility and altered plant morphology 2008; Nap et al. 2003). Risk analysts and regulators have also been tested in experimental field trials. generally assess GE crops using a case-by-case Herbicide-resistant A. stolonifera has generated the approach with detailed knowledge about the biology most research and scientific debate regarding gene of the crop, the biotechnology-derived trait, and the flow and long-term ecological impacts, and it has environment in which the crop will be grown (EPA escaped experimental field trials in the western U.S. 1998). The biggest challenges today in ERA are the (Reichman et al. 2006; Watrud et al. 2004; Zapiola identification of potential harms to valued communi- et al. 2008). A. stolonifera and some closely related ties and ecosystems (problem formulation), and species are perennial weeds in the U.S. and other research that allows quantification of future ecolog- countries (Behrendt and Hanf 1979; MacBryde 2006). ical changes (Wilkinson and Tepfer 2009). Concerns They are also considered to be invasive in some about the impact of novel grasses are not theoreti- natural areas (Invasive Plant Atlas 2009; Levine cal; non-native grass invasion has been associated 2000). Bentgrasses can be dispersed by seed and with the decreased abundance of birds and arthropods vegetative stolons, the latter being a trait common to in comparison to native grassland (Flanders et al. many weedy and invasive plants (Otfinowski and 2006). Kenkel 2008; Cadotte et al. 2006). Intraspecific and In the case of ERA for cultivated grasses, under- interspecific pollen-mediated gene flow has been standing plant community dynamics is important to documented for Agrostis in experimental and natural characterize direct or indirect harms to non-target conditions (reviewed in MacBryde 2006). A. stolo- species and the distribution of receiving populations nifera and the closely related A. gigantea are able to for crop-to-wild gene flow. Unfortunately, regional hybridize and form persistent populations in roadsides floras and botanical references are generally insuffi- (Hart et al. 2009). However, there is little informa- cient to assess these risks because they are often tion about their habitat types, plant community 123 Plant Ecol (2011) 212:1629–1642 1631 associations, or species co-occurrence in today’s Materials and methods natural and managed ecosystems. Panicum virgatum is a native, warm-season, Study site, botanical surveys, and habitat perennial grass most commonly associated with the definitions tall grass prairies of North America (Weaver and Fitzpatrick 1934). However, in northeastern North Field studies were conducted in 2009 and 2010 in two America, the presettlement distribution pattern for ecoregions: Lower New England Ecoregion (subeco- switchgrass is believed to have been a narrow zone region Southern New England Coastal Hills and Plains, adjacent to the coastal salt marsh (Niering and abbreviated CHP) and North Atlantic Coast Ecoregion Warren 1980). Switchgrass is commonly sub-divided (subecoregion Southern New England Coastal Low- into two broad ecotypes, upland and lowland. Low- land, abbreviated CL) (Metzler and Barrett 2006; TNC land ecotypes are notable for their larger stature and 2010) (Fig. 1). The CHP transects were located within are typically tetraploids, while Upland ecotypes are the western boundary of 72°32015.121800 to the eastern somewhat smaller and can be either tetraploid or boundary of 71°4808.167800 and the northern boundary octaploid (Martinez-Reyna and Vogel 2002; Porter of 42°1018.994800 to the southern boundary of 1966). Switchgrass is an outcrossing species with 41°25033.92700. The CL transects along the Long Island strong self-incompatibility, increasing the likelihood Sound were located within the western boundary of intraspecific gene flow (Martinez-Reyna and Vogel of 73°3002.620200 to the eastern boundary of 2002). In the northeastern U.S., the Panicum genus 71°27024.364200 W and from the northern boundary includes native species