• Parker, V.T. Establishment of oak seedlings as influenced by mycorrhizae and other soil organisms (ends 6/90).
  
• Zedler, P.H. Effect of fire on seedlings and saplings of Quercus engelmanii (ends 6/90).
  
• Lathrop, E. The effect of fire on seedlings and saplings of Southern California oaks (continuing).
  
• Rice, K.J., J.W. Menke, J. Welker. Ecology and regeneration of hardwood rangelands (ends 6/90).
  
• Rice, K.J. Ecology and regeneration of hardwood rangelands (new project).
  
• Riggs, L.A. Genetic architecture and ecolypic variation in oaks (continuing).
  Plumb, T.R. and N. Pillsbury. Oak woodland regeneration (ends 6/90).
  McBride, J.R. and A. Mossadegh. Ecotypic variation in blue oak (new project).
  Dahlgren, R.A., M. Firestone, M.J. Singer. Nutrient cycling in managed oak woodland-grass ecosystems (new project).
  Byrne, R. Long-term changes in structure and extent of oak vegetation types (new project).
  

CDF-Funded Regeneration Research:
Regeneration and restoration research funded by CDF under the Integrated Hardwood Range Management Program has focused on defining the extent of regeneration problems in California hardwood range species, the mechanisms leading to regeneration failure and the silvicultural techniques that can be used to mitigate regeneration failure.

While it is generally assumed that certain hardwood species are not regenerating well, a CDF-funded review of the literature (Lang, F.J. 1988. Oak regeneration assessment – a problem analysis) indicated that a detailed assessment of regeneration failure has been hindered by the absence of measured rates of mortality of mature hardwoods. Nevertheless the review summarized existing expert opinion on regeneration failure in the form of criteria that define areas of high probability of regeneration failure for blue, valley and Engelmann oak.

The diseases and insects that kill oaks have been cataloged within a database that aids diagnosis and organizes future research (Disease and insect impacts on oaks). Wood rot fungi appears to be the major cause of mortality of mature oaks. The incidence and virulence of the infection seems to be modulated by water stress, so that climatic and management influences which reduce soil moisture availability to oaks may shift the balance toward disease. Insect herbivory appears to be a more important cause of mortality for seedlings.

Recruitment of blue oak saplings into mature age classes does not appear to be prevented by prescribed fires, at least in wetter environments (Effect of fire and grazing on blue oak regeneration). Fires kill the tops of seedlings and saplings, but the roots resprout to form apparently even-aged stands that are indistinguishable from unburned stands after several years. However, annual fires and extensive browsing can deplete the supply of saplings and prevent their escape through the browse line to the mature size class.

In the face of uncertain regeneration, CDF has funded several projects that have developed silvicultural techniques for the artificial regeneration of oak stands. A major effort involving blue, valley and Engelmann oak in several different regions of the state (Restoring native oaks) has shown that barerooted seedlings which are transplanted into pre-augered holes with deeply-buried fertilizer and which are protected from weeds and herbivories can develop into robust saplings within 3-4 years. Direct seeding of acorns and other cultural techniques were also investigated. These general prescriptions are being adapted for valley and Engelmann oak on particular sites by several follow-on projects. A dichotomous key that leads one to an appropriate mix of technology has been developed for valley oak (Restoring valley oak) while a better definition of appropriate planting sites has been the focus for Engelmann oak (Restoring Engelmann oak).


Education and Applied Research Results on Oak Regeneration

Artificial Regeneration
Since the beginning of the IHRMP, solving the problem of poor regeneration has been a principal goal. One of the major thrusts in this area has been to develop practical techniques for artificially regenerating those species that are not naturally regenerating well. Developing successful regeneration procedures, however, involves a number of steps including seed collection, seedling propagation, planting and protection.

