Dendroclimatology from Regional to Continental Scales: Understanding Regional Processes to Reconstruct Large-Scale Climatic Variations Across theWestern Americas - Dendroclimatology - page 185

America, there is a gradual environmental gradient from the relatively dry-warm
subtropics to the wet-cold high latitudes. Tree-ring records from subtropical regions,
such as the southwestern United States and central Chile, are remarkably sensitive
to precipitation variations (Boninsegna 1988 ; Cook et al. 2004 ; LeQuesne et al.
2006 ) . In the transitional zones to higher latitudes, tree-ring responses to climate
are largely determined by site conditions. Depending on elevation, aspect, slope,
and soil characteristics, tree growth can be influenced by temperature, precipita-
tion, or more commonly by a combination of both. In the extreme wet and cold
environments at high-elevation or high-latitude upper tree lines, temperature is the
major limiting factor controlling tree growth (Wiles et al. 1996 ; Luckman et al.
1997 ; Wiles et al. 1998 ; Aravena et al. 2002 ; Villalba et al. 2003 ; Laraetal.
2005 ) . These changes in tree response with latitude were instrumental in setting the
strategies for selecting tree-ring records sensitive to temperature and precipitation
variations along the western Americas. Temperature reconstructions based on upper-
elevation chronologies on mountains near the coasts around the Gulf of Alaska and
northern Patagonia were selected as proxy records of temperature for North and
South America, respectively. Tree-ring records from mesic to dry environments in
the southern-central United States, the Bolivian Altiplano, and central Chile were
used for the interhemispheric comparison of precipitation-sensitive records across
the American Cordilleras (Fig. 7.1 ) . The available data and maturity of dendrocli-
matological research differ considerably between regions, and therefore the kind
of comparison between regional records and forcings will be different across the
north-south transect.
7.3.1 Temperature-Sensitive Records
The strong cross-equatorial symmetries of SST, continental temperature, and con-
tinental precipitation patterns documented from instrumental records motivated
the search in high-resolution proxy records for common spatial patterns of cli-
mate variability across the western Americas during the past centuries. Have the
patterns of climate variability documented during the instrumental period been
recurrent in previous centuries? Were these patterns different during the domi-
nantly cooler conditions during the first half of the nineteenth century? Answers
to these questions can provide useful information on the stationary nature of cli-
mate variations and how they could change under different global atmospheric
conditions.