Table 7 Effects of treatments to reduce herbaceous fuels on vegetation and fuel structure, fire behavior, fire management implications, and ecological response

Herbicides to reduce annual grass fuel

Imazapic

• Decreases invasive annual fuels for 2–3 years

• Invaders increase over time without successful restoration or repeated applications in areas dominated by invasive annuals

• May reduce seeding success of native perennials with lesser effects on introduced grasses

• Tradeoffs exist between reduced seedling establishment and invasive annual grass control

• Decreases rates of fire spread when used in conjunction with fuel treatments in relatively warm and dry areas

• Intended to decrease establishment and growth of annual grasses and forbs long enough for residual native herbs to recover and seeded species to establish

• May prevent development of annual grass fire cycles where effective in promoting seeding success

• Imazapic is effective at reducing several annual grasses, but is only partially selective and may decrease residual native annual and perennial species as well as seeded species

• Increases in relative resilience and resistance may occur where effects of controlling invasive annual grasses outweigh decreased seeding success and perennial grass recovery

Indaziflam

• Decreases native and invasive annual fuels for 3–4 years

• Invaders increase over time without successful restoration or repeated applications in areas with abundant invasive annuals

• Results in consistent decreases in native seedbanks, especially annuals

• In remnant native systems, decreases perennial natives and reduces seeding success in relatively warm and dry areas; has neutral or positive effects in relatively cool and wet areas

• No data found, but likely decreases short-term fire ignition, flame length and fire spread in invasive annual dominated areas

• May increase fire spread in remnant native communities where perennial herbaceous species increase

• Intended to decrease establishment and growth of invasive annual grasses and forbs long enough for residual native herbs to recover and seeded species to establish

• Effects appear highly dependent on site conditions

• Desired results are more likely in cool and moist areas that receive relatively high summer precipitation

• Indaziflam reduces the seed banks of both native and invasive grasses and forbs

• In areas with relatively low resilience and resistance (warm and dry) it appears to reduce invasive species, seeded species, and residual perennial species

• In areas with relatively high resilience and resistance (cool to cold and moist) it appears to reduce invasive species, and increase residual perennial forbs and especially grasses

Targeted grazing to reduce herbaceous fuel

High-intensity targeted grazing

• High-intensity grazing in areas dominated by invasive annual grasses decreases fine fuels

• Invasive annual grass biomass can be reduced by 70 to 90%

• Residual native perennial herbaceous species may be further decreased

• Vegetation stays green longer reducing flame length and rate of spread

• Repeated high-intensity grazing in spring may prevent fires from carrying

• High-intensity grazing will likely require enclosures or protein supplements to concentrate livestock

• High-intensity grazing to create fuel breaks may decrease fire risk and aid fire-suppression operations

• High-intensity grazing of annual grass dominated areas can decrease invasive annual grass cover and seed banks

• Native perennial herbaceous species also can be reduced

• Return to a perennial community following high-intensity grazing requires active restoration

Dormant season targeted grazing

• Dormant season grazing decreases fine fuel carryover and increases fuel moisture in the following year

• In intact Wyoming big sagebrush ecosystems moderate utilization appears to have minor effects on native herbaceous perennials

• Decreases in fine fuels with dormant season grazing may decrease fire ignition, flame length and fire spread where shrub fuels are relatively low

• Greater flame length and fire spread is likely with higher shrub fuels (> 15%) regardless of reductions in herbaceous fuels

• Dormant season grazing that effectively reduces fine fuels, fire ignition, and fire spread may slow fire growth and aid suppression efforts

• Repeated fall (dormant season) grazing at low to moderate utilization rates appears to have relatively minor effects on composition of intact sagebrush ecosystems over time

• Heavier dormant season grazing utilization rates or spring grazing has negative effects on perennial herbaceous species