California Oaks and Deer
Some of California's most conspicuous and important wildlife habitats are the oak woodlands that ring the central valley and hardwood-conifer forests of the Sierra Nevada, Cascade and Coast ranges. Oak trees in these woodlands and forests are important for California's resident and migratory deer populations, particularly those west of the Sierra Crest. Deer enthusiasts have long recognized the importance of oaks to deer for food and cover. However, oak woodlands and forests, like most of California's wildlife habitats, are being adversely affected by the increasing demands of our growing human population. Oaks are being cut down and cleared for firewood, timber harvesting, conversion to rangeland and agriculture, and residential and commercial development.
Deer and Oak Relationships
The importance of oaks to California's deer populations cannot be overemphasized. However, documenting the overall value of oaks is based on a few studies conducted over relatively small geographic areas. These studies illustrate the critical role that oaks play in the management and conservation of California's deer.
Acorns from black oak, blue oak, Oregon white oak and coast and interior live oak are important food for deer in late summer, fall and early winter. For example, acorns comprise about 40% of deer diets in September and December and almost 30% in October and November in Mendocino County. Acorns comprise as much as 35% of deer diets in November in Tehama County and over 50% of the November and December diet of the North Kings Deer Herd in Fresno County. Deer are a significant consumer of the annual acorn production exemplified by their consumption of 27% of the annual production in Mendocino County.
Movements by deer are influenced by acorn production. Deer in Tehama County tend to move to the winter range in large numbers earlier in years of good acorn production than in years of acorn failure. Deer in Stanislaus County appear to make increased use of fall holding areas in Stanislaus County when acorn production is high.
Oak leaves and twigs supply the dietary requirements of deer for protein and phosphorous in spring and fall. Deer prefer to feed on the oak species which have the greatest amount of protein and are easiest to digest, including valley, black, blue, scrub, and live oaks.
Oak leaves and twigs (browse) are very important from spring to fall, especially in early spring when the new growth is emerging. In Mendocino County, oak browse is the most common food item contributing almost 60% of the yearly diet. In Tehama County, black oak browse provides 21% and 28% of deer diets in May and October, respectively. Black oak is also a highly preferred browse species in the central Sierra Nevada.
Oaks are key features for habitats used by deer in summer and fall. For example, in the central Sierra Nevada, deer move quickly from summer range to winter range avoiding the fall range if oak mast crops are low. On the Shasta-Trinity National Forest, deer use is greatest in conifer forests dominated by Oregon white oak and is directly related to the amount of oak trees.
Status of the Hardwood Resource
Oak woodlands and hardwood rangelands have been declining in California for many years. Some of the largest declines have occurred in foothill counties where residential-commercial development and rangeland conversion are occurring. Decreases greater than 5% have been noted for 29 of 45 (64%) California counties for which data are available. Sixteen of the 29 counties had declines greater than 21%, including Tehama, Glenn, Colusa, Sutter, Sierra, Placer, Sacramento, Solano, Marin, San Joaquin, Amador, Calaveras, Tuolumne, Mariposa, San Luis Obispo and Santa Barbara. Several of these counties have important migratory deer habitat.
Despite the concern and conservation efforts resulting from these large localized losses of hardwood habitat, threats to the resource continue. Recently, biomass harvesting has affected some important deer habitat. In these operations almost all of the understory vegetation and lower canopy trees are mechanically removed as the stand is harvested. Since oak removal reduces mast and browse that would be available to deer, the California Department of Fish and Game (CDFG) has recently begun to ask timber landowners and operators to retain the mast producing trees when biomass harvesting.
Conservation Efforts by CDFG
There are several efforts underway to conserve and manage California's oak woodlands and forests. CDFG has a hardwood habitat management program that plans and coordinates oak management efforts across California. As part of the program, data are collected each year on acorn production and compared to various measures of deer populations. This information is used to assess habitat conditions and deer populations for management purposes. Hardwood retention guidelines were written in 1989 and are being used to modify development projects to minimize adverse environmental impacts to deer and other wildlife.
In the early 1980s concern about California's oak resources peaked with the increased occurrences of clearing oak woodlands for range improvement and harvesting oaks in critical deer habitat. Government biologists and the public felt that regulatory action was needed to require state permitting for cutting oaks on hardwood rangelands. However, in early 1987 the California Board of Forestry adopted a policy statement on hardwood conservation instead of regulations for oak species of hardwood rangelands. Harvesting of oaks such as California black oak and Oregon white oak which occur on private and state forestlands require the preparation of a timber harvesting plan because these species are considered commercial species by the Board of Forestry.
The future of California's oak resources and dependent wildlife such as deer is still uncertain. However, research and education efforts are beginning to increase awareness and conservation emphasis for oak resources. The future is brighter, but much work remains to be done to ensure the long-term existence of two of California's most characteristic natural resources - oaks and deer.
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prepared and edited by John M. Harper, Richard B. Standiford, and John W. LeBlanc