Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 1

APPENDIX B - 1 

Vegetation Modeling and Timber Suitability 

Introduction 

The basic analytical framework for the revision of the Wasatch-Cache Forest Plan is 

prescribed in the NEPA process. A set of alternative scenarios, representing different 

approaches to the identified needs for change and issues, was simulated over time to 

provide information to compare and contrast those alternatives in terms of their ability to 

achieve the Desired Future Conditions (DFC) in cost-effective and least-risk ways. 

Analyzing the effects of the alternatives included evaluation of vegetation dynamics; 

terrestrial, aquatic and botanical resource diversity and viability; roads analysis, 

recreation opportunity spectrum and scenery management system application, and timber 

suitability, range capability/suitability, oil and gas reasonably foreseeable development, 

and social and economic analysis. Succession within the aspen, conifer, and oak 

vegetation types were modeled by using the Vegetation Dynamics Development Tool as 

described in the following section. Succession within the sagebrush vegetation type was 

done using a simple model that focused on existing conditions and desired conditions, 

and how each alternative would move toward those desired conditions. This model is 

described in more detail in the section titled Sagebrush Modeling starting on page B1-25 

of this appendix. 

Analysis Processes 

Modeling effects on forested vegetation was accomplished using the Vegetation 

Dynamics Development Tool (VDDT). VDDT is the property of its developers, ESSA 

Technologies, Ltd., of Vancouver, B. C. 

Projecting changes in vegetation structure and composition over time is an important part 

of landscape-level analyses. Vegetation can change due to a variety of factors such as 

human activity, fires, insects, pathogens, animals, weather, growth, and competition. The 

interaction of these factors can be quite complex, and it can be difficult to project the 

combined effects over long periods of time. VDDT is a software tool that allows the 

construction of models for the purpose of simplifying those combined effects over time, 

and examining the roles of various disturbance agents and management activities in 

vegetation change. 

VDDT models were constructed for the Forest for each alternative to address three main 

questions. These are: first, what set of management activities, if any, must be placed on 

the landscape to achieve the objectives of a particular alternative? Objectives were 

generally defined as a mix of structural stages within each vegetation cover type at a 

particular time. Second, where natural succession and natural disturbances, rather than 

management activities, determine the future conditions of the forest, what will the forest 
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 2

look like and how will it function in the near and distant future? Third, what level of 

timber harvest, if any, is sustainable for this alternative? 

Using VDDT software, models covering ten to twenty decades were formulated for each 

alternative, with analysis units that represented approximately 42 vegetative conditions, 

described by landscape location, vegetation cover types, and structural stages, moving 

through time along disturbed or undisturbed successional pathways. The undisturbed 

pathways followed basic successional processes and were the default unless either a 

natural disturbance event occurred or a management activity was imposed. Natural 

disturbances included wildland fire with failed suppression, catastrophic insect and 

disease events, and catastrophic large-scale fire. Management activities such as livestock 

grazing, prescribed fire, and timber harvest pushed the analysis units off the undisturbed 

pathways and onto disturbed pathways that reflected the outcome from such treatment. 

Desired future conditions (DFC) for each alternative were represented as goals for the 

number of acres to be maintained in specific structural stages, by cover type or groups of 

cover types. 

Disturbances, both natural and managed, were introduced into the modeling process via 

probabilities. Some disturbance probabilities were non-linear, allowing, for example, the 

probability of a catastrophic insect infestation to increase as the proportion of a particular 

cover type that is prone to infestation (such as old Spruce-Fir) increases. This allowed 

some recognition of the dynamics of contagion in both fire and insects; however, none of 

the analysis units were spatially specified beyond the landscape unit in which they 

occurred, so the spatial component of contagion was ignored. 

Developing Analysis Units 

Analysis units are made up of forested land with distinctly different characteristics that 

can be estimated, modeled, combined, and then projected through time to analyze change. 

The Forest team combined a variety of characteristics to develop analysis units that 

would focus on ecosystem processes and function while meeting the intent of the 

National Forest Management Act. The two major vegetation characteristics or 

components that were combined were structural stage (size class and canopy closure) and 

cover type. These groupings were then overlaid with rule sets or GIS coverages such as 

Management Prescription Categories (MPC) to finalize the analysis units and develop the 

analysis unit acreages for the VDDT model. Analysis units are the acres of a structural 

stage/cover type combination within a MPC. 

Landscapes 

The Forest was divided into 3 distinct geographic areas, the Uinta Mountains, the 

Overthrust Mountains and the Bonneville Basin. The Uinta Mountains region covers the 

north slope of the range, and includes the Kamas, Evanston and Mountain Ranger 

Districts. The Overthrust region covers the Bear River Range, including the Ogden and 

Logan Ranger Districts. The Bonneville Basin is the western portion of the Forest, 

including the west desert and Stansbury Mountains. Modeling was limited to the Uinta 
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 3

Mountains and Overthrust Mountains because the likelihood of management activities 

(other than fire) was considered greater in those areas than in the Bonneville Basin. 

Size Classes 

The Forest vegetation layer in GIS was used as the basis for determining the breakdown 

of size classes to be used in modeling. Size classes used in the model were simplified 

from the vegetation layer to streamline the modeling process, and were based age of the 

vegetation. Limits of the classes were selected to represent changes that were significant 

for management purposes. 

Conifer Size Classes are: 

Grass/Forb - The length of time a stand remains in the grass/forb stage depends 

upon the species and the level of disturbance that created the grass/forb stage. For 

most types, the grass/forb persists for approximately 5 years; however, significant 

disturbance such as stand replacement fire may create a grass/forb stage that 

persists for several decades 

Seedling/Sapling - The seedling/sapling stage is reached when regeneration has 

progressed to the point that trees become the dominant vegetation on the site. For 

most forest types, this stage is from 5 to 15 years. 

Immature Tree - This class is defined as ages 15 to 80 years. 

Mature Tree - Stands between 80 and 150 years are considered mature for 

purposes of modeling. 

Old - The old class is defined as trees greater than 150 years old. 

Aspen and Oak Size Classes are: 

Grass/forb/seedling/sapling - The grass/forb and seedling/sapling classes are 

combined in these models, because the sprouting of the aspen and oak occurs 

concurrently with the grass and forb establishment. The class is defined as 0-10 

years in the Overthrust Mountain model, and 0-20 years in the Uinta Mountains 

model. 

Immature tree - The immature class is defined as 10-35 in the Overthrust 

Mountain model, and 20 to 70 years in the Uinta Mountains model. 

Mature tree - Aspen and oak are considered mature after 35 years in the Monte 

Cristo area, and 70 years in the Uinta Mountains. 
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Wasatch-Cache National Forest B1 - 4

Canopy Closure 

The density of the vegetation was categorized into 3 canopy closure categories. They are 

used to determine the potential risks from insects or wildfire, to estimate species 

composition, and to reflect the effects of management activities and natural disturbances. 

The higher the stand density, the less light reaches the forest floor, which favors climax 

species and increases the risk to insects and lethal fire. Some cover types, due to the 

harsh sites, do not reach a high-density condition, but only progress to moderate canopy 

closure. Management activities such as thinning and grazing may move stands from a 

high-density class to a lower density class. Similarly, fire, both natural and prescribed, 

may modify the density of the vegetation resulting in a shift from one class to another. 

Canopy Closure groups are: 

• Low (less than 40% canopy closure) 

• Medium (40-70% canopy closure)

• High (greater than 70% canopy closure)

Vegetation Cover Types 

Vegetation composition is influenced by environmental (site) characteristics. Using 

cover types to classify the landscape provides a logical framework for studying 

succession, or vegetation changes over time. 

Cover types were then used to group size class and canopy closure into ecological units 

that would have similar responses to disturbances and have similar pathways through the 

successional stages. These groupings became the basis for the VDDT model, and 

understanding the ecological process and function of the vegetation. A model was 

developed for each cover type. The 6 individual cover type models were combined into a 

forest vegetation model that projected changes for all cover types simultaneously. A 

version of the combined model was run for each Forest Plan alternative to project 

vegetation changes associated with that alternative. 

