Long tree-ring chronologies reveal 20th century increases in water-use efficiency but no enhancement of tree growth at five Iberian pine forests

Laia Andreu-Hayles, Octavi Planells, Emilia Gutiérrez, Elena Muntan, Gerhard Helle, Kevin J. Anchukaitis, Gerhard H. Schleser

Research output: Contribution to journalArticlepeer-review

153 Scopus citations

Abstract

We investigated the tree growth and physiological response of five pine forest stands in relation to changes in atmospheric CO2 concentration (ca) and climate in the Iberian Peninsula using annually resolved width and δ13C tree-ring chronologies since ad 1600. 13C discrimination (Δ≈ci/ca), leaf intercellular CO2 concentration (ci) and intrinsic water-use efficiency (iWUE) were inferred from δ13C values. The most pronounced changes were observed during the second half of the 20th century, and differed between stands. Three sites kept a constant ci/ca ratio, leading to significant ci and iWUE increases (active response to ca); whereas a significant increase in ci/ca resulted in the lowest iWUE increase of all stands at a relict Pinus uncinata forest site (passive response to ca). A significant decrease in ci/ca led to the greatest iWUE improvement at the northwestern site. We tested the climatic signal strength registered in the δ13C series after removing the low-frequency trends due to the physiological responses to increasing ca. We found stronger correlations with temperature during the growing season, demonstrating that the physiological response to ca changes modulated δ13C and masked the climate signal. Since 1970 higher δ13C values revealed iWUE improvements at all the sites exceeding values expected by an active response to the ca 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 CO2'fertilization' effect on growth. The iWUE improvements found for all the forests, reflecting both a ca rise and warmer conditions, seem to be insufficient to compensate for the negative effects of the increasing water limitation on growth.

Original languageEnglish (US)
Pages (from-to)2095-2112
Number of pages18
JournalGlobal change biology
Volume17
Issue number6
DOIs
StatePublished - Jun 2011
Externally publishedYes

Keywords

  • Global warming
  • Intrinsic water-use efficiency (iWUE)
  • Mediterranean region
  • Ring width
  • Rise of atmospheric CO concentration
  • Tree rings
  • δC ratios

ASJC Scopus subject areas

  • Global and Planetary Change
  • Environmental Chemistry
  • Ecology
  • Environmental Science(all)

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