28 DISTRIBUTION OF FORESTS IN UNITED STATES 



eludes the maples, cherries, plum, shad-bush, ash, beech, hazel, birch, 

 alder, willows, elms, and many of the pines and tirs, which when speci- 

 fically different are closely allied.^ 



The influences which api)ear to determine the distribution and char- 

 acter of forest growth are chiefly tenqycrature and moisture, and these 

 rather according to their distribution tlirough the year, than their ex- 

 treme degree, or annual amount. Ligkt is another important element, 

 and in foresi growth the outside trees of a grove are seldom symmetri- 

 cal, on account of the undue development of the side most exposed to 

 the full light. The chemical properties of the soil have also a marked in- 

 fluence, but quite subortlinate to these above mentioned. 



It is found that the existing forest-trees of America have a close rela- 

 tion, and sometimes actual identity, with the fossil forms found in the 

 Arctic region and in the Tertiary formations of Europe. This is observed 

 with respect to the two redwoods of California, the bald cypress of the 

 Atlantic region, the hickories, and many other kinds. This has led to 

 the conjecture that the vegetation of the eastern borders of the two 

 continents is in part due to the more ancient character of their geolog- 

 ical formations.^ Besides being " old fashioned," the number of species 

 of native American trees is very much greater than in Europe, as will 

 be elsewhere more particularly noticed. 



GENERAL DISTRIBUTION OF FORESTS IN THE UNITED STATES. 



As a general rule, the whole region east of the Mississippi River, ex- 

 cepting the prairies and "openings" in tiie States north of the Ohio, and 

 the "barrens" of Kentucky and Tennessee, was, when first known to 

 Europeans, a timbered country. There were also large bodies of tim- 

 ber westward of the Mississippi, but as we go west we find that these 

 become limited to the neighborhood of streams, and gradually become 

 less, until the last fringe of willows and cottonwoods disappears, and we 

 find a broad treeless belt extending across our domain from Mexico 

 northward to the Arctic Ocean. The Eocky Mountain region affords a 

 more limited range on the divides and northern slopes, and in valleys 

 and summer-spots among them, extending irregularly along their whole 

 course, and up to a well marked limit known as the "timber-line," above 

 which vegetation for all useful purposes ceases, and we find peaks 

 always crowned with snow. Beyond this we find a region still more 

 arid, until we approach the mountains watered by rains from the Pacific. 

 On approaching the coast, where these rains are excessive at certain 

 seasons, and the soil and climate are otherwise favorable, we meet with 

 limited areas bearing a forest growth incomparable from the immense 

 size of the trees and their extraordinary density. 



Throughout the w^hole of our domain we find a close relation between 

 forests and rain-fall — the native growth having been found everywhere 

 ample where the rains were sufficient and well distributed through the 

 year — except in places where, from known or probable causes sufficient 

 to explain it, this growth was absent. But in speaking of " woodlands," 

 it may be proper to remark, that there is no word in our language more 



' Lake Superior, its Physical Character, Vegetation, and Animals, pp. 137-190. 



^ Agassiz^s Lake Superior, p. 150. lu the address of Professor Gray, already quoted, 

 certain strikiii}; coincidences are pointed out in the widely-separated occurrence of 

 closely-allied species, some of which are very limited and local in the places where, 

 found. Thus, the redwoods of California, Iho bald cypress of the Southern Atlantic 

 Coast, and the Ghjptostrobus of China have strong points of resemblance. The Torreya, 

 belonging to the yew family, is found on a very limited area in Florida, in Japan, and 

 in Northern China, as also in California. Other examples quite as striking are cited 

 by this author. 



