Natural Resources
Conservation Service
Scenario model
Current ecosystem state
Select a state
Management practices/drivers
Select a transition or restoration pathway
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Transition T1A
Reduced native competitiveness allow for introduced grass colonization and expansion.
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Transition T1B
Severe disturbance makes resources available to opportunistic species.
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Transition T1C
Woody encroachment leading to woody dominance
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Restoration pathway R2A
Reduced invasive grass competitiveness allows natives to reclaim resources.
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Transition T2A
Reduced native competitiveness allow for introduced grass colonization and expansion.
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Transition T2B
Severe disturbance makes resources available to opportunistic species.
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Transition T2C
Woody encroachment leading to woody dominance
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Transition T3C
Reduced invasive grass competitiveness allows natives to reclaim resources.
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Transition T3B
Severe disturbance makes resources available to opportunistic species.
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Transition T3A
Woody encroachment leading to woody dominance
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Restoration pathway R4A
Successional processes tie up resources in a more stable community
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Transition T4B
Successional processes tie up resources in a more stable community
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Transition T4C
Successional processes tie up resources in a more stable community
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Restoration pathway R5A
Woody removal for return to herbaceous dominance
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Transition T5B
Woody removal for return to herbaceous dominance
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Transition T5C
Woody removal for return to herbaceous dominance
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No transition or restoration pathway between the selected states has been described
Target ecosystem state
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Description
This state comprises the communities within the range of natural variability under historic conditions and disturbance regimes. Patterns created by wildlife use and fire would have created a mosaic of communities across the landscape; however, warm-season tallgrasses are dominant, with a subdominant to minor contribution from native cool-season grasses, forbs, and shrubs.
Fire and bison herbivory were the dominant disturbance regimes that historically maintained the tallgrass dominance with a diverse forb component. Furthermore, bison grazing was closely linked to fire patterns as the animals preferred grazing burned areas offering lush regrowth devoid of decadence and of higher nutritive quality. Thus, historic plant communities were subjected to occasional burning and grazing, with substantial rest/recovery periods as the fuel load rebuilt to eventually start this process again. Fire return intervals of 3-4 years served to suppress woody species, particularly the various tree and shrub species prevalent in adjacent riparian corridors.
The degree to which observed conditions represent this state largely depends on how closely the management has mimicked these past disturbance effects.
Dominant plant species
little bluestem (Schizachyrium scoparium), grass
sideoats grama (Bouteloua curtipendula), grass
blue grama (Bouteloua gracilis), grass
needle and thread (Hesperostipa comata), grass
Submodel
Description
This state can manifest in three ways: 1) the appearance of introduced cool-season grasses, 2) the expansion of shrubs and/or trees, or 3) some combination of these. Kentucky bluegrass and Smooth brome are the primary cool-season grass invaders in this region, commonly found in roadsides, disturbed areas, and pastures intentionally seeded for cool-season forage. Management practices and/or environmental conditions that are not favorable to native grass vigor may allow introduced grasses to invade the site thereby decreasing native diversity and abundance, particularly of forbs.
In the absence of the historic fire regime, woody species may also expand to become an influential component of the community. The invasive component tends to have very high resilience, is extremely difficult to eradicate, and what might be considered a new "contemporary" range of natural variability is seen as competition between the native grasses and introduced/woody species for space and resources.
Dominant plant species
little bluestem (Schizachyrium scoparium), grass
sideoats grama (Bouteloua curtipendula), grass
smooth brome (Bromus inermis), grass
Kentucky bluegrass (Poa pratensis), grass
Submodel
Description
Introduced cool-season invasion has progressed to the point that native species comprise a negligible portion of the community and the aggressively rhizomatous invasives preclude native germination and seedling survival. The native component may be completely absent, and the site resembles a seeded pasture. Alternatively, the dominant invasives may be woody species. Woody competitiveness for sunlight, water, space, and other resources continues to increase as desirable herbaceous species are shaded out, crowded out, or otherwise suppressed.
Dominant plant species
smooth brome (Bromus inermis), grass
Kentucky bluegrass (Poa pratensis), grass
Submodel
Description
Nutrient cycling, hydrologic function, and/or soil stability have been severely altered, and possibly compromised. This is a highly variable state in which the specific plants observed will depend largely on the original community and the nature of the disturbance. This condition encompasses (but is not necessarily limited to) events such as severe fire impacts, heavy continuous grazing, heavy nutrient inputs, and abandoned cropland.
Dominant plant species
ragweed (Ambrosia), grass
hoary verbena (Verbena stricta), grass
pigweed (Amaranthus), grass
thistle (Cirsium), grass
Submodel
Description
Under historic disturbance regimes, frequent and uncontrolled fire and wildlife browsing served to keep woody species in check. However, in the absence of fire (either wild or prescribed), it's not uncommon for the woody trees and shrubs normally limited to riparian areas to expand into the floodplains, regardless of herbaceous community composition. Wildlife may introduce a seed source to areas not associated with a waterway, such as interdunal depressions.