Cover Type Groups used in modeling are: 

1. Douglas Fir 

2. Spruce Fir 

3. Mixed Conifer / Lodgepole Pine 

4. Stable Aspen 

5. Seral Aspen 

6. Oak 

Seral aspen presented a unique challenge because it is associated with all of the other 

forest types. Generally, seral aspen is shown on the vegetation layer as aspen/conifer (if 

conifer comprises less than 50% of the stand composition) or conifer/aspen (if conifer 

comprises more than 50% of the stand composition). It represents aspen stands that are 

currently undergoing conversion to conifer due to encroachment. If the conifer 
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Wasatch-Cache National Forest B1 - 5

encroachment continues long enough, aspen will be replaced by conifer to the point that 

eventually it will disappear from the stand. To reflect this potential, the seral aspen 

model was incorporated into each of the conifer models as a separate successional 

pathway parallel to the conifer pathway, which merges with the conifer at advanced 

stages. This permits us to model the loss of aspen in the absence of fire or mechanical 

disturbance, and to reflect the potential to maintain or increase the aspen component 

through disturbance of aspen/conifer or conifer/aspen stands. 

Seral aspen stands were included in the appropriate model based on the major conifer 

species present in the stand. For example, a Douglas-fir/aspen stand was modeled in the 

seral aspen pathway of the Douglas-fir model. 

Tentatively Suited Timberlands 

Reassessment of tentatively suited timberlands has been completed in accordance with 

the National Forest Management Act, as contained in Forest Plan regulations 36 CFR § 

219.14 and Forest Service Handbook FSH 2409.13, Chapter 20. The National Forest 

Management Act requires that, as a minimum, lands previously identified as not suited be 

reassessed at least every 10 years. Since current efforts to revise the Forest Plans 

coincide with the need to reassess timberlands not suited, a complete reassessment of 

suited timberlands has been performed. This allowed for a comprehensive examination 

of the status of timberlands that took into account changes since the previous assessment 

of timberlands. Some of these changes include changes in land ownership, increased 

knowledge and experience with reforestation efforts, wildfire events, and increased 

knowledge and experience regarding timber management effects on soils and watersheds. 

Assessment of tentatively suited timberlands was accomplished using Geographic 

Information Systems (GIS). Use of GIS results in consistent identification of each of the 

following data elements: 

• Net National Forest land area administered. 

• National Forest lands that are not forested. 

• National Forest lands that have been withdrawn from timber production. 

• Areas that are physically unsuited for timber production due to the inability to assure 

adequate restocking, or irreversible damage to soils or watersheds. 
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 6

Table B-1. Steps and Data Sources for Assessing Tentatively Suited Lands 

Steps for Assessing Tentatively Suited Lands Data Sources 

1). Determine net National Forest system land area 

for each National Forest. 

Lands data in GIS 

2). Identify non-forested lands. These lands include: 

• Non-forest vegetation cover types 

• Roads. 

• Streams. 

• Lakes, ponds and reservoirs >= 1 acre is size.

• State and county roads on National Forest 

system lands

Non-forest vegetation cover for the cover 

types identified here came from satellite 

imagery. 

The remaining items identified are from 

several data layers in GIS. 

3). Identify and subtract National Forest system lands 

that have been withdrawn from timber production 

including: 

• Designated wilderness areas. 

• Research Natural Areas. 

• Wild segments of wild & scenic rivers (outside 

of wilderness areas). 

• Experimental Forests 

• Other withdrawn areas 

* Utility right-of-way corridors. 

* Electronic sites. 

* Administrative sites (unless previously 

identified in step 2 as areas withdrawn from 

timber production). 

* Developed campgrounds. 

The products resulting from completion of steps 1, 2 

and 3 will be: 

Identification of available forested lands, identification 

of unavailable withdrawn lands, and non-forested 

lands. 

Each of the identified items is available 

from data layers in GIS 

. 

4). Identification of physically unsuited lands. 

 Slopes greater than 40% 

 Elevations over 10,000 feet 

 Timber operability limits 

 

Vegetation Cover Type Maps , USGS 

digital elevation models, Timber 

operability mapping (wet areas). 

Vegetation Dynamics 

The primary conceptual model for vegetation dynamics is that any given unit of 

vegetation will change over a period of time, succeeding through some arbitrarily defined 

set of stages if undisturbed; if disturbed, either naturally or by management, the 

vegetation will instead change through a different set of stages. Each potential set of 

stages, in sequence, is called a pathway. 

Pathways and Probabilities 

Successional pathways, with or without disturbances, summarize scenarios in vegetation 

dynamics. Modeling such scenarios so as to have a quick and simple, yet useful, way of 
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 7

observing changes over time necessarily requires that only the most basic driving forces 

be included. Perhaps more importantly, many of those forces exert themselves as events 

which are expected to occur but for which the timing and frequency are essentially 

random. While management activities are disturbances that may be accurately predicted, 

natural disturbances may only reasonably be predicted in terms of historical probabilities. 

The outcomes from those disturbances, then, are also necessarily probabilistic. Clearly, 

the interaction of the many biological and physical factors that are at work can be quite 

complex, and it can be difficult to project their combined effects over long periods of 

time; the longer the scenario, the less certain the outcome. 

Scenarios can define different sets of assumptions about fire suppression, insects and 

disease, or forest management objectives, by assigning probabilities to the applicable 

successional pathways. In each scenario, changes in the dominant disturbance types and 

their frequency result in changes in the vegetation. For example, a reduction in fire 

frequency, representing an assumption of increased fire suppression success, may 

increase the number of acres in a condition that is more susceptible to insects. In that 

case, without changing the probability of insect-caused disturbance, more insect-caused 

disturbance will occur in the model because more land area is in the more susceptible 

condition. 

Undisturbed Succession 

Changes in vegetative conditions due to dynamics such as regeneration, growth, and selfthinning, form the basic successional pathway in the absence of disturbance. Some 

successional pathways are cyclical, indicating the likelihood of some self-limited 

lifespan, followed by self-regeneration and repetition of the cycle, unless disturbed. 

Other successional pathways have an end condition that represents a steady state that can 

be maintained perpetually. 

Modeled changes due to successional dynamics are defined by the time that a vegetative 

unit remains in a particular stage, and by the stage into which it will move after that time 

has passed. Figure B-1 displays an example of a VDDT model showing successional 

pathways, and the time required to move between classes. 
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 8

Figure B-1. Example of successional pathways in VDDT models, 

showing successional classes and length of time required moving to next 

class in the absence of disturbance. 

Natural Disturbances 

Disturbance-related pathways specify, for each stage, the type of disturbance, its 

probability (which defines its return frequency) and its impact on the vegetation. The 

impact is represented by the different stage to which the vegetative unit has been 

transferred as a result of the disturbance. That new stage may be on the undisturbed 

pathway, representing a simple setback in succession, or it may be on another pathway 

entirely. Figure B-2 is an example of a model showing successional pathways and 

natural and management disturbance pathways. 

Insects and Disease 

For example, a unit defined as being Douglas-fir, mature, with greater than 70% canopy 

closure, may be given a 0.1% probability of experiencing an infestation of beetles. If the 

infestation does not occur, that unit may remain in its current stage for a defined number 

of years, eventually succeeding to the next stage along the undisturbed pathway. 

However, if the infestation does occur, the unit may be transferred to a different stage, 

defined as Douglas-fir, mature, 30%-70% canopy closure, with high fuel loads. This new 

stage is not on the undisturbed successional pathway. 

SS <40%

GF

Post-CF

M 30-70%

Lo Fuel

Old

M 30-70%

Hi Fuel M >70%

GF

Regen

IM >40%

Hi Fuel

IM >40%

Lo Fuel

5 yr

25 yr

10 yr

55 yr

55 yr

40 yr

40 yr

90 yr
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Wasatch-Cache National Forest B1 - 9

Wildland Fire 

The same vegetative unit may also have some probability of incurring the effects of a 

wildfire. If that disturbance occurs, the unit may be transferred to a stage defined as 

Douglas-fir, grass-forb stage, regenerated. This new stage is on the undisturbed 

successional pathway, representing the starting point for the pathway. 

