Representatives of jurisdictions meet to view sage-steppe restoration of the Modoc Plateau.
BLM’s Alturas Field Office led development of a multi-jurisdictional strategy to guide restoration of the sagebrush steppe ecosystem on California's Modoc Plateau. (BLM)

Sagebrush-Steppe Restoration on the Modoc Plateau

By Tim Burke

The Modoc Plateau is a remote area of northeastern California known primarily for its “Old West” culture and long, cold winters.  It is an area of vast basalt plains, lava rims, and undulating uplands.  The 85-mile-long Warner Mountain Range runs north and south along the eastern edge of the plateau, reaching an elevation of just under 10,000 feet at Eagle Peak.  However, one of the most distinctive features of the area is not cultural, climatological, or topographical, but rather botanical—it is the ubiquitous western juniper (Juniperus occidentalis).

Western juniper is a western native conifer that typically grows to about 15-30 feet in height, occasionally reaching up to 65 feet.  Trunks are usually composed of a single erect stem with circumferences measuring up to 12 feet.  These trees represent the northwestern extent of the pinyon-juniper region in the Intermountain West.  And, according to packrat midden investigations, they have been an important component of the region’s flora for over 5,000 years.  However, during the past 140 years, western juniper has been expanding within its geographic range at an unprecedented rate.

Back in the 1860s, juniper occupied approximately 300,000 acres within the 6.5-million-acre Modoc Plateau.  It was in equilibrium with the sagebrush grassland, which was the dominant vegetation type in the area.  Depending on elevation and aspect, the grassland featured bluebunch wheatgrass, Idaho fescue, needlegrass, or squirreltail.  Juniper grew naturally in the rocky, shallow soil inclusions that did not support the sage steppe vegetation.  Due to the lack of this vegetation to provide “ladder fuels,” these juniper strongholds were somewhat fire resistant.  Over time, juniper seedlings would begin to migrate out from the inclusions into the adjacent grassland, but inevitably, before many trees could become established, a wildfire fed by the grasslands shrubs and grasses would run through the area, pushing the juniper back to the rocky ridges.  The average interval between wildfire events was about 25-50 years.

Once the Modoc Plateau began to be settled around 1870, heavy livestock grazing reduced the accumulation of fuels within the grasslands.  This significantly lessened the potential for wildfire.  As a result, the junipers, which had been restricted to the rocky inclusions, began to move into the sagebrush steppe with impunity.  By the 1930s, heavy livestock grazing was being more intensively managed, but the human inhabitants were also becoming much more adept at fighting wildfire, allowing continued juniper expansion and infilling.

Today, western juniper occupies about 3 million acres within the Modoc Plateau.  This is a tenfold increase over presettlement days, and the encroachment now includes second and third generation junipers.  As the tree canopy closes, native grasses and shrubs are lost from the ecosystem.  And since the juniper is extremely long lived, the resulting vegetation type is frequently a juniper monoculture.  This loss of vegetative diversity negatively affects wildlife, resulting in dwindling numbers of key species such as sage-grouse, mule deer, and pronghorn.

Juniper encroachment also affects the water-holding capacity of the ecosystem.  As grasses and shrubs are lost, erosion increases dramatically.  Analyses indicate that juniper encroachment significantly decreases late season spring flow and decreases the availability of late season soil moisture.

These ecosystem impacts translate directly into economic impacts.  The loss of forage impacts the livestock industry.  The loss of game species impacts the hunting and tourism industries.  The potential inclusion of sage-grouse and pygmy rabbits on the federal threatened and endangered species list reduces land use options.  The loss of water impacts farming, hydroelectric projects, and, ultimately, freshwater availability in the San Francisco Bay Delta.

Based on these concerns, the BLM’s Alturas Field Office led development of a multijurisdictional strategy and environmental impact statement (EIS) to guide restoration of the sagebrush steppe ecosystem on the Modoc Plateau.  Modoc County, California, took a leadership role in the partnership by contributing $250,000 towards the planning effort.  The BLM matched the $250,000 as part of its Challenge Cost Share Initiative.  The Modoc National Forest contributed staff to lead development of the EIS.

The resulting strategy recommends an adaptive management approach to achieve an environmentally sensitive reduction in the level of western juniper encroachment on the Modoc Plateau.  The strategy calls for treating 1.2 million acres over a 48-year timeframe with wildfire, prescribed fire, and mechanical and hand treatment methods.  Decisions to implement the strategy were signed in late 2008.

By early 2011, more than 27,000 acres had been treated.  These treatments are the first step down the road toward restoring western juniper to its appropriate role as a supporting actor in the ecosystem of the Modoc Plateau.

Tim Burke is currently the Alturas field manager and has served in that position since 1998.  He has worked for BLM since 1978 and has held a variety of positions in California, Nevada, Utah, and New Mexico.