Dominant plant species
maple (Acer), tree
eastern cottonwood (Populus deltoides), tree
boxelder (Acer negundo), tree
ash (Fraxinus), tree
Submodel
Transition T1A
Reduced native competitiveness allow for introduced grass colonization and expansion.
Mechanism
In the presence of introduced cool-season grasses, environmental conditions and/or management that reduces native vigor and stand resilience, and frees up resources (space, sunlight, nutrients, water) will allow for colonization of Kentucky bluegrass and Smooth brome. Likewise, similar processes may also allow for woody species to expand.
Mechanism
There are many possible triggers for this transition that may occur as acute events (e.g. plowing) or cumulative impacts of chronic events (e.g. long-term undermanaged grazing.) The absence of deep-rooted perennial cover exposes the site to topsoil loss, open nutrient cycle, and free space which collectively allow for opportunistic annual species to dominate.
Mechanism
All herbaceous communities are vulnerable to woody encroachment in the absence of fire and/or browsing and hoof action impacts. This is particularly prominent in areas adjacent to riparian corridors which supply a constant seed source. As tree establishment progresses, the conditions grow increasingly favorable for woody germination and growth.
Restoration pathway R2A
Reduced invasive grass competitiveness allows natives to reclaim resources.
Mechanism
Eradication of introduced cool-season grasses from this site will require long-term, targeted management efforts to create an adverse environment during the spring and late fall when bluegrass and brome are most actively growing, with favorable conditions during the summer to promote native warm-season species. Targeted practices such as prescribed burning, flash grazing, and herbicide are often employed at strategic times of the year to set back undesirable species. The combination of practices should strive to mimic the historic disturbance regimes to which the desirable native species are best adapted.
Transition T2A
Reduced native competitiveness allow for introduced grass colonization and expansion.
Mechanism
If the conditions which initiated and fomented the colonization and expansion of cool- season invasion are not removed or mitigated, stand composition will continue to shift in this direction and begin to resemble a monoculture of brome and/or bluegrass. Due to the dense rhizomatous root mat of brome and bluegrass, native species suffer decreasing opportunities to contribute propagules, and individual plants lost are not replaced by desirable natives.
Mechanism
There are many possible triggers for this transition that may occur as acute events (e.g. plowing) or cumulative impacts of chronic events (e.g. long-term undermanaged grazing.) The absence of deep-rooted perennial cover exposes the site to topsoil loss, open nutrient cycle, and free space which collectively allow for opportunistic annual species to dominate.
Mechanism
All herbaceous communities are vulnerable to woody encroachment in the absence of fire and/or browsing impacts. This is particularly prominent in areas adjacent to riparian corridors which supply a constant seed source. As tree establishment progresses, the conditions grow increasingly favorable for woody germination and growth.
Transition T3C
Reduced invasive grass competitiveness allows natives to reclaim resources.
Mechanism
Aggressive intervening actions will be required to simultaneously recolonize native grasses and suppress vigor in undesirable species. Restoration follows the same principles as the R2A pathway but may also require native range seeding if the latent seedbank is inadequate.
Mechanism
Nutrient cycling, hydrologic function, and/or soil stability have been severely altered, and possibly compromised. This is a highly variable state in which the specific plants observed will depend largely on the original community and the nature of the disturbance.
Mechanism
All herbaceous communities are vulnerable to woody encroachment in the absence of fire and/or browsing impacts. This is particularly prominent in areas adjacent to riparian corridors which supply a constant seed source. As tree establishment progresses, the conditions grow increasingly favorable for woody germination and growth.
Restoration pathway R4A
Successional processes tie up resources in a more stable community
Mechanism
Restoration strategies will depend on the nature of the disturbance and the viability of the seedbank. On pastures, changes to gazing management and favorable moisture conditions may produce a perennial community. However, in abandoned cropland range seeding will likely be necessary to recolonize desirable perennial species.
Mechanism
As the site matures from the annual / pioneer stage, it will transition over to a mix of native and invaded species depending on the seed sources available. In many cases this will be a mix of Smooth brome and Kentucky bluegrass for these sites.
Mechanism
The annual / pioneer stage can transition to an invasive dominant stage if the seed source available after the disturbance is predominantly non-native species.
Mechanism
The combination of tree size, reduced herbaceous understory, and more mesic conditions makes it increasingly difficult for natural disturbances to restore/maintain the historic tallgrass community, and mature woodlands can no longer be restored with fire. Intensive brush management will be required to mechanically remove the established overstory. Woody control and maintenance will be an ongoing process and may also require chemical methods if sprouting species are present.
Mechanism
Any type of natural act or management practices that kill off the woody species can transition the woody dominant site back to a native / invaded mix as the remaining herbaceous plants and seed source thrive due to the introduction of more sunlight and less woody competition.
Mechanism
Any type of natural act or management practices that kill off the woody species can transition the woody dominant site back to invasive dominant regime as the remaining herbaceous plants and seed source thrive due to the introduction of more sunlight and less woody competition.
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.
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