Lupinus lepidus var. cusickii population monitoring in Denny Flat, Baker County, Oregon
The purpose of this project was to locate and resample the previously established L. lepidus var. cusickii monitoring plots. Specifically, we compared current population size and plant performance with data
The purpose of this project was to locate and resample the previously established L. lepidus var. cusickii monitoring plots. Specifically, we compared current population size and plant performance with data from previous years and analyzed differences between plots that were fenced and plots that were open to ORVs and cattle. This will provide the BLM with important information to assess management plans for the conservation of this sensitive species.
Fences were erected at three subpopulations of L. lepidus var. cusickii in fall 1993 to exclude off road vehicles (ORVs) and livestock from portions of each subpopulation. Randomly placed permanent plots were established and sampled inside and outside of these exclosures to evaluate the hypothesis that fencing improves plant growth and population dynamics by limiting ORV and cattle access (null hypothesis: fencing has no effect).
Survey results show that the average population density (plants/m2) varied from site to site and year to year between 1993 and 2012. Generally, the subpopulations that increased in mean population density between 2002 and 2009 have continued to increase, while those that experienced a decrease across the same time period have continued to decline. The trends at the Amphitheater and Elms Reservoir subpopulations appear similar inside and outside fences. ORV Hill was the only subpopulation exhibiting a distinct difference between treatments, where the mean population density outside the exclosures increased and the mean population density inside the exclosures decreased. It seems likely that these patterns are due to small microhabitat differences where areas outside of the exclosures may present microhabitats that L. lepidus var. cusickii are responding more favorably to, including areas of slightly increased disturbance.
Plant characteristics varied between sites and by treatment. Because the different sites represent geographically distinct areas, such differences are not necessarily surprising or meaningful from an ecological perspective. For instance, there might be genetic differences between sites that differentially influence the response of inflorescence production to annual climatic variability. Alternatively, differences may simply be attributable to subtle environmental variability between sites.
As is common among many annual and short-lived perennial species in arid climates, variability in the weather potentially has a large effect on the population dynamics of L. lepidus var. cusickii. The huge swings in growth rates and variation in plant density suggest that climate may play a strong role in determining annual population growth or decline. Consistent annual monitoring data will be necessary to determine if there is a significant correlation between climatic variables (such as timing and amount of seasonal precipitation) and population dynamics.