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2022 Conference

2022 Conference

  • Tracing the Monitoring and Evaluation of Tamarix Control and its Outcomes in the American Southwest: A Systematic Review and Meta-Analysis
    Alexander R. B. Goetz,1* Eduardo González,2 Mayra C. Vidal,3 Patrick Shafroth,4 Annie L. Henry,1 Anna A. Sher1
    1Department of Biological Sciences, University of Denver, Denver, CO, USA;
    2Department of Biology, Colorado State University, Fort Collins, CO, USA
    3Department of Biology, University of Massachusetts Boston, Boston, MA, USA
    4Fort Collins Science Center, United States Geological Survey, Fort Collins, CO, USA
    Control of invasive Tamarix spp. and associated riparian restoration in the American Southwest has been of great interest to scientists and resource managers for decades. Hundreds of studies have reported highly variable outcomes of Tamarix control efforts, as measured by a range of response variables, temporal and spatial scales, and monitoring strategies. We conducted a literature search, quantitative meta-analysis, and vote count on published papers that quantitatively measured a variety of responses to removal of Tamarix. From 1206 publications obtained through a global search on terms related to Tamarix removal, we filtered/selected 54 and 68 for a quantitative meta-analysis and vote count, respectively. Sources were included in our analysis if they covered active removal or biological control removal of Tamarix spp. in North America and had some measure of comparison between pre- and post-removal (Before-After removal; BA) and/or restored and unrestored sites (Control-Impact; CI). We estimated responses to control by treatment type (e.g., cut-stump removal, burning, biocontrol) and ecosystem component response (e.g., vegetation, fauna). Within the vegetation component, we separately analyzed vegetation metrics by growth habit (overstory, understory, both) and desirability (noxious invasive, native/non-noxious exotic). There were typically multiple response metrics in each paper, and the final sample sizes were 778 for the meta-analysis and 1,461 for vote counting. For the quantitative meta-analysis, we calculated standardized mean differences to determine effect sizes, and for the vote count we calculated the relative percentages of cases that increased (desirable outcomes), decreased (undesirable outcomes), and did not change. We assigned positive values to desirable outcomes, as defined by the author. Overall, vegetation metrics were the most commonly assessed/represented, particularly Tamarix metrics.  Characteristics such as fauna, soils, and hydrogeomorphic dynamics were underrepresented, especially across removal method categories. While “fauna” as a category was the second best represented after vegetation, there was insufficient replication to examine patterns within taxa. From the quantitative meta-analysis, we found significantly positive responses of combined vegetation metrics to biocontrol, herbicide, and cut-stump treatments. However, analysis of vegetation metrics by category showed that while treatments are effective at reducing Tamarix cover, there was no statistically significant impact on desirable vegetation. Biocontrol had a significantly negative effect on fauna metrics. Herbicide increased measures of fire intensity. These results were largely corroborated by the vote count; most treatments saw largely positive effects, but unequivocal positive outcomes were rare. In the vote count, biocontrol had largely negative effects on fauna and was associated with an increase in fire. Overall, our results suggest that common removal methods are generally effective at reducing Tamarix cover, but the more indirect effects on other aspects of the environment are variable and still remain understudied. Further research could help to elucidate the less commonly studied responses to invasive species control and restoration including fauna, soil, and hydrogeomorphic characteristics.

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