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Monday, September 23, 2013
Grand Canyon National Park
Grand Canyon National Park, a World Heritage Site, encompasses 1,218,375 acres and lies on the Colorado Plateau in northwestern Arizona. The land is semi-arid and consists of raised plateaus and structural basins typical of the southwestern United States. Drainage systems have cut deeply through the rock, forming numerous steep-walled canyons. Forests are found at higher elevations while the lower elevations are comprised of a series of desert basins.
Well known for its geologic significance, the Grand Canyon is one of the most studied geologic landscapes in the world. It offers an excellent record of three of the four eras of geological time, a rich and diverse fossil record, a vast array of geologic features and rock types, and numerous caves containing extensive and significant geological, paleontological, archeological and biological resources. It is considered one of the finest examples of arid-land erosion in the world. The Canyon, incised by the Colorado River, is immense, averaging 4,000 feet deep for its entire 277 miles. It is 6,000 feet deep at its deepest point and 18 miles at its widest. However, the significance of Grand Canyon is not limited to its geology.
Over 1,500 plant, 355 bird, 89 mammalian, 47 reptile, 9 amphibian, and 17 fish species are found in park. The Park containsseveral major ecosystems. Its great biological diversity can be attributed to the presence of five of the seven life zones and three of the four desert types in North America. The five life zones represented are the Lower Sonoran, Upper Sonoran, Transition, Canadian, and Hudsonian. This is equivalent to traveling from Mexico to Canada. The Park also serves as an ecological refuge, with relatively undisturbed remnants of dwindling ecosystems (such as boreal forest and desert riparian communities). It is home to numerous rare, endemic (found only at Grand Canyon), and specially protected (threatened or endangered) plant and animal species. The Grand Canyon is considered one of the natural wonders of the world largely because of its natural features. The exposed geologic strata - layer upon layer from the basement Vishnu schist to the capping Kaibab limestone - rise over a mile above the river, representing one of the most complete records of geological history that can be seen anywhere in the world. Geologic formations such as gneiss and schist found at the bottom of the Canyon date back 1,800 million years. This geologic incline creates a diversity of biotic communities, and five of the seven life zones are present in the park.
The entire park area is considered to be semi-arid desert, but distinct habitats are located at different elevations along the 8,000 foot elevation gradient. Near the Colorado River, riparian vegetation and sandy beaches prevail. Just above the river corridor a desert scrub community exists complete with a wide variety of cacti and warm desert scrub species. A pinyon pine and juniper forest grows above the desert scrub up to 6,200 feet, while between 6,200 feet and 8,200 feet ponderosa pine is abundant. On the North Rim at elevations above 8,200 feet, a spruce-fir forest tops out the park.
As in all natural habitats, the type and abundance of organisms is directly related to the presence or absence of water. The Colorado River and its tributaries, as well as springs, seeps, stock tanks and ephemeral pools provide oases to flora and fauna in this semi-arid southwest desert area.
The arid climate has been a benefit to the Paleontological resources of the park. The dry climate has been instrumental in preserving many prehistoric fossils deep within caves in Grand Canyon's geologic formations.
There are approximately 1,737 known species of vascular plants, 167 species of fungi, 64 species of moss and 195 species of lichen found in Grand Canyon National Park. This variety is largely due to the 8,000 foot elevation change from the river up to the highest point on the North Rim. Grand Canyon boasts a dozen endemic plants (known only within the Park's boundaries) while only ten percent of the Park's flora is exotic. Sixty-three plants found here have been given special status by the U.S. Fish and Wildlife Service.
Grand Canyon National Park contains 129 vegetation communities, and the composition and distribution of plant species is influenced by climate, geomorphology and geology.
Colorado River vegetation
Along the Colorado River and its perennial tributaries, a riparian community exists. Coyote willow, arrowweed, seep willow, western honey mesquite, catclaw acacia, and exotic tamarisk (saltcedar) are the predominant species. Hanging gardens, seeps and springs often contain rare plants such as the white-flowering redbud tree, stream orchid, and McDougall's flaveria.
Blackbrush along the Tonto Trail, Coleogyne ramosissima Torr.
Above the river corridor a desert scrub community, composed of North American desert flora, thrives. Typical warm desert species such as creosote bush, white bursage, brittle brush, catclaw acacia, ocotillo, mariola, western honey mesquite, four-wing saltbush, big sagebrush, blackbrush and rubber rabbitbrush grow in this zone.
Pinyon pine and juniper zone
Above the desert scrub and up to 6,200 feet is a pinyon pine, Utah and one seed juniper woodland. Within this woodland one can find big sagebrush, snakeweed, Mormon tea, Utah agave, banana and narrowleaf yucca, snakeweed, winterfat, Indian ricegrass, dropseed, and needlegrass.
Ponderosa pine forest
Ponderosa pine forests grow at elevations between 6,500 feet and 8,200 feet, on both North and South rims. Additional species such as Gambel oak, New Mexico locust, mountain mahogany, elderberry, creeping mahonia, and fescue have been identified in these forests. Above 8,200 feet, spruce-fir forests characterized by Englemann spruce, blue spruce, Douglas fir, white fir, aspen, and mountain ash, along with several species of perennial grasses, groundsels, yarrow, cinquefoil, lupines, sedges, and asters, brave the sub-alpine climate.
Meadow on the North Rim
Montane meadows and subalpine grassland communities are rare and located only on the North Rim. Both are typified by many grass species. Some of these grasses include blue and black grama, big galleta, Indian ricegrass and three-awns. The wettest areas support sedges and forbs.