Wednesday, August 8, 2007 - 8:40 AM

COS 68-3: Considering spatial and temporal change in southwest Oregon Garry oak communities as a basis for restoration

Paul E. Hosten, Bureau of Land Management, Medford District

Historic records indicate a range of vegetation structures and compositions in Garry oak dominated plant communities. High elevation short-statured thickets, close-canopied woodlands, and chaparral incorporating Garry oak indicate that not all oak communities were more “open” historically. Repeat photography also indicates diverse patterns of change in composition and structure of formerly open stands. Within a geographic range of 100 miles, formerly open oak savanna can show tree interspaces filled by juniper, buckbush, whiteleaf manzanita, or a younger cohort of Garry oak. Dense oak thickets have also developed in formerly dry meadows. Lower elevation areas with soils dominated by shrink-swell clays show a maintenance of a savanna-like structure regardless of recent fire-history. While some oak dominated stands have been replaced by dense stands of shade-tolerant conifer (likely due to the absence of fire), other sites show a loss of “open-grown” conifer. Changes in spatial extent of oak dominated communities are characterized by invasion of  meadows, and replacement by shade tolerant conifer. In other areas, high clay soils contribute to the patchiness of oak thickets. In many communities,  oaks appear larger and have more mistletoe, a testament to elongated fire-return intervals. This diversity of structure, composition, as well as spatial and temporal patterns of change reflects the  diverse topography of southwest Oregon. Clearly, restoration requires an understanding of historic conditions relative to landscape topography and soils.

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