CHAPTER THREE

AFFECTED ENVIRONMENT

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Introduction

Yosemite National Park occupies about 1,170 square miles, or 748,955 acres (302,816 hectares), on the western slope of the Sierra Nevada, the highest and most continuous mountain range in California. The Sierra Nevada runs half the length of the state, dividing the Central Valley of central and northern California from the arid, western edge of the Great Basin to the east. Yosemite National Park lies within three counties – Mariposa, Tuolumne, and Madera – and abuts a fourth, Mono. The park shares boundaries with the Stanislaus, Sierra, Inyo, and Toiyabe National Forests. Ninety-four percent of the park (about 704,624 acres) is designated wilderness.

Elevations in the park rise to 13,114 feet (3,998 m) near the eastern boundary, and drop to 2,127 feet (648 m) at the western boundary. This wide elevation range supports a variety of environments, each with distinct climatic conditions, vegetation, and animal life. Yosemite, like much of California, has a Mediterranean climate. Cool, moist winters and hot, dry summers prevail. The extreme differences in elevation and terrain affect both temperatures and precipitation. At higher elevations, most of the precipitation falls as snow. Weather patterns and climate have a major influence on the distribution of plants and animals in the park.

Elevation and weather patterns form large-scale vegetation zones along the north-south axis of the Sierra. On the west side, forest types change with elevation from live oak to mixed conifer to mountain hemlock and pine at high elevations. Straddling the crest of the Sierra Nevada is a zone of subalpine and alpine vegetation. Secondary vegetation patterns are created by deep river canyons and the east-west orientation of watersheds that drain the Sierra Nevada. The range contains the headwaters of 24 major east-west river basins, two of which are in the park—the Merced and the Tuolumne Rivers.

Four Sierra Nevada national parks – Lassen Volcanic, Yosemite, Sequoia, and Kings Canyon – contain most of the large contiguous areas of old-growth forest in middle-elevations. Patches of old-growth are relatively well distributed throughout the Sierra Nevada, though many of the patches of old-growth forest outside of the parks are smaller and have been compromised by the effects of fire suppression and grazing (U.C. Davis 1996a). Plant diversity in the Sierra Nevada is rich—containing about half of California’s 7,000 plant species. More than 400 of these plant species are found only in the Sierra Nevada, and of this total, over 200 are considered rare by conservation organizations and/or state and federal agencies (Shevok 1996). Rare local geologic formations and associated soils support unique habitats that sustain plant species that are found only in these specialized habitats. As a group, Sierra Nevada plants are most at risk where habitat has been reduced or altered.

About 300 terrestrial vertebrate species (including mammals, birds, reptiles, and amphibians) use the Sierra Nevada as a significant part of their range. Of these, three species once well distributed in the range are now extinct from the Sierra Nevada: Bell’s vireo, California condor, and grizzly bear. Sixty-nine species (17% of the Sierra Nevada fauna) are considered at risk of extinction or extirpation by state or federal agencies. The most important identified cause of the decline of Sierra Nevada vertebrates has been the loss of habitat, especially foothill and riparian habitats and old growth forests.

Fire ignited by lightning and American Indians prior to the mid-1800s has influenced ecosystems in the Sierra Nevada for millennia. Fire has affected the diversity of plant and animal life, insect outbreak and disease cycles, wildlife habitat, and soil and nutrient cycling (U.C. Davis 1996b). In most low-elevation oak woodland and conifer forest types, fires were frequent. Fires collectively covered large areas and burned for months at a time. Most fires were of a low to moderate intensity, though patterns of severity were complex and fires were at times extreme. Over the last 150 years, fire suppression and changes in land use have dramatically changed fire regimes and consequently altered ecological structures and functions in plant communities. Live and dead fuels in conifer forests, especially at lower elevations, are more abundant and continuous than in the past.

Humans have been a part of Sierra Nevada ecosystems for at least 10,000 years. Numerous, distinct American Indian cultures were widely distributed throughout the region well before settlement by Euro-Americans in the mid-19th century. Although the record is incomplete, archaeological evidence indicates that, prior to the 1850s, the American Indian population in the Sierra Nevada may have been as large as 90,000 to 100,000 people (Anderson and Moratto 1996).

The human population of the Sierra Nevada doubled between 1970 and 1990; 40% of the population growth occurred north of the park. Official projections indicate that the 1990 Sierra Nevada population of 650,000 will triple by the year 2040. Communities in the Sierra Nevada are dependent on a combination of natural resources, including non-economic benefits associated with aesthetics and scenery (U.C. Davis 1996a). Projected population trends show that more and more homes will be intermixed with flammable wildlands. Unless hazardous fuels are reduced more and more homes and people will be at high risk of loss from wildland fire. Only about one-third of the Sierra Nevada is privately owned. The U.S. Forest Service manages most of the public land; the Bureau of Land Management and National Park Service manage most of the remainder. The majority of the land at high elevations throughout the Sierra Nevada is public, as are large proportions of the eastern Sierra Nevada. Private lands are predominately below 3,000 feet elevation, along the western slope of the range (U.C. Davis 1996b).

The Sierra Nevada region is a popular tourist destination, containing some of the world’s most renowned natural features. Annually, millions of visitors from around the country and the world are drawn to destinations like Lake Tahoe, Mono Lake, Yosemite National Park, and Sequoia and Kings Canyon National Parks. They come to experience the natural beauty along the Sierra crest. Most recreational activity in the Sierra takes place on land administered by the U.S. Forest Service (57-67%). Lands of the California Department of Parks and Recreation (15-27%), the Bureau of Reclamation (7-8%), the National Park Service (6-7%), and the U.S. Bureau of Land Management (3%) provide additional recreational opportunities. Other public lands, utility-owned properties, and private lands are also used for recreation (U.C. Davis 1996a).

Wildland Fire Management Situation

Wildland fires can potentially burn throughout the year in Yosemite, but the recognized fire season is May to November, when fuels are driest and the weather is more conducive to fires starting and spreading. The suppression of wildland fires for the last 80 to 100 years have changed the forests in Yosemite by creating a dangerous accumulation of fuels. In what once were forests with a high frequency, low-severity fire regime, fire suppression and passive management of vegetation has resulted in forests prone to high-severity fires. During the 1990’s, Yosemite experienced three of the largest and most severe fires in the history of the park: the Steamboat and A-Rock Fires (22,000 acres) in 1990, and the Ackerson Fire (47,000 acres) in 1996. No evidence exists that these types of large, stand-replacing fires had ever previously occurred in the park (van Wagtendonk 2000).

