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Global environmental changes have strongly affected forest demographic rates, particularly amplified tree mortality in high latitude forests (e.g., two to five times greater mortality probability over the half‐century). Although forest functional composition is critical for multitrophic biodiversity and ecosystem functioning, it remains unclear how functional composition has changed over time across large high latitude regions, which have been warming twice the rate of the globe as a whole. Using extensive spatial and long‐term forest inventory data (17,107 plots monitored 1951–2016) across Canada, we found that after accounting for stand age‐dependent functional shifts, functional composition shifted toward fast‐growing deciduous broadleaved trees and higher drought tolerance over time. The temporal shift toward deciduous broadleaved trees was consistent across the baseline climate. However, over the study period, drought tolerance increased (or shade tolerance decreased) by 300% in colder boreal regions, while drought tolerance did not shift significantly in warmer temperate climates. A further analysis accounting for temporal changes in atmospheric CO2, temperature, and water availability indicated that the functional composition of colder regions shifted toward drought tolerance more rapidly with rising CO2 than warmer regions, suggesting the greater vulnerability of boreal forests than temperate forests under ongoing global environmental changes. Future ecosystem management practices should consider spatial differences in functional responses to global environmental change, focusing on high latitude forests experiencing higher rates of warming and compositional changes. [ABSTRACT FROM AUTHOR]

Aim: Forest net biomass change (ΔAGB; the difference between biomass gain from growth and loss through mortality) determines how forests contribute to the global carbon cycle. Understanding how plant diversity affects ΔAGB in diverse abiotic conditions is crucial in the face of anthropogenic environmental change. Recent studies have advanced our understanding of the effects of plant diversity on growth dependent on the abiotic context, either supporting or rejecting the stress gradient hypothesis. However, we know little about how diversity influences mortality, which prevents us from knowing how diversity affects ΔAGB in diverse abiotic conditions. Location: Across Canada (43–60° N, 52–133° W). Time period: 1951–2016. Major taxa studied: Ninety‐three tree species. Methods: We modelled the relationships of growth, mortality and ΔAGB with functional diversity that represented niche complementarity, while simultaneously accounting for the influence of functional identity and stand age. Results: Growth and mortality increased, on average, with functional diversity, but the magnitude of the increase in growth was greater than that of mortality, resulting in an increase of ΔAGB. The positive relationship between growth and functional diversity was more prominent in more humid sites than in drier sites. Mortality increased with functional diversity in drier sites but did not increase in wetter sites. The positive relationship between ΔAGB and functional diversity was strengthened with water availability. Moreover, the positive relationship between growth and functional diversity became stronger with temperature, but the positive associations of diversity with mortality and ΔAGB were consistent across the gradient of temperature. Main conclusions: Our results suggest that higher functional diversity leads to an increase in forest biomass accumulation owing to a greater positive effect of functional diversity on productivity than on mortality. However, in contrast to the stress gradient hypothesis, our findings show that the positive effect of functional diversity is more pronounced in an environment favourable for growth. [ABSTRACT FROM AUTHOR]

ABSTRACT Precipitation, temperature, and evaporative demand are the most dominant factors affecting water availability in a region. This study examines projected changes in these hydro-climatic variables over western Canada under two greenhouse gas emissions scenarios using statistically downscaled, high resolution climate data generated by six Global Climate Models ( GCMs) from the latest Coupled Model Intercomparison Project ( CMIP5). Potential changes in the spatial and seasonal distributions of water availability over nine major western Canadian river basins are examined by computing the 3- and 12-month standardized precipitation and evapotranspiration indices ( SPEI-3 and SPEI-12). While individual GCM projections vary on the rate and seasonality of changes, they all indicate similar spatial and temporal patterns. The highest projected increases in precipitation and temperature are primarily in the northern basins, with some decreases in summer precipitation in the southern basins. The evolution of the SPEI-12 values for the southern basins such as Columbia, Saskatchewan, Fraser and Athabasca indicate a gradual increase in the magnitude and duration of water deficit, while the reverse was found for most of the northern basins such as Peel/Lower Mackenzie, Liard, and Northern Pacific that show a gradual increase in water surplus on an annual basis. The SPEI-3, however, shows that almost all river basins in western Canada, with the exception of Peel/Lower Mackenzie that are located in the extreme north of the study region, are projected to experience decreasing water availability in summer. In general, the study highlights the potential changes in the spatial and seasonal distribution of western Canadian water resources and sets the stage for a more detailed and process based hydro-climate modelling study to be conducted in the region. [ABSTRACT FROM AUTHOR]

