Population viability analysis for the clustered lady’s slipper (Cypripedium fasciculatum)

The purpose of this project was to survey populations of clustered lady’s slipper in the Medford District BLM in order to expand on earlier analyses and better model the probability of extinction [Population Viability Analysis (PVA)] for this species.

The data collected suggest an ongoing trend of population decline and local extinction. Our data set includes 236 populations of C. fasciculatum from Oregon and California that were revisited 1 to 29 years after the previous site visit. We found that 61% of these populations declined in size and 34% fell to zero. Small populations (<10 plants) went extinct in 50% of the cases, and mid-sized populations (10-30 plants) went extinct in 34% of the cases, while only 3% of large populations (>30 plants) declined to zero. Our analyses of all site revisits indicated that population size, time between site visits, and elevation were important factors in predicting extinction probability.  The PVA indicated that small populations had a greater risk of extinction than those with large populations, and predicted extinction risk was near zero for populations >100 individuals, regardless of the length of time between samples. Further, extinction risk increased as the time between visits increased, most notably for smaller populations. Of the ten higher elevation sites visited in 2012, seven had declined to zero, and of the three that were not extinct, two were in decline.

The data provided by multiple years of surveying have not altered the overall predictions of this model compared to our previous reports, but rather increased the confidence of these predictions.