Graduation Date

Spring 2022

Document Type

Thesis

Program

Master of Science degree with a major in Biology

Committee Chair Name

Dr. Erik Jules

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Dr. Daniel Barton

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Dr. Kerry Byrne

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Dave Imper

Fourth Committee Member Affiliation

Community Member or Outside Professional

Subject Categories

Biology

Abstract

Lupinus constancei (Lassics lupine) is an exceptionally rare forb with a population that in 2020 consisted of 1,300 individuals located on two adjacent mountaintops in northwestern California, USA. Past work has demonstrated the species is threatened by high levels of seed predation by small mammals, which is likely the result of fire exclusion and the subsequent vegetation encroachment that both increases small mammal habitat and directly reduces suitable habitat for the species. Because of this, active management through caging of reproductive individuals to reduce seed consumption has been conducted every year since 2003. In addition, growing season temperatures have increased by 1.5°C while annual precipitation has fluctuated drastically over the past 50 years. In 2015, the first fire in 100 years burned through, or immediately adjacent to, most of the species’ range and induced high mortality that year and, in the second through fifth years following the fire, increased seed production and seedling emergence. Here, I use demographic data collected from 2001 to 2020 to build staged-based matrix models to project the species under various scenarios of active management such as caging and prescribed fire along with forecasted climate change impacts on temperature and precipitation. I varied the degree of caging proportions between no caging, the current caging rate (37%) and all reproductive individuals being caged. Additionally, I varied the frequency of fire in my model between no fires, and fire every 5, 10, 15, and 25 years. Lastly, I incorporated forecasted climate change scenarios (i.e., warmer climate and increased drought) in combination with caging rates and fire-return intervals to explore the impacts of multiple stressors. I found that a 13-year fire-return intervals is optimal for population growth, however the model suggests that fire alone cannot be used to avoid extinction. Instead, caging at the current rate or more remains a necessary management strategy to avoid population decline under current climate conditions. Nevertheless, my models suggest that climate change may threaten the species with extinction regardless of caging and prescribed burnings. If the high climate scenario were to be realized, the current caging rate (perhaps the most realistic) coupled with fires every 10-25 years creates the best opportunity for L. constancei, though at best this translates into a 51% chance of extinction over 50 years. The role of fire in reducing seed predation continues to need further evaluation, as future fires may have different impacts on small mammals, seed predation rates, and L. constancei demography than did the 2015 fire. Overall, my finding suggests that caging will continue to benefit L. constancei, but that additional management strategies should be explored further if forecasted climate changes occur, because no scenario produced in my models suggest there are any strategies that result in assured species viability. Furthermore, prescribed burning may have positive effects on the demography of L. constancei, but further investigation is needed to verify the positive impacts observed after the 2015 Lassics fire as additional fire events may yield different effects on the demography of L. constancei. Lastly, if climate change scenarios are realized, it is possible that management strategies such as caging and prescribed burning may prove to be inadequate in avoiding L. constancei extinction and other strategies such as assisted migration should be considered.

Citation Style

Ecology

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