COMMUNITY-LEVEL PATTERNS

ERDC TR-04-1

4.2

COMMUNITY-LEVEL PATTERNS

Minckley and Brown (1994) described and classified the riparian biotic

communities of the southwestern U.S. and northwestern Mexico. At the most

general level they identified four wetland biotic communities in this region:

Arctic-Boreal Wetlands, Cold-Temperate Wetlands, Warm-Temperate Wetlands,

and Tropical-Subtropical Wetlands. The four major communities can be

subdivided into seventeen series, which can be further subdivided into more

specific associations based on species assemblages (Table 12). For example,

Szaro (1990) identified 28 riparian plant community types on perennial streams

in the mountains of New Mexico and Arizona within the Interior Riparian

Deciduous Forest: Mixed Broadleaf Series and the Montane Riparian Wetlands:

Deciduous Forest of Minckley and Brown (1994) (Table 12). These included

communities dominated or co-dominated by Acer negundo (boxelder), Populus

angustifolia (narrrowleaf cottonwood), Juglans major (walnut), Fraxinus

velutina (ash), Platanus wrightii (sycamore), Populus fremontii (Fremont

cottonwood), Salix gooddingii and S. bonplandiana (willows), and Sapindus

saponaria (soapberry), among others. Similarly, Durkin et al. (1995) identified

58 community types within the riparian and wetland vegetation of the upper and

middle Rio Grande in New Mexico. These included communities dominated or

co-dominated by P. angustifolia, Alnus incana (thinleaf alder), Salix spp., Alnus

oblongifolia (Arizona alder), P. deltoides (Rio Grande cottonwood), Tamarix

spp. (saltcedar), Eleaegnus angustifolia (Russian olive), J. major, P. wrightii, and

P. fremontii, among others (Durkin et al. 1995). Although such detailed commu-

nity classification schemes provide valuable information, a coarser level of sub-

regional community delineation will be more useful in efforts to determine

general vegetative indicators of the ordinary high water mark.

Elevation is probably the most important factor distinguishing riparian plant

communities of the arid southwest at a sub-regional scale (Szaro 1990, Bendix

1994, Minckley and Brown 1994). Elevation influences the distribution of the

biotic communities described by Minckley and Brown (1994). For example,

Arctic-Boreal Wetlands are restricted to subalpine environments in the arid

southwest. In central Arizona the Mixed Broadleaf Series of the Interior Riparian

Deciduous Forest Association of the Warm-Temperate Wetland community type

occurs at mid-elevations, while the Populus-Salix and Prosopis Series of the

Sonoran Riparian Deciduous Forest Association of the Tropical-Subtropical

Wetland community type occur at relatively low elevations (Minckley and

Brown 1994). For the present purpose a first-order distinction between two

elevation zones provides a useful framework for considering sub-regional