Spatial and temporal variability in the growth and climate response of treeline trees in Alaska

Twelvemile Summit, White Mountains, Alaska Spatial and temporal variability in the growth and climate response of treeline trees in Alaska
Climatic Change, Volume 58, 481-509, 2002.

Andrea Lloyd and Christopher L. Fastie
Department of Biology, Middlebury College

ABSTRACT:
In this study, we investigated the response of trees growing at the cold margins of the boreal forest to climate variation in the 20th century. Working at eight sites at and near alpine and arctic treeline in three regions in Alaska, we compared tree growth (from measured tree ring-widths) to historical climate data to document how growth has responded to climate variation in the 20th century. We found that there was substantial regional variability in response to climate variation. Contrary to our expectations, we found that after 1950 warmer temperatures were associated with decreased tree growth in all but the wettest region, the Alaska Range. Although tree growth increased from 19001950 at almost all sites, significant declines in tree growth were common after 1950 in all but the Alaska Range sites. We also found that there was substantial variability in response to climate variation according to distance to treeline. Inverse growth responses to temperature were more common at sites below the forest margin than at sites at the forest margin. Together, these results suggest that inverse responses to temperature are widespread, affecting even the coldest parts of the boreal forest. Even in such close proximity to treeline, warm temperatures after 1950 have been associated with reduced tree growth. Growth declines were most common in the warmer and drier sites, and thus support the hypothesis that drought-stress may accompany increased warming in the boreal forest.
Tree growth trends, 3 Alaska regions Figure 2. Growth trends of trees in three regions of Alaska. The bars indicate the number of chronologies within which region that showed significant positive trends in growth, significant negative trends in growth, or no significant trend in growth from (a) 1901 to 1950 and (b) 1950 to the end of the chronology (1997-1999). Significance of growth trends was assessed using simple linear regression.
(Click for Numerical Values,
tab-delimited text or MS Word format).

DATA:

Download the tree ring data used in this study from the International Tree Ring Data Bank at the WDC Paleo:
Site (download chronology or measurements) Lat. ( N) Long. ( W) Treeline Type Azimuth Tree Density Elevation (m)
Alaska Range
Usibelli below treeline (.rwl file) 63 54' 148 40' Alpine W 542 182 762
Usibelli treeline (.rwl file) 63 54' 148 40' Alpine W 542 182 762
Canyon Creek (.rwl file) 63 15' 147 47' Alpine NE 422 62 884
Monahan Flats (.rwl file) 63 16' 147 55' Alpine N 201 101 884
Seward Peninsula
Fox River Bank (.rwl file) 64 49' 163 42' Arctic NNE N/A 61
Grasshopper Hill (.rwl file) 64 55' 163 40' Arctic SE N/A 150
White Mountains
Eagle Summit below treeline (.rwl file) 65 30' 145 20' Alpine S 225 79 945
Eagle Summit treeline (.rwl file) 65 30' 145 20' Alpine S 225 79 945
Twelvemile Summit below treeline (.rwl file) 65 22' 145 56' Alpine NW 93 33 945
Twelvemile Summit treeline (.rwl file) 65 22' 145 56' Alpine NW 93 33 945
Nome Creek below treeline (.rwl file) 65 22' 146 37' Alpine SE 175 65 884
Nome Creek treeline (.rwl file) 65 22' 146 37' Alpine SE 175 65 884

To read or view the full study, please visit the Kluwer website.
It was published in Climatic Change, Volume 52, 481-509, 2002.

Contact Us
National Oceanic and Atmospheric Administration
23 July 2002