Background
The authors write that with late-20th-century changes in temperature, "variations in phenology have acquired particular importance," and they note, in this regard, that the longest monitoring periods of plants have been carried out in the botanical gardens of temperate Europe and deal with the effects of temperature changes on the growth dynamics of primary meristems (buds, leaves and flowers), while there has been no historical documentation relative to the phenology of the secondary meristem or cambium, as it is not a macroscopically-perceptible phenomenon like leaf development or flower maturation.

What was done
In an attempt to begin filling this research void, Lugo et al. monitored the timing of xylogenesis (wood formation) in black spruce (Picea mariana) trees for nine years on a weekly basis at four sites in the boreal forest of Quebec, Canada. This they did in order to reconstruct the onset, duration and ending of xylogenesis in trees of this species between 1950 and 2010, as well as the relationships of these phenomena to chronologies of maximum and minimum air temperatures.

What was learned
The three researchers first report that "all sites exhibited increasing trends of both annual and May-September temperatures, with the greatest changes observed at the higher latitudes," after which they state that "phenological events in spring were more affected than those occurring in autumn, with cambial [growth] resumptions occurring 0.5-0.8 days/decade earlier."

What it means
"If the observed trend is maintained unaltered in the long term," in the words of Lugo et al., "the demonstrated advancement of cambial activity could dramatically modify the short time window for growth of boreal species and markedly affect cell production of the secondary meristem," with the result that "long-term increases in temperature can substantially extend wood formation and, consequently, the dynamics and productivity of cold ecosystems, by removing the thermal constraints to the activity of carbon sinks in trees."