Tree canopy is usually open or interrupted and singularly layered. This cover type often grades into forests at its upper boundary and into semi-arid grassland below. Winter deciduous and generally found at elevations below 1,200m. Semi-arid grasslands are generally positioned in elevation between evergreen woodland above and desertscrub below. Within the San Pedro river basin this community is often dominated by one of at least three species, i.e. creosotebush, tarbush, and whitethorn acacia.
Many desertscrub species are drought-deciduous.
Riparian Vegetative communities adjacent to perennial and intermittent stream reaches. Trees can potentially exceed an overstory height of 10m and are frequently characterized by closed or multi-layered canopies depending on regeneration. Species within the San Pedro basin are largely dominated by two species, i.e. cottonwood and Goodding willow. Riparian species are largely winter deciduous. In the San Pedro River basin these are primarily found along the upper terraces of the riparian corridor and are dominated by hay and alfalfa.