Since 1972, approximately 75% of the park has been managed under a year-round prescription to allow wildland fires to burn in a “Prescribed Natural Fire Zone.” Another 8% has been managed as “Conditional Zone” where fires have been allowed to burn under some conditions. Almost 80,000 acres have burned in thirty years. Fires that start within these zones or fires that burn into these zones from neighboring public land are managed for resource benefits—provided management criteria are met. The Prescribed Natural Fire Zone extends from the northwest park boundary near Kibbie Creek and Lake Eleanor, skirts around Yosemite Valley and the southwest corner of the park, and terminates at Chiquito Pass on the southern boundary (map 2-12). Natural and human-caused barriers and prominent topographic features form the western edge of this zone, while the park boundary forms the north, east, and south edges. Wildland fire is the primary fire management tool, although prescribed fire may be used. Hand thinning has been used to protect values at risk such as backcountry camps, cabins, and archaeological resources.

The other 17% of the park is in a “Suppression Zone.” This area encompasses the western edge of the park, including the El Portal Administrative Site. Most of the park’s developed areas are within this zone, including Hodgdon Meadow, Aspen Valley, Crane Flat, Foresta, El Portal, Yosemite Valley, Glacier Point, Wawona, and Yosemite West adjacent to the west boundary. All of the park’s sequoia groves (Tuolumne, Merced, and Mariposa) are also within this zone. Unplanned ignitions that occur within this zone are suppressed, using appropriate management response strategies. This concept offers managers a full spectrum of responses based on objectives, environmental and fuel conditions, constraints, safety, and the ability to accomplish objectives. It includes wildland fire suppression at all levels, including aggressive initial attack. Use of this concept dispels the interpretation that there is only one way to respond to each set of circumstances (Zimmerman and Bunnell 1998). Most of the prescribed fires and a majority of the fuel reduction techniques take place in this zone, especially in and around the developed areas and Special Management Areas (sequoia groves, wildland/urban interface, and boundary areas). Since 1970, when the prescribed fire program was initiated, 43,065 acres have been burned.

Because Yosemite has distinct wet and dry seasons, the fire season is concentrated during the dry, hot summer. In the upper elevations, moisture levels in dead and down fuel can remain high late into the summer, resulting in a short fire season. The average number of years between fires, or fire return interval, ranges from 4 to 508 years in the upper elevations (above 8000 feet) depending on vegetation type. In the mid-elevations, at 5000 feet to 8000 feet, fire return intervals range from 3 to 75 years, depending on vegetation type. At lower elevations fire return intervals can range from 1 to 60 years, again depending on vegetation type.

The park averages 55 wildland fire starts per year, and approximately 95% of those are from lightning (map 3-1). Most starts go out quickly, are contained at less than 10 acres, or are successfully managed. In the past 10 years, the consequences of suppressing fires and the resulting build-up of fuels have exacerbated the fire danger, especially at the lower elevations along the park’s western boundary. During fire season, fires starting in the early afternoon on steep slopes, when vegetation is dry, have the potential to grow large rapidly, despite aggressive initial attack. When the slope, wind, and sun are all in alignment, fires can burn with rapid rates of spread and high flame lengths through the abundant, continuous fuels. This problem becomes more complex when summer thunderstorms cause gusty, erratic winds and multiple ignitions.

During dry conditions in places where fuels are not continuous, spotting, or fires started at a distance from the main fire by wind-blown embers, can also facilitate fire spread and resistance to control. For example, an individual tree or a group of trees may torch (go up in flames) and spread airborne embers one half mile or more. Trees in these areas might then ignite, torch, and then spread additional embers—thus starting more spot fires. Fires that spread by spotting are difficult to control.

Another potential control problem unique to this portion of the Sierra Nevada are strong easterly winds called foehn or Mono winds. However, there is no record or evidence of fires being driven by Mono winds in the park.

Biological Environment

Vegetation and Fire Ecology

National parks provide major concentrations of high-quality late-successional forest, especially at the landscape level, and, on a percentage basis, have about twice as much highly-rated forest as adjacent national forests. Yosemite National Park is 54% high-quality, late successional forest (Franklin and Fites-Kaufmann 1996). The vegetation of Yosemite is varied and complex and is a significant part of the beauty and biological diversity of the park. Vegetation plays a vital role in maintaining ecosystem health and environmental quality. Plants recycle nutrients, provide wildlife habitat and food, contribute to regulation of microclimates, regulate stream discharge, maintain water quality, prevent soil erosion, and, perhaps most significant to this plan, provide fuel for fires.

At least 1,374 vascular plant species and numerous bryophytes and lichens occur in Yosemite National Park (NPS 1997). Yosemite’s forests include three world record trees, they are the largest red fir, the largest white fir, and the worlds tallest recorded pine tree—a sugar pine. A number of species are considered globally or locally rare. The park has five plants that are species of concern, no federally listed plant species, four State of California listed species, and 109 special-status plant species (NPS 1997a, see also Appendix 11, Biological Assessment).

The vegetation zones of the park follow general elevation bands across the Sierra Nevada (Sawyer and Keeler-Wolf 1995).  From chaparral and oak woodlands at the lowest elevations, through towering conifers of lower and upper montane forests, and weather worn subalpine forests and alpine meadows in the highest mountains, plant communities quickly blend from one to the next, revealing dramatic environmental differences in elevation. At about 2000 feet above mean sea level, slopes are covered with chaparral and oak woodland. Lower montane mixed-conifer forests range from about 3000 to 6700 feet, changing to upper montane conifer forests from 6000 to 10,000 feet in elevation. Subalpine conifer forests occur from 8,000 to 11,000 feet, although alpine communities dominate above 10,000 feet.

For the purpose of this plan, data from the park’s 1934 vegetation map was reclassified so that it matched current vegetation community typology while grouping vegetation communities by fuel type and fire behavior. The groupings are based on the analysis for the Vegetation Management Plan (based on 1934 data), a map of the dominant species from the 1934 data, the park’s 1982 Botti vegetation map, and a determination by fire professionals about the similarity of potential fire behavior in each type. Appendix 10 includes a table showing how the various Vegetation Management Plan types were grouped into the 15 fire management vegetation types.

Neighborhood analyses were performed for meadows, riparian vegetation types, and western juniper. These were lumped into the fire management vegetation types according to their physical proximity. For example, if a subalpine meadow adjoins a lodgepole pine forest, it would be lumped with the forest since the meadow would be likely to burn if the forest were ignited. If, however, the meadow were surrounded by barren rock, it would be lumped with the rock since it would be unlikely to be ignited

The 15 vegetation types and the bare rock and water categories are listed in table 3.1 for the 747,955 acres in Yosemite National Park and in table 3.2 for the 1,137 acres in the El Portal Administrative Site. The types are listed generally from higher to lower elevation. More detailed descriptions for each type are found in the Vegetation Management Plan. For convenience, types were further grouped, based on elevation.

