The Sudden Oak Death (SOD) epidemic in East Bay Park District forests dominated by coast live oaks, Quercus agrifolia, and bay laurels, Umbellularia californica, presents major management challenges. Coast live oaks play a disproportionately large role in these forest ecosystems even when they are not the dominant overstory tree species. There are no other tree species in these forests that support as many other organisms (insects, bird, mammals, and fungi) as well as produce high quality protein in the form of acorns. In addition to problems faced by other forests at the urban-wildland interface, such as invasive plants and degraded habitats, managers of these lands must now contend with the effects of Phytophthora ramorum, the pathogen that causes SOD.

Figure 1. In coast live oaks, sudden oak death exhibits a predictable, progressive sequence of symptoms. 

            Phytophthora ramorum is a water mold apparently introduced through the nursery trade from Asia. This organism, unknown prior to 2000, infects a remarkably large number of native plant species, causing different diseases in different species (Rizzo and Garbelotto, 2003). Typically these infections take the form of leaf or stem lesions and are not fatal. However, most oaks native to California that are in the red oak group (section Lobatae), which includes coast live oaks, are highly susceptible to the pathogen. Infection in oaks follows a consistent sequence: 1) a viscous exudate, referred to as bleeding, appears on the bark, typically no higher than about 1.5-m above the soil; 2) both ambrosia and bark beetles tunnel into these infected patches (often 10-15 cm deep into the sapwood); 3) fruiting bodies of fungi appear on the bark above the beetle tunnels; and 4) tree death follows (Figure 1). Because of beetle and fungus damage, up to 25% of infected coast live oaks may fail while still alive, typically snapping within 2-4 feet above the soil (McPherson et al., 2010). In the course of maintaining long-term study plots in Marin County, we have identified critical parameters for understanding the response of coast live oaks to infection by P. ramorum (McPherson et al., 2010) (Table 1).

Table 1. Survival estimates (years + standard error) for coast live oaks infected by P. ramorum in two Marin County forests, 2000-2008, based on Weibull survival models (McPherson et al., 2010). CCSP: China Camp State Park; MMWD: Marin Municipal Water District.

Disease Stage	Median survival, CCSP	Median survival, MMWD
Asymptomatic	15.8 (1.5)	11.7 (0.8)
Bleeding	11.7 (2.7)	7.5 (1.6)
Bleeding  + Beetles	3.3 (0.4)	2.0 (0.2)

            Management of forested ecosystems that are being affected by this introduced pathogen depends critically on understanding the magnitude of the threat.  The Park District was aware that P. ramorum had been detected in their forests as early as 2001, but in the absence of knowledge of the distribution and severity of the problem, rational management plans cannot be developed. Beginning in 2009, with funding from the Park District, a team consisting of David Wood, Greg Biging, Maggi Kelly, Brice McPherson, and numerous field workers initiated a project to map the location and severity of SOD in coast live oaks in the five major forested parks that lie along the East Bay Hills using a network of permanent plots. These parks are Wildcat Canyon and Tilden Regional Parks, Huckleberry Regional Botanic Preserve, and Redwood and Anthony Chabot Regional Parks. These all lie directly east of densely settled Richmond, El Cerrito, Berkeley, Oakland, and San Leandro. The goal of this study is to develop models of change in disease incidence and severity and to predict future stand characteristics.

Figure 2. Plots in Redwood Park with coast live oaks in the first stage (bleeding) of sudden oak death. Image produced by Sam Blanchard, GIF Berkeley.

Figure 3. Plots in Redwood Park with both symptomatic and dead coast live oaks. Image produced by Sam Blanchard, GIF Berkeley.

            Analysis of the Redwood Park survey data illustrates this approach. We used geographic information system (GIS) technology and GPS devices to locate 105 plot sites randomly assigned within oak-bay habitats that were identified by vegetation type maps. Stand characteristics recorded for each plot include stem diameter at breast height (DBH) for every woody plant >2 cm DBH, health of each stem, and recruitment of woody plants, estimated by counting the seedlings and saplings in two linear transects. Dead, previously infected trees are reliably identified by extensive beetle tunneling and associated fungal activity.

            In Redwood Park in 2011, 19% of the coast live oaks in plots were symptomatic or killed by SOD. Comparison with the situation in Marin County in 2003 implies that considerably greater impacts are yet to come in East Bay forests (Figure 4). Resulting maps for Redwood Park show large spatial variation in the presence and severity of infected coast live oaks and differences in the proportions of trees in different stages of the disease (Figures 2 and 3). Note that in 2011 there were areas in Redwood Park with little or no actively detected bleeding coast live oaks (green) but with trees already killed by SOD. Because SOD is a progressive disease (i.e., unidirectional), knowledge of the distribution of the disease stages can be used to project stand-level change and to infer the history of the disease at a site.

