Coast live oak woodland study offers management tips for landowners

Lawrence E. Bonner and Norman H. Pillsbury

Coast live oak (Quercus agrifolia) woodland is an underutilized, rapidly diminishing resource containing many values beyond its aesthetic tranquility and wildlife habitat. While the potential of wood for supplying energy has resulted in increased harvesting pressure on California¹s woodlands, coast live oak has largely been ignored.

To try to gain an understanding of the suitability of coast live oak woodlands to provide a continuous source of wood fiber for energy and wood products given proper management, a growth and yield study was begun in 1984 by Dr. Norman Pillsbury, California Polytechnic State University.

In addition, the study looked at the response of the woodland ecosystem to selective thinning management. This study has also allowed for the analysis of natural disturbances, such as fire, on this resource and may help answer some of the many questions surrounding Sudden Oak Death (Phytophthora ramorum), a disease currently plaguing the coastal woodlands in California.

Coast live oak woodlands and society
California¹s coast live oak woodlands usually grow in dense, even-aged stands that cover approximately 700,000 acres from San Diego to Mendocino County. Stands typically average 60–80 years of age.

Urban sprawl and a desire for economic returns from properties containing coast live oak have resulted in unregulated conversion of this resource. Although most landowners greatly value their oak woodlands for aesthetic beauty, many are forced to find a way to make those acres generate profit. Due to the ever-increasing need for housing, these holdings are often converted into suburban home developments. Woodlands are also being converted into open land for planting grapes or converted to increase grazing acreage.

Currently, little is known about site productivity, tree growth, and the potential effects and response of harvesting or other management practices on oak woodlands. By gaining understanding of these ecosystem attributes as well as changes in understory vegetation, regeneration, and erosion, landowners can have management options and make factual decisions affecting coast live oak woodlands.

The long-term thinning study
The ten sites selected for this study were distributed throughout Central California: four sites in Monterey County, five in San Luis Obispo County, and one in Santa Clara County. Three plots were established at each site consisting of one control and two experimental plots. The two experimental plots were thinned after an initial inventory was taken. One plot per site was selectively thinned heavily (leaving 50 square feet per acre) and one was selectively thinned lightly (leaving 100 square feet per acre). The thinning was done in 1984.

Approximately every five years the plots are revisited and remeasured. With each new set of data, analysis of growth, yield and changes in the ecosystem are conducted. The results and their interpretation can be useful for landowners making management decisions or implementing a management plan in their oak woodlands.

What this means to you
The ³Coast Live Oak Thinning Study in the Central Coast of California —Twelve Year Results² is the third report published on this long-term study and extends our knowledge about the effects of thinning in coast live oak stands to a 12-year period. Analysis was conducted on the number of stems per acre, basal area per acre, total volume, wood volume, sawlog volume, tree movement by diameter class, economics, predicting incomes and rates from sustained thinning, economic considerations based on forage, wildlife and aesthetics, changes in the forage layer in the thinned plots, and analysis of regeneration.

The discussion of many of these topics may be useful to landowners. The most useful information for a majority of landowners, however, is the conclusions of the study.
Two major forest fires occurred during the 12 years of the study. Our data shows that the denser, unthinned (control) plots sustained greater damage from fire than the thinned (treatment) plots. If landowners actively manage their oak woodlands, losses from catastrophic wildfire can be kept to a minimum. Thinning in oak woodlands can generate profit in the short term while protecting the resource (and thus investment) against losses from crown fires.

Stands whose growth has declined due to crown closure and high densities respond well to thinning. The benefits of thinning were apparent in the 1989 analysis and further proven in the 1997 analysis. Both basal area and total volume growth percentages were significantly greater in the thinned plots than the control plots. Average per acre growth rates for the 12-year interval ranged between 20 and 31 percent for treatment plots but only 1 percent for control plots. In general, total volume growth was approximately twice as great in the treated plots compared to the control plots.

The fact that growth rates and biomass/fuelwood yields increased significantly after thinning means that landowners can expect a direct income that represents the minimum economic benefit of managing oak woodlands.

Economic benefit as a result of thinning can also be realized through improved forage production for domestic livestock, improved habitat for game and non-game wildlife, and through enhanced landscape aesthetics giving rise to increased homesite property values. Greater forage production following thinning means that landowners can graze additional head per acre.

Thinning in oak woodlands increases the amount of ³edge² across a landscape. This can lead to increased wildlife production that can be managed by landowners for economic gain through the selling of permits to hunt on their land. Thinning oaks around existing homesites, to enhance visual corridors, can increase the overall fair market value for the property by opening up views of the surrounding landscape.

Conclusion
The increased growth rates of the remaining trees in a stand coupled with managed forest regeneration can result in the realization of economic gains from oak woodlands in perpetuity.

Simple models designed from this study preliminarily suggest that a cutting cycle of every 15 years may be optimal to ensure an even flow of dollars per acre for oak woodland owners. Managing coppice regeneration to prevent browsing by wildlife and domestic livestock can accelerate the growth of the future crop of trees. Within 15 years the growth rate of the trees remaining from the previous thinning slows, an indication that another selective thinning is needed. By using the single tree selection silviculture method of thinning, a baseline of volume is always present within a stand. This ensures that the ecological values associated with oak woodlands will remain intact.

Pursuing additional economic gain by increasing the amount of head that can be grazed or through the implementation of hunting programs makes thinning in oak woodlands an option worth serious consideration for landowners desiring to realize a profit from their oak woodlands.

Future Analysis
Data was collected during the summer of 2001 for the fourth analysis of this long-term study. The researchers hope to have the results from this latest round of analysis by the end of the summer of 2002. This new information is expected to increase our awareness of the growth and yield potential of stands of coast live oak and further answer the questions of the economic viability of profitably managing this resource without jeopardizing its ecological values.

It is our intent to raise landowners¹ awareness of oak woodland¹s potential through additional articles published here and in other natural resource publications. For more information regarding this study, please feel free to contact the researchers directly.

Lawrence Bonner is the owner of Elwood¹s Ecosystem Management and can be reached at 805-549-3801 or elwoo02@attglobal.net. Dr. Norman Pillsbury is a Professor of Forestry, Natural Resources Management Department, Cal Poly State University and can be reached at 805-756-2271 or npillsbu@calpoly.edu.