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Long tree‐ring chronologies reveal 20th century increases in water‐use efficiency but no enhancement of tree growth at five Iberian pine forests
Author(s) -
ANDREUHAYLES LAIA,
PLANELLS OCTAVI,
GUTIÉRREZ EMILIA,
MUNTAN ELENA,
HELLE GERHARD,
ANCHUKAITIS KEVIN J.,
SCHLESER GERHARD H.
Publication year - 2011
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/j.1365-2486.2010.02373.x
Subject(s) - dendrochronology , δ13c , environmental science , water use efficiency , climate change , zoology , growing season , pinus <genus> , ecology , biology , botany , photosynthesis , paleontology , physics , quantum mechanics , stable isotope ratio
We investigated the tree growth and physiological response of five pine forest stands in relation to changes in atmospheric CO 2 concentration ( c a ) and climate in the Iberian Peninsula using annually resolved width and δ 13 C tree‐ring chronologies since ad 1600. 13 C discrimination (Δ≈ c i / c a ), leaf intercellular CO 2 concentration ( c i ) and intrinsic water‐use efficiency (iWUE) were inferred from δ 13 C values. The most pronounced changes were observed during the second half of the 20th century, and differed between stands. Three sites kept a constant c i / c a ratio, leading to significant c i and iWUE increases (active response to c a ); whereas a significant increase in c i / c a resulted in the lowest iWUE increase of all stands at a relict Pinus uncinata forest site (passive response to c a ). A significant decrease in c i / c a led to the greatest iWUE improvement at the northwestern site. We tested the climatic signal strength registered in the δ 13 C series after removing the low‐frequency trends due to the physiological responses to increasing c a . We found stronger correlations with temperature during the growing season, demonstrating that the physiological response to c a changes modulated δ 13 C and masked the climate signal. Since 1970 higher δ 13 C values revealed iWUE improvements at all the sites exceeding values expected by an active response to the c a increase alone. These patterns were related to upward trends in temperatures, indicating that other factors are reinforcing stomatal closure in these forests. Narrower rings during the second half of the 20th century than in previous centuries were observed at four sites and after 1970 at all sites, providing no evidence for a possible CO 2 ‘fertilization’ effect on growth. The iWUE improvements found for all the forests, reflecting both a c a rise and warmer conditions, seem to be insufficient to compensate for the negative effects of the increasing water limitation on growth.