Evaluation of population trends and potential threats to a rare serpentine endemic, Calochortus coxii (Crinite mariposa lily)

• The major threats of C. coxii noted over the course of our study include encroachment by conifers and invasion by exotic species. Recent treatments at Bilger 1 in close proximity to long-term monitoring transects indicate that careful canopy thinning was associated with an increased number of flowering individuals in those areas, though response may be short-lived and continued maintenance will be necessary. These data suggest that canopy thinning treatments can be effective at increasing number of flowering plants, however they must be carefully implemented to not increase spread of invasive species or impact areas of dense C. coxii abundance.
• While we had observed a decline of vegetative C. coxii from 2011 to 2014 in long-term monitoring transects, in 2015 we noted an increase in vegetative plants which led to an overall increase in total number of individuals. This was following a year of increased reproductive individuals.
• Maximum temperature in 2015 exceeded temperatures experienced since 2011, including long-term normal, this was coupled with 2015 having one of the lowest precipitation years since 2011. It is increasingly likely that these climate trends are affecting population dynamics of C. coxii along with other factors including microclimate and canopy cover.
• Calochortus coxii has greater abundances of flowering individuals in open habitats without canopy cover. In forested areas, the species tends to be predominately vegetative. These trends have been consistent over the course of this study.
• Surveys of C. coxii historical populations in 2011 and 2012 indicate that for all but one of the populations (Myrtle Creek 4) there were significantly fewer C. coxii than had previously been recorded at these sites. At some sites the discrepancy was extremely large (for example 5.6 million plants reported at Bilger Ridge previously while we found only 6,118). Our results indicate that additional measures might be needed to improve habitat.
• Parts of Bilger 1 are in very close proximity to the area for the planned LNG Pipeline. While plans for the pipeline do not directly dissect areas that house this species, there are plants present, in some cases, just meters away from the proposed area. We have documented that population dynamics of this species can vary depending on changes in microclimate (canopy thinning) and that exotic species invasion is a continued threat in these sensitive systems. Implementation of the LNG Pipeline in very close proximity to this population C. coxii is cause for concern for these reasons.