Wind and Exposure as Limiting Factors in the Establishment of Forest Plantations

Abstract

The influence of air in motion, or wind, upon the distribution of tree species is a climatic factor that has received but passing notice. Major attention seems rather to have been centered upon the factor of transpiration, and upon the mechanical effects of wind on tree form and structure. It has also been recognized that wind, combined with low temperatures, plays an important part in the geographic distribution of a given species. Wind in particular seems to definitely limit the extension of forests on the high arctic tundras. It is only in the valleys sheltered from the winds that tree growth persists in the far northern extension of their ranges. But the influence of the wind in the local distribution of a species, particularly in its establishment, or rather as affecting its ability to establish itself on a given site, has received little attention. It has been noted that forests usually cease on hilly regions when the mountain structures commence to break into isolated peaks. Above this point tree growth is only found where there is local shelter from the wind. Specifically was this called to the attention of the writer in the examination of some plantations established on the campus of Syracuse University. The site of the plantations was a high hill directly south of the University buildings, perhaps one of the highest hills in the vicinity. The top of this hill marks the break of the northern escarpment of the Great Northern Appalachian Plateau. Its elevation is some 400 feet above Onondaga Lake, to the level of which it drops in less than a mile. From the base of the hill the land stretches north and west with no other features than the gentle undulations of the Great Lake Plains of which it is a part, to the shore of Lake Ontario forty miles away. The general slope of the hill is toward the northwest and west, with a degree of slope on the site of the plantations of about 6o degrees. This combination of factors has presented a site particularly exposed to winds from this quarter, winds that have an uninterrupted sweep clear from the northern shores of the Great Lakes. The intensity of the exposure and susceptibility of the trees to damage is further aggravated by heavy clay glacial soil rather impervious to water and susceptible to loss or the intragranular frozen moisture by drying. The plantation was established in the spring of I920. Red pine and white were set out 6 ft. x 6 ft. in alternate rows. Failures were filled in the