Habitat Associations of a Threatened Cactus: Vegetation and Soil Characteristics.

Sclerocactus wetlandicus, a federally listed threatened cactus endemic to northeastern Utah, USA, is threatened by energy development. While we have a basic understanding of site, soil, and vegetation characteristics of S. wetlandicus habitat, there are no data quantifying edaphic or plant community characteristics of occupied habitat, whether these characteristics differ from those of unoccupied habitat, and how closely reclaimed well pads resemble undisturbed sites in these characteristics. A thorough understanding of the habitat characteristics of S. wetlandicus will help: 1) guide energy development compatible with conservation, 2) identify areas suitable for introduction of additional populations, and 3) determine the suitability of reclaimed well pads for cactus reintroduction. The objectives of our study were to determine: 1) Whether vegetation and soil properties differ between cactus-occupied and cactus-unoccupied sites, and 2) How similar vegetation and soil properties of reclaimed well pads are to cactus-occupied sites. The five densest populations were identified and occupied polygons (sites) were created around them. These were paired with unoccupied polygons with similar geologic features Lastly, 18 reclaimed well pads were selected. We sampled vegetation with the line-point intercept method and excavated soils to describe soil profiles in the field and to collect material for laboratory analyses. An NMDS of vegetation data (species relative cover) revealed two clusters, with well pads separated from occupied and unoccupied sites. PERMANOVA showed a significant difference among habitat types. If well pads were removed from the analysis there was no longer a significant difference, demonstrating that well pads were significantly different in vegetation from undisturbed rangeland, whether cactus-occupied or not. Properties of undisturbed soil at occupied sites were not significantly different from undisturbed soils at unoccupied sites. However, chemical and physical properties of undisturbed soils at both occupied and unoccupied sites differed significantly from the soils of well pads (p<0.05). Well pad soils/sediments were significantly higher in available phosphorus, electrical conductivity, soluble boron (borate), soluble sulfur (sulfate), soluble sodium, soluble magnesium, and soluble potassium, which indicate much higher salt content. Compared to undisturbed sites, well pads had significantly lower slopes because they had all been excavated/constructed to be a level surface. Bare soil cover was much higher and biological crust cover was much lower on well pads than on undisturbed soils. In conclusion, vegetation and soils of occupied and unoccupied sites are indistinguishable, and reclaimed well pads do not resemble undisturbed rangeland in vegetation or soils.