Great Basin Semi-Desert Chaparral

This system includes chaparral on sideslopes transitioning from low-elevation desert landscapes up into pinyon-juniper woodlands of the western and central Great Basin. There are limited occurrences extending as far west as the inner Coast Ranges in central California. These are typically fairly open-canopy shrublands with open spaces either bare or supporting patchy grasses and forbs. Characteristic species may include Arctostaphylos patula, Arctostaphylos pungens, Ceanothus greggii, Ceanothus velutinus, Cercocarpus montanus var. glaber, Cercocarpus intricatus, Eriogonum fasciculatum, Garrya flavescens, Quercus turbinella, Purshia stansburiana, and Rhus trilobata. Cercocarpus ledifolius is generally absent. Typical fire regime in these systems varies with the amount of organic accumulation.

The vegetation in stands of this system are dominated by sclerophyllous shrubs that are adapted to freezing temperatures and cold winters. These are typically open-canopy shrublands 1-3 m tall with interspaces of either bare ground or patchy grasses and forbs. Characteristic species include Arctostaphylos patula, Arctostaphylos pungens, Ceanothus greggii, Ceanothus velutinus, Ceanothus leucodermis, Ceanothus martinii, Ceanothus prostratus, Cercocarpus intricatus, Eriogonum fasciculatum, Purshia stansburiana, Purshia tridentata, and Rhus trilobata. Cercocarpus ledifolius is generally absent. Sometimes other shrubs such as Amelanchier utahensis, Artemisia tridentata ssp. vaseyana, Artemisia tridentata ssp. wyomingensis, Cercocarpus montanus, Ephedra viridis, Fremontodendron californicum, Garrya flavescens, or Quercus gambelii may be present to codominant. The herbaceous layer is variable but typically sparse. The vegetation description is based on several references, including Kauffman (1986), Tirmenstein (1989), Pavek (1993), Holland and Keil (1995), Reid et al. (1999), Zouhar (2000), Anderson (2001a, 2004a), League (2005), Barbour et al. (2007), Hauser (2007), and Sawyer et al. (2009).

This chaparral system is found in the western and central Great Basin, and east slopes of the Sierra Nevada and Cascades on slopes between lower-elevation desert landscapes and higher-elevation pinyon- or juniper-dominated woodlands. It is also found in limited, small-patch occurrences in the montane zone of many mountain ranges in the western U.S. and a few small pockets in the inner Coast Ranges of central California. These shrublands occur in summer-dry habitats from 800 to 3000 m elevation, typically on piedmont slopes, foothills, plateaus and mountains. Much of the precipitation comes as winter snow, and summer drought-stress is characteristic. These shrublands are mostly found on steep, usually south-facing slopes, where soils are rocky and well-drained. These are typically zonal disclimax or, occasionally, edaphic climax brushfields which occur in association with dry needle-leaved evergreen forests or woodlands. These shrublands are typically established after stand-replacing fires or clearcut logging in Pinus ponderosa, Abies concolor, or Pseudotsuga menziesii forests or pinyon-juniper woodlands, and are seral to forest after several decades. Excessively rocky or droughty, fire-prone sites in the forest may support relatively persistent stands of this system. In the Rocky Mountains, stands are found in small patches within a matrix of montane conifer forest and woodland. Adjacent systems in alpine include California Montane Jeffrey Pine-(Ponderosa Pine) Woodland (CES206.918), Southern Rocky Mountain Dry-Mesic Montane Mixed Conifer Forest and Woodland (CES306.823), Great Basin Pinyon-Juniper Woodland (CES304.773), and Rocky Mountain Cliff, Canyon and Massive Bedrock (CES306.815) above and Mojave Mid-Elevation Mixed Desert Scrub (CES302.742) or Great Basin Xeric Mixed Sagebrush Shrubland (CES304.774) below. The environmental description is based on several other references, including Kauffman (1986), Tirmenstein (1989), Pavek (1993), Holland and Keil (1995), Reid et al. (1999), Zouhar (2000), Anderson (2001a, 2004a), League (2005), Barbour et al. (2007), Hauser (2007), and Sawyer et al. (2009).

Disturbance dynamics in this system are variable because of variation in the compositions; however, most dominant shrubs are evergreen species that are adapted to medium-frequency, medium- to large-sized and medium- to high-intensity fire in late summer or fall (Hauser 2007, Sawyer et al. 2009). Some species, such as Arctostaphylos patula, Ceanothus velutinus, Ceanothus leucodermis, and Fremontodendron californicum, are generally top-killed in burns, but then vigorously resprout from rootcrowns or buried lignotubers. Most have seeds stored in soil and duff that need fire scarification to germinate (Pavek 1993, Anderson 2001a, Hauser 2007, Sawyer et al. 2009). Other chaparral shrubs, such as Arctostaphylos pungens and Ceanothus greggii, are killed or sprout only weakly after fire and regenerate from fire-scarified seeds in the seedbank (Zouhar 2000, League 2005, Sawyer et al. 2009). The shorter-lived species such as Ceanothus leucodermis are dependent on fire for regeneration and will disappear after 40-70 years if not burned (Minnich 1976, Tirmenstein 1989). Higher-severity fires cause greater seedling establishment than lower-severity fires in chaparral (Kauffman 1986). Some deciduous species such as Rhus trilobata are also adapted to fire, vigorously resprout after burning and have fire-scarified seeds (Anderson 2004a). Fire-return interval (FRI) for this systems is medium (10-100 years) on most of the dominant species (Sawyer et al. 2009).

Much of this chaparral system has been impacted by livestock use because of high accessibility and relatively gentle terrain, especially in lower-elevation stands (Brown 1982). Higher-elevation stands on rocky sites with sparse grass understory and dominated by relatively unpalatable browse such as Arctostaphylos patula and Ceanothus velutinus (USFS 1937) have little or no livestock impacts.

Human development has impacted many locations throughout the ecoregion. 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.

The primary land uses that alter the natural processes of this system are associated with livestock practices, annual exotic species, fire regime alteration, direct soil surface disturbance, and fragmentation. Excessive grazing stresses the system through soil disturbance (also ORV use), 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 and other exotic annual bromes.

Western and central Great Basin.