Management Disturbances 

From a modeling perspective, there is no technical difference between natural 

disturbances and management disturbances. They go into the models in exactly the same 

way. The conceptual difference is in the calculation of probabilities, and in how they are 

used. 

Management disturbances are the controlling input factors for the models. The objectives 

for a particular scenario may call for a certain mix of vegetative stages by a certain time, 

and the management disturbances must be adjusted up or down in terms of probability so 

as to achieve those objectives. 

For example, where initial conditions are that most of a cover type is in older stages, the 

scenario objectives may require that at least half of that cover type is in an immature or 

younger condition within some time span. To accomplish that, some combination of 

management activities that result in moving the vegetation to younger stages must be 

implemented. A set of initial probabilities can be calculated as a starting point for the 

model; after running the model, if the objectives are not achieved, the probabilities can be 

adjusted up or down in successive runs until the desired results are seen, or until it is 

reasonably proven that the desired results are not feasible. 

Prescribed Fire 

Intentional disturbance by setting fire to the vegetation, or by allowing naturally 

occurring fires (wildland fire use) to burn, are treated as “prescribed fire” in these 

models. The result of the fires depends on the cover type and structural stage in which 

they occur. The impacts in some cases are lethal, causing the vegetation to be transferred 

to a “regenerated” stage; or the impacts may be non-lethal, resulting in transfer to a less 

dense stage. In some cases, fire simply maintains the vegetation in its current stage, 

preventing it from moving along its undisturbed successional pathway. 

Timber Harvest 

Harvest disturbances include partial harvests such as thinnings, regeneration harvests, and 

salvage harvests. They are designed to achieve silvicultural objectives and to produce 

salable timber products. The stages to which vegetation units are transferred after a 

harvest disturbance are intended to represent the desired silvicultural conditions that 

prompted the planned activity. For example, a partial harvest on a unit in a stage defined 

as Douglas-fir, immature, greater than 40% canopy closure, may result in the transfer of 

that unit to a stage defined as Douglas-fir, mature, 30%-40% canopy closure. Such a 

disturbance would represent the planned thinning of an overly dense unit by removing the 
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 10

smaller and younger trees, thereby reducing the density and increasing the average size 

and age of the remaining trees to achieve silvicultural objectives related to increased 

resistance to insects while increasing the commercial timber value of the unit. 

Livestock Grazing 

Grazing by permitted livestock was included in the models as a management disturbance 

due to the effects that grazing has on many aspects of vegetation dynamics. For example, 

in a vegetation unit consisting primarily of seral aspen, grazing may increase the rate at 

which the aspen converts to conifer by eliminating aspen sprouts through browsing while 

leaving the conifer seedlings untouched. 

Mechanical Treatment 

The oak cover type model included mechanical treatment to reduce densities and average 

ages of the vegetation units. Essentially similar to a thinning harvest treatment, there is 

no commercially viable commodity produced by this management activity. The primary 

objective is to reduce frequency and intensity of fires through the construction and 

maintenance of fuel breaks in the urban interface. This treatment will tend to occur 

periodically on the same acres, so was not modeled. Prescribed fire that is used to change 

the structural stage of the stand was modeled. 

Figure B-2. Example of VDDT model showing successional and disturbance pathways. 

SS <40%

5,000

SS <40%

GF

Post-CF 500

GF

Post-CF

M 30-70%

Lo Fuel

15,000

M 30-70%

Lo Fuel

Old

40,000

Old

M 30-70%

Hi Fuel

2,000

M 30-70%

Hi Fuel M >70%

25,000

M >70%

GF

Regen

1,000

GF

Regen

IM >40%

Hi Fuel

1,500

IM >40%

Hi Fuel

IM >40%

Lo Fuel

10,000

IM >40%

Lo Fuel

5 yr

25 yr

10 yr

55 yr

55 yr

40 yr

40 yr

90 yr

Fire

Insects

Harvest
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Wasatch-Cache National Forest B1 - 11

Development of Alternative Models 

The same models were used for the two geographic areas modeled; however, differences 

in growth potential of the sites were reflected in longer time spans to move between 

classes where appropriate. Where differences existed, the models were modified to 

reflect those differences. The primary occurrence of this was in modeling stable aspen 

stands. Stable aspen in the Overthrust Mountains attains greater size than does aspen in 

the Uintas, so two separate stable aspen pathways were developed. 

Assumptions Used in Model Development 

As discussed above, succession pathways were developed to display how stands would 

progress over time in the absence of disturbance. Disturbances serve to “deflect” acres 

from the successional path, with the affected acres being directed to different endpoints, 

depending upon which disturbance caused the deflection. The general assumptions used 

in model construction are outlined below. 

Aspen: 

Aspen occurs in two distinct types on the Wasatch-Cache: (1) stable or self-regenerating 

stands, and (2) successional stands which occupy a site following disturbance, and which 

will eventually be replaced by conifers in the absence of continued disturbance. Two 

separate models were developed to reflect the differences between these aspen types. 

The stable aspen type regenerates quickly following disturbance by sprouting from the 

root system. Typically, large numbers of seedlings occur on the site and grow rapidly 

into the seedling/sapling and immature classes. Stands reach maturity in approximately 

35 years, and will persist in the absence of disturbance for several decades. Harvest or 

fire or insect/disease caused mortality will move the affected acres back to the grass/forb 

and seedling/sapling stage. Heavy grazing pressure from livestock or wildlife can reduce 

the number of aspen sprouts and delay stand development. To reflect the successional 

and disturbance pathways for this type, a model with 4 stages or classes was developed. 

The classes are: grass/forb/seedling/sapling (GS/SS), Immature (IM), Mature with 40-

70% canopy closure (M4-7), and Mature/Old with greater than 70% canopy closure. The 

time required to move along the successional path between classes is: GS/SS to IM - 10 

Years, and IM to M/O - 25 years. Grazing disturbance will send affected acres into the 

M4-7 class, which then takes 35 to 70 years to move into the M/O. This latter path 

reflects the effects of continued heavy grazing pressure on stand succession. Prescribed 

fire or failed fire suppression will move acres from their current class to the GS/SS class, 

where they begin the successional sequence over again. 

Successional aspen required a different model because of its unique role. We assume that 

conifers, aspen, or both may occupy an acre of land in this type. Aspen typically occurs 

immediately following fire or other major disturbance on acres where it had a predisturbance presence and had a root system to provide sprouting. Rapidly growing root 

sprouts gain early dominance of the site and provide a moderating effect on the site 

conditions that facilitates conifer seedling establishment. Conifers will begin to seed in 

and will continue to increase in numbers and size throughout the life of the stand. 
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Wasatch-Cache National Forest B1 - 12

Eventually, without disturbance to reduce the conifer competition and promote aspen 

regeneration, conifers will come to dominate the stand. Over many decades, the shorterlived aspen will die out, and eventually the stand will be converted to conifer. To display 

the effect of this relationship, successional aspen was modeled as an alternate pathway of 

the dominant conifer model (aspen/Douglas-fir, aspen/spruce, aspen/mixed conifer). The 

aspen successional pathway in the model uses the same 4 classes as the stable aspen, but 

has 3 additional classes representing the increasing dominance of conifers. Disturbances 

that occur before aspen has been eliminated from the stand will send affected acres back 

to the aspen pathway. However, after approximately 300 years without stand replacing 

disturbance, acres will move into the conifer pathway. Disturbances occurring after 300 

years will move acres back along the conifer pathway, reflecting elimination of aspen 

from the stand. 

