Cool Dry Conifer Foothills and Mountains (PIPO/FEID-PSSPS)
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
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Transition T1a
Long term fire exclusion (50-100+) years
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Transition T1b
Widespread catastrophic stand replacing fire event
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Transition T1c
Invasion of introduced cool season grasses or exotic annual grass
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Transition T1d
Site converted to annual cropland or pasture/hayland
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Restoration pathway R2a
Restoration practices that reduce excessive fuel loads and reduce overstory crown bulk density
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Transition T2a
Widespread catastrophic fire occurs
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Restoration pathway R3a
Conifer planting
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Restoration pathway R4a
Practices that promote the reestablishment of native understory species
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Restoration pathway R4a
Practices are applied which reduce or eliminate unwanted weeds and invasive species
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Restoration pathway R5a
Practices that promote the reestablishment of native understory species
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Transition T5a
Poor management or abandonment leads to weed invasion
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No transition or restoration pathway between the selected states has been described
Target ecosystem state
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Description
Ponderosa pine forests of this type tended to be heterogeneous and spatially complex. The primary disturbance regime that maintained this ecological site in the historical context was frequent low intensity surface fire and less frequent mixed severity fire., which resulted in multiple age and size classes of ponderosa pine. A wide array of wildlife species benefited from the edge effects created by the spatial intersections within the larger landscape, and by naturally occurring snags and large woody debris. Across the overall landscape stand structure was expressed by a combination of patch openings, clumpy (dense or overstocked) tree groups, and as well-spaced mature overstory trees encompassing larger stand groups. These mosaic patterns could occur over the landscapes in a scale of upwards of tens of thousands of acres. Disturbances from fire and other biotic and abiotic sources impacted much smaller areas within the larger landscape, on the order of thousands of acres.
Following a disturbance occurrence that eliminated or significantly reduced much of the established Ponderosa pine within the forest stand, the key to re-establishing and sustaining the reference state was dependent on the successful recruitment of Ponderosa pine seedlings from adjacent sources, from soil banked viable seed, or from remnant surviving seed trees. Larger sized patches and impacted areas approaching landscape level scales, isolated from seed sources and devoid of remnant Ponderosa pine of any size class, tend to revert to long term grass/shrub conditions.
Submodel
States 1, 5 and 2 (additional transitions)
1.1. Reference Plant Community, Mature, Open canopy
1.5. Mature, Closed canopy
1.2. Stand regeneration
Description
Conditions favorable to the development of this alternative state began to occur within the Reference State around the turn of the twentieth century. The impacts of fire exclusion, a management goal of post-European settlers, has allowed many stands to progress without the natural occurrence of fire, especially frequently occurring and beneficial fire episodes. Fire suppression has shifted the age expression and density of the younger stands, and changed the composition of understory vegetation, leading to reduced spatial variation. Fuel levels and fuel stratum layers have increased, shifting the fire regime/condition class toward a greater likelihood of stand replacement fire episodes.
Description
This state represents conditions immediately following a catastrophic wildfire event. Long term detrimental impacts to wildlife, hydrology and soil quality occur immediately due to the abnormally high intensity of the catastrophic burn. Microbial populations, organic matter levels, nitrogen cycling and other structural elements of the native soil resources are negatively impacted. The number of wildlife snags will usually increase in the short term following the fire. Recolonization of the site by conifers will depend greatly on distance to seed sources as most on site seed will be eliminated.
Description
This state has developed with the introduction and invasion of introduced grasses and noxious weeds. In this site, cheatgrass (Bromus tectorum), Medusahead rye (Taeniatherum caput-medusae), and North Africa grass (Ventenata dubia) may invade the stand. These conditions are more likely to develop on areas which were near developed farm and pasture lands, road and trail networks and other converted lands.
Description
This state follows a very intensive or total harvest of the mature overstory, followed by stump removal and the elimination of all other native forest vegetation. Cultivation follows. In this state virtually all the natural forest functions were eliminated by the converted use to agricultural lands (including annually tilled crops as well as hay and pasture production).
Mechanism
Long term fire exclusion (50-100+) years (resulting in Alternative State 2).
Mechanism
A widespread catastrophic stand replacing fire event occurs as a natural (but rare) event in the reference state. Ponderosa pine and Douglas-fir are virtually eliminated across all age/size classes, leading to a long-term deficiency of seed source to re-establishment Ponderosa pine (resulting in Alternative State 3).
Mechanism
Introduced cool season grasses invading sites near homesteads, pastureland, and other converted land. This includes exotic annual grass invasion of improperly grazed sites, as well as other excessive disturbance(s) of the native vegetation (resulting in Alternative State 4).
Mechanism
Site converted to annual cropland or pasture/hayland (leading to Alternative State 5).
Mechanism
Restoration practices that reduce excessive fuel loads and reduce overstory crown bulk density, as well as treatment of overstocked clumpy areas, may help to simulate historical stand densities. Tree planting in larger, un-stocked areas where Ponderosa pine and other native seed sources are absent, as well as the introduction of prescribed burning, can contribute to increased resiliency and a return to natural ecologic integrity.
Mechanism
Widespread catastrophic fire occurs, similar to that of T1B, but the intensity and impact of the wildfire event is much greater in scope due to the unnatural buildup of fuels in Alternative State 2 (resulting in Alternative State 3).
Mechanism
Ponderosa pine and Douglas-fir are planted due to the widespread lack of adequate seed source or surviving trees of any size or age class. Natural recovery will be extremely long without tree planning efforts, up to many 100’s of years as conifers would have to slowly re-establish parameter areas and then migrate inwards by natural reproduction under favorable circumstances. It is possible that persistent brush or grass/brush cover may exist for years if un-planted. Soil integrity may be slow to respond to pre-fire levels, especially considering increases in hydrophobicity, reductions in organic matter and potential for erosion immediately following fire.
Mechanism
Practices that promote the reestablishment of native understory species, for example tree and/or native grass planting in properly prepared seedbed conditions, have the potential to restore some of the function of native Ponderosa pine and Douglas-fir communities in this ecological site. Complete restoration to references conditions, however, is unlikely and rather a transition to a “current potential state” with improved ecological processes yet still including some degree of invasive species is more likely.
Mechanism
Practices are applied which reduce or eliminate unwanted weeds and invasive species, followed by the application of sound agronomic practices or by applying pasture/hayland management. Returns to Alternative State 5, and not to the Reference State.
Mechanism
Practices that promote the reestablishment of native understory species, for example tree and/or native grass planting in properly prepared seedbed conditions, have the potential to restore some of the function of native Ponderosa pine and Douglas-fir communities in this ecological site. Complete restoration to references conditions, however, is unlikely and rather a transition to a “current potential state” with improved ecological processes yet still including some degree of invasive species is more likely.
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.