Warm-Frigid Xeric Loamy Foothills of Basalt Mountains and Plateaus Douglas-fir Warm Dry Shrub
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 total fire exclusion (50 to 100 or more years)
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Transition T1B
A widespread catastrophic fire event
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Transition T1C
Conversion to annual cropland, pasture, or hayland
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Restoration pathway R2A
Common fuel reduction practices are applied.
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Transition T2A
Widespread catastrophic fire occurs
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Transition T2B
In the absence of a catastrophic wildfire, results in increased levels of root disease.
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Restoration pathway R3A
Reforestation
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Restoration pathway R4A
An extended period of time followed by afforestation.
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Restoration pathway R4B
Widespread catastrophic fire occurs
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Restoration pathway R5A
Afforestation
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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The Historical Reference State had a variable but predictable plant expression across the landscape. These forests tended to be heterogeneous and spatially complex, represented by a combination of patch openings, clumpy (dense or overstocked) trees which were often pole size or smaller, and as well-spaced mature overstory trees encompassing larger stand groups. The wide range of age and structural expression was possible due to the influence of the mixed fire regime, in combination with the more frequent surface under-burns. The ecologic site supported a diverse array of wildlife species which benefited from the edge effects created by numerous spatial intersections within the larger landscape, and from naturally occurring snags and large woody debris. Every stage of development provided value to the watershed--to adapted plants, animals, hydrologic functions, as well as to other valuable ecologic components of the upland forest.
The ecological site was maintained primarily by fire disturbance(s) that initiated changes to the structure, vegetation composition, and structural patterns across the large-scale forested landscape. Longer-term fire-free intervals allow Douglas-fir and a very limited occurrence of grand-fir to increase in relative abundance in the secondary (understory) stands.
Following a replacement fire, the key to conifer re-establishment in the Reference State relied on the recruitment of seed from adjacent sites or from remnant surviving “banked” seed in the soil. A surviving understory component of remnant, young regeneration was also possible. In a replacement fire, the overstory trees that survived tended to be mature early seral species as they are fairly resistant to mortality from fire.
Summary of the historic fire regime of the reference community:
Fire Regime Group Overall Mean Fire Return Interval
I (MFRI, in years) (mixed/low) 20
Replacement Mixed Low *
Fire Severity (% of all fires) 15 18 67
Average Fire Return Interval (AFRI-years) 135 110 30
* Low severity fires occur predominantly in the mid and late “open” plant community phases of the Reference State—(phase(s) 1.1 and 1.4). The AFRI reflects the variable range of occurrence of these two states. If all states are included, the low severity fire frequency interval increases.
Source: BpS model 910450 and FEIS “Fire Regime/Blue Mountains” publication.
The historic regime average size of any given wildfire event was 1,000 acres
Fire Severity Classes: Replacement, greater than 75 percent kill or top kill of the upper canopy layer; Mixed 26 to 75 percent, and low severity, less than 25 percent.
Production and Site Quality Interpretations of the ABGR/CARU Reference State:
Site index (SI) and the resulting derivation of the Culmination of Mean Annual Increment (CMAI) are different indicators of site quality. They serve as well as potential approximations of potential yield, and as a general economic rotation age of the site.
Site index is a common unit of measure for forest trees and stands. It is a simple measure of the age and height of dominant and codominant trees in a stand, usually referenced to 50 or 100 years of age. The site index age is projected either at the “age at breast height” (breast height is four and a half feet above the ground) or is given as the total tree age. The Culmination of Mean Annual Increment, is expressed as the cubic foot volume at that point (age) where periodic and mean annual increment rates intersect—in other words, where the annual incremental volume growth is at a maximum over the lifespan of a (well managed) stand.
Site Index and CMAI values for the Douglas-fir Warm Dry Shrub Ecological Site:
Ponderosa pine site index values range from 68 to 116 within the MLRA (Meyer, 1961-ADP code 600). CMAI values range from 53 to 134 cubic feet per acre per year* at 50 and 40 years respectively. This is a wide span of values.
