Oak Regeneration: Ecological Dynamics and Restoration Techniques

Abstract

The acreage of oak woodlands has decreased in California and Spain, especially in the twentieth century. Currently, most surviving stands in Spain suffer from oak regeneration failure and it has been noted as a problem in many stands in California. A lack of dispersers transferring acorns to safe (shaded) sites is the main recruitment limitation in dehesas, where shrub encroachment generally results in higher oak recruitment rates. In California, recruitment failure is due to a combination of factors. The effects of introduced Mediterranean annuals, heavy livestock grazing, fire suppression, and predation by native and non-native wildlife on acorns and seedlings are all implicated, depending on locale and time period. Afforestation has been the main instrument for addressing the regeneration problem, especially in Spain. Natural regeneration at local scales is favored by shrubs, but also supported by protecting seedlings and by modifying the environment so young oaks can grow to a safe height. Complete livestock exclusion is of limited value in California as it hampers seedling establishment due to increasing rodent density. In dehesas, however, natural regeneration can only occur in seasonally grazed or wholly ungrazed sites, though livestock-dependent landowners are generally reluctant to carry out these measures.