Oak Seedling Regeneration on California Rangelands
Poor regeneration of blue oak (Quercus douglasii) and valley oak (Q. lobata) in many locations on California hardwood rangelands has encouraged examination of factors suspected to be responsible so that management strategies for enhancement of regeneration can be developed. To examine selected factors, exclusive of large herbivore impacts, a series of acorn seeding experiments was initiated in 1985 in 6 counties on sites suitable for each species.
Factorial experiments organized in a randomized complete block design were used. In 1985, the design included examination of weed competition and fertilizer, the latter not repeated in subsequent years. Both weed competition and predation by insects and small mammals were examined beginning in 1987. Rainfall and edaphic factors were used to help interpret measures of seedling emergence, survival, and growth. Weed control for reduction of moisture stress was the most important factor examined. Emergence was significantly improved by weed control in 85% of blue oak and 33% of valley oak seedings. Average first year survival, expressed as a proportion of acorns planted, was significantly improved with weed control in seedings of both blue oak (29% vs. 16%) and valley oak (37% vs. 19%). Limited data suggests the differential in survival remains consistent over time as overall survival declines. In this study, fertilizer was not beneficial and contributed to mortality of both species. With few exceptions, the addition of screen protection to discourage predation significantly enhances survival and growth. Shade provided by window screen cages is suspected of making an unmeasured positive contribution. Little interaction between weed control and protection was demonstrated.
prepared and edited by John M. Harper, Richard B. Standiford, and John W. LeBlanc