Douglas-fir site index values range from 60 to 77 (Monserud, 1985-ADP 771), with CMAI values of 54 to 89 cubic feet per acre per year at 100 and 78 years respectively.
Three early Douglas-fir site index values for Tekoa and Gateway soils were projected using King (1966-ADP 795) The values ranged from 67 to 78. CMAI values are not projected for site index values below 70; the CMAI for the site index of 78 is 94 cubic feet per acre per year at 90 years. This particular reference is intended for west side Douglas-fir and is a poor fit for soils in this MLRA.
Western larch site index ranges from 50 to 86 (Schmidt, Shaerer, Roe 1976 ADP 265), with CMAI values of 63 to 132 cubic feet per acre per year at 70 years each.
One additional Western larch site index was calculated using Cochran, 1985 (ADP 261)—That value is 86, with corresponding CMAI value of 95 cubic foot per acre per year at 93 years
* cubic foot per acre per year (ft3/ac/yr.)
Representative Plants list of the Ecological Site:
Trees:
Species Name Scientific Name ADP Code Ecological Interpretation
Western larch Larix occidentalis LAOC Early Seral
Douglas-fir Pesudotsuga menziesii PSME Mid Seral
Ponderosa pine Pinus ponderosa PIPO Early Seral, dominant fire-maintained conifer
Shrubs:
Species Name Scientific Name ADP Code Ecological Interpretation
Serviceberry Amelanchier alnifolia AMAL Sprouts from surviving root crowns, also from seed.
Creeping Oregon grape Berberis repens BERE Sprouts from surviving rhizomes following fire
Snowbrush ceanothus Ceanothus velutinus CEVE Moderately resistant to fire-kill—limited occurrence
Oceanspray Holodiscus discolor HODI Moderately resistant to fire kill, can be enhanced.
Oregon boxwood Pachistima Myrsinites PAMY Moderately resistant to fire-kill
Ninebark Physocarpus malvaceus PHMA Susceptible to fire kill, occupies patch openings (occurs only in the modal PA)
Chokecherry Prunus virginiana PRVI Sprouts from surviving root crowns
Baldhip rose Rosa gymnocarpa ROGY Sprouts from surviving root crowns
Scouler’s willow Salix scouleriana SASC Sprouts vigorously after fire
Common snowberry Symphoricarpos albus SYAL Maintains pre-fire frequency/coverage
Grasses:
Species Name Scientific Name ADP Code Ecological Interpretation
Bromes Bromus spp. Variable fire responses
Pinegrass Calamagrostis rubescens CARU Survives cool to moderately severe fires: rhizomatous
Elk Sedge Carex geyeri CAGE Sprouts from surviving rhizomes
Western fescue Festuca occidentalis FEOC Fire response varies with surface intensity
Wheeler’s bluegrass Poa Nervosa PONE
Forbs:
Species Name Scientific Name ADP Code Ecological Interpretation
Common Yarrow Achillea milleforlium lanulosa ACMIL Survives most fires, can increase rapidly
Heartleaf Arnica Arnica cordifolia ARCO Tolerates sun and shade
Strawberries Fragaria spp. Susceptible to fire kill
Sweetscented Bedstraw Galium triflorum GATR Susceptible to fire kill, can increase following spring or fall fires
Hawkweeds Hieracium spp
Lupines Lupinus spp
Western Meadowrue Thalictrum occidentale THOC Susceptible to fire kill
Estimated total herbage production (in pounds/acre, air dried—this is an approximation from a similar plant association in “Plant Associations of the Blue and Ochoco Mountains” publication) are as follows:
• PSME/PHMA 150-535 (average 273)
• PSME/SYAL 125-1,000 (average 412)
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 ecological benefits of the low intensity fires were lost, and shifted to a fire regime/condition class with a greater likelihood of stand replacement fires (“lethal” fires).