Biomass change of the world's forests is critical to the global carbon cycle. Despite storing nearly half of global forest carbon, the boreal biome of diverse forest types and ages is a poorly understood component of the carbon cycle. Using data from 871 permanent plots in the western boreal forest of Canada, we examined net annual aboveground biomass change (Δ AGB) of four major forest types between 1958 and 2011. We found that Δ AGB was higher for deciduous broadleaf ( DEC) (1.44 Mg ha−1 year−1, 95% Bayesian confidence interval ( CI), 1.22-1.68) and early-successional coniferous forests ( ESC) (1.42, CI, 1.30-1.56) than mixed forests ( MIX) (0.80, CI, 0.50-1.11) and late-successional coniferous ( LSC) forests (0.62, CI, 0.39-0.88). Δ AGB declined with forest age as well as calendar year. After accounting for the effects of forest age, Δ AGB declined by 0.035, 0.021, 0.032 and 0.069 Mg ha−1 year−1 per calendar year in DEC, ESC, MIX and LSC forests, respectively. The Δ AGB declines resulted from increased tree mortality and reduced growth in all forest types except DEC, in which a large biomass loss from mortality was accompanied with a small increase in growth. With every degree of annual temperature increase, Δ AGB decreased by 1.00, 0.20, 0.55 and 1.07 Mg ha−1 year−1 in DEC, ESC, MIX and LSC forests, respectively. With every cm decrease of annual climatic moisture availability, Δ AGB decreased 0.030, 0.045 and 0.17 Mg ha−1 year−1 in ESC, MIX and LSC forests, but changed little in DEC forests. Our results suggest that persistent warming and decreasing water availability have profound negative effects on forest biomass in the boreal forests of western Canada. Furthermore, our results indicate that forest responses to climate change are strongly dependent on forest composition with late-successional coniferous forests being most vulnerable to climate changes in terms of aboveground biomass. [ABSTRACT FROM AUTHOR]

Climate change impacts on temperatures, precipitations, streamflows, and recharges were studied across eastern, central, and western Prince Edward Island (PEI) between climate normals in 1991–2020, 2021–2050, and 2051–2080 using observed and projected data, and SWAT modeling. Average annual temperature can significantly rise from the existing 5.90–6.86 °C to 8.26–11.09 °C in different parts during the next 30–60 years under different RCP scenarios. Average annual precipitations would not significantly change except in western PEI where a 17% likely increase would offset further warming impact; therefore, current streamflows (~650 mm/year) and recharges (~320 mm/year) would not be much affected there. However, warming and increased pumping together in its Wilmot River watershed could reduce streamflows up to 9%, and 13% during 2021–2050, and 2051–2080, respectively. In the eastern forest-dominated Bear River watershed, no significant reductions in current streamflows (~692 mm/year) or recharges (~597 mm/year) are expected. Nevertheless, near constant precipitation and warming could cumulatively reduce streamflows/recharges up to 8% there, as pumping will be negligible. In the central zone, precipitation could insignificantly increase up to 5%, but current streamflows (~737 mm/year) and recharges (~446 mm/year) would not be significantly affected, except for RCP8.5 under which streamflows could reduce by ~16% during 2051–2080. Overall, more attenuated streamflows and recharges are likely with higher quantities in late winter and early spring, and somewhat lesser ones in summer, which could reduce water supplies during the growing season. Besides, precipitation uncertainty of ~300 mm/year between dry and wet years continues to be a major water management challenge. Adapting policies and regulations to the changing environment would ensure sustainable water management in PEI. [ABSTRACT FROM AUTHOR]

• Effects of tree diversity and identity on soil C stocks were highly context-dependent. • Soil C decreased with tree diversity in well-drained and moist temperate forests. • Soil C increased with tree diversity in ecotone between boreal and temperate forests. • Acquisitive tree communities had higher soil C stocks in warm or well-drained sites. Soil carbon (C) plays an important role in mediating global climate change and sustaining environmental condition. Although experimental studies primarily from grasslands revealed the positive effects of plant diversity on soil C storage, there is uncertainty about the directions and magnitudes of tree diversity and soil C relationships in natural forests. Using Canada's National Forest Inventory data from temperate to boreal forests, we examined the relationships between soil C stocks and tree functional diversity and identity, and how these relationships varied along environmental gradients (i.e., biomes, mean annual temperature, climate moisture index, and soil drainage). In contrast to the results from grassland experiments, we found a negative relationship between tree diversity and soil C stocks in temperate forests and a nonsignificant relationship in boreal forests. Moreover, soil C stocks increased with functional diversity in moist and poorly drained sites, but decreased in dry and well-drained sites within the temperate forest biome. Within the boreal biome, soil C stocks increased with functional diversity in warm climates, but decreased in cold climates. Our findings at the macro-ecological scale indicated that the positive effects of plant diversity might be the highest at the boreal-temperate forests' ecotone. In addition, within the temperate biome, tree communities with higher leaf nitrogen, phosphorus content and specific leaf area were associated with greater mineral horizon soil C stocks, especially in warm or well-drained sites. Our finding of the abiotic context-dependent relationships between soil C stocks and tree functional diversity and identity can guide forest management across different environmental conditions. [ABSTRACT FROM AUTHOR]