Influence of vegetation on permafrost

• Main Author: Brown, R. J. E.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Building Research Advisory Board at Purdue University 1963
• Subjects: permafrost; pergélisol; soils; sol (terre); vegetation; végétation; frost penetration; pénétration du gel
• Online Access: https://nrc-publications.canada.ca/eng/view/ft/?id=4c989143-5d15-4404-9363-db1742108798; https://nrc-publications.canada.ca/eng/view/object/?id=4c989143-5d15-4404-9363-db1742108798; https://nrc-publications.canada.ca/fra/voir/objet/?id=4c989143-5d15-4404-9363-db1742108798

One terrain feature of great significance to the extent, thickness and thermal regime of permafrost is vegetation. Its thermal properties determine the amount of heat leaving or entering the underlying ground. Vegetation has an indirect effect on climate, which influences permafrost. Treeless vegetation such as lichen and mosses may have a different albedo. Net radiation is also an important factor. Direct measurement of the convection component is extremely difficult and it may be evaluated as the difference between the sum of the other measurements and the total. Bowen's ratio is also sometimes used. Evaporation, including evapotranspiration, withdraws heat from the surrounding atmosphere and from incident solar radiation. Vegetation draws water by transpiration thus depleting the soil of heat held by that water. There are great variations between species. Vegetative cover of dead material has a large insulating effect on the underlying permafrost. Depth of thaw increases where vegetation cover has been removed. The micro climate resulting from vegetation is probably most effective by influencing the wind speed. The density of the vegetation and height of tree cover influences are well known. Ground that permits the greatest degree of water penetration usually thaws to the greatest depths. The low thermal conductivity of snow and its double role as inhibitor of frost penetration during winter and soil thawing in the spring has been noted. Where strong winds prevail more snow accumulates under vegetative cover in open areas. The most easily observed and measured characteristic of permafrost is the depth of thaw and variations in types of vegetation are often readily noticeable. La végétation est un élément du milieu possédant une très grande importance en ce qui concerne l'étendue, l'épaisseir et le régime thermique du pergélisol. Ses propriétés thermiques déterminent la quantité de chaleur sortant du sous-sol ou y entrant. Peer reviewed: No NRC publication: Yes