PARENT SESSION
Poster Session # 14: Forest Ecology.
Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Interactions between oak regeneration and Rubus discolor, an invasive blackberry, in Northern California.
Williams, Kimberlyn*,1, Williams, Bob2, Westrick, Lawrence1, 1 California State University-San Bernardino, San Bernardino, CA2 Shasta County Cattlemen's Association, Redding, CA
ABSTRACT- California's oak woodlands and savannahs have experienced a number of changes over the past century or more. Low recruitment of blue oak (Quercus douglasii) has been noted, and extensive research on oak regeneration has focused on effects of grazing and browsing, fire suppression, and competition with introduced annual grasses. A second change in this system has been the invasion of some areas by Rubus discolor (Himalayan blackberry) an invasive species forming dense thickets of canes. This invasion has received less attention from ecologists, but more attention from cattle ranchers who expend enormous efforts in trying to control its spread. Initial observations of oak sapling distribution on a ranch in Northern California, suggested that saplings were associated with blackberry thickets. To determine if blackberry thickets provided a favorable environment for oak seedling establishment, we planted 300 acorns of Quercus douglasii and 300 acorns of Quercus lobata in an oak savannah/berry thicket mosaic in December 2001. We planted one third of the acorns at the edge of thickets, one third inside thickets (1 m from the edge), and one third in adjacent grassland. The only live seedlings found the following spring were in the grassland, and planting sites inside berry thickets showed signs of extensive rodent activity. Given the rodent populations during the year of our study, therefore, berry thickets did not provide a safe site for oak regeneration. We speculate that the association of saplings with berry thickets may result from protection of the rare seedling from browsing by large animals. However, those rare seedlings must have established during years with lower rodent populations or in grassland before the blackberry thicket covered the site.
Key words: Quercus lobata, seedling recruitment, Quercus douglasii, Himalayan blackberry