Spruce-fir: 

The spruce-fir successional pathway proceeds from grass/forb (GF) to seedling/sapling 

(SS), immature (IM), mature (M), and ultimately, to old (O). The assumption is that it 

will take 10 years to regenerate and move from GS to SS, 10 years from SS to IM, 60 

years from IM to M and 60 years from M to O. Therefore, an acre of this type will 

require 140 years to reach the oldest class, and will remain there for many decades in the 

absence of disturbance. Disturbances will affect the time it takes to reach a particular 

class, and in some cases, the class that the affected acre moves into. For example, insect 

outbreaks that kill the overstory trees will create a structure of seedlings with a heavy fuel 

loading resulting from the dead trees. Some of the acres from this new class will follow 

the successional path and move toward the endpoint. However, the high fuel loading will 

predispose the stand to wildfires. Fires in this class will tend to be high intensity and will 

create conditions that make regeneration difficult (large openings, potential for soil 

erosion, subject to temperature extremes, etc.) Therefore, regeneration will take 

considerably longer than projected in the normal successional pathway. To reflect this 

possible outcome, insect outbreaks in the model put acres on a pathway to a 

seedling/sapling high fuel class, from which some acres will proceed to the immature 

class, and some will follow the fire path into post-fire GF class. Once in the post-fire GF 

class, acres will remain there for 50 years, reflecting the long regeneration period as a 

result of the high intensity fire. 

Harvest treatment disturbances move acres into various classes, depending upon the level 

of harvest. Regeneration harvest will move acres to the GF class; thinning will move 

acres into a class with a lower canopy closure, and will reduce the length of time needed 

for them to move into the next higher class on the successional pathway. For example, 

partial harvest that occurs within the IM class will direct those acres to a mature, 40-70% 

canopy closure class. From that class, it takes 25 years to reach the M class, instead of 

the 60 years required without thinning. 

Douglas-fir: 

The Douglas-fir model is very similar to the spruce-fir model, with succession 

progressing through the same classes. However, Douglas-fir tends to occur on lower 

quality sites than spruce, so requires a longer time period to reach the old class (155 years 
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 13

vs. 130 for spruce). Douglas-fir stands are also susceptible to bark beetle mortality, and 

acres affected by beetles are directed to a high fuel SS class similar to that in the sprucefir model. As with spruce-fir, fires occurring in the high fuel class will tend to be high 

intensity and move the affected acres back to a post-fire GF class. Douglas-fir is more 

tolerant of these conditions than is spruce, so while the effect is to delay regeneration, it 

delays it approximately 25 years, rather than the 50 years in the spruce-fir model. Low or 

moderate intensity prescribed fires can be used to perpetuate Douglas-fir stands, by 

removing excess trees and preparing sites for natural seeding. The model addresses the 

use of fire at every class, with the effects depending upon the severity of the fire. High 

intensity prescribed fire will send acres along a path to GF, while moderate or low 

intensity fires will send acres to less dense classes (such as mature, 30-70% canopy 

closure, low fuel), or cycle them back through their current class. 

Mixed Conifer/Lodgepole: 

The mixed conifer/lodgepole pine model is similar to the other conifer models, with some 

differences based on geographical area and the presence of lodgepole pine. Lodgepole 

pine is a fire-adapted species, and seeds in readily after stand replacing fires, even over 

extensive areas. Therefore, the model displays a relatively rapid progression through 

the GF and SS classes. 

Mixed conifer stands in the Bear River range grow rapidly, moving to the mature class in 

approximately 50 years, and the old class in 145 years. Stands in the mature and old 

classes are susceptible to bark beetles, but the mixed species composition tends to prevent 

stand replacement epidemics. Rather, a beetle attack will affect only a particular species 

while leaving the other species unaffected. The result is a thinning of the canopy closure 

of the stand, a shift in the species composition, and an increased fuel loading from the 

dead trees. To reflect this, the Overthrust model contains a mature, low canopy closure, 

high fuel class (M<4H). Acres reach this class via the insect disturbance path from the 

mature and old classes. Once in this class, acres will either follow the succession 

pathway, or one of several disturbance pathways, including regeneration harvest, salvage, 

or a high intensity fire. In the latter case, the presence of lodgepole pine will rapidly 

regenerate the stand, avoiding the delay experienced by spruce-fir and Douglas-fir stands. 

Mixed conifer stands in the Uinta Mountains grow more slowly, taking approximately 80 

years to reach the mature class versus 50 years for the Bear River Mixed Conifer type. 

This is in part due to the extremely high number of trees per acre that reduces the growth 

of the individual trees. In addition, some acres are so densely regenerated that the stand 

stagnates, or grows very slowly, such that trees 80 years old may be only 4 – 6 inches in 

diameter. Without some disturbance, these stagnated stands will remain in that condition 

for many decades. Therefore the Uinta Mountain Mixed Conifer/Lodgepole pine model 

contains an additional pathway from GF to dense seedling/sapling (SS>4) and ending at a 

stagnated pole class (P>7). Stands will remain in that class unless harvest, prescribed 

fire, or failed fire suppression moves them along a disturbance pathway. Insect affects 

are modeled the same as for the Bear River MC. 
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 14

Oak: 

Oak is a very simple model compared to those for aspen and conifer forest types. The 

model contains only 3 classes, seedling/sapling, mature, and old. Oak sprouts prolifically 

from the root collar following disturbance, and reaches the old class in only 40 years. 

The disturbances modeled are limited to mechanical treatment, prescribed fire, and failed 

fire suppression, with all disturbance pathways leading to the seedling/sapling class. 

Populating the Model 

Once the models were constructed, the existing forest types were assigned to a class in 

the model. Forest GIS layers were used to sort and summarize forest stand data based on 

species, size class and density. The forest stands on the Wasatch-Cache tend toward the 

oldest classes, and have not been significantly affected by disturbances for several 

decades. Therefore, the majority of stands were put in the oldest class that was the 

closest fit to the size class and density, regardless of the actual stand age. Mixed 

conifer/aspen stands were put into classes within the MC model based on the dominant 

species, i.e., conifer/aspen stands in the database (those with conifer representing more 

than half the stand) went into classes within the model that had conifer as the dominant 

species. Aspen/conifer (stands with aspen comprising more than half the stand) went into 

classes with aspen dominant. The database did not have size class and density data for 

oak, so the determination of where in the model those stands were placed was based on 

knowledge of Forest personnel. We know that approximately 4000 acres had burned 

within the last 10 years, so that number of acres was placed in the seedling class. The 

rest of the oak acres were split with approximately 75% put in the oldest class, and 25% 

in the mature. 

Management Prescription Categories (MPCs) 

The array of MPC assignments to the alternatives was modeled in VDDT. See Appendix 

D-1 in this EIS for a complete description of MPCs. 

All National Forest lands were assigned to a particular management prescription category 

based on the capabilities of the land, management opportunities and needs, and the 

management emphasis of the alternative. GIS layers were created for each alternative 

that displayed the MPC assignments. These layers were merged with the vegetation layer 

to determine the number of acres in each MPC for each alternative. The resultant data 

was used to create initial conditions files for each alternative in VDDT that reflected the 

distribution of acres into MPCs. A particular area may be assigned to 5.2 in Alternative 

5, while it may be assigned to 3.2 in Alternative 6, for example. 

In the model, MPCs were sorted into the following 6 groups, with each consisting of 

MPCs that would have similar probabilities of various disturbances or treatments for each 

cover type, age class, alternative and prescription. 

• Group 1 includes all wilderness, and other MPCs that would not allow vegetation 

manipulation (1.x, 2.4,2.7). 

• Group 2 includes backcounty and recreation emphasis (2.6, 4.1,4.2,4.3,4.4, and 

roadless portions of 3.1,3.2,5.1,6.1). 

• Group 3 includes scenic byway and developed recreation MPCs (2.5, 4.5). 
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 15

• Group 4 includes aquatic and terrestrial habitat emphasis (3.1, 3.2). 

• Group 5 includes forest and range vegetation treatments designed to meet PFC 

(5.1, 6.1). 

• Group 6 includes commercial and economic opportunities from timber 

management and forage production (5.2 and 6.2). 

The number of acres within each management prescription category and where those 

prescriptions are mapped on the land are the primary differences between alternatives. 

For example, Alternative 1 designates no forested lands as MPC 5.2/6.2 (commodity 

emphasis), while Alternative 5 designates a high percentage of forested lands as MPC 

5.2/6.2. Therefore, Alternative 1 would project no commodity-emphasis harvest, while 

Alternative 5 would project a relatively high level of harvest. Other alternatives have 

varying amounts in MPCs that permit harvest or other types of management activities. 

