13

Figure 3—Area included in the salt desert shrub, Wyoming big sagebrush–warm, Wyoming big sagebrush–cool, basin big

sagebrush, threetip sagebrush, and low sagebrush–xeric potential vegetation types within the interior Columbia basin as

mapped at the 1-km scale. ICBEMP data on file with: USDA Forest Service, Pacific Northwest Research Station, P.O. Box

3890, Portland OR 97208.
14

Within the basin BLM and FS lands, this PVT is

located primarily in south-central and southeastern Oregon with lesser extents in southwestern

Idaho and small scattered patches in eastern

Washington and north-central Oregon (Hann

et al. 1997; ICBEMP source data, Pacific Northwest Research Station, P.O. Box 3890, Portland,

OR 97208). Most of this type occurs within intermontane basin, plateau, and plains landforms at

moderate elevations (table 3) and within the low

precipitation zone (table 4).

Wyoming Big Sagebrush–Warm PVT

The Wyoming big sagebrush–warm PVT includes

vegetation dominated primarily by Wyoming big

sagebrush with minor amounts of other sagebrush

species (fig. 3). Foothills sagebrush, primarily

found in the lower Weiser and Payette River

drainages of Idaho and adjacent Oregon, also

was included within this PVT. Herbaceous species typically include bluebunch wheatgrass,

bottlebrush squirreltail, Sandberg bluegrass, and

Thurber’s needlegrass. Livestock grazing, agriFigure 4—The salt desert shrub PVT usually occurs on saline soils. Vegetal coverage is typically sparse, and

plant interspaces are frequently occupied by biological soil crusts. This community near Grand View, Idaho, is

dominated by shadscale and budsage. (Photo by Stephen Bunting.)

culture, and invasive annual grasses, particularly

cheatgrass and medusahead, have severely affected this PVT (figs. 5a and 5b). Annual grasses

produce abundant, highly flammable fuel. The

result has been frequent fire, enhanced annual

grass dominance, and near elimination of sagebrush species in many locations (Pellant 1990).

Sagebrush moth (Aroga websteri Clarke) may

cause local centers of mortality (Passey and

Hugie 1962). Extensive areas have been planted

with introduced perennial wheatgrasses.

Biological soil crusts, including cyanobacteria,

lichens, algae, and mosses, occur commonly on

or near the soil surface in many sites within this

PVT, increasing soil stability in the plant interspaces (Belnap et al. 1994, Belnap and Gardner

1993, Evans and Ehleringer 1993). They also may

provide for nitrogen (Mayland et al. 1966, West

and Skujins 1977) and carbon (Lange et al. 1997)

input into the soil, and enhance availability of essential minerals for higher plants (Harper and

Pendleton 1993). Biological soil crusts are susceptible to disturbances such as fire (Johansen
15

Table 3—Percentage and area by elevation class for each of 17 rangeland potential

vegetation types on BLM- and FS-administered lands within the environmental impact

statement planning area

Percentage

Potential vegetation type (PVT) Elevation of PVT Area

Hectares Acres

Salt desert shrub Low 9 59 000 145,800

Moderate 91 623 700 1,541,200

High 0 300 700

Total 100 683 000 1,687,700

Wyoming big sagebrush–warm Low 6 349 800 864,400

Moderate 92 4 976 900 12,298,200

High 1 71 700 177,200

Total 99 5 398 400 13,339,800

Wyoming big sagebrush–cool Low 4 17 700 43,700

Moderate 71 334 900 827,600

High 26 121 800 301,000

Total 101 474 400 1,172,300

Basin big sagebrush Low 33 58 500 144,600

Moderate 64 113 800 281,200

High 3 4 600 11,400

Total 100 176 900 437,200

Threetip sagebrush Low 3 1 000 2,500

Moderate 72 21 700 53,600

High 25 7 700 19,000

Total 100 30 400 75,100

Low sagebrush–xeric Low 36 66 900 165,300

Moderate 59 109 200 269,800

High 5 10 300 25,500

Total 100 186 400 460,600

Low sagebrush–mesic Low 1 4 900 12,100

Moderate 96 469 600 1,160,400

High 3 17 000 42,000

Total 100 491 500 1,214,500

Low sagebrush–mesic with juniper Moderate 100 7 800 19,300

Total 100 7 800 19,300

Mountain big sagebrush–mesic east Low 7 77 900 192,500

Moderate 64 739 200 1,826,600

High 29 336 000 830,300

Total 100 1 153 100 2,849,400
16

Table 3—Percentage and area by elevation class for each of 17 rangeland potential

vegetation types on BLM- and FS-administered lands within the environmental impact

statement planning area (continued)

