To what extent has invasive riparian vegetation (IRV) treatment reversed channel narrowing and reduced dynamism trends? Paired treated and untreated reaches at 15 sites along 13 rivers were compared before and after treatment using repeat aerial imagery to assess long-term (~10 year) channel change due to treatment on a regional scale across the Southwest U.S. Wieting et al. found that IRV treatment significantly increased channel width and floodplain destruction.
Does hybridization among tamarisk beetles change the risk of non-target attack in the field? Clark et al. study the consequences of hybridization in tamarisk beetles (Diorhabda). They paired laboratory phenotyping with genomics to assess changes in risk of non-target attack and body size and fecundity. Body size and early fecundity were similar in pure and hybrid females, indicating that hybridization is not detrimental to insect fitness or the biocontrol program and may provide variation that allows populations to become locally adapted.
What site conditions are associated with greater recovery and overall higher cover of willows? Goetz et al. performed a meta-analysis of tamarisk removal and willow (Salix) recovery across the southwest, compiling data from 260 sites where tamarisk was subject to active removal and/or biocontrol and 132 reference sures. Cut-stump method with biological control was the most effective method to improve native species dominance. Willow cover was generally highest in locations with low drought stress, as reflected by soil properties, distance to water, and climate.
A study subjecting tamarisk from two distinct populations originating from areas with greatly varying soil salinities to a range of different salinities. Results showed dramatic differences between growth with the low salinity population accumulating 72% more biomass when grown at 4 ppt compared to 16 ppt, while the high salinity population produced 50% more biomass when grown at 16 ppt. Additionally, the high salinity population had a lower turgor loss point and exhibited greater stomatal control relative to the low salinity population.
The northern tamarisk beetle Diorhabda carinulata (Desbrochers) was approved for release in the United States for classical biological control of a complex of invasive saltcedar species and their hybrids (Tamarix spp.). An aggregation pheromone used by D. carinulata to locate conspecifics is fundamental to colonization and reproductive success.
In this chapter, Carothers et al have three objectives: first, they document the value of nonnative Tamarix as summer habitat for birds compared to native riparian habitats of mesquite bosques and cottonwood/willow, and mixed deciduous gallery woodlands; second, they specifically focus on the unintended consequences to native avifauna of dam construction, Tamarix invasion, native vertebrate colonization of the Tamarix-dominated riparian habitat, and subsequent biocontrol along approximately 300 miles of the Colorado River in Grand and Glen Canyons; and, third, the
Remote sensing methods are commonly used to monitor the invasive riparian shrub tamarisk (Tamarix spp.) and its response to the northern tamarisk beetle (Diorhabda carinulata), a specialized herbivore introduced as a biocontrol agent to control tamarisk in the Southwest USA in 2001.
A 2006 review of the saltcedar (Tamarix) biocontrol program.
DeLoach, C.J., Milbrath, L.R., Carruthers, R., Knutson, A.E., Nibling, F., Eberts, D., Thompson, D.C., Kazmer, D.J., Dudley, T.L., Bean, D.W. and Knight, J.B., 2006. Overview of saltcedar biological control. In Monitoring science and technology symposium: unifying knowledge for sustainability in the Western Hemisphere. Proceedings RMRS-P-42CD. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fort Collins, Colorado (pp. 92-99).
Stabler and Still estimate density and standing biomass of tamarisk along waterways in a northwest to southeast transect in Oklahoma to test the hypothesis that environmental conditions in northwest Oklahoma would make successful invasion by tamarisk more likely. They found that the invasive potential of tamarisk in Oklahoma is likely limited by streamflow and climate but not by soil salinity.
Nagler et al. test the assumption that removing saltcedar (Tamarix spp.) will save water and create environments more favourable to these native species. They compared sap flux measurements of water used by native species in contrast to saltcedar, and compared soil salinity, ground water depth and soil moisture across a gradient of 200–1500 m from the river's edge on a floodplain terrace at Cibola National Wildlife Refuge (CNWR).