Texas Savanna

The Texas savanna originally may have been largely mixed prairie grassland, but currently is a high-shrub savanna. It occupies the western end of Gulf Coastal Plain and the southern end of the Great Plains. Elevation ranges from 200 meters near the Gulf of Mexico to over 1000 meters at the western edge of the Edwards Plateau. The area is relatively flat but is cut through by ravines and arroyos.

Climate. The climate of this region is relatively warm and humid with the frost-free season ranging from 200 to 350 days to frost-free. Precipitation comes mostly in summer and ranges from 50 to 75 centimeters. Potential evaporation is roughly twice that of precipitation.

Soils. The soils of the region include mollisols, alfisols, vertisols, and entisols. Mollisols make up a major portion of the region and support the juniper-oak and the mesquite-acacia savannas. The entisols are covered by the mesquite-liveoak savanna type. Alfisols support the mesquite oak savanna.

Vegetation. The entire area could be classed a mesquite shrubland. Five distinct vegetation types exist in the region: (1) the mesquite-liveoak savanna, (2) the mesquite-acacia savanna, (3) the mesquite-oak, (4) the juniper-oak savanna, and (5) the ceniza shrub.

• Mesquite-liveoak savanna occurs in the West Gulf Coast Plain and has live oaks and mesquites as dominants of the overstory. Seacoast bluestem (Andropon littoralis), Texas wintergrass (Stipa leucotricha), curylmesquite, and threeawns are the dominant grasses. Numerous forbs are also present.

• Mesquite-acacia savanna varies greatly in the amount of tree overstory from nearly open to closed. Acacia species are the most abundant shrubby tree species. Seacoast bluestem, plains bristlegrass (Setaria macrostachya) and buffalograss are the dominant perennial grasses. Forbs make up nearly one-third of the composition.

• The juniper-oak and mesquite-oak savannas are characteristic of the Edwards Plateau of Texas. Mesquite and oak dominate the deciduous shrubby tree portion of the mesquite-oak savanna, while live oaks and Ashe juniper (Juniperus ashii) are codominants in the juniper-oak savanna. Both have similar understory vegetation with little bluestem, curylmesquite, tobosa, and buffalograss as the principal perennial grasses. Cacti are moderately abundant in these two vegetation types.

• The ceniza shrub type is dominated by deciduous and evergreen shrubs with scattered openings with grass species. Located along the Rio Grande valleys and bluffs, the dominant shrubs are creosotebush, ceniza (Leucophyllum frutescens) and mesquite. Grasses, curylemesquite, alkali sacaton (Sporobolus airoides), Arizona cottontop (Tricachne californica) and threeawn are the principal perennial grasses. Cacti are common as well as other spring shrubs.

Management. Cattle are the primary grazers in this region, but sheep and goats are also important with combinations of those three species likely providing the best grazing use. Conversion of the brushy areas to a grassland is frequent, but revision of the shrubby species is rapid. Deer management is a common practice with hunting leases sold over much of the area.