Percentage

Potential vegetation type (PVT) Elevation of PVT Area

Hectares Acres

Mountain big sagebrush–mesic east Low 0 100 200

 with conifers Moderate 97 45 600 112,700

High 3 1 300 3,200

Total 100 47 000 116,100

Mountain big sagebrush–mesic west Low 7 47 000 116,100

Moderate 93 610 600 1,508,800

High 0 1 500 3,700

Total 100 659 100 1,628,600

Mountain big sagebrush–mesic west Low 21 111 300 275,000

 with juniper Moderate 73 379 300 937,300

High 6 30 500 75,400

Total 100 521 100 1,287,700

Wheatgrass grassland Low 52 64 700 159,900

Moderate 31 38 800 95,900

High 17 21 400 52,900

Total 100 124 900 308,700

Antelope bitterbrush Low 16 4 200 10,400

Moderate 83 21 300 52,600

High 1 300 700

Total 100 25 800 63,700

Mountain shrub Moderate 41 1 400 3,500

High 59 2 000 4,900

Total 100 3 400 8,400

Fescue grassland Low 6 5 700 14,100

Moderate 48 46 500 114,900

High 46 44 000 108,700

Total 100 96 200 237,700

Fescue grassland with conifer Low 10 65 700 162,300

Moderate 50 320 800 792,700

High 40 258 900 639,800

Total 100 645 400 1,594,800

Grand total 10 724 800 26,501,600

Note: Elevation classified from 0.5-km Digital Elevation Model (DEM): Low ≤1000 m; moderate >1000 m and

≤2000 m; high >2000 m. (Source: ICBEMP data available at http://www.icbemp.gov/spatial; theme number: 426;

theme abbreviation: PHYSDEM50)
17

Table 4—Percentage and area by precipitation zone for each of 17 rangeland potential

vegetation types on BLM- and FS-administered lands within the environmental impact

statement planning area

Percentage

Potential vegetation type (PVT) Precipitation of PVT Area

Hectares Acres

Salt desert shrub Low 89 605 000 1,495,000

Moderate 11 78 000 192,700

Total 100 683 000 1,687,700

Wyoming big sagebrush–warm Low 70 3 785 400 9,353,900

Moderate 29 1 561 200 3,857,800

High 1 51 800 128,000

Total 100 5 398 400 13,339,700

Wyoming big sagebrush–cool Low 72 342 200 845,600

Moderate 27 126 100 311,600

High 1 6 100 15,100

Total 100 474 400 1,172,300

Basin big sagebrush Low 55 97 100 239,900

Moderate 40 70 500 174,200

High 5 9 300 23,000

Total 100 176 900 437,100

Threetip sagebrush Low 15 4 600 11,400

Moderate 60 18 300 45,200

High 25 7 500 18,500

Total 100 30 400 75,100

Low sagebrush–xeric Low 88 163 100 403,000

Moderate 12 23 200 57,300

High 0 100 200

Total 100 186 400 460,500

Low sagebrush–mesic Low 43 209 100 516,700

Moderate 57 279 400 690,400

High 1 3 000 7,400

Total 101 491 500 1,214,500

Low sagebrush–mesic with Low 3 200 500

juniper Moderate 88 6 900 17,100

High 9 700 1,700

Total 100 7 800 19,300

Mountain big sagebrush– Low 33 374 000 924,200

mesic east Moderate 59 682 300 1,686,000

High 8 96 800 239,200

Total 100 1 153 100 2,849,400
18

Table 4—Percentage and area by precipitation zone for each of 17 rangeland potential

vegetation types on BLM- and FS-administered lands within the environmental impact

statement planning area (continued)