Seedling Production. This past year there has been a concerted effort to evaluate alternative production practices for growing both bareroot and container seedlings. Two studies at the Sierra Field Station have examined the field performance of blue oak seedlings produced in various sizes of containers ranging from 12-cubic inch tubes to large 200-cubic inch pots. These studies have demonstrated that seedlings can be produced in a variety of container sizes and still perform well after planting. Interestingly, after two years in the field, seedlings produced in the smallest containers have grown about as rapidly as those grown in the largest. This suggests that smaller containers are more cost-effective for producing seedlings.

Two other studies have evaluated bareroot nursery production. While this is a common method of growing conifers, until recently no bareroot oaks were grown in California (See case study below). The research in this area has been very promising. Blue oak seedlings grown for one year in a nursery and outplanted in unirrigated plots have had over 80% field survival and have grown vigorously as long as their roots were cultured properly in the nursery and they were outplanted by February. We are currently evaluating the field performance of bareroot valley oak seedlings and are comparing the performance of seedlings inoculated with beneficial mychorrizae fungi to uninoculated controls. We have also compared the performance of bareroot and container seedlings and have found these to be very similar in terms of initial survival and growth. This research suggests that there are a variety of methods for producing the stock needed for regenerating native oaks in California.

Seedling Protection. How to protect seedlings in the field is another area that is being investigated at several locations throughout the state. One of the main factors limiting both natural and artificial regeneration of oaks in California is damage to young plants from a whole host of animals. In order to successfully establish seedlings it is often necessary to protect them for several years. In Tuolumne County a study is underway to evaluate the effectiveness of electric fencing in protecting oak seedlings from livestock damage. This study is also comparing direct seeding of acorns with planting of seedlings to determine the effectiveness and cost of each approach.

Other types of seedling protection are being evaluated elsewhere. On a site in the central coast where firewood harvesting has occurred, a study is evaluating whether or not brush piles placed around planted seedlings can reduce browsing by deer and cattle. At another site on the north coast, several individual seedling protective devices are being compared including screen cages, plastic tents, and rigid translucent plastic tubes. This study will not only compare how well these devices protect seedlings from insect and rodent damage, but will also evaluate how each device changes the environment around the seedlings which, in turn, affects growth and survival.

Site Preparation and Maintenance. In addition to seedling protection, other practices including irrigation, augering, fertilization and weed control can have a substantial impact on regeneration success. In several different studies it has been amply demonstrated that eliminating competing vegetation can dramatically improve the survival and growth of outplanted seedlings. The effect of fertilizers, however, has been more ambiguous and both positive and negative results have been observed. Augering is another approach that is currently being studied. Oaks tend to produce very deep root systems, but have difficulty penetrating hard, compacted range soils. Loosening soils with augering may promote deeper root development. Initial results from augering trials are promising and indicate that seedlings tend to grow taller and grow for a longer duration in the summer when they are planted in augered holes. However, augered holes should be allowed to settle with early fall rains before planting, since the holes tend to sink considerably after they become wet. The effect of irrigation on the survival and growth of valley and coast live oak seedlings is also being evaluated. While irrigation may not always be practical at remote sites, it is important to determine how rapidly seedlings will grow under ideal conditions.


Natural Regeneration
While the main focus of regeneration research has been to develop successful artificial regeneration procedures, several other studies are evaluating the factors that affect natural oak seedling establishment and what can be done to promote more natural regeneration. In the southern Sierras a survey has been done along an elevational transect to determine what, if any, environmental variables are associated with changes in regeneration patterns. Further south, in Kern County, another project has identified and monitored over 600 blue oak seedlings in order to document their fate over time. It’s well known that acorns often germinate and become small seedlings, but that few of these survive to grow into larger saplings. This study should help determine the factors causing seedling mortality.

Another form of natural regeneration of oaks is stump sprouting. Even after trees are killed by fire or are harvested for firewood, many oaks will sprout from their stumps, eventually producing a new tree from the original root system. For the past 3 years a large statewide study has been evaluating the sprouting response of blue oaks to different cutting dates and stump heights. Information from this project will be used to make thinning recommendations for thick, densely stocked stands. By continually recruiting new trees through sprouting, dense stands would become uneven aged and could be managed on a sustained basis.

