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1. Introduction There is considerable evidence that arctic and boreal ecosystems in Alaska are responding to recent climate changes ( Goetz et al. 2005 ; Hinzman et al. 2005 ; Jorgensen et al. 2001 ; Keyser et al. 2000 ; Serreze et al. 2000 ) in ways that could feed back to the global climate system ( Bonan et al. 1995 ; Chapin et al. 2000 ; McGuire and Chapin 2006 ). An expected increase in naturally occurring wildfires in the boreal forest ( Stocks et al. 2000 ; Westerling et al. 2006
1. Introduction There is considerable evidence that arctic and boreal ecosystems in Alaska are responding to recent climate changes ( Goetz et al. 2005 ; Hinzman et al. 2005 ; Jorgensen et al. 2001 ; Keyser et al. 2000 ; Serreze et al. 2000 ) in ways that could feed back to the global climate system ( Bonan et al. 1995 ; Chapin et al. 2000 ; McGuire and Chapin 2006 ). An expected increase in naturally occurring wildfires in the boreal forest ( Stocks et al. 2000 ; Westerling et al. 2006
1. Introduction The most interesting features of summer climate in the Arctic/sub-Arctic regions are frontal zones and rainbelts south of the Arctic coastal line in northern Eurasia and North America. The frontal activity and rainfall of these two northern landmasses, which are closely related to each other, peak in the summer season ( Serreze et al. 2001 ). As observed by Krebs and Barry (1970) , the summer frontal activity and rainfall geographically lie along boreal forests (indicated by
1. Introduction The most interesting features of summer climate in the Arctic/sub-Arctic regions are frontal zones and rainbelts south of the Arctic coastal line in northern Eurasia and North America. The frontal activity and rainfall of these two northern landmasses, which are closely related to each other, peak in the summer season ( Serreze et al. 2001 ). As observed by Krebs and Barry (1970) , the summer frontal activity and rainfall geographically lie along boreal forests (indicated by
ecosystem-scale isoprene fluxes are needed to provide data for testing and improving inventory modeling systems. Existing forest canopy isoprene flux data come largely from short-term studies, representing conditions during the middle of the growing season ( Baldocchi et al. 1999 ). Studies on seasonal isoprene emissions at the ecosystem level are rare. Therefore, in 1994 we conducted a field research project to determine isoprene fluxes from a deciduous forest in the southern boreal region of Canada
ecosystem-scale isoprene fluxes are needed to provide data for testing and improving inventory modeling systems. Existing forest canopy isoprene flux data come largely from short-term studies, representing conditions during the middle of the growing season ( Baldocchi et al. 1999 ). Studies on seasonal isoprene emissions at the ecosystem level are rare. Therefore, in 1994 we conducted a field research project to determine isoprene fluxes from a deciduous forest in the southern boreal region of Canada
-latitude boreal forests have a very low surface albedo in summer, around 0.08–0.09, and rather low values in winter, typically <0.2 ( Betts and Ball 1997 ), since the canopy shades the snow from the low elevation angle solar insolation. This paper focuses on the second factor: the controls on forest evaporation that can be inferred from a long observational record. Only recently have long-term eddy covariance flux measurements become feasible ( Wofsy et al. 1993 ), which permits the seasonal study of the
-latitude boreal forests have a very low surface albedo in summer, around 0.08–0.09, and rather low values in winter, typically <0.2 ( Betts and Ball 1997 ), since the canopy shades the snow from the low elevation angle solar insolation. This paper focuses on the second factor: the controls on forest evaporation that can be inferred from a long observational record. Only recently have long-term eddy covariance flux measurements become feasible ( Wofsy et al. 1993 ), which permits the seasonal study of the
estimated in W1 . Although these preceding analyses principally focus on midlatitude grasslands, the methodologies developed in them may have broader applications in other regions. For boreal forests, for instance, many studies have shown that vegetation there is largely regulated by variations in surface temperature (e.g., Myneni et al. 1997 ; Zhou et al. 2001 ; Zhou et al. 2003 ). However, the intrinsic variability of these forests at intraseasonal time scales is less well studied. Also, the link
estimated in W1 . Although these preceding analyses principally focus on midlatitude grasslands, the methodologies developed in them may have broader applications in other regions. For boreal forests, for instance, many studies have shown that vegetation there is largely regulated by variations in surface temperature (e.g., Myneni et al. 1997 ; Zhou et al. 2001 ; Zhou et al. 2003 ). However, the intrinsic variability of these forests at intraseasonal time scales is less well studied. Also, the link