Percentage

Potential vegetation type (PVT) Precipitation of PVT Area

Hectares Acres

Mountain big sagebrush– Low 2 1 000 2,500

mesic east with conifer Moderate 76 35 500 87,700

High 22 10 500 25,900

Total 100 47 000 116,100

Mountain big sagebrush– Low 40 263 300 650,600

mesic west Moderate 60 393 000 971,100

High 0 2 800 6,900

Total 100 659 100 1,628,600

Mountain big sagebrush– Low 60 315 100 778,600

mesic west with juniper Moderate 38 197 300 487,500

High 2 8 700 21,500

Total 100 521 100 1,287,600

Wheatgrass grassland Low 42 52 700 130,200

Moderate 47 58 200 143,800

High 11 14 000 34,600

Total 100 124 900 308,600

Antelope bitterbrush Low 19 4 800 11,900

Moderate 73 18 800 46,500

High 9 2 200 5,400

Total 101 25 800 63,800

Mountain shrub Low 32 1 100 2,700

Moderate 65 2 200 5,400

High 3 100 200

Total 100 3 400 8,300

Fescue grassland Low 2 2 400 5,900

Moderate 52 50 200 124,000

High 45 43 600 107,700

Total 99 96 200 237,600

Fescue grassland with conifers Low 11 72 400 178,900

Moderate 56 359 300 887,800

High 33 213 700 528,100

Total 100 645 400 1,594,800

Grand total 10 724 800 26,501,000

Note: Precipitation classified using PRISM Model: Low ≤30 cm; moderate >30 cm and ≤61 cm; high >61 cm.

(Source: ICBEMP data available at http://www.icbemp.gov/spatial; theme: 741; theme abbreviation: ATMPRISM)
19

Figure 5A—Slightly altered community within the Wyoming big sagebrush–warm PVT located near Vantage,

Washington. The community is dominated by Wyoming big sagebrush with an understory of bluebunch

wheatgrass. (Photo by Stephen Bunting.)

Figure 5B—Severely altered community within the Wyoming big sagebrush–warm PVT near Boise, Idaho. The

community is dominated by invasive species, primarily cheatgrass. Perennial grass in the photo is bottlebrush

squirreltail. (Photo by Stephen Bunting.)
20

et al. 1982, 1993) and mechanical damage from

large herbivores (Beymer and Klopatek 1992,

Kleiner and Harper 1972, Marble and Harper

1989). Recovery of biological soil crusts may

be slow after disturbance, particularly for the

lichens. The time required for full recovery has

been estimated at 20 to 85 years (Anderson et al.

1982b, Belnap and Gardner 1993). Johansen et al.

(1993) found, however, that soil algae may recover within 2 to 5 years postburn.

Slightly altered sites typically have an intact

shrub overstory of Wyoming big sagebrush and

an understory modified by livestock grazing and

invasive plants. Most native herbaceous plants

are represented, and biological soil crusts and

tortula (Tortula ruralis (Hedw.) Gaerten., Meyer

and Scherb.) are present, at least under mature

shrubs (Hironaka et al. 1983). The most common

invasive grasses are cheatgrass on moderate to

light textured soils and medusahead on heavier

textured soils (Dahl and Tisdale 1975). Invasive

forbs include diffuse knapweed, spotted knapweed and rush skeletonweed.

Severely altered sites in this PVT present one

of the greatest restoration challenges in the basin

because of the large area involved, the difficulty

in controlling wildfires, and the difficulty in establishing perennial species. Some areas currently

burn once every 5 years compared to the historical fire return interval of 50 to 100 years

(Whisenant 1990). Frequent fire has, in many

places, depleted sagebrush and fire-sensitive herb

and grass species (e.g., Thurber’s needlegrass

and Idaho fescue) seed sources. Soils have eroded or been modified in many cases. Some researchers consider these changes irreversible

(Young et al. 1979). Many severely altered sites

have been planted previously with introduced

perennial wheatgrasses. The introduced perennial

grasses protect sites from further invasion by

invasive plant species and additional soil erosion.

