Tree-ring investigations into changing climatic responses of yellow-cedar, Glacier Bay, Alaska

Abstract

Yellow-cedar (Callitropsis nootkatensis (D. Don) Örsted ex D.P. Little) is in a century-long decline coinciding with the end of the Little Ice Age (LIA). The leading hypothesis explaining this decline is a decrease in insulating snowpack due to warming and increased susceptibility to damaging frosts in the root zone. A ring-width series from yellow-cedar on Excursion Ridge (260 m a.s.l.) in Glacier Bay National Park and Preserve, Alaska, and another from trees on Pleasant Island (150 m a.s.l.) in the Tongass National Forest in Icy Strait were compared with regional monthly temperature and precipitation data from Sitka, Alaska, to investigate the changing growth response to temperature at these sites. Comparisons with monthly temperatures from 1832 to 1876 during the end of the Little Ice Age show that the high-elevation Excursion Ridge and the low-elevation Pleasant Island sites strongly favored warmer January through July temperatures. Both tree populations have markedly changed their response from a positive to a strong negative correlation with January through July temperatures since 1950. This strong negative response to warming by the yellow-cedar together with a positive relationship with total March and April precipitation suggests that these yellow-cedar sites may be susceptible to decline. Furthermore, these analyses are consistent with the hypothesis that the yellow-cedar decline is linked to decreased snowpack.Résumé : Le faux-cyprès de Nootka (Callitropsis nootkatensis (D. Don) Örsted ex D.P. Little) connaît une période de dé-périssement qui dure depuis un siècle et dont le début coïncide avec la fin du Petit Âge glaciaire. La principale hypothèse pour expliquer ce dépérissement est la réduction du couvert nival et de ses propriétés isolantes à cause du réchauffement climatique ainsi que l'augmentation de la sensibilité aux dommages causés par le gel dans la zone des racines. Une série dendrochronologique du faux-cyprès de Nootka provenant d'Excursion Ridge (260 mètres au-dessus du niveau de la mer), dans le parc national de Glacier Bay, en Alaska, et une autre provenant d'arbres sur Pleasant Island (150 mètres au-dessus du niveau de la mer) dans la forêt nationale de Tongass à Icy Strait ont été comparées aux données régionales de précipitation et de température mensuelles provenant de Sitka en Alaska pour étudier la variation de la réaction de la croissance à la tempé-rature dans ces stations. Les comparaisons avec les températures mensuelles de 1832 à 1876, à la fin du Petit Âge glaciaire, montrent que la station d'Excursion Ridge à une altitude élevée et la station de Pleasant Island à plus basse altitude étaient très favorables aux températures plus chaudes de janvier à juillet. Les deux populations d'arbre ont nettement changé leur réaction passant d'une corrélation positive à fortement négative avec les températures de janvier à juillet depuis 1950. Cette forte réaction négative du faux-cyprès de Nootka combinée à une relation positive avec la précipitation totale des mois de mars et avril indi...

A Warming-Induced Biome Shift Detected in Tree Growth of Mountain Hemlock [Tsuga mertensiana(Bong.) Carrière] Along the Gulf of Alaska

“…By the second half of the 20th century both sites had become strongly negatively correlated to temperature. This strong negative response to warming by the yellow cedar together with a positive relationship with total March and April precipitation suggested that the yellowcedar sites may be susceptible to decline and is consistent with the hypothesis that the yellow-cedar decline is linked to decreased snowpack (Wiles et al, 2012).…”

A Warming-Induced Biome Shift Detected in Tree Growth of Mountain Hemlock [Tsuga mertensiana(Bong.) Carrière] Along the Gulf of Alaska

“…While no mountain hemlock sites have become negatively correlated to temperature as the yellow cedars have, the patterns in growth response to climate observed over the 20th century at the low-elevation mountain hemlock sites resemble those observed by Wiles et al (2012) from the LIA to the first half of the 20th century in the higher elevation cedar site in Glacier Bay. This suggests that the change in growth response of both species is related and elevationally determined, the effects traveling upslope with time and warming.…”

“…low temperature) and are now tracking the rising air temperature (Fritts, 1976;Holtmeier and Broll, 2007). Wiles et al (2012) found a shift in the relationship between yellow-cedar growth and January-July temperature since the LIA. A slight negative correlation to temperature was present at the lowelevation site at the end of the LIA, while the higher-elevation site was significantly positively correlated to temperature.…”

“…Little], which has been attributed to warming (Hennon et al, 2005;Beier et al, 2008). Using long-term temperature and precipitation data from the Sitka Magnetic Observatory in Sitka, Alaska, Wiles et al (2012) demonstrated that this decline can be detected as a decreased STEPHANIE K. JARVIS ET AL. / 211 1523-0430/6 $7.00 correlation between ring widths and temperature, beginning with the period of warming marking the end of the Little Ice Age (LIA).…”

Yellow-cedar blue intensity tree-ring chronologies as records of climate in Juneau, Alaska, USA

“…Extensive work has been done testing this hypothesis and exploring the forest dynamics and ecology associated with the decline (Oakes et al, 2014(Oakes et al, , 2015 driven by concerns of species loss and determination of whether the species is endangered (Buma et al, 2017;Barrett andPattison, 2017, Bidlack et al, 2017). Dendroclimatic studies of RW in southeast Alaska have shown that the growth response of yellow-cedar can be spatially and temporally complex (Beier et al, 2008;Wiles et al, 2012) and, in general, results have not been promising for climate reconstruction. Beier et al (2008) analyzed RW from declining cedar sites in southeast Alaska and from the healthy stand at Cedar Lake, one of our study sites.…”