Stumps from cut trees may also provide sites where shoots from other trees can be grafted. A recent study in San Luis Obispo found that both blue and valley oak scions could be successfully grafted onto blue oak stumps.


Regeneration Education
In addition to trying to develop information about oak regeneration through applied research projects, the IHRMP has also taken an active role in educating the public through acorn collection projects, seedling give-aways and classroom programs. Many of these efforts have focused on children who seem particularly fascinated by oaks and are very enthusiastic about planting and protecting them. In Calaveras County, the Farm Advisor developed a 4-H project for growing and planting oaks which has been used extensively not only within the county, but in other regions of the state also including San Diego (See case study below).

In an effort to stimulate interest among teachers in projects for growing and planting oaks, the IHRMP, in cooperation with the California Oak Foundation, spoke to a large group of science teachers at an October conference on science curriculum. A similar presentation was also made to local Sacramento teachers and youth group leaders.

In several other counties throughout the state there have also been workshops on how to plant seedlings, as well as seedling give-aways. At events during, and just after Earth Day, nearly a thousand oak seedlings were distributed in Nevada and Butte Counties. To ensure that seedlings given away at these events were planted and cared for properly, a brochure titled "How to Grow California Oaks" was handed out with each seedling. This brochure was also included as a 4-page supplement in one of the issues of the IHRMP newsletter, Oaks ’n Folks.

An oak planting project in San Luis Obispo County went a step further by having the people who received and planted free seedlings maintain records on survival, growth and damage. This information will help determine the long-term fate of outplanted seedlings and help identify what are some of the factors limiting the success of these types of projects.

Another educational project initiated in 1989 on oak regeneration involved working with the state prison system. A number of penal institutions have greenhouses as well as programs to teach inmates about horticulture and nursery practices. The IHRMP began pilot projects at two youth authority prisons to grow oak seedlings. Specialists provided acorns, planting materials, and information about proper culturing practices. Educational programs about oaks in general and why they are being grown were presented to the inmates working on these projects. Some of the seedlings produced in this pilot program are being used in research projects and others will be given away to the public. If these pilot projects are successful, an expanded program at other institutions using inmate labor and available facilities will likely be undertaken.


Trends and Future Needs
During the last year there were significant gains in the effort to produce and outplant quality oak seedlings. There is a much clearer idea of the physiological requirements of seedlings and how to meet these needs. This past year has also been a time when more and more people throughout the state have become aware of the importance and value of native oaks and have expressed a desire to plant them. While the number of oak seedlings being grown and outplanted is continually increasing and techniques are now available for successfully growing and outplanting seedlings, it’s still costly to provide adequate site preparation, maintenance and protection to ensure success. The challenge for the future is to develop low cost techniques which will allow extensive wildland plantings.

4-H Oak Tree Project In order to make a long-term change in public attitudes towards native California oaks, it is necessary to reach out and educate the children—those who will be making decisions and managing the lands in years to come. And what better way to teach kids about oaks than to get them involved in a project to collect acorns, grow seedlings, and plant small oak trees. Thus originated the 4-H Oak Tree Project which was developed this past year by the Calaveras County Cooperative Extension’s 4-H Farm program. The 4-H Acorn Project consists of a video tape and instructional pamphlet which outlines, step-by-step, the procedures for growing and planting oaks. Though only available for a short time, it has already been used extensively not only by 4-H kids but also by numerous classes of students. In Calaveras County alone, 1400 students participated in classroom projects this past year. It has also been used in other areas of the state and the numbers using this project should increase as more and more educators become aware of it.

