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6 FOREST TREES OF NORTH AMERICA. 



beyond the western limits of tlie prairie as here laid down, tbe permanent establishment of forests there does not 

 seem practicable, and, sooner or later, a period of unusual drought must put an end to all attempts at forest 

 cultivation in a region of such insufficient and uncertain rainfall (Maj) No. 1, portfolio). 



It remains to consider the Semi-tropical Forest of Florida and the Mexican Forest of Southern Texan. 



A group of arborescent species of West Indian origin occupies the nan'ow strip of coast and islands of 

 southern Florida. This belt of semi-tropical vegetation is confined to the immediate neighborhood of the coast 

 and to occasional hummocks or i.slands of high ground situated in the savannas which cover a great i)ortiou of 

 southern Florida, checking, by the nature of the soil and want of drainage, the spread of forest growth across the 

 peninsula. This semi-tropical forest belt reaches cape Malabar on the east and the shores of Tampa bay on the 

 west coast, while some of its representatives extend fully 2 degrees farther noith. It is rich in coiiiijosition ; 

 nearly a quarter of all the arborescent species of the Atlantic forest are found within this insignificant region. 

 The semi-tropical forest, in spite of its variety, is of little economic importance. The species of which it is composed 

 here reach the extreme northern limit of their distribution; they are generally small, stunted, and of comparatively 

 little value. Certain species, however, attain respectable ])roportions ; the mahogany, the mastic, the royal i)alm, 

 the mangrove, the sea-grape, the Jamaica dogwood, the nianchineel, and other species here become considerable 

 and important trees. 



In western and southern Texas the trees of the Mississippi basin, checked by insufficient moisture from farther 

 extension southward outside the river bottoms, are replaced by species of the plateau of northern Mexico. The 

 streams flowing into the gulf of Mexico are still lined, however, east of the one-hundredth meridian, with the species 

 of the Atlantic basin, which thus reach southward to beyond the Eio Grande. The Mexican forest belt of Tt-xas 

 extends from the valley of the Colorado river, near the ninety-eighth meridian, to the Eio Grande. It touches the 

 coast not far from the Nueces river and extends to the eastern base of the mountain ranges west of the Pecos; 

 here the species of which it is composed mingle with those peculiar to the Pacific-Mexican forest. The forest of 

 this region, like that of all countries of insufficient moistui-e, is open, stunted, and comparatively of little value. 

 It is characterized by enormous areas covered with chai)arral (dense and often impenetrable thickets of thorny 

 shrubs and small trees), by a stunted and occasional arborescent growth upon the hills and plains, and by fringes 

 of heavier timber iilong the river bottoms. The most valuable and perhaps the most characteristic species of this 

 whole region, the mesquit, extends to the Pacific coast. With this exception, none of the arborescent species 

 peculiar to this region attain any considerable size or importance, although the forest of small junipers which 

 covers the low limestone hills of the Colorado valley are locally valuable in a country so generally destitute of 

 trees. The region immediately adjoining tlie liio Grande abounds in different speciesof Acacia, Leucwna, and other 

 Mexican Leguminona; and farther west, upon the dry plains of the Presidio, the Spanish bayonet {Tueca baccata) 

 covers wide areas with a low, open, and characteristic forest growth. 



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THE PACIFIC REGION, 



'The Pacific forest region is coextensive with the great Cordilleran Mountain system of tlie continent. The causes 

 whicti have influenced the present position and density of these forests must be sought in the peculiar <Ustribntion 

 of the rainfall of the region. The precipitation of moisture upon the northwest coast is unequaled by that of any 

 other part of the continent. It gradually decreases with the latitude until, in southern California, the temperature 

 of the land so far exceeds that of the ocean that precipitation is impossible through a large part of the year. The 

 interior of all this great region, shut off by the high mountain ranges which face the ocean along its entire extent, 

 is very imperfectly supplied with moisture. It is a region of light, uncertain, and unequally distributed rainfall, 

 heavier at the north, as upon the coast, and decreasing gradually with the latitude in neiirly the same proportion. 

 This entire region is composed of a mass of mountain ranges with a general north and south trend, separating long 

 and generally narrow valleys. The precipitation of moisture within the interior region is largely regulated by the 

 position of the mountain chains. Warm currents ascending their sides become cold and are forced to deposit the 

 moisture they contain. It follows that, while the interior valleys are rainless or nearly so, the mountain ranges, 

 and esi)ecially the high ones, receive during the year a considerable precipitation of both rain and snow. If the 

 distribution of the forests of any region is dependent upon the distribution and amount of moisture it receives, 

 forests exceeding in density those of any other part of the continent would be found upon the northwest coast; 

 they would gradually diminish toward the south, and entirely disapi)ear near the southern boundary of the United 

 States, while the forests of all the interior region, from the summit of the principal Coast Kanges to the eastern base 

 of the Rocky mountains, woul.? be confined to the flanks and summits of the mountains. These forests would be 

 heavy upon the high ranges, especially toward the north ; they would disappear entirely from the valleys and 

 low mountain ranges. An examination of the forests of the Pacific region will show that in general distribution 

 and density they actually follow the distribution of the rainfall of the region. These forests well illustrate the 

 influence of moisture upon forest growth. Witliin the Pacific region the heaviest and the lightest forests of the 

 continent coexist with its heaviest and lightest rainfall. 



The forests of the Pacific region may be considered under four divisions : the Northern Forest, the Coast 

 Forest, the Interior Forest, and the Mexican Forest (Map No. 2, portfolio). 



