Native and Non‐Native Community Assembly through Edaphic Manipulation: Implications for Habitat Creation and Restoration

Chemical and physical (abiotic) conditions can be determining factors of community assembly and invasibility, but can this observation be used as a practical tool for habitat creation? Serpentine soils, in particular, have three abiotic components thought to confer invasion resistance: a low Ca:Mg ratio, low water‐retention capacity, and high concentrations of heavy metals. Consequently, not only do some serpentine‐adapted native plants persist only on serpentine soils, but also the community members that depend upon those plants become dependent upon serpentine as well. In an effort to provide additional habitat for the threatened and serpentine‐restricted Bay checkerspot butterfly (Euphydryas editha bayensis), we experimentally altered a non‐serpentine site to mimic the abiotic conditions of serpentine. Attempts to lower the Ca:Mg ratio of soils through the addition of MgSO₄ were unsuccessful. We then altered soil depth through the addition of gravel beds to determine the effects of water stress on native and non‐native community composition. We found that shallow soils had lower water content and correspondingly had significantly lower non‐native species richness and cover. The results present promising means, but also cautionary information, for habitat creation efforts and demonstrate the possible utility of edaphic manipulation in abating non‐native plant invasions. None of the experimental plots supported communities capable of sustaining E. editha populations, emphasizing that the manipulation of physical conditions is only likely to be successful in coordination with other restoration techniques.