Fine-scale variation of historical fire regimes in sagebrush-steppe and juniper woodland: an example from California, USA

Abstract

Coarse-scale estimates of fire intervals across the mountain big sagebrush (Artemisia tridentata spp. vaseyana (Rydb.) Beetle) alliance range from decades to centuries. However, soil depth and texture can affect the abundance and continuity of fine fuels and vary at fine spatial scales, suggesting fire regimes may vary at similar scales. We explored variation in fire frequency across 4000 ha in four plant associations with differing soils in which mountain big sagebrush and western juniper (Juniperus occidentalis subsp. occidentalis Hook.) were diagnostic or a transitory component. We reconstructed fire frequency from fire-scarred ponderosa pine (Pinus ponderosa P. & C. Lawson) in one association. The other three associations lacked fire-scarred trees so we inferred fire frequency from establishment or death dates of western juniper and a model of the rate of post-fire succession we developed from current vegetation along a chronosequence of time-since-fire. Historical fire frequency varied at fine spatial scales in response to soil-driven variation in fuel abundance and continuity and spanned the range of frequencies currently debated. Fire intervals ranged from decades in areas of deep, productive soils where fine fuels were likely abundant and continuous, to centuries in areas of shallow, coarse soils where fine fuel was likely limited.

Fire patterns in the range of the greater sage-grouse, 1984-2013 - Implications for conservation and management

“…Reduction of fuels caused by livestock grazing and fire suppression activities are thought to have increased fire return intervals to the point where conifer species (especially juniper and pinyon) can establish and eventually outcompete sagebrush, leading to a reduction of perennial grasses and forbs (Miller and Tausch, 2001). This reduction in habitat quality for the greater sage-grouse (Miller and Rose, 1999;Miller and Heyerdahl, 2008) has led to avoidance of areas with trees (Casazza and others, 2011) and declines in population persistence (Baruch-Mordo and others, 2013). Conifer encroachment was ranked tenth among threats across the range of the species, and fourth in the western part of its range in the 2005 listing decision (U.S. Fish and Wildlife Service, 2005).…”

“…Mean fire return intervals may have ranged from decades in colder-moister sagebrush ecosystems (Miller and Heyerdahl, 2008) to hundreds of years in hotter-drier sagebrush ecosystems (Bukowski and Baker, 2013), allowing for recovery and persistence of sagebrush communities adapted to those conditions. However, during recent decades, fire probability and occurrence have increased across large portions of the cold desert ecoregion of Western United States (Whisenant, 1989;Knick and Rotenberrry, 1997;Chambers, 2008;Miller and others, 2011;Baker, 2013;Balch and others, 2013), hindering recovery of sagebrush and threatening sage-grouse habitat.…”

Sagebrush steppe recovery after fire varies by development phase of Juniperus occidentalis woodland

“…vaseyana (Rydb.) Beetle), a main area of piñon-juniper expansion, are estimated to have been ,20 to ,100 years Miller and Heyerdahl 2008). Woodland development has a range of adverse effects on structural and functional properties of A. t. ssp.…”

Summary of science, activities, programs, and policies that influence the rangewide conservation of Greater Sage-Grouse (Centrocercus urophasianus)

“…In contrast, lack of fire at higher elevations, where moisture and productivity are greater than neighboring communities at lower elevations, has contributed to an increase in juniper cover (Miller and Rose, 1995;Miller and others, 2000;Miller and Heyerdahl, 2008;Sankey and Germino, 2008;Shinneman and others, 2008;Bradley, 2010). In these areas, active restoration using fire or "fire-mimic" (mechanical) treatments may be needed to maintain sage-grouse habitats by reducing juniper cover (Bradley, 2010;Rowland and others, 2010).…”

“…arbuscula). These values capture differences among sagebrush types and provide approximate time frames that support the juxtaposition of disturbance (fire) and recovery (in this case, re-colonization by sagebrush); additional information on fire and fire-return intervals, especially relating to particular ecological types and (or) conditions, is available in the literature (Nelle and others, 2000;Miller, 2001;West and Yorks, 2002;Mensing and others, 2006;Lesica and others, 2007;Miller and Heyerdahl, 2008), and consideration of these and other local details may be necessary for comprehensive planning and mitigation.…”