Differences between alternative objectives also are reflected in the probabilities assigned 

to each disturbance. Probabilities were assigned based on the emphasis of the alternative. 

Those alternatives that permit timber harvest have relatively high probabilities for various 

harvest treatments and lower probabilities for other treatments such as prescribed fire. 

Timber harvest probabilities are higher for MPC 5.2 and 6.2 than for MPC 3.2, because 

in the latter case, while harvest may be used to improve or maintain wildlife habitat, it is 

not a regular occurring activity and would generally occur on a smaller scale than in 

MPC 5.2/6.2. 

MPCs that preclude mechanical treatments or where management direction focuses on 

restoration without providing for a sustainable level of outputs were considered 

“unsuited”, and any timber volume removed from them would not accrue to the 

Allowable Sale Quantity (ASQ). MPCs 5.2 and 6.2 emphasize commodity production 

and are labeled as “suited”. Mechanical treatments within unsuited MPCs will accrue 

volume (based on outcome of meeting Desired Future Conditions) toward the Total Sale 

Program Quantity (TSPQ). Mechanical treatments within MPC 5.2 and 6.2 will accrue 

volume (based on outcome of meeting DFCs) towards the Allowable Sale Quantity. 

Limits 

Limits, in a modeling sense, are used to represent physical, ecological, financial, legal, or 

social thresholds that simulation must fall within in order to be considered reasonable or 

appropriate. For example, budgetary requirements to implement an alternative must be 

within reason compared to experienced budget levels and Desired Future Conditions 

attainment must comply with other resource management objectives consistent with a 

given alternative. Models of alternatives had to satisfy numerous types of limits in order 

to be feasible. The most common limits applied were for acres treated in any given time 

period; the number of acres had to be feasible given expected funding levels for the 

alternative. 

Timber Harvest Program 

The model projects outputs in relation to (1) the probability of occurrence assigned in the 

model and (2) the number of acres in a particular class. Harvest levels were estimated by 
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 16

the model by running successive iterations with different probabilities to develop a nondeclining harvest level. If additional funding would be required to achieve the output 

level of a particular alternative, that is noted in the discussion of effects in Chapter 3 of 

the EIS. 

Inventory Volume 

Inventory data was pulled from RMRIS for the various vegetation types. The number of 

stands varied considerably within the database, ranging from less than 10 for aspen in the 

Cache to 80 Douglas-fir stands in the Cache, to a maximum of over 1200 lodgepole pine 

stands in the Uinta Mountains. The average volume for all stands in the database that 

met the criteria for location and type was summarized for the Cache and the Wasatch 

portions of the forest. Stand data was sorted based on the predominance of the trees in 

the stand into sapling, medium (majority of basal area in trees 5-8.9 inches), large 

(majority of basal area in trees 9-15.9), and very large (majority of basal area in trees 

16+). The average volume was determined for all the stands within a size class. 

In addition, since some age categories were not represented in the database (primarily the 

younger age classes such as sapling and immature), Stands were modeled with FVS and 

the projected volume at the various ages was determined. Projected data was compared 

with inventory data to determine a reasonable average volume to be used in the model, 

based on personal knowledge of the variety of stand conditions. For example, because 

DF and SF often occur as dense clumps within a patchy mosaic, the projected volumes 

were compared with the actual inventory volumes and reduced to account for the patchy 

nature. For example, the DF projection for the Uinta Mountains showed a volume per 

acre of 36 ccf for stands >130 years old. While that is probably reasonable for a 

continuous stand, it may overstate the actual volume within a mapped polygon due to 

openings of various sizes and uneven distribution of trees. In addition, the model classes 

cover a range of ages, and applying the projected volume to the entire class would 

overstate the volume for those stands near the lower limit of the class. 

Harvest Removal Volume 

Harvest volume was determined as a percentage of the inventory volume for cover type 

and model class. It was decided to use a percentage rather than a volume value, because 

it is easier to discuss harvest levels as a percentage of the standing volume than to try to 

determine the actual volume from a variety of stand conditions. The following 

percentages were used in the model. 

• Regeneration harvest other than spruce fir = 90% 

• Regeneration harvest in spruce fir = 50% (reflects group selection/shelterwood) 

• Heavy Partial harvest = 40% 

• Medium partial harvest = 30% 

• Light partial harvest = 20% 

The VDDT model output displayed the volume harvested by applying the above 

percentages to the inventory volume for each acre that followed the particular harvest 

pathway. For example, if the model determined (based on the probability of disturbance) 
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 17

that a particular acre of spruce-fir would be harvested for regeneration, 50% of the 

inventoried volume for that acre would be shown as harvest volume. 

Non-Declining Yield 

Non-declining yield was defined as no decrease in yield from one decade to the next that 

exceeded 15%. This level of variation seemed reasonable, given the errors associated 

with the various components that go into determining yields. We know there is a margin 

of error associated with the land classification; a margin of error associated with the 

prescription boundaries, and a margin of error associated with the timber yield data. 

When those three are multiplied together to generate yields for ASQ, the error is 

multiplied, also. If each of those had 95% accuracy, the result would be 86% accurate. 

We therefore concluded that a 15% deviation between decades would not be 

unreasonable when estimating non-declining flow. Successive runs of the model were 

made to determine the long-term trend of a given harvest level. Probabilities were 

adjusted to produce a relatively even flow of timber volume over a 100-year period. 

Projected ASQ levels for each alternative were tested to make certain they reflected a 

non-declining harvest level. 

Long-Term Sustained Yield Capacity 

Long-term sustained yield capacity was calculated by the model and reflects the highest 

uniform wood yield that can be sustained from lands being managed for timber 

production for each alternative. 

Disturbance Probabilities 

Probabilities were determined for each disturbance (management or natural) for each 

model class within the 6 groupings, based on the likelihood of that disturbance occurring 

in that MPC group under a particular alternative. Alternatives that emphasis natural 

rather than management disturbances would have a relatively high probability for 

wildfire and insect disturbances, and low probabilities for harvest and prescribed fire. 

For example, Alternative 1 permits no harvest or prescribed burning, but does permit 

wildland fire use. Therefore, the probability of harvest is 0, and the probability of 

prescribed fire is relatively low (prescribed fire in the model includes both management 

ignition and naturally ignited wildland fires) because the only occurrence would be 

wildland fire use. However, the probability of failed fire suppression was relatively high, 

due to the age and condition of the forests. 

In contrast, Alternative 5 emphasizes economic benefits from timber harvest and grazing. 

A high percentage of the forested lands are within group 6 MPCs permitting a relatively 

high level of timber management. Therefore, the probabilities for harvest disturbances 

are relatively high, and the probability of high intensity prescribed fire are low. With the 

emphasis on management, failed fire suppression is less likely, due to the presence of 

roads and the amount stand structure manipulation that would occur with a harvest 

emphasis. 
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 18

Wildland Fire 

Fire probabilities were estimated using fire frequency and size data collected on the 

Forest over the last 30 years. From this data it was determined that 83% of the fires were 

less than 1 acre in size, 15% were between 1 and 1000 acres, and 2% exceeded 1000 

acres. The number of fires and the size of the average fires were used to estimate the 

frequency of normal, high, and severe fire years. These frequencies were entered into the 

model to help understand potential for the occurrence and size of unplanned fires on the 

Forest. A projection of two severe fire years in a 100 year period was used in the model. 

Although the model does not predict when such years will occur (or if in fact they will 

occur), it is useful to look at the effects on vegetation of large burns in comparison to 

smaller, more frequently occurring fires.

Insects and Disease 

Probabilities for insect attack are dependent upon the age and size of forest stands. 

Older, denser stands of large trees are most susceptible to the important insects, such as 

spruce beetles and mountain pine beetles. Therefore the older structural stages in the 

model received relatively high probabilities, while younger or less dense stages received 

low probabilities. 

