Natural Resources
Conservation Service
Mesic, Xeric, Loamy Foothills and Canyons (Ponderosa Pine Warm Dry Shrub) Pinus ponderosa/Symphoricarpos albus
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
- Transition T1D More details
- Restoration pathway R2A More details
- Transition T2A More details
- Restoration pathway R3A More details
- Restoration pathway R4A More details
- Transition R4B More details
- Restoration pathway R5A More details
- Restoration pathway T5A 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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Description
The reference state has a variable but predictable plant expression across the landscape. In the larger context, these forests tended to be heterogeneous and spatially complex. 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.
The Ponderosa pine forest is comprised of pure, self-replacing stands that function under the ecological parameters that were described in the section entitled “Ecological Dynamics of the Site.”
Fire is the most important disturbance agent in this reference state of the ecological site. The fire regime of the historic reference community phase is summarized as follows:
Fire Regime Group Fire Interval (years)
I 6
Replacement Mixed Low
Fire Severity (%—probability of occurrence) 5 18 77
Range of Fire Return Interval (MFRI- years) >100 – 400+ 50-80 2-30
Average Fire Return Interval (AFRI – years) 125 35 8
Source: BpS model 910531 and FEIS “Fire Regime/Blue Mountains” publication.
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.
When the understory was impacted by wildfire (with or without overstory impacts), fire adapted species responded well following a light to moderate severity fire impact at the surface. Bluebunch wheatgrass, pine grass and elk sedge usually survived and were rejuvenated by the surface. Spirea, fireweed and limited amounts of common snowberry and bitterbrush all increase following these events.
The reference plant community was a mature pine/shrub-grass savanna. The various common successional stages are shown on the state and transition diagram. Those conditions occur in shifting locations across the overall larger landscape, at various scales, over long periods of time.
Dominant plant species
ponderosa pine (Pinus ponderosa), tree
common snowberry (Symphoricarpos albus), shrub
creeping barberry (Mahonia repens), shrub
white spirea (Spiraea betulifolia), shrub
bluebunch wheatgrass (Pseudoroegneria spicata), grass
Idaho fescue (Festuca idahoensis), grass
Submodel
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, allowed many stands to progress without the natural occurrence of fire, especially frequently occurring and beneficial fire episodes. Fire suppression 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 increased, shifting the fire regime/condition class toward a greater likelihood of stand replacement fire episodes.
Submodel
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, 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.
Submodel
Description
This state developed with the introduction and invasion of introduced grasses and noxious weeds, most notably cheatgrass. These conditions were more likely to develop on areas which were near developed farm and pasture lands, and other converted lands.
Submodel
Characteristics and indicators
This state results from human intervention beginning with 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. These sites were often referred to as “cut over farm lands”. In this state virtually all the natural forest functions were eliminated by the conversion to agricultural land use (including annually tilled crops as well as hay and pasture production).
Submodel
Mechanism
Long term fire exclusion (50-100+) years (resulting in Alternative State 2).
Mechanism
A wide spread catastrophic (also referred to as “stand replacing”) fire event occurs as a natural (but rare) event in the reference state. Ponderosa pine is 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 cheatgrass invasion of overgrazed 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
Treatment practices commonly used to rehabilitate forest lands and reduce fuels are applied. Practices include thinning and pruning, and associated practices as needed. Restoration practices that reduce excessive fuel loads and reduce overstory crown bulk density, as well as treatment of overstocked clumpy areas, are beneficial. 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
Wide spread 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 as well to Alternative State 3).
Mechanism
Ponderosa pine is planted due to the widespread lack of adequate seed source or surviving Ponderosa pine of any size or age class. Natural recovery will be extremely long without tree planning efforts, up to many 100’s of years as Ponderosa pine would have to slowly re-establish parameter areas and then migrate inwards by natural reproduction under favorable circumstances. It is likely that persistent brush or grass/brush cover would exist for years if un-planted. Soil quality (e.g. soil microbial populations and nutrient cycling) is slow to respond to pre-fire levels, especially with the lack woody debris and other contributors to soil health.
Mechanism
Site preparation and reseeding with native forest vegetation is practiced on sites that had been converted and managed in non-forest condition for a long period of time. (This process is referred to as afforestation). Practices that enable the site to revert to native understory species, for example tree and/or native grass planting in properly prepared seedbed conditions, have the potential to restore the function of native Ponderosa pine communities in this ecological site.
Mechanism
Areas that were converted to cropland and had transitioned to introduced grasses and noxious weeds are once again properly treated to re-establish viable cropland, pasture or hayland. Practices are applied which 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
Efforts like those described in Restoration Pathway 4A are needed in order to restore these areas to conditions found in the Reference State. Site preparation and reseeding with native forest vegetation is on sites that had been converted and managed in non-forest condition for a long period of time. (This process is referred to as afforestation). Practices that enable the site to revert to native understory species, for example tree and/or native grass planting in properly prepared seedbed conditions, have the potential to restore the function of native Ponderosa pine communities in this ecological site.
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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