Figure 4. Percentages of coast live oaks with symptoms of P. ramorum infection and those that died with these symptoms. The year indicates when each survey was done.

            The data for the different stages of SOD will be used to develop a predictive model to facilitate management of these forests as the epidemic continues and expands into previously unaffected stands. Although no cure or treatment is likely to prevent further wildland infections and mortality, the ability to make data-based predictions at the landscape scale will enable planning decisions to be based on a factual foundation.

            This work was initiated in collaboration with Nancy Brownfield, East Bay Regional Park District IPM Specialist, who died recently. Her presence will be missed.

 

 

References 

McPherson, B.A., Mori, S.R., Wood, D.L., Svihra, P., Kelly, N.M., Storer, A.J., and Standiford, R.B. 2010. Responses of oaks and tanoaks to the sudden oak death pathogen after 8 y of monitoring in two California forests. Forest Ecology and Management 259: 2248-2255.

McPherson, B.A., Mori, S.R., Wood, D.L., Storer, A.J., Svihra, P., Kelly, N.M., Standiford, R.B. 2005. Sudden oak death in California: Disease progression in oaks and tanoaks. Forest Ecology and Management 213:71-89.

Rizzo, D. M., and M. Garbelotto. 2003. Sudden oak death: endangering California and Oregon forest ecosystems. Frontiers in Ecology and Environment 1:197-204.

 

The goldspotted oak borer (GSOB; Agrilus auroguttatus) continues to attack and contribute to the high mortality of tens of thousands of oaks in San Diego County and the threat to oaks throughout southern California remains a considerable concern. In effort to inform professionals who are responsible for the stewardship of oaks and oak woodlands, a series of workshops has been offered in six southern California counties in which oaks may be at risk: Ventura, Los Angeles, Riverside, San Bernardino, Orange and San Diego. The overlying objective was to spread the knowledge of goldspotted oak borer and minimize the spread of this non-native insect into new areas. These day-long events offered multi-agency presentations, hands-on displays, outreach materials and in some locations, short field trips.

           Figure 1. Dead oak trees due to GSOB                         Figure 2. Two Adult GSOB on penny
  (Photo source: Tom Coleman, USDA Forest Service)    (Photo source: Tom Coleman, USDA Forest Service)

In cooperation, the USDA Forest Service, CAL FIRE, and the University of California have partnered with other local agencies, tribes and organizations to provide these workshops. Presenters at each session were coordinated from a cadre of specialists and researchers. Key speakers included Tom Coleman, Paul Zambino, Sheri Smith, Larry Swann, Lisa Fischer and Matthew Bokach (USDA Forest Service and Forest Health Protection); Tom Smith, Kim Camilli and Kathleen Edwards (CAL FIRE);Tom Scott, Doug McCreary, Jim Downer and Kevin Turner (University of California Cooperative Extension); and Vanessa Lopez (PhD candidate in the Entomology Department, UC Riverside). Introductory workshops were held monthly from September 2010 through February 2011. Topics covered were:

• GSOB history and distribution
• GSOB identification and biology
• Ecological and economic impacts of infested oaks and oaks at-risk
• Integrated best management practices for GSOB infested and at-risk oak woodlands
• How to prepare for potential outbreak
• Utilization of GSOB infested oak wood
• Restoring oak woodlands impacted by GSOB

 Figure 3. Larvae Feeding Galleries, seen in cambium     Figure 4. GSOB larvae in firewood (Photo source:
        of oak wood cross-section (Photo source:                     Tom Scott, UC Cooperative Extension)
                     Kim Camilli, CAL FIRE)               

In early May 2012, two additional workshops were held to provide updates from on-going research, best management practices and mitigation and education efforts. The session on May 1^st was held in Altadena in partnership with the Los Angeles County Fire Department-Forestry Division and the County Parks and Recreation Department.  The following workshop, held on May 2^nd, was hosted in partnership with the Pechanga Band of Luiseño Indians in Temecula.

