Article scientifique | Paludification reduces black spruce growth rate but does not alter tree water use efficiency in Canadian boreal forested peatlands | par Joannie Beaulne, Étienne Boucher, Michelle Garneau et Gabriel Magnan | Géographie et GÉOTOP UQAM | Revue Forest Ecosystems – Mai 2021

Nouvelle publication | Article scientifique

Paludification reduces black spruce growth rate but does not alter tree water use efficiency in Canadian boreal forested peatlands

AUTEUR.E.S
Joannie Beaulne | Étudiante à la maîtrise | Département de géographie, GEOTOP – UQAM
Étienne Boucher | Professeur | Département de géographie, GEOTOP – UQAM
Michelle Garneau | Professeure | Département de géographie, GEOTOP – UQAM
Gabriel Magnan | Chargé de cours | Département de géographie, GEOTOP – UQAM

Revue Forest Ecosystems | Volume 8; Article 28

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RÉSUMÉ (en anglais seulement)

Background
Black spruce (Picea mariana (Mill.) BSP)-forested peatlands are widespread ecosystems in boreal North America in which peat accumulation, known as the paludification process, has been shown to induce forest growth decline. The continuously evolving environmental conditions (e.g., water table rise, increasing peat thickness) in paludified forests may require tree growth mechanism adjustments over time. In this study, we investigate tree ecophysiological mechanisms along a paludification gradient in a boreal forested peatland of eastern Canada by combining peat-based and tree-ring analyses. Carbon and oxygen stable isotopes in tree rings are used to document changes in carbon assimilation rates, stomatal conductance, and water use efficiency. In addition, paleohydrological analyses are performed to evaluate the dynamical ecophysiological adjustments of black spruce trees to site-specific water table variations.

Results
Increasing peat accumulation considerably impacts forest growth, but no significant differences in tree water use efficiency (iWUE) are found between the study sites. Tree-ring isotopic analysis indicates no iWUE decrease over the last 100 years, but rather an important increase at each site up to the 1980s, before iWUE stabilized. Surprisingly, inferred basal area increments do not reflect such trends. Therefore, iWUE variations do not reflect tree ecophysiological adjustments required by changes in growing conditions. Local water table variations induce no changes in ecophysiological mechanisms, but a synchronous shift in iWUE is observed at all sites in the mid-1980s.

Conclusions
Our study shows that paludification induces black spruce growth decline without altering tree water use efficiency in boreal forested peatlands. These findings highlight that failing to account for paludification-related carbon use and allocation could result in the overestimation of aboveground biomass production in paludified sites. Further research on carbon allocation strategies is of utmost importance to understand the carbon sink capacity of these widespread ecosystems in the context of climate change, and to make appropriate forest management decisions in the boreal biome.

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Département de géographie
Local A-4030
1255, St-Denis
Montréal (Québec) H2X 3R9