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UBC Theses and Dissertations

Cassiope tetragona as a dendroecological proxy : a retrospective analysis of experimental warming in the Arctic Tundra Gallois, Elise


Annual stem growth and reproductive effort of the evergreen dwarf-shrub, Cassiope tetragona, exhibit a strong positive relationship to summer temperature and have been used in dendroclimatological analyses to reconstruct climate in the High Arctic through the application of transfer function equations. Retrospective analysis of the annual growth increments have also previously been used to examine the impact of short term warming in a few tundra sites. This thesis presents a full retrospective analysis approach to reconstruct the impact of long-term experimental warming in tundra communities at Alexandra Fiord (Ellesmere Island) from before the installation of open-top-chambers in 1992 to the present day, using a before-after-control-intervention design on growth and reproduction variables. We found a positive, significant effect of experimental warming on the stem growth of C. tetragona and revealed that phenology stages (such as bud break, flowering, and fruit production) take place significantly earlier in the warming plots in comparison to the control plots. Furthermore, the relationship between both July Average and August Maximum air temperature time series at Alexandra Fiord and the annual stem growth and reproductive chronologies from the control plots were used to construct summer air temperature models with good predictive abilities, explaining up to 68% of the variance. We compared chronologies of C. tetragona samples from multiple International Tundra Experiment sites to investigate the extent to which growth and reproductive responses to experimental warming vary across the Arctic. An effect size analysis and linear mixed effects model was used to determine the fact that experimental warming has a significant and positive effect on plant growth, increasing annual stem growth by an average of 0.665 mm across the Arctic, with 60% of the overall variance in the stem growth data being explained by Region. This regional signal was also revealed in a Principal Components Analysis which included descriptive stem characteristics statistics at 23 circumarctic sites. These findings complement existing research about the warming effect of treatment on tundra plant growth and phenology, and provide novel information on the value of C. tetragona as a dendroecological proxy and the regional differences in C. tetragona growth and reproduction patterns.

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