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Regional Interpretation - Texas and Oklahoma (excluding panhandles and W. Texas)

Great Plains | Intermountain West | Southwest | Texas and Oklahoma | Other


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NRI Rangeland Resource Assessment - Texas and Oklahoma Regional Interpretation (PDF; 3.5 MB)

Overview

Rangelands in this area of Texas and Oklahoma are extremely diverse. They include the Gulf prairies and marshes, post oak savannahs, blackland prairies, tall- and mixed-grass prairie, cross timbers and prairies, south Texas plains, and the eastern fringe of the Edwards Plateau and Rolling Plains. Climate in this region is variable, but is characterized as a warm-temperate/subtropical zone. Winters are dry and summers are humid. Drought, a recurring phenomenon in Texas, is generally unpredictable and can have an extreme effect on vegetation.

Soil and Site Stability

Soil and site stability show moderate or greater levels of departure for relatively high proportions of rangeland in this region (Figure 1). The proportion of the area showing significant departure is particularly high along the Rio Grande. An increase and dominance of mesquite (Figures 2-5), a simultaneous loss of grasses, and increased bare ground (Figures 6-10), runoff, and erosion may explain a portion of the change.

Figure 1. Non-Federal rangeland where soil and site stability shows at least moderate departure from reference conditions
(Source: Rangeland Health Table 2) (PDF Download; 1.0 MB)
Map showing Non-Federal rangeland where soil and site stability shows at least moderate departure from reference conditions


 

Figures 2-5. Non-Federal rangeland where native invasive mesquite species are present or make up at least 15, 30, or 50 percent of the plant cover
(Source: Native Invasive Woody Species Table 2 & Table 6)

Figure 2. Present
(PDF Download; 1.0 MB)

Map showing Percent non-Federal rangeland where mesquite species are present
Figure 3. At least 15%
(PDF Download; 1.0 MB)

Map showing Percent non-Federal rangeland where mesquite species are present comprise at least 15% of the plant cover
Figure 4. At least 30%
(PDF Download; 1.0 MB)

Map showing Percent non-Federal rangeland where mesquite species are present comprise at least 30% of the plant cover
Figure 5. At least 50%
(PDF Download; 1.0 MB)

Map showing Percent non-Federal rangeland where mesquite species are present comprise at least 50% of the plant cover

 

Figure 6. Bare ground on non-Federal rangeland
(Source: Bare Ground, Intercanopy Gaps, and Soil Aggregate Stability Table 1) (PDF Download; 1.0 MB)

Map showing percent of bare ground on non-Federal rangeland


 

Figures 7-10. Non-Federal rangeland that is at least 20, 30, 40, or 50 percent bare ground (Source: Bare Ground, Intercanopy Gaps, and Soil Aggregate Stability Table 2)

Figure 7. At least 20%
(PDF Download; 1.0 MB)

Map showing percent non-Federal rangeland that is at least 20% bare ground
Figure 8. At least 30%
(PDF Download; 1.0 MB)

Map showing percent non-Federal rangeland that is at least 30% bare ground
Figure 9. At least 40%
(PDF Download; 1.0 MB)

Map showing percent non-Federal rangeland that is at least 40% bare ground
Figure 10. At least 50%
(PDF Download; 1.0 MB)

Map showing percent non-Federal rangeland that is at least 50% bare ground

 

Hydrologic Function

Hydrologic function shows patterns similar to soil and site stability in this region, with even higher proportions of land showing at least moderate departure in many parts of the region (Figure 11). This is due to the sensitivity of hydrologic function to both soil degradation and, frequently, changes in the plant community associated with invasive woody plants. Mesquite (mainly Prosopis glandulosa Torr.) and juniper (Juniperus spp.) are particularly widespread in this region (Figures 12-15). While native, they can and do increase in the absence of fire. Where increased woody cover is associated with reduced grass cover, infiltration capacity can decline with increased runoff in interspace areas between shrubs. Accelerated runoff over time can result in changes of natural water flow paths and the formation of interspace rills which may develop into gullies. Soil loss can be excessive, and recovery on these sites can be slow. On shallow soils, these channels can quickly erode to bedrock. In contrast, dense grass cover and associated root mass tend to increase soil porosity, soil aggregate stability (Figure 16), and overall soil health.

Figure 11. Non-Federal rangeland where hydrologic function shows at least moderate departure from reference conditions
(Source: Rangeland Health Table 2) (PDF Download; 1.0 MB)

Map showing Non-Federal rangeland where hydrologic function shows at least moderate departure from reference conditions


 

Figures 12-15. Non-Federal rangeland where native invasive woody species are present (Source: Native Invasive Woody Species Table 2)

12. Juniper including eastern redcedar
(PDF Download; 1.0 MB)

12. Juniper including eastern redcedar
13. Eastern redcedar
(PDF Download; 1.0 MB)

13. Eastern redcedar
14. Juniper excluding eastern redcedar
(PDF Download; 1.0 MB)

14. Junipers other than eastern redcedar
15. Mesquite
(PDF Download; 1.0 MB)

15. Mesquite

 

Figure 16. Non-Federal rangeland where soil aggregate stability is 4 or less indicating unstable soil (Source: Bare Ground, Intercanopy Gaps, and Soil Aggregate Stability Table 4) (PDF Download; 1.0 MB)
Map showing percent of non-Federal rangeland where soil aggregate stability is 4 or less indicating unstable soil.


Biotic integrity

Significant shifts in plant community composition associated with increased dominance of invasive species, both grasses and shrubs, are reflected in significantly reduced biotic integrity throughout most of this region (Figure 17). While many of these species (e.g. mesquite and juniper) are native throughout this region, the high biotic integrity departure ratings reflect the fact that they have invaded soils where they would not normally occur, become dominant under a natural disturbance regime, or significantly increased on soils where they are native. The potential plant communities for most of this region are grassland and savanna ecosystems.

Figure 17. Non-Federal rangeland where biotic integrity shows at least moderate departure from reference conditions
(Source: Rangeland Health Table 2) (PDF Download; 1.0 MB)

Map showing Non-Federal rangeland where biotic integrity shows at least moderate departure from reference conditions

 

More Information

 

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