Information Highlights:

• The goldspotted oak borer in an introduced, non-native beetle attacking and killing coast live oak (Quercus agrifolia), California black oak (Quercus kelloggii), and canyon live oak (Quercus chrysolepis) trees in San Diego County.
• The adult goldspotted oak borer (GSOB) Agrilus auroguttatus is a small, bullet-shaped beetle about 10mm (0.4 in.) long and has six golden yellow spots on its dark green forewings.
• Mature larvae are white, legless, slender and about 18mm (0.75 in.) long with two pincher-like spines at the tip of the abdomen. Larvae feed under the bark on the trunk and larger branches.
• Larval feeding kills patches and strips of cambium tissue beneath the bark, which causes dark staining and sap flow. The larvae pupate in the outer bark and leave D-shaped exit holes about 1/8 in. wide when they emerge.
• GSOB produce only one beetle generation per year.
• The goldspotted oak borer’s peak flight and breeding season is May through October.
• There is on-going research being conducted on biological and chemical GSOB control methods for preventative management; trees at various degrees of infestation; and the wood from infested, dead and felled trees.
• Currently, there are no effective treatments that can eradicate GSOB once it becomes established.
• Goldspotted oak borer larvae and pupae can survive under the bark of wood from large branches and trunks for up to a year after a tree dies.
• Currently, best management practices to minimize introduction of GSOB to new areas is to let wood cure at least two years after the tree dies before moving firewood from infested areas or grind wood into 3-inch particles.
• Before any type of treatment on oaks is initiated for GSOB infested trees or as a preventative measure on high-valued trees, a management plan should be developed first.
• There are no quarantines or zones of infestation in place by statewide authorities for GSOB; however, in 2011 the California Pest Council established the California Firewood Taskforce, a coalition of stakeholders that initiates and facilitates efforts within the state to protect our native and urban forests from invasive pests that can be moved on firewood.
• The Early Warning System is a citizen scientist program established to enlist the help of those concerned about oaks for the purpose of identifying oak tree health in southern California urban and woodland areas.
• Information and resources may be found on the Goldspotted Oak Borer website, www.gsob.org. To stay informed of current news, information and future training opportunities, we recommend you join the GSOB email list.

                                                   Figure 5. Tom Scott Workshop speaker 
                                (Photo source: Lorin Lima, UC Cooperative Extension-San Diego)

Nearly 500 professionals attended these workshops. Findings from follow-up workshop surveys indicate that potentially more than 2,600 others will learn about GSOB through outreach extended by workshop participants. Although evaluation and survey responses point towards a successful series of GSOB workshops, the threat of further goldspotted oak borer attacks remains. As the peak emergence and flight season occurs during the same time of year of increased vacation travel and camping in southern California, we are all encouraged to share the news about GSOB and it’s threat to oaks with others along with the message to not move firewood – “Buy It Where You Burn It.”

                                                              For more information:

Goldspotted Oak Borer website: http://www.gsob.org

California Firewood Task Force: http://www.firewood.ca.gov

Goldspotted Oak Borer - The Center for Invasive Species Research, UC Riverside:  
http://cisr.ucr.edu/goldspotted_oak_borer.html

Goldspotted Oak Borer – UC Statewide Integrated Pest Management: http://www.ipm.ucdavis.edu/NATURAL/index.html

Most of the oak woodlands in California are privately owned. The major use of Oak Woodlands is for grazing, primarily for beef cattle. The ranching industry plays an important role in maintaining a sustainable, culturally meaningful, and ecologically rich landscape (Huntsinger and Hopkinson, 1996) in our oak woodlands. Of the many challenges facing ranchers, droughts can be severe.

The great drought of 1862–1865 wreaked havoc on the state and the cattle industry (Burcham, 1957). Since that time we have had severe droughts about 8 times (George et. al. 2010).  Even with less severe droughts, cattlemen have a stressful time dealing with changes in forage production.  With less forage production, cattlemen either have to reduce herd size, move cattle to other states or locations, or provide extra feed at a great expense. If cattle are sold, it may take several years to build the herd back. 

Not all droughts are equal. Droughts tend to be more common in the rain shadow along the Coast Range adjacent to the west edge of the San Joaquin Valley (George et. al. 2010). Even though drought conditions create havoc with management of ranches, ranchers also have to deal with wetter than normal years. There is no such thing as an average year, which makes management decisions very difficult. Forage production and quality can vary greatly from year to year, and is strongly influenced by the timing and amount of rainfall (George et. al. 2001). For example, forage production in San Luis Obispo County over the last 11 years has varied by as much as 4000 lbs/ac (Figure 1). Rainfall amount and timing played a significant role in this variation, which varied by 18 inches of annual precipitation.

