Graduate Thesis Or Dissertation


Long-term Fuel Succession in the Sagebrush-steppe Public Deposited

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  • Historically fire has been the primary disturbance factor in the sagebrush-steppe. The settlement of the West by Euro-Americans, grazing by domestic livestock, and the concomitant spread of invasive species have altered the historical fire regime. Understanding the long-term vegetation structure and fuel succession of the various sagebrush-dominated communities of this biome is important for managing the landscape in a way that will facilitate the complicated life histories of wildlife species of concern. The objectives of this study were to address the following current knowledge gaps: a lack of studies examining long-term post-fire fuel succession, a lack of studies that address repeated burns, and a lack of studies in basin big sagebrush (Artemisia tridentata spp. tridentata) and low sagebrush (Artemisia arbuscula). To assess long-term fuels succession, the effects of repeated burns, and basin big and low sagebrush fuel structures, I conducted 2 different studies. I resampled previous fire effects studies where pre-fire and immediate post fire fuels data existed at Hart Mountain National Antelope Refuge (HMNAR), John Day Fossil Beds National Monument, Sheep Rock Unit (JODA), and on Prineville BLM land adjacent to Bear Creek (BEAR). Two of these studies were conducted in basin big sagebrush communities (JODA, BEAR), and one of these studies had re-burned since the study’s inception (JODA). The studies were designed so that fuel loads could be statistically tested and compared to their corresponding past studies. Fuels were first stratified into overstory and understory fuels. Overstory fuels consisted of all living and dead shrubs. Understory fuels consisted of downed wood (DWD); duff and shrub-related litter, bryophitic materials; and herbaceous fuels. Herbaceous fuels where then further divided into living grasses and forbs, standing dead grasses and forbs, and detached grass and forb litter.In Wyoming big sagebrush communities at HMNAR that are now seventeen years post fire (YPF), overstory fuels only recovered to 13% of pre-fire levels and understory fuels only reached 25% of pre-fire levels. When compared to adjacent un-unburned control plots, the 17YPF plots had herbaceous fuels that were 5 times greater than controls (17YPF=154±20 kg ha⁻¹, controls=30.2±6 kg ha⁻¹; P<0.01). However, total fuel loads were >7x greater in unburned controls (6014.88±779.76 kg ha⁻¹) than in burned sites (831.2±192.8 kg ha⁻¹; P<0.01).In contrast, in the Basin big sagebrush sites of BEAR and JODA, (25-26YPF) fuels recovered to 7-191% of pre fire levels (pre-fire, 36.2-16.8 Mg ha⁻¹; 25 years after fire, 69.1-2.3 Mg ha⁻¹ [BEAR]), and to 113-209% (pre-fire, 6.2 Mg ha⁻¹; 26 years after fire, 13.0-7.1 Mg ha⁻¹[JODA]). Repeated burns at JODA significantly altered fuels composition. Fifteen years post a single fire (15YPF), herbaceous fuels made up 44%, and shrubs were 39% of total fuels. The fuel loads (aboveground biomass) of twice-burned sites (2xB;burned 26 years and 15 years prior) had a composition of 71% herbaceous and 12% shrub mass. Total fuel loads in 15YPF and 2xB sites ranged from 3.5-6.0 Mg ha⁻¹ and did not differ by site (P=0.85).Sites from these study all showed high levels of resilience to disturbance by fire, with none of them converting to an alternative state dominated by invasive annual grasses. This is encouraging, and managers and scientists interested in exploring the use of fire as a tool to manage sagebrush steppe ecosystems in a way creates a mosaic of various habitats and fuel loads can use results from this study to facilitate their specific needs
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