The Landscapes of Sonoma Mountain Are Dominated by Oaks

by Kerry Heise and Adina Merenlender
University of California, Hopland Research and Extension Center

The structure and composition of the natural vegetation of Sonoma Mountain are due to a number of factors, including climate, topography, soils, and natural disturbances such as fire.

Recent human disturbance from vineyard expansion, residential development, logging, livestock grazing, road building, firewood removal, and fire suppression have shaped the current configuration and composition of vegetation on Sonoma Mountain. Located at the eastern edge of the coastal fog belt, the climate of Sonoma Mountain is intermediate between the cool, moist maritime conditions of the coast and the extremes of the more continental climate of the inland valleys. These factors have produced a rich flora and a diverse mix of vegetation types and plant communities, including mixed conifer forest, mixed conifer-hardwood forest, oak woodland, mixed hardwood forest, grasslands, and a variety of riparian and other wetland habitats.

Perhaps no other plant reflects this biological diversity better than the oak (Quercus). Sonoma Mountain supports at least nine different species, along with many undescribed hybrids. Large stands of Oregon oak (Quercus garryana var. garryana) reach their southern-most limit in the Coast Ranges here, and together with black oak (Q. kelloggii), coast live oak (Q. agrifolia), and shreve oak (Q. parvula var. shrevei) are common on wooded slopes. Other oaks found throughout the Sonoma Mountains include blue oak (Q. douglasii), valley oak (Q. lobata), interior live oak (Q. wislizeni), canyon live oak (Q. chrysolepis), and Scrub Oak (Q. berberidifolia).

Due to the exceptionally high oak species diversity, this habitat type supports a myriad of birds and other wildlife. Our field studies across different housing densities in these oak-dominated landscapes document over 300 plant species and more than 80 bird species. Some of you are fortunate enough to know the thrill of spotting a black-throated gray warbler, warbling vireo, or Wilson's warbler; hearing a downy woodpecker; or gazing at osprey and red-shouldered hawks above.

While Sonoma Mountain still harbors a remnant of wilderness for residents to enjoy, there is much to do to protect these species for future generations. Maintaining connected open space is clearly valued by the Sonoma Mountain Preservation Group and can be accomplished through private land conservation tools in addition to augmenting public lands.

Conservation easements offer one way for private landowners to donate future development rights for open space protection and in return reduce the value of their property for their heirs. Given the lack of state and local regulations to prevent the clearing of oaks, these alternative methods are essential if we want to maintain the biotic diversity supported by the oak dominated landscapes of Sonoma Mountain.