                             Figure 1: Peak Forage Production in San Luis Obispo County from 2001 – 2011.
                                                     An average of 12 sites across the county.

It is just a fact of life that rainfall amount and timing varies. For example, the lowest rainfall recorded in downtown Paso Robles was 4.8 inches in 1898 (Figure 2).  The highest recorded was 31.3 inches in 1969, the year of the big flood. It is important to notice that 6 out 10 years are below average (Figure 2). This means that the four years that are above average are usually wet years, which often produces extra forage. For more practical purposes, the years that are below the average determine what and how much forage can be produced on a ranch, which determines the number of cattle that can be grazed on a sustainable basis.  It is very important to the ecological health of the oak woodlands / grasslands to maintain proper stocking rates to achieve the desired grazing level. Maintaining the proper amount of residual dry matter (RDM) has become the standard to determine grazing use on oak woodlands and annual grasslands. Properly managed RDM provides protection from soil erosion and nutrient losses, and also plays an important role determining the following year’s production and composition of species (Bartolome et. al. 2006). To accomplish this requires constant change in management by ranchers. I applaud those ranchers who work so hard to accomplish this.
   
                         Figure 2: Rainfall records at the down town Paso Robles. Data is based on water
                                         year July 1 – June 30. Average precipitation is 15 in/yr.

Below are images taken of the peak forage production for San Luis Obispo County: 

                                         Spring 2006 normal, wet conditions


                       Soda Lake Site                                               Cambria Site

                                          Spring 2007 drought conditions


                     Soda Lake Site                                                Cambria Site

References

Burcham, L.T.  1957. California range land: An historico-ecological study of the range resource of California. Division of Forestry, Department of Natural Resources, State of California, Sacramento, California, USA.

Bartolome, J.W., W.E. Frost, N.K. McDougald, and M. Connor. 2006. California guidelines for residual dry matter (RDM) management on the coastal and foothill annual rangelands. Oakland, CA USA: Division of Agriculture and Natural Resources, University of California, Publication 8092.

Huntsinger, L. and P. Hopkinson. 1996.  Viewpoint: Sustaining rangeland landscapes: a social and ecological process. Journal of Range Management 49(2):167-173.

George, M.R., R.E. Larsen, N.M. McDougald, C.E. Vaughn, D.K. Flavell, D.M. Dudley, W.E. Frost, K.D. Striby, and L.C. Forero.  2010.  Determining Drought on California’s Mediterranean-Type Rangelands: The Noninsured Crop Disaster Assistance Program.  Rangelands 32(3):16-20.

Towards the end of January, an unusual phenomenon occurred in the Sierra foothills - some of the blue oaks began leafing out. While the vast majority of trees remained leafless, one could see occasional light-green canopies interspersed with their bare neighbors. This is unusual in that the earliest leaf-out most people recall observing doesn’t start until late February or early March.

So what is causing this? Clearly the weather pattern this past winter has been very unusual in terms of precipitation. There was abundant early rainfall in October and November, followed by a December and January that were some of the driest on record. However, dormancy and its subsequent breaking are much more controlled by temperature than by rainfall. That is, a significant period of cold is necessary before most temperate plants resume growth in the spring. Photoperiod – or the relative daily lengths of light and darkness - also often plays an important role but this obviously doesn’t vary from year to year.

Has the temperature pattern been abnormal? The CIMIS (California Irrigation Management Information System) long-term data was compared with this past winter’s averages and nothing stood out as particularly different, although there is apparent, large variability from year to year. There was a day or two of somewhat colder-than-average temperatures in mid-January, but below-freezing temperatures in the foothills occur almost every year. Therefore, at this point, the cause of early leaf-out remains a mystery.

                                      Example of an oak tree leafing-out

What about the impacts? It is likely that some of these “early leafers” will suffer frost damage. This occurred several years ago in mid-spring when there was an unusually late freeze and many blue oaks had their foliage killed back.  Most of this occurred at mid-elevations, presumably because trees at higher elevations hadn’t leafed out yet, and those at lower elevations were so far advanced that their foliage was hardier. While this certainly wasn’t good for the trees, they were able to recover and produce a new crop of leaves within a month or 6 weeks and no increase in mortality was noted. It seems likely that, as a species, blue oaks have evolved individuals that leaf out at different times of the year so that at least a portion of their population can take advantage of different weather conditions. The “risk takers” might get hammered now and then, but under the right conditions, they can take better advantage of unusual weather patterns than their more conservative colleagues. In the event of significant warming in California as a result of climate change, these may even be better adapted to survive and prosper in a changing environment.