Search

Highlights: [•] A soil moisture model was developed that requires only basic climate inputs. [•] The model was tested using 9 years of measurements at a boreal aspen tower site. [•] The model was applied in tree-ring studies of Canadian boreal aspen forests. [•] Results show that aspen growth responds to soil moisture rather than precipitation. [•] “Soil moisture memory” explains multi-year impacts of drought on aspen growth. [ABSTRACT FROM AUTHOR]

We examined a network of 17 lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) sites in Alberta in the cordilleran forests along the eastern slopes of the Rocky Mountains and in western Cypress Hills, using a dendrochronological approach to identify the principal climatic factors that have influenced the historical, regional-scale pattern of radial growth of lodgepole pine. Correlation and regression analysis of the regional growth–climate relationships showed that radial growth was negatively associated with late-summer temperatures, and positively related to the late-summer precipitation totals from the previous growth season. Radial growth also responded positively to winter and spring temperatures, and was negatively related to late winter–early spring precipitation. The results suggested that the lag in response to heat and moisture stress, cold and snowy winters, and the length of the current growing season are important determinants of the radial growth of lodgepole pine in Alberta. [ABSTRACT FROM AUTHOR]

Presents a study to evaluate the correlation between past insect defoliation events and the formation of pale tree rings on the trembling aspen in western Canada. Consideration of the hypothesis that defoliation causes the formation of white rings; Status of insect outbreaks; Measurements of ring widths; Characteristics of the forest tent caterpillar.

Presents three-ring analyses and forest health assessments in healthy and stressed aspen forests in Canada. Basis for reconstructing defoliation histories; Factors contributing the observed dieback of aspen forests; Threat of global change to the future health and productivity of aspen forests.

Examines the effect of forest phenology on seasonal climate patterns in the Western Canadian interior. Use of a sinusoidal model for the study; Measurement of the mean temperature in the area; Detection of low average precipitation.

Quantitative assessment of Canada's boreal forest mitigation potential is not yet possible, though the range of mitigation activities is known, requirements for sound analyses of options are increasingly understood, and there is emerging recognition that biogeophysical effects need greater attention. Use of a systems perspective highlights trade-offs between activities aimed at increasing carbon storage in the ecosystem, increasing carbon storage in harvested wood products (HWPs), or increasing the substitution benefits of using wood in place of fossil fuels or more emissions-intensive products. A systems perspective also suggests that erroneous conclusions about mitigation potential could result if analyses assume that HWP carbon is emitted at harvest, or bioenergy is carbon neutral. The greatest short-run boreal mitigation benefit generally would be achieved by avoiding greenhouse gas emissions; but over the longer run, there could be significant potential in activities that increase carbon removals. Mitigation activities could maximize landscape carbon uptake or maximize landscape carbon density, but not both simultaneously. The difference between the two is the rate at which HWPs are produced to meet society's demands, and mitigation activities could seek to delay or reduce HWP emissions and increase substitution benefits. Use of forest biomass for bioenergy could also contribute though the point in time at which this produces a net mitigation benefit relative to a fossil fuel alternative will be situation-specific. Key knowledge gaps exist in understanding boreal mitigation strategies that are robust to climate change and how mitigation could be integrated with adaptation to climate change. [ABSTRACT FROM AUTHOR]

The seasonal phenology of the leaf area index (LAI) is a major determinant of net ecosystem production in deciduous forest ecosystems. This study describes seasonal and inter-annual differences in LAI in a boreal aspen-hazelnut forest in central Saskatchewan, Canada, between 1994 and 2003, and relates the differences in LAI to annual net ecosystem production (FNEP). A robust method is developed to fill gaps in the annual LAI cycle from systematic but sparse measurements using associated radiation and temperature indices. The ratio of the photosynthetically-active radiation reflectance to the shortwave reflectance is shown to have a particularly distinct LAI signature.Optical estimates of the fully-leafed LAI agreed well with measurements from autumn litterfall and showed moderate inter-annual variability for the trembling aspen overstory (mean ± S.D. of 2.44 ± 0.30) and the hazelnut understory (1.98 ± 0.44). Two features of the annual LAI cycle differed among years—the timing of leaf emergence in spring, which varied by up to four weeks, and the fully-leafed value for LAI, which varied between 3.66 and 5.22. The timing of leaf senescence in autumn was nearly constant among years. The seasonal cycles of FNEP and LAI were tightly coupled and the correspondence between their respective inter-annual differences was remarkable, particularly during leaf emergence in spring. Annual FNEP was positively correlated with the canopy duration and the annual maximum LAI, with increases in annual FNEP of 6.9gCm-2 for each additional day in full leaf and 83gCm-2 for each additional unit of LAI. [Copyright &y& Elsevier]

Canadian boreal woodlands and forests cover approximately 3.09 × 106 km2, located within a larger boreal zone characterized by cool summers and long cold winters. Warming since the 1850s, increases in annual mean temperature of at least 2 °C between 2000 and 2050 are highly probable. Annual mean temperatures across the Canadian boreal zone could be 4-5 °C warmer than today's by 2100. All aspects of boreal forest ecosystem function are likely to be affected. Further, several potential 'tipping elements' - where exposure to increasing changes in climate may trigger distinct shifts in ecosystem state - can be identified across the Canadian boreal zone. Approximately 40% of the forested area is underlain by permafrost, some of which is already degrading irreversibly, triggering a process of forest decline and re-establishment lasting several decades, while also releasing significant quantities of greenhouse gases that will amplify the future global warming trend. Warmer temperatures coupled with significant changes in the distribution and timing of annual precipitation are likely to cause serious tree-killing droughts in the west; east of the Great Lakes, however, where precipitation is generally nonlimiting, warming coupled with increasing atmospheric carbon dioxide may stimulate higher forest productivity. Large wildfires, which can cause serious economic losses, are expected to become more frequent, but increases in mean annual area burned will be relatively gradual. The most immediate threats could come from endemic forest insect pests that have the potential for population outbreaks in response to relatively small temperature increases. Quantifying the multiple effects of climate change will be challenging, particularly because there are great uncertainties attached to possible interactions among them, as well as with other land-use pressures. Considerable ingenuity will be needed from forest managers and scientists to address the formidable challenges posed by climate change to boreal ecosystems and develop effective strategies to adapt sustainable forest management practices to the impending changes. [ABSTRACT FROM AUTHOR]