Data from: Vegetation response to control of invasive Tamarix in southwestern US rivers: a collaborative study including 416 sites

Most studies assessing vegetation response following control of invasive Tamarix trees along southwestern U.S. rivers have been small in scale (e.g., river reach), or at a regional scale but with poor spatial-temporal replication, and most have not included testing the effects of a now widely-used biological control. We monitored plant composition following Tamarix control along hydrologic, soil and climatic gradients in 244 treated and 172 reference sites across six U.S. States. This represents the largest comprehensive assessment to date on the vegetation response to the four most common Tamarix control treatments. Biocontrol by a defoliating beetle (treatment #1) reduced the abundance of Tamarix less than active removal by mechanically using hand and chain-saws (#2), heavy machinery (#3) or burning (#4). Tamarix abundance also decreased with lower temperatures, higher precipitation, and follow-up treatments for Tamarix resprouting. Native cover generally increased over time in active Tamarix removal sites, however, the increases observed were small and was not consistently increased by active revegetation. Overall, native cover was correlated to permanent stream flow, lower grazing pressure, lower soil salinity and temperatures, and higher precipitation. Species diversity also increased where Tamarix was removed. However, Tamarix treatments, especially those generating the highest disturbance (burning and heavy machinery), also often promoted secondary invasions of exotic forbs. The abundance of hydrophytic species was much lower in treated than in reference sites, suggesting that management of southwestern U.S. rivers has focused too much on weed control, overlooking restoration of fluvial processes that provide habitat for hydrophytic and floodplain vegetation. These results can help inform future management of Tamarix-infested rivers to restore hydrogeomorphic processes, increase native biodiversity and reduce abundance of noxious species.

目前针对美国西南部河流入侵性柽柳（Tamarix）防治后植被响应的相关研究，多数规模较小（如仅针对单个河段），或虽在区域尺度开展但时空复现性不足；且绝大多数研究未纳入当前已广泛应用的生物防治措施的效应评估。本研究于美国6个州的244个治理样地与172个对照样地中，沿水文、土壤与气候梯度监测了柽柳防治后的植物群落组成。本数据集是目前规模最大的综合评估研究，旨在解析植被对4种最常用柽柳防治措施的响应。其中，由食叶甲虫介导的生物防治（处理1）对柽柳种群多度的降低效果，弱于人工手锯/链锯机械清除（处理2）、重型机械清除（处理3）或焚烧（处理4）等主动防治手段。柽柳种群多度还会随温度降低、降水量增加以及针对其萌蘖的后续防治措施而下降。在主动清除柽柳的样地中，本土植物盖度通常随时间推移有所提升，但增幅有限；且主动植被恢复措施并未持续促进本土盖度的增加。综合来看，本土植物盖度与永久性溪流流量、较低的放牧压力、较低的土壤盐分与温度以及较高的降水量呈正相关。柽柳清除样地的物种多样性亦有所提升。但柽柳防治措施，尤其是造成高强度扰动的焚烧与重型机械清除手段，往往会引发外来阔叶草本的次生入侵。治理样地中的水生植物（hydrophytic species）多度显著低于对照样地，这表明美国西南部河流的治理工作过于侧重杂草防控，却忽视了为水生植物与泛洪平原植被提供栖息地的河流过程修复。本研究结果可为未来受柽柳入侵的河流治理提供参考，助力恢复水文地貌过程、提升本土生物多样性并降低有害物种的种群多度。