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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

FROM VOLUME 12, NUMBER 3, MARCH 1999

JOURNAL ARTICLES...
GROWING SEASON

Item #d99mar13

“Growing Season Extended in Europe,” A. Menzel and P. Fabian,Nature 397, 659 (1999).

Observations at the International Phenological Gardens indicated that, since 1959, spring has arrived an average of six days earlier and autumn has come an average of five days later. The Gardens consist of 77 research sites across Europe that contain genetically identical clones of various trees and shrubs. The calculations of the timing of spring and fall were made from records of the dates on which those trees and shrubs bud and flower and when their leaves change color and fall off. These changes in seasonal timing are attributed to the region’s temperatures, which have risen during the past three decades. These observational results agreed closely with and validated computer models of the effects of rising temperatures on plant behavior.

Item #d99mar14

“Effects of Climatic Variability on the Annual Carbon Sequestration by a Boreal Aspen Forest,” W. J. Chen et al.,Global Change Biology 5 (1), 41-53 (1999).

To determine variability, CO₂ fluxes above an old aspen forest in Canada were measured in 1994 and again in 1996. Carbon sequestration was found to be 200 ± 30 g C/m2-y in 1994 and 130 ± 30 g C/m2-y in 1996. The difference was caused by the leaf-emergence date’s being 18 to 24 days earlier in 1994 than in 1996, which exposed the forest to 16% more solar irradiance in 1994 than in 1996. In addition, the early growing months in 1994 were 4.8° C warmer than in 1996, increasing respiration by 20 g C/m2-y.