Université de Sherbrooke
Postdoctoral fellow candidate
Supervisor: Mark Vellend
Start: 2013-07-01
End: 2015-06-01
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Project

Drivers controlling the regeneration of sugar maple (Acer saccharum Marsh.) along an altitudinal gradient
The main goal of this project is to determine the biotic and abiotic factors controlling the altitudinal distribution of sugar maple (Acer saccharum Marsh.). The studied altitudinal gradient located in Parc naturel du Mont Mégantic (Québec) is composed of the deciduous forest-boreal forest ecotone and thus the abundance of sugar maple adult trees decreases with altitude. Notably, we observed a higher regeneration of sugar maple at its upper altitudinal limit (and so at the edge of its distribution) than at the core of its current distribution toward lower altitudes. This increase of abundance of seedlings toward higher altitudes is expected in response to climate change. Indeed, new habitats become favorable for their establishment because of the increase of temperature. However, the detected low regeneration at lower altitudes at the core of current sugar maple distribution where adult trees are the most abundant is surprising. The specific objectives of this project are (i) to evidence and precisely describe this trend (that we called “Happy edge”) and (ii) to understand the factors leading to a higher regeneration at the edge than at the core of the current sugar maple distribution. The two main hypotheses explaining this ‘Happy edge” are (i) differences of the herbivory pressure by insects on sugar maple seedlings along the altitudinal gradient – it would be higher at the core of the maple distribution because the adult trees are more abundant than at the edge (Janzen-Connell hypothesis) and would cause an higher mortality of seedlings- and (ii) differences of edaphic conditions (concentrations in nutrients, soil water content, etc.) along the gradient with a soil more favorable for the seedlings survival at the edge of the sugar maple distribution. These hypotheses are currently tested thanks to a transplantation experiment within Parc national du Mont Mégantic. This project is crucial to assess the tree abilities to track the shifts of their bioclimatic envelope in response to climate change.

Keywords

Sugar Maple, altitudinal distribution, biogeography, climate change, recruitment, range edge, regeneration, biotic interactions, abiotic factors

Publications

1- Xylem embolism threshold for catastrophic hydraulic failure in angiosperm trees
Urli, M., A. J. Porte, H. Cochard, Y. Guengant, R. Burlett, S. Delzon
2013 Tree Physiology