Organic layer thickness: Wickersham fire sites (1971 - 2004)

In June of 1971, the Wickersham fire burned 6313 ha in an open black spruce forest underlain with permafrost and provided an opportunity to study fire and fireline effects on the rate and patterns of permafrost, soil, and vegetation recovery. When wildfire burns through a northern black spruce forest the degree of soil organic layer consumption greatly influences the post-fire community characteristics. The construction of firelines with heavy machinery involves the complete removal of vegetation and the soil organic layer down to mineral soil and likewise affects the community characteristics after fire and fire suppression. Reduction in organic layer thickness and the subsequent loss of thermal insulation has been shown to cause increased soil temperatures and increased depth of thaw of the active layer. This long-term study is a comparison between the organic layer thickness on firelines, burned and unburned open black spruce forests underlain by ice rich permafrost.1971年6月，威克舍姆大火（Wickersham Fire）在一片下伏永久冻土(permafrost)的开放黑云杉林中燃烧，过火面积达6313公顷，为探究火灾及防火线(fireline)对永久冻土、土壤与植被恢复的速率及格局的影响提供了重要研究契机。当野火蔓延穿过北部黑云杉林时，土壤有机层的消耗程度会显著影响火后群落特征。采用重型机械修筑防火线时，需彻底清除植被及土壤有机层直至矿质土壤(mineral soil)层面，该操作同样会对火灾及灭火后的群落特征造成影响。已有研究证实，有机层厚度的缩减及其随之丧失的隔热性能，会导致土壤温度升高，同时增大活动层(active layer)的解冻深度。本项长期研究将对比三类区域的有机层厚度：防火线上的区域、下伏富冰永久冻土的过火开放黑云杉林，以及下伏富冰永久冻土的未过火开放黑云杉林。