Читать книгу Hike the Parks Sequoia-Kings Canyon National Parks - Scott Turner - Страница 18

In the early 1960s, park foresters began to recognize that sequoias were not reproducing as expected. Before receiving federal protection, fires rolled through sequoia groves, clearing out competing vegetation and setting the stage for regeneration. Fire suppression, therefore, eliminated the ability of the tree to regenerate while creating clusters of smaller trees, which allowed fires to climb into the sequoias’ crowns. Today, the parks set periodic controlled fires to clear out the competing understory and allow the sequoia to regenerate. Most controlled burns occur during the early summer over a small area, usually about 150 acres (60 hectares).

Chaparral. Chaparral, a low-growing scrub and shrub community, tends to occupy sunny, south-facing slopes in the lower elevations. Most chaparral species have evolved tough, leathery foliage that maximizes the plants’ ability to retain moisture. Principal species within chaparral communities include chamise, ceanothus (lilac), manzanita, scrub oak, flannel bush, and a number of flowering vines and annual flowers.

Oak Woodland. Woodlands are low-density forests often of nonconiferous trees that proliferate throughout the foothills. As elevation increases, the species composition changes. Lower elevation woodlands feature open stands of deciduous blue oaks, interior live oaks, and California buckeye. At higher elevations, from 2500 feet (760 m) to 4000 feet (1220 m), canyon live oaks and California bay laurel replace blue, live, and valley oaks. Above 4000 feet, conifers and the deciduous black oak begin to appear among everdenser woodlands of broadleaf evergreens.

Riparian Woodland. The word riparian means “water loving,” and plants within this community depend on reliable sources of water to survive. In the foothills, you will find sycamores, maples, alders, cottonwoods, and willows forming dense gallery forests with a thriving understory of lush ferns, herbs, and flowers. Within the yellow pine forest, watercourses and meadows support black cottonwood, willows, and occasional groves of quaking aspens. In the red fir–lodgepole belt and subalpine habitats, larger groves of quaking aspen join black cottonwood along watercourses, particularly in meadows. The foliage of the quaking aspen, which gets its name for the leaves’ tendency to shimmer in the slightest breeze, changes into a variety of brilliant colors during early autumn.

Mixed-Conifer Forest. The western Sierra Nevada contains two distinct bands of mixed-conifer forest: the yellow pine belt (also known as lower montane forest), which thrives between 5000 feet (1500 m) and about 7500 feet (2290 m), and the red fir–lodgepole belt (also known as upper montane forest), which blankets the elevations from 7500 feet (2290 m) to 9500 feet (2900 m). These forest belts take their names from the predominant tree species. Yellow pine refers to a class of pines that includes ponderosa pines in lower elevations and Jeffrey pines in higher elevations. The yellow pine belt also includes white firs, sugar pines, incense cedars, black oaks, and sequoias. Red fir and lodgepole pines characterize the higher belt, although you will also find Western junipers, Western white pines, and Jeffrey pines. The two conifer belts receive the greatest amounts of precipitation in the parks, with the yellow pine belt averaging between 30 and 45 inches (75 and 115 cm) annually and the red fir–lodgepole belt averaging between 60 and 90 inches (150 and 230 cm) annually.

A tiger swallowtail sampling nectar from a Western wallflower

Meadows. Meadows tend to occur in depressions bounded by granitic masses. Water flowing through these depressions creates marsh conditions where trees cannot grow. A rich mixture of grasses creates brilliant-green open spaces dotted by a wide variety of wildflowers. Given this mixture of succulent vegetation, meadows tend to attract more wildlife than any other part of the forest. Visit a meadow early in the morning or early in the evening, and you stand a good chance of spotting deer, black bears, and other forest creatures.

Subalpine and Alpine Habitat. As the elevation increases, temperatures grow colder to a point most conifers cannot tolerate. Shorter growing seasons and lingering snow packs tend to reduce understory plants to grasses and wildflowers. The subalpine zone, a narrower coniferous belt ranging from about 9500 feet (2900 m) to the tree line at 10,500 to 11,000 feet (3200 to 3350 m), features conifers of dwindling size and density, including Western white pines, lodgepole pines, and ancient foxtail pines that live for up to three thousand years. At tree line, most trees become little more than shrubs that often grow in a prostrated form known as krummholz, until they disappear entirely at the boundary of icy alpine habitats that lie beneath snow for most of the year.