Maintaining fuel treatments with prescribed fire in ponderosa pine forests of the Black Hills, South Dakota
Date
2007
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Abstract
Recent wildfires in ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forests have increased efforts to create forest structures that reduce the risk of crown fire. In the Black Hills, these fuel-reduction treatments often result in a new cohort of ponderosa pine regeneration. If no action is taken, the efficacy of these fuel treatments eventually diminishes as the regeneration grows and creates a ladder fuel complex. In this dissertation, I examine the utility of using prescribed fire to control this regeneration. I also explore if restoration of historical forest structure would result in reduced crown fire risk.
Models that predict ponderosa pine regeneration mortality after dormant season fires in the Black Hills were developed. The models showed that tree size, crown damage, ground char severity, and basal char severity were important factors in predicting mortality. With these models, I examined the temporal susceptibility of regeneration to prescribed fire. I then examined the use of prescribed fire to maintain fuel treatments by evaluating the temporal dynamics of regeneration, surface fuel accumulation, and associated fire behavior under prescribed fire conditions for a 120-year time since fire chronosequence. Current fire prescriptions and fuel loads were adequate to maintain low densities of seedlings (<90 cm tall) if burns occurred every 10 to 15 years, but bigger regeneration would not be susceptible. Burn intervals exceeding 15 years allowed regeneration to attain sizes that reduced susceptibility to fire. Flame lengths exceeding 1-2 meters were required to obtain significant mortality. Achieving these flame lengths will require burning under drier weather conditions or fuel load augmentation.
Finally, I explore the idea that restoration of Black Hills historical forest structure results in reduced crown fire risk. Potential fire behavior of these forest structures was modeled under various weather conditions and fire return intervals. Simulation results suggested that the historical Black Hills landscape was shaped by a mixed-severity fire regime, indicating that restoration of some historical Black Hills forest structures would be in conflict with the goals of fuel-reduction treatments. Furthermore, the simulations highlighted the importance of maintaining low densities of regeneration to limit crown fire initiation during a wildfire.
Models that predict ponderosa pine regeneration mortality after dormant season fires in the Black Hills were developed. The models showed that tree size, crown damage, ground char severity, and basal char severity were important factors in predicting mortality. With these models, I examined the temporal susceptibility of regeneration to prescribed fire. I then examined the use of prescribed fire to maintain fuel treatments by evaluating the temporal dynamics of regeneration, surface fuel accumulation, and associated fire behavior under prescribed fire conditions for a 120-year time since fire chronosequence. Current fire prescriptions and fuel loads were adequate to maintain low densities of seedlings (<90 cm tall) if burns occurred every 10 to 15 years, but bigger regeneration would not be susceptible. Burn intervals exceeding 15 years allowed regeneration to attain sizes that reduced susceptibility to fire. Flame lengths exceeding 1-2 meters were required to obtain significant mortality. Achieving these flame lengths will require burning under drier weather conditions or fuel load augmentation.
Finally, I explore the idea that restoration of Black Hills historical forest structure results in reduced crown fire risk. Potential fire behavior of these forest structures was modeled under various weather conditions and fire return intervals. Simulation results suggested that the historical Black Hills landscape was shaped by a mixed-severity fire regime, indicating that restoration of some historical Black Hills forest structures would be in conflict with the goals of fuel-reduction treatments. Furthermore, the simulations highlighted the importance of maintaining low densities of regeneration to limit crown fire initiation during a wildfire.
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Rights Access
Subject
Black Hills
forests
fuel treatments
Pinus ponderosa
ponderosa pine
prescribed fire
South Dakota
ecology
forestry
environmental science