Sierra Nevada
Location map, M261E


Vegetation at foothill elevations on the west side of the Sierra Nevada section is dominated by blue oak, interior live oak, and gray pine; ponderosa pine, incense-cedar, and black oak become prevalent as elevation increases. The mid-elevations are characterized by ponderosa pine, sugar pine, incense-cedar, white fir, and Douglas-fir (north of the Merced River); ponderosa pine decreases and white fir increases as elevation increases. Hardwood species in these areas include canyon live oak, maple, dogwood, and black oak. Red fir is found on both the west and east slopes from about 7,000 to 9,000 feet. The subalpine areas consist of western white pine, lodgepole pine, and mountain hemlock, with Jeffrey pine replacing ponderosa pine at the higher elevations and colder sites. On the east side of the Sierra Nevada, Jeffrey pine dominates in the mid-elevations in association with white fir, incense-cedar, and lodgepole pine. Hardwoods include alder, willow, and at higher elevations, quaking aspen. The Sierra Nevada vegetation has been influenced by grazing, forestry, mining, recreational activities, and changes in fire patterns.

Forest Health Issues

In the late 1980s and early 1990s, mortality of ponderosa and sugar pine was high in many areas throughout the Sierra Nevada section where those species predominated. The mortality was caused by a combination of drought, root disease, dwarf mistletoe, overstocking, and the western and mountain pine beetles. Since 1994, mortality of these two tree species has returned to rates seen in the early 1980s.

Giant sequoia. The long-lived giant sequoias are often thought to be impervious to insect and pathogen effects. As giant sequoia ecosystems are more closely monitored, however, pest effects may become more noticeable. On a calm morning in May of 1992, a living 13-foot-diameter (dbh) sequoia fell near Round Meadow (Giant Forest area) in Sequoia National Park. The tree had decay in several large support roots and was growing on the edge of an annosus root disease center. A study in the 1970s (Piirto 1977) concluded that this disease was the most common factor found in the failure of giant sequoia root systems (12 of 29). The 1992 failure and the study information convinced Park officials to close an administration building and adjacent parking lot next to a leaning, 21-foot-diameter giant sequoia, which was also growing in an annosus root disease center.

Pest problems of planted 10-year-old giant sequoia seedlings appeared in a plantation on the Hume Lake District of the Sequoia National Forest in 1994. Thirteen saplings died in two years in an area of about 1 acre. One overstory sequoia, 49 inches in dbh, also died. Conks of the annosus fungus were found in white fir and incense-cedar stumps in the plantation, and mycelial fans of Armillaria sp. were present at the root collar of each dead tree. Tests are in progress to determine what species of Armillaria are present. No evidence has yet been discovered to explain what triggered the mortality.

Jeffrey pine. Increasing Jeffrey pine mortality became evident in 1990 around the east and south sides of Lake Tahoe. Death of Jeffrey pines is often the result of interactions between moisture stress, the Jeffrey pine beetle, overstocking, and annosus root disease in some locations. The mortality is of particular concern because it is in high-use, developed sites and dispersed recreation areas, as well as on private properties. Such mortality causes unwanted reductions in vegetative cover, increases in fuels, and—depending on location—hazardous trees.

Concentrated mortality has also appeared in several locations from the Sierraville area on the Tahoe National Forest in the north to the Mammoth Lakes area on the Inyo National Forest in the south (fig. 18). Between 1993 and 1995, 950 Jeffrey pines were killed by the Jeffrey pine beetle over about 166 acres near the Inyo Craters on the Mammoth District. More than 2,000 Jeffrey pines were killed over about 500 acres of developed recreation sites around the Lake Tahoe basin, along with more than 5,000 Jeffrey pines in a 100-acre dispersed recreation area near Spooner Lake. Additional concentrations of Jeffrey pine were killed by the beetle in Rice Canyon, Cold Creek, Antelope Valley, Onion Valley, and Smithneck Creek on the Sierraville District; in the Truckee River drainage along Highway 89 south of Truckee; near Secret Harbor, Slaughterhouse Canyon, Skunk Harbor, Glenbrook, and Logan House on the east side of Lake Tahoe (fig. 19); near Tahoe Valley on the south shore of Lake Tahoe; and in the Deadman Creek area on the Mammoth District.

