129-58 Southeast Alaska’s Western redcedar exhibit an enigmatic cold-season climate response

Abstract:

The Western redcedar (Thuja plicata) is under researched in dendroclimatology despite the species’ ecological and cultural importance in North America’s Pacific Northwest. No previous studies have explicitly examined the climate response of the Western redcedar of Southeast Alaska (SEAK). A new 750-year ring-width chronology based on 80 redcedar cores from Ketchikan was compared with monthly climate records of the region. The Ketchikan chronology was also combined with the previously collected records from Kake and Klawock to build a composite SEAK Western redcedar chronology (150 series) to obtain a regional tree response.

In all chronologies, particularly in the Ketchikan record, there is a clear upward trend in ring width since the 1870s, especially in the last 60 years, likely a response to recent rising temperatures in SEAK. The positive correlations with cold-season NE Gulf of Alaska (GOA) sea surface temperatures (r = 0.52, p < 0.0001) show that Alaska redcedar are sensitive to decadal modes of climate variability in addition to warming. A significant low growth marker in 1876 CE is notably the same start year as the most recent super El Niño that contributed to massive famine in parts of Asia, Brazil, and Africa. El Niño years bring warmer than usual conditions to Southeast Alaska, and the extreme El Niño in 1876 may have raised temperatures beyond T. plicata’s range of tolerance, inhibiting tree ring growth. With climate scientists predicting a 2026 super El Niño, there could be a similar impact on these trees in the coming years. In addition, the SEAK redcedar records exhibit a winter/spring signal, the first tree species growing along the GOA to show a strong winter response. While the climate driving mechanism is not known for certain, increasing temperatures in SEAK, especially in the past 200 years, could continue to be favorable for tree growth as winters slightly warm and T. plicata tolerates the warming. This enigmatic winter signal could be partially explained by further investigating the response to the 1876 event. Ongoing research is framed in the context of the upcoming possible super El Niño, particularly examining the regional redcedar latitude/altitude range to better construct historical environmental conditions and tree response. 

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