Abstract
Old-growth forests in the Pacific Northwest are being fundamentally altered by climate change. A primary example of this is yellow-cedar (Callitropsis nootkatensis), a culturally and economically important species, which has suffered widespread decline across its range since the beginning of the twentieth century. We used tree rings to compare the climate-growth response of yellow-cedar to two co-occurring species; western hemlock (Tsuga heterophylla) and Sitka spruce (Picea sitchensis), in an old-growth forest on Haida Gwaii, Canada, to better understand the unique climatic drivers of a species that is declining across its range. We developed three species-specific chronologies spanning 560–770 years, reconstructing a long-term record of species growth and dynamics over time. The climate is strongly influenced by the Pacific Decadal Oscillation (PDO), a multi-decadal pattern of ocean-atmospheric climate variability. Climate varied across three time periods that have coincided with major shifts in the PDO during the twentieth century [1901–1945 (neutral/positive), 1946–1976 (negative) and 1977–2015 (positive)]. Conditions were significantly warmer and wetter during positive phases, with the greatest maximum temperatures in the most recent period. We used complimentary methods of comparison, including Morlet wavelet analysis, Pearson correlations, and linear-mixed effects modeling to investigate the relations between climate and species growth. All three species exhibited multi-decadal frequency variation, strongest for yellow-cedar, suggesting the influence of the PDO. Consistent with this, the strength and direction of climate-growth correlations varied among PDO phases. Growing season temperature in the year of ring formation was strongly positively correlated to yellow-cedar and western hemlock growth, most significantly in the latter two time periods, representing a release from a temperature limitation. Sitka spruce growth was only weakly associated with climate. Yellow-cedar responded negatively to winter temperature from 1977 to 2015, consistent with the decline mechanism. Increased yellow-cedar mortality has been linked to warmer winters and snow loss. This study provides new insights into yellow-cedar decline, finding the first evidence of decline-related growth patterns in an apparently healthy, productive coastal temperate rainforest.
Highlights
Forest ecosystems are becoming increasingly impacted by warming associated with climate change (Adams et al, 2009; van Mantgem et al, 2009; Allen et al, 2010)
The British Columbia (BC) Government Vegetation Resources Inventory (VRI), a landscape wide data layer derived from aerial photo interpretation and ground sampling, indicates there was no evidence that stand-level wind, fire, insects, pathogens, or yellow-cedar decline were driving tree mortality at our study site (BC Government, 2020)
This pattern was strongest for yellow-cedar, less consistent for western hemlock and noticeably absent for Sitka spruce during the twentieth century, suggesting the Pacific Decadal Oscillation (PDO) had a lesser effect on growth variation
Summary
Forest ecosystems are becoming increasingly impacted by warming associated with climate change (Adams et al, 2009; van Mantgem et al, 2009; Allen et al, 2010). At high elevation and high latitude, increased growing season temperature and length as the regional climate warms (Cayan et al, 2001; Christidis et al, 2007) will likely facilitate increased tree growth (Nemani et al, 2003). Research on divergence in tree-ring widths has revealed that for many species warm temperatures eventually become limiting, due to direct temperature stress or moisture stress (D’Arrigo et al, 2004; Wilmking et al, 2004; Driscoll et al, 2005; Lloyd and Bunn, 2007). Predicting the response of forests to climate is highly species-specific, as tree species have unique environmental adaptions and competitive strategies (Lévesque et al, 2013; Meyer et al, 2020), and within a species there can be divergence in climate-growth responses through time (D’Arrigo et al, 2008)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
