Fire and Ecosystem Effects Interactions
How do spatial and landscape patterns of fire relate to fuels?
Wildland fire as a self-regulating mechanism: the role of previous burns and weather in limiting fire progression
Stands that are within unaltered, short-interval fire regimes tend to self-regulate the burn severity of secondary fires, and burn at the same or lower severity, suggesting that the initial fire moderated the burn severity of the second fire. However, this effect decays as time since fire increases. Specifically, the drier forests of New Mexico, the ability of wildfire to act as a fuel break decayed after only 6 years. Weather conditions conducive to fire ignition and spread, however, can weaken the effect of a previous reburn to limit fire spread or severity.
Climate change is expected to increase the frequency of extreme fire weather events, likely reducing the effectiveness of fire-created fuel breaks during extreme fire seasons. Still the authors suggest that using fire to regulate future fire severity may present opportunities to increase ecosystem resilience to future fire, especially in non-extreme fire years.
Changes in severity distribution after subsequent fires on the North Rim of Grand Canyon National Park, Arizona, USA
The authors found a positive feedback between the initial severity of a fire and the severity of a later reburn, especially concerning high severity forest fire. Conversely, low- or moderate-severity fires may regulate future fires to similar severities, which follows historical patterns of frequent, low-severity fires in dry coniferous forest systems.
Pattern and process of prescribed fires influence effectiveness at reducing wildfire severity in dry coniferous forests
The authors found that landscape context of the burn strongly influenced wildfire severities. Fire severity was lower further inside contiguous patches of burned area and increased with increasing distance from the center of the disturbance. The authors suggest that fire size and burn continuity may be more important in reducing subsequent fire severity than the severity of the prescribed fire.
Bottom-up control of a northern Arizona ponderosa pine forest fire regime in a fragmented landscape
The study landscape was characterized by patches of ponderosa pine forest divided by a matrix of pinyon–juniper (PJ), sagebrush shrublands, and small grasslands. The authors did not find regional synchrony between the patches of ponderosa pine within the study area, suggesting that bottom-up controls, such as fuels, may have more strongly influenced the historical occurrence of fire in this region than climate. The authors suggest that climate may be less influential on fire activity in ecosystems that are fuel limited.
Characterizing fire-on-fire interactions in three large wilderness areas
The authors found that low- or moderate-severity fires generally regulated subsequent fires to similar severities, similar to historical patterns of frequent, low-severity fires in dry coniferous forest systems. Smaller burns created openings in both the understory and overstory vegetation, which adds diversity to the landscape, provides mechanisms for plant succession, and promotes differential tree establishment. In contrast to small burns, they found that large burns may create a homogeneous setting of burned areas which may not enhance species diversity following fire. Finally, the authors suggest that although typically previous fires kept the spread of subsequent fires in check most of the time, climate and weather can override fuel limitations and spread into recently burned landscapes.
'Minimal-impact' restoration treatments have limited effects on forest structure and fuels at Grand Canyon, USA
The authors found minimal changes to forest structure under the thinning treatments. These treatments reduced duff and litter in the understory, but did not affect the canopy significantly. The prescribed fire treatments constituted the greatest treatment impact on future crown fire behavior potential by raising the canopy base height. The thin and burn treatment and prescribed fire only treatment had nearly indistinguishable effects on forest structure, suggesting that resources may be better spent on increasing prescribed fire than on minimal thinning activities.