Sensitivity of tree growth to the atmospheric vertical profile in the Boreal Plains of Manitoba, Canada (original) (raw)
Related papers
Canadian Journal of Forest Research, 2004
Trends and periodicities in summer drought severity are investigated on a network of Canadian Drought Code (CDC) monthly average indices extending from central Quebec to western Manitoba and covering the instrumental period . The relationship and coherency between CDC indices and ocean-atmosphere circulation patterns are also examined. Trend analyses indicate that drought severity is unchanged in eastern and central Canada. Composite analyses indicate that for most of the corridor, severe drought seasons occur with a combination of positive 500-hPa geopotential height anomalies centered over the Gulf of Alaska and over the Baffin Bay. Additional severe drought seasons develop across the corridor in the presence of positive height anomalies located over or upstream of the affected regions. According to spectral analyses, the North Atlantic and the North Pacific circulation patterns modulate the drought variability at the decadal scale. Our results lead us to conclude that climate warming and the increases in the amount and frequency of precipitation in eastern Canada during the last century had no significant impact on summer drought severity. It is unlikely that linear climate change contributed to the change in the boreal forest dynamics observed over the past 150 years.
Atmosphere-Ocean
We identify Dry and Wet months for the Canadian Prairies during the 40-year period 1946-1985 and investigate their relationship to the Northern Hemisphere circulation at the 50-and 100-kPa levels. The target area is first subdivided into five zones on the basis of characteristic differences in precipitation climatology, and for each zone the dates of occurrence of dry and wet months are determined. These events are then stratified into five "seasons". Much of the analysis focuses on the two growing seasons: Spring, defined as April and May, and Early Summer, June and July. Composite anomaly fields for the Northern Hemisphere are constructed for the 50-kPa level by "season" and zone, and for the Dry and Wet groupings. For each zone, the two 50-kPa anomaly fields Dry and Wet are clearly distinguishable, not only over North America but in many instances, upstream and downstream of the continent. Composite anomalies are shown to be zone-sensitive. The 100-and 50-kPa anomalous wind fields associated with the Dry and Wet regimes, respectively, are found to be consistent with dynamic and thermodynamic processes that control the production of precipitation. Anomaly field structures over the oceans and North America are related to Northern Hemisphere tropospheric circulation modes, including the PNA, NPO and NAO. High-latitude blocking over the North Atlantic and North Pacific is often associated with Wet months, particularly in Spring, whereas "in situ" blocking over western Canada or simply amplified ridging extending northward from the western United States is almost invariably associated with the Dry months. RÉSUMÉ Après avoir identifié les mois humides et secs pour lapériode de 1946 à 1985, dans les Prairies canadiennes, on étudie la relation avec la circulation hémisphérique septentrio
2006
Five independent multicentury reconstructions of the July Canadian Drought Code and one reconstruction of the mean July-August temperature were developed using a network of 120 well-replicated tree-ring chronologies covering the area of the eastern Boreal Plains to the eastern Boreal Shield of Canada. The reconstructions were performed using 54 time-varying reconstruction submodels that explained up to 50% of the regional drought variance during the period of 1919-84. Spatial correlation fields on the six reconstructions revealed that the meridional component of the climate system from central to eastern Canada increased since the mid-nineteenth century. The most obvious change was observed in the decadal scale of variability. Using 500-hPa geopotential height and wind composites, this zonal to meridional transition was interpreted as a response to an amplification of long waves flowing over the eastern North Pacific into boreal Canada, from approximately 1851 to 1940. Composites with NOAA Extended Reconstructed SSTs indicated a coupling between the meridional component and tropical and North Pacific SST for a period covering at least the past 150 yr, supporting previous findings of a summertime global ocean-atmosphereland surface coupling. This change in the global atmospheric circulation could be a key element toward understanding the observed temporal changes in the Canadian boreal forest fire regimes over the past 150 yr.
