Soil-vegetation Patterns in the Central Peloncillo Mountains, New Mexico

soils and land forms in the central Peloncillo Mountains are described. Piedmont desert grassland (dominated by low shrubs, species of Bouteloua, and other grasses) is wide- spread on both erosional and depositional soils of foothills and lower elevations. Madrean oak woodlands (dominated by evergreen species of Quercus) are found on depositional soils. At higher elevations are interior chaparral (dominated by evergreen sclerophyll shrubs) and pinyon-juniper woodlands {Pinus cembroides, Juniperus deppeana, J. mono- sperma) . The former, mostly of southerly sites, occupy droughty soils on either stable or erosional surfaces; the latter, on northerly sites, are identified with erosional soils. At subgroup and family classification levels mollisols, aridisols and entisols are related to vegetational pattern. Soil drainage, water storage capacity, depth to bedrock, and degree of stability are important features of each soil. Successional sequences on steeper slopes are hypothesized on the basis of changing soil properties. A rock land vegetation comprises the ultimate desertification of the landscape. Erosion control appears to be the most serious resource management problem. Introduction The Peloncillo Mountains extend from near the Mexico border northward ca. 110 km (70 miles) along the New Mexico-Arizona line. They are one of a series of ranges in the Mexican Highlands section of the Basin and Range Physiographic Province (Wilson, 1962). Several biogeographically important features of this range sparked my interest in vegetation and soils. The long axis of the Peloncillo Mountains is doubtless a major migratory corridor between the Sierra Madre Occi- dentale and the Mogoll?n Plateau. The main intrusions of Sierra Madrean floristic elements in southwestern United States occur in the vicinity of the Peloncillo Moun- tains and adjoining valleys and ranges of New Mexico and Arizona (Wagner, 1977). On an E-W axis this chain of low peaks (elevations mostly under 2100 m) is the meeting place of numerous plants of deserts and steppes. Mosaics of piedmont desert grassland, Madrean woodland and interior chaparral plant communities are found. In many ways this range is typical of numerous minor, primarily steppic low moun- tains on both sides of the U.S.-Mexico border. Few of these have been studied ecologically. Existing knowledge of soil and vegetation relationships is very gener- alized (Soil Conservation Service, 1973). It has been suggested that grasslands in this region have been disappearing since the advent of the white man?by conver- sion to desert at lower elevations and encroachment of woody species from chaparral and woodlands at the higher elevations. Erosion has been given as a possible at- tendant and causal process of the loss of grasslands, particularly in mountain topog- raphy. I find little data to substantiate this hypothesis, but vegetation and soil patterns in the Peloncillo Mountains presented an excellent study area. Such study begins with descriptions of existing soils and vegetation, which are presented here. In this paper I discuss soil-geomorphic relations, erosion and deposition, and the vegetation currently existing on the variety of soil types (Gil?, 1975a; Buoi, 1966). Study Area My study includes that portion of the Peloncillo Mountains between Peloncillo Peak (31? 33' ? Lat; 109? 5' W Long) and Owl Canyon (31? 46' ? Lat), ca. 24 km along the mountain axis. Most investigations centered around Post Office Canyon and vicinity, about 11-15 km SE of Rodeo, New Mexico. The entire area consists of rhyolite-welded tuff and related volcanics deposited primarily as ash-flow sequences in early- to mid-Miocene (Marjaniemi, 1969). Intricate faulting of these 317