Abstract
Tree growth has been reported to increase in response to recent global climate change in controlled and semi-controlled experiments, but few studies have reported response of tree growth to increased temperature and atmospheric carbon dioxide (CO2) concentration in natural environments. This study addresses how recent global climate change has affected height growth of trembling aspen (Populus tremuloides Michx) and black spruce (Picea mariana Mill B.S.) in their natural environments. We sampled 145 stands dominated by aspen and 82 dominated by spruce over the entire range of their distributions in British Columbia, Canada. These stands were established naturally after fire between the 19th and 20th centuries. Height growth was quantified as total heights of sampled dominant and co-dominant trees at breast-height age of 50 years. We assessed the relationships between 50-year height growth and environmental factors at both spatial and temporal scales. We also tested whether the tree growth associated with global climate change differed with spatial environment (latitude, longitude and elevation). As expected, height growth of both species was positively related to temperature variables at the regional scale and with soil moisture and nutrient availability at the local scale. While height growth of trembling aspen was not significantly related to any of the temporal variables we examined, that of black spruce increased significantly with stand establishment date, the anomaly of the average maximum summer temperature between May-August, and atmospheric CO2 concentration, but not with the Palmer Drought Severity Index. Furthermore, the increase of spruce height growth associated with recent climate change was higher in the western than in eastern part of British Columbia. This study demonstrates that the response of height growth to recent climate change, i.e., increasing temperature and atmospheric CO2 concentration, did not only differ with tree species, but also their growing spatial environment.
Highlights
Since the beginning of the Industrial Revolution in 1750, atmospheric carbon dioxide (CO2) concentration has increased steadily from 278 to 385 ppm
Tree growth has been shown to increase with recent atmospheric CO2 increase [8,9,10], while others found that increased tree growth is linked to global warming [11,12,13] or a combined effect of several factors such as atmospheric CO2 fertilization, global warming, and anthropogenic atmospheric nitrogen (N) deposition because of the inherent co-variation among these variables in natural environments [14]
Spruce site index increased with growing degree-days .5uC (GDD), MST (Figs. 2a and c), but it did not change with MAT, MAP or MSP (Figs. 2d and 2e)
Summary
Since the beginning of the Industrial Revolution in 1750, atmospheric carbon dioxide (CO2) concentration has increased steadily from 278 to 385 ppm. LaMarche et al [3] were the first authors to report increase of tree growth in relation to atmospheric CO2 fertilization. Various greenhouse and open top chamber experiments have shown higher growth of tree seedlings or short-lived trees with increased CO2 [4,5]. These experiments have provided significant insights into the potential effects of global change, but the growing conditions and durations in controlled environments have led to concerns about their possible implications in the real world [6,7]. Tree growth has been shown to increase with recent atmospheric CO2 increase [8,9,10], while others found that increased tree growth is linked to global warming [11,12,13] or a combined effect of several factors such as atmospheric CO2 fertilization, global warming, and anthropogenic atmospheric nitrogen (N) deposition because of the inherent co-variation among these variables in natural environments [14]
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