78
R.D . D'Arrigo and G.c. Jacoby
take place. The expected positive response to warming (i.e., northward
and elevational tree-line movement and/or increased rates of tree growth)
may be complicated by the more adverse effects on growth of increased
insect infestation and disease, changes in stand dynamics, and moisture
stress that may accompany warmer conditions.
Figure 5.2 shows tree-ring width and density chronologies for white
spruce (Picea glauca) near the northern tree-line in Alaska (ARR in
Figure 5.1). These trees are inferred to be temperature sensitive, based in
part on field observations as well as modeling of tree-growth variations
with local and regional temperature data . For reviews of northern tree
growth in relation to temperature, see Jacoby, Cook, & Ulan (1985) and
Jacoby & D'Arrigo (1989) . Tree-ring widths from Alaska and other
selected temperature-limited northern sites demonstrate overall enhanced
growth since the middle to late 1800s, but with shorter-term growth
decreases (cooling) such as during the 1970s (e.g., D'Arrigo & Jacoby,
2
fiHH I GETCH HI NG WIDTH
1.6
1.2
8.8
8
1 .1
8.9
8.8
1.2
8.4
.... ..... u
= Z
8 . 7 1->- - -...J...
.L.L-...J...
.L.L.......
16581788175818881858198819582888
YERRS
Figure 5.2. Tree-ring width and maximum-latewood density chronologies for a
tree-line site in the Arrigetch Peaks, Brooks Range, northern Alaska. Note the
overall increase in growth in the ring width series since the turn of the century,
with the density series showing primarily high-frequency variability. Also note
extremely low density value in 1783 (see text) .