Date of Award


Degree Name

MS in Biological Sciences


Biological Sciences


College of Agriculture, Food, and Environmental Sciences


Matt Ritter

Advisor Department

Biological Sciences

Advisor College

College of Science and Mathematics


California is currently in the midst of a biodiversity crisis. There are approximately 5,000 native species of plants in California, a quarter of which are considered rare. Determining threats to these rare plants is often times difficult. Despite California's botanical resources, we still know very little about much of California’s rare plants. San Luis Obispo County is home to 2,000 of California’s native plant taxa, one- third of which are rare or endemic to the county. These species are of great local and environmental concern.

In Chapter 1, we attempted to assess the impact of non native species on a threatened species in eastern San Luis Obispo County. We conducted an invasive thatch removal experiment on 10 vegetation plots of Camatta Canyon Amole, Hooveria purpurea var. reducta. The Camatta Canyon Amole (CCA) is a federally listed “threatened” plant that is only known to occur on 21.15 ha of land on Los Padres National Forest (LPNF). In the 1980s, U.S. Fish and Wildlife Service established 10 plots to monitor the population of CCA. These biologists recorded a decrease in the CCA since the establishment of those plots in the 1980s. One hypothesis for the decline is the absence of cattle grazing from LPNF, which has resulted in the accumulation of a dense thatch layer. We experimentally removed this thatch layer in five of the 1980s vegetation plots to test this hypothesis. While our the experiment was designed to be a long term treatment, from the first 1.5 years, we found no relationship between thatch removal and the amount of CCA in each plot. The effect of our treatment may take many years to materialize.

In Chapter 2, we conducted extensive botanical surveys of the Camatta Ranch, a 32,000 acre cattle ranch in eastern San Luis Obispo County. The goal of these surveys was to estimate the distribution and population size of CCA on private property, which has never before been accessed or surveyed. We did this in two ways: 1) We created a density ratio estimate based off of plot sampling done on the ranch and 2) we created a species distribution model (SDM) to predict the likelihood of presence throughout the ranch. Our surveys of Camatta Ranch, coupled with our SDM suggest that a majority of CCA’s preferred habitat is on Camatta Ranch, making the ranch of paramount concern for CCA’s protection. Our estimates suggest that 90% of the total population of CCA occurs on Camatta Ranch.

In Chapter 3, we attempted to quantify biases in the literature about California’s flora. The California Floristic Province is one of the most biologically diverse floras in the world. Considerable legal and conservation attention is given to rare plants in California. However, there is no information as to the research effort given to rare species in California. Here we ask the question: Is there more research done on rare plants in California than on non-rare species? To answer this question, we quantified the amount of literature available on Google Scholar for California’s rare plants, weeds, and non-rare natives. To account for the differences in species geographic extent, we aggregated occurrence data for each species from GBIF to determine their ranges. We found that rare species were severely under-represented in the literature, even after accounting for the differences in species extent.