Abstract
Restoration of pine forests has become a priority for managers who are beginning to embrace ideas of highly heterogeneous forest structures that potentially encourages high levels of regeneration. This study utilizes stem-mapped stands to assess how simulated regeneration timing and magnitude influence longevity of reduced fire behavior by linking growth and yield model outputs to a crown fire prediction model. Treatment longevity was assessed as return time to within 10% of pre-treatment predicted wind speeds for the onset of passive (Torching) and active (Crowning) crown fire behavior. Treatment longevity in terms of Torching and Crowning was reduced 5 years for every 550 and 150 seedlings ha−1, respectively. Introducing regeneration as a single pulse further reduced Torching treatment longevity 10 years compared to other regeneration distributions. Crowning treatment longevity increased at higher site indices, where a 6 m increase in site index increased longevity 4.5 year. This result was contrary to expectations that canopy openings after treatments would close faster on higher productivity sites. Additionally, Torching longevity was influenced by the rate of crown recession, were reducing the recession rate decreased longevity in areas with higher site indices. These dependencies highlight a need for research exploring stand development in heterogeneous sites.
Highlights
Dry forests of Western North America face increasingly extensive, frequent, and severe disturbances from insects, disease, and wildfire due to growing climatic and anthropogenic pressures [1,2,3]
The removal of half the trees in each stand reduced the crown bulk density (CBD) on average by 36% and increased the fuel stratum gap (FSG) on average by 2.7 m, which is a near tripling of the pre-treatment average (Table 2)
The results demonstrate a significant relationship between the number of seedlings on a site and length of time before a stand will return to an undesirable fire hazard condition
Summary
Dry forests of Western North America face increasingly extensive, frequent, and severe disturbances from insects, disease, and wildfire due to growing climatic and anthropogenic pressures [1,2,3]. These disturbances can have large social and financial implications for the communities that are reliant on the resources and ecological benefits provided by these systems [4]. Lawson) and dry-mixed conifer forests of the Rocky Mountains have arguably been exacerbated by what is thought to be uncharacteristically high uniformity and continuity of forest vegetation [5]. The high continuity of forest vegetation currently seen across the landscape is attributed to a combination of early 1900s livestock grazing and timber management practices and a century of fire exclusion causing changes in forest structure from spatially heterogeneous pre-Euro-American settlement conditions [6,7,8].
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