Zonation of Vegetation within the Tularosa Basin, New Mexico

Abstract

The vegetation on two unusual substrates (lava and gypsum sand) is compared, and causative factors influencing distribution are dis- cussed. The Tularosa Basin in south central New Mexico provides a situa- tion which illustrates the interaction of several rigorous environ- mental factors in determining plant distribution. The north central part of the basin is an arid valley upon which two strikingly contrast- ing smaller environments are superimposed. One, a deposit of drifting gypsum, the Alamogordo White Sands, lies in the lowest part of the basin at the site of a Quaternary lake. The other, a lava bed, the Carrizozo malpais or badlands, believed to have been extruded within the past one thousand years, parallels the main axis of the basin, approximately the northern two-thirds lying within the Upper Sonoran and the lower third with the Lower Sonoran Zone. The lava flow extends at the southern tip to within 15 miles of the gypsum sand. The present paper analyzes the several causal factors determining plant distribution in the gypsum deposit, the neighboring lava flow to the north, and the alkaline plain surrounding these two areas. PHYSIOGRAPHY AND CLIMATE. - Bounded on the south by a low divide and on the three remaining sides by mountains, the Tularosa Basin is an internal drainage area approximately 40 miles wide with a long axis extending north and south for 150 miles. There are no permanent lakes or streams, flood waters discharged from the moun- tains being absorbed by the highly porous gypseous soil. The water table of the basin floor varies from 25 to more than 100 feet deep except in a small area west of the lava where it lies at around 200 feet (Meinzer and Hare, 1915). Somewhat west of the southern tip of the lava water emerges from the margin as the gypseous Malpais Spring. Annual precipitation varies with altitude, over a period of 23 years averaging 8.20 inches at 4,156 feet between the gypsum bed and the southern tip of the lava, but for the same period amounting to 11.37 inches at Carrizozo along the east margin of the lava toward the norther tip at an altitude of 5,438 feet (Benson, 1933).