During the past century, fire has often been portrayed as a destructive force that should always be eliminated to "protect" ecosystems. Ignition sources have changed from a combination of lightning and use of fire as a tool by American Indians, to the suppression of most fires regardless of cause. Suppression has altered ecosystem composition and structure by changing the mortality and recruitment patterns of many tree species. Fire frequency has generally decreased, but the proportion of acres burning in stand-replacing fires has increased. Less frequent fires allow greater fuel accumulation and more trees per acre to persist on the landscape.
Logging practices have been as important as fire exclusion in increasing the severity of fires in many timbered areas. Spatially diverse, relatively open-canopy forests dominated by large trees were often replaced by closed-canopy forests, some of which are single-layered and others are vertically diverse. Forests with closed canopies of small trees or with multilayered, variable canopies are more susceptible to stand-replacing fires than are open-canopy forests dominated by large trees. Thinning programs in the closed-canopy forests have reduced susceptibility over thousands of acres.
Attitudes toward fire are shifting once again: the awareness of the role of fire in ecosystem dynamics and function is increasing. In California's Mediterranean climate, the question is not whether fire will happen, but when, where, and what kind. Managing fire frequency and intensity will help maintain biological diversity, integrity, and sustainability.
Figure 2 — The focus of prescribed burning programs is shifting from slash treatments (above) to treatment of natural fuel accumulation and restoration of fire as a natural process (below).
Some 287,250 acres of National Forest land in California were treated with prescribed fire from 1990 to 1995. The number of acres per forest differed greatly, with fuel treatments such as slash removal and site preparation for tree planting accounting for much of the acreage. In 1993, 35,865 acres were treated. In 1994, another 29,368 acres were treated with prescribed fire.
During 1995, the weather was especially favorable for prescribed burning in much of California. The average size of individual prescribed burns increased; the Stanislaus River burn on the Stanislaus National Forest was the largest project at 4,800 acres. This project was also notable because several vegetation types were burned.
Prescribed burning programs are shifting from the district scale toward the forest and province scales. This shift encourages the selection of large, landscape-scale projects and the pooling of resources to execute complex burns.
The increase in interagency cooperative burns is an example. The Cleveland and Eldorado National Forests cooperated on burns with the California Department of Forestry and Fire Protection; the Modoc and Stanislaus National Forests cooperated on burns with National Parks in 1995.
Many current forest management practices are designed to reduce the potential of a forest to burn in large, high-severity fires. These practices include salvage sales, large-scale thinning, and the creation of defensible fuel-profile zones around communities and other strategic locations. Some stands are being mechanically treated to reduce hazardous fuels. Because of extensive conifer mortality on the east side of the Sierra Nevada, fire cannot be reintroduced without first removing trees and dead material. Therefore, defensible zones are being constructed, with plans to underburn in the future. The results of these and other practices must be monitored carefully to determine how the treatments change the distribution and effects of fires.
Fire and fuel management are now central issues in forest planning on a watershed scale. Fuel treatments are being tailored to consider the vegetative potential and historical fire regimes in an effort to match unique qualities and situations found in each area. Fire and fuel specialists are being asked to participate in designing projects that restore fire as a natural ecosystem process. Fuel treatments must be large and strategically placed to decrease the incidence of large, severe fires. Treatments must be reapplied at appropriate intervals to maintain the ecosystem, or areas will quickly revert to their prior condition.
The prescribed burning program in California is gaining momentum, but its scope is dwarfed by the fire suppression program. Although awareness of how important fire and fuel management are to ecosystem management is growing, progress toward managing fire on the landscape is slow. Full suppression of all fires is still the norm. The number of acres in natural fuel being treated is still only a fraction of what is needed to manage fuel on a landscape scale.
Figure 3 — Total acres
burned on National Forest lands in California, 1970 to 1995; the average
year is 1992.
On September 18, 1994, lightning started the Barkley Fire. The fire burned in mixed conifer forest, oak woodland, and grassy areas on steep rocky slopes in the Deer Creek drainage. Temperatures in the high nineties with Foehn winds (warm, dry winds coming off the lee slopes of a mountain range) and 10 to 15% relative humidities hampered suppression efforts. A wind shift on September 24 provided higher humidities, aiding suppression efforts. A total of 44,430 acres burned, a large proportion of which was within the Campbell/Ishi Wilderness.
Between August 4 and September 4, 1994, two large wildfires burned on the Tahoe National Forest. The Crystal Fire covered 7,310 acres and the Cottonwood Fire 46,800 acres. The areas burned were in eastside pine at lower elevations, mixed conifer at mid elevations, and red fir on the ridgetops. Several decades of fire exclusion had allowed dense stands of white fir to occupy formerly open, eastside pine and mixed conifer forests. Several years of drought and bark beetle infestations left large patches of standing dead trees (fig. 4). Past logging practices left other areas of deep slash with heavy fuel loading. The fires were both high intensity and stand replacing over most of the burned areas. Similar fuel conditions persist in unburned areas adjacent to the burned areas.
Figure 4 — Crystal Fire, 1994. Fire
exclusion combined with drought and tree mortality resulted in heavy fuel
loadings that increased the potential for high-intensity fire.