Sensitivity Testing the Model 

The VDDT model estimates various outcomes based on probabilities of a particular 

disturbance occurring over time. Determining the sensitivity of the model to these 

disturbances is critical to understanding the reliability of the results in predicting the 

relative differences between alternatives. The model contains 2 stochastic disturbances 

(insects and failed fire suppression) and 2 management disturbances (harvest and 

prescribed fire). To determine how sensitive the model is to each of these disturbances, 

runs were made with the base level disturbance probability and with a 1% increase in the 

probability. The results of the two runs were compared to see how great the difference in 

results for each disturbance. A disparity between the increased probability for a 

particular disturbance and the estimated acres disturbed indicates that the model is 

sensitive to that particular disturbance. If the model is not overly sensitive, a 1% increase 

in a disturbance should result in approximately a 1% increase in projected acres affected 

in the model output. Generally, a 1% increase in probability resulted in slightly less than 

a 1% increase in disturbed acres for all 4 disturbances tested, when comparing individual 

decade results. Over the 10 decades projected, the increase was approximately 1%. 

Tables B-2a through B-2d presents the results of the sensitivity testing for disturbances. 

The sensitivity of the model to the initial conditions was also tested, to make certain the 

projected results were not dependent upon the number of acres in a particular class at the 

beginning of the model run. The procedure to test initial conditions was to select a class 

that contained a large acreage of a particular species, remove a percentage of the acres in 

the class and redistribute them equally to the other classes in the model. The model was 

then run and the distribution of acres over time reviewed to make sure the acres moved 

through the model in the expected manner during the decades projected. If the acres had 

built up in a particular class instead of moving through, it would have indicated that the 
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 19

results were dependent upon the initial conditions. To test the model, spruce-fir in the 

Uinta Mountains was selected, because it has the largest acreage in the old class, and no 

acres in the two youngest classes. The initial conditions were reset by removing 20% of 

the acres from the old class and distributing those acres uniformly to the remaining 4 

classes (GF, SS, IMM, MAT). The model was then run for 100 years to see if the acres 

moved through the classes over time. Table B-3 displays the results of this test. Acres 

did not accumulate in a particular class, but moved through the classes in accordance 

with the succession pathways. 
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 20

 Table B-2a. Sensitivity Test Results for Harvest Probabilities. 

Decade SS IMM MAT OLD Total

1 41 1,315 11,469 4,357 17,183

2 41 1,274 11,634 3,042 15,991

3 123 1,973 11,757 3,453 17,307

4 123 2,220 9,825 2,631 14,799

5 82 2,713 10,688 2,713 16,197

6 41 3,289 8,715 1,809 13,853

7 164 3,823 8,386 1,727 14,100

8 0 3,864 8,879 1,932 14,676

9 0 3,700 7,235 3,823 14,758

10 41 4,152 9,003 3,289 16,484

Decade SS IMM MAT OLD Total

1 41 1,315 11,469 4,316 17,142

2 41 1,274 11,551 3,042 15,909

3 123 1,973 11,716 3,453 17,265

4 123 2,179 9,825 2,672 14,799

5 82 2,713 10,524 2,754 16,073

6 0 3,289 8,756 1,809 13,853

7 164 3,823 8,468 1,809 14,265

8 0 3,823 8,797 1,932 14,552

9 0 3,700 7,153 3,782 14,634

10 0 4,111 9,044 3,248 16,402

Decade SS IMM MAT OLD Total

1 1.0000 1.0000 1.0000 1.0095 1.0024

2 1.0000 1.0000 1.0071 1.0000 1.0052

3 1.0000 1.0000 1.0035 1.0000 1.0024

4 1.0000 1.0189 1.0000 0.9846 1.0000

5 1.0000 1.0000 1.0156 0.9851 1.0077

6 #DIV/ 0! 1.0000 0.9953 1.0000 1.0000

7 1.0000 1.0000 0.9903 0.9545 0.9885

8 #DIV/ 0! 1.0108 1.0093 1.0000 1.0085

9 #DIV/ 0! 1.0000 1.0115 1.0109 1.0084

10 #DIV/ 0! 0.9955 1.0127 1.0050

Percent Change in Results

Resulting From 1% Change in Probability

Sensitivity Test of Harvest Disturbance

One Percent Increase in Disturbance Probability

Sensitivity Test of Harvest Disturbance

Base Level Disturbance Probability
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 21

Table B-2b. Sensitivity Test Results for Prescribed Fire. 

Decade IMM MAT OLD Total

1 123 3,206 2,220 5,550

2 123 2,754 1,521 4,399

3 123 2,590 1,973 4,686

4 123 3,042 1,439 4,604

5 247 2,425 1,480 4,152

6 206 2,590 1,439 4,234

7 206 2,097 987 3,289

8 247 2,631 1,069 3,946

9 329 2,384 1,110 3,823

10 370 1,891 1,192 3,453

Dec ade IMM MAT OLD Total

1 123 3206 2220 5550

2 123 2754 1562 4440

3 123 2590 1973 4686

4 123 3083 1439 4645

5 247 2425 1480 4152

6 206 2672 1480 4357

7 206 2097 987 3289

8 247 2713 1069 4029

9 329 2425 1110 3864

10 411 1891 1233 3535

Dec ade IMM MAT OLD Total

1 1.0000 1.0000 1.0000 1.0000

2 1.0000 1.0000 1.0270 1.0093

3 1.0000 1.0000 1.0000 1.0000

4 1.0000 1.0135 1.0000 1.0089

5 1.0000 1.0000 1.0000 1.0000

6 1.0000 1.0317 1.0286 1.0291

7 1.0000 1.0000 1.0000 1.0000

8 1.0000 1.0313 1.0000 1.0208

9 1.0000 1.0172 1.0000 1.0108

10 1.1111 1.0000 1.0345 1.0238

Percent Change in Results

Resulting From 1% Change in Probability

Sensitivity Test Rx Fire

Base Level Disturbance Probability

Sensitivity Test Rx Fire

One Percent Increase in Disturbance Probability
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 22

Table B-2c. Sensitivity Test Results for Insects. 

Decade IMM MAT OLD Total

1 0 6,575 5,013 11,588

2 0 6,780 3,205 9,985

3 0 7,684 3,164 10,848

4 82 8,917 2,794 11,793

5 0 11,218 3,739 14,957

6 41 9,616 2,507 12,164

7 41 10,314 3,671 14,026

8 123 9,164 3,287 12,574

9 0 7,479 4,520 11,999

10 82 7,027 5,465 12,574

Decade IMM MAT OLD Total

1 0 6,616 5,054 11,670

2 0 6,862 3,205 10,067

3 0 7,766 3,123 10,889

4 82 8,999 2,794 11,875

5 0 11,424 3,739 15,163

6 41 9,657 2,507 12,205

7 41 10,396 2,712 13,149

8 123 9,287 3,287 12,697

9 0 7,602 4,561 12,163

10 82 7,109 5,342 12,533

Decade IMM MAT OLD Total

1 #DIV/ 0! 1.0062 1.0082 1.0071

2 #DIV/ 0! 1.0121 1.0000 1.0082

3 #DIV/ 0! 1.0107 0.9870 1.0038

4 1.0000 1.0092 1.0000 1.0070

5 #DIV/ 0! 1.0184 1.0000 1.0138

6 1.0000 1.0043 1.0000 1.0034

7 1.0000 1.0080 0.7388 0.9375

8 1.0000 1.0134 1.0000 1.0098

9 #DIV/ 0! 1.0164 1.0091 1.0137

10 1.0000 1.0117 0.9775 0.9967

Percent Change in Results

Resulting From 1% Change in Probability

Sensitivity Test Insects

Base Level Disturbance Probability

Sensitivity Test Insects

One Percent Increase in Disturbance Probability
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 23

Table B-2d. Sensitivity Test Results for Failed Fire Suppression. 

