A-7 Ranch, Bellota Redington Pass area

Arid Lands Resource Sciences 642
Spring 2000

USE AND MANAGEMENT OF ARID LANDS

Adapting land use to climate variability in arid lands:
Ranching and the concept of grass banks in southern Arizona


IV. Vegetation, Fire, and Climate History

 

Kathryn Mauz, Rick Krenzer, and Luis Cervera

[Excerpt by RNH, June 23, 2007]

4.4. SEMIARID GRASSLAND AND OAK-SAVANNA VEGETATION IN SOUTHEASTERN ARIZONA

4.4.1. Regional Biogeographic Setting

The semidesert grassland in southeast Arizona is contiguous with the Chihuahuan desert and is probably allied more with the Chihuahuan than the Sonoran biome, although this community may be found with Sonoran Desert taxa at its western limits (Brown, 1994). At a regional scale, the Redington Pass area and A-7 Ranch occur near the northwestern limit of this vegetation community. Here, the semidesert grassland occurs between about 1100 m and 1400 m (3600-4600 feet) elevation (Brown, 1994), with transitions to Madrean Woodland above in the foothills of the Santa Catalina and Rincon Mountains and to Arizona Upland and Chihuahuan Desertscrub vegetation communities below in the lower San Pedro River valley. These transitions may be complex, reflecting elevational, spatial, topographic, and edaphic gradients underlain and structured by Basin-and-Range bedrock and surficial geology, and local and regional climatic patterns.

 

4.4.2. Vegetation Communities in the Area of the A-7 Ranch

Regional-scale vegetation maps that include southeastern Arizona have been developed by Brown and Lowe (1994), the USDA Natural Resource Conservation Service (NRCS), and as part of the Arizona Gap Analysis Project (GAP) (see Hobbs, 1999). The vegetation types identified for the area including the A-7 Ranch are summarized in Table 4-2. A portion of the NRCS Major Land Resource Areas map is included as Figure 4-10.

Table 4-2. Correlation of vegetation communities for the area of the A-7 Ranch as defined in three regional vegetation maps.

 

Figure 4-10. USDA-NRCS Major Land Resource Areas in southeast Arizona,with the location of the A-7 Ranch indicated (NRCS,1999).

 

Quimby (1976) reported four species of grama grasses (Bouteloua chondrosioides, B. hirsuta, B. curtipendula, B. filiformis) as the primary forage grasses on the Bellota grazing allotment of the Coronado National Forest, an area of about 36,000 acres that straddles Redington Pass and borders the A-7 ranch on the west. Other important forage plants on the allotment at that time included fairy duster (Calliandra eriophylla), ratany (Krameria spp.), and shrubby buckwheat (Eriogonum wrightii), along with minor amounts of several other grasses (Quimby, 1976). Scrub-shrub taxa are diverse and, along with both stem and leaf succulents, are present in all areas of the A-7 Ranch. Arboreal taxa, notably velvet mesquite (Prosopis velutina) may be common, as well, and oak-savanna vegetation (NRCS Oak-Savanna and GAP Encinal Mixed Oak) may occur as the upper elevation transition to Brown's (1994) Madrean Woodland.

In the Redington Pass area, oak-savanna species include oaks (Quercus oblongifolia, Quercus emoryi) and juniper (Juniperus sp.), along with several chaparral-shrub taxa (e.g., Arctostaphylos pungens, Garrya wrightii) that become more common at higher elevations (see Figure 4-11b). Leaf succulents at upper elevations on the Bellota Ranch include Agave schottii, Agave palmeri, Nolina microcarpa, Dasylirion wheeleri, and Yucca sp. Descending into semidesert grassland and Sonoran-Chihuahuan desertscrub communities of the San Pedro River valley (see Figure 4-11a), creosote bush (Larrea divaricata subsp. tridentata) becomes ubiquitous, ocotillo (Fouquieria splendens) and soaptree yucca (Yucca elata) appear, and saguaro (Carnegiea gigantea) is increasingly common, particularly on alluvial surfaces, in the grassland. Woody vegetation of wash margins, seeps, and occasionally swales may include the shrubs Acacia constricta, Acacia greggii, Zizyphus obtusifolia, and Celtis pallida, the trees Cercidium floridum and Cercidium microphyllum (at mid- to lower elevations), Celtis reticulata (all areas), and, uncommonly, broad-leaf deciduous trees (e.g., Populus sp.) in well-watered drainages and at lower elevations.

 

Malusa and Porter (1990) surveyed canyon vegetation on and peripheral to the A-7 ranch (e.g., Figure 4-11c). These canyons and others are illustrated in Figure 4-12. The authors identified Arizona sycamore (Platanus wrightii), velvet ash (Fraxinus velutina), Goodding's willow (Salix gooddingii), Arizona walnut (Juglans major), and Fremont's cottonwood (Populus fremontii) along Buehman Canyon. Cottonwood, ash, and walnut were observed in Youtcy and Espiritu Canyons, and willow, along with cattail (Typha domingensis), were noted in Youtcy Canyon. The canyon bottom in Espiritu Canyon is described as supporting more xeroriparian species, including burrobush (Hymenoclea salsola), desert broom (Baccharis sarothroides), and, on hillsides, jojoba (Simmondsia chinensis). Roble Canyon has relatively fewer cottonwood and ash, but is notable for other riparian vegetation including maiden's hair fern (Adiantum cappilus-veneris). The authors emphasize that these riparian areas provide important habitat for several rare and endangered plants and animals, and serve as nurseries for young trees and sources of seed to support future recruitment. As such, potentially damaging land uses (e.g., mining, cattle grazing) should be minimized or eliminated in these canyons (Malusa and Porter, 1990).

 

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