Dracophyllum longifolium

Its common sense, isn't it? As temperatures increase globally and the growing season gets longer, trees and shrubs in colder climates will see an increase in growth as a result of the longer growing season. However, a new study finds that this is not the case.

Melanie Harsch, postdoctoral student at University of Washington biology and applied mathematics and lead author of the study states, "When winter temperatures fluctuate between being cold and warm enough for growth, plants deplete their resources trying to photosynthesize and end the winter with fewer reserves than they initially had. In the summer they have to play catch up."

Harsch continues on saying that the roots are especially sensitive to temperature fluctuation which results in higher root respiration. When higher root respiration occurs, it uses up the plants carbon, making less of it available during the regular growing season.

Harsch based her study on her research done on two species of shrubs on the UNESCO World Heritage site in the Southwest Pacific Ocean called Campbell Island. Located 375 miles south of New Zealand, on Campbell Island, Harsch studied Dracophyllum longifolium and Dracophyllum scoparium, are evergreen broadleaf plants that reach about 15 feet and can live up to 240 years. During the study, researchers cut out discs from the plant, called "cookies," just from above the root collar. They then measured the rings within the cookies to measure plant growth.

Harsch stated, "On Campbell Island the snow is ephemeral, so the plants usually are not covered. If we're going to see an effect in changing winter conditions, we're going to see it at Campbell Island decades before we see it at, say, Mt. Rainier, where there is a lot of snow and winters are colder."

While the plants may eventually adjust to warmer winters, the transition period may be tough on them and result in many plants withering or experiencing long periods of dormancy.