Table 3.1   Vegetation groups, corresponding fire vegetation types, and acreage for Yosemite National Park

Table 3.2   Vegetation groups, corresponding fire vegetation types, and acreage for the El Portal Administrative Site

Vegetation Classification: Ecology and Natural Fire Conditions

Subalpine Forests

The subalpine zone includes whitebark pine and/or mountain hemlock forests and lodgepole pine forests (map 2-1), which together occupy about 35% of the park. Characteristic tree species include lodgepole pine, mountain hemlock, and whitebark pine, with smaller amounts of red fir, western white pine, and western juniper (SNEP 1996). Although this zone receives approximately 35% of the lightning strikes in the park, fires are infrequent and rarely become large (van Wagtendonk 1991). These fires usually smolder or spread as low intensity surface fires.

Whitebark pine/mountain hemlock forest

Whitebark pine and mountain hemlock forests cover 87,582 acres of the park and comprises much of the subalpine forest from 9,600 to 11,000 feet. Pure stands of whitebark pine and intermixed stands of mountain hemlock, whitebark pine, and lodgepole are common. Mountain hemlocks occasionally form pure stands on north-facing slopes and occur as low as 8,000 feet. At or near tree line, this community can be open forest or dense shrub like krummholz. Fuel loads average about 44 tons per acre underneath clusters of whitebark pines and about 54 tons per acre underneath mountain hemlock (van Wagtendonk et al. 1998). Fuel Model 8 (table 3.3) is most appropriate for this type, although Fuel Model 4 should be used for krummholz stands of whitebark pine.

Between 1930 and 2000, 56 lightning fires burned a total of 121 acres of the whitebark pine/ mountain hemlock type once and less than one acre twice. The largest area burned in the type by a single lightning fire was 20 acres. Over the same time period, three human-caused fires burned slightly more than one-quarter acre in the whitebark pine/mountain hemlock type, and no prescribed burns have been conducted. Based on the area in the park burned by all lightning-caused fires that were allowed to burn in whitebark pine forest between 1972 and 1993, van Wagtendonk (1994) calculated that the fire rotation (the number of years it would take to burn all of the type in Yosemite at the present rate of burning) would be over 23,000 years. Fire scar analyses of whitebark pine and mountain hemlock forests indicate that fire return intervals range from 4 to 508 years with a median of 187 years (Caprio et al. 1991). Due to the long median and maximum return intervals for this group, the fire return interval departures (FRID) tend to be low with all of the type within the maximum and median fire return intervals (FRID_{max /med} = 0). This indicates existing vegetation does not have a severely altered fuel load or stand structure because of fire exclusion.

Lodgepole pine forest

The lodgepole pine forest is the most common vegetation type in the park covering 175,516 acres. It often grows in dense pure or almost pure stands of trees up to 130 feet tall. Lodgepole pine tolerates large variation in soil type and moisture conditions. It commonly occurs on rocky, well-drained soils from 6,800 to 10,400 feet and at lower elevations in cold-air drainages. It is nearly continuous between 8,500 and 10,000 feet and in long narrow stringers at lower elevations. Fuel Model 8 best represents lodgepole pine forests where fuel loads average 30 tons per acre (van Wagtendonk et al. 1998). In areas where there is a substantial amount of herbaceous understory, Fuel Model 2 can be applied.

A total of 465 fires have burned 9,110 acres of lodgepole pine forest since 1930. Fires  include 427 lightning fires, 25 human-caused fires, and 13 prescribed fires. Of the total area, 7,467 acres have burned once, 989 acres twice, and 157 acres three times. The largest area of lodgepole pine forest to burn with a single lightning fire was 773 acres in 1987. These fires usually remain as very low intensity surface fires, often spreading from log to log or smoldering in the thin, densely packed duff. The fire rotation is 764 years (van Wagtendonk 1994). Kiefer (1991) determined fire return intervals for lodgepole pine forests from four to 163 years with a median value of 102 years. Based on both the maximum and median fire return interval, all of the lodgepole pine forest has a FRID of zero (FRID_{max /med} =0). Consequently, the structure of this type does not appear to have been altered by fire exclusion.

Upper Montane Forests

The upper montane zone includes red fir forest, western white pine/Jeffrey pine forest, and montane chaparral and makes up about 30% of park vegetation. Characteristic trees include red fir, western white pine, Jeffrey pine, western juniper, and aspen (SNEP 1996). This zone receives 23% of the lightning strikes in the park, and fires are numerous, generally remain small, and are of low intensity (van Wagtendonk 1991). However, under extremely dry and windy conditions, large stand replacing fires can occur.

Red fir forest

Red fir forest covers 68,125 acres of the park and is associated with the areas of greatest snow accumulation in the park. This plant community dominates at elevations between 6,500 and 9,000 feet. Forests occur in large stands, separated by barren areas, ridges, meadows, or lower-elevation lodgepole pine forest. In drier sites and at lower elevations, it intergrades with Jeffrey pine and montane chaparral. Because fires have been suppressed, the community is currently shifting to favor more shade-tolerant red fir and moving into areas that were dominated by lodgepole pine, montane chaparral, and Jeffrey pine. Fuel loads are relatively high, averaging about 49 tons per acre (van Wagtendonk et al. 1998). Despite the heavy fuel loads, Fuel Model 8 best fits the red fir forest because surface fires are usually carried by fuels less than one inch in diameter.

Since 1930, 591 lightning fires have burned 16,767 acres, 18 human-caused fires have burned 1004 acres, and five prescribed fires have burned 307 acres of red fir forest. Out of the total 18,074 acres, 16,084 have burned only once, while 1,476 acres have burned twice, 81 acres three times, and one acre four times. The Lost Bear Fire that burned 1,265 acres of red fir forest in 1999 has been the largest to occur in this type. It would take 197 years to burn all of the red fir forest in Yosemite given the rate of burning that occurred between 1972 and 1993 in the Prescribed Natural Fire Zone (van Wagtendonk 1994). Return intervals determined from fire scars indicate a minimum of nine years, a median of 30 years, and a maximum of 92 years (Caprio et al. 1991). In red fir, 50,484 acres have missed one maximum fire return interval (FRID_max = 1), while and additional 17,641 acres have not missed any (FRID_max = 0).  Minor departures in stand structure are beginning to occur.

Western white pine / Jeffrey pine forest

The park contains 132,708 acres of western white pine and Jeffrey pine forest. They grow in pure stands and intergraded with montane chaparral and other species. Both western white and Jeffrey pine tend to occur in dry sites. Western white pine grows from 8,000 to 10,000 feet. Trees are widely spaced and may have an understory of montane chaparral. Existing vegetation is probably within the natural range of variability. Jeffrey pine grows from 6,000 to 9,000 feet intergrading with montane chaparral, red fir, and white fir/mixed-conifer forest. Fuel loads range from 13 tons per acre for western white pine to 43 tons per acre for Jeffrey pine (van Wagtendonk et al. 1998). Fuel Model 9 can be used for both species, although in some cases Fuel Model 8 may be necessary for western white pine. In areas where montane chaparral exists in the understory, Fuel Model 5 is appropriate. Existing conditions at lower elevations and more mesic sites show an increase of shade-tolerant conifers, such as white fir, in the understory and accumulations of surface fuels.