The 1995 wildfire season was below average: 8,492 fires burned 209,815 acres, of which 1,526 fires burned 22,125 acres of National Forest lands. Only 250 acres of National Forest land required investments to reforest. The winter of 1994-95 was unusually wet, and the typical California summer pattern of high-pressure ridge did not form until late summer. It stayed in the area until late in the season, resulting in low fuel moisture in southern California, and fire activity remained low.
Figure 6 — Palmer Hydrologic Drought
Index for 1995 by climate zone.
Source: California Department of Water Resources
Except for a few storms in early December and February, dry weather prevailed in northern California during the winter of 1993-94. Northern California had only 80% of its normal snowpack by March 1, and 1994 had the 14th driest March since 1895. The wet season was disappointing (fig. 5), except in southern California.
Precipitation and snow were unusually high in December and the early
months of 1995. Serious flooding in the northern and coastal southern parts
of the state culminated with a record-setting deluge on January 9 and 10,
1995. Rainfall totaled 17.36 inches in 48 hours at Brandy Creek, west of
Redding. Blue Canyon recorded 5.05 inches of rain, and downtown Sacramento
recorded an unprecedented 4.45 inches within a 24-hour period. By April
1, the 1995 statewide average for precipitation was 165% of normal, and
the snow pack was 175% of normal. For the northern Sierra Nevada, 1995
was the second wettest year since records began in 1922. Seven of the previous
nine years had average annual precipitation and snowpack below normal (fig.
7). The annual average or "norm" was derived from the average precipitation
rates for the years 1922 to 1995; July 1 to June 30 of the following year
mark the beginning and end of a "precipitation year" in California.
Figure 7 — Percentage of average annual precipitation in
California, 1987 to 1995.
Source: California Department of Water Resources
Storms damaged trees in several areas in 1994 and 1995. Serious storms were the wet, heavy snows of late March and early April in 1995 that caused extensive breakage of tree branches and boles over about 2,000 acres of the Foresthill District, Tahoe National Forest (fig. 8).
Figure 8 — Ponderosa pine broken by
heavy snow in early spring of 1995, Foresthill District, Tahoe National
Forest.
The wet winter was also the cause of two avalanches on Mount Shasta during December 1994. The larger of the avalanches is still visible from Interstate 5 on the west side of the mountain. The smaller avalanche, on the south side of the mountain, cut across the Everett Memorial Highway near Panther Meadows. The major tree species damaged was Shasta red fir—more than six million board feet. In late 1994, a strong windstorm leveled knobcone pine over about 120 acres near Lake Siskiyou, Siskiyou County. Most of the trees were salvaged, and the site is being regenerated.
Winter storms in early December 1995 brought winds clocked at 103 miles per hour (mph) at Eureka and 86 mph at Redding. Windthrow during this or other storms in the winter of 1995-96 affected more than 20,000 acres outside of wilderness areas on the Six Rivers and Shasta-Trinity National Forests (Sections M261A and M261B). More than 30 million board feet of timber was damaged in an area of high-value fisheries and late-successional reserves. Concentrations of blowdown fell at South Fork Mountain, Stuart Gap, and Rat Trap Gap on the Shasta-Trinity. Damage to oaks, especially canyon live oak and valley oak, was widespread in the northern part of the Sacramento Valley. The winds also damaged stands on the Almanor District, Lassen National Forest. Heaviest concentrations of damage were in the Swain Mountain Experimental Forest, on Morgan Summit, and in Grizzly Campground near HumBug Pass (Section M261D). Losses across all the Lassen National Forest were near 30 million board feet (MMBF). The same storm felled an estimated 1,000 trees in Golden Gate Park in San Francisco.
Winter needle desiccation affected ponderosa pines on about 1,000 acres of private and National Forest lands on the northeast side of Goose Valley (Shasta County). Many of the affected trees died as a result of needle drop and bark beetle attacks.
Pocket gophers, the most destructive vertebrate in the state, damage seedlings and saplings by clipping and girdling roots and stems, usually killing the tree. Increased tree mortality from pocket gophers often can be traced to vigorous growth of competing vegetation that provides suitable habitat (Crouch 1982, Teipner et al. 1983). All major forest types throughout the state suffer animal damage, but most problems are in eastside pine, mixed conifer, and true fir stands.
Deer feed on the foliage of seedlings, which causes suppression, growth loss, and sometimes death of recently planted seedlings. Deer feeding causes injuries throughout the state in all major forest types.
Porcupines girdle seedlings, saplings, and poles, causing growth loss, deformity, and dead tops. Porcupines primarily cause damage in eastside pine and true fir stands of northeastern California.
Black bears are primarily a problem in Douglas-fir and redwood stands on private timber lands in the Northern California Coast Section (263A). They peel the bark from pole-sized to mature trees to feed on the cambium. The wounds become entry points for boring insects and decay fungi; girdling results in dead tops and tree mortality. The injury is repeated annually, often in the same vicinity, and ranges from 1 to 60 trees per acre.
