Natural Resources
Conservation Service
Warm-Mesic, Xeric, Unglaciated, Loamy Slopes (Ponderosa Pine Warm Dry Grass)
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
- Transition T1A More details
- Transition T1B More details
- Transition T1C More details
- Restoration pathway R2A More details
- Restoration pathway R3A More details
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No transition or restoration pathway between the selected states has been described
Target ecosystem state
Select a state
State 1
Reference State - Open Ponderosa pine/Bunchgrass
Reference State - Open Ponderosa pine/Bunchgrass
Description
This state is dependent on the occurrence of frequent low intensity ground fires keeping an open grown pine stand with a dominant ground cover of bunchgrass. When fire intervals are infrequent pine regeneration can survive and a patchy pine woodland develops underneath the large old pine. With drought stress the large old pine can be subject to beetle kill and the understory pine stands subject to dwarf mistletoe infestation. It is also possible to have a stand replacement fire when stand density is increased and ladder fuels can reach the larger pine crowns.
Forest productivity is measured using site index (SI) and culmination of annual increment (CMAI). Ponderosa pine is the key tree species and site indexes ranges greatly depending on local site characteristics. Available data indicates a mean site index of 100 using (Meyer, 1961) with a CMAI of 102 cu. ft./yr at age 40 years.
The bulk of grass production is bluebunch wheatgrass and Idaho fescue. Other grass species included needle and thread grass, prairie junegrass, rough fescue, pine grass and sandberg bluegrass. The most prominent forbs were lupine, basalmroot, pussytoes, hawkweed, and yarrow. Shrubs tend to be present in only trace amounts. Tree regeneration is mostly ponderosa pine with an occasional Douglas-fir.
Submodel
State 2
Alternative State 2 – Fire Exclusion – Pine Woodland
Alternative State 2 – Fire Exclusion – Pine Woodland
Description
Fire Exclusion for 50+ years leads to a light to medium dense pine woodland with all ages present. Canopy cover ranges from 30- 60%. Canopy cover will be higher in the pine/fescue habitat. Mixed severity fires will create a mosaic of pine stands between burned areas which will seed in with pine maintaining a multi-level pine woodland.
Submodel
Description
Invasion of introduced perennial and annual cool season grasses from adjacent pastures, homesteads, and abandoned areas. One particular annual grass of concern from past overgrazing is the invasion of cheat grass. Once it gets established in the understory it will prevent native bunchgrasses from reestablishing and restoring site.
Submodel
Description
Lower level terrain converted to crops, pasture or urban development. Much of the ponderosa pine ESDs are adjacent to local towns and cities. They have been converted to housing developments, shopping malls, or urban recreation areas. In the more rural areas, these sites have been converted to pastures and dry or irrigated cropland.
Submodel
Transition T1A
Mechanism
The natural fire regime intervals changed to 50+ years allowing understory pine regeneration to survive and grow creating more of a woodland site. Older larger pine now more susceptible to mortality from stand replacing fire.
Mechanism
Invasion of introduced perennial and annual grasses which outcompete native bunchgrasses
Restoration pathway R2A
Mechanism
Overstory thinning and understory burning for specified time intervals to return site to Reference State 1.
Model keys
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Ecological site groups
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.
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