Rehabilitation of a Blue Oak Restoration Project 1

Two remediations were tested for improving height growth and survival on a 2-yearold, failing, blue oak (Quercus douglasii) restoration project. Replanting acorns and seedlings with plastic treeshelters resulted in 75 and 88 percent survival, respectively, in areas previously showing almost total mortality. After 3 years, average height of replants (141 cm) exceeded the original planting (19 cm). In a second remediation, treeshelters retrofitted onto original planting survivors showed highly significant differences in height (P < 0.0001) and survival (P = 0.0001) between protected and unprotected pairs. Protected survivors were almost five times taller than unprotected, and averaged nearly an eight-fold height increase (130 cm), while average height of unprotected plants had not quite doubled (28 cm). Treeshelters inhibited vole, but not grasshopper predation. Results indicate treeshelters release stunted seedlings and could rehabilitate poorly performing projects. Natural regeneration of two endemic California oaks, blue oak (Quercus douglasii) and valley oak (Q. lobata), has been widely recognized to be a problem statewide on many sites (Bolsinger 1988, Griffin 1971, Muick and Bartolome 1987, Swiecki and Bernhardt 1993). Lack of recruitment to the sapling stage has been identified as a widespread occurrence. This has created great interest in developing techniques for artificial regeneration of these species (see Adams, and Plumb and DeLasaux in these proceedings for general reviews). At the Sierra Foothill Research and Extension Center (SFREC), located 27 km northeast of Marysville, California, we have been able to grow blue oaks to sapling size within 5 years on small (approximately 0.25-ha) plots inside cattle exclosures. This has been accomplished using weed control and with little or no irrigation, with and without screen protection of seedlings (McCreary 1991). When attempting to expand these successful attempts on a larger scale, however, we encountered setbacks. In a 1.6-ha plot intended as a demonstration for oak woodland landowners, we found that we could not duplicate the rapid height growth we had experienced previously, and that herbivory by insects and mammals was greater than anticipated. Since a large number of restoration and mitigation oak plantings have been established in the past decade throughout the state in response to perceived oak regeneration problems, we believed it likely that some of these efforts might be similarly frustrated in meeting their goals. We therefore attempted to rehabilitate our original planting, in order to evaluate readily available measures applicable to improving oak restoration efforts.