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Table 1. Land cover class descriptions for the Upper San Pedro Watershed
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Forest |
Vegetative communities comprised principally of trees potentially over 10m in height and typically characterized by closed or multi-layered canopies. Species in this category are evergreen (with the exception of aspen), largely coniferous (e.g. ponderosa pine), and restricted to the upper elevations of mountains that arise off the desert floor. |
|
Oak Woodland |
Vegetative communities dominated (>30% total cover) by evergreen trees (Quercus spp.) with a mean height usually between 6 and 15m. 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. |
|
Mesquite Woodland |
Vegetative communities dominated by leguminous trees (Prosopis spp.) whose crowns cover 15% or more of the ground often resulting in dense thickets (30-75% total cover). Historically maintained maximum development on alluvium of old dissected flood plains; now present without proximity to major watercourses. Winter deciduous and generally found at elevations below 1,200m. |
|
Grassland |
Vegetative communities dominated by perennial and annual grasses (>35% total cover) with occasional herbaceous species present. Trees and shrubs do not exceed 20% of the total cover. Generally grass height is under 1m and they occur at elevations between 1,100 and 1,700m; sometimes as high as 1,900m. This is a landscape largely dominated by perennial bunch grasses separated by intervening bare ground (45-50% total cover) or low-growing sod grasses and annual grasses with a less-interrupted canopy. Semi-arid grasslands are generally positioned in elevation between evergreen woodland above and desertscrub below. |
|
Desertscrub |
Vegetative communities comprised of short shrubs with sparse foliage (>35% total cover) and small cacti that occur between 700 and 1,500m in elevation. 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. Individual plants are often separated by significant areas of barren ground (40-45% total cover) devoid of perennial vegetation. 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. |
|
Agriculture |
Crops actively cultivated (and irrigated). 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. They are minimally represented in overall extent (less than 3% total cover) within the basin and are irrigated by ground and pivot-sprinkler systems. |
|
Urban |
This is a land-use dominated by small ejidos (farming villages or communes), retirement homes, or residential neighborhoods (Sierra Vista). Heavy industry is represented by a single open-pit copper mining district near the headwaters of the San Pedro River at Cananea, Sonora (Mexico). |
|
Water |
Sparse free-standing water is available in the watershed. This category would be mostly represented by perennial reaches of the San Pedro and Babocomari rivers with some attached pools or repressos (earthen reservoirs), tailings ponds near Cananea, ponds near recreational sites such as parks and golf courses, and sewage treatment ponds east of the city of Sierra Vista, Arizona. |
|
Barren |
A cover class represented by large rock outcropping or active and abandoned mines (including tailings) that are largely absent of above-ground vegetation. |
