Title: Establishment patterns of Oregon white oak and California black oak woodlands in northwestern California
Author: Schriver, Madelinn; Sherriff, Rosemary;
Source: Gen. Tech. Rep. PSW-GTR-251. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 529-539
Publication Series: General Technical Report (GTR)
Description: Mixed-Oregon white oak (Quercus garryana) and California black oak (Q. kelloggii) woodlands are unique ecosystems that support high biodiversity in the Pacific Northwest, yet little is known about their current and historical stand establishment patterns in northwestern California. With concerns of local extirpation due to Douglas-fir (Pseudotsuga menziesii) succession, research objectives were to characterize the variability of age structure, stand structure, and current tree regeneration in four mixed oak-conifer woodlands in northwestern California. Each site varied in stand type from open-oak woodland to transitional woodland-forest to closed mixed hardwood-conifer forest. While very low densities of white and black oak saplings (>30 cm tall and <5 cm DBH) characterized all stand types, regeneration of shade-tolerant tree species in closed-forest stands was common. Across all four sites most living white and black oak trees (=5 cm DBH) established during the mid-to late 1800s with no establishment since 1937. Conversely, the majority of Douglas-fir trees have been continuously establishing since around 1950. Within sites, most oaks established over a relatively narrow period of time (40 years), suggesting a stand-level disturbance during the mid-to-late 1800s that promoted regeneration. Less commonly (6 percent of plots), oaks established over a longer period of time (100 years) with plot-level age distributions indicating evidence of more localized stand-initiation events. The establishment of shade-tolerant tree species in some plots at each site, and the lack of oak tree establishment for the last 70 to 100 years, likely reflects the effects of altered disturbance regimes. Tree establishment patterns appear to be consistent with findings in Oregon and Washington, where studies suggest Oregon white oak ecosystems are transitioning into conifer-dominant stands due to land use changes, representing a loss of endemic biodiversity and structural heterogeneity on the landscape.
Keywords: age structure, California black oak, conifer encroachment, Oregon white oak, stand dynamics
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Schriver, Madelinn; Sherriff, Rosemary 2015. Establishment patterns of Oregon white oak and California black oak woodlands in northwestern California. In: Standiford, Richard B.; Purcell, Kathryn L., tech. cords. Proceedings of the seventh California oak symposium: managing oak woodlands in a dynamic world. Gen. Tech. Rep. PSW-GTR-251. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 529-539.
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