They are, however, effective competitors that

prevent the establishment of many native herbaceous plants and reduce the rate of increase in

species diversity on the site.

Within the basin BLM and FS lands, this PVT is

located in a band across the southern portion of

Oregon and Idaho with scattered patches in

northern Oregon and central Washington (Hann

et al. 1997, ICBEMP source data). Most of this

type occurs within intermontane basin, plateau,

and plains landforms at moderate elevations

(table 3), with most in the low precipitation zone

(table 4) and much of the remaining in the moderate zone associated with warm aspects and

droughty soils.

Wyoming Big Sagebrush–Cool PVT

The Wyoming big sagebrush–cool PVT is found

primarily in valley bottoms in eastern Idaho,

southwestern Montana, and the west slopes of

the Blue Mountains in Oregon (fig. 3). The herbaceous component is similar to the Wyoming big

sagebrush–warm PVT. Climatic differences such

as a greater proportion of summer precipitation

and colder winters have resulted in this PVT not

being as affected by invasive annual grasses as

the Wyoming big sagebrush–warm PVT. Consequently, wildfire occurrence has not increased as

greatly from past conditions for most of this PVT.

Slightly altered sites usually have an intact sagebrush overstory with a slightly to moderately altered understory composition. Invasive species

are present but have not disrupted the natural

processes to the extent they have in some other

PVTs. Sites respond to changes in management

(Eckert and Spencer 1986, Wambolt and Payne

1986, Yeo et al. 1990), but increases in perennial

species may be slow. Restoration strategies primarily include livestock management to prevent

further depletion of the understory and fire suppression to prevent loss of the shrub component.

An understory depleted of native perennial species usually characterizes severely altered sites.

Wildfires are uncommon because there is minimal

fine fuel production. When fire does occur, it

results in an early seral community of native and

invasive species. Reestablishment of sagebrush

and perennial herbaceous species is slow, and

recovery may take many decades (Eckert and

Spencer 1986, Harniss and Murray 1973). Seeding of introduced wheatgrasses has been used

successfully as a rehabilitation practice in some

areas.
21

Within the basin BLM and FS lands, this PVT is

scattered diagonally from southwestern Oregon

to northeastern Oregon and in a relatively large

zone in east-central Idaho with scattered patches

in southeastern Idaho (Hann et al. 1997). Most of

this PVT type occurs in intermontane basins and

draws of foothills and mountains at moderate

elevations (table 3) within the low precipitation

zone. Most of the remaining is in the moderate

zone (table 4) but on warm aspects and droughty

soils.

Basin Big Sagebrush PVT

Basin big sagebrush with a native understory of

basin wildrye and bluebunch wheatgrass dominates the basin big sagebrush PVT (figs. 3 and

6). Livestock grazing and invasive species have

affected most sites. When surrounded by sites

dominated by annual grass, they are subject to

frequent fires that often eliminate sagebrush.

Most of this PVT has been converted to intensive

agriculture (Hironaka et al. 1983). Few extensive

areas of basin big sagebrush PVT remain except

in central Washington (fig. 3). Most occur in a

mosaic with the Wyoming big sagebrush–warm

PVT and have suffered similar histories. Annual

grasses and frequent fire have heavily affected

those that remain (Daubenmire 1975b). The

restoration options for the Wyoming big sagebrush–warm PVT apply equally to the basin big

sagebrush PVT. Care must be taken to match

sagebrush subspecies to site conditions. Once

Wyoming big sagebrush becomes established, it

may preclude or slow the development of basin

big sagebrush. Relatively deep soils typical in this

PVT may permit altered sites to respond more

rapidly to management changes than sites in the

Wyoming big sagebrush–warm PVT. When managed within a mosaic of Wyoming big sagebrush–

warm vegetation, livestock management must be

closely monitored because these sites are found

on less steep terrain and closer to water, which

tends to encourage livestock use.

