Reduced abundance of non-native Tamarix shrubs in western U.S. riparian systems following biological control by a defoliating beetle has led to concerns that replacement plant communities could be dominated by other invasive species and/or not provide some of the ecosystem services that Tamarix was providing. In previous studies, Tamarix decline following biocontrol was accompanied by small increases in native and non-native herbaceous species, with variable responses of woody vegetation. However, none of these studies spanned periods longer than a decade since beetle release. This is an important caveat, given the cyclical nature of plant-herbivore interactions and potential lags in vegetation recovery. We report plant community response to an eight-year-long second cycle of Tamarix defoliation-refoliation in two reaches of the upper Colorado River in eastern Utah, 11–13 years after beetle arrival. Tamarix cover across sites initially declined an average of ca. 50% in response to the beetle, but then recovered. Changes in the associated plant community were small but supported common management goals, including a 47% average increase in cover of a native shrub (Salix exigua), and no secondary invasions by other non-native plants. We suggest that the effectiveness of biocontrol programs must be assessed case-by-case, and on a long-term basis.

落叶甲虫进行生物防治后，美国西部河岸系统中非本地Tamarix灌木的数量减少，引起了人们的担忧，即替代植物群落可能被其他入侵物种所主导，并且/或者无法提供Tamarix提供的某些生态系统服务。在先前的研究中，Tamarix生物防治后生物量下降，伴随着本地和非本地草种的少量增加，木质植被的响应也有所不同。但是，这些研究自甲虫释放以来没有跨越十多年的时间。考虑到植物与草食动物相互作用的周期性和植被恢复的潜在滞后性，这是一个重要的警告。我们报告了甲虫抵达后11–13年，植物群落对犹他州东部科罗拉多河上游两个河段的Tamarix落叶-再落叶第二个周期长达八年的反应。柳最初，各个站点的覆盖率平均下降了 50％对甲虫有反应，但随后恢复了。相关植物群落的变化很小，但是支持共同的管理目标，包括原生灌木（Salix exigua）的平均覆盖率增加47％，并且没有其他非本地植物的二次入侵。我们建议必须逐案并长期评估生物防治计划的有效性。