Tamarix spp. (a.k.a. saltcedar, tamarisk) invasion is considered a major ecological threat at both national and global levels, with supposed impacts on soil chemistry.  One of the most often cited mechanisms of ecosystem change by Tamarix is through its ability to deposit salty exudates and salt-rich leaf litter. The degree to which Tamarix relates to elevated soil salinity, however, has not been adequately quantified, especially in the context of environmental factors that may also influence salinity.   If Tamarix does elevate localized salinity by means of salty deposits, then we might expect that the magnitude of its impact would be influenced by stand characteristics such age and density. Therefore, we analyzed soil salinity levels associated with Tamarix stands across a gradient of aboveground ages and densities along an arid reach of the Middle Rio Grande in central New Mexico.  Stands were sampled both in the current, active floodplain and in the historic floodplain (outside the levees) to account for potential hydrologic impacts on soil chemistry.  Paired soil samples were collected underneath Tamarix canopies and in adjacent open areas to compare solute concentrations associated with Tamarix cover to those in soils exposed to greater rates of surface evaporation.

Results/Conclusions

Soils inside of the levees and thus subject to overbank flooding were significantly lower in salinity than soils outside the levees.  With regard to biotic effects, results indicate that elevated environmental salinity is related to Tamarix stand age but the relationship with stand density is weak. While older Tamarix stands are assumed to have higher surface soil salinity, our results show that these stands possess some of the lowest salt levels. In areas outside of the levees, soils under Tamarix canopies had relatively lower surface soil salinity compared to open areas, suggesting that surface evaporation may contribute more to elevated salt concentrations than leaf exudates. This research provides a unique opportunity to investigate the relationship between soil salinity and an invasive species versus other environmental variables.  Results can be used to guide management decisions related to soil remediation and native species revegetation for Tamarix-invaded areas.