Notes on Wind and its Effects in Arctic-Alpine Vegetation

Wilson, J

The vegetation of arctic-alpine regions is strongly affected by wind; in exposed sites the plants grow poorly and may be wind-pruned or even killed. Observations at Jan Mayen Island (71⚬ N) showed that the difference in growth-rates between an exposed hilltop and a sheltered hollow was greater than that reported in similar comparisons in temperate regions. Arctic-alpine regions are characteristically windswept, but wind speeds fall off sharply close to the ground surface owing to its braking effect. Foliage also offers strong resistance. Consequently, shoots projecting above the general level suffer especially high winds, but most foliage (being low-growing) lies in comparatively calm air. Wind speeds in normal weather among vegetation in exposed positions in the Cairngorms were not high--a few decimetres per second generally, and less in dense foliage and in eddy zones. Evaporation rates around these plants were closely related to wind speeds. Excessive transpiration may kill projecting shoots rarely in summer and more often (at least in the case of shrubs and trees) in winter when the soil is frozen; but the general depression of growth-rates by wind seems not to be primarily a result of drying, since in summer the plants of most--though not all--arctic-alpine regions have a high water status. Wind cools foliage, especially in sunny weather, and this effect is unusually marked in arctic-alpine vegetation; it amounted to up to 7⚬ C in observations at Cornwallis Island (75⚬ N). Moreover, at low temperatures plant growth becomes especially sensitive to temperature conditions. It is concluded that the potent effect of wind on arctic-alpine vegetation is generally a result not so much of high wind speed as of special sensitivity of plant growth to wind; and that this sensitivity is due less to drying and more to cooling than under temperate conditions.

Notes on Wind and its Effects in Arctic-Alpine Vegetation

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