Figure 6—Most of the historical area of the basin big sagebrush PVT within the basin has been converted to

intensive agriculture. What remains is mostly in small areas within other PVTs, such as this example found north

of Mountain Home, Idaho. Vegetation in background is primarily Wyoming big sagebrush–warm PVT. (Photo by

Stephen Bunting.)
22

Within the basin BLM and FS lands, this PVT is

thinly scattered through central Washington and

Oregon and across southeastern Oregon and

southern Idaho (Hann et al. 1997, ICBEMP

source data). Most of this PVT occurs in intermontane basins, plains, and plateaus at low elevations and moderate elevations (table 3) within the

low and moderate precipitation zones (table 4),

typically on droughty soils.

Threetip Sagebrush PVT

An overstory of threetip sagebrush, one of the

few species of sagebrush that resprouts after fire,

dominates the threetip sagebrush PVT (Bunting

et al. 1987, Tisdale and Hironaka 1981) (fig. 3).

Common native herbaceous species include

bluebunch wheatgrass, Idaho fescue, arrowleaf

balsamroot, and several species of lupine. Environmentally this PVT occurs between the more

xeric Wyoming big sagebrush–warm PVT and

the more mesic mountain big sagebrush PVTs.

Threetip sagebrush is more resistant to fire than

most other sagebrush species in the basin (Beetle

1960, Morris et al. 1976), and may increase after

fire (Bunting et al. 1987). Threetip sagebrush

may occur as a seral community in the mountain

big sagebrush PVTs after repeated fires because

of its resprouting capability. Whereas this PVT

is widespread geographically within the basin, it

normally occurs in small patches intermixed with

other sagebrush-dominated PVTs on the landscape, and thus only a minor area was included in

the ICBEMP broad-scale map. The most extensive areas of threetip sagebrush PVT are found

primarily on the Snake River plain and adjacent

valleys, most often in a mosaic with the Wyoming

big sagebrush PVTs.

Slightly altered sites of threetip sagebrush steppe

have an intact shrub overstory and an herbaceous

understory composition dominated by native perennials. Most are found within the environmental

range of Idaho fescue (table 1), where greater

precipitation has made them more resistant to

alteration. The primary disturbance factor has

been livestock grazing, and this PVT often responds well to changes in management. Because

threetip sagebrush resprouts, recovery after fire

is more rapid than many other sagebrush steppe

PVTs.

Most threetip sagebrush steppe sites that have

been severely altered are in the bluebunch

wheatgrass zone (table 2). The shrub overstory

component is generally intact, but the perennial

understory species have usually been depleted.

Cheatgrass is not usually invasive in this PVT as

it is in Wyoming big sagebrush steppe vegetation

(Hironaka et al. 1983). However, this PVT is

susceptible to frequent fires that often occur

where annual grasses have invaded.

Within the basin BLM and FS lands, this PVT is

scattered in a few areas of eastern Washington,

Oregon, and southern Idaho with a concentration

in south-central Idaho (Hann et al. 1997, ICBEMP

source data). Most of this type occurs in intermontane basin, plateau, and plains landforms at

moderate elevations with some on warmer aspects at higher elevations (table 3). Most occurs

in the moderate precipitation zone, but some also

occurs in the high precipitation zone on the warmer aspects and droughty soils (table 4).

Low Sagebrush–Xeric PVT

The low sagebrush–xeric PVT occurs as a

fine-scale mosaic of distinct vegetation types

that include communities dominated by Wyoming

big sagebrush, winterfat, and Nuttall saltbush

(Yensen and Smith 1984) (fig. 3). The soils, which

are usually derived from sediments within the

basin, are similar to those supporting sagebrush

steppe vegetation except for greater salinity.

