For almost a century there has been concern that blue oak (Quercus douglasii Hook. & Arn.), a California endemic, is not regenerating adequately in portions of its range. For the last 20 years, there have been concerted efforts to develop successful procedures for artificially regenerating this species so that it can be planted in areas where natural regeneration is unsuccessful, or in areas where it once grew but has been lost. These efforts have been successful in identifying procedures that will work, but unfortunately, such procedures often require intensive management and are costly. Since 80% of the oak woodlands in California are privately owned and the principal activity is livestock grazing, many large woodland owners and managers have marginal incomes and are reluctant to spend a great deal to regenerate oak trees.
An alternative, but untested, approach is to use naturally regenerating oak seedlings and take measures to promote their advancement to the sapling stage. This could be critical since research has demonstrated that the bottleneck for successful regeneration is often getting seedlings to grow into saplings. If successful, using natural seedlings could result in considerable savings because no effort or cost would be expended to collect acorns, or to grow and plant seedlings. An additional advantage would be that only genetically adapted plant material would be used, alleviating concerns about using “offsite” planting stock. Because of these economic, ecologic, and low input (i.e., less work) advantages, the development of techniques to advance natural regeneration holds great promise for being adopted and implemented by landowners.
To test this strategy, a study was initiated in 2007 at six field sites in the range of blue oak throughout the state. At each site, 144 naturally occurring blue oak seedlings were identified. Half of these were under the canopy of onsite trees and half were in the open. In addition, treatments included protecting seedlings with tree shelters and controlling weeds. When the plots were established, the height of each seedling was recorded. Yearly assessments of survival and height growth have been made every fall since establishment to evaluate the efficacy of the treatments.
After three years, seedlings in treeshelters have consistently grown taller than unprotected seedlings. In addition, the survival of those receiving an annual weed treatment has been significantly higher than those not receiving it. These results suggest that utilizing existing natural seedlings could contribute to increased blue oak regeneration at lower cost, thus improving the chances that this important species can be managed sustainably and conserved for future generations.