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The evolutionary dynamics of tree species are influenced by their specific climatic environments, and their ability to persist is determined by adaptive strategies such as broad climate tolerance, phenotypic plasticity or genetic differentiation. Biogeographical predictions indicate that populations located at the edges of their ranges are more likely to experience heightened vulnerability to climatic fluctuations due to approaching tolerance limits. However, if local phenotypic acclimation or genetic adaptation has taken place, trees near the edge of their range could demonstrate comparable sensitivity to freeze and drought as the rest of the sampled population. Nevertheless, there remains uncertainty regarding the extent of developmental and evolutionary adjustments in climate sensitivity across the entire ranges of many tree species.Here, we document the biogeography of tree growth sensitivity to freeze and soil water and vapour pressure deficits during 1950–2018 using an extensive multi‐species tree‐ring dataset of 35,784 trees at 4535 sites covering boreal, temperate conifer and temperate deciduous forests of Canada. We quantify the relationships between tree radial growth increment and seasonal climate variables and explore factors driving the observed patterns of annual growth and climate sensitivity such as species, regional climate and local site conditions, and tree age and size.Freeze and drought had widespread impacts on tree growth that were contingent on the presence of focal species in interaction with tree size. An indirect growth thermal limitation towards cold/wet edges, occurring through the site moisture conditions, was observed in seven widespread species (e.g. Picea glauca, Picea mariana and Larix laricina). Moreover, six species had negative drought impacts more strongly expressed towards their warm/dry edges (e.g. Abies balsamea, Betula papyrifera and Pseudotsuga menziesii). However, widespread Picea, Pinus and Populus species showed no indication of increased sensitivity to soil water conditions at these edges.Synthesis. Our findings support the idea of evolutionary or acclimatization adjustments in the development of populations in response to long‐term climate conditions experienced in their respective locations. This underscores the importance of incorporating phenotypic and genomic data into future analyses of climate change impacts, which would enhance our ability to predict potential ecological shifts. [ABSTRACT FROM AUTHOR]

Linkages between the terrestrial ecosystem and precipitation play a critical role in regulating regional weather and climate. These linkages can manifest themselves as positive or negative feedback loops, which may either favor or inhibit the triggering and intensity of thunderstorms. Although the Canadian Prairies terrestrial system has been identified as having the potential to exert a detectable influence on convective precipitation during the warm season, little work has been done in this area using in situ observations. The authors present findings from a novel study designed to explore linkages between the normalized difference vegetation index (NDVI) and lightning duration (DUR) from the Canadian Lightning Detection Network for 38 census agricultural regions (CARs) on the Canadian Prairies. Statistics Canada divides the prairie agricultural zone into CARs (polygons of varying size and shape) for the purpose of calculating agricultural statistics. Here, DUR is used as a proxy for thunderstorm activity. Statistical analyses were undertaken for 38 CARs for summers [June--August (JJA)] between 1999 and 2008. Specifically, coefficients of determination were calculated between pairs of standardized anomalies of DUR and NDVI by season and by month. Correlations were also calculated for CARs grouped by size and/or magnitude of the NDVI anomalies. The main findings are as follows: 1) JJA lightning activity is overwhelmingly below average within larger dry areas (i.e., areas with below-average NDVI); that is, the linkages between NDVI and DUR increased significantly as both the area and magnitude of the dry anomaly increased. 2) In contrast, CARs with above-average NDVI did not consistently experience above-average lightning activity, regardless of the CAR size. 3) The lower threshold for the length scale of the dry anomalies required to affect the boundary layer sufficiently to reduce lightning activity was found to be approximately 150 km (~18 000 km2). 4) The authors'' analysis suggests that the surface-convection feedback appears to be a real phenomenon, in which drought tends to perpetuate drought with respect to convective storms and associated rainfall, within the limits found in 1) and 3). [ABSTRACT FROM AUTHOR]

In 2001–03, continuous eddy covariance measurements of carbon dioxide (CO2) flux were made above mature boreal aspen, black spruce, and jack pine forests in Saskatchewan, Canada, prior to and during a 3−year drought. During the 1st drought year, ecosystem respiration ( R) was reduced at the aspen site due to the drying of surface soil layers. Gross ecosystem photosynthesis (GEP) increased as a result of a warm spring and a slow decrease of deep soil moisture. These conditions resulted in the highest annual net ecosystem productivity (NEP) in the 9 years of flux measurements at this site. During 2002 and 2003, a reduction of 6% and 34% in NEP, respectively, compared to 2000 was observed as the result of reductions in both R and GEP, indicating a conservative response to the drought. Although the drought affected most of western Canada, there was considerable spatial variability in summer rainfall over the 100−km extent of the study area; summer rainfalls in 2001 and 2002 at the two conifer sites minimized the impact of the drought. In 2003, however, precipitation was similarly low at all three sites. Due to low topographic position and consequent poor drainage at the black spruce site and the coarse soil with low water-holding capacity at the jack pine site almost no reduction in R, GEP, and NEP was observed at these two sites. This study shows that the impact of drought on carbon sequestration by boreal forest ecosystems strongly depends on rainfall distribution, soil characteristics, topography, and the presence of vegetation that is well adapted to these conditions. [ABSTRACT FROM AUTHOR]