. Animal Ecology. Animal ecology. FIG. 26-1 Faclatlons of the desert biome in North America (after Axelrod 1950, Jaeger 1957). in some localities. Sagebrush, Artemisia tridentata, often occurs in nearly pure stands, but where grazing is limited, several species of perennial grasses, espe- cially wheat grass, Agropyron spicatum, become in- termixed to form a continuum leading into the bunch grass prairie to the north. Only a few opuntia cacti occur. Sagebrush is widely distributed as a subcli- max, because of overgrazing, in the bunch-grass prairie and short-grass plains. Various species of Art
. Animal Ecology. Animal ecology. FIG. 26-1 Faclatlons of the desert biome in North America (after Axelrod 1950, Jaeger 1957). in some localities. Sagebrush, Artemisia tridentata, often occurs in nearly pure stands, but where grazing is limited, several species of perennial grasses, espe- cially wheat grass, Agropyron spicatum, become in- termixed to form a continuum leading into the bunch grass prairie to the north. Only a few opuntia cacti occur. Sagebrush is widely distributed as a subcli- max, because of overgrazing, in the bunch-grass prairie and short-grass plains. Various species of Artemisia also extend into central and southern Cali- fornia and together with associated species have been called coastal sagebrush. It may be subclimax to chaparral. The original vegetation of these two asso- ciations has become greatly modified as result of overgrazing by domestic animals and increased ero- sion with reduction in grasses and edible shrubs and introduction of exotic species (Fautin 1946, Cottam 1947, Billings 1949). A tropical thorn forest occurs on the west coast of Mexico, in northern Venezuela, and in other scat- tered localities. It is made up of a dense scrubby growth of small, often thorny and leguminous trees. Cacti are common. Some authors distinguish a thorn forest and a short-tree forest, but there is consider- able intergrading between the two (Gentry 1942) as well as with the tropical deciduous forest. PALEO-ECOLOGY During early Tertiary, the present desert regions in North America were largely dominated by tropical and warm-temperate forests. Following Eocene, rainfall gradually decreased, and forests were replaced first by grassland, then by desert. Des- ert began to appear during middle Tertiary on the lee side of high mountain ranges, but did not become extensive until middle and late Pliocene time. The present deserts in North America are therefore of comparatively recent origin. Desert plants have apparently originated through gradual adaptatio
Size: 1335px × 1873px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionbiodive, booksubjectanimalecology
