Assessment of seedling failure in peripheral populations of Umpqua green gentian (Frasera umpquaensis)

Frasera umpquaensis is a long-lived perennial that may live up to 80 years (Kaye 2001). Most populations are found along the Rogue-Umpqua divide. This report describes activities at five sites in peripheral populations along the Calapooya divide; Sourgrass Mountain, Sourgrass Mountain Southeast, Elk Meadows, Elk Camp Shelter and Nevergo. Seedling recruitment at these sites had been reported to be absent and therefore the success of these populations was in question.

In order to test seed production and viability, seeds were collected at each site and tested for germination using both germination and tetrazolium tests. Germinated seeds were used to grow plants that were used in our experimental plots. In order to test the effects of litter, canopy type, propagule type (seeds vs. transplants), and exposure on seedling recruitment and survival, treatment plots were set up in the meadow and along the forest edge adjacent to existing populations. Plants were monitored in 2009 and 2010 to assess the survival of the plants within the treatment plots. We also surveyed the populations for natural recruitment. Briefly, we found that,

• Viability of seeds collected at the sites range from 5% – 92%.
• On the forest edge, plants had higher survival with northern exposure.
• Mortality of seedlings (both natural and seeded) is high from one year to the next.
• Survivorship of transplants is higher than seeds.
• We found no evidence for significant effects of canopy type (forest vs. meadow), litter depth or soil moisture.
• Natural seedlings were found at most sites.
• Due to the low recruitment in these populations, one of the most important activities for their preservation is prevention of anthropogenic impacts. In 2010, we observed significant damage by ORVs in the boggy area adjacent to the F. umpquaensis population at Elk Camp Shelter. Given its location, this site is at the most risk for ORV damage; however the others could also be affected.

Given our observations of natural recruitment at some of the sites, apparently synchronous flowering of most plants every 3rd or 4th year, and variations in plants size between years, we recommend establishing two levels of annual monitoring. First, all sites should be surveyed each year for all individuals, including seedlings. Second, all individuals should be tagged and monitored for characteristics including height, number of leaves, and flowering status. Monitoring should include introduced plants. Annual data of this type would allow us to detect important population changes, rates of establishment in years after flowering events, and determine correlations between climate variables and population traits. Given the short duration of this study, continuous monitoring of the plants introduced through this project is necessary to provide insight into the population dynamics of this species.

Finally, our research suggests seed addition and planting seedlings may both be successful methods to augment declining populations of F. umpquaensis. Although these populations are not continuous with populations in the core of this species habitat, they may contain genetic diversity not represented elsewhere that may be important for the long term viability of the species.