Traumatic Resin Ducts in Alaska Mountain Hemlock Trees Provide a New Proxy for Winter Storminess

• Published in: Journal of geophysical research. Biogeosciences 2019-07, Vol.124 (7), p.1923-1938
• Main Authors: Gaglioti, Benjamin V., Mann, Daniel H., Williams, A. Park, Wiles, Gregory C., Stoffel, Markus, Oelkers, Rose, Jones, Benjamin M., Andreu‐Hayles, Laia
• Format: Article
• Language: English
• Subjects: Aleutian Low; Annual rings; Architecture; Climate change; Cold season; dendrochronology; Divergence; Ducts; Ecosystems; Forests; Growth rings; Mountains; North Pacific; Plant structures; Precipitation; Resins; Snowpack; Snowstorms; Storm damage; Storms; traumatic resin ducts; Treeline; Trees; Tsuga mertensiana; Wind damage; Winter; winter storminess; Wood
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1029/2018JG004849

Winter is a critical season for land‐surface feedbacks and ecosystem processes; however, most high‐latitude paleo‐environmental reconstructions are blind to cold season conditions. Here we introduce a winter‐sensitive, paleo‐proxy record that is based on the relative frequency of tangential rows of traumatic resin ducts (TRDs) in the annual growth rings of mountain hemlocks (Tsuga mertensiana) growing near treeline in Southeast Alaska. Hemlocks produce a row of TRDs in the earlywood portion of their annual rings in response to cambial damage incurred during winter. Multidecadal bouts of TRD production were followed by growth‐leader replacement, reaction wood formation, and divergence in radial growth between storm‐damaged trees and less exposed mountain hemlock forests. These patterns are consistent with TRDs being a response to tree damage caused by ice and snowstorms, a conclusion supported by the krummholz tree architecture at these sites. This relationship is further corroborated by significant correlations between our TRD record and the strength of the wintertime Aleutian Low (AL) pressure system that is linked to tree‐damaging agents like wind, precipitation, and ice storm strength in Southeast Alaska. The combined TRD/krummholz architecture record indicates that abrupt shifts between strong and weak AL phases occurred every several decades since CE 1700 and that the 1800s had relatively long AL phases with heavy snowpacks. In addition to describing the magnitude and tempo of wintertime climate change in Northwestern North America, these results suggest that North Pacific Decadal Variability underlies the long‐term dynamics of treeline ecosystems along the northeast Pacific coast. Key Points Traumatic resin ducts in the cross‐dated tree rings of subalpine mountain hemlocks record tree damage during winter storms in Southeast Alaska Warmer, windier winters that accompany strong Aleutian Low pressure systems result in more tree damage Decadal‐scale variability in North Pacific climate has impacted treeline ecosystems throughout this region