Grant: Discovery Grants Program - Individual

Trembling aspen (Populus tremuloides Michx.) is the most widely distributed tree species in north America that regenerates abundantly by root suckering after a natural or man-made stand-replacing disturbances. Although it can also regenerate sexually by seed, all aspen stands of fire-origin that we have excavated in the past were of sucker-origin, as confirmed by the presence of parental roots in the root system of all trees, i.e. roots older than the trees themselves, validated through dendrochronology techniques. We thus failed to observe concurrent vegetative and sexual regeneration in the same aspen stand that could explain the presence of many intermixed clones.  In the long term, this research program aims to better understand the role that root connections and grafts between trees play in the ecology of boreal forests. Because root connections and grafts allow the sharing of substances or the buffering of stressful events (e.g. insect defoliation), forests are more than an assembly of individual trees competing for resources. However, this idea has a hard time making its way into traditional forestry concepts and more work is required in the long term to reveal ecological implications of root connections between trees. In the short term, I aim to: 1) Demonstrate that "new" genotypes can vegetatively emerge after a stand-replacing disturbance through the formation of root grafts between roots of a dead tree and roots of a live tree. I hypothesize that since root grafts can maintain the roots of dead trees alive, "dead genotypes" can vegetatively be regenerated by the production of new suckers following a stand-replacing event. 2) Demonstrate that concurrent vegetative and sexual regeneration does not occur in a same stand after large forest fires at the origin of new stands. I hypothesize that seed regeneration is most efficient in colonizing new areas i.e. where aspen was not previously present and that regeneration through root suckering exclusively occurs in stands where aspen was the dominant species prior to the fire. 3) Explain the role that hormones shared between connected trees (auxins) play in the regeneration and establishment success of aspen. I hypothesize that root sucker regeneration and establishment of harvested trees is restricted by auxin transfers from adjacent live trees that are connected through their roots. 4) Verify the assumption that root grafting gives trees better stability against windthrow. I hypothesize that trees that are grafted to their neighbours are more likely to snap than to be overturned during windthrow events because their surface of anchorage is wider and more elaborated than "single" trees.