The number of acres affected by vertebrates differs considerably from year to year (fig. 9). Losses range from 1 to 500 trees per acre. Protection from animal damage is needed on more than 50,000 acres of National Forest land each year, but currently only about half of these acres are treated (unpublished survey data, California National Forests).
Figure 9 — Forest acres in
California with reported animal damage, 1991 to 1995.
In 1995, species rankings based on the acres of damage differed considerably from previous years: woodrat (25% of the acres), porcupine (23%), black bear (20%), deer (20%), pocket gopher (6%), and all others (6%). This change in ranking of species is the result of one new respondent reporting large numbers of acres affected by woodrats and porcupines. This respondent also reported a total of 336,813 acres for four species, which also accounts for the substantial increase in the total acres reported over previous years (2 to 3 times). Removal of this one response to the annual animal damage control questionnaire of the California Forest Pest Council would give about 139,000 acres and rankings similar to previous years.
Forest workers, rural workers, and outdoor enthusiasts are probably at higher risk of exposure to vector-borne diseases associated with forested environments than is the general public. Workers and others in potentially high-risk settings should be informed about possible areas of exposure and symptoms associated with vector-borne diseases. Sensible precautions should be taken to avoid contact with rodents and other mammals, their burrows, dens, and droppings, especially in rural settings. Plague and hantavirus are two diseases of concern.
Plague in California occurs in the foothills, plateaus, mountains, and the coastal belt (fig. 10) but is absent from the southeastern desert and the Central Valley. Areas posing the most threat to people are the recreational, wilderness, and rural parts of the state, as well as the suburban foothill areas of some of the large cities. Campgrounds in the Sierra Nevada that are inhabited by rodents known to be carrying the plague are often closed to the public and chemically treated.
Figure 10 — Area of plague
incidence in California.
In 1994, plague was recorded in 18 counties. Two human cases of plague were diagnosed: one in Inyo County and a second in El Dorado County. One case of unknown source was fatal. Other counties known to have plague areas during 1994 were Butte, Plumas, Alpine, Siskiyou, Kern, Los Angeles, Mono, Mariposa, Nevada, Riverside, San Bernardino, Sierra, San Luis Obispo, Tuolumne, and Ventura.
In 1995, plague was reported in 15 California counties. Two human plague cases were found in Kern county, one of which was fatal. In the fatal case, exposure may have been primary pneumonic exposure from an unknown animal source. In the second case, all indications point to flea bite exposure from a household pet. Other counties with areas of known plague during 1995 were Butte, El Dorado, Inyo, Los Angeles, Mono, Mariposa, Nevada, Riverside, San Bernardino, San Diego, Sierra, San Luis Obispo, Tuolumne, and Ventura.
In California, about 6,500 mammals of 44 species in 12 families have been tested for antibodies to SNV. The deer mouse appears to be the primary reservoir for SNV in California. Antibodies have been found, though rarely, in a few other wild rodent species: wood rat, ground squirrel, and kangaroo rat. Domestic and wild carnivores have not shown evidence of infection. Mice testing positive for antibodies (seropositive) have been identified in 18 counties (fig. 11).
Figure 11 — Counties with
seropositive mice, indicating exposure to sin nombre virus (hantavirus).
Engaging in activities that result in exposure to rodents, particularly deer mice, is considered a primary risk factor. Occupying poorly ventilated places with heavy rodent infestations, such as cabins and trailers, may be particularly hazardous. Several patients have reported cleaning infrequently used, rodent-infested buildings or other structures before becoming ill.
From 1980 to 1995, 13 California residents were diagnosed with HPS; 8 of them died. One case was diagnosed in 1993, three in 1994, and five in 1995. Four HPS cases were diagnosed retrospectively from 1980 to 1992 by testing stored serum samples, preserved tissue specimens, or both. The probable sites of exposure were Mono, Nevada, Kern, Inyo, Plumas, and Santa Barbara counties. Notably, the majority of California cases are spatially clustered in the eastern Sierra Nevada.
Aerial and ground surveys of National Forests in 1994 and 1995 found
tree mortality primarily in overstocked stands, on poor tree-growing sites,
and on sites inappropriate for the tree species dying (figs. 12,13,14).
Large pines and firs were also frequent casualties. North of Highway 50,
mortality continued to be high even though acreage and volume decreased
substantially in 1995. The fir engraver in overstocked fir stands and the
mountain pine beetle in overstocked lodgepole pine stands were largely
responsible for the losses. Jeffrey pine beetle continued to kill large
Jeffrey pines throughout much of the region.
Figure 12 — Acres of pine and true fir mortality on
National Forests in four regions of California, 1993 to 1995.
Figure 13 — Volume of pine and true fir mortality on National
Forests in four regions of California, 1993 to 1995.
Figure 14 — Areas of cumulative
tree mortality in California National Forests, 1994 and 1995, based on
aerial surveys.
The most dramatic declines in acres and volumes affected were in the
central and southern Sierra Nevada and southern California. Trees were
killed early in the drought cycle in these regions, and the loss of low-vigor
trees and an earlier return to nearly normal precipitation may account
for the declines. Southern California showed a variation from this trend
in 1994.
___________________________________
Contents
