Mechanism of Desiccation Damage of Conifers Wintering in Soil‐Frozen Areas

In 1966—67 in the eastern part of Hokkaido, where severe cold weather and a dry state prevailed throughout the winter, most young conifers, especially those wintering on the southern slopes, were seriously damaged. Minimum temperature was about —30°C, and soil temperature at 10—cm depth even on the southern slopes remained below zero for 3.5 months. Soil was frozen down to about 40 cm. Temperatures of stems and leaves of young conifers wintering on the southern and northern slopes rose to about 17° and 9°C, respectively, in midday and remained unfrozen for about 6 and 2 hr, respectively, in the daytime. Under these conditions, the conifers wintering on the southern slopes were intensely dehydrated towards the end of February. In most damaged trees, browning was observed on the stem bark. Trees in which desiccation damage was artificially induced exhibited nearly the same browning as that observed in trees suffering damage under natural conditions. Stems and leaves of young Sakhalin fir and Ezo spruce could stand freezing in winter below —50C, and white pine and American arborvitate which sustained damage seriously under natural conditions also survived freezing below —120°C. Young conifers wintering in frozen soil were damaged by dehydration resulting from a combination of freezing of soil and exposure to sunshine.

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