The western white pine/Jeffrey pine forest burns frequently and fires burn with high intensity. Lightning is prevalent and has resulted in 893 fires burning 41,982 acres between 1930 and 2000. The largest number of acres of this type burned by a lightning was during the Starr King fire in 1974 when 3,274 acres burned. Forty-seven human-caused fires have burned an additional 6,385 acres, and 24 prescribed fires have restored 5,584 acres. Over 25% (34,477 acres) of the forest has been burned once. Reburns have been common and 6,884 acres have burned two times, 2,423 acres three times, 243 acres four times, and 13 acres five times. Fire return intervals are variable; some are very long because many of the stands are isolated by broad expanse of granite while others are short because of the presence of montane chaparral species that help spread fire. Taylor and Skinner (2001) reported a minimum fire return interval of four years, a median of 12 years, and a maximum of 96 years. If the maximum fire return interval is used, all of the type would have a FRID equal to zero (FRID_max =0). However, calculations based on the median fire return interval show that 15,929 acres have missed one interval (FRID_med =1), 3,970 acres have missed two (FRID_med =2), 326 acres have missed three (FRID_med =3), 2,709 have missed four (FRID_med =4), and 88,703 acres have missed five intervals (FRID_med =5). This indicates that some of the existing vegetation has an increased fuel load and altered stand structure due to fire exclusion.

Fuel Models

Fire behavior fuel models quantify the fuel bed characteristics and are used in fire behavior models to predict the likelihood of ignition, the rate of spread, and the intensity of fire in a vegetation type. Fuel models take into account fuel load, ratio of surface area to volume for each size class of fuel, the depth of the fuel bed, and fuel moisture, including the moisture at which a fire will not spread in that fuel. Fuels are roughly classified in Yosemite and El Portal as grass, brush, and conifers (map 3.2). For fire behavior analysis, each vegetation type is assigned to at least one fuel model, depending on its characteristics (table 3.3).

Table 3.3   Fuel Models and Vegetation Types of Yosemite and El Portal

Montane Chaparral

Montane chaparral covers 15,137 acres of the park, normally on south facing slopes ranging from 5,500 to 9,500 feet. Dominant species include greenleaf manzanita, pinemat manzanita, mountain white thorn, huckleberry oak, and, at lower­ elevations, bitter cherry and chinquapin. Mature stands form dense brush fields between one and five feet in height. Fuel Model 5 best describes montane chaparral fuels, although this model under predicts flame length (van Wagtendonk and Botti 1984). This community intergrades with Jeffrey pine, red fir, and white fir/mixed-conifer forest types. The size and extent of the community has probably decreased with fire suppression. However, existing conditions show mature fields with higher densities of Jeffrey pine than in the historic range of variability.

Since 1930, lightning has ignited 126 fires that have burned 2,651 acres of montane chaparral. Eleven human-caused fires have burned 1,175 acres and 22 prescribed fires have burned 755 acres. The largest lightning fire to burn in montane chaparral covered 641 acres during the Le Conte fire in 1999. Of the total acreage, 2,787 acres have burned once, 874 acres have burned twice, 185 acres have burned three times, and six acres have burned four times. Skinner and Chang (1996) reported fire return intervals from 10 to 75 years with a median of 30 years. Based on the maximum fire return interval, all of the type had a FRID of zero (FRID_max =0). However, the median return interval shows 430 acres that have missed one interval (FRID_med =1) and 11,293 acres have missed two intervals (FRID_med =2). This indicates that some of the existing vegetation has an increased fuel load and altered stand structure, including an increase of Jeffrey pine in unburned areas.

Lower Montane Forests

The lower montane zone, which includes giant sequoia, white fir, ponderosa pine/mixed-conifer forests, and ponderosa pine/bear clover forest, covers about 15% of the park. Dominant tree species include ponderosa pine, sugar pine, incense-cedar, and white fir. This zone also contains Douglas-fir/mixed-conifer forest, California black oak woodlands, canyon live oak forests, and dry montane meadows. The most common understory shrubs are white leaf manzanita and deerbrush.

Although the lower montane forest receive only 17% of the lightning strikes in the park, the mixed-conifer community experiences frequent, low-intensity fires (van Wagtendonk 1991). Nearly 100 years of fire suppression has resulted in a change from open forest to dense thickets of shade-tolerant tree species (including incense-cedar, white fir, and Douglas-fir) at the upper elevations of the zone and an increase in shrubs at the lower elevations. Under natural conditions, the return interval for fire is estimated to be from two to 35 years (NPS 1990b). Existing conditions, however, often generate fires of much greater intensity than under a natural fire regime.

Giant sequoia/mixed-conifer forest

Giant sequoia/mixed-conifer forest covers 218 acres in three groves found between 5,300 and 6,700 feet. Mariposa Grove, the largest of the groves, contains about 86% of the sequoias in the park. The giant sequoia type is a subset of the white fir/mixed-conifer forest, but because the ecological and cultural significance of this species this type is treated separately. The groves are Special Management Areas and are discussed in Chapter 1, Goals and Objectives. This type exists in micro sites that are remnants from extensive giant sequoia forests existing about 100,000 years ago (Raven and Axelrod 1979). Giant sequoia is currently limited in its distribution by soil moisture, water table, air temperature, and ecological tolerance of seedlings (Rundel 1972). The groves are wetter and more moist than typical in the white fir/mixed-conifer forest. Dominant species include giant sequoia, white fir, sugar pine, and incense-cedar. Broadleaf lupine and little-leaf ceanothus dominate the abundant shrub and herbaceous layer. Existing vegetation has more shade-tolerant seedling, pole, and small, overstory conifers, particularly white fir and incense-cedar, than would have been present historically. Fuel load averages 75 tons per acre and is evenly split between duff and woody fuels (van Wagtendonk et al. 1998). Fuel Model 8 best represents the giant sequoia forest, although Fuel Model 10 should be used for areas with heavy fuel concentrations.

Only one lightning fire has been recorded in the giant sequoia groves since 1930. That fire burned in the top of a single giant sequoia tree in 1976 and was extinguished. Two human-caused fires burned less than one acre. In 1971, prescribed burning in the groves started as a result of reports that fuel conditions threatened the survival of the giant sequoias. Since the initiation of the program, 14 prescribed fires have burned 241 acres in the Mariposa Grove, and three fires have burned nine acres in the Merced Grove. Of the three groves, 88 acres of giant sequoia have burned once, while 81 acres have burned twice, nine acres three times, two acres four times, and two acres five times. Swetnam et al. (1991) used fire scars to determine fire return intervals for giant sequoias and found a minimum value of three years, a maximum value of 15 years, and a median value of 10 years. Only 82 acres have departed one interval from the maximum value (FRID_max =1), while 45 acres have departed one interval (FRID_med =1) and 80 acres have departed two intervals from the median value (FRID_med =2). In addition, 36 acres surrounding the Clark Cabin have missed seven fire return intervals (FRID_med =7).  This shows that the recent burning in the groves has returned much of the area to within the natural range of variability.  However, in the areas that have moderate to high departures from the median FRID, increased fuel loading and altered stand structure are seen.

White fir/mixed-conifer forest

White fir/mixed-conifer forest covers 46,871 acres, forming an almost continuous band of dense forest between 5,500 and 7,500 feet in elevation. Conditions vary from almost pure stands of white fir on north facing slopes to white fir mixed with co-dominant sugar pine, Jeffrey pine, Douglas-fir, and incense-cedar. Existing vegetation has thickets of shade-tolerant seedling, pole, and small, overstory conifers, particularly white fir and incense-cedar, that would not have been present historically. These thickets and a lack of adequate seedbed have limited sugar and Jeffrey pine regeneration as well. Fuel loads vary from 33 tons per acre for Douglas-fir to 46 tons per acre for sugar pine; white fir and incense-cedar fall in between with 41 and 43 tons per acre, respectively (van Wagtendonk et al. 1998). Fuel Model 8 is generally appropriate for white fir/mixed-conifer forests, and Fuel Model 10 can be used where heavy fuels exist (van Wagtendonk and Botti 1984).

Since 1930, 569 fires have burned 28,407 acres of white fir/mixed-conifer forest. Out of that total, 427 lightning fires have burned 20,436 acres, 25 human-caused fires have burned 625 acres, and 13 prescribed burns have restored fire to 7,387 acres. Although 22,426 acres have not burned in over 70 years, 20,000 acres have burned once, 3,797 acres twice, 448 acres three times, and 18 acres four times. The largest area of white fir/mixed-conifer forest to burn with a single lightning fire was 1,092 acres in the Walker fire in 1988. The fire rotation for white fir forests based on lightning fires allowed to burn in the Prescribed Natural Fire Zone between 1972 and 1993 was 82 years (van Wagtendonk 1994). Fire return intervals range from three years to 35 years with a median of eight years (Skinner 2001). Departures from the maximum fire return interval included 274 acres that have missed one interval (FRID_max =1) and 22,429 acres that have missed two  (FRID_max =2). Based on the median fire return interval, 6,925 acres have missed one interval (FRID_med =1) and 2,928 acres have missed two intervals (FRID_med =2). Many areas have missed from three to seven intervals and 22,436 acres have missed eight intervals (FRID_med =8). Much of this vegetation type shows moderate to high departures from median fire return intervals. The fuel load has increased and stand structure has been altered by an increase of seedlings, poles, and small, overstory white fir and incense-cedar.

Ponderosa pine/mixed-conifer forest

Ponderosa pine/mixed-conifer forest covers 33,998 acres of the park and forms a fairly continuous band between 3,000 and 5,500 feet in elevation. In the El Portal Administrative Site, this type covers 146 acres on north facing slopes down to 1,800 feet. It intergrades with several other vegetation types including white fir/mixed-conifer forest at higher elevations and ponderosa pine/bear clover forest, California black oak woodland, foothill pine/live oak/chaparral woodland, canyon live oak forest, and foothill chaparral at lower elevations. Ponderosa pine is a dominant species with white fir and California black oak as co-dominants. Mariposa manzanita and deerbrush are often found in forest openings. Existing vegetation has thickets of shade-tolerant seedling, pole, and small, overstory conifers; particularly white fir and incense-cedar, that would not have been present historically. Incense-cedar and white fir have increased in dominance in the overstory tree canopy as well. Continued fire exclusion in this forest will cause a type conversion from ponderosa pine to incense-cedar and white fir dominated forests. Ponderosa pine surface fuels average 57 tons per acre for ponderosa pine, 41 tons per acre for white fir, 43 tons per acre for incense-cedar, and 12 tons per acre for black oak (van Wagtendonk et al. 1998).  Fuel beds dominated by ponderosa pine or black oak are best modeled by Fuel Model 9 (van Wagtendonk and Botti 1984). Surface fuels will continue to increase in the absence of periodic fire, and, combined with the thickets of understory vegetation, may lead to catastrophic fires.

In the ponderosa pine/mixed-conifer forest, fires burn regularly and with relatively low intensities. Since 1930, 341 lightning fires have burned 15,536 acres. Exclusive of the A-Rock and Steamboat fires in 1990, which were burning in unnaturally high surface and understory fuels under extreme weather conditions, the largest area of the park burned by a lightning fire in ponderosa pine/mixed-conifer forest occurred during the Eleanor fire in 1999 when 960 acres burned. The A-Rock fire burned 17 acres of this type in the El Portal Administrative Site. Nineteen human-caused fires have burned an additional 809 acres of the ponderosa pine/mixed-conifer type. This forest type has been the focus of much of the park’s prescribed fire program. Seventy-nine prescribed burns have restored fire to 10,976 acres in the park, and nine burns have restored fire to 32 acres in the El Portal Administrative Site. Although 14,300 acres have not burned, 12,609 acres have burned once, 6,178 acres twice, 792 acres three times, 45 acres four times, and two acres have burned five times.

The fire rotation for this type, based on the small number of acres of ponderosa pine forests that were allowed to burn in the Prescribed Natural Fire Zone between 1972 and 1993, is 138 years (van Wagtendonk 1994). Compared to calculated fire return intervals, this number is unexpectedly high and indicates that these forests are falling further and further behind in maintaining their natural fire regime. Fire return intervals are short in this type, ranging from a low of three years to a high of 14 years, with a median of nine years (Kilgore and Taylor 1979). Departures from the maximum fire return interval range up to five missed intervals (14,399 acres) while the highest number of missed median return intervals is seven (14,403 acres). Much of this vegetation type shows moderate to high departures from median fire return intervals. The fuel loads has increased and stand structure altered by an increase of seedlings, poles, and small, overstory white fir and incense-cedar. Stands will be converted to white fir/mixed-conifer forest if fire is not reintroduced throughout the type. 

Ponderosa pine/bear clover forest

Ponderosa pine/bear clover forest covers 33,846 acres of the park’s south and west facing slopes and ridgelines between 3,000 and 5,500 feet. It intergrades with ponderosa pine/mixed-conifer forest at higher elevations and with California black oak, foothill pine/live oak/chaparral woodland, canyon live oak forest, and foothill chaparral at lower elevations. Ponderosa pine is a dominant species with California black oak and canyon live oak as common associates. The type is characterized by areas of almost continuous understory of bear clover. Existing vegetation has thickets of shade-tolerant seedling, pole, and small overstory conifers, particularly white fir and incense-cedar, that would not have been present historically. Incense-cedar and white fir have increased in dominance in the overstory tree layer. The vigor of California black oak overstory trees has been reduced and regeneration of this species is uncommon. Natural fuel loads were kept relatively low by periodic low intensity surface fires, but are currently accumulating in unburned areas. Typical fuel loads are 47 tons per acre for ponderosa pine and in areas where bear clover is present Fuel Model 2 is the best fit (van Wagtendonk and Botti 1984, van Wagtendonk et al. 1998). There is a large potential for type conversion due to the unnaturally high fuel loads and effects of high severity fires.

Fire is common in the ponderosa pine/bear clover forest. Between 1930 and 2000, 247 lightning fires burned 19,160 acres, 59 human-caused fires burned 1,494 acres, and 121 prescribed fires burned 11,619 acres. The largest lightning fire other than the A-Rock fire burned 1,247 acres in this type in 1987. Combined, these fires have resulted in 12,441 acres burning once, 7,201 acres burning twice, 1,731acres burning three times and 295 acres burning four times. An additional 40 acres have burned from five to seven times. Caprio and Swetnam (1991) reported a minimum fire interval of two years, and median of four years, and a maximum of 6 years. Because of the relatively short fire return intervals and years of fire suppression in this type, 12,169 acres have missed up to 11 maximum return intervals (FRID_max =11) or 17 median intervals (FRID_med =17). Much of this vegetation type shows moderate to high departures from median fire return intervals. The fuel load has increased and stand structure altered by an increase of seedlings, poles, and small, overstory white fir and incense-cedar.  California black oak will continue to decrease in number and stands will be converted to white fir/mixed-conifer forest if fire is not reintroduced throughout the type. 

California black oak woodland and forest

From 4,000 to 6,000 feet in elevation, 3,156 acres of the park are covered in California black oak woodland and forest. These are in almost pure stands or as the co-dominant species. It intergrades with ponderosa pine/bear clover at higher elevations and foothill pine/live oak/chaparral woodland and canyon live oak forest at lower elevations. It is rarely found without Ponderosa pine as a component. Other common trees found in this type include, incense-cedar and canyon live oak. Bear clover is a common shrub in this type, which often has a well developed understory. The extent and vegetation in this type have been severely altered by decades of fire suppression and the change in fire regime brought about by other human influences. This type composes less than 0.5% of all park land. In Yosemite Valley, black oak woodlands are estimated to cover less than 10% of the area indicated by 1860's photographs (Gibbens and Heady 1964). Existing vegetation has thickets of shade-tolerant seedling, pole, and small overstory conifers, particularly white fir and incense-cedar, that would not have been present historically. Ponderosa pine and other species now dominate the overstory while the vigor of California black oak overstory trees is reduced and regeneration of this species is uncommon. Fuel loads are low (12 tons per acre) underneath black oaks, and Fuel Model 9 is appropriate for those locations.

Because of the low fuel loads, low intensity surface fires with flame lengths less than one foot are typical. Only 24 lightning fires have ignited in the California black oak forest since 1930, and these fires burned only 353 acres. Three human-caused fires have burned an additional 81 acres, and 22 prescribed fires have been used to restore 868 acres of black oak forest. Repeated prescribed burning has resulted in some areas of black oak burning two or three times 158 acres and 27 acres, respectively). However, most the type has not burned at all (2,012 acres) or burned only once (959 acres). Fire return intervals are difficult to determine, but Stephens (personal communication; Skinner and Chang 1996) believes that intervals from two to 18 years with a median of eight years would be appropriate. Based on those estimates, 2,013 acres of California black oak forest have a maximum FRID of three (FRID_max =3) and a median FRID of eight (FRID_med =8). Two thirds of this type has not burned and shows high departures from median fire return intervals.  The fuel load has increased and stand structure altered by an increase of seedlings, poles, and small, overstory white fir and incense-cedar.  California black oak will continue to decrease in number and stands will be converted to ponderosa pine/mixed-conifer forest if fire is not reintroduced throughout the type. 

Canyon live oak forest

Canyon live oak forest covers 21,344 acres of the park on both north- and south-facing talus slopes. It often forms pure or almost pure stands between 2,500 and 5,000 feet in elevation. In the El Portal Administrative Site, the type covers an additional 129 acres down to 1,900 feet. Structure of the forest varies from low shrub-like trees on south-facing slopes to erect forest up to 65 feet in height in more mesic sites. Canyon live oak is the dominant species with some incense-cedar and California laurel but little understory vegetation. Information about historical vegetation composition and patterns for this type is lacking (SNEP 1996). Because of this we are unable to compare existing vegetation with a historic range of variability. Photographs of this type taken in the 1860s and 1870s in Yosemite Valley indicate that communities are denser today. Fuels have not been quantified in this type, but loads of up to 25 tons per acres seem reasonable. Fuel Model 5 is used for crown fires, while surface fires are best characterized by Fuel Model 8.

Frequent torching and occasional crown fires are typical for canyon live oak. Between 1930 and 2000, these forests have been ignited 108 times by lightning—the fires burned 10,510 acres. Human-caused fires are less common but larger. In Yosemite, 21 human-caused fires have burned 5,001 acres. A total of 22 prescribed fires in canyon live oak forests have burned 2,025 acres. Over half of the type in the park has been burned once (4,871 acres) or twice (5,596 acres), while only 661 acres have burned three times, and 94 acres have burned four times. No fires have burned in canyon live oak in the El Portal Administrative Site since 1930. The Le Conte fire burned 3,517 acres of canyon live oak forest in 1999. Taylor and Skinner (2001) determined fire return intervals for canyon live oak that range from seven years to 39 years with a median of 13 years. Departures from the maximum return interval include 10,615 acres that have missed only one interval (FRID_max =1). However, half of this type shows high departures from median fire return intervals.  The fuel load has increased and stand structure has been altered.

Meadow

Montane meadow

Montane meadows cover 1,530 acres from 4,000 to 6,000 feet in elevation on fine-textured, continuously moist or wet soils. Some of these meadows dry out late in the growing season. This type is made up of grasses and sedges with sedges predominating in wetter areas. These areas are generally less than 100 acres in size and normally surrounded by California black oak or ponderosa pine/mixed-conifer and ponderosa pine/bear clover forest. Fuel loads are usually less than one ton per acre, making Fuel Model 1 the appropriate model.

Most of Yosemite’s meadows are also classified as wetlands. They are included in this discussion of montane meadows to assure that fire management activities are discussed as they relate to all fire-dependent communities, including meadows. Meadows are also discussed under the heading wetlands, but meadows are only one of the types of sites that fall under that heading.

