NATURAL AREAS AND REGIONS 



503 



for much of the topography of the region, 

 while in the sand areas, as the sand dunes 

 of Padre island, the wind is all impor- 

 tant, keeping the sands so constantly 

 in motion that vegetation is nearly 

 impossible. 



8. Climate 



As the topography is varied, so is the 

 climate. Over most of the state the 

 climate is mild, healthful and pleasant. 

 The summers are very long, and, near the 

 coast, at least, considerably tempered by 

 the gulf winds. The winters are not 

 severe except in the high northern por- 

 tions, where the cold becomes intense. 

 Thus at Brownsville, according to Gree- 

 ley, a light frost (but a serious one!) 

 occurs about once in four years, while at 

 Amarillo, on the Staked Plains, a severe 

 winter brings a biting cold and a drop to 

 the neighborhood of -20. The entire 

 state, except the extreme western por- 

 tion, is affected during the winter 

 months by severe and extremely sudden 

 drops of temperature, known locally as 

 "northers," during which spells a drop of 

 50 or more within a very few minutes 

 is common. Rainfall varies greatly, 

 and is of great importance to the distri- 

 bution of plants and animals, both be- 

 cause of its presence and because of its 

 absence. There is a general decrease in 

 rainfall from the east to the west. Thus 

 the forests of the eastern limits of the 

 state have an annual rainfall exceeding 

 50 in., while on the staked plains 15 in. 

 is about normal. This decreases still 

 more to the southwest, where from 7 to 

 10 in. is considered a "wet" year. Fur- 

 thermore, it must be remembered that in 

 some regions this precipitation is peri- 

 odic, and this periodicit}' is again of 

 importance. In Kinney County, in 

 southwestern Texas, March, April and 

 May have a total mean precipitation 

 of only 1.1 in. out of a total of 23.4 in. 

 for the year; Crosby County, in the 

 northwest, has 1.9 in. during December, 

 January, February and March; El Paso, 

 in the extreme southwestern corner, has 

 but 0.9 in. during March, April and May. 

 It can be seen at once that such varied 



precipitation must have a profound in- 

 fluence on the biota, and we find, there- 

 fore, a gradation in the flora and fauna 

 ranging from the southeastern conifer 

 forest type to arid desert. 



II. ORIGINAL BIOTA 



From an ecological viewpoint, Texas, 

 the largest state in the Union, is of 

 primary interest. Within the 265,896 

 sq. mi. of territory which compose it 

 lie conditions of great diversity. This 

 diversity is due not so much to the size 

 of the state as to its geographical posi- 

 tion, its varied climate and diversified 

 topography. Within its boundaries 

 faunistic and floristic elements of east 

 and west, of north and south meet and 

 overlap, producing a biotic complex 

 probably exceeded by no other state. 

 This complexity is further increased by 

 the extension of the major floristic divi- 

 sions^-encroachments one upon another 

 producing a great variety of local con- 

 ditions that are certain to confuse the 

 ecologist unless he is aware that such 

 conditions are mere local aspects of a 

 larger unit. Such local conditions are 

 well illustrated in the mesquite semi- 

 desert of southern Texas, and in the 

 Rio Grande succulent desert, where local 

 aspects of other larger units are found as 

 extensions up river valleys. Through- 

 out the state there is a beautiful transi- 

 tion from the southeastern coniferous 

 forest with its rainfall of over 50 in. 

 annually to the desert conditions of the 

 trans-Pecos, with an annual rainfall of 

 less than 7 in., and a similar transition 

 from the low marshes of the gulf coast to 

 the mountains of igneous rock in the 

 Guadaloupe range. Due to the fact 

 that Texas has such a large area, coupled 

 with a population that is scattered, there 

 once was much big game within its 

 limits, and a considerable amount still 

 remains, though in constantly decreas- 

 ing abundance. 



In the following discussion an attempt 

 has been made to divide Texas into its 

 natural ecological areas, based on floris- 

 tic composition as outlined by Shreve 

 and by Bray, and to correlate with these 