Journal of Climate, 2006
Five independent multicentury reconstructions of the July Canadian Drought Code and one reconstruction of the mean July-August temperature were developed using a network of 120 well-replicated tree-ring chronologies covering the area of the eastern Boreal Plains to the eastern Boreal Shield of Canada. The reconstructions were performed using 54 time-varying reconstruction submodels that explained up to 50% of the regional drought variance during the period of 1919-84. Spatial correlation fields on the six reconstructions revealed that the meridional component of the climate system from central to eastern Canada increased since the mid-nineteenth century. The most obvious change was observed in the decadal scale of variability. Using 500-hPa geopotential height and wind composites, this zonal to meridional transition was interpreted as a response to an amplification of long waves flowing over the eastern North Pacific into boreal Canada, from approximately 1851 to 1940. Composites with NOAA Extended Reconstructed SSTs indicated a coupling between the meridional component and tropical and North Pacific SST for a period covering at least the past 150 yr, supporting previous findings of a summertime global ocean-atmosphereland surface coupling. This change in the global atmospheric circulation could be a key element toward understanding the observed temporal changes in the Canadian boreal forest fire regimes over the past 150 yr.
Radial growth response of white oak to climate in eastern North America
Canadian Journal of Forest Research-revue Canadienne De Recherche Forestiere, 2009
Predicting forest responses to climate change requires an understanding of the cause-effect relationships linking climate to tree growth. Dendroecological analyses across sites that span climate gradients provide one means of characterizing such relationships. Dendroecological analyses for white oak (Quercus alba L.) at 149 sites spanning the species range in eastern North America identified spatially replicated growth-climate associations. Early growing season site water balance variables for the year of annual ring formation had the strongest, most spatially replicated associations with growth. There was little evidence of phenological variation of these associations related to the latitudinal temperature gradient. Most spatial variation in growth-climate associations was along an east-to-west precipitation gradient. Radial growth was most strongly correlated with site water balance at sites in the northwest quadrant of the range, characterized by continental climate and high interannual variability in precipitation. There was little evidence that dormant season temperature affects white oak growth, even at the northern range limit. Correlations with dormant season precipitation were common in the northwest part of the range, where winter soil water recharge may be more variable. Spatial replication was a useful criterion for distinguishing growth-climate correlations that reflect cause-effect relationships.
Reduced sensitivity of recent tree-growth to temperature at high northern latitudes
Nature, 1998
Consistent with low modelled reactive chlorine concentrations, several workers report model underpredictions of ozone depletion of between 25 and 40% (refs 16, 17), although these discrepancies may be due partly to incorrectly modelled gas-phase reactions rather than heterogeneous processing. Edouard et al. 22 have suggested that such underprediction by three-dimensional models may be caused by averaging small-scale structure in species concentration over large grid boxes. This arises because of the nonlinear dependence of key reaction rates on concentration. This offers a possible explanation for underpredicted ozone loss in three-dimensional models, but does not explain low modelled ClO and does not refer to predictions of trajectory models 13 . Whether uncertainties in the temperature fields used in models are responsible for model underpredictions 13,15 , or whether the mountain-wave activation mechanism suggested here is inappropriate can only be assessed by undertaking a multi-year model simulation and comparison with available data. However, it should be noted that mountain waves can act as a continuous source of inhomogeneities in reactive chlorine concentrations on a scale of a few kilometres, which, according to the findings of Edouard et al. 22 , will make their inclusion in three-dimensional models highly problematic.
Canadian Water Resources Journal, 2006
Forest fires in Canada are directly influenced by the state of the climate system. The strong connection between climate and fire, along with the dynamic nature of the climate system, causes the extent, severity and frequency of fires to change over time. For instance, many reconstructions of the history of forest fires across boreal Canada report a general decrease in fire activity since ~1850 which could, in part, result from changes in climate. This paper describes progress in characterizing the variability in fire-conducive droughts in the central and eastern Canadian boreal forests during the past three centuries. An extensive network of drought-sensitive tree-ring records from Manitoba, Ontario and Quebec was used to develop five multi-century reconstructions of the mean July Canadian Drought Code and one reconstruction of mean July and August temperatures. Correlation analyses with regional fire statistics (common period 1959−1998) showed that drought estimates are accurate enough to approximate fire activity and, hence, the estimates are relevant for the study of climate change impacts on Canadian forests. Spatial correlation analysis over the period 1768−1998 revealed that variability between the west and east has increased since the mid−19th century, specifically the decade-to-decade variability and the frequency of extreme events. Based on the synoptic characteristics of recent droughts, we interpret this change in variability as a response to an increasing frequency of upper level ridging and troughing over western and eastern Canada, respectively. The increasing horizontal movement of humid air masses over eastern Canada since ~1850 could have contributed to the creation of moister conditions that are less suitable for fire.