Impact of Non‐Native Plant Removal on Lizards in Riparian Habitats in the Southwestern United States

Abstract

Many natural processes in the riparian cottonwood (Populus deltoides) forest of the Middle Rio Grande (MRG) in the southwestern United States have been disrupted or altered, allowing non-native plants such as saltcedar (Tamarix spp.) and Russian olive (Elaeagnus angustifolia) to establish. We investigated reptilian responses to restoration efforts by sampling communities of lizards at 12 study sites invaded by non-native plants along the MRG in New Mexico for 7 years (2000)(2001)(2002)(2003)(2004)(2005)(2006). Sites within three regions were randomly assigned to one of the three treatments to remove non-native plants and woody debris, or as untreated controls. We used pitfall and funnel traps to capture, mark, and release lizards from June to September. Principal components analysis of 15 vegetation variables identified five factors that best explained variation among sites before and after removal of non-native plants. Relative abundances for four of six common species of lizards were associated with vegetation characteristics that significantly changed after plant removal. Species were either positively associated with the more open, park-like understory found in treated sites or negatively associated with debris heaps and thickets of non-native plants found in untreated sites. Eastern fence lizards (Sceloporus consobrinus) and New Mexico whiptails (Aspidoscelis neomexicana) increased in relative abundance after nonnative plants were removed. Overall, removal of nonnative plants seems beneficial, or at least is non-damaging, to lizard communities of the MRG forest. Providing information on habitat associations of lizard communities will help land managers balance management objectives with other considerations, such as providing important wildlife habitat.

Classical biological control for the protection of natural ecosystems

“…have defoliated hundreds of thousands of hectares, and are beginning to kill saltcedar trees (Hudgeons et al, 2007;Carruthers et al, 2008;Deloach et al, 2008;Tracy and Robbins, 2009). If saltcedar tree deaths from biological control agents become widespread, this should significantly improve wildlife habitat, as physical removal of saltcedar is documented to benefit native plants (Lovich and Bainbridge, 1999), reptiles (Bateman et al, 2008), fishes (Kennedy et al, 2005), and birds (Longland and Dudley, 2008). Field assessments of potential non-target risk to native Frankenia species, the taxon identified as potentially at risk from Diorhabda feeding, found no significant impacts under field ''worst case" conditions (Dudley and Kazmer, 2005).…”

Riparian Forest Restoration: Conflicting Goals, Trade-Offs, and Measures of Success

“…Descriptions of herpetofauna sampling techniques are described in [21]. We compiled a list of historic species present in the MRG from 1938 to 1995 from monitoring projects along the MRG [22][23][24] and records of specimens from the Museum of Southwestern Biology.…”

“…Numbers of non-native saltcedar and Russian olive trees and amount of fuels were measured along 50 m transects and in 4 m radius plots in conjunction with herpetofauna sampling (also described in [21]). Ground fuel load (metric tons per ha) was estimated with Fuels Management Analyst software [25].…”

“…This is similar to results of analyses on the effects of treatments on relative abundances of species of lizards. For example, Southwestern fence lizards (Sceloporus cowlesi, formerly S. undulatus complex) and Chihuahuan spotted whiptails (Aspidoscelis exanguis) responded positively to treatments and were associated with open understory habitats of restored sites [21], whereas amphibian species (i.e., Woodhouse's toad (Bufo woodhousii)) did not respond to treatments and instead responded to hydrological variables in the years following restoration (i.e., spring flooding in 2005 and summer rainfall in 2006; [40]. In Case Study II, structurally and compositionally heterogeneous stands of vegetation support diverse species assemblages [41,42].…”

Ecosystem-wide management of invasive species in the face of severe uncertainty

“…Without monitoring consequent changes, valuable opportunities will be missed for a fast response, leading to prolonged and exacerbated side effects of management. One study revealed adverse herbicide impacts after revisiting the managed site 16 years later, finding that the target invader became more abundant and two native forbs had become extremely rare, presumably due to residual chemical effects and fish assemblages, reported beneficial or at least non-damaging outcomes (Kennedy et al 2005, Bateman et al 2008, Nelson and Wydoski 2008, while other studies suggested some avian species using Tamarix habitats may have been negatively affected (Sogge et al 2008, Dudley andBean 2012). Thus, for large scale eradications involving numerous species, conclusions can be less informative and lead to ill-advised management decisions when these decisions are made upon the responses of a specific species group without consideration for others.…”