Lowland
Scenario model
Current ecosystem state
Select a state
Management practices/drivers
Select a transition or restoration pathway
- Transition T1b More details
- Transition T5 More details
- Transition T1a More details
- Transition T5 More details
- Transition T2b More details
- Transition T2a More details
- Transition T2c More details
- Restoration pathway R3a More details
- Restoration pathway R3b More details
- Transition T3 More details
- Transition T4 More details
- Transition T5 More details
-
No transition or restoration pathway between the selected states has been described
Target ecosystem state
Select a state
Description
This state description represents the natural range of variability that dominated the dynamics of this ecological site. Historically, this state ranged from a tall, warm season grass dominated site to one dominated by deciduous shrubs, saplings, and trees depending upon disturbance regime. The primary disturbance mechanisms for this site in the reference condition included periodic fire and grazing by large herding ungulates. Timing of fires and grazing coupled with weather events dictated the dynamics that occurred within the natural range of variability. Dominance during the herbaceous phases of this state shifted between warm-season and cool-season grasses. Although slight shifts may have occurred in timing of energy capture, hydrologic function and nutrient cycling between plant community phases within the Reference State, overall the ecological processes were functioning at near optimum levels. High basal density and deep root systems resulted in low runoff rates and high infiltration rates.
Areas of trees and shrubs existed within this state due to irregularity of burn patterns. Areas which escaped fire may have permitted trees/shrubs to become established. These areas may have served as a seed source for further expansion of the woody dominated plant communities as the fire frequency was altered after settlement.
Submodel
Description
This state is very similar to the reference state. The invasion of introduced cool-season sodgrasses has altered the natural range of variability for this ecological site. This state is typically dominated by tall native warm-season grasses, but invasive introduced cool-season grasses are now present in all community phases of this state. The primary disturbance mechanisms for this state include grazing by domestic livestock and infrequent fires. Timing and intensity of grazing events coupled with weather dictate the dynamics that occur within this state. The cool-season native grasses can decline and an increase in introduced sod grasses will occur. Many times, this state appears as a mosaic of community phases caused primarily by continuous season-long grazing.
Submodel
Description
This state is the result of invasion and dominance of introduced species. This state is characterized by the dominance of Kentucky bluegrass and smooth bromegrass, and an increasing thatch layer that effectively blocks introduction of other plants into the system. Plant litter accumulation tends to favor the more shade tolerant introduced grass species. The nutrient cycle is also impaired, and the result is typically a higher level of nitrogen which also favors the introduced species. Increasing plant litter decreases the amount of sunlight reaching plant crowns thereby shifting competitive advantage to shade tolerant introduced grass species. Studies indicate that soil biological activity is altered, and this shift apparently exploits the soil microclimate and encourages growth of the introduced grass species. Once the threshold is crossed, a change in grazing management alone cannot cause a reduction in the invasive grass dominance. Preliminary studies would tend to indicate this threshold may exist when Kentucky bluegrass exceeds 30% of the plant community and native grasses represent less than 40% of the plant community composition.
Once the state is well established, even drastic events such as high intensity fires driven by high fuel loads of litter and thatch may not result in more than a very short term reduction of Kentucky bluegrass. These events can reduce the dominance of Kentucky bluegrass, but due to the large amount of rhizomes in the soil there is little opportunity for the native species to establish and dominate before Kentucky bluegrass rebounds and again dominates the system.
Submodel
Description
Historically, this state existed as small patches of trees and shrubs scattered across the site. Repeated intense disturbances (e.g., fire, fire coupled with grazing) would have reverted these smaller patches of trees to the herbaceous dominated Reference State (State 1) in pre-European times, while it will likely revert to the Invaded State (State 3) today. For simplification purposes, the pre-European transition returning from the wooded state to the reference state is not shown on the state and transition diagrams. Likewise the pre-European and modern day conditions of the Wooded State are combined within this state description. Community phases 4.1 and 4.2 would have occurred in pre-European times without the presence of non-native species; whereas, community phase 4.3 will only be present in modern times, and all three community phases will likely have some amounts of non-native species in the present day. Otherwise, the community pathways between 4.1 and 4.2 would generally apply in both pre-European and under modern day circumstances.
In pre-European times, periodic low intensity fires typically would have maintained these small, wooded patches in a tree dominated state. Alterations to the historic fire and grazing disturbance regimes have resulted in these scattered tree/shrub patches forming almost continuous woody dominated plant communities across the site. This state is characterized by an overstory of tall trees, an understory of shrubs and, depending upon the amount of canopy cover, an herbaceous understory of sedges and/or Kentucky bluegrass.
Submodel
Mechanism
Encroachment of non-native grasses such as Kentucky bluegrass and smooth bromegrass, and disruption of natural disturbance regimes (typically as a result of fire suppression following settlement) led this state over a threshold to the Native/Invaded State (State 2). The threshold between these states was crossed when non-native species became established on the site.
Mechanism
Encroachment of non-native invasive/noxious species, abandonment of cropping, or seeding of introduced and/or native improved varieties of forage species may lead this plant community phase over a threshold to the Invaded State (State 3) and more specifically to the 3.3 Annual/Pioneer, Non-native Perennial Plant Community Phase. In the case of a seeding, refer to the corresponding Forage Suitability Group description for adapted species and expected production (production estimates in the Forage Suitability Group description may be unrealistically high due to the degraded condition of the site at this phase).