Jeffrey pine killed by Jeffrey pine beetle
Figure 19 Jeffrey pines killed by Jeffrey pine beetle on the east side of Lake Tahoe, August 1995.

White fir. High mortality continues in some white fir stands in the northeast part of the Sierra Nevada section and around Lake Tahoe. Most of the mortality is related to interactions of drought, overstocking, and fir engraver. The species composition of some eastside ecosystems has shifted from pine-dominated stands with small amounts of white fir to almost complete dominance by white fir. White fir regeneration and growth coincides with adequate or above normal moisture, which allows this species to occupy sites once dominated by more drought-tolerant pine species. During protracted drought periods, however, white fir mortality exceeds acceptable amounts and affects management goals in many watersheds. Although the majority of the white fir mortality associated with the recent drought happened before 1994, some areas are still experiencing dramatic increases in tree decline and death. Areas still experiencing high mortality include the east side of the following Districts: Eagle Lake District, Lassen National Forest; Beckwourth District, Plumas National Forest; the Sierraville and Truckee Districts on the Tahoe National Forest; and areas around Lake Tahoe.

Lodgepole pine. In the northeast part of this ecological section, lodgepole pine is mainly in frost pockets or along riparian areas. Many stands have chronic mortality despite normal precipitation. During droughts, increased mountain pine beetle activity contributes to even higher rates of tree mortality. Over the past two years, increases in tree mortality have been observed primarily on the Truckee District, Tahoe National Forest, and at Donner Memorial State Park. Tree mortality is apparent along the Truckee River in and around campground sites and in undeveloped areas. Mortality over the past few years now covers about 100 acres in Donner Memorial State Park; this area is the largest reported contiguous area of lodgepole pine mortality.

Conifer health declined suddenly near Horseshoe Lake on the Inyo National Forest in 1992. Extensive mortality and severe needle loss were observed on 15 acres, which included primarily lodgepole pine but also red fir, mountain hemlock, and western white pine. All trees of these species within the 15 acres were affected. Investigations eliminated insects and pathogens as the primary causes. The mortality spot increased to over 30 acres by 1995, and new areas of similar damage were found. Recently, the mortality has been linked to geothermal activity that has produced very high concentrations of carbon dioxide in the soil.

Red fir. Red fir in the northern part of this section has had continual mortality over the past three to five years. Mortality of large trees is associated with attacks by fir engravers and inadequate precipitation; however, small trees (<5 inches in dbh) are also dying directly from drought, without fir engraver attacks. The recent red fir mortality in this section is on the southern edge of the Eagle Lake District, Lassen National Forest. Several special-emphasis wildlife habitat areas have been negatively affected.

Western white pine. Western white pine grows at higher elevations throughout the Sierra Nevada. As a five-needle pine, the species is susceptible to white pine blister rust. In California, however, concerns have focused on sugar pine, a far more abundant and valuable timber resource. In recent years, questions about the distribution of blister rust on western white pine have increased, but only limited surveys have been completed. In one stand on the Stanislaus National Forest at about 7,000 feet elevation, virtually every western white pine is infected with blister rust. Surveys of drainages in Sequoia and Kings Canyon National Parks during 1995 showed that blister rust infection frequencies of 20% were common in western white pine stands. This percentage implies that blister rust is still spreading to new sites in California and threatens the higher elevation five-needle pines. To date, the rust has not been observed above 7,500 feet elevation in the John Muir Wilderness. Western white pine, whitebark pine, and the alternate hosts (Ribes spp.) of the pathogen were free of rust, although conditions seemed favorable (R.S. Smith, Jr., personal communication).

Air pollution. Ozone is the major plant-damaging component of photochemical oxidant air pollution (smog), and the air pollutant most damaging to conifers in California. Nitrogen dioxide and hydrocarbons from automobiles and other sources react with sunlight to produce ozone (Scharpf 1993). When ozone enters the needles through the stomates, it destroys the chlorophyll and impairs metabolic processes (Tainter and Baker 1996).

