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沿岸入侵柽柳（Tamarix）防治后的植被响应开展的相关研究，多数尺度较小（如单河段尺度），或虽为区域尺度但时空重复度不足，且大多未纳入当前已广泛应用的生物防治措施的效应评估。本研究沿水文、土壤与气候梯度，在美国6个州的244个防治样地与172个对照样地中，监测了柽柳防治后的植物群落组成。本研究是目前为止针对四种最常用柽柳防治措施下植被响应的最全面的大型评估：采用食叶甲虫的生物防治（处理方案1）对柽柳种群多度的降低效果，弱于人工手持链锯机械移除（方案2）、重型机械移除（方案3）或焚烧（方案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柽柳萌蘖的后续防治措施而下降。在主动防治柽柳的样地中，本地植物盖度通常随时间推移有所提升，但增幅较小，且主动植被恢复措施并未持续提升本地盖度。整体而言，本地植物盖度与常年溪流径流、较低的放牧压力、较低的土壤盐度与温度以及更高的降水量呈正相关。在柽柳被移除的样地中，物种多样性也有所提升，但柽柳防治措施，尤其是引发最高程度干扰的焚烧与重型机械移除方案，往往会加剧外来阔叶草本的次生入侵。防治样地中的水生植物多度远低于对照样地，这表明美国西南部河流的治理过于聚焦杂草防控，却忽视了为水生植物与河漫滩植被提供栖息地的河流地貌过程的修复。本研究结果可为未来受柽柳入侵的河流治理提供参考，以修复水文地貌过程、提升本地生物多样性并降低有害入侵物种的多度。