Forest Ecology Research Group

Research Note : Tree-ring analysis of Picea mariana – Growth response to permafrost dynamics and climate change

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The study of tree-rings, or “dendrochronology”, provides an archive of information about past conditions that a tree has experienced. Tree-rings are produced annually in regions with distinct growing and dormant seasons, and the distance between two subsequent rings reflects how rich or poor growth conditions were in that particular year.  At Scotty Creek NWT, where treed permafrost plateaus have been rapidly degrading into open wetlands, tree-rings are being utilized to answer questions about how the boreal forest has changed in light of the warming temperatures and melting permafrost.

Many models have predicted increased growth of temperature-limited boreal species as the climate warms, though tree-ring studies have uncovered a decoupling of temperature and growth over the last several decades. By examining relationships between annual radial growth of P. mariana (the dominant tree species at Scotty Creek), archival weather data, and the distance of each tree sampled to a degrading permafrost edge,we aim to understand how this important boreal species is affected by warming temperatures, degrading permafrost, and the relative effects of these two influences.

What story might the tree-rings tell? Preliminary analysis has shown that trees near the edge of a permafrost plateau are growing much slower than those on interior parts of the plateau, indicating that the permafrost degradation is decreasing productivity in these edge trees.  A likely mechanism for this result is that as the permafrost melts and the high and dry plateaus become wetlands, P. mariana trees experience severe waterlogging. In regards to the changing climate, the increasing temperatures and longer growing seasons could lead to increased forest productivity as many models have predicted. Alternatively, the warmer temperatures may inhibit growth due to temperature stress and increased transpiration – analysis of this component is not yet underway, but will be soon. Stay tuned to find out the whole story told by the trees of Scotty Creek!

Core Sample

This core was taken from a P. mariana at Scotty Creek. The diameter at breast height (DBH) of this tree is 8.1 cm, yet the tree is over 170 years old – an average of only 0.2 mm of outward growth per year.

 

Rxn wood

Many of the cores from Scotty Creek exhibit reaction wood, such as this one, exhibit reaction wood. Reaction wood is characterized by dark wide growth rings that occur when a tree is perturbed from its upright position, such as changes in the permafrost layer. We are exploring whether reaction wood can be used to help reconstruct fine-scale permafrost changes that have occurred.

 

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