Ozone injury to trees in the Sierra Nevada was first reported in 1971. Currently, two plot networks are established to assess ozone effects on pines in this section: the Forest Pest Management network includes long-term vegetation assessment plots that were first installed on the Sierra and Sequoia National Forests in 1977; and Project FOREST (Forest Ozone REsponse STudy) is a multi-agency network that includes ozone-monitoring instrument sites and associated vegetation-assessment plots on three National Parks and five National Forests from Lassen National Park south to the Sequoia National Forest (fig. 20). The Project FOREST area also includes sites on the San Bernardino National Forest. Data on this network were collected between 1991 and 1994. Both of the networks use the foliar symptom called "chlorotic mottle" (fig. 21) produced by ozone on conifer needles as the primary indicator of injury.

Ozone damage study map
Figure 20 Two plot networks for monitoring ozone injury in the Sierra Nevada.

Chlorotic mottle of ponderosa pine needles caused by ozone
Figure 21 Chlorotic mottle of ponderosa pine needles caused by ozone.

Project FOREST data shows the status of ozone on a very large forested federal land base over a short period. Symptoms of ozone injury have been found throughout the Sierra Nevada; injury is lowest in the north (Lassen National Park) and generally increases toward the south. The most heavily affected plots in the southern Sierra Nevada (Grant Grove and Giant Forest in Sequoia and Kings Canyon National Parks) fall in the range of injury found on the San Bernardino National Forest in southern California east of Los Angeles.

The Forest Pest Management network traces ozone injury over 18 years but on a relatively small land base (two National Forests); the categories of ozone injury ratings for plots on the Sierra and Sequoia National Forests in 1977 and 1994-95 are given in figures 22 and 23. Plots having no injury decreased proportionally on each forest during the period of observations; moderate and severe injury became more prevalent.

Sequoia National Forest ozone injury
Figure 22—Ozone injury on the Sequoia National Forest, 1977 and 1994

Ozone injury on the Sierra National Forest
Figure 23 — Ozone injury on the Sierra National Forest, 1977 and 1995.

In summary, evidence of ozone injury is found throughout the Sierra Nevada and increases in severity from north to south. All chlorotic mottles do not translate into measurable damage to trees, however, and slight amounts of injury may simply have cosmetic effects.

Current Forest Health Activities

Insect and pathogen considerations are an integral part of landscape-scale ecosystem analyses. These analyses evaluate current conditions, define desired conditions for diverse resources, such as vegetation structure and composition, and identify and set priorities for potential projects for subsequent site-specific analyses. The site-specific projects include insect and pathogen prevention and management components, such as thinning and the removal of trees infested with dwarf mistletoe.

In 1995, the Donner Ecosystem, covering 96,000 acres, was analyzed by the Truckee District, Tahoe National Forest. Project implementation is planned for 1996-97. In the Lake Tahoe basin, the North Shore Project Environmental Impact Statement was completed in 1996, covering 20,000 acres between Tunnel Creek (Washoe County, NV) and the Truckee River corridor (Placer County, CA). Activities will be implemented over about 7,000 acres of the analysis area beginning in 1996. Also in the Lake Tahoe basin, the East Shore Project, initiated in 1994 over 6,600 acres, continued in 1995 and included Jeffrey pine beetle suppression and preventive thinning. Analysis of the West Shore was initiated in the spring of 1996. Other projects with a specific thinning component aimed at bark beetle prevention include the North Fork Project on the Minarets District, Sierra National Forest; the Basin Biomass Thinning Project on the Summit District; and the Sawmill Mountain Thinning Project on the Groveland District, Stanislaus National Forest. In addition, a cooperative project between the Nevada-Tahoe Conservation District, the Kingsbury General Improvement District, and the Forest Service was initiated to prepare and implement a Forest Stewardship Plan for the Kingsbury area.

A cooperative change-detection project will begin in 1996 for the southern Sierra Nevada, covering lands of multiple ownerships from Calaveras County south to Kern County. The purpose of the project is to implement a procedure to produce baseline landscape-change data. Such information has several applications, including assessing land-use patterns, analyzing riparian areas, and monitoring changes in vegetative cover resulting from, for example, management practices, tree mortality, or fire. Landsat Thematic Mapper satellite imagery from 1990 and 1995 will be used. In addition to the Forest Service, cooperating agencies include the California Department of Forestry and Fire Protection, the National Park Service, and the Bureau of Land Management.

