5. Past Changes in Climate and Tree Growth in the Western Americas 79
1993a; Jacoby & Cook, 1981; Jacoby et aI., 1985; Jacoby & D 'Arrigo,
1989). The density chronologies for these same sites show primarily highfrequency variations associated with changes in warm-season temperature
(D'Arrigo et aI., 1992; Jacoby et aI., 1988). The extremely low density
value in 1783 (Figure 5.2), also present in other density records for
Alaska, may be linked to climatic changes following the eruption of Laki
in Iceland in that year.
Pacific Northwest
Tree-ring width and density chronologies from the Pacific Northwest
(northwest Washington state and near Vancouver Island, British Columbia)
were also utilized for dendroclimatic study (Buckley, D'Arrigo, & Jacoby,
1991). Four sets of chronologies were produced (raw measurements
obtained from Schweingruber) for these sites for either Douglas fir
(Pseudotsuga menziesii), Pacific silver fir (Abies amabilis), or mountain
hemlock (Tsuga mertensiana). These data were used to test possible
correlations between tree growth and variables such as North Pacific seasurface temperatures (SST), the EI Nino-Southern Oscillation (ENSO),
and sea-level pressure (SLP).
The search for such linkages is reasonable since climatic conditions in
the Pacific coastal/near-coastal land areas appear to be strongly influenced
by ENSO, the Aleutian low-pressure cell , and Pacific North America
(PNA) patterns of atmosphere-ocean circulation (e.g. , Cayan, 1980;
Emery & Hamilton, 1985; Namias, Xiaojun, & Cayan, 1988; Niebauer,
1988; Trenberth, 1990). McBean (this volume) describes some of the
processes through which Pacific atmosphere-ocean circulation affects the
climate of western North America. Changes in aspects of Pacific circulation
can also influence coastal temperate rainforests and watersheds by modifying the composition and concentration of nutrient inputs from marine
aerosol sources (Hedin & Hetherington, this volume) .
There have been a few studies relating tree-ring widths from western
North America locales to SLP and SST (e .g. , Blasing & Fritts, 1975;
Douglas, 1980) and ENSO (Lough & Fritts, 1985; Michaelson, Haston, &
Davis, 1987). Yet there have been relatively few such efforts utilizing
maximum-latewood density data. When compared to a grid of monthly
SST for the northeast Pacific Ocean, the strongest correlations were
found between maximum-latewood density and ring widths and summer
(July-August-September) SST (Buckley et aI., 1991). Buckley et al.
(1991) concluded that with further modeling, there is potential for
eventual reconstruction of North Pacific SST based on tree-ring width and
density data from this region. Significant correlations were also found
between these tree-ring data and winter and spring SLP variations in the
general vicinity of the Aleutian low-pressure cell in the northeast Pacific
(D'Arrigo, Jacoby, & Wiles, 1993).
1993a; Jacoby & Cook, 1981; Jacoby et aI., 1985; Jacoby & D 'Arrigo,
1989). The density chronologies for these same sites show primarily highfrequency variations associated with changes in warm-season temperature
(D'Arrigo et aI., 1992; Jacoby et aI., 1988). The extremely low density
value in 1783 (Figure 5.2), also present in other density records for
Alaska, may be linked to climatic changes following the eruption of Laki
in Iceland in that year.
Pacific Northwest
Tree-ring width and density chronologies from the Pacific Northwest
(northwest Washington state and near Vancouver Island, British Columbia)
were also utilized for dendroclimatic study (Buckley, D'Arrigo, & Jacoby,
1991). Four sets of chronologies were produced (raw measurements
obtained from Schweingruber) for these sites for either Douglas fir
(Pseudotsuga menziesii), Pacific silver fir (Abies amabilis), or mountain
hemlock (Tsuga mertensiana). These data were used to test possible
correlations between tree growth and variables such as North Pacific seasurface temperatures (SST), the EI Nino-Southern Oscillation (ENSO),
and sea-level pressure (SLP).
The search for such linkages is reasonable since climatic conditions in
the Pacific coastal/near-coastal land areas appear to be strongly influenced
by ENSO, the Aleutian low-pressure cell , and Pacific North America
(PNA) patterns of atmosphere-ocean circulation (e.g. , Cayan, 1980;
Emery & Hamilton, 1985; Namias, Xiaojun, & Cayan, 1988; Niebauer,
1988; Trenberth, 1990). McBean (this volume) describes some of the
processes through which Pacific atmosphere-ocean circulation affects the
climate of western North America. Changes in aspects of Pacific circulation
can also influence coastal temperate rainforests and watersheds by modifying the composition and concentration of nutrient inputs from marine
aerosol sources (Hedin & Hetherington, this volume) .
There have been a few studies relating tree-ring widths from western
North America locales to SLP and SST (e .g. , Blasing & Fritts, 1975;
Douglas, 1980) and ENSO (Lough & Fritts, 1985; Michaelson, Haston, &
Davis, 1987). Yet there have been relatively few such efforts utilizing
maximum-latewood density data. When compared to a grid of monthly
SST for the northeast Pacific Ocean, the strongest correlations were
found between maximum-latewood density and ring widths and summer
(July-August-September) SST (Buckley et aI., 1991). Buckley et al.
(1991) concluded that with further modeling, there is potential for
eventual reconstruction of North Pacific SST based on tree-ring width and
density data from this region. Significant correlations were also found
between these tree-ring data and winter and spring SLP variations in the
general vicinity of the Aleutian low-pressure cell in the northeast Pacific
(D'Arrigo, Jacoby, & Wiles, 1993).