Dendroclimatology from Regional to Continental Scales: Understanding Regional Processes to Reconstruct Large-Scale Climatic Variations Across theWestern Americas - Dendroclimatology - page 186

Box 7.2 Studies from the Canadian Cordillera

During the last 5 years, significant progress has been made in dendrochrono-
logical and dendroclimatic studies in the Canadian Cordillera (49 ◦ − 65 ◦ N),

building on limited earlier collections. Sampling has targeted temperature-
sensitive sites at altitudinal tree line ( Picea engelmanni , P. glauca , Larix
lyallii , Pinus albicaulis , and Abies lasiocarpa ) and moisture-sensitive sites
at the lower forest border ( Pseudotsuga menziesii and Pinus ponderosa ),
mainly using a network approach to isolate regional rather than local signals.
Although initially focused on the southern Cordillera (ca. 125 chronologies),
over 100 new sites have been sampled in the Yukon over the last 5 years.
Studies at tree line in the Coast Ranges of British Columbia and Vancouver
Island have developed several single- and multiple-species chronology net-
works ( Tsuga mertensiana , T. heterophylla , and Chamaecyparis nootkatensis )
that include sites with the potential for millennial-length reconstructions
(see http://geog.uvic.ca/dept/uvtrl/uvtrl.htm ). In the southern Cordillera, the
network of low-elevation, moisture-sensitive sites has been used to recon-
struct spatial patterns of precipitation and drought over the last three to four
centuries (Watson and Luckman 2004a , 2005 ) , and these data have been incor-
porated into the new gridded Palmer Drought Severity Index (PDSI) network
developed by Cook et al. ( 2004 ) .
New ring width and density data have been used to revise and extend a
millennial-length (950-1994) summer temperature record from the Canadian
Rockies (Box Fig. 7.3 ) . Comparison with adjacent areas (e.g., Wiles et al.
2004 ) and global Northern Hemisphere curves suggests this is a regionally
representative record. The influence of Pacific-forced decadal-scale variabil-
ity in this record is more subtle, but the low-frequency signal suggests solar
forcing has been an important control of summer temperature patterns in this
region.
The use of multispecies networks allows the combination of temperature-
and/or precipitation-sensitive chronologies to investigate climate-related phe-
nomena that are influenced by the combined variation of temperature and
precipitation. Box Figure 7.4 shows a reconstruction of glacier mass balance
using independent tree-ring-derived summer and winter balances. Although
winter balance (precipitation input) is strongly controlled by atmospheric
circulation patterns from the Pacific, summer balance (mass loss through
melt) is driven primarily by solar radiation. The major periods of positive
net balance reflect a combination of higher winter inputs and cooler sum-
mers rather than summer temperatures alone. Future work can adopt similar
approaches to the reconstruction of streamflow and other climate-related
variables.

—B.H. Luckman, R.J.S. Wilson, and E. Watson