Background
When periodically looking through piles of publications on our desks, we often find a noteworthy paper from the past that we never got around to reviewing. This review is of one such paper that was published in Ecology in 1997.

What was done
Bert et al. calculated a 120-year (1860-1980) history of intrinsic water-use efficiency (defined as the ratio of CO2 assimilation rate to stomatal conductance for water vapor) for silver fir (Abies alba Mill.) trees, based on δ¹³C data obtained from cores extracted from individual trees of this species that grew within 208 pure stands in the Jura Mountains near the border that separates France and Switzerland.

What was learned
From 1860 to 1930 there was little net change in silver fir water-use efficiency; but over the next half-century (1930 to 1980), when the atmosphere's CO2 concentration rose at a rate that was more than three times greater than its rate-of-rise over the earlier period, this important tree physiological property rose by approximately 30%.

What it means
The three researchers state that their results -- which were "obtained at the level of mature trees" -- are "consistent with the physiological effects of increasing CO2 concentrations as observed in controlled experiments on young seedlings," and that they are additionally "consistent with the strong increases in radial growth observed for Abies alba in western Europe over the past decades."

These findings and inferences are also consistent with the findings of many other investigators, numerous examples of which may be found in our Subject Index under the sub-headings associated with Water Use Efficiency and the Greening of the Earth.