Establishing soil and surficial geologic habitat criteria for presumed gypsophiles — The example of Eriogonum corymbosum var. nilesii, Mojave Desert, U.S.A.

Detailed soil and surficial geologic data are needed for ecological interpretations, yet are often absent or incomplete in published studies of arid land ecology or biogeography. Clear, edaphic habitat definitions are needed for gypsophilic plants including the Las Vegas buckwheat, E. corymbosum var. nilesii (LVB), a rare shrub endemic to the Mojave Desert. As a case study, we use soil profile data and high resolution (1:3000 scale) surficial geologic maps to identify likely edaphic controls of LVB habitat, potential habitat, and non-habitat distributions. We confirm gypsiferous substrates lacking hard, physical surface crusts as a boundary condition in most, but not all population clusters, but find that fine-grained, carbonate-rich soil lacking gypsum is also viable habitat, as is shallow (< 1 m) sandy alluvium overlying gypsiferous sediments. Deep (> 1 m), coarse-grained alluvium and/or surfaces with tightly interlocking desert pavement exclude LVB. Our results challenge the view of this target species as a true gypsophile, however, it remains unclear whether carbonate-rich habitats represent ideal conditions or refugia. This study underscores the important merits of surficial geologic mapping and soil morphological description for ecological research, conservation, restoration, and land management in arid environments, especially gypsum soils, worldwide.