DENDROGEOMORPHIC EVIDENCE OF FREQUENT MASS WASTING FROM REACTION WOOD IN BLACK SPRUCE, NORTHWAY JCT., ALASKAN INTERIOR

Understanding mass-wasting events along remote transportation corridors such as the Alaska Highway is a crucial infrastructure need. To better understand a problematic road segment near Northway Junction, Alaska we focused on the most intensely deformed area (4.8 hectares) between mileposts 1265-1267, which is dominated by complex, slumping blocks of thawing, perennially frozen, sandy silt. We deliberately sampled 30 Picea mariana, which were tilted and thus visibly affected by mass-wasting processes. Each tree was radially cored (n=60) in the direction of the tilt and at 90° to the first core. Reaction wood and suppression and release events were characterized using microscopic analysis and recorded as modified skeleton plots of event-response phenomena, resulting in a replication-summary plot. Of the 30 trees sampled, 26 contain reaction wood, suppression was present in 24 trees and release was present in 15. Of the trees with reaction wood, the onset of reaction wood occurred in five, area-wide events, occurring in 1966 (5 trees), 1989 (8 trees), 1995 (6 trees), 2006 (7 trees), and 2011 (6 trees), with the 1966 and 1989 events followed by significant growth suppression. Eighty percent of tilting events occurred in areas where the active layer depth was ≤30cm. Between 1900-1988 the area was relatively stable with reaction wood accounting for only 5.2 percent of recorded radial growth. Onset of widespread instability occurs in 1989 with reaction wood accounting for 32.7 percent of recorded radial growth from 1989-2013. Highway realignments and patchwork along this section of the highway have occurred in the past 10 years. Patchwork completed in October 2011, for example, can be linked to the onset of reaction wood in 2011 due to mass wasting outside the growing season (late summer 2010-late spring 2011). Further research is needed to correlate climate data with the mass-wasting events, which may provide insight for effective maintenance decisions.