The overall consequences of the changes to the forest structure and function due to the combined management actions in the last century are:
INCREASED
• Stand Density
• Shift towards mid seral species
• Amount of understory and secondary conifer occupancy
• Fuel loads and elevated risk of catastrophic high severity fires
• Habit for dense-forest wildlife (such as white-tail deer)
• Older aged fire adapted shrub species dominate the area
DECREASED
• Large, old age pine and larch (in both occupancy and phenotypical expression)
• Regeneration of early seral species
• Habit for species dependent on open stands of old pine forests
• Decreased levels of snags and large organic debris
• Reduction in soil quality due to loss of soil wood and organic matter
• Decrease in genetic variation of early seral species
Submodel
Description
State 3 represents conditions immediately following a stand replacement fire. These types of fires, when they occurred within the historic context of the Reference State, transitioned the stand to this alternative state when the vast majority of the cone producing conifers were eliminated by the fire, and when other sources of conifer recruitment are also absent (i.e. resulting in un-stocked stand conditions).
Submodel
Description
This state may seem to mimic the conditions of Alternative State 3 in that forest stocking is virtually non-existent, but the underlying cause leading to the un-stocked condition and the recovery options are vastly different. In this state, immediate restoration by planting is not feasible because the root mass is still active in the soil, and young developing conifer seedlings will succumb to root disease mortality in a short period of time. Poorer quality sites are at greater risk of root disease occurrence and impacts, and species such as grand fir and Douglas-fir are most susceptible, although grand fir is limited in natural occurrence.
A catastrophic wildfire under these circumstances would transition the site to Alternative State 3, in the same manner as T2A. The risk of catastrophic fire declines as brush levels increase.
Submodel
Mechanism
Long-term total fire exclusion (50 to 100 or more years) results in Alternative State 2.
Mechanism
A widespread catastrophic (also referred to as “stand replacing”) fire event occurs as a natural (but relatively rare) event in any phase within the Reference State. Due to the size and intensity of the wildfire, a deficiency of seed source(s) inhibits the re-establishment of the early seral Ponderosa pine and other conifers, resulting in the development of Alternative State 3.
Mechanism
Forested site converted to annual cropland, pasture, or hayland, leading to State 5.
Mechanism
Common fuel reduction practices are applied. These practices include low thinning and pruning to reduce ladder fuels. In addition, stands are managed to shift conifer species composition to early seral Ponderosa pine and to improve overall stand health and vigor.
Mechanism
Widespread catastrophic fire occurs, similar to that of T1B, but the intensity and impact of the wildfire event is much greater in scope because of the unnatural buildup of fuels in Alternative State 2. The transition results in the development of Alternative State 3, but with a larger degree of resource impact to the site than in T1B.
Mechanism
In the absence of a catastrophic wildfire, the long-term site occupancy of mid seral Douglas-fir (and lesser levels of grand fir) results in increased levels of root disease, especially on poor nutritional soils. In time all conifer species are impacted and are eliminated from the site, leading to long-term brush dominated occupancy.
Mechanism
Reforestation (e.g. the planting of Ponderosa pine with limited Douglas-fir) is applied in the short-term aftermath of a catastrophic, stand replacing wildfire. Native fire-adapted understory species rebound naturally.
Mechanism
An extended period of time (up to 100 or more years) is needed for the extensive (infested) below ground root mass to decompose. After this time, afforestation can be applied in order to establish viable forest stands.
Mechanism
Widespread catastrophic fire occurs, similar to that of T1B, but the intensity and impact of the wildfire event is much greater in scope because of the unnatural buildup of fuels in Alternative State 4. This is essentially the same type of event that is described in T2A. Note that a catastrophic wildfire can occur during the shift from Alternative State 2, or in the aftermath of the establishment of Alternative State 4. The threat of wildfire is reduced as the stand changes from dead and dying conifers to persistent brush.
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