Tree-Rings Reveal Accelerated Yellow-Cedar Decline with Changes to Winter Climate after 1980

Abstract

Research Highlights: Yellow-cedar decline on the island archipelago of Haida Gwaii is driven by warm winter temperatures and low winter precipitation, which is caused by anthropogenic climate change and exacerbated by the positive phase of the Pacific Decadal Oscillation (PDO). Background and Objectives: Declining yellow-cedars are limited by physiological drought during the growing season, caused by freezing damage to fine roots through a complex pathway identified by research in Alaska. Given this, we hypothesized: (1) yellow-cedars on Haida Gwaii were limited by the winter climate. (2) Trees of different health classes were responding differently to climatic variation. (3) Changing climate-growth relations would vary among phases of the PDO. Materials and Methods: We sampled 15 stands exhibiting crown symptoms and developed three regional chronologies from trees that were healthy, had crown or tree-ring symptoms of decline, and trees that had died. We tested for growth responses to inter-annual and multi-decadal variation in climate among trees of different health statuses using correlation functions and wavelet analyses. Results: The three chronologies had similar patterns from the early 1500s to 1900s and responded to climate in the same way, with multi-decadal variability, and common narrow marker years. Climate-growth responses among trees of different health statuses diverged after the 1976/1977 switch in the PDO. Warm growing season temperatures facilitated the growth of trees in the healthy chronology. By contrast, growth of trees that showed symptoms of decline or had died was negatively associated with low winter precipitation. After 1986, growth of trees in the declining chronology decreased sharply and mortality increased, which is concurrent with the warmest winter temperatures and consistent with the root-freezing hypothesis from Alaska. Conclusions: Yellow-cedar decline is driven by climate change, exacerbated by the PDO. Warming winter temperatures, accelerated by anthropogenic climate change, have led to dieback and death of yellow-cedars, even with the temperate ocean-moderated climate of Haida Gwaii.

Climate Response of Metasequoia glyptostroboides Inferred from Tree Rings, Secrest Arboretum, Wooster, Ohio, USA

“…These aforementioned studies show that warm winters can be detrimental to tree growth due to warmer temperatures leading to a loss of snowpack and subsequent root injury due to freezing. Furthermore, for the sites in the Pacific Northwest, climatic analyses using tree-rings are consistent with these findings (Wiles et al 2012;Comeau et al 2019;Wiles et al 2019). Similar to the findings in Alaska, where mean winter temperatures at Alaska cedar sites are at a critical transition between 2 and −2 °C, the Wooster, Ohio, site falls within this zone as mapped by Buma et al (2017).…”

Climate‐induced yellow‐cedar decline on the island archipelago of Haida Gwaii

“…This period also corresponds to a switch in the Pacific Decadal Oscillation (PDO) to warmer and wetter conditions with lower snowpacks, which occurred in 1976/1977 (Mantua and Hare 2002). There is evidence on Haida Gwaii of shifts in the climate growth response of yellow-cedar around switches in the PDO, including a negative response to warmer winter temperature and low winter precipitation during the warm period following 1977, consistent with the thaw-freeze hypothesis (Comeau et al 2019). In addition, evidence that increased mortality and onset of decline follow years with warmer winter conditions suggests that a warming climate has driven yellow-cedar decline on Haida Gwaii.…”

“…Pulses of tree mortality in the 1970s and 1980s (Hennon and Shaw 1994) correspond to the 1977 shift in the PDO from negative to positive phase (Mantua and Hare 2002). Similarly, on Haida Gwaii there was a divergence in growth response to climate after the 1977 shift; where healthy yellow‐cedars experienced increasing growth in response to warmer growing season temperatures, while trees experiencing decline or that had died did not (Comeau et al 2019). In addition, all yellow‐cedars became negatively associated with January temperature and positively associated with winter precipitation, consistent with the thaw–freeze hypothesis (Comeau et al 2019).…”

“…Similarly, on Haida Gwaii there was a divergence in growth response to climate after the 1977 shift; where healthy yellow‐cedars experienced increasing growth in response to warmer growing season temperatures, while trees experiencing decline or that had died did not (Comeau et al 2019). In addition, all yellow‐cedars became negatively associated with January temperature and positively associated with winter precipitation, consistent with the thaw–freeze hypothesis (Comeau et al 2019). During the positive phase, regional climate is warmer, and the snow–rain threshold is elevated so that lower‐elevation forests have shallower and less persistent snowpacks making yellow‐cedars more vulnerable to thaw–freeze events.…”

Contrasting root and shoot cold tolerance of a conifer with indeterminate growth

“…Abiotic environmental factors, mainly soil and air temperatures, were found to best correlate with yellow-cedar decline. This led to the currently accepted hypothesis that yellow-cedar decline is occurring due to a changing climate (Wooton and Klinkenberg 2011, Hennon et al 2012, Buma et al 2017, Comeau et al 2019. Anthropogenic climate change is now widely acknowledged as a contributor to global forest decline.…”