Forest Ecology Research Group

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

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.


Amazing species at Scotty Creek, NWT

Typically the Taiga Plains Ecoregion is not known for its species diversity. But there are a lot of examples of beautiful and unique species that occur there, particularly in Scotty Creek, NWT. Mélissa Fafard, a MSc candidate in the Forest Ecology Research Group photographed and identified numerous plant species during her field season in the North.

Melissa’s pictures and notes have been added to Phyto Images, a website dedicated to cataloguing plant species in locations around the world. This resource is often used in plant identification and contains thousands of images. We are very pleased to contribute to this wonderful resource and highlight some of the biodiversity in Scotty Creek.

To view all the species catalogues at Scotty Creek go to: type “Scotty Creek” into the “Locality” field.

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Research Note : Galling herbivory in Scotty Creek

Galling herbivory in Scotty Creek

Numerous arthropod herbivores are found in the forest-wetland complex at Scotty Creek. One prominent guild of specialist arthropods found here are the group of gall-inducing arthropods (insects and mites).

Diversity of galling herbivory: An preliminary survey of galling herbivory revealed that a large majority of deciduous shrub species found here are galled by eriophyoid mites (Family: Eriophyoideae). These mites induce galls on species of willow (Salix), birch (Betula) and alder (Alnus). An initial assessment of gall-inducing insects indicates that insect gallers found on the various Salix species in this area are primarily sawflies (Hymenoptera: Tenthrenididae).

Impacts of galling herbivory in plant hosts: We examined leaf-level impacts of a gall-inducing mite (Vasates olfiedi) on birch (Betula) hosts in bogs, fens, and permafrost plateaus. This mite induces galls on leaves of Betula glandulosa (dwarf birch) growing in all three of the above habitats. Additionally, this mite also galls leaves of B. occidentalis (bog birch) and B. neoalaskana (Alaska white birch) on plateaus. We found that galling by this mite significantly reduced photosynthetic capacity in leaves of all three species found on upland permafrost plateaus. However, strong habitat-linked responses were seen in B. glandulosa leaves – while individuals of this species showed drastic declines in photosynthesis on plateaus, individual plants in bogs and fens showed no such responses. Based on these findings, is appears that the impacts of mite galling are variable, and are likely to be most pronounced in habitats and on individuals that are already exposed to abiotic stresses such as the cooler but more variable soil temperatures experienced by individuals on permafrost plateaus.

Leaves galled by Vasates olfieldi on A. Betula neoalaskana, B. B. occidentalis, and C. B. glandulosa from permafrost peat plateau sites at Scotty Creek, Northwest Territories.

Leaves galled by Vasates olfieldi on A. Betula neoalaskana, B. B. occidentalis, and C. B. glandulosa from permafrost peat plateau sites at Scotty Creek, Northwest Territories.