This spruce has battled against frost damage for eleven years. Ola Langvall is concerned. Photo: Mats Hannerz
Spruce freezes as temperature rises (!)
It may sound paradoxical but, as we move towards a warmer climate, there is an increasing risk that forest plantations will freeze. At any rate, this applies to spruce in southern Sweden during the spring. This can be important when the forestry sector is selecting plants for the future.
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Future Forests researcher Ola Langvall has been working with forecasts about how the frost risk changes over time. He uses a model that calculates the risk of spring and autumn frost damage to spruce. The model uses daily average and minimum temperatures from all over Sweden for the period 1961-1990. He was able to calculate future temperatures using the climate scenarios A1 and B2 developed by the SMHI Rossby Centre.“When the climate becomes warmer, shoots will develop earlier on the spruce plants. We´re talking about a whole month earlier by 2050 compared with the reference period 1961-1990," says Ola Langvall. “In northern Sweden, it will be a week or so earlier."
The spruce´s start to the spring is governed almost entirely by temperature. When a certain accumulated temperature has been reached, the buds start to swell and new shoots appear. It is then, and for several subsequent weeks, that the spruce is most sensitive to a cold snap.
"The earlier appearance of shoots increases the risk of spring frost damage. In the country as a whole, we´re talking about an 8-15 percent greater risk, but in southern Sweden the risk can be double," warns Ola Langvall.
He recommends that the forestry sector use more late-budding plants in future plantations. This can affect the types of trees selected for seed orchards already today. At the same time he urges caution in order to avoid increasing the risk of autumn frost damage.
“Trees that develop shoots later generally continue growing a little further into the autumn, when they are vulnerable to damage by early frosts," he says. “The risk is greatest in the harsh climate of northern Sweden."
In a Future Forests programme, climate predictions will now be incorporated in the existing model for calculating the risk of frost. The Frostrisk tool is available on Skogforsk´s management portal, Kunskap Direkt.
/Mats Hannerz
