Biomass Productivity and Range Condition on Range Sites in Southern Arizona

Abstract

Range condition is usually defined by similarity of current to climax or potential vegetation. It is often assumed that rangelands in low condition are biologically less productive than those in higher condition. The objective of this study was to determine if range condition (ecological status) is related to total productivity or to forage production for livestock. Adjacent areas along fencelines representing differences in range condition were sampled in 58 locations. These comparisons represented 31 different range sites across southern Arizona. Weight by species of above-ground peak standing crop current year's growth of vegetation was estimated using the dry-weight-rank/comparative yield methods. Range condition was rated with Soil Conservation Service range site descriptions. Species were classified as forage or non-forage to estimate forage available for cattle. In 75-85% of comparisons of good condition sites to fair condition, good to poor, and fair to poor, total current year's standing crop did not differ significantly. Where differences were significant, productivity was not consistently more on the high condition class. Forage production, however, was more from the stand in the higher condition class in about 213 of the comparisons. We concluded that in southern Arizona rangelands in higher condition (higher seral) classes usually produce more forage for cattle than lower condition classes on the same range site. Nevertheless, il is not usually true that total biomass productivity on low condition range is less than the same range site in higher condition.

New Concepts for Assessment of Rangeland Condition

“…Invasion of exotic species may increase diversity rather than decrease it (Johnson productive potential is not necessarily true. In Arizona range condition class was found to be correlated with livestock forage production but not to total biomass production across a wide cross section of range sites (Frost and Smith 1991). Much of our research and experience in revegetation throughout the West shows that "poor condition" ranges are as productive as ever if the "undesirable species" are removed and "desirable" ones reintroduced.…”

Mera Vejetasyonu Durumunun Zaman Serisi NDVI Verileri ile Belirlenmesi

“…Although productivity has been suggested as a measure of range condition, it is not a universally accepted indicator of rangeland health. For example, range condition assessment methods, which focus on the climax approach, are not indicative of changes in total biomass production of a rangeland (Frost and Smith, 1991). Moreover, some current methods of determining rangeland condition place more reliance on change in species composition than on site productivity.…”

Applicability of Montreal Process Criterion 2 — productive capacity — to rangeland sustainability

“…Often, but not always, late-sera1 sites have higher forage productivity than early seral sites (Uresk, 1990;Frost and Smith, 1991;Samuel and Hart, 1994). Differing seral conditions may be desired from a management standpoint depending upon management objectives (Uresk, 1990;Benkobi and Uresk, 1996).…”