Success of Active Revegetation after Tamarix Removal in Riparian Ecosystems of the Southwestern United States: A Quantitative Assessment of Past Restoration Projects

Abstract

Invasion by the non-native tree Tamarix has led to implementation of restoration projects aimed at maintaining the ecological integrity of many riparian communities in the southwestern United States. These restoration efforts may include Tamarix removal, manipulation of hydrologic regimes, and active revegetation of native species. The goal of this study was to determine which site characteristics are correlated with restoration success, defined in terms of reductions of undesirable species such as Tamarix and establishment of desirable, native species. To accomplish this, vegetative and environmental data were collected at 28 sites in the southwestern United States where active revegetation was completed after Tamarix removal. These data were incorporated into regression tree models with predictor variables that included number of years since removal (1-18 years) and multiple management, climate, soils, and hydrological variables to determine success of Tamarix control, revegetation success, and general plant community responses. Our results suggest that there are easily measurable site characteristics that are associated with greater native cover and richness, planting success, and Tamarix control. Close proximity to perennial water, sufficient precipitation, recent flooding, and good drainage as well as coarser soil texture, and lower soil pH all favored native species. Overall, those site characteristics associated with native species success were the same as those related to lower Tamarix cover. These quantitative models are intended to assist researchers and land managers to design more effective riparian restoration efforts in this critical arid lands ecosystem.

Russian Olive (Elaeagnus angustifolia) Removal in the Western United States: Multi-Site Findings and Considerations for Future Research

“…When electroconductivity was less than 2.35 mmhos, richness was 16 as compared to 13 when electroconductivity was higher than 2.35 mmhos. Among sites with less than 2.35 mmhos of electroconductivity, and when organic matter was less than 5.4%, richness was even higher [18].…”

“…Non-native Tamarix is the most well-understood example of this, dominating in areas that are more arid [6], generally as a consequence of dam building and channelization of rivers, which dis-favor native trees [9,33]. Previous surveys of riparian restoration sites have similarly found associations between increased exotic cover and low water availability [18,19].…”

“…Two studies report on a quantitative synthesis of vegetation response across sites and over time after Tamarix spp. removal [17,18]. Still others report on the restoration of mixed native and invasive stands [12,19,20], but none have synthesized vegetation response across sites after removal of E. angustifolia alone.…”

“…was removed has used ordination analysis [17] and regression trees [18]. While no significant pattern was found among abiotic and biotic variables in the first study, the later study was able to identify several, easy to measure environmental variables associated with higher native cover across the 28 Tamarix removal sites surveyed, including moisture availability and soil characteristics [18]. In light of the complexity of riparian ecosystems, regression tree analysis appears to be a useful way to deal with many variables across highly variable sites.…”

The Biology of Invasive Alien Plants in Canada. 11. Tamarix ramosissima Ledeb., T. chinensis Lour. and hybrids

“…In addition to characteristics that influence population dynamics discussed in previous sections, others include the ability to produce a continual supply of seeds during the growing season providing an ecological advantage over other woody riparian species (DiTomaso 1998) and the ability to recover faster after fires than native riparian species (Busch and Smith 1993), and the ability to produce allelopathic compounds such as flavenol bisulfates and bisultate-glucuronides (Brock 1994). However population dynamics change at sites where water and soil conditions have not been disturbed by humans and saltcedar seedlings have not competed well against Populus seedlings (Sher and Marshall 2003) or against Salix species (Sher et al 2002;Bay and Sher 2008).…”