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Thresholds for warming‐induced growth decline at elevational tree line in the Yukon Territory, Canada
Author(s) -
D'Arrigo Rosanne D.,
Kaufmann Robert K.,
Davi Nicole,
Jacoby Gordon C.,
Laskowski Cheryl,
Myneni Ranga B.,
Cherubini Paolo
Publication year - 2004
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2004gb002249
Subject(s) - tree line , latitude , environmental science , precipitation , dendrochronology , climatology , atmospheric sciences , climate change , browning , global warming , physical geography , geography , ecology , biology , meteorology , geology , horticulture , geodesy , archaeology
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 11.3°C 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.