In the next century, the boreal ecosystems are projected to experience greater rates of warming than most other regions of the world. As the boreal forest constitutes a reservoir of trees of huge ecological importance and only partially known economic potential, any possible climate-related change in plant growth and dynamics has to be promptly predicted and evaluated. A model for assessing xylem phenology in black spruce [Picea mariana (Mill.) B.S.P.] using daily temperatures and thermal thresholds was defined and applied to predict changes in onset, ending and duration of xylem growth under different warming scenarios with temperatures rising by up to 3 1C. This was achieved by collecting and analyzing a dataset obtained from a 7-year monitoring of cambium phenology and wood formation on a weekly time-scale in trees growing in four sites at different latitudes and altitudes in the Saguenay-Lac-Saint-Jean region (Quebec, Canada). The onset of xylem growth occurred between mid-May and early June while the end ranged between mid-September and early October, resulting in a growing season of 101-141 days. The model predicted longer duration of xylem growth at higher temperatures, with an increase of 8-11 days/ 1C, because of an earlier onset and later ending of growth. With an increase of 3 1C in the mean temperature during the year, the duration of xylem growth changed on average from 125 to 160 days. The predicted changes in cambial phenology could significantly affect future wood production of the boreal ecosystems.
In the boreal forest of Quebec, 80% of harvested black spruce (Picea mariana [Mill.] BSP) stands regenerate naturally. In the remaining 20%, forest regeneration is ensured by planting seedlings and these plantations are expected to increase future forest yields. However, predictions of future yields using the information from very young plantations in this ecosystem may have low accuracy. To compare juvenile growth in plantations versus naturally regenerated stands, and also to evaluate the impacts of spruce budworm Choristoneura fumiferana (Clemens) defoliation periods during the juvenile phase, annual height and volume growth were calculated from measurements on nine black spruce stands. The nine sites consisted of two plantations and seven post-fire, naturally regenerated stands. Of the seven naturally regenerated sites, four were epidemic and 3 endemic. The term "epidemic" refers to stands regenerated during known spruce budworm defoliation periods. The term "endemic" refers to stands regenerated during periods without severe defoliation. For height and volume growth, 5 different methods were used and compared. The annual height and volume growth of all black spruce showed a sigmoid trend, characterized by low values in the first years after germination, followed by an exponential acceleration and finally oscillation around a horizontal asymptote. The black spruce stands established during endemic periods were more productive than those established during epidemic periods, but plantations were the most productive.Key words: black spruce, juvenile growth, plantation, post-fire stands, spruce budworm outbreak, volume, yield
RÉSUMÉDans la forêt boréale du Québec, 80% des peuplements récoltés d' épinette noire (Picea mariana [Mill.] BSP) se régénèrent naturellement. La régénération du 20% restant est assurée par des plantations qui devraient augmenter le rendement futur des forêts. Le jeune âge (< 20 ans) des plantations dans cet écosystème limite cependant la portée des prédictions futures. Afin d' évaluer la croissance juvénile et l'impact possible de la tordeuse des bourgeons de l' épinette (Choristoneura fumiferana (Clemens)) (TBE) durant la phase juvénile de croissance, les accroissements en hauteur et en volume ont été calculés dans neuf peuplements d' épinette noire. Cinq méthodes différentes de calcul ont été comparées. Les neuf sites consistaient en deux plantations et sept peuplements régénérés naturellement après feu. De ces 7 peuplements régénérés naturellement, quatre étaient épidémiques et trois endémiques. Le terme « épidémique » fait référence aux peuplements régénérés durant des périodes connues de défoliation par la TBE. Le terme « endémique » fait référence aux peuplements régénérés durant des périodes sans défoliation par la TBE. La croissance annuelle en hauteur et en volume de toutes les épinettes présente une tendance sigmoïde, caractérisée par des valeurs faibles dans les premières années après la germination, suivie ensuite par une accélération exponentielle et enfin une phase de...
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