• Airborne synthetic aperture radar analysis of rangeland revegetation of a mixed prairie

      Smith, A. M.; Major, D. J.; Hill, M. J.; Willms, W. D.; Brisco, B.; Lindwall, C. W.; Brown, R. J. (Society for Range Management, 1994-09-01)
      Microwave radar is a potentially useful tool for monitoring the condition of the rangeland. A study was conducted in a mixed prairie community at the Agriculture Canada Research Substation at Onefour, Alberta in 1991 to examine the effects of historical management on synthetic aperture radar (SAR) data obtained from 2 aircraft flights, 24 May 1991 and 1 August 1991. Ground-truthing expeditions were conducted on the same days to obtain estimates of vegetation amounts, species distribution and soil moisture. A former grazing experiment established in 1955 and abandoned 20 years ago enabled comparison of 3 grazing treatments, continuous, rotation and free choice superimposed on native range, crested wheatgrass (Agropyron cristatum (L.) Gaertn.) and Russian wildrye (Elymus junceus Fish.). The ground data and imagery were integrated in a Geographic Resource Analysis Support System (GRASS). Fields that had been cultivated and seeded to Russian wildrye had higher radar backscatter than native range. The radar backscatter from crested wheatgrass fields was similar to native range in May but higher than native range in August. Radar backscatter was positively correlated with number of years since seeding with Russian wildrye. Generally there was little difference in radar backscatter with grazing treatment. Correlation analyses between radar digital number extracted from the ground truth sites and vegetation and soil parameters revealed, depending upon swath mode, significant relationships between radar backscatter and the amount of certain grass species, radar backscatter and canopy moisture, and radar backscatter and soil moisture in May. A significant negative correlation was observed between radar backscatter from the August images, in both swath modes, and percent ground cover. The results of this study indicated a role for SAR imagery in evaluating range characteristics.
    • Changes in pinyon-juniper woodlands in western Utah's Pine Valley between 1933-1989

      Yorks, T. P.; West, N. E.; Capels, K. M. (Society for Range Management, 1994-09-01)
      Changes in woodland vegetation integrate the consequences of livestock grazing intensity, the alteration of fire regimes, and possible climate alterution, as well as other factors. Quantitative measurements of these changes, if taken over sufficient intervals, can allow evaluation of conservation management strategies. In 1933, vegetation along a 37-km transect in southern Pine Valley, Utah was described from circular 19-m2 plots located every 42 m. The major intermediate management treatment has been reduction of grazing pressure by introduced animals, although a fraction of the area was chained and burned in 1977. During a period climatically and phenologically similar to the original study, we reexamined representative segments of this transect by a more detailed updating of the original "square-foot-density" method. Significantly greater shrub and perennial grass covers (more than threefold increases) were found in 1989, even where overall dominance is still by pinyon-juniper [Pinus monophylla (Torrey & Fremont) and Juniperus osteosperma (Torrey) Little]. This change is more obvious on steeper slopes away from roads and water, where both human and livestock disturbances would be expected to be minimized. Except in the chained portion, the observed shifts in dominance/diversity are contrary to widely accepted expectations.
    • Observation: Cattle diets on excellent and good condition Chihuahuan desert rangelands

      Smith, G.; Holechek, J. L.; Cardenas, M. (Society for Range Management, 1994-09-01)
      Information is limited on the influence of range condition on cