mixed conifer forests were comprised of large, thick-barked, fire-resistant trees, which were widely spaced with open understories. Fire suppression throughout the Sierra in the past century has greatly reduced the number and frequency of beneficial, low- to moderate-intensity fires that may have burned for weeks, or even months, cleansing the forest of the excess buildup of “ladder fuels” such as dead branches, small trees, and brush that fuel severe crown fires. There has also been a widespread increase in shade-tolerant tree species such as incense cedars and white firs within formerly pine-dominated stands.
In unburned and/or unlogged mixed conifer forests, huge conifers provide nesting habitat for Northern Goshawks, Spotted and Great Horned Owls, and foraging habitat and singing perches for Western Tanagers, Black-headed Grosbeaks, and Warbling Vireos. Hermit Warblers sound their buzzy songs from the deeper, shaded woods while White-headed and Pileated Wood-peckers call loudly from ancient snags. Golden-crowned Kinglets thrive in these forests, whispering high-pitched notes throughout the day.
FIGURE 3 Upper Conifer zone
Red Fir Forests
North 6,500 to 8,500 feet; South 7,000 to 9,000 feet
Red fir forests receive the heaviest Sierra snows. In these shady groves deep drifts often last long into summer, gradually releasing moisture into the soil. Small numbers of red firs grow on north slopes in the mixed conifer zone, but higher up their dark, silent columns reign supreme. Entire forests consist of only these trees, with rings of chartreuse lichen circling their trunks above the snow line. Often lodgepole and western white pines are mixed in, as are white firs at the lower edge of these forests. Particularly common in the northern and central Sierra, red firs grow only in limited areas farther south. At Porcupine Flat and Badger Pass in Yosemite and near Soda Springs on Interstate 80, impressive stands of red firs and lodgepole pines grow together. Lodgepole pines may form extensive stands in this zone, particularly in cold sites, around meadows, and on dry, rocky slopes. Heavy snows and deep forest litter prevent much growth of shrubs, grasses, or flowers; most birds in red fir forests search bark surfaces and sprays of conifer needles for food.
Red fir forests often seem lacking in birds, but if one listens carefully, rhythmic tapping of Williamson’s Sapsuckers may be heard. The characteristic sounds of Mountain Chicka-dees, Hermit Thrushes, Townsend’s Solitaires, Yellow-rumped Warblers, and Golden-crowned Kinglets echo through towering trees, and the complex, hyperspeed song of Pacific Wrens rises from the deep drainages. Flocks of Pine Siskins, Red Crossbills, or Evening Grosbeaks may fly overhead. Open areas with shrubs, wildflowers, and grasses draw Dark-eyed Juncos, Chipping Sparrows, and Cassin’s Finches that search the ground for insects and seeds. Some “edge” species such as Mountain Quail and “Mountain” White-crowned Sparrows use trees and shrubs for cover but feed in open areas nearby. At dusk, listen for the peents and booms of Common Nighthawks overhead and, as darkness comes, the incessant tooting of Northern Saw-whet Owls.
Mountain Chaparral
North 4,500 to 8,500 feet; South 5,000 to 9,500 feet
Brushfields of huckleberry oak, greenleaf manzanita, snowbrush, or chinquapin occupy steep, rocky slopes or forest clearings created by treefalls, logging, or fire. Especially prevalent on south-facing exposures, montane chaparral habitats may grow in impenetrable thickets but can be quite open on steep slopes or recently established sites. Some soil types are capable of only supporting chaparral. Although usually dry, these shrubfields are cooler than their foothill counterparts. Widespread above the foothills, montane chaparral habitats can be easily seen along Interstate 80 near Dutch Flat, Highway 120 west of Crane Flat in Yosemite, and on the slopes below Giant Forest in Sequoia National Park. Here the whistled melodies of Fox Sparrows may mingle confusingly with the similar songs of Green-tailed Towhees. Although they are often found in moist streamside habitats, Yellow Warblers and MacGillivray’s Warblers also nest in montane chaparral. Mountain Quail sneak through the underbrush and nest under this protective cover. At the edges where chaparral meets forest, you may find species such as Dusky Flycatchers and Western Wood-Pewees.
In some places, montane chaparral is an early stage of succession following a stand-replacing fire, destined to be gradually replaced by forest. In other spots, where the soils cannot support forest, the chaparral may represent a relatively permanent condition.
SUBALPINE ZONE
Lodgepole Pine Forests
North 7,500 to 9,000 feet; South 8,000 to 9,500 feet
Mountain lakes and springs spawn tiny streams that meander through meadow grasses and open stands of lodgepole pine. These pines also grow in dense groves that dominate the Subalpine zone, especially in the northern and central Sierra on both slopes, where they are sometimes joined by mountain hemlocks. Here and there, majestic specimens of western juniper occupy isolated, prominent cliffside locations. These trees, second only to the giant sequoia in longevity among Sierra trees, often bear the scars of numerous lightning strikes. Echo Summit (U.S. 50), Donner Summit (Interstate 80), and Tuolumne Meadows in Yosemite National Park have good examples of lodgepole pine forests. Hardy Mountain Chickadees reside in these forests year-round, moving along sprays of conifer needles and swinging down to inspect them from below. Dusky Flycatchers and Ruby-crowned Kinglets sound their familiar calls from forest edges and open ridge lines, while flocks of Red Crossbills and Pine Grosbeaks rove the treetops, even in winter. Hairy and Black-backed woodpeckers along with Williamson’s Sapsucker and Northern Flickers attack dead and dying lodgepole pines.
Lodgepoles growing at the edges of wet meadows and streams provide important nesting strata and cover for species closely associated with riparian habitats (this includes many migrating Neotropical songbirds such as flycatchers, vireos, warblers, and so on). The abundance of nesting and migratory songbirds draws predatory birds such as Cooper’s and Sharp-shinned Hawks, and Northern Goshawks. These hawks may nest in lodgepole pine forests but more frequently use them as hunting sites for ambushing prey, primarily birds but also rodents.
Subalpine Pine Forests
North 9,000 to 10,000 feet; South 9,500 to 11,500 feet
Backpackers head for these high forests where serrated ridges, perpendicular cliffs, and massive granite domes form spectacular vistas. On both sides of the Sierra, wind-sculpted whitebark pines grow with stunted lodgepoles on exposed ridges and north-facing slopes up to treeline. In the southern Sierra, erect stands of foxtail pine largely replace the gnarled whitebarks. The higher slopes of the Great Western Divide in Sequoia and Kings Canyon National Parks and the areas near Tioga Pass in Yosemite National Park have good examples of subalpine pine forests. Clark’s Nutcrackers and Pine Grosbeaks bound from tree to tree searching for pine nuts but dive for cover if the shadow of a Prairie Falcon skims by. Mountain Bluebirds, Dark-eyed Juncos, and “Mountain” White-crowned Sparrows forage in open, rocky areas. Here they are also joined by Common Ravens that prey on small birds and their eggs and nestlings and search for road-killed animals along high mountain roads.
FIGURE 4 Subalpine zone
ALPINE ZONE
Alpine Fell-Fields
North 8,500 to 10,800 feet; South 9,500 to >14,500 feet
The line of demarcation between the upper subalpine pine forests and treeless Alpine meadows is known as “timberline,” the point where trees cease to exist because of extremes in climate, shallow rocky soils, and high elevation. Here, freezing temperatures are possible any day of the year, and even the intense high-elevation sun does little to warm the cool, clear air.
