Project 2005-USGS-552-P Final Report for Effectiveness Monitoring of Springfed Wetlands and Riparian Restoration Treatments: Progressive Management of Invasive Tamarisk in the Southern Nevada Region Submitted by: Tom Dudley, Research Biologist Marine Science Institute, University of California Santa Barbara & Dept. of Natural Resource and Environmental Science, University of Nevada, Reno Co-Principal Investigator: Matthew Brooks, Research Botanist US Geological Survey, Western Ecological Science Center, Yosemite Field Station, El Portal, CA Co-operating Researchers: 1 2 1,3 4 5 5,6 Kumud Acharya , Dan Bean , Benjamin Conrad , Curt Deuser , Gail Drus , Michael Kuehn , Iwona Kuczynska5, Kevin Hultine7, J. R. Matchett8, Steven M. Ostoja8, Susan Roberts8 1Desert Research Institute, Las Vegas, NV 2Colorado Department of Agriculture,, Palisade, CO 3University of Nevada, Las Vegas 4National Park Service, Lake Mead National Recreation Area 5University of California Santa Barbara 6Western Foundation for Vertebrate Zoology, Camarillo, CA 7Northern Arizona University, Flagstaff, AZ 8USGS Western Ecological Research Center (WRRC), El Portal/Bishop, CA 0 TABLE OF CONTENTS 2 EXECUTIVE SUMMARY 7 PROJECT DESCRIPTION AND OBJECTIVES OBJECTIVE 1. Effectiveness Monitoring of Tamarisk Treatments 12 SECTION I An Evaluation of the Effectiveness of Tamarisk Control as a Riparian Restoration Treatment: 12 Case study A. – Floodplain Riparian/Virgin River; 24 Case Study B. – Spring-fed Upland Seeps and Springs 31 SECTION II Avian Response to Tamarisk Removal on the Virgin River 43 Covered and Special Status Avian Species OBJECTIVE 2. Tamarisk and Fire 45 SECTION III Wildfire in Tamarix-invaded Desert Riparian Areas 46 Sub-Section III-A. Regional Survey of Tamarisk-Fire Relations 51 Sub-Section III-B. Tamarisk Condition and Flammability OBJECTIVE 3. Tamarisk Mortality Following Fire 65 Sub-Section III-C. Fire and Tamarisk Mortality 67 Overall Conclusions – Tamarisk and Fire OBJECTIVE 4. Effectiveness of Treatments for Secondary Weeds 68 SECTION IV Effectiveness of herbicide treatments for control of Russian knapweed (Acroptilon repens) as a secondary invasive weed in southern Nevada OBJECTIVE 5. Effectiveness Monitoring of Tamarisk Treatments: Biological Control 74 SECTION V Monitoring Biological Control of Tamarisk 74 Section V-A Documenting the Tamarisk Biocontrol Process in Clark County and the Virgin River Watershed 87 Section V-B Other Elements related to Tamarisk Biocontrol 89 Section V-C Temperature Effects on Life History Traits of Diorhabda carinulata 98 Section V-D Rapid Evolution of Phenology and Range Expansion of an Introduced Insect 106 GENERAL DISCUSSION 115 Restoration for Endangered Species Habitat 123 MANAGEMENT RECOMMENDATIONS 124 ACKNOWLEDGEMENTS 125 REFERENCES 137 APPENDIX 1 Tamarisk versus Native Plants as Breeding Habitat for Birds - Potential Impacts of Biocontrol on the Avian Community 158 APPENDIX 2 Bats Associated with Vegetation Types and Implications of Biocontrol 155 APPENDIX 3 Effects of Tamarisk Biocontrol on Evapotranspiration and Water Resources 1 EXECUTIVE SUMMARY Effective management of non-native plant invasions that threaten native vegetation and associated wildlife species depends on control treatments that provide sustained weed reduction and facilitate their replacement with self-replicating native and/or beneficial non-native plants. This research project involved an Effectiveness Monitoring assessment of riparian locations in which actions to control invasive weeds, particularly tamarisk but including other noxious taxa, have been applied in Clark County and adjacent regions. Research was to characterize and evaluate control methods (chemical and mechanical treatments, fire, biological) to determine management approaches that yielded, or will yield, desired results (recovery of native vegetation and wildlife habitat, improved substrate condition, reduced wildfire risk) while resisting re-invasion by secondary noxious weeds. The effects of simulated biological control of tamarisk were to be addressed as part of the original project to understand the potential impacts and responses when and if biocontrol agents were introduced into Clark County. However, the unanticipated introduction of the tamarisk leaf beetle, Diorhabda carinulata, into the project area during the course of this research provided the opportunity and need to evaluate biological control as a weed management method and its potential to facilitate ecosystem recovery from exotic species invasion, and subsequent improvement of habitat for Covered and other riparian dependent species. Goal and Objectives of the Project Thus, the Goal of this multi-agency research program was to promote adaptive weed management that provides optimal, cost-effective