6 FOREST TREES OF NORTH AMERICA. 



beyond the western limits of the prairie as here laid down, the 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 (Map No. 1, portfolio). 



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



A group of arborescent species of West Indian origin occupies the narrow 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 islands of high ground situated in the savannas which cover a great portion 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 north. It is rich in composition ; 

 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 speeies, however, attain respectable proportions; the mahogany, the mastic, the royal palm, 

 the mangrove, the sea-grape, the Jamaica dogwood, the manchineel, 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 soutli ward 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 Rio Grande. The Mexican forest belt of Texas 

 extends from the valley of the Colorado river, near the ninety-eighth meridian, to the Rio 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 moisture, is open, stunted, and comparatively of little value. 

 It is characterized by enormous areas covered with chaparral (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 along 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 the Rio Grande abounds in different speciesof Acacia, Leucccna, and other 

 Mexican LegwminotfBj and farther west, upon the dry plains of the Presidio, the Spanish bayonet (Yucca baccata) 

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



THE PACIFIC REGION. 



The Pacific forest region is coextensive with the great Cordilleran Mountain system of the continent. Thecauses 

 which have influenced the present position and density of these forests must be sought in the peculiar distribution 

 of the rainfall of the region. The precipitation of moisture upou 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 otf 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 upou the coast, and decreasing gradually with the latitude in nearly 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 especially the high ones, receive during the year a considerable precipitatioii 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 disappear near the southern boundary of the United 

 States, while the forests of all the interi >r region, from the summit of the principal Coast Ranges 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. Within 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). 



