Quantifying impacts on soil and groundwater chemistry by an invasive tree (Tamarix spp) along the Middle Rio Grande, New Mexico

Background/Question/Methods Tamarix spp (a.k.a. saltcedar, tamarisk) invasion is considered a major threat to ecological health at both national and global levels, with supposed impacts on soil and water dynamics.  One of the most devastating effects of Tamarix lies within its ability to deposit salty exudates and salt-rich leaf litter, however the degree to which Tamarix impacts soil and groundwater chemistry has not been adequately quantified.   If Tamarix does indeed elevate localized salinity by means of these deposits, then we might expect that the magnitude of its impact would be influenced by stand characteristics such as density, stand age, and whether flooding occurs.   To address this issue, we analyzed soil and groundwater salinity levels associated with Tamarix stands across a gradient of densities and aboveground ages along the Middle Rio Grande in central New Mexico.   Stands were sampled both in the current, active floodplain and in the historic floodplain (typically outside of the levees) to account for potential hydrologic impacts on soil and groundwater chemistry in Tamarix-infested areas. 

Results/Conclusions Preliminary findings indicate that areas dominated by Tamarix had significantly higher levels of soil salinity than areas with mixed (cottonwood and Tamarix) or native vegetation canopies.  At this time, it is assumed that decadent or older Tamarix stands may have already altered the soil too much to make restoration feasible.  Our initial findings, however, show that these decadent stands have the lowest salt levels and therefore seem more conducive to native riparian vegetation growth.  Preliminary results also suggest that while flooding does mitigate the impact of Tamarix on salt-loading, salinity levels are higher on average in Tamarix-invaded areas when compared with sites dominated by natives.  Identification of patterns between Tamarix stand characteristics and soil and groundwater chemistry could have important implications for riparian habitat restoration following Tamarix removal.  This research provides a unique opportunity to quantify the effects of an invasive species on an ecosystem, and will be used to assist in identifying revegetation potential for riparian areas infested by Tamarix.  Prioritization of restoration efforts will likely ensure the proper allocation of funds to areas of greatest concern and of greatest potential for revegetation.