Basis for restoration of saltcedar (Tamarix spp., Tamaricaceae) invaded sites through an adaptive management approach

Abstract

Biological invasions are considered one of the most serious drivers of global biodiversity degradation in the face of ecological restoration. Saltcedar (Tamarix spp.) is an aggressive invader in arid environments of the United States, Mexico, Australia, and Argentina, causing profound alteration of riparian habitats, the composition and structure of natural communities, and ecosystem functioning. Given the severity of the reported invasion processes, and considering that Tamarix's responses to the wide range of existing control techniques are still poorly explored, the objectives of this investigation were to assess the implementation of different control techniques based on active adaptive management and to define indicators to measure the effectiveness of both the techniques and the recovery of the system, as a first action in ecological restoration projects of invaded sites. The experiment was carried out in the Llancanelo Wetland Provincial Reserve and Ramsar site, where 540 ha of marsh environment were replaced by monospecific saltcedar forests. Thirteen treatments were proposed combining control techniques (mechanical and chemical), saltcedar population situation (forest, shrubland, resprouts), and times of the year. Simultaneously, an assisted revegetation experiment was performed on four of the controlled plots. Finally, the costs associated with each treatment were estimated. The most effective control techniques were mechanical extraction and root burning for areas with mature, low-density forests, and cutting and herbicide application for shrublands and resprouts in late summer-early spring. The cutting and shading technique is recommended in places where the herbicide application can put the ecosystem integrity at risk. Assisted revegetation only provided 2% coverage in the intervened plots, a non-significant value considering that natural recovery presented up to 35% coverage and a low percentage of invasive alien species. In spite of this, the species composition reported in the monitoring suggests adjusting revegetation techniques to assist native species recovery.