weed control with a minimum of collateral impacts to associated beneficial species, and integrates ecosystem functions into the habitat recovery process. The overall Objective was to undertake an extensive evaluation of regional infestation sites, those where tamarisk has been treated and those where treatments were anticipated, to understand the underlying interrelationships among species and environmental processes, including physical disturbance, fire (natural and prescribed), and hydrologic conditions. The specific Objectives of the research project are as follows: 1. Conduct a multivariate study evaluating relationships among current tamarisk dominance, dominance of other non-native and native plant species, wildlife habitat structure and wildlife associations, tamarisk control treatments, fire, and other environmental variables to assess effectiveness of weed control and riparian vegetation restoration treatments. 2. Compare vegetation structure and composition, and tamarisk flammability in relation to foliage condition, in response to experimental herbicide treatments to simulate anticipated defoliation effects of tamarisk biocontrol. 3. Compare mortality of tamarisk following fire with and without previous herbicide treatments. 4. Evaluate herbicide and cultural treatments for the control of Russian knapweed, a recent invasive species that responds positively to disturbance and may function as a surrogate for treatment of other secondary weed invasions. 2 5. Monitor dispersal and establishment of the tamarisk leaf beetle, document life cycles, genetic changes, and factors that may limit its establishment (predation, premature winter diapause, extreme temperatures); assess effects of this biological control agent on tamarisk condition, defoliation-re- growth dynamics and responses by associated vegetation and wildlife to tamarisk defoliation; evaluate fire risk dynamics related to defoliation. Vegetation Responses to Treatments (Objective 1) This multi-disciplinary project encompassed several research elements, the primary objective targeting vegetation responses to prior tamarisk control treatments carried out by NPS and BLM during the prior decade in floodplain systems, particularly the Virgin River, and in regional upland spring wetlands. Primary findings were that the tamarisk control treatments in floodplains have been effective in significantly and strongly reducing tamarisk stem densities and vegetative cover (from 25% to 1.3% total woody plant cover) compared with untreated control sites, and opening the canopy with much greater areal cover of open space (45% vs. 5% as expected less than 5 years following mechanical treatments. These reductions in tamarisk cover are associated with significant increases in diversity (53 vs. 32 species) and vegetative cover of native shrub and tree species, although herbaceous species did not show significant differences in density nor cover. However, the physical disturbance associated with these treatments also promoted invasion and/or expansion of weedy plant species such as Russian thistle (tumbleweed; Salsola tragus) that can interfere with native plant recruitment, and provide poor habitat for wildlife. Some non-native species, particularly grasses (Bromus spp. and Schismus barbatus), were more common in association with tamarisk in untreated areas so treatments can reduce multiple invasive species. In upland spring sites, time since treatment has a major role in promoting tamarisk reduction and native woody plant increases. Sites initially treated >6 years prior to surveys had lower tamarisk density and cover than more recently treated sites, primarily because NPS policy is to return to sites for follow-up treatments. Native woody plants showed minor enhancement over time, while herbaceous species were significantly more abundant in relation to time since initial treatment. These results indicate that traditional methods of tamarisk removal have mixed effects. They have been effective in meeting some objectives, particularly increasing diversity and abundance of native plants, as well as reducing the likelihood of wildfire (sparser distribution of plant biomass, or ‘fuels’ in treated area) [Fuels management was the primary driver of weed control/restoration treatments in non-NPS locations.] However, a general conclusion is that conventional treatments have the undesirable effect of increasing the abundance of other noxious, non-native species that can interfere with native vegetation recovery. Ecosystems managed for invasive plant control will need repeated attention, and probably active restoration of important taxa, to eventually reach to goal of sustainably increasing native species abundances and diversity in Clark County wetlands. Restoration