Biological Invasions

, Volume 14, Issue 12, pp 2665–2685 | Cite as

Edaphic, salinity, and stand structural trends in chronosequences of native and non-native dominated riparian forests along the Colorado River, USA

  • David M. MerrittEmail author
  • Patrick B. Shafroth
Original Paper


Tamarix spp. are introduced shrubs that have become among the most abundant woody plants growing along western North American rivers. We sought to empirically test the long-held belief that Tamarix actively displaces native species through elevating soil salinity via salt exudation. We measured chemical and physical attributes of soils (e.g., salinity, major cations and anions, texture), litter cover and depth, and stand structure along chronosequences dominated by Tamarix and those dominated by native riparian species (Populus or Salix) along the upper and lower Colorado River in Colorado and Arizona/California, USA. We tested four hypotheses: (1) the rate of salt accumulation in soils is faster in Tamarix-dominated stands than stands dominated by native species, (2) the concentration of salts in the soil is higher in mature stands dominated by Tamarix compared to native stands, (3) soil salinity is a function of Tamarix abundance, and (4) available nutrients are more concentrated in native-dominated stands compared to Tamarix-dominated stands. We found that salt concentration increases at a faster rate in Tamarix-dominated stands along the relatively free-flowing upper Colorado but not along the heavily-regulated lower Colorado. Concentrations of ions that are known to be preferentially exuded by Tamarix (e.g., B, Na, and Cl) were higher in Tamarix stands than in native stands. Soil salt concentrations in older Tamarix stands along the upper Colorado were sufficiently high to inhibit germination, establishment, or growth of some native species. On the lower Colorado, salinity was very high in all stands and is likely due to factors associated with floodplain development and the hydrologic effects of river regulation, such as reduced overbank flooding, evaporation of shallow ground water, higher salt concentrations in surface and ground water due to agricultural practices, and higher salt concentrations in fine-textured sediments derived from naturally saline parent material.


Tamarix Populus Soil salinity Colorado River Flow regime Dams 



We would like to acknowledge David Canter, Julie Roth, Ron Osborne, Eligio Aragon, Kirsten Romig, Brett Wolk, Chris Dodge, John Swett, David Graf, and Steven Rauth for assistance in the field and with logistics. Thank you to Terry Waddle who directed the topographic surveying on the lower Colorado River, Rick Anderson who directed the topographic surveying on the upper Colorado River, Tammy Fancher for preparing Fig. 1, and L. Scott Baggett for assisting with the smearing technique for Figs. 2 through 6. Cathy Stewart provided assistance with soil texture analysis. We extend special appreciation to Laura Perry who provided helpful review and editorial suggestions. Funding from Bureau of Reclamation, Lower Colorado River Regional Office and the U.S. Geological Survey Invasive Species Program supported PBS and funding from TNC David H. Smith fellowship program and an interagency agreement (no. 2216-08-IA-312) with the Bureau of Reclamation supported DMM’s work. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.


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Copyright information

© Springer Science+Business Media B.V.(outside the USA) 2012

Authors and Affiliations

  1. 1.USFS National Watershed, Fish and Wildlife StaffFort CollinsUSA
  2. 2.Natural Resource Ecology LaboratoryColorado State UniversityFort CollinsUSA
  3. 3.US Geological Survey, Fort Collins Science CenterFt. CollinsUSA

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