December 30, 2014

Experimental habitat manipulation of wayside aster (Eucephalus vialis)

Rachel E. Newton, et al. | 2010

Eucephalus vialis, wayside aster, is an herbaceous perennial known only from Lane and Douglas Counties in Oregon. It is listed as a State Threatened species, a Species of Concern by

Eucephalus vialis, wayside aster, is an herbaceous perennial known only from Lane and Douglas Counties in Oregon. It is listed as a State Threatened species, a Species of Concern by the U.S. Fish and Wildlife Service (ORBIC 2010), and is classified as Bureau Sensitive in Oregon under a Draft Bureau of Land Management (BLM) Special Status Plant Policy. Prior to this study, many populations of this species were observed to have little to no reproduction, plants were often stunted, and recruitment rates were very low. These observed declines in populations and plant vigor may be a result of increasing canopy closure caused by a lack of natural disturbance; fires potentially beneficial to E. vialis ceased with the arrival of European settlers to the area. The goal of our study was to discover what factors were limiting the growth, reproduction, and recruitment of E. vialis to provide scientifically-backed guidance for management of this species. Over 10 years, we performed three sets of experiments in the Eugene District Bureau of Land Management to test different potential limiting factors. First, we tested the effects of forest canopy thinning. Second, we tested the effects of prescribed fire in the Willamette Valley Oak Savannah Habitat Conservation Project plots (WVOPHCP). Third, we examined factors potentially influencing seedling recruitment and transplant survival at Long Hill. Key findings from these experiments include:

  • Forest canopy thinning improves plant vigor and reproduction
    • Thinning increased light availability, which in turn led to greater plant height, increased probability of flowering, and increased seed set.
    • Plant mortality was lower in thinned plots.
    • Deer herbivory was very common and reduced plant height and seed set. Deer herbivory was less common in thinned areas.
    • Thinning led to increases in the cover of native grasses, forbs, and tall shrubs. Cover of non-native species also increased with thinning, but their total cover remained low.
  • Small-scale burns have neutral effects
    • We did not find any negative effects of burning treatments on E. vialis, suggesting that fire may be an appropriate habitat management treatment in sites occupied by E. vialis. However, as the fires generally were small and low intensity, these results should be applied with some caution.
    • These treatments had little effect on overall species composition. While there was a general increase in non-native cover, this trend started in 2006, and is unlikely to have resulted from burning treatments.
  • Both transplants and seeding into mineral soil can be used for population reintroduction or augmentation.
    • Seeds of E. vialis have higher germination rates when sown on bare soil. In each year of this study, more seedlings established on soil that had been scraped to the mineral layer than on soil where the litter layer remained undisturbed.
    • For seedlings that germinated from sown seed, the long term survivorship rate was 27%.
    • Transplanting E. vialis is a viable means of reintroduction. Over half of the transplants planted in 2001 survived until 2010. Mortality was highest the first few years after planting, with numbers staying relatively constant after 2004.
    • Newly germinated seedlings and transplants may need to be protected from deer herbivory. Severe deer browsing was a likely cause of slow growth and delayed reproduction.

    Eucephalus vialis populations responded to reductions in canopy cover through increased stem height and flowering, despite prevalent deer herbivory. Natural recruitment was low, suggesting further intervention is required to ensure population stability. Additionally, both seeding and transplanting were found to be successful methods of reintroduction. Continued monitoring of these populations will help capture further changes in these populations, especially if thinning treatments continue.