Great Basin Dry Sagebrush Shrubland

This ecological system occurs in the Great Basin on dry flats and plains, alluvial fans, rolling hills, rocky hillslopes, saddles and ridges at elevations between 1000 and 2600 m. Sites are dry, often exposed to desiccating winds, with typically shallow, rocky, non-saline soils. Shrublands are dominated by Artemisia nova (mid and low elevations), Artemisia arbuscula ssp. longicaulis, or Artemisia arbuscula ssp. longiloba (higher elevation) and may be codominated by Artemisia tridentata ssp. wyomingensis or Chrysothamnus viscidiflorus. Other shrubs that may be present include Atriplex confertifolia, Ephedra spp., Ericameria spp., Grayia spinosa, Lycium shockleyi, Picrothamnus desertorum, and Tetradymia spp. The herbaceous layer is likely sparse and composed of perennial bunchgrasses, such as Achnatherum hymenoides, Achnatherum speciosum, Achnatherum thurberianum, Elymus elymoides, or Poa secunda.

These shrublands are dominated by Artemisia nova (mid and low elevations), Artemisia arbuscula ssp. longicaulis (lower elevations), or Artemisia arbuscula ssp. longiloba (higher elevations) and may be codominated by Artemisia tridentata ssp. wyomingensis or Chrysothamnus viscidiflorus. Other shrubs that may be present include Atriplex confertifolia, Ephedra spp., Ericameria spp., Grayia spinosa, Lycium shockleyi, Picrothamnus desertorum, Purshia tridentata, Sarcobatus vermiculatus, and Tetradymia spp. The herbaceous layer is likely sparse and composed of perennial bunchgrasses, such as Achnatherum hymenoides, Achnatherum speciosum, Achnatherum thurberianum, Elymus elymoides, Festuca idahoensis, Hesperostipa comata, Poa fendleriana, Poa secunda, or Pseudoroegneria spicata. The floristic description is based on several other references, including Blackburn and Tueller (1970), Zamora and Tueller (1973), Hironaka et al. (1983), West (1983a), Barbour and Major (1988), Chappell et al. (1997), Howard (1999), Steinberg (2002), Barbour et al. (2007), Fryer (2009), Sawyer et al. (2009), and NatureServe Explorer (2011).

Climate: Climate is semi-arid with 20 to 30 cm of annual precipitation and warm summers and cold winters.

Physiography/landform: This ecological system is widely distributed in the interior Great Basin of the western United States on dry flats and plains, alluvial fans, rolling hills and foothills, saddles and ridges at elevations between 1000 and 2600 m. Sites are xeric, flat to steep, and often exposed to desiccating winds or with typically shallow, rocky, non-saline soils. It occupies flat to steeply sloping upland sites, on a wide variety of topographic positions. Sloping sites tend to have southerly aspects.

Soil/substrate/hydrology: Sites with low slope tend to have deeper soils, while those with steeper slopes have shallow to moderately deep soils that are well-drained. Soil texture is loam, sandy loam, or clay loam (Hansen and Hoffman 1988), and there is often a significant amount of coarse fragments in the soil profile. Hironaka et al. (1983) reported that most of the habitat occurred on calcareous soils, often with a cemented duripan. Low sagebrush tends to grow where claypan layers exist in the soil profile and soils are often saturated during a portion of the year; black sagebrush tends to grow where there is a root-limiting layer in the soil profile, whereas Wyoming sagebrush and basin big sagebrush generally occur on moderately deep to deep soils that are well-drained (LANDFIRE 2007a). The environmental description is based on several other references, including Blackburn and Tueller (1970), Zamora and Tueller (1973), Hironaka et al. (1983), West (1983a), Barbour and Major (1988), Chappell et al. (1997), Howard (1999), Steinberg (2002a), Barbour et al. (2007a), Fryer (2009), and Sawyer et al. (2009).

The diagnostic species of this system, Artemisia nova, Artemisia arbuscula ssp. longicaulis, or Artemisia arbuscula ssp. longiloba, grow in more xeric sites than other Artemisia shrublands (Hironaka et al. 1983). This shrubland system is associated with shallow, rocky soils which experience extreme drought in summer. The plants are low and widely spaced, which tends to decrease the risk of fire (Chappell et al. 1997). Fire is uncommon because of discontinuous and low fuel buildup on the generally unproductive sites (Young and Palmquist 1992, Fryer 2009, Sawyer et al. 2009). Most sites are thought to have relatively long fire-return intervals (100-200 years) according to LANDFIRE models developed by experts (LANDFIRE 2007a). These shrubs are fire-sensitive and rarely sprout after burning. They reproduce from light wind-dispersed seeds from adjacent unburned areas into disturbed areas (Howard 1999, Steinberg 2002a, Fryer 2009). It generally takes around 30 years for a burned stand to recover to pre-fire density (Zamora and Tueller 1973, Hironaka et al. 1983, Howard 1999, Steinberg 2002a, Fryer 2009). Artemisia tridentata ssp. wyomingensis may be present to codominant and shares similar ecological characteristics on these relatively xeric sites (Howard 1999).

