Thresholds for warming-induced growth decline at elevational tree line in the Yukon Territory, Canada

LDEO Publication: 
Publication Type  Journal Article
Year of Publication  2004
Authors  D'Arrigo, R. D.; Kaufmann, R. K.; Davi, N.; Jacoby, G. C.; Laskowski, C.; Myneni, R. B.; Cherubini, P.
Journal Title  Global Biogeochemical Cycles
Volume  18
Issue  3
Pages  -
Journal Date  Sep 24
ISBN Number  0886-6236
Accession Number  ISI:000224126400002
LDEO Publication Number  6633
Key Words  temperature; threshold; tree-rings; cointegrating vectors; high-latitudes; white spruce; time-series; carbon sink; ring width; unit-root; temperature; climate; variability

A few tree ring studies indicate recent growth declines at northern latitudes. The precise causes are not well understood. Here we identify a temperature threshold for decline in a tree ring record from a well-established temperature-sensitive site at elevational tree line in northwestern Canada. The positive ring width/temperature relationship has weakened such that a pre-1965 linear model systematically overpredicts tree ring widths from 1965 to 1999. A nonlinear model shows an inverted U-shaped relationship between this chronology and summer temperatures, with an optimal July-August average temperature of 11.3degreesC based on a nearby station. This optimal value has been consistently exceeded since the 1960s, and the concurrent decline demonstrates that even at tree line, trees can be negatively affected when temperatures warm beyond a physiological threshold. If warming continues without significant gains in effective precipitation, the large-scale greening of recent decades could be replaced by large-scale browning. Such browning could slow or reverse carbon uptake by northern forests.


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URL  <Go to ISI>://000224126400002
DOI  Doi 10.1029/2004gb002249