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

Abstract

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.

Early Holocene bark-stripping damages as an indicator of large herbivores: Evidence from a submerged Mesolithic landscape in the Haväng area, southern Baltic basin

“…This indicates that the position of the trees has changed in such a way that the trees have been forced to change their growth pattern so as not to fall. Reaction wood is common in trees that grow on slopes and areas with ground movement (Gardiner et al, 2014), and can also be noted in trees affected by storms or in areas with a prevailing wind direction which causes the trees to tilt (Gaglioti et al, 2019). The submerged landscape in the Haväng area consists of loose, well-sorted sand and was relatively flat (Hansson et al, 2018a).…”

Holocene Hydroclimatic Reorganizations in Northwest Canada Inferred From Lacustrine Carbonate Oxygen Isotopes

“…In contrast, the prominent rises in Squanga‐δ 18 O values that occurred in the last millennium, which appear to reflect a shift to drier conditions for lowland interior regions, are well documented by other regional studies. The cooler temperatures during this period, combined with warm North Pacific moisture source and multiple lines of evidence for renewed AL strength, appear to have contributed to alpine glacier growth, increased coastal storminess and enhanced leeward rain‐shadow aridity in the interior Yukon (Anderson et al., 2011; Barron & Anderson, 2011; Gaglioti et al., 2019; Osterberg et al., 2017). The AL clearly has an important role in controlling moisture availability around the broader North Pacific region and additional high‐resolution records like Squanga will further clarify the spatio‐temporal evolution of the atmospheric system.…”

Is the modern-day dieback of yellow-cedar unprecedented?

“…Based on what we currently know about the dynamics of the AL / PDO over the last 500 years from paleoclimate records, it is likely that the warm winters thought to be driving YC decline in recent times were preceded by similar periods during the long and climatically variable LIA period (Anderson et al 2005;Osterberg et al 2017;Bailey et al 2018;Gaglioti et al 2019b). The LIA was not an 650-year-interval of uniformly cold winter climate in Southeast Alaska as suggested by the MDE hypothesis; instead it encompassed multiple warmer and colder episodes.…”

“…However, pulses of recruitment also occurred in mountain hemlock (Wiles et al 2014;Gaglioti et al 2019b), Sitka spruce (Barclay et al 2001), and shore pine (Sullivan et al 2015) during the LIA in Southeast Alaska. Because widespread tree recruitment occurred D r a f t in all major tree species during the LIA, the observation that mature, living YC germinated during a 650-year period prior to 1900 should not be used as evidence for a 'healthier' YC population existing at that time.…”