These communities are restricted by high soil

salinity typical of soil supporting communities

in the salt desert shrub PVT (Blaisdell and

Holmgren 1984, West 1982). The distributions

of many species within the PVT are defined

environmentally by minor changes in soil salinity

as well (Knight 1994). Other common native

species include Sandberg bluegrass, bottlebrush

squirreltail, sixweeks fescue, budsage, and spiny

hop-sage. These areas have long been used by

sheep and more recently by cattle as winter

range (Blaisdell and Holmgren 1984).
23

Slightly altered communities have a relatively

intact shrub overstory. Some reduction in winterfat, Nuttall saltbush, and biological soil crusts

has resulted from past livestock use. Invasive

species such as cheatgrass, tumblemustard, and

tansy mustard are present in small amounts. As

livestock use increases, winterfat decreases

(Blaisdell and Holmgren 1984); cheatgrass increases as the shrub cover decreases. Normally

winterfat-dominated sites do not contain adequate

fuels to carry a wildfire readily (Pellant and

Reichert 1984). However, after more than 1

year with above-average precipitation, fine fuels

may build to a level that is sufficient to carry a

fire when cheatgrass is present. Although Nuttall

saltbush readily resprouts after fire, winterfat

mortality after wildfire is high. Pellant and

Reichert (1984) reported 95 percent mortality of

winterfat following an intense wildfire in southern

Idaho. Once an initial fire has occurred, cheatgrass can dominate the site, and the probability

of subsequent fires increases. Several fires can

extirpate winterfat and Wyoming big sagebrush

from the site. Severely altered sites are primarily

dominated by invasive annual species such as

cheatgrass, tumblemustard, and tansy mustard.

Within the basin BLM and FS lands, this PVT

was mapped at a 1-km resolution where large

patches occur (Hann et al. 1997, ICBEMP

source data). These large patches appear to be

concentrated in areas of southeastern Oregon,

and southwestern and south-central Idaho on

shallow soils of plains and plateau landforms.

They are typically dominated by winterfat-saltbush species of the salt desert with some intermingled Wyoming big sagebrush and low sagebrush. However, based on plot data, historical

and current oblique landscape photography, and

mid-scale photo interpretation, it is apparent

that much of this PVT actually occurs in small

patches not mapped at 1-km resolution, on shallow soils intermingled within large patches of the

Wyoming big sagebrush–warm PVT (Hann et al.

1997, Hessburg et al. 1999). This portion of the

low sagebrush–xeric PVT appears to be dominated by scattered Wyoming big sagebrush with a

short growth form and has been included in the

area estimate for the Wyoming big sagebrush–

warm PVT. It is estimated that because of the

mapping scale used, the low sagebrush–xeric

PVT may account for as much as 10 percent

of the Wyoming big sagebrush–warm PVT

area estimate.

Most of this type occurs in intermontane basin,

plateau, and plains landforms at moderate elevations with some at lower elevations (table 3).

Most occurs in the low precipitation zone

(table 4).

Low Sagebrush–Mesic PVT

The low sagebrush–mesic PVT is dominated

by dwarf sagebrush species such as low, stiff,

and little sagebrush. Low sagebrush is the most

prevalent of the sagebrush species included in

this PVT and is one of the most abundant in the

basin (Tisdale and Hironaka 1981) (fig. 7). Low

sagebrush occurs over a wide range of annual

precipitation (15 to 50 cm) and probably includes

at least two ecotypes (Hironaka et al. 1983). This

PVT includes the most xeric portions of the sites

occupied by low sagebrush and occurs at the

lower elevations and on shallow poorly developed

lithic soils (Passey and Hugie 1962, Tisdale and

Hironaka 1981, Zamora and Tueller 1973). Low

sagebrush vegetation often occurs on soils that

have an impermeable B horizon within 33 cm of

the surface (Tisdale and Hironaka 1981), which

results in a waterlogged condition for a portion of

the year. Understory species commonly include

Sandberg bluegrass, western needlegrass, Idaho

fescue, onespike oatgrass, yampah, lupines, and

several species of biscuitroot. Apart from its

edaphic relations, little has been published on

low sagebrush and other dwarf sagebrushes

or the vegetation types (Tisdale and Hironaka

1981). Sparse herbaceous cover and production

limits fire in this PVT, but sagebrush recovery

is slow when fire does occur. Low sagebrush

is susceptible to the sagebrush moth (Aroga

websteri Clarke) that causes small patches of

high mortality (Furniss and Barr 1975). Extensive

portions of sites dominated by stiff sagebrush

have been invaded by cheatgrass.
24

Figure 7—Area included in the low sagebrush–mesic, low sagebrush–mesic with juniper, mountain big sagebrush–mesic east,

