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Increased water‐use efficiency during the 20th century did not translate into enhanced tree growth
Author(s) -
Peñuelas Josep,
Canadell Josep G,
Ogaya Romà
Publication year - 2011
Publication title -
global ecology and biogeography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.164
H-Index - 152
eISSN - 1466-8238
pISSN - 1466-822X
DOI - 10.1111/j.1466-8238.2010.00608.x
Subject(s) - biome , temperate climate , environmental science , ecology , climate change , boreal , range (aeronautics) , temperate rainforest , δ13c , taiga , dendrochronology , nutrient , atmospheric sciences , geography , biology , ecosystem , stable isotope ratio , materials science , physics , archaeology , quantum mechanics , geology , composite material
Aim The goals of this study are: (1) to determine whether increasing atmospheric CO 2 concentrations and changing climate increased intrinsic water use efficiency (iWUE, as detected by changes in Δ 13 C) over the last four decades; and if it did increase iWUE, whether it led to increased tree growth (as measured by tree‐ring growth); (2) to assess whether CO 2 responses are biome dependent due to different environmental conditions, including availability of nutrients and water; and (3) to discuss how the findings of this study can better inform assumptions of CO 2 fertilization and climate change effects in biospheric and climate models. Location A global range of sites covering all major forest biome types. Methods The analysis encompassed 47 study sites including boreal, wet temperate, mediterranean, semi‐arid and tropical biomes for which measurements of tree ring Δ 13 C and growth are available over multiple decades. Results The iWUE inferred from the Δ 13 C analyses of comparable mature trees increased 20.5% over the last 40 years with no significant differences between biomes. This increase in iWUE did not translate into a significant overall increase in tree growth. Half of the sites showed a positive trend in growth while the other half had a negative or no trend. There were no significant trends within biomes or among biomes. Main conclusions These results show that despite an increase in atmospheric CO 2 concentrations of over 50 p.p.m. and a 20.5% increase in iWUE during the last 40 years, tree growth has not increased as expected, suggesting that other factors have overridden the potential growth benefits of a CO 2 ‐rich world in many sites. Such factors could include climate change (particularly drought), nutrient limitation and/or physiological long‐term acclimation to elevated CO 2 . Hence, the rate of biomass carbon sequestration in tropical, arid, mediterranean, wet temperate and boreal ecosystems may not increase with increasing atmospheric CO 2 concentrations as is often implied by biospheric models and short‐term elevated CO 2 experiments.