Threat assessment for Limnanthes pumila ssp. pumila (dwarf woolly meadowfoam) on Table Rocks ACEC

EXECUTIVE SUMMARY

Upper and Lower Table Rocks, located northeast of Medford, Oregon, are collectively designated as an Area of Critical Environmental Concern (ACEC) by the Bureau of Land Management (BLM). The Table Rocks are characterized primarily by vernal pool and mound habitats that support several rare species.
Since 2006, the Institute for Applied Ecology (IAE) has monitored experimental plots to determine population trends and the effects of grazing, trampling, and invasive species on L. pumila ssp. pumila, and used transects to document plant community types, disturbances (including trails and animals activity), and distribution of habitat types. In 2018, we monitored L. pumila ssp. pumila populations and focus discussion on population trends of L. pumila ssp. pumila on Upper and Lower Table Rocks.
Limnanthes pumila ssp. pumila
• Following a steady decline from 2010 to 2012, the number of L. pumila ssp. pumila in long-term monitoring plots on Lower Table Rock have fluctuated. While 2015 had the lowest number of L. pumila ssp. pumila observed over the course of this study, we recorded increases in the number of plants in 2016 and 2017, and no significant change in 2018.
• At Upper Table Rock, our lowest numbers of plants were also observed in 2015, but after a rebound in 2016 have remained relatively stable over the last two years.
• In 2018, we observed significantly fewer L. pumila ssp. pumila in high traffic areas than in moderate traffic areas at Lower Table Rock, but no significant difference was observed in the mean number of plants at Upper Table Rock, or in the mean number of flowers per plant at either site.
Long-term monitoring plots were also used to assess impacts of a prescribed fire that occurred in the area of the fire retardant drop in October, 2015. The mean number of flowers per plant was lower in burned plots than in unburned plots in 2018, contrary to findings from 2016. Litter cover remained similar in burned and unburned plots. These results should be interpreted cautiously as plots were not designed to monitor fire effects.
Community monitoring of the fire retardant drop
• Monitoring was not conducted on the transects in the area of the fire retardant drop in 2018.
• From 2013 to 2017 we observed a decline in non-native grasses both within and outside of the fire retardant drop; over the final two years of sampling (2016-2017), non-native grass cover remained stable.