mountain big sagebrush–mesic east with conifers, mountain big sagebrush–mesic west, and mountain big sagebrush–mesic

west with juniper potential vegetation types within the interior Columbia basin as mapped at the 1-km scale. ICBEMP data on file

with: USDA Forest Service, Pacific Northwest Research Station, P.O. Box 3890, Portland, OR 97208.
25

Because the low sagebrush–mesic PVT occurs

over a wide range of precipitation, the potential

herbaceous production varies accordingly. Fire

occurrence is normally less than in the adjacent

sagebrush steppe vegetation owing to low sagebrush coverage and lower herbaceous productivity (Bunting et al. 1987). This variation affects

its historical and present fire regime. Fires often

spread from surrounding vegetation into low

sagebrush steppe. At the drier end of the PVT’s

precipitation range, it is often surrounded by

Wyoming big sagebrush vegetation that has been

invaded by annual grasses. Consequently, fire

occurrence is high, and many low sagebrush

sites have burned, resulting in an increase of

invasive species. At the upper end of its precipitation range, low sagebrush steppe is often in a

mosaic of mountain big sagebrush steppe that

increases fire occurrence. Because the site retains soil moisture in the A horizon, it may be

susceptible to soil displacement by large-animal

herbivory in spring.

Slightly altered sites have been affected by improper grazing strategies that have reduced the

herbaceous species and caused mechanical plant

displacement. The PVT responds relatively

quickly to changes in management when seed

sources are available on site. Severely altered

sites have greatly reduced native perennial herbaceous coverage. Invasive species have increased on some sites. Low fine-fuel production

makes wildfire occurrence less probable than in

surrounding vegetation. Management-ignited

wildland fire (prescribed fire) is difficult to implement (Blaisdell et al. 1982) and is seldom

used in this PVT.

Within the basin BLM and FS lands, this PVT

was mapped at a 1-km scale, and thus only

large patches were detected (Hann et al. 1997,

ICBEMP source data). These large patches

appear to be concentrated in areas of southcentral and southeastern Oregon, and southwestern and southeastern Idaho. Some of the

low sagebrush–mesic PVT appears to have

been included in the area estimate for the

Wyoming big sagebrush–warm PVT. It is estimated that because of the mapping scale used,

the low sagebrush–mesic PVT may account for

as much as 20 percent of the Wyoming big sagebrush–warm PVT area estimate.

Most of this type occurs within plateau and plains

landforms at moderate elevations (table 3). Nearly

equal amounts occur in the moderate precipitation

and low precipitation areas (table 4).

Low Sagebrush–Mesic with

Juniper PVT

The low sagebrush–mesic with juniper PVT is

similar in composition to the low sagebrush–mesic

PVT but occurs in a mosaic with western juniper

woodlands (fig. 7). Juniper historically occurred as

a sparse overstory (less than 5 percent coverage).

Fires, although historically infrequent, maintained

the savannah-like physiognomy of this PVT. Juniper establishment and growth are slow on these

sites but have been increasing in the past 150

years (Miller and Rose 1999, Miller and Wigand

1994). Active fire suppression and use of fine

fuels by livestock have been effective in reducing

fire occurrence in this PVT.

Sites slightly altered by improper grazing strategies

have a reduced herbaceous component resulting

from herbivory and mechanical plant displacement. The PVT responds relatively quickly to

changes in management when seed sources are

available on site. Severely altered sites exhibit

greatly reduced native perennial herbaceous coverage, increased western juniper coverage, or

both. Low fine-fuel production makes wildfire

occurrence unlikely and management ignited wildland fire use (prescribed fire) difficult (Blaisdell

et al. 1982).

Within the basin BLM and FS lands, this PVT

was mapped at a 1-km resolution where a few

large patches occur (Hann et al. 1997, ICBEMP

source data). These large patches occur primarily

in south-central Oregon and southwestern Idaho.

