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Introduction

New Mexico's rangelands can generally be divided into grasslands, shrublands, woodlands, and forests. The accompanying map shows the wide diversity of range types within these broad categories. Eastern New Mexico is gently rolling in topography while central, northern and western portions of the state are characterized by rugged mountain terrain. These topographic variations result in diverse patterns of precipitation, temperature, and vegetational patterns.

Grasslands
The plains grassland, broadly defined, encompasses nearly 1/4 of the state's rangelands, mostly on the eastern side. Here it represents an extension of the short-grass prairie on the central U. S. Blue grama (Bouteloua gracilis) is the dominant species throughout the type. It occurs on many topographic positions and elevations. Another warm-season species buffalo grass (Buchloe dactyloides) is associated with blue grama in the northeast and east-central portion of the state. Western wheatgrass (Agropyron [now Elymus] smithii) occurs in swales on heavier soils and in northern grassland areas. Cool season species include New Mexico feathergrass (Stipa neomexicana) and needle-and-thread grass (Stipa comata). Galleta (Hilaria [now Pleuraphis] jamesii) is also common in northwestern grasslands as part of the Great Basin elements. Broom snakeweed (Gutierrezia sarothrae), a half-shrub, is common following drought or on areas grazed heavily by livestock. Yuccas are also common components of these grasslands. Annual precipitation varies from over 20 inches (about 50 cm) in Union County in northeast New Mexico to less than 14 in (about 33 cm) in Lincoln county in central New Mexico. Precipitation is generally low in the spring and high in the summer when warm season species make most of their growth. In the southern portion of the state, desert grasslands occupy low-lying areas on about 20% of the rangelands of the state. On the uplands, black grama (Bouteloua eriopoda) was dominant, but has declined in abundance because of drought and heavy livestock grazing. Now mesa dropseed (Sporobolus flexuosus) and several three-awn species (Aristida) are dominant on many sites. In addition shrubs such as mesquite (Prosopis glandulosa) and creosotebush (Larrea tridentata have encroached onto desert grasslands. Forbs such as leatherweed croton (Croton corymbulosus), desert baileya (Baileya multiradiata) are common in desert grasslands. Broom snakeweed is also widespread in these grasslands. Annual precipitation varies from less than 9 in (23 cm) in parts of Doņa Ana County to nearly 14 in (35 cm) in Eddy County. In some areas of higher rainfall, there is a transition from desert grassland to plains grassland. Mountain grasslands are the smallest grassland type in the state with less than 15% of the rangelands occupied with this grassland type. These grasslands generally occur as small patches within forests above 8500 ft (2900 n), Many of the grasses in mountain grasslands are cool-season. Festuca, Muhlenbergia, Poa, Koeleria, and Deschampsia are important genera. Annual precipitation may approach 25 in (64 cm) at higher elevations.

Shrublands
Desert shrubs in southern New Mexico occupy about 19% of the total rangeland area of the state. Mesquite (Prosopis glandulosa) and creosotebush (Larrea tridentate) are the two dominant woody species on upland areas while tarbush (Flourensia cernua) is more restricted to low-lying areas with fairly heavy soil. Desert shrubs have encroached onto grasslands in the past 100 years throughout southern New Mexico. Factors related to this increase are in dispute, but livestock grazing, drought, small mammal activities, reduction in extent and severity of wildfires, and introduction of alien species are probably involved. In northern New Mexico, sagebrush occurs on less than 3% of the rangeland area of the state. Density of sagebrush varies depending on intensity of livestock grazing and other environmental factors. Important understory species include galleta, Indian ricegrass (Oryzopsis hymenoides), and blue grama. The major woody species is big sagebriush (Artemisia tridentata). This type is likely an extension of Great Basin vegetation.

Woodlands
Woodland vegetation in New Mexico consists mainly of piņon-juniper woodland and juniper savanna, depending of the amount of Rocky Mountain piņon (Pinus edulis) and density of trees. The main juniper species are one-seed (Juniperus monosperma) and alligator juniper (J. deppeana) in central and western New Mexico. Rocky mountain (J. scopulorum) and Utah juniper (J. osteosperma) occur in northern New Mexico. Understory species are quite varied depending on tree spacing, elevation, precipitation, and other environmental variables. Blue grama is the most widespread species, but often occurs in open spaces rather than under tree canopy. Wolftail (Lycurus setosus), Chihuahua lovegrass (Eragrostis erosa), several species of Muhlenbergia, and piņon ricegrass (Piptochaetium fimbriatum) are other important grass species. Important shrubby species include Mountain mahogany (Cercocarpus montanus), algerita (Berberis haematocarpa), Wright's silktassel (Garrya wrightii)) and wavyleaf oak (Quercus undulata). Several other oak species are important, especially in western New Mexico.

Forests
Ponderosa pine (Pinus ponderosa) forests provide habitat for livestock and many other wildlife species including birds. The other forest types at high elevations are less important as rangelands although they are grazed to some extent by livestock and other wildlife species. In ponderosa pine forests Arizona fescue (Festuca arizonica) and mountain muhly (Muhlenbergia montana) are important forage species, but many other grasses and forbs occur in the understory along with many shrubs such as Gambel oak (Quercus gambelii.). The abundance of herbs and shrubs depends on the canopy cover of trees and other environmental factors. Reduction of wildfire frequency and extent has changed the character of ponderosa pine forests across the Southwest, and many believe has increased the likelihood of catastrophic fires.

Land Ownership
New Mexico is considered a public land state although nearly 50 % of the state is in private ownership. The Bureau of Land Management is the single largest land owner with 16.5% of the state followed closely by the Forest Service (12.0%) and the state (11.9%). Other entities include Indian Trust Lands (9.6%), National Parks and Monuments, military reservations, and other miscellaneous owners. Often there are small parcels within larger blocks with different ownerships. Such "checkerboard" patterns make integrated management difficult. Land exchanges have been implemented in some cases to help resolve these problems.

For additional information on rangelands of New Mexico, the following publications are recommended:
Allred, K. W. 1996. Vegetative changes in New Mexico rangeland. In:Herrera, E. A. and L. F. Huenneke (eds.). New Mexico's natural heritage: Biological diversisty in the land of enchantment. New Mex. J. Sci. 36:168-231.
Dick-Peddie, W. A. 1993. New Mexico vegetation past,present, and future. Univ. New Mex. Press. Albuquerque, NM.
Donart, G. B., D. Sylvester, and W. Hickey. 1978. A vegetation classification system for New Mexico, U.S.A. In: Hyder, D. N. (ed.). Proc. First International Rangeland Congr. Pp. 488-490. Soc. Range Manage. Denver, CO.