Winter drying injury
Damage, symptoms and biology
Winter drying is a very common condition that affects all conifer species. Typically, damage occurs to needles above the snow line. The browning of the foliage becomes evident in late winter. The portion of the crown below the snow line is protected and undamaged. Damage is most severe during years of cold temperatures but little or no snow cover. The damage may be localized, or can cover a vast area, affecting many hectares of conifer forest.
Winter drying generally occurs in mid-winter or early spring during periods of sunny, warm days accompanied by light winds. The combination of these conditions results in the transpiration of moisture from the conifer needles. This water loss cannot be replaced because the water in the soil is frozen and not available to the roots, or the main stems are frozen and block the upward movement of the water. The needles soon completely dry out, discolour, die, and eventually drop off the tree. This drought condition within the tree will persist until the spring thaw when moisture becomes available once again.
Canadian Forest Service Publications
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