Warmer temperatures could stop Norwegian spruces from growing so big (Image: ddp USA/REX Features)

Our warming climate is bad news for Christmas trees. Norwegian spruces risk getting cold feet as the insulating blanket of snow that protects their roots from Scandinavian winters thins.

Snow can be surprisingly cosy – acting like loft cladding to prevent sub-zero air penetrating the soil. Less of the white stuff means frigid soil that takes longer to thaw in spring. This limits trees’ new growth and ultimately has a knock-on effect on health, says Sirkka Sutinen, from the Finnish Forest Research Institute.

Sutinen and her team spent two seasons studying a clump of 47-year-old spruces in eastern Finland. They simulated the effect of a thinner snow pack by allowing the soil to freeze then applying insulation to prevent it thawing as quickly. When the thaw was delayed until mid-summer, buds opened much later, and fewer, smaller pine needles sprouted (Forest Ecology and Management, doi.org/xpn).


These conditions were more extreme than happen naturally, but modelling studies hint that lower snowfall is possible in the near future. “If the climate changes how we expect it to, the trees are not going to be happy,” Sutinen says. “If we had several years like this in a row, we could see significant damage.”

And spruce may be threatened by more than just cold feet, according to Paal Krokene from the Norwegian Forest and Landscape Institute.

Warmer temperatures are good news for the trees’ arch nemesis – the spruce bark beetle – which may soon be producing two generations a year in an extended breeding season. A double attack wave could be too much for the trees, particularly in high summer when they are most vulnerable, Krokene says.

Christmas revellers can breathe a sigh of relief, though. The iconic species that livens up homes and city centres across the Western world is in no danger of dying out any time soon.

But things could be different in the long term. “Insects benefit much more from climate change than the trees,” Krokene says.

Journal reference: Forest Ecology and Management, DOI: 10.1016/j.foreco.2014.10.029