Annual Jeffrey pine beetle suppression in the Lake Tahoe basin has been implemented because of continuous, unacceptably high Jeffrey pine mortality in high-use, high-value, developed recreation sites. Jeffrey pine beetle biology and past observations imply that removing infested trees from overstocked areas or mortality groups should help reduce further mortality in the immediate treated area. The annual removal of infested trees over 165 acres in the South Shore Recreation Complex at Lake Tahoe reduced mortality 99%, from 330 trees in 1983 to 4 trees in 1987. Since 1994, the Lake Tahoe Basin Management Unit has conducted annual suppression activities in 14 developed sites, about 600 acres. Ultimately, more than 40 sites covering more than 1,100 acres may be included in the effort to suppress Jeffrey pine beetle in the Lake Tahoe basin. In addition, the Inyo National Forest plans to implement suppression activities for Jeffrey pine beetle on about 160 acres near the Inyo Craters Trailhead, Mammoth District, in 1996.

In 1992, Forest Pest Management initiated a study to evaluate the effectiveness of Jeffrey pine beetle suppression by comparing the number of trees killed by Jeffrey pine beetle in areas where infested trees are removed annually (treated areas) with the number of beetle-killed trees in areas where the infested trees are not removed (untreated areas). A summary of preliminary results to date indicate that, for selected areas in Lake Tahoe between 1993 and 1995, mortality was reduced by 87% in the treated areas, and mortality in the untreated areas increased 182% (table 3).
                                      - - - - -Infested Jeffrey pines by location (number)- - - - -

Status 1992 - 93 1993 - 94 1994 - 95 Increase/decrease
Nevada Beach and Zephyr Cover 
developed sites 
(136 sites)
909 240 121 -87%
Spooner Summit 
(98 acres)
1213 1966 2213 +182%
Table 3—Results of Jeffrey pine beetle suppression on the Lake Tahoe Basin Management Unit, 1993 - 1995.

Actions were also taken in 1995 to reduce lodgepole pine mortality caused primarily by mountain pine beetle. Two treatments were implemented in the historic Donner Camp area on the Truckee District, Tahoe National Forest. The objectives were to reduce the number of lodgepole pine killed by mountain pine beetle and maintain the older lodgepole pine. In early spring, infested trees were identified, felled, and removed before the emergence of mountain pine beetle adults. In addition, five plots were established surrounding the camp area at 1/4-mile intervals. Each plot had three traps containing the aggregation pheromones of the mountain pine beetle. The purpose of the traps was to direct the mountain pine beetles away from the immediate camp area to areas planned for thinning in 1996, thus reducing lodgepole pine mortality near Donner Camp.

Tree removal and trapping appear successful. The number of infested lodgepole pine declined from 149 trees in 1994 to 11 in 1995. Seventy-eight pines associated with the pheromone trap plots were infested by the mountain pine beetle. A total of 8,133 mountain pine beetles were caught in the pheromone traps between July 6 and October 12, 1995. All lodgepole pines infested in 1995 were felled and bucked in late October. Similar efforts will be implemented in 1996.

The California fivespined ips heavily infested wind and snow breakage in a ponderosa pine plantation on the Foresthill District, Tahoe National Forest, in 1995 (see weather section). To keep the ips population from emerging and attacking residual trees, 364 acres were treated by felling standing green snags, chipping, and lopping and scattering slash.

In 1995, branch pruning of sugar pine infected by white pine blister rust was completed over 70 acres of 12-year-old mixed conifer plantations on the Foresthill District, Tahoe National Forest. Sugar pine represented between 20 and 40% of the growing stock. Trees with lethal stem cankers were removed. Three different pruning treatments were used to evaluate the effectiveness of pruning in reducing later infections.

The Douglas-fir tussock moth is a native defoliator in western North American coniferous forests. Its preferred host in California is white fir. In 1980, an early-warning system of detection traps was established throughout the Sierra Nevada and northeastern California. The purpose of the monitoring network is to identify where tussock moth populations may increase to outbreak and focus more intensive detection efforts there. Trap catches remained low since an outbreak from 1987 to 1989, but populations at a few sites began to increase in 1994. This increasing trend continued in 1995 and indicated the potential for an outbreak in several locations in the Sierra Nevada. Intensive egg-mass surveys and larval sampling will be conducted in the spring and summer of 1996 in areas ranging from Tuolumne County in the south to Plumas County in the north. These surveys will provide area-specific information on which to base further resource management decisions.


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