However, based on plot data, historical and current

oblique landscape photography, and midscale photo

interpretation, some of this PVT actually occurs

in small undetectable (at 1-km mapping scale)

patches intermingled within large patches of the

mountain big sagebrush–mesic west with juniper
26

and within Wyoming big sagebrush–warm PVT

(Hann et al. 1997, Hessburg et al. 1999). Because of the limitations of the mapping scale

used, this PVT may actually have a greater geographic range and as much as 20 percent more

area than shown on the maps. All of this type

occurs within plateau, plains, foothill, and mountain landforms at moderate elevations (table 3)

with most in the moderate precipitation zone

(table 4).

Mountain Big Sagebrush–Mesic

East PVT

The mountain big sagebrush–mesic east PVT is

typically dominated by mountain big sagebrush

and may include other shrubs such as rabbitbrush,

antelope bitterbrush, and snowberry, and various

herbaceous species such as Sandberg bluegrass,

bluebunch wheatgrass, Idaho fescue, lupine, wild

buckwheat, and arrowleaf balsamroot. This

PVT occurs primarily in valley bottoms and

mountain slopes in southwestern Montana and

eastern Idaho (fig. 7). That portion east of the

Bitterroot Mountains in the basin often includes

species typical of the shortgrass prairie such as

bluegrama and western wheatgrass. Common

invasive species are leafy spurge and knapweed

species (Dunn 1979, Rinella et al. 2001). Invasive

annual grasses occur within this PVT on sites

that have been severely affected by livestock

grazing or other disturbance. Much of this PVT

had a shorter fire-return interval during historical

times (Arno and Gruell 1983, Bunting et al. 1987,

Houston 1973). Some changes in composition,

such as increased sagebrush coverage, reflect

this decrease in fire occurrence resulting from

reduction of fine fuels by livestock grazing and

active fire suppression.

Alteration of this PVT has largely resulted from

historical livestock grazing and decreased fire

occurrence. Both have resulted in greater sagebrush coverage and a decreased herbaceous

coverage on these sites. The composition of

the slightly altered communities responds readily

to changes in grazing and fire management.

Invasive annual grasses are present but have

not affected the dynamics of disturbance and

composition to the extent they have in many other

sagebrush steppe vegetation types. The native

herbaceous species are commonly reduced on

severely altered communities. Changes in fire

and grazing management may not be adequate to

restore these sites. Additional active restoration

measures such as seeding may be necessary to

reestablish these herbaceous species.

Within the basin BLM and FS lands, this PVT

was a dominant type with many large patches

when mapped at a 1-km scale (Hann et al. 1997,

ICBEMP source data). These large patches are

distributed throughout the foothills and mountains

of central Oregon and central and southern

Idaho. Much of this type occurs at moderate

elevations and in the moderate precipitation zone,

with a lesser amount occurring at high elevations

and in low and high precipitation areas (tables 3

and 4).

Mountain Big Sagebrush–Mesic East

with Conifers PVT

The mountain big sagebrush–mesic east with

conifers PVT is common throughout the eastern

portion of the basin but occurs in small patches

that were not mapped at the 1-km resolution.

Most of the mapped areas of the PVT are found

in central Oregon (fig. 7). Composition is similar

to the mountain big sagebrush–mesic east PVT

except having a greater conifer component, particularly Douglas-fir and Rocky Mountain juniper.

Historically this PVT probably occurred as a

mosaic of mature conifer stands interspersed

with grassland, mountain big sagebrush steppe,

and young developing conifer communities. Decreased fire occurrence has resulted in more

continuous conifer overstory development and

conifer expansion into adjacent sagebrush-dominated communities (Arno and Gruell 1983). Increased conifer overstory has diminished the

grassland and shrub-steppe herbaceous and shrub

species and facilitated changes in understory

composition to species more adapted to forest

environments, such as pinegrass, Idaho fescue,

western snowberry, and heartleaf arnica (Arno

and Gruell 1986, Ferguson 2001, Sindelar 1971).