Mechanism
Non-use (or very light use) and no fire for extended periods of time (typically for about 10 years or more) would have caused a further shift to dominance by woody species, and allowing the tree species to become mature enough to at least partially survive periodic fire. This would result in a transition over a threshold leading to the Wooded State (State 4). As trees increased in size, canopy cover increased which altered micro-climate and reduced fine fuel amounts resulting in reduced fire intensity and frequency. This would have been the primary pathway under the historic disturbance regime and would have resulted in a mosaic pattern of small wooded patches interspersed within herbaceous plant community phases.
Mechanism
Encroachment of non-native invasive/noxious species, abandonment of cropping, or seeding of introduced and/or native improved varieties of forage species may lead this plant community phase over a threshold to the Invaded State (State 3) and more specifically to the 3.3 Annual/Pioneer, Non-native Perennial Plant Community Phase. In the case of a seeding, refer to the corresponding Forage Suitability Group description for adapted species and expected production (production estimates in the Forage Suitability Group description may be unrealistically high due to the degraded condition of the site at this phase).
Mechanism
Heavy continuous grazing (stocking levels well above carrying capacity for extended portions of the growing season, and at the same time of year each year) will cause a shift across a threshold leading to the 3.2 Kentucky Bluegrass Sod/Forbs Plant Community Phase within the Invaded State (State 3).
Mechanism
Non-use and no fire for extended periods of time (typically for 10 or more years) will likely lead this state over a threshold resulting in the 3.1 Kentucky Bluegrass/Smooth Brome/Shrubs Plant Community Phase within the Invaded State (State 3).
Mechanism
Non-use and no fire for extended periods of time (typically for 10 or more years) will likely lead this state over a threshold resulting in a shift leading to the Wooded State (State 4). Rather than patches of trees and shrubs interspersed within herbaceous dominated plant communities as they exist within the Native/Invaded State (State 2) and as they existed in the Reference State (State 1), this transition results in an expansion of the patches into an almost continuous woody dominated site.
Mechanism
Prescribed grazing (moderate stocking levels coupled with adequate recovery periods, or other grazing systems such as high-density, low-frequency intended to treat specific species dominance, or periodic light to moderate stocking levels possibly including periodic rest) coupled with prescribed burning may lead this plant community phase over a threshold to the Native/Invaded State (State 2). Pest management (i.e., herbicide) may also be needed to suppress cool-season invasive grasses. This will likely take a long period of time, possibly up to 10 years or more, and recovery may not be attainable. Success depends on whether native reproductive propagules remain intact on the site.
Relevant conservation practices
Practice | External resources |
---|---|
Prescribed Burning |
|
Prescribed Grazing |
|
Integrated Pest Management (IPM) |
Mechanism
Seeding of selected varieties of native species coupled with prescribed grazing may result in a plant community that approaches something very near the functioning of the Native/Invaded State (State 2). Application of chemical herbicides and the use of mechanical seeding methods using adapted varieties of the dominant native grasses are possible and can be successful. After establishment of the native plant species, management objectives must include the maintenance of those species, the associated reference state functions and continued treatment of the introduced grasses.
Relevant conservation practices
Practice | External resources |
---|---|
Prescribed Grazing |
Mechanism
Non-use and no fire for extended periods of time (typically for 10 or more years) will likely lead this state over a threshold resulting in a shift leading to the Wooded State (State 4). Rather than patches of trees and shrubs interspersed within herbaceous dominated plant communities as they exist within the Invaded State (State 3) and as they existed in the Reference State (State 1), this transition results in an expansion of the patches into an almost continuous woody dominated site.
Mechanism
Fire of high enough intensity to remove and/or kill many of the trees, or timber harvest that effectively reduces the stand to scattered over-mature individual trees will lead to a shift over a threshold to the Native/Invaded State (State 3). Encroachment of non-native cool-season grasses will have also occurred to effect this transition. Potentially, this transition could also be initiated or compounded with the introduction of various tree and/or shrub diseases or pests.
Mechanism
Encroachment of non-native invasive/noxious species, abandonment of cropping, or seeding of introduced and/or native improved varieties of forage species may lead this plant community phase over a threshold to the Invaded State (State 3) and more specifically to the 3.3 Annual/Pioneer, Non-native Perennial Plant Community Phase. In the case of a seeding, refer to the corresponding Forage Suitability Group description for adapted species and expected production (production estimates in the Forage Suitability Group description may be unrealistically high due to the degraded condition of the site at this phase).
Model keys
Briefcase
Add ecological sites and Major Land Resource Areas to your briefcase by clicking on the briefcase () icon wherever it occurs. Drag and drop items to reorder. Cookies are used to store briefcase items between browsing sessions. Because of this, the number of items that can be added to your briefcase is limited, and briefcase items added on one device and browser cannot be accessed from another device or browser. Users who do not wish to place cookies on their devices should not use the briefcase tool. Briefcase cookies serve no other purpose than described here and are deleted whenever browsing history is cleared.
Ecological sites
Major Land Resource Areas
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.