Table 4 Effects of treatments to reduce shrub fuels in sagebrush ecosystems that are not experiencing pinyon-juniper expansion on vegetation and fuel structure, fire behavior, fire management implications, and ecological response
| Â | Vegetation/fuel structure | Fire behavior | Fire management implications | Ecological effects |
|---|---|---|---|---|
Prescribed fire | Decreases fuel loads of all fuel types in years 1 and 2; subsequent increases vary by fuel type and depend on site conditions and initial species | Decreases in rate of spread until herbaceous fuels increase; longer-term reduction in flame length and reaction intensity dependent on shrub establishment and growth | Warmer and drier types with low resilience and resistance less likely to respond favorably than cooler and moister types | Ecological effects depend on ecological site type, relative resilience and resistance, and current ecological conditions |
Wyoming big sage | • High risk of increases in invasive annual grass and forb fuel • Slow sagebrush establishment and slow increase in woody fuels • Increases in woody fuels due to any root-sprouting shrubs | • Longer-term risk of increased rates of fire spread due to annual invaders • Flame length and rates of spread influenced more by herbaceous than woody fuel | • Low sagebrush cover and high perennial grass and forb cover lowers burn severity and promotes recovery • Risk of annual grass is very high on sites with low resistance and perennial herbaceous cover • Patchy burns may help maintain sagebrush habitat and promote recovery | • May reduce resilience to fire and resistance to invasion • Increases herbaceous and reduces shrub biomass • Recovery of ecosystem production and vegetation structure will likely be slow |
Mountain big sage | • Lower risk of invasive annuals • Increases in perennial grasses and forbs likely • Higher probability of increases in sagebrush fuels over time due to more favorable establishment conditions • Increases in woody fuels due to any root-sprouting shrubs | • Rates of spread determined by recovery of perennial herbaceous fuels • Flame length and reaction intensity influenced by recovery of woody fuel | • Prefire vegetation is a good indicator of postfire effects • Risk of annual grass dominance if present before fire or perennial herbaceous vegetation is diminished • Patchy burns may help maintain sagebrush habitat and promote recovery | • May increase resilience to wildfire and resistance to invasion • Increases herbaceous and reduces shrub biomass • Ecosystem production returns to prefire conditions quickly (~ 2 years); vegetation structure in ~ 25–50 years |
Mowing | Shifts woody fuel from shrub canopy to herbaceous, downed wood, and litter layers | Reduction in rates of spread, flame lengths, and reaction intensity relative to controls | Potential for use in areas such as fuel breaks to provide anchor points for suppression | Ecological effects depend on ecological site type, resilience and resistance, relative cover of shrubs and perennial herbs |
Wyoming big sage | • High risk of increases in annual grasses and forbs • Slow establishment and growth of sagebrush | • Reduced flame lengths due to shorter fuelbed • Potential for higher rates of spread with increases in annual herbaceous fuels • May reduce reaction intensity (heat per unit area) but increase potential for smoldering | • Risk of increase in annual grasses is high if perennial herbaceous vegetation cover is low and sagebrush cover is high • Tradeoffs between decreasing flame lengths and increasing fire spread and intensity | • Unlikely to increase resilience to fire and resistance to invasion • Increases in annual grass likely under most conditions • Decreases in sagebrush cover and downed wood may reduce habitat quality |
Mountain big sage | • Lower risk of annual invaders • Increases in perennial herbs likely • More rapid sagebrush establishment and growth and thus increases in woody fuels | • Shorter fuelbed resulting in reduced flame lengths • Increases in perennial herbaceous fuels may influence rates of spread • May reduce reaction intensity (heat per unit area) but increase potential for smoldering | • Increases in perennial herbaceous vegetation (fuel) likely • Tradeoffs between decreasing flame lengths and increasing fire spread and intensity • Less time sensitive and costly implementation compared to prescribed fire | • Fire surrogate that may increase resilience to wildfire and resistance to invasive annuals • Reductions in shrub biomass and increases in perennial native grasses and forbs • Effects on habitat quality unknown |
Herbicides to suppress shrubs | Converts live woody fuel to standing dead in short term and to downed woody debris and duff in the long term | No effect on the modeled rate of fire spread, flame length, or reaction intensity | No apparent benefits to fire management | Ecological effects depend on ecological site type, resilience and resistance, relative cover of shrubs and perennial herbs |
Wyoming big sage | • Delayed mortality of shrubs and reductions in woody fuels • Increases in invasive annual fuels over time likely | • Increases in downed woody fuel and invasive annual fuels over time • No effect on rates of spread, flame length or reaction intensity • Increased woody ground fuels may increase smoldering and decrease flaming combustion | • Risk of annual grass is high if perennial herbaceous vegetation cover is low • No benefits to fire management based on modeled fire behavior • Less time sensitive and costly implementation compared to prescribed fire | • Unlikely to increase resilience to fire and resistance to invasion • Invasive annual grass likely to increase over time • Decreases in sagebrush cover and downed wood may reduce habitat quality |
Mountain big sage | • Delayed mortality of shrubs and reductions in woody fuels • Lower risk of invasive annual fuels • Increases in perennial grass and forb fuels over time possible | • Increases in perennial herbaceous and downed woody fuels over time • Effect on rates of spread, flame length and reaction intensity minimal • Increased woody ground fuels may increase smoldering and decrease flaming combustion | • Longer-term increases in perennial grasses and forbs likely • Fire behavior models from Wyoming big sage sites indicate no benefits to fire management • Less time sensitive and costly implementation compared to prescribed fire | • Fire surrogate that may increase resilience to wildfire and resistance to invasion • Reductions in shrub biomass and increases in perennial native grasses and forbs • Effects on habitat quality unknown |