Effects of crested wheatgrass soil on native plant production

Background/Question/Methods

Restoring native plant communities in areas previously dominated by crested wheatgrass has proven to be a challenging endeavor. The difficulties associated with reintroduction of native plants may be caused either by direct competition for resources from crested wheatgrass or by changes in chemical and/or biological properties in the soil due to the long term presence of crested wheatgrass. A greenhouse experiment was conducted to determine whether the growth of native early-, mid-, and late-seral plants was inhibited by soil from crested wheatgrass stands. Twenty-eight species of graminoids, forbs, and shrubs native to sagebrush grasslands in western Colorado were germinated prior to transplanting in one of three soil treatments (sterilized sand alone, sterilized sand with soil from crested wheatgrass stands [4:1 ratio], and sterilized with soil from native rangelands [4:1 ratio]).  Seven weeks after planting, all plants were fertilized. At sixteen weeks, aboveground and belowground biomass was harvested, oven dried, and weighed. Analysis of variance was used to determine the effects of plant category and soil treatments on total biomass. Pairwise comparisons of treatment means were conducted using Tukey’s adjustment.

Results/Conclusions

Early-seral graminoids were the only plants that produced more total biomass in native rangeland soil than in soil from crested wheatgrass stands. All other plants produced similar amounts of total biomass in native rangeland soil and crested wheatgrass soil. Forbs and graminoids from all seral stages produced less total biomass in sterilized sand than one, or both treatments with field soil. Mid- and late-seral shrubs did not respond to any of the soil treatments. Based on these results we can conclude that chemical and/ or biological properties of the soil are not the primary cause for difficulties associated with the reintroduction of native plant species to areas previously dominated by crested wheatgrass. Early-seral graminoids may be the exception given their tendency to produce greater biomass in native rangeland soil treatment.  For plants other than early-seral graminoids, the lack of successful native plant restoration in areas once dominated by crested wheatgrass may be caused by direct competition from crested wheatgrass.