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Individual Highlight

Scientists analyze trends in tree growth to assess change in Interior Alaska’s spruce forest

Photo of Field crew collect forest inventory data in a stand of black spruce in Interior Alaska. Field crew collect forest inventory data in a stand of black spruce in Interior Alaska. Snapshot : Tree-ring analysis adjusted for age-related changes in growth indicate that recent growth of black and white spruce in Interior Alaska is near the historic mean, but lower than a peak in growth in the mid-1900s.

Principal Investigators(s) :
Gray, AndrewHollingsworth, Teresa
Research Station : Pacific Northwest Research Station (PNW)
Year : 2017
Highlight ID : 1398

Summary

Boreal forests are critical carbon sinks in the global carbon cycle; however, recent studies reveal increased frequency and extent of wildfires, decreased landscape greenness, increased tree mortality and a decline in growth of black and white spruce in boreal North America. To learn more about these research results, Forest Service scientists and their partners analyzed tree growth rings of black and white spruce in interior Alaska. Changes in the width of tree rings over time make it possible to assess changes in growth affected by climate. To account for effects of stand density and standard changes in ring width as trees become larger, scientist need to "detrend" the ring width. They did this by using several different methods that all revealed a pronounced growth peak for black and white spruce centered near 1940. Most detrending methods showed a decline from the peak, leaving recent growth of both species near the long-term mean. Climate-growth analyses for both species revealed growth declined with increases in temperatures during the growing season (a negative correlation) but increased in years when August precipitation was higher (a positive correlation). These results provide important historical context for recent growth of black and white spruce. Growth of both species might decline with future warming, if not mitigated by increasing precipitation but widespread drought-induced mortality probably is not imminent given that recent growth was near the long-term mean.

Forest Service Partners

External Partners

  • USDA Forest Service Boreal Cooperative Research Unit
  • University of Alaska Anchorage