Scattered trees may be present in some stands of this system. Fire reduces sagebrush abundance in both sagebrush and pinyon-juniper systems. Where these systems are adjacent, periodic fire likely prevents establishment of juniper and pinyon trees in sagebrush stands (Wright et al. 1979). Blackburn and Tueller (1970) noted rapid invasion of these communities by Juniperus osteosperma and Pinus monophylla at some sites in Nevada. In order to maintain dominance of sagebrush, fire-return interval must be long enough to permit sagebrush stands to mature, but short enough to prevent establishment and growth of trees in these sites. Fire-return intervals of 150-250 years for stand-replacing fire will likely maintain these shrublands. Expansion and contraction of trees into sagebrush shrublands are regulated by a combination of climate, fire, and bark beetle infestations with trees seedlings establishing during wetter periods (Wright et al. 1979, Clifford et al. 2008).

The black and low sagebrush type tends to occur adjacent to Inter-Mountain Basins Big Sagebrush Shrubland (CES304.777). The Wyoming big sagebrush and basin big sagebrush types create a mosaic within the black and low sagebrush types. These big sagebrush types have a different fire regime that acts to carry the fire, with black and low sagebrush serving as firebreaks most of the time (LANDFIRE 2007a).

Black sagebrush (Artemisia nova) generally supports more fire than other dwarf sagebrushes (LANDFIRE 2007a). This type generally burns with mixed severity (average FRI of 100-140 years) due to relatively low fuel loads and herbaceous cover (LANDFIRE 2007a). Bare ground acts as a micro-barrier to fire between low-statured shrubs. Stand-replacing fires (average FRI of 200-240 years) can occur in this type when successive years of above-average precipitation are followed by an average or dry year (LANDFIRE 2007a). Stand-replacement fires dominate in the late-successional class where the herbaceous component has been diminished or where trees dominate (LANDFIRE 2007a). This type fits best into Fire Regime Group IV (LANDFIRE 2007a).

Grazing by wild ungulates occurs in this shrubland system. Native browsing tends to open up the canopy cover of shrubs but does not often change the successional stage (LANDFIRE 2007a).

Insects are an important component of many shrub-steppe and grassland systems. Mormon crickets and grasshoppers are natural components of many rangeland systems (USDA-APHIS 2003, 2010). There are almost 400 species of grasshoppers that inhabit the western United States with 15-45 species occurring in a given rangeland system (USDA-APHIS 2003). Mormon crickets are also present in many western rangelands and, although flightless, are highly mobile and can migrate large distances consuming much of the forage while travelling in wide bands (USDA-APHIS 2010). Following a high population year for grasshoppers or Mormon crickets and under relatively warm dry spring environmental conditions that favor egg hatching and grasshopper and Mormon cricket survival, there may be large population outbreaks that can utilize 80% or more of the forage in areas as large as 2000 square mile. Conversely, relatively cool and wet spring weather can limit the potential for outbreaks. These outbreaks are naturally occurring cycles and, especially during drought, can denude an area of vegetation leaving it exposed to increased erosion rates from wind and water (USDA-APHIS 2003).

LANDFIRE developed a VDDT model for this system which has three classes (LANDFIRE 2007a, BpS 1210790). This model includes sites where there is potential for pinyon (Pinus monophylla) and/or juniper (Juniperus osteosperma) establishment in classes C and D.

A) Early Development 1 All Structures (15% of type in this stage): Shrub cover is 0-5%. Early-seral community dominated by herbaceous vegetation; less than 6% sagebrush canopy cover; up to 24 years post-disturbance. Fire-tolerant shrubs (green/low rabbitbrush) are first sprouters after stand-replacing, high-severity fire. Replacement fire (mean FRI of 250 years) maintains vegetation in class A. Prolonged drought every 200 years on average maintains vegetation in class A. Succession to class B after 25 years.

