Savannah
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
- Transition T1-2 More details
- Transition T1-3 More details
- Transition T More details
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No transition or restoration pathway between the selected states has been described
Target ecosystem state
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State 1
Reference State
Description
This state describes the range of vegetative community phases that occur on the Savannah site where the natural processes are mostly intact.
The Reference Community is a representation of the native plant community phase that occupies a site that has been minimally altered by management. The Degraded Savannah, the At-Risk, and the Excessive Litter Communities are the phases that result from management decisions that are unfavorable for a healthy Reference Community. The Ephemeral Forb Community is the result of a high intensity disturbance event.
High perennial grass cover and production allows for increased soil moisture retention, vegetative production, and overall soil quality.
Submodel
States 1, 5 and 2 (additional transitions)
1.1. Tallgrass Savannah Community
1.5. Ephemeral Forb Community
1.2. Degraded Savannah
Description
This state has been degraded from the Reference State and much of the native warm-season grass community has been replaced by less desirable plants. The loss of tall and mid- warm-season grasses has negatively impacted energy flow and nutrient cycling. The woody component has expanded significantly, and shading due to the overstory has increased. Water infiltration is reduced due to the shallow root system and rapid runoff characteristics of the grazing-evasive plant communities. Alteration of the soil, and the hydrological processes make return to reference state unlikely.
The Invasive Woodies and the Eastern Redcedar are the communities in this state.
Submodel
Description
This threshold is crossed as a result of mechanical disturbance to facilitate production agriculture. If farming operations are suspended, the site can be abandoned, which will result in the Naturally Reclaimed Community, or be re-seeded to a desired perennial forage mixture, which is described as the Re-seeded Community.
Permanent alterations of the soil community and the hydrological cycle make restoration to the original native Reference Community extremely difficult, if not impossible. Formation of a compacted plow pan in the soil profile is likely.
Submodel
Mechanism
Heavy grazing or haying without adequate recovery periods will cause this state to lose a significant proportion of tall and mid- warm-season grass species and cross a threshold to the Native/Invaded State. Water infiltration and other hydrologic functions will be reduced due to the root matting presence of sod-forming grasses. With the decline and loss of deeper penetrating root systems, soil structure and biological integrity are catastrophically degraded to the point that recovery is unlikely. Once this occurs, it is highly unlikely that grazing management alone will return the community to the Reference State. Additionally, increasing woody encroachment also results from overgrazing and lack of fire. The expansion of the overstory blocks more of the sunlight, creating a more competitive environment for a shade tolerant understory. Mechanical removal with follow-up stump treatment of the root-sprouting species and implementation of a prescribed burning regime will alleviate the invasion of woodies.
Mechanism
The Reference State is significantly altered by mechanical tillage to allow the site to be placed into production agriculture. The disruption to the plant community, the soil and the hydrology of the system make restoration to a true reference state unlikely.
Model keys
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The Ecosystem Dynamics Interpretive Tool is an information system framework developed by the USDA-ARS Jornada Experimental Range, USDA Natural Resources Conservation Service, and New Mexico State University.