Finnish Forest Research Institute  Metla

Press release 02.05.2006

Height growth of pine under way earlier than usual in Northern Finland

Pine has started to grow height this year unusually early, and even ahead of the rest of Finland in southern parts of Northern Finland, pampered by a wave of warm weather. The two-week spell of warm conditions has considerably accelerated awakening of trees into a new growing season.

At the latitude of the Arctic Circle, the crown bud of pine started to grow as early as April 26, an event recorded in the past decades only on one occasion, in 1990. Growth has started in April five times in the last 45 years. Under normal circumstances, height growth begins halfway through May. The latest date recorded for commencement of pine height growth on the Arctic Circle has been May 24.

This year, pine began to grow height on the same day as the effective temperature sum indicating length of growing season, i.e. the accumulated temperature, began to rise. In addition to the warmth and rapid snow melt, activation of growth has been accelerated by low levels or lack of ground frost. Unfrozen ground facilitates water uptake of trees.

Height growth of pine reacts quickly to changes in temperature, and growth may also pause if cold conditions unexpectedly return in May. However, frost damage is usually avoided, as it is only caused by very low temperatures. Depending on temperature, pine radial growth begins 1-3 weeks after the start of height growth.

The height growth of spruce starts clearly later than that of pine, and due to susceptibility to cold, the crown bud is the last to start growing. Changes in buds of broad-leaved trees are also already discernible.

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