Decade IMM MAT OLD Total

1 41 0 41 1,603 5,383 7,068

2 247 329 1,192 17,464 56,584 75,816

3 41 41 329 4,849 8,506 13,766

4 0 0 0 1,890 2,383 4,273

5 0 0 123 2,424 1,644 4,191

6 164 329 1,644 29,299 26,053 57,489

7 0 82 41 1,808 1,274 3,205

8 0 41 329 4,150 2,630 7,150

9 0 82 329 6,205 3,863 10,479

10 0 82 205 4,233 3,616 8,136

Decade GF SS IMM MAT OLD Total

1 41 0 41 1,603 5,547 7,232

2 247 329 1,192 17,505 56,790 76,063

3 41 41 329 4,849 8,547 13,807

4 0 0 0 1,890 2,383 4,273

5 0 0 123 2,466 1,644 4,233

6 164 329 1,644 29,340 26,094 57,571

7 0 82 41 1,808 1,274 3,205

8 0 41 329 4,150 2,589 7,109

9 0 82 370 6,205 3,904 10,561

10 0 82 205 4,233 3,616 8,136

Decade GF SS IMM MAT OLD Total

1 1.0000 #DIV/ 0! 1.0000 1.0000 1.0305 1.0232

2 1.0000 1.0000 1.0000 1.0023 1.0036 1.0033

3 1.0000 1.0000 1.0000 1.0000 1.0048 1.0030

4 #DIV/ 0! #DIV/ 0! #DIV/ 0! 1.0000 1.0000 1.0000

5 #DIV/ 0! #DIV/ 0! 1.0000 1.0173 1.0000 1.0100

6 1.0000 1.0000 1.0000 1.0014 1.0016 1.0014

7 #DIV/ 0! 1.0000 1.0000 1.0000 1.0000 1.0000

8 #DIV/ 0! 1.0000 1.0000 1.0000 0.9844 0.9943

9 #DIV/ 0! 1.0000 1.1246 1.0000 1.0106 1.0078

10 #DIV/ 0! 1.0000 1.0000 1.0000 1.0000 1.0000

Percent Change in Results

Resulting From 1% Change in Probability

Sensitivity Test Failed Fire Suppression

Base Level Disturbance Probability

Sensitivity Test Failed Fire Suppression

One Percent Increase in Disturbance Probability
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 24

Table B-3. Initial Conditions Sensitivity Test Results. 

Outcomes From the Modeling Process 

The VDDT model projects a wide variety of outcomes from the different alternatives and 

other model formulations such as baseline and sensitivity runs. These outcomes can be 

used to gain an understanding and to discuss effects of the alternatives related to a wide 

range of resource areas and social/economic considerations. 

National Forest Management Act (NFMA) regulations (36 CFR 219.12(f) (9)) require 

that each alternative indicate 

• the conditions and uses that would result from long-term application of the 

alternative; 

• the goods and services to be produced, and the timing and flow of these resource 

outputs together with associated costs and benefits; 

• standards and guidelines for resource management; and 

• the purpose of the proposed management direction. 

Chapter 3 and Appendix B of the Environmental Impact Statement along with the 

Proposed Forest Plan meet the requirements as listed above for the NFMA. 

Acres by Class by Cover Type 

The formulation of the VDDT model is driven by how forested vegetation changes over 

time with and without management actions being applied. The primary output from the 

modeling for effects analysis is the acres of the different forest vegetation structures over 

Decade GF SS IMM MAT OLD

0 6654 6654 12902 14626 95415

1 9038 7723 17915 26008 77950

2 11176 9490 23914 34719 60856

3 8134 11997 31228 41499 48980

4 2916 9490 41460 47787 42078

5 1602 4395 48447 54032 37352

6 2793 3368 51159 58879 30818

7 16805 3614 47460 60813 14915

8 1561 17421 43021 67222 15532

9 1109 2752 50953 72482 19723

10 12162 2341 41626 72361 14873

Spruc e-fir Initial Conditions

Sensitivity Test Results
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 25

time by cover type. This information is critical for understanding habitat conditions for 

wildlife, insect and wildfire hazards, species composition, integrating ecological 

processes and predicting short- and long-term effects. Table B-4 displays sample output 

from the VDDT model. The change in acreage within the structural stages between 

decades reflects the effect of prescribed burning approximately 6000 acres each year. 

Table B-4. Distribution of Overthrust Mountain Stable Aspen Acres Over 100 Years. 

Decade SS IMM MAT 

0 0 844 101,038

1 55,894 6,236 37,804

2 6,885 67,521 23,904

3 1,234 73,822 21,890

4 30,269 38,519 26,307

5 37,869 37,317 18,058

6 7,210 72,328 16,304

7 1,072 73,530 19,227

8 54,985 23,644 19,032

9 14,290 66,774 14,745

10 2,079 79,798 12,504

Estimation of Allowable Sale Quantity (ASQ) 

The sustainable level of timber harvest volume from suited acres is referred to as ASQ 

and the National Forest Management Act requires estimation of this outcome. Suited 

acres are defined by MPC and were discussed above. 

Estimates of the timber volume generated from mechanical treatments on suited acres 

were included in the VDDT model to estimate ASQ. Yield estimates for the activities 

within Management Actions, discussed above, were the basis for determining ASQ. The 

objective of non-declining flow was included in all alternatives. Table B-5 displays the 

ASQ by Alternative for the Forest. 

Estimation of Total Sale Program Quantity (TSPQ) 

The level of timber harvest volume from forested acres is referred to as Total Sale 

Program Quantity and the National Forest Management Act requires estimation of this 

outcome. This total volume amount includes the ASQ. 

Estimates of the timber volume generated from mechanical treatments on forested acres 

were included in the VDDT model to estimate the modeling portion of Total Sale 

Program Quantity (TSPQ). Yield estimates for the activities within Management 

Actions, discussed above, were the basis for determining the modeled portion of TSPQ. 

It is important to note that any volume in excess of the ASQ level is potential volume that 

is dependent upon other resource needs and would be offered only if opportunities arose, 
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 26

and on an irregular basis. Table B-4 displays the model-generated portion of Total Sale 

Program Quantity by Alternative as calculated by VDDT. Additional volume estimates 

from salvage, post and poles, and firewood were added to the model estimates to 

determine the final amount of Total Sale Program Quantity in the Forest Plan. 

Table B-5. ASQ And TSPQ Estimates From VDDT For All Alternatives 

In Millions Of Cubic Feet (mmcf) and Millions of Board Feet (mmbf) 

Wasatch-Cache National Forest Alt. 1 Alt. 2 Alt. 3 Alt. 4 Alt. 5 Alt.6 Alt.7 

Allowable Sale Quantity mmcf/yr 0 0 .3 .67 1.3 .40 .40 

Allowable Sale Quantity mmbf/yr 0 0 1.6 3.3 6.2 2.0 2.0 

Total Sale Program Quantity mmcf/yr 0 .4 .6 1.28 1.55 .81 .90 

Total Sale Program Quantity mmbf/yr 0 2.1 3.2 6.2 7.4 3.9 4.5 

Sagebrush Modeling 

A simple tool was used to model sagebrush succession by alternative. The following 

assumptions were made based on estimations of the rate of succession from low canopy 

cover (0-5%) to moderate canopy cover (6-15%), and from moderate canopy cover to 

high canopy cover (>15%). In addition estimations were made on the amount of juniper 

(and pinyon-juniper) communities that were historically maintained in a sagebrush stage 

of succession from historical, natural fires. 

First, it was assumed that 90 percent of the acres treated in this type during any decade, 

were sagebrush communities with high canopy cover. Ten percent of the communities 

treated were juniper communities that now occur on what historically was dominated by 

sagebrush. Not all existing juniper communities occur on these sites. We estimate that 

50 percent of the juniper communities occupy rocky sites that did not support sagebrush 

and did not have fine fuels to carry fire as frequently as those stands that did have 

sagebrush and associated fuels. An of the 50 percent that does currently occupy sites that 

are typically dominated by sagebrush, only half of those acres (19,225 acres) were 

maintained in a sagebrush state on a continuous basis. 

It was also assumed that, on the average, sagebrush communities reach high canopy 

cover within 20 years of disturbance. And that in each decade, 50 percent of the 

moderate canopy cover moved into the high cover class stage. All treated acres would 

move to the low canopy cover stage. 

