Arizona’s Grasslands

Grassland systems around the world have great social, economic, and ecological value. Historically, grasslands occurred across one-third of Arizona—over 24 million acres. They have played an important role in the state’s history, provide unique wildlife habitat, and form the headwaters of rivers such as the Verde and San Pedro.

Grassland status and diversity

Grasslands in Arizona have changed considerably over the last 130 years. Based on a recent state-wide assessment,

• 31% of the state’s former grasslands are in good condition with native perennial grasses and low shrub cover
• 34% are shrub-invaded but have the potential to be restored
• 26% have crossed a threshold where former grasslands have transitioned to shrubland
• 9% are now dominated by exotic species
• 4% have low shrub cover but also little to no perennial grass

Southwest grasslands. Click image to enlarge.

These data may underestimate the extent of grassland change, particularly for grasslands imbedded within pinyon-juniper woodland and ponderosa pine forest, two areas not covered by our study but for which there has been considerable encroachment by trees.

Arizona grasslands—an important part of the southwestern grassland mosaic

Arizona’s grasslands are part of a large and diverse network of grasslands found throughout the southwestern U.S. and northern Mexico. Semi-desert grasslands in central and southeastern Arizona extend into New Mexico and Sonora, Mexico. Grasslands in northern Arizona share affinities with those found in the Great Basin and on the Colorado Plateau in Utah, Colorado, and New Mexico. Finally, high elevation grasslands – those in alpine areas and meadows interspersed within our conifer forests – are found throughout most of the mountain ranges of northern Arizona and New Mexico.

Grassland assessment

To better understand the extent and condition of southwestern grasslands, we initiated several studies to map and classify the status of grasslands across Arizona, southwestern New Mexico, and northern Sonora, Mexico. The study was done in two phases, first as part of our ecoregional assessment for the Apache Highlands Ecoregion and, second, as part of an assessment the Bureau of Land Management’s Fire Management Plans.

Those studies, along with a GIS data set containing the results of our state-wide grassland assessment, can be downloaded from this page. For more information on grassland studies see our page on Adaptive Management at the BLM’s Las Ciénegas National Conservation Area.

Inter-agency collaboration

Our grassland assessment was completed with assistance from subject experts within:

• BLM
• Natural Resources Conservation Service
• U.S. Forest Service
• University of Arizona
• Arizona State Land Department.
• New Mexico Natural Heritage Program
• Instituto Nacional de Investigaciones Forestales, Agricolas y Pecuarias
• Instituto del Medio Ambiente y el Desarrollo Sustentable del Estado de Sonora