California Oak Savannas and Grasslands

Abstract

Abstract California s oak savannas and associated grasslands occupy roughly 3\xa0million\xa0ha. They are defined by the presence of scattered oak trees, in monospecific or mixed stands, with an herbaceous ground cover, composed predominantly of annual grasses and forbs. Supporting natural communities rich with native flora and fauna, oak savannas and grasslands contribute significantly to the designation of the California Floristic Province as a “biodiversity hotspot”. These systems also provide numerous benefits to humans: in the past sustaining indigenous cultures who depended on oak acorns for food, and in the more recent past and present as a source of wood, timber, livestock grazing, and recreation. Climate in California s oak savannas is Mediterranean, with cool, wet winters and hot, dry summers. Both climate and soil type exert broad control on the distribution of grasslands and co-occurring woody vegetation in California. At a finer scale, plant and animal interactions strongly influence community structure and dynamics, as do human impacts such as livestock grazing and the use of fire. Two of the most significant threats to the longterm sustainability of California s oak savannas and grasslands are land-use conversion to agriculture and residential development, compounded by low rates of natural regeneration in extant stands of oaks.