Document Type


Date of Degree Completion

Spring 2023

Degree Name

Master of Science (MS)



Committee Chair

Mary Poulson

Second Committee Member

Eric Graham

Third Committee Member

Alison Scoville


Cacti are iconic, conspicuous, and important contributors to arid ecosystems. They stabilize soil and provide essential food and habitat to wildlife. Pediocactus nigrispinus is a species of cactus endemic to the Pacific Northwest and has been listed as a sensitive species due to its vulnerability to habitat loss. Pediocactus nigrispinus is being threatened by habitat fragmentation, poaching, and a changing climate. Best conservation methods for this species are poorly understood, due in part to a limited understanding of its demography and associations that may help define its occurrence.

A demographic study in Washington State was implemented in 2016 to give a baseline understanding of the population dynamics for P. nigrispinus. Five years of size, fecundity, and survival information were recorded. A stochastic analysis was performed to assess survival and fecundity rates for climatic variables. Biotic and abiotic associations were assessed in an additional 16 plots throughout Washington and Oregon through in situ assessment of vegetation and ground cover associations. These variables were compared with population density, overall size of the individuals, and number of fruits to assess how changes in associations may correlate with changes in these population traits. The demography study found no juvenile recruitment and a declining population over the four years of analysis regardless of annual precipitation levels. The association analysis found no correlation in population metrics with the associations but indicated higher fruit production in Oregon compared to Washington.

Available for download on Wednesday, July 30, 2025