1. Introduction Numerous modeling studies have indicated that vegetation can substantially impact the atmosphere, both locally and remotely. Fully coupled climate models have shown that vegetation’s influence on the atmosphere is established through biophysical feedbacks involving surface albedo (energy), evapotranspiration (moisture), and surface roughness (momentum). Within the boreal forests, the vegetation albedo feedback appears to be critical, particularly when the forest canopy masks the
1. Introduction Numerous modeling studies have indicated that vegetation can substantially impact the atmosphere, both locally and remotely. Fully coupled climate models have shown that vegetation’s influence on the atmosphere is established through biophysical feedbacks involving surface albedo (energy), evapotranspiration (moisture), and surface roughness (momentum). Within the boreal forests, the vegetation albedo feedback appears to be critical, particularly when the forest canopy masks the
release of carbon, methane, and other greenhouse gases, which have a long-term effect on the climate. This study focused on the land surface exchange processes in the boreal zone in northern high latitudes. This is a region where climate change due to increased atmospheric CO 2 will be most pronounced according to general circulation model (GCM) predictions ( Houghton et al. 1996 ). The boreal zone is dominated by evergreen forests, with open areas of lakes, bogs, and arable fields spread out in a
release of carbon, methane, and other greenhouse gases, which have a long-term effect on the climate. This study focused on the land surface exchange processes in the boreal zone in northern high latitudes. This is a region where climate change due to increased atmospheric CO 2 will be most pronounced according to general circulation model (GCM) predictions ( Houghton et al. 1996 ). The boreal zone is dominated by evergreen forests, with open areas of lakes, bogs, and arable fields spread out in a
timescales ( Viterbo and Beljaars 1995 ; Henderson-Sellers 1996 ; Chen et al. 1997 ; Verseghy 2000 ). Verseghy (2000) also emphasized the importance of addressing the ability to reproduce fluxes from homogeneous surfaces prior to tests for heterogeneous surfaces at regional and global scales. The evaluation of land surface schemes for different ecosystems has still been rather limited, because of the lack of suitable datasets. The boreal forests at high latitudes have a great influence on the annual
timescales ( Viterbo and Beljaars 1995 ; Henderson-Sellers 1996 ; Chen et al. 1997 ; Verseghy 2000 ). Verseghy (2000) also emphasized the importance of addressing the ability to reproduce fluxes from homogeneous surfaces prior to tests for heterogeneous surfaces at regional and global scales. The evaluation of land surface schemes for different ecosystems has still been rather limited, because of the lack of suitable datasets. The boreal forests at high latitudes have a great influence on the annual
regions ( Davin and de Noblet-Ducoudré 2010 ; Lee et al. 2011 ). In boreal regions, the albedo-induced cooling (warming) caused by permanent forest cover reduction (increase) has generally been found to be greater than the associated warming (cooling) from reduced (increased) terrestrial carbon storage ( Betts 2000 ; Claussen et al. 2001 ; Bala et al. 2007 ; Bathiany et al. 2010 ; Bernier et al. 2011 ) or to at least have the same magnitude ( Arora and Montenegro 2011 ; Pongratz et al. 2011
regions ( Davin and de Noblet-Ducoudré 2010 ; Lee et al. 2011 ). In boreal regions, the albedo-induced cooling (warming) caused by permanent forest cover reduction (increase) has generally been found to be greater than the associated warming (cooling) from reduced (increased) terrestrial carbon storage ( Betts 2000 ; Claussen et al. 2001 ; Bala et al. 2007 ; Bathiany et al. 2010 ; Bernier et al. 2011 ) or to at least have the same magnitude ( Arora and Montenegro 2011 ; Pongratz et al. 2011
using two new and contrasting sets of test data. One dataset comes from a homogeneous, boreal aspen stand and the other comes from a temperate, mixed-species, oak–maple forest. Measurements The homogeneous forest stand consists of trembling aspen ( Populus tremuloides Michx.), an effective isoprene emitter ( Fuentes et al. 1996 ). The forest is situated in the southern range of the boreal forest of Canada (53°63′N, 106°20′W), near Prince Albert, Saskatchewan; these measurements were made under the
using two new and contrasting sets of test data. One dataset comes from a homogeneous, boreal aspen stand and the other comes from a temperate, mixed-species, oak–maple forest. Measurements The homogeneous forest stand consists of trembling aspen ( Populus tremuloides Michx.), an effective isoprene emitter ( Fuentes et al. 1996 ). The forest is situated in the southern range of the boreal forest of Canada (53°63′N, 106°20′W), near Prince Albert, Saskatchewan; these measurements were made under the
