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Growth and phenology of mature temperate forest trees in elevated CO 2
Author(s) -
ASSHOFF ROMAN,
ZOTZ GERHARD,
KÖRNER CHRISTIAN
Publication year - 2006
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.1365-2486.2006.01133.x
Subject(s) - quercus petraea , beech , fagus sylvatica , carpinus betulus , basal area , shoot , phenology , canopy , botany , temperate forest , biology , fagaceae , deciduous , horticulture , temperate climate , ecology
Are mature forest trees carbon limited at current CO 2 concentrations? Will ‘mid‐life’, 35 m tall deciduous trees grow faster in a CO 2 ‐enriched atmosphere? To answer these questions we exposed ca. 100‐year‐old temperate forest trees at the Swiss Canopy Crane site near Basel, Switzerland to a ca. 540 ppm CO 2 atmosphere using web‐FACE technology. Here, we report growth responses to elevated CO 2 for 11 tall trees (compared with 32 controls) of five species during the initial four treatment years. Tested across all trees, there was no CO 2 effect on stem basal area (BA) increment (neither when tested per year nor cumulatively for 4 years). In fact, the 4th year means were almost identical for the two groups. Stem growth data were standardized by pretreatment growth (5 years) in order to account for a priori individual differences in vigor. Although this experiment was not designed to test species specific effects, one species, the common European beech, Fagus sylvatica , showed a significant growth enhancement in the first year, which reoccurred during a centennial drought in the third year. None of the other dominant species ( Quercus petraea , Carpinus betulus ) showed a growth response to CO 2 in any of the 4 years or for all years together. The inclusion or exclusion of single individuals of Prunus avium and Tilia platyphyllos did not change the picture. In elevated CO 2 , lateral branching in terminal shoots was higher in Fagus in 2002, when shoots developed from buds that were formed during the first season of CO 2 enrichment (2001), but there was no effect in later years and no change in lateral branching in any of the other species. In Quercus , there was a steady stimulation of leading shoot length in high‐CO 2 trees. Phenological variables (bud break, leaf fall, leaf duration) were highly species specific and were not affected by elevated CO 2 in any consistent way. Our 4‐year data set reflects a very dynamic and species‐specific response of tree growth to a step change in CO 2 supply. Stem growth after 4 years of exposure does not support the notion that mature forest trees will accrete wood biomass at faster rates in a future CO 2 ‐enriched atmosphere.