Faculty advisor University of California, Riverside Riverside, California, United States
Background/Question/Methods
Plant invasions are an expanding challenge for many land management agencies. Mitigating them can be problematic when invasions occur in areas with restricted treatment options - such as designated Wilderness areas in the United States. One such effort in Sequoia National Park is an attempt to stop the spread of Holcus lanatus in wet meadows of the Kern Canyon using manual removal. While target species populations have declined, it is unclear whether disturbances associated with removal have impacted the native plant community positively or negatively. Our project investigated this question, and how variable site factors like N availability and length of the growing season may interact with treatment effects.
We sampled species composition in 5 paired plots, in treatment areas and nearby uninvaded reference sites. We measured relative availability of NHx and NOx nutrients using buried ion-exchange resin bags, and length of the growing season using iButton thermometers. We hypothesized that disturbance associated with removing H. lanatus will not substantially alter the native plant community from reference conditions, and that differences between sites could be attributed to environmental factors. We used generalized linear mixed models and NMDS to assess relationships between treatment variables and overall plant community composition between sites.
Results/Conclusions
Native plant richness and diversity was similar and PERMANOVA did not detect differences in overall community composition between the treated and reference sites. Plant community cover was over 90% native species in all plots. This indicates that 15 years of manual disturbance have largely reversed the impacts of invasion without altering the native plant community from reference conditions. Additionally, significant differences in N availability and length of the growing season across sites did not measurably impact plant community composition. These results indicate a highly successful outcome of one of the largest and longest-running invasive plant management projects in the park in line with specific guidelines of the 1964 Wilderness Act, wherein the community “generally appears to have been affected primarily by the forces of nature, with the imprint of [human] work substantially unnoticeable.”
