Treesearch

Tejon Ranch, encompassing 109 000 ha, is the largest contiguous private property in California. In 2008, the Tejon Ranch Company and a coalition of five environmental organizations executed the Tejon Ranch Conservation and Land Use Agreement that placed 90 percent of the property into permanent conservation and created the Tejon Ranch Conservancy as its steward. Tejon Ranch supports extensive, diverse, and regionally significant oak woodlands. The Conservancy is characterizing the composition and structure of these woodlands to inform land management. Deciduous oak woodlands at Tejon Ranch...

California deciduous oak woodlands provide many ecological, cultural, and economic benefits, and often represent unique plant communities that harbor native rare and declining species. Oak woodlands have suffered substantial losses in area and ecological integrity in the post-settlement era due to land conversion and widespread fire exclusion. Remnant oak woodlands in many areas are undergoing further conversion to conifer forest as shade-tolerant, and often less fire-tolerant species invade and increase in abundance. This process, known as conifer encroachment, has been identified across...

The loss of oak woodlands to conifer encroachment is widely recognized as a major conservation concern. The increased occupancy of oak woodlands by Douglas-fir (Pseudotsuga menziesii) and other conifers has been reported throughout portions of California and the Pacific Northwest in multiple oak habitat types. In California, Oregon white oak (Quercus garryana) and California black oak (Quercus kelloggii) are particularly impacted by encroachment. Studies point to altered disturbance regimes, and the suppression of low-intensity fire in particular, as the primary cause of increased conifer...

Conifer encroachment into oak woodlands is becoming a pressing concern for oak conservation, particularly in California's north coast. We use Object-Based Image Analysis (OBIA) with historical aerial imagery from 1948 and recent high-spatial-resolution images from 2009 to explore the potential for mapping encroachment using remote sensing. We find that pre-processing historical aerial imagery is time-consuming and that OBIA requires training and experience but has promise for mapping the phenomenon of interest. We also find that identifying conifer and oak in the imagery without ground-base...

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...

California coast live oaks (Quercus agrifolia) trees have suffered large losses from sudden oak death, caused by the introduced oomycete Phytophthora ramorum. In this review paper, we discuss oak plant chemistry as a potential predictor of disease susceptibility. We have recorded an annual mortality rate of three percent in long-term monitoring plots in Marin County, resulting in greater than 40 percent loss since 2000. Despite this mortality rate, asymptomatic trees still persist in many heavily infected stands. We hypothesized that varying responses to P. ramorum, including apparent...

Two chloroplast lineages of tanoak (Notholithocarpus densiflorus) meet between Korbel and Hoopa in the North Coast of California. Our earlier work suggests these lineages arose from southern and northern glacial refugia and this region represents their colonizing fronts. Earlier, we detected only one population of mixed lineages, suggesting that seedling establishment is limited locally, by short distance seed dispersal in tanoak. North western California and southern Oregon is recognized as a region of divergent lineages for a number of taxa, but it has not been confirmed whether the...

Starting in 1989, we used minimum-input methods to restore native oaks to parts of their former ranges in Vacaville, California. Each restoration site was analyzed, and only those inputs deemed necessary to overcome expected limiting factors for oak establishment were used. We avoided unnecessary inputs that added to cost and could have unintended negative consequences. All projects were direct-seeded by volunteers using locally collected acorns of valley oak (Quercus lobata) and other native oaks. Other inputs included mulch and protection from herbivores (cattle, voles) or mowing crews....

Quercus pacifica, the island scrub-oak, is the dominant species in oak chaparral on the three largest California Channel Islands. While the population on Santa Cruz Island has experienced a strong recovery, the populations on Santa Rosa and Santa Catalina islands are of conservation concern, and managers are actively restoring oak habitat by planting acorns. Previous work shows that acorn size, a factor that is known to affect planting success, varies significantly across the range of the species. To determine whether acorn size in Q. pacifica affects early seedling growth, I planted over...

We present the methods used to establish a provenance test in valley oak, Quercus lobata. Nearly 11,000 acorns were planted and 88 percent of those germinated. The resulting seedlings were measured after 1 and 2 years of growth, and were outplanted in the field in the winter of 2014-2015. This test represents a long-term resource for both research and conservation.