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NATURALIST'S GUIDE TO THE AMERICAS 



original arid deciduous forest of this 

 part of Yucatan has disappeared. 



In some parts of the tropical zone 

 small sections of original forest are cut 

 and cleared by burning during the dry 

 season. With the opening of the rain 

 season these are planted to corn, beans, 

 and other crops which owing to the 

 absence of competing vegetation mature 

 with little or no further attention. The 

 second year some cultivation is required 

 as intrusive non-forest plants are begin- 

 ning to secure a foothold. The third 

 year the clearing is often abandoned 

 owing to an exuberant growth of her- 

 baceous and shrubby vegetation with 

 which the ordinary native and his 

 primitive tools can not cope. At this 

 stage he often prefers to fell more 

 forest, leaving the cleared area to 

 revert through a succession of dominant 

 plant types leading again after many 

 years to a climax, or near-climax forest. 

 It is evident that in this manner, piece 

 by piece, a very large share of the area 

 covered by the present extensive for- 

 ests of tropical Mexico has at some time 

 been brought under cultivation by man; 

 and vast areas lost their original forests 

 by clearing many centuries ago. 



Fires started by lightning and by 

 human agency have had a profound 

 effect in limiting forest growth, espe- 

 cially along the Sierra Madre Occidental 

 and on the mixed savannas and arid 

 deciduous forested plains along the west 

 coast. While vast bodies of timber 

 remain uncut there has been, aside from 

 general clearing, much destruction of 

 forest through lumbering operations, 

 especially in connection with the devel- 

 opment of the vast mining industry of 

 Mexico. The tropical forests of the 

 Atlantic watershed have been exploited 

 for the more valuable timber, such as 

 Spanish cedar, mahogany and logwood 

 until most of the supply within easy 

 reach of navigable streams has been 

 removed. Forest products of the same 

 region include rubber from the rubber 

 tree Castilla elastica, and chicle, the 

 basis of most of the chewing gum of 

 commerce, from Achras zapota. The 



process of gathering these gums tends 

 to exhaust the trees, causes premature 

 decay and finally their destruction. 



Some of the largest marshes including 

 those in the Valley of Mexico and the 

 Laguna de Chapala in Jalisco are re- 

 ported to have been partially drained 

 within recent years, one result being 

 the obliteration of extensive breeding 

 and feeding grounds for many thousands 

 of migratory and non-migratory water- 

 fowl. This drainage is serious in its 

 effect on water fowl and other aquatic 

 animal life, especially in view of the 

 fact such water areas are very limited 

 in extent in the region under review. 



As elsewhere much of the larger game 

 has disappeared over extensive areas 

 due to human occupation of the country. 

 Those especially affected have been the 

 antelope, mule deer, and mountain 

 sheep. The sparse settlement of the 

 country, however, has permitted these 

 game animals to continue their exist- 

 ence in the less frequented sections and 

 efforts are being made by the Mexican 

 government through presidential de- 

 crees and recently enacted game laws to 

 protect them. Little organized effort 

 has been made to control predatory 

 animals, but wolves formerly very de- 

 structive to domestic stock apparently 

 have been exterminated in the southern 

 part of the high plateau region. 



III. Accessibility of Natural Areas 



The railroad system of Mexico sup- 

 plemented by stage lines affords, under 

 normal conditions, easy access to many 

 interesting regions, but owing to the 

 rugged character of the country many 

 others can only be reached by under- 

 taking rather long trips with pack out- 

 fits. The principal gateways on the 

 north are by rail through Nogales, El 

 Paso, Ciudad Porfirio Diaz, Laredo and 

 Brownsville. The route through No- 

 gales affords access to much of the west 

 coast region, and a connection through 

 Jalisco with the main system of the 

 Republic. A railroad across the Isth- 

 mus of Tehuantepec connects the sea- 

 ports of Coatzacoalcos (now Puerto 



