Forest Investment Account

Abstract of FII Project R02-19

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Natural Disturbance History in the ICHwk3

Author(s): Sanborn, Paul (University of Northern British Columbia)
Subject: Forestry
Series: Forest Investment Account (FIA) - Forest Science Program


Increased public interest in the management and conservation of the northern Interior Cedar-Hemlock biogeoclimatic zone requires a better understanding of disturbance regimes, and in particular, the role of infrequent but severe stand-destroying fires. In the Rocky Mountain Trench, geomorphic processes have created a particularly rich record of Holocene fires in the form of charcoal buried in colluvial and alluvial fans derived from dissected glaciolacustrine terraces in the lower Morkill River valley of the Robson Valley Forest District.
Radiocarbon dating of these charred wood and forest floor materials has yielded dates up to 8500 BP (before present), indicating that wildfires have been an important disturbance agent throughout the Holocene, with recurrence intervals of perhaps 500 - 1000 years.
Complex soil profiles in these colluvial and alluvial fan settings frequently included stacked multiple charcoal-bearing strata, which were usually laterally discontinuous, with overlapping age ranges. Observation of modern fire-triggered slope failures suggested mechanisms for formation of such deposits, and have provided criteria for distinguishing in situ from transported charred horizons.
In these glaciolacustrine landscapes, the lower-energy environment of colluvial toeslopes appears to be more suitable than alluvial fans for creating and preserving such records. Similar dissected glaciolacustrine landforms occur in several other major valleys in the western slopes of the Rocky Mountains, so this technique has potential for much wider application.
Land managers need to recognize that wildfire has been an important disturbance agent in this portion of the ICHwk3 throughout postglacial time. Therefore, silviculturists should not exclude prescribed fire as a management tool, and managers of protected areas should consider this historical perspective when developing policies for responding to wildfires.

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Updated August 26, 2005 

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