These meadows compose less than 0.5% of all park land and are ecologically and culturally significant. All areas have had severe encroachment by conifer species. One study of Yosemite Valley estimates that at least 50% of the meadows have succeeded to forest in the last 120 years (Ernst 1961). There is little information about historical vegetation composition and patterns for this type (SNEP 1996) so we are unable to compare existing vegetation with historic conditions. Kentucky bluegrass and other a non-native cool season grasses and non-native forbs are found throughout many of the montane meadows. Many of these communities, particularly in Yosemite Valley, have been altered by development and/or alteration of the hydrologic regime. Intensive ecological restoration efforts are on going in some of these areas.

Fires can burn rapidly through the grasses and flame lengths can range from two to 10 feet. Only 16 lightning fires have occurred in this type since 1930. Those fires burned 421 acres. The largest lightning fire burned 35 acres of meadows in the Walker fire in 1988. Humans have caused three meadow fires, which burned 54 acres. Meadows have been burned with 36 prescribed fires for a total of 433 acres. Over one-fourth of the acres (402) have burned once, while another 218 acres have burned twice or more. Fire return intervals are low in areas that were maintained by American Indians; in other areas the interval was more likely determined by the adjacent forest. Anderson (1993) reported anthropocentric fire regimes of from one to five years with a median of two years. Such short return intervals produce maximum departures of one for 911 acres of meadows (FRID_max =1) and median departures of 35 (FRID_med =35) for the same 911 acres. Most of the meadows show high departures from median fire return intervals.  Fuel loads have increased and encroachment has altered much of this type. 

Foothill Woodlands

The foothill woodlands zone includes foothill pine/live oak/chaparral woodland, foothill chaparral, and blue oak woodland vegetation types (SNEP 1996). This zone covers about 5% of the park at 1,700 to 6,000 feet elevation. Dominant tree species include California black oak, foothill pine, canyon live oak, interior live oak, and blue oak. Many of the vegetation types are better recognized by the dominant shrubs which include redbud, poison oak, various manzanitas, deerbrush, buckbrush, and mountain mahogany. Only 2% of the park’s recorded lightning strikes hit the foothill zone (van Wagtendonk 1991). Even when made proportional to the size of the zone, only 8% of the strikes occur there—but when lightning fires occur they spread quickly and burn intensely.

Foothill pine/live oak/chaparral woodland

The foothill pine/live oak/chaparral woodland covers 6,985 acres in Yosemite and 372 acres in the El Portal Administrative Site. It is found on canyon sides and open rocky areas between 2,200 and 6,000 feet. The type covers a fairly contiguous area around Hetch Hetchy and Poopenaut Valleys. Dominant species include foothill pine, canyon live oak, interior live oak, Mariposa manzanita, deerbrush, buckbrush, and mountain mahogany. Little information about historical vegetation composition and patterns (SNEP 1996) exists so it is not possible to compare existing vegetation with historic vegetation condition or extent. This community has been invaded by cheat grass and other non-native annual grasses. Fuel loads can reach 22 tons per acre for foothill pine but are usually much lower (van Wagtendonk et al. 1998). In most cases, Fuel Model 5 depicts fire behavior in this type, but if brush over six feet tall is present Fuel Model 4 is a better fit.

Fires spread quickly and often torch and crown in trees and brush in the foothill pine/live oak/chaparral woodlands. Lightning is infrequent. Since 1930, 34 lightning fires have burned 8,514 acres in the park, and the A-Rock fire burned 41 acres of the type in the El Portal Administrative Site. Five human-caused fires have burned 1,424 acres in Yosemite, and three have burned 17 acres in El Portal. Only three prescribed burns have been conducted in these woodlands in the park covering 302 acres, while none have been ignited in El Portal. Over 90% of the foothill pine/live oak/chaparral woodland has burned during the past 70 years, leaving only 607 acres unburned. A total of 3,637 acres in the park have burned one time, 2,340 acres have burned two times, 312 acres have burned three times, and 90 acres have burned four times. In El Portal, 29 acres have burned once and 17 acres have burned twice. The small area burned in the Prescribed Natural Fire Zone in this type resulted in a fire rotation of 615 years, considerably longer than the fire return interval (van Wagtendonk 1994). McClaran and Bartolome (1989) determined that the minimum fire return interval for the woodlands was two years, the maximum 49 years, and the median eight years. Based on maximum intervals, 657 acres have missed one interval  (FRID_max =1). Median departures ranged from 189 acres missing one interval (FRID_med  =1) to six acres having missed two (FRID_med = 2). It is assumed that the fuel load and stand structure are not significantly altered from the natural range of variability.

Foothill chaparral

Foothill chaparral covers 1,768 acres of the park on the north side of the Merced River Canyon between 1,600 and 5,000 feet in elevation and 17 acres in the El Portal Administrative Site near the park boundary. Manzanita, whitethorn, buckbrush, deerbrush, mountain mahogany, and interior live oak are all types of shrubs that occur in chaparral. This type grows on rocky dry sites on steep slopes with little soil and seldom has any understory vegetation. There is little information about historical vegetation composition and patterns for this type (SNEP 1996) and it is not possible to compare existing vegetation with historic vegetation. It is assumed that fire suppression has significantly altered typical species diversity and the age class mosaic that would have existed in this community under a natural fire regime. Fuel loads can reach 13 tons per acre but are usually much lower. In most cases, Fuel Model 5 depicts fire behavior in this type, but if brush over six feet tall is present, Fuel Model 4 is a better fit.

Between 1930 and 2000, seventeen lightning fires burned 520 acres of the foothill chaparral type in the park, and all 17 acres in El Portal were burned by the A-Rock fire. Other than the A-Rock Fire, the largest lightning fire to burn in this type in the park covered 43 acres during the Stanislaus Complex fires in 1987. Three human-caused fires in the park burned 25 acres, while six prescribed fires burned another 110 acres. In El Portal, the only human-caused fire was the Canyon fire that burned 12 acres in 1968. There have been no prescribed fires in foothill chaparral in El Portal. Although 1,243 acres of foothill pine/live oak/chaparral have not burned, 503 acres have burned once, and 39 acres have burned twice, including 12 acres in El Portal that were burned by the A-Rock Fire but which had previously burned in the Canyon Fire. Reported fire return intervals include a median interval of 30 years and a maximum interval of 60 years (SNEP 1996). Maximum departures of one interval occurred on 1,243 acres in the park (FRID_max =1), while median departures of two intervals occurred on those same acres (FRID_med =2). In El Portal, the type was within one fire return interval (FRID_max =0). The natural mosaic of fuel load and patch ages may be moderately altered from the natural range of variability.

Blue oak woodland

Blue oak woodland covers 473 acres on the north side of the Merced River Canyon between 1,700 and 2,600 feet in elevation in the El Portal Administrative Site. Blue oak, interior live oak, foothill pine, California buckeye, and poison oak are the common woody species. A grassy understory is composed of non-native annual grasses and some native forbs. The grassy understory is the dominate ground cover between widely spaced shrubs and trees. Yellow star thistle, an invasive non-native, is also found in this type. There is little information about historical vegetation composition and patterns for this type (SNEP 1996) and we are unable to compare existing vegetation with a historic range of variability. Because non-native annual grasses have invaded the community, it can be assumed that the composition and structure of this grassland is significantly different than the native grassland. Fire suppression may have increased the density of shrub and trees in this area as well. Fuels are sparse and Fuel Model 1 best approximates fire behavior in this type.

