The Effective Rate of Altitudinal Change in Temperate Atlantic Climates

Abstract

SINCE the early pioneering days the brusque alternations of the eastern American climate have provided abundant material for discussion; for example, the results of instrumental comparisons between the two sides of the Atlantic are often found in English scientific journals of the eighteenth century. The effects, real or presumed, of the American climatic environment on European plants, animals, and man, and of course on man's inventions and ideas, have also given rise to a voluminous literature. Geographers are familiar with the stimulating virtues of the New England climate as expounded by Professor Ellsworth Huntington. But it is noteworthy that European forms of life have frequently survived in competition with the native American product, especially those from the cool northwestern fringe; witness, for example, the rapid displacement of the native grasses of New England by the European grasses.I Although the climatic extremes are less marked in England, the somewhat astringent climate,2 especially in the north, provides certain advantages, both as a selective agency and as a long-period stimulus to individual and local differentiation, that are not easy to parallel elsewhere. This follows from consideration of an aspect of climatology not hitherto brought under review, namely the effective rate of change of climatic environment with altitude. American officers in training in British hills are frequently surprised by the extremely low tree line; conversely, the Englishman who ascends Mt. Washington is struck by the fact that in spite of the New England winter the alpine zone is not reached till about 5000 feet.3 The coasts of northwestern Ireland and the northwestern Highlands of Scotland are, of course, treeless, on account of exposure to wind and the extensive blanket bog or poorly drained peaty soil resulting from an excessive rainfall; farther inland, vast areas of treeless upland above Iooo feet are the result of deforestation in the past combined with present-day grazing. Nevertheless, it is evident from a variety of sources that at best the climatic tree line is little above 2000 feet. Through the combination of a low tree line with the results of past glaciation the traveler in the Lake District sees