What was done
Working in Japan's Tomakomai Experimental Forest (a mature deciduous woodland located at 42°40'N, 141°36'E), the authors employed a construction crane to lift themselves some 18 to 20 meters above the ground, where they attached, via adhesive tape, 120-meter-long electric heating cables to some of the top canopy branches of three tall, mature Quercus crispula oak trees, by which means they continuously warmed their developing shoots approximately 5°C above local ambient temperature for the next full year, starting on 15 May 2008. Then, in the autumn of 2008 and spring of 2009, they determined leaf fall and leaf flushing, respectively, on warmed and control branches, while from 11 to 13 September 2008 they measured acorn production on the two sets of branches.

What was learned
The five researchers report that time of leaf flush in the spring was unaffected by warming; but they found that the growing season of canopy leaves was extended by later leaf fall, which on warmed branches occurred about 10 days later than it did on control branches. And, perhaps most impressive of all, they discovered that "when acorns were present, warmed branches had about double the number of acorns found on control branches."

What it means
In the final sentence of the abstract of their paper, Nakamura et al. write that the "application of this technique should lead to a better understanding of how tall, mature trees respond to global warming." And we have to agree with them, as they state in the final paragraph of their paper, that these "changes in the phenologies of canopy leaves and acorn production will play major roles in forest ecosystem processes," which roles, we hasten to add, would appear to be both very positive and very important.