Changes in Texas Ecoregions - PDF Free Download

Comment On Lesson Changes in Texas Ecoregions The state of Texas can be divided into 10 distinct areas based on unique combinations of vegetation, topography, landforms, wildlife, soil, rock, climate, and other factors. The locations of these areas, which are known as ecoregions, are shown in the map below. The specific characteristics of each Texas ecoregion are determined in large part by the dynamic processes of weathering, erosion, and deposition. East Texas Pineywoods Based on map from EPA As the name implies, this ecoregion is dominated by native pine forests, which are part of a regional pine forest throughout the southeastern United States. Wildlife in this rainy ecoregion include squirrels, River Otter, Louisiana Black Bear, and several species of birds. The land in the Pineywoods region has rolling hills and low-lying areas that are regularly flooded by rivers. As in other regions of Texas, many of the rivers in the Pineywoods have been dammed by humans. These dams help provide freshwater, hydroelectricity, recreational areas, and flood control. However, the dams also have some negative effects. For example, the dams decrease the amount of sediment the rivers can carry downstream. This reduces the amount of soil that can be replenished in downstream areas. Also, many bottomland river habitats are completely lost when they are covered by the dams' lakes. Page 1 of 11

Gulf Coast Prairies and Marshes The inland portion of the Gulf Coast consists mostly of flat grassland. Along the coast, where freshwater rivers meet the saltwater of the Gulf of Mexico, are found marshes, estuaries, bays, barrier islands, and many other coastal features. These unique environments are formed both by Texas rivers, which provide sediment and nutrients from farther upstream, and by the waves and tides of the Gulf, which shape coastal landforms and increase water salinity. A wide variety of coastal bird species, many of which are endangered or threatened, can be found along the Gulf Coast. Unique habitats are found in Texas where land and rivers meet the saltwater of the Gulf of Mexico. This image shows marsh habitat in the Nueces Bay. Image courtesy of U.S. Department of the Interior Post Oak Savannah With drier soils than the neighboring Pineywoods region, the Post Oak Savannah was originally known for gently rolling native grasslands separated by clumps of post oaks, blackjack oaks, and several other hardwood trees. While a few areas of the region retain these original characteristics, most of most of the region has been converted to pastureland by humans. As in other regions of Texas, rivers are the dominant force in shaping the landscape. Periodic flooding adds sediment to adjacent flooplains. This helps to replenish the soil, which supports floodplain ecosystems. Blackland Prairies The Blackland Prairies region originally consisted mainly of gently rolling grasslands, with fewer tree clumps than the adjacement Post Oak Savannah. Named for its characteristic Page 2 of 11

black, fertile soil, the Blackland Prairies region has been nearly completely converted to farmland and pastureland. Heavy farming in this region has led to soil loss by wind erosion and surface runoff. Today farmers reduce soil loss by planting cover crops between harvests. Cross Timbers and Prairies West of the Blackland Prairies lies the Cross Timbers and Prairies. This region is named for long, linear strips of forest that crosscut the local grasslands. Remnants of these "cross timbers" can still be seen today. As in most regions of Texas, running water is the dominant force of weathering, erosion, and deposition. In many parts of the Cross Timbers and Prairies region, the Brazos River has cut down through limestone bedrock to form tall, steep cliffs along the river's banks. South Texas Plains Between the Chihuahuan Desert of Mexico and the prairies of the Gulf Coast lie the South Texas Plains. The South Texas Plains region is very dry and has mostly low-growing vegetation, with isolated clumps of brushy vegetation. Trees are more abundant along the southern border of this region in the Rio Grande Valley. The Rio Grande Valley supports rare species of plants, mammals, reptiles, and amphibians. Like other Texas Rivers, the Rio Grande River constantly reshapes the land. Where the river curves, or meanders, sediment is deposited along the inside edge to form a point bar. Along the outside edge, erosion by the river forms a cut bank. A tight curve in the course of a river is called a meander. As water flows through a meander, slower speeds along the inside edge result in sediment deposition, forming a point bar. Along the outside edge of the meander, water flows faster and erodes rock and soil, forming a cut bank. Page 3 of 11

Edwards Plateau The Edwards Plateau is a rugged, elevated region of Central Texas covered by Ashe juniper and many types of oaks. Wildlife include a wide variety of mammals, birds, reptiles, and amphibians. Some of these animals live or breed only in the Edwards Plateau region. For example, the Golden-Cheeked Warbler is a migratory bird that lives only in Central Texas during the warm season. The warblers depend on the unique combination of Ashe juniper and live oak that is found in this region. Another example is the Texas Blind Salamander. This salamander lives only in certain caves found in the Edwards Plateau. These caves form from chemical weathering and erosion of the region's limestone. Both the Golden-Cheeked Warbler and the Texas Blind Salamander are endangered species. The Texas Blind Salamander is an endangered amphibian species found only in the Edwards Plateau ecoregion of Texas. Image courtesy of Joe N. Fries, U.S. Fish and Wildlife Service Rolling Plains West of the Cross Timbers and Prairies and north of the Edwards Plateau is the Rolling Plains ecoregion. As part of the Great Plains region of the United States, the Rolling Plains originally consisted of vast native grasslands stretching over flat areas and low hills. Over the last 100 years, most of the Rolling Plains has been converted to farmland, especially cotton fields. High Plains To the west of the Rolling Plains is found the High Plains ecoregion. The High Plains ecoregion sits atop a plateau and, like the Rolling Plains, originally consisted of vast grasslands before being converted to agricultural land. Some remnants of the original Page 4 of 11

ecoregion are still preserved and support diverse birds and mammals. The High Plains region is separated from the Great Plains region by a distinct escarpment, which is a cliff or steep slope, called the Caprock Escarpment. The Caprock Escarpment marks a sudden change between the regions' rock and soil. The surface of the High Plains is a made of a layer of caliche, which is a special kind of rock that forms in soil. Because caliche is very hard and very resistant to erosion, the High Plains are left standing as a plateau, while the materials in the Rolling Plains are more easily eroded by wind and running water. The Caprock Escarpment is a regional landform marking the boundary between the elevated High Plains and the lower-lying Rolling Plains in West Texas. Image modified from Wikipedia Trans-Pecos The westernmost ecoregion of Texas, the Trans-Pecos, is dry, rugged, and consists of a wide diversity of wildlife and landscapes, such as grasslands, plateaus, and forested mountains. The highest mountain peaks in Texas are found in this region. Most of these peaks, such as El Capitán shown below, are the products of erosional differences. The hard, resistant rock of the mountains is left standing, while the the less resistant rock surrounding them is more easily weathered and eroded. Page 5 of 11