Physiognomy and Structure: This upland shrubland is typically dominated by a moderate to dense evergreen sclerophyllous shrub canopy usually less than 3 m tall. Herbaceous layers may be present and are typically dominated by perennial graminoids.

Floristics: The vegetation is characterized by a moderate to dense evergreen shrub layer less than 3 m tall that is dominated by the scrub oaks (Quercus turbinella, Quercus intricata, and Quercus toumeyi) along with wide diversity of other sclerophyllous shrubs that include Ceanothus greggii, Cercocarpus montanus var. paucidentatus, Garrya wrightii, and Rhus trilobata, with Arctostaphylos pringlei and Arctostaphylos pungens at higher elevations (Carmichael et al. 1978). In desert chaparral stands in the western extent, Arctostaphylos glauca, Arctostaphylos patula, Cercocarpus montanus var. glaber, Garrya flavescens, Juniperus californica, and Nolina parryi, Quercus cornelius-mulleri, Rhamnus ilicifolia, and Rhus ovata, characterize this shrubland (Keeler-Wolf 2007). Scattered remnant pinyon and juniper trees may be present; however, in the western Mojave, Juniperus californica sometimes forms an open, shrubby tree layer over the evergreen oaks and other shrubs (Keeler-Wolf 2007). In the eastern extent, stands in the Chihuahuan Desert mountains and the Sierra Madre Oriental are dominated by evergreen shrub oak species, such as Quercus mohriana, Quercus pungens, and Quercus vaseyana, and several widespread chaparral species, such as Arctostaphylos pungens, Ceanothus greggii, Cercocarpus montanus, Eriodictyon angustifolium, Fallugia paradoxa, and Garrya wrightii. Other Madrean Orientale species include Arbutus xalapensis (= Arbutus texana), Fraxinus greggii, Fendlera rigida (= Fendlera linearis), Garrya ovata, Juniperus pinchotii, Purshia mexicana, Rhus virens var. choriophylla (= Rhus choriophylla), Salvia lycioides (= Salvia ramosissima), Salvia roemeriana, and Salvia regla (Brown 1982a). The herbaceous layer is variable, but is generally composed of perennial grasses, such as Achnatherum speciosum, Bouteloua curtipendula, Bouteloua hirsuta, Bothriochloa barbinodis, Eragrostis intermedia, Lycurus phleoides, Muhlenbergia emersleyi, and several species of Aristida, which are largely restricted to rocky, protected areas because of past heavy livestock grazing (Brown 1982a).

Dynamics:  Many of the communities in this macrogroup are dominated by fire-adapted shrubs. Quercus cornelius-mulleri sprouts vigorously from root crowns after fire. Since Quercus cornelius-mulleri chaparral occurs in areas of lower rainfall and sparser vegetation cover, it typically has less frequent fire and slower recovery rates than typical cismontane chaparral types elsewhere in California. Quercus turbinella in Arizona and New Mexico is a fire-type; it sprouts vigorously from the root crown and rhizomes. Typical fire intervals in Arizona exceed 74 years (Reid et al. 1999, Tirmenstein 1999d). Plants in the New York Mountains of California are treelike, suggesting that fires have been absent for perhaps greater than 100 years. Instead, flooding has initiated stem breakage and sprouting of some canyon bottom stands. Ceanothus greggii is an obligate seeder and germinates from seed after fire, and older stands will lose dominance of this shrub to other longer-lived sprouting shrubs.

Site conditions aside, the dynamics of fire within chaparral are still complex. In southern California, it has been suggested that the even-aged and large size of modern chaparral patches are a function of 20th century fire suppression feedbacks whereby intensive suppression has led to large fuel buildups over large areas of landscape leading to large stand-replacement fires of ever increasing size (Minnich 1983, 2001). Others contend that the large patch patterns are within that natural range of variability, and that they are driven more by climate trends, prevailing weather patterns, increased human ignition frequencies with increased population density, changes in land use, and landscape characteristics rather than suppression (Keeley and Fotheringham 2001a, 2001c, Moritz 2003). The pattern of chaparral distribution in southern New Mexico suggests that the latter scenario might be the case here. Because of the rugged country, effective suppression has been minimal. Hence, the large patches of chaparral may be representative of a more or less natural fire regime, but one possibly modified by increased human caused fires and fire suppression on neighboring forested lands. More frequent, intense fires leads to the decline of the grassy woodland savannas on the ridge top summits and a favoring of shrublands (possibly enhanced by increased fine fuels with the cessation of livestock grazing). In this type of fire regime, Keeley and Fotheringham (2001a) and Moritz (2003) contend that prescribed burning may be useless or even harmful and that fire suppression, at least in the short term, may be more appropriate for maintaining an ecosystem near its natural state. Minnich (2001) would likely argue the opposite saying it is fire suppression that generates the large patch pattern and that prescribed fire is needed to restore a small patch mosaic with imbedded natural fuel firebreaks. Detailed fire history studies that focus on chaparral patch age structure in a landscape context would be useful (and perhaps necessary) to help resolve these conflicting viewpoints and generate management options that are tailored to interior chaparral.

At the other end of the elevation spectrum, repeated burning of chaparral, particularly Pinchot juniper, has been suggested as a way to increase grass cover in shrubland communities (Ahlstrand 1982). Most of our understanding of how to manage of Pinchot juniper comes from the high Plains of Texas where it is seen as an invader of fine textured plains grasslands soils, and where management has focused on control and eradication to increase livestock forage. Research from the high plains indicates that the effectiveness of fire in controlling Pinchot juniper is a function of fire intensity, climatic conditions and position of the bud zone above or below the soil (Steuter and Britton 1983). Fire was particularly effective in inducing mortality in young plants with exposed buds on rocky sites, but this dropped off significantly with older plants. In addition, increased grass cover (grama grasses) can inhibit reproduction (Smith et al. 1975). As Ahlstrand (1982) has shown, fires can lead to at least short-term increases in grass cover, but because Pinchot juniper can recover 50% or more of its original cover within six or seven years of a burn, repeated prescribed fires at 10- to 15-year intervals would be needed to sustain a grassland type.