Growth of Valley Oak (Quercus Lobata Nee) in Four Floodplain Environments in the Central Valley of California

Although there have been numerous studies of California upland oak regeneration and growth there has been no research investigating oak sapling growth in riparian environments. This study looks at the growth response of young valley oak (Quercus lobata Nee), a dominant late successional riparian species in California, across environmental variation on a floodplain. Growth was measured over the course of three years at four different sites. The sites were chosen to represent the range of successional stages and surface age. Growth was significantly higher on younger, unforested sites. There was no difference in growth rate in the two forested sites (early successional cottonwood willow forest and late successional mature oak forest). Herbivory was highest in the cottonwood willow forest, where density of young oaks was also highest. The impact of flooding was measured on the youngest floodplain surface, an open floodplain restoration site where acorns were planted the year our study began. There was a significant negative impact of flooding on sapling growth in all but the first year of growth. Taken together these results suggest that existing forest trees and flooding both inhibit the growth of valley oaks on the floodplain, and that restoration in open sites may be more successful than restoration under an existing canopy.