Mapping Regeneration Failure of Blue Oak Blue oak woodlands are the most extensive hardwood type in California. Blue oak also appears to suffer regeneration failure in some areas. These two facts suggest that portions of the California landscape could change from woodland savannas to annual grasslands during the next century. While it is important to understand the mechanisms underlying this change in vegetation it is equally important to understand where this change may occur. Blue oak woodlands that appear to be regenerating ought to be conserved since they contain the genetic material that confers success in the current environment, while stands that are not regenerating might be candidates for artificial regeneration to the maintain values such as wildlife habitat or watershed protection. Beyond the fate of each individual stand, the landscape pattern that regeneration failure produces will have important impacts on the value of the entire landscape for the conservation of biological diversity and visual quality. CDF/FRRAP has begun to investigate the geographic incidence of regeneration failure using statewide data on blue oak regeneration from the Forest Inventory and Assessment program of the USFS/PNW Experiment Station. Stand structure from 92 field plots containing blue oak was sampled, permitting the calculation of a regeneration index—the ratio of saplings to mature trees within the plot. The key to mapping regeneration failure lies in relating such point-based data to vegetation mapping units. The most current and detailed map of hardwood vegetation is that produced by Norm Pillsbury of Cal Poly, San Luis Obispo, and maintained by FRRAP. When the Bolsinger point data were overlaid with the Pillsbury hardwood polygons, 71 of the plots fell within a hardwood polygon. The remaining plots had coordinates that were obviously incorrect or fell in stands that did not meet the minimum size of 40 acres used by Pillsbury. A statistically significant 74% of the variation in the regeneration index could be explained by geographic region, cover type, canopy density, and the interactions between these factors. The average regeneration index for each combination of region, cover type and canopy density included in the data was attributed to every mapped polygon with those characteristics. Since some vegetation types in some regions were not included in the data, no estimates are made for these areas. There is considerable variation in the value of the regeneration index across regions, cover type and densities. For this project, polygons with more than two saplings per mature tree were assumed to regenerate; those with two or less were assumed to have potential regeneration problems. The following map shows the expected pattern of hardwood vegetation for a section of the southern Sierra Nevada foothills. The relatively continuous band of valley foothill hardwoods mapped by Pillsbury becomes an archipelago of habitat islands of various sizes. The potential hardwood habitat loss and fragmentation is considerable. These initial estimates demand verification and correction by more detailed studies which should permit the designation of critical blue oak sites.

Future Hardwood Extent and Fragmentation: Southern Sierra Foothills

Click on map to see larger view.

CDF Nursery Grows 90,000 Oak Seedlings Until recently, relatively few native oak seedlings have been produced in California. Little information was known about how to grow them and few people were interested in buying large quantities for planting. That is changing, however. As production technologies are being refined and more and more people want to plant oaks, the supply of seedlings is increasing. A case in point is the CDF nursery system. Four years ago they did not produce any oak seedlings. Since then a cooperative study with UC as part of the IHRMP was conducted to evaluate alternative procedures for growing bareroot seedlings. This study demonstrated that vigorous, healthy stock could be grown in one year. As a result of the nursery program’s regeneration research efforts and the growing demand for oaks by the public, CDF plans to provide almost 70,000 bare root seedlings and 20,000 container stock for 1990-91. To date, CDF’s nursery program has raised bare root and container blue, black, valley and canyon live oak seedlings. The seedlings are sold at prices slightly higher than average commercial rates to minimize competition with private nurseries. CDF continues to expand the geographical area, or the number of seed zones, from which acorns are collected to increase the availability of genetically-adapted seedlings for different planting sites. Seedlings from CDF nurseries have contributed to a variety of projects. Several large orders have been used for restoration, including a valley oak restoration project by the Los Padres National Forest in southern California. Most of the seedlings, however, have been purchased in relatively small lots of 50 or 100 and are being used for purposes such as small scale erosion control, habitat enhancement, and general environmental amenity values.

ABOVE: Large scale restoration demonstrations have shown the importance of protection and weed control. RIGHT: Stump sprouting as a regeneration strategy is being evaluated.

ABOVE: Acorn collection, storage and direct seeding techniques have been discovered.