Fires burn rapidly through the light fuels with flames from two to 10 feet in length. Since 1930, only two lightning fires have burned 315 acres of blue oak woodland; 311 acres were in the A-Rock fire alone. An additional 120 acres have been burned by three human-caused fires, and seven prescribed fires have burned 62 acres. A total of 208 acres have burned once, and re-burns have occurred twice on 135 acres and three times on 16 acres. The fire return intervals derived by McClaran and Bartolome (1989) for foothill pine/live oak/chaparral are used for blue oak woodland. All areas were within the maximum departures (FRID_max =0), while the median fire return interval showed 322 acres missing one interval (FRID_med =1), 21 acres missing two intervals (FRID_med =2), and 114 acres missing four intervals (FRID_med =4). The natural mosaic of fuel load and patch ages may be moderately altered from the natural range of variability.

Wetlands

This heading addresses areas that have attributes of wetlands, some of which do not sustain fire-dependent plant communities, but do nonetheless, require protection or consideration during fire management activities. Most meadows are considered wetlands, and thus, they are included in this discussion, as well as under Vegetation and Fire Ecology.  Wetlands, as defined by the U.S. Fish and Wildlife Service and adopted by the National Park Service, are lands transitional between terrestrial and aquatic systems, where the water table is usually at or near the surface or the land is covered by shallow water. These ecosystems act to buffer hydrologic and erosional cycles, control and regulate biogeochemical cycles of nitrogen and other key nutrients, and create unique microclimates for animal species (Rundel 1998). Wetland types in Yosemite include meadows, and wet areas along rivers, streams, lakes, and ponds. Wetlands greater than five acres  were mapped through interpretation of aerial photography by the US Fish and Wildlife Service in 1995 as part of the National Wetlands Inventory (USFWS 1995). For the purposes of the Draft Yosemite Fire Management Plan/EIS meadows and riparian areas were classified according to the surrounding vegetation type. Montane meadows are also addressed under Vegetation and Fire Ecology due to their ecological and cultural significance. Wetlands burn infrequently and are unlikely to play a role in fire ignition or maintenance. However, they are important in inhibiting fire spread. When wetlands do burn the fire usually spreads into them from adjacent vegetation.

Wildlife

Wildlife in Yosemite National Park is diverse and abundant, reflecting the wide range of Sierra Nevada habitats and vegetation types that are in relatively intact condition (table 3.4). Areas of concentrated human use in Yosemite and the El Portal Administrative Site have affected wildlife and their habitats, primarily by displacing animal populations that may have once been much more abundant. Fire suppression for over 70 years has significantly impacted habitat, also affecting wildlife populations.

Forest habitats and microclimates are in part created by forest structure. Structure is influenced by fire, or a lack of fire. For example, a stand replacement fire opens the forest and changes vegetation composition and thus, habitat, while fire suppression may allow the forest to fill with dense underbrush, again changing the habitat. Catastrophic events may replace large areas of old growth with plant communities not seen in those areas for many decades. Animals that use mature forests will likely leave the area and animals that favor more open vegetation will move in. Following a stand replacement fire, deerbrush ceanothus and greenleaf manzanita are early seral species that provide high quality forage for deer.

Wildlife populations respond to fire-caused habitat changes in many ways. If increased nutrients follow a fire, vegetation production will increase and it is likely that herbivores and other animals relying on the increase in nutrients will move into the area. If a change in forest structure creates favorable conditions for a prey species to increase substantially, the predators that rely on this prey will soon increase in numbers. Similarly, if the structure of a forest is deteriorating in condition, due to the absence of natural changes, certain wildlife species may move out because they cannot find the requirements to live. Many elements required by wildlife are increased or reduced by the presence or absence of fire.

The greatest impacts to wildlife and habitat from fire are those from fires exhibiting behavior that is unnatural to the fire regime for that area. Forest conditions conducive to large stand- replacement fires hold the biggest threat to wildlife because mature old growth forests can be converted to early seral stage communities more often and over a larger area then historically occurred. During and after these large, high-intensity fires there is significant displacement of wildlife. Yosemite National Park protects sizable tracts of old growth forest types that have disappeared from much of the Sierra Nevada because of logging. These protected habitats benefit California spotted owls (Verner et al. 1992), northern goshawk (Maurer 2000) and many other wildlife species that are dependent on them. Although logging no longer occurs in Yosemite, old growth habitats are at risk of catastrophic fire because of the long history of fire suppression in Yosemite and surrounding forests.

Habitat

For wildlife populations to be viable, resources and environmental conditions must be sufficient for animals to forage, hide, nest or den, and disperse. Distribution, types, and amounts of territory, shelter, and food must be sufficient for the needs of viable populations daily, seasonally, and annually. Habitat must be well distributed over a broad geographic area to allow breeding individuals to interact spatially and temporally within and among populations.

The burned area often responds beneficially within two or three growing seasons. The fire management program in Yosemite is a landscape level program applied to allow natural processes to maintain heterogeneity of the vegetation and wildlife in the park. Fire in its natural role would create and maintain a mosaic of different kinds and age structures of the native vegetation types. As of the year 2001, the habitat associated with the lower montane forests is that most impacted by fire exclusion prior to 1970.

Fire exclusion or altered fire regimes have two major effects on wildlife habitat that cause significant population shifts. As fire is excluded, there becomes a greater continuity and abundance of late-successional plants. This reduces open space and creates landscapes with extensive ladder fuels and nearly continuous thickets of dense tree regeneration. The results of this are not clearly known but it can be postulated that the composition of wildlife that once occupied these areas has likely been shifting with this increased biomass.

Mammals

Approximately 85 native mammalian species in six families inhabit Yosemite . Of the insectivore family, five shrews and one mole live here. Seventeen species of bats inhabit the forests and cliffs of Yosemite, nine are either California species of special concern or federal species of concern. Many of these bat species depend on riparian and meadow habitats for foraging and large trees or snags for roosting. Carnivores include black bears, bobcats, coyotes, raccoons, weasels, gray foxes, mountain lions, and ringtails. Six species of squirrels, eight species of chipmunks, eight species of mice, and other species of rodents, including wood rats, voles, gophers, and porcupines inhabit the park and El Portal. Yosemite’s largest mammal, the grizzly bear, was extirpated from the region and from the state in the 1920s. There are two native species of hoofed mammals: the Sierra Nevada bighorn sheep and mule deer. Other mammal species that occur but are rarely seen are the fisher, wolverine, and Sierra Nevada red fox.

Birds

Yosemite’s wide range of elevations and habitats