B) Mid Development 1 Open (60% of type in this stage): Mid-seral community with a mixture of herbaceous and shrub vegetation; 6-25% sagebrush (sagebrush/brush) canopy cover present; between 20-59 years post-disturbance. Drought every 200 years causes two transitions: 50% of times drought thins shrubs while maintaining vegetation in class B, whereas 50% of times drought causes a stand-replacing event. Replacement fire (FRI of 250 years) causes a transition to class A, whereas mixed-severity fire (FRI of 100 years) maintains the site in its present condition. In the absence of fire for at least 120 years, the site will follow an alternative successional path to class C. Otherwise, succession and mixed-severity fire keeps site in class B.

C) Late Development 1 Open (15% of type in this stage): Late-seral community with a mixture of herbaceous and shrub vegetation; 10-25% sagebrush canopy cover present; and dispersed conifer seedlings and saplings established at less than 6% cover (Juniperus osteosperma and/or Pinus monophylla). Insects attack the vegetation in this state every 60 years on average but does not cause a transition to another state. Severe droughts (return interval of 200 years) cause two thinning disturbances: to class B (50% of times) and within class C. Replacement fire is every 200 years on average, whereas mixed-severity fire is less frequent than in class B (FRI of 130 years). Succession is to class D after 75 years.

D) Late Development 1 Closed (10% of type in this stage): Late-seral community with a closed canopy of conifer trees (6-40% cover). The degree of tree canopy closure differs depending on whether it is a low sagebrush (maximum 15%) or black sagebrush (maximum 40%) community. In low sagebrush communities a mixture of herbaceous and shrub vegetation with >10% sagebrush canopy cover would still be present. In black sagebrush communities the herbaceous and shrub component would be greatly reduced (<1%). When Ips beetle outbreaks occur the pinyon pine component is reduced (return interval of 60 years): 75% of times thinning is not intense enough to cause a transition whereas in 25% of cases a transition to class C will occur. The only fire is replacement (FRI of 150 years) and driven by a greater amount of woody fuel than in previous states. Prolonged droughts have the same effect as before.

The primary land uses that alter the natural processes of this system are associated with livestock grazing and introduction of exotic annual grasses. Barbour and Major (1988) report that Artemisia nova is utilized by livestock to a much greater degree than other species of Artemisia, resulting in low, pruned plants (West 1983a). Excessive grazing stresses the system through soil disturbance, diminishing or eliminating the biological soil crust, altering the composition of perennial species, and increasing the establishment of native disturbance-increasers and annual grasses, particularly Bromus madritensis, Bromus tectorum, Schismus spp., and other exotic annual grasses. The introduction of exotic annual grasses has altered many stands by increasing the amount of fine fuels present that can substantially increase fire frequency and intensity which reduces the cover of fire-sensitive shrubs such as Artemisia nova (Fryer 2009, Sawyer et al. 2009).

Direct and indirect fire suppression are a threat to this system where stands are adjacent to pinyon-juniper woodlands. Over the long term, heavy grazing by livestock removes the fine fuels that carry fire that indirectly leads to a reduction in fire frequencies, which can lead to pinyon-juniper encroachment with subsequent loss of shrub and herbaceous understory (LANDFIRE 2007a).

When grasshopper and Mormon cricket populations reach outbreak levels, they cause significant economic losses for ranchers and livestock producers, especially when accompanied by a drought (USDA-APHIS 2003, 2010). Both rangeland forage and cultivated crops can be consumed by grasshoppers. The U.S. Department of Agriculture's (USDA) Animal and Plant Health Inspection Service (APHIS) is the Federal agency responsible for controlling economic infestations of grasshoppers on western rangelands with a cooperative suppression program. They work with federal land managing agencies to conduct grasshopper suppression. The goal of APHIS's grasshopper program is not to eradicate them but to reduce outbreak populations to less economically damaging levels (USDA-APHIS 2003). This APHIS effort dampens the natural ecological outbreak cycles of grasshoppers and Mormon crickets but does not eradicate the species.

Human development has impacted many locations throughout the range of this system. High- and low-density urban and industrial developments also have large impacts. For example, residential development has significantly impacted locations within commuting distance to urban areas. Impacts may be direct as vegetation is removed for building sites or more indirectly through natural fire regime alteration, and/or the introduction of invasive species. Mining operations can drastically impact natural vegetation. Road building and power transmission lines continue to fragment vegetation and provide vectors for invasive species.

This system occurs in the Great Basin on dry flats and plains, alluvial fans, rolling hills, rocky hillslopes, saddles and ridges at elevations between 1000 and 2600 m.