Various biological, environmental, and management characteristics and factors play a 

role in sagebrush succession. An intrinsic variability in sagebrush communities is caused 

by the different habitats and life history of the 8-9 different sagebrush taxa that occur on 

the Forest. Silver sagebrush and spiked big sagebrush sprout following disturbance, 

while the others do not. Some, including low sagebrush and some mountain big 

sagebrush communities occur on rocky soils that naturally do not have a high amount of 
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 27

fuels to adequately carry fire. Some stands have historically been overgrazed, which has 

resulted in low fuels and a subsequent inability to carry fires as historically occurred. 

The following tables illustrate how this modeling was completed. Given the natural 

variability in these ecosystems and the probability that some assumptions are not correct, 

the results of these models are only indicators of how the different alternatives would 

affect change in the sagebrush type. 

The desired condition for Sagebrush and for Pinyon-Juniper communities is as follows: 

• Sagebrush: 208,800 acres 

• Pinyon-Juniper: 57,700 acres 

Currently there are 189,600 acres of sagebrush communities and 75,900 acres of pinyonjuniper communities. As noted above, of these p-j communities, approximately 50 

percent occur on sites where sagebrush once was able to maintain dominance through 

frequent natural fires (every 20 to 30 years). And of these acres, with a 50-200 year fire 

frequency for p-j, it was assumed that only half of this was actually dominated by 

sagebrush (25% of total p-j acres or 19,225 acres) at any given time. It is these acres, in 

the desired condition (Forest Plan, Chapter 4) that are moved back toward dominance by 

sagebrush through actions (primarily prescribed fire). This model shows how those and 

the following desired conditions are addressed by alternative. It was assumed that 10% 

of the treatment acres (e.g. 1000 acres of 10000 acre treated - Alternatives 3 and 4) would 

focus on returning pinyon-juniper to sagebrush; that portion that historically was 

controlled by fire and dominated by sagebrush. 

The desired condition for cover classes in sagebrush are as follows: 

• Low Cover (0-5% sagebrush cover) = 5-15 percent of total acres 

• Moderate Cover (6-15%) = 30-50 percent of total sagebrush acres. 

• High Cover (>15%) = 30-50 percent of total sagebrush acres. 

• Acres of P-J that should be Sagebrush = 0-5% of total acres 
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 28

Table B-6. Existing and Future Condition of Sagebrush Cover Type by Alternative 

 Conditions Alt 1 Alt 2 Alt 3 Alt 4 Alt 5 Alt 6 Alt 7 

Existing Condition 

Juniper and Pinyon-Juniper 76,900 76,900 76,900 76,900 76,900 76,900 76,900

Sagebrush 189,600 189,600 189,600 189,600 189,600 189,600 189,600

Total Acres of Sagebrush and PJ 266,500 266,500 266,500 266,500 266,500 266,500 266,500

Existing Condition 

Acres in Grass Forb Stage 9,480 9,480 9,480 9,480 9,480 9,480 9,480

Acres in Moderate Canopy Cover Stage 47,400 47,400 47,400 47,400 47,400 47,400 47,400

Acres in High Canopy Cover Stage 132,720 132,720 132,720 132,720 132,720 132,720 132,720

Acres that should be dominated by 

sagebrush that are dominated by juniper. 19,225 19,225 19,225 19,225 19,225 19,225 19,225

Total Acres of Sagebrush and PJ that 

should be dominated by sagebrush 208,825 208,825 208,825 208,825 208,825 208,825 208,825

Percent in Grass Forb Stage 5% 5% 5% 5% 5% 5% 5%

Percent in Moderate Canopy Cover Stage 23% 23% 23% 23% 23% 23% 23%

Percent in High Canopy Cover Stage 64% 64% 64% 64% 64% 64% 64%

Percent of sagebrush type that is

dominated by juniper 9% 9% 9% 9% 9% 9% 9%

Acres Treated per decade 0 40,000 20,000 10,000 10,000 20,000 30,000

Decade 1 

Percent in Grass Forb Stage 0% 19% 10% 5% 5% 10% 14%

Percent in Moderate Canopy Cover Stage 16% 16% 16% 16% 16% 16% 16%

Percent in High Canopy Cover Stage 75% 58% 66% 71% 71% 66% 62%

Percent of sagebrush type that is 

currently dominated by juniper 9% 7% 8% 9% 9% 8% 8%

Decade 2 

Percent in Grass Forb Stage 0% 19% 10% 5% 5% 10% 14%

Percent in Moderate Canopy Cover Stage 8% 27% 18% 13% 13% 18% 22%

Percent in High Canopy Cover Stage 83% 48% 66% 74% 74% 66% 57%

Percent of sagebrush type that is 

currently dominated by juniper 9% 5% 7% 8% 8% 7% 6%

Decade 3 

Percent in Grass Forb Stage 0% 19% 10% 5% 5% 10% 14%

Percent in Moderate Canopy Cover Stage 4% 33% 18% 11% 11% 18% 26%

Percent in High Canopy Cover Stage 87% 45% 66% 76% 76% 66% 55%

Percent of sagebrush type that is 

currently dominated by juniper 9% 3% 6% 8% 8% 6% 5%

Decade 4 

Percent in Grass Forb Stage 0% 19% 10% 5% 5% 10% 14%

Percent in Moderate Canopy Cover Stage 2% 36% 19% 10% 10% 19% 27%

Percent in High Canopy Cover Stage 89% 44% 66% 78% 78% 66% 55%

Percent of sagebrush type that is 

currently dominated by juniper 9% 2% 5% 7% 7% 5% 3%
Final Environmental Impact Statement - Appendices 

Wasatch-Cache National Forest B1 - 29

 Conditions Alt 1 Alt 2 Alt 3 Alt 4 Alt 5 Alt 6 Alt 7 

Decade 5 

Percent in Grass Forb Stage 0% 19% 10% 5% 5% 10% 14%

Percent in Moderate Canopy Cover Stage 1% 37% 19% 10% 10% 19% 28%

Percent in High Canopy Cover Stage 90% 44% 67% 78% 78% 67% 56%

Percent of sagebrush type that is 

currently dominated by juniper 9% 0% 4% 7% 7% 4% 2%

Decade 6 

Percent in Grass Forb Stage 0% 19% 10% 5% 5% 10% 14%

Percent in Moderate Canopy Cover Stage 0% 38% 19% 10% 10% 19% 28%

Percent in High Canopy Cover Stage 90% 43% 68% 79% 79% 68% 57%

Percent of sagebrush type that is 

currently dominated by juniper 9% 0% 3% 6% 6% 3% 1%

Decade 7 

Percent in Grass Forb Stage 0% 19% 10% 5% 5% 10% 14%

Percent in Moderate Canopy Cover Stage 0% 38% 19% 10% 10% 19% 29%

Percent in High Canopy Cover Stage 91% 43% 69% 80% 80% 69% 57%

Percent of sagebrush type that is 

currently dominated by juniper 9% 0% 3% 6% 6% 3% 0%

Decade 8 

Percent in Grass Forb Stage 0% 19% 10% 5% 5% 10% 14%

Percent in Moderate Canopy Cover Stage 0% 38% 19% 10% 10% 19% 29%

Percent in High Canopy Cover Stage 91% 43% 70% 80% 80% 70% 57%

Percent of sagebrush type that is 

currently dominated by juniper 9% 0% 2% 5% 5% 2% 0%

Decade 9 

Percent in Grass Forb Stage 0% 19% 10% 5% 5% 10% 14%

Percent in Moderate Canopy Cover Stage 0% 38% 19% 10% 10% 19% 29%

Percent in High Canopy Cover Stage 91% 43% 71% 81% 81% 71% 57%

Percent of sagebrush type that is 

currently dominated by juniper 9% 0% 1% 5% 5% 1% 0%

Decade 10 

Percent in Grass Forb Stage 0% 19% 10% 5% 5% 10% 14%

Percent in Moderate Canopy Cover Stage 0% 38% 19% 10% 10% 19% 29%

Percent in High Canopy Cover Stage 91% 43% 71% 81% 81% 71% 57%

Percent of sagebrush type that is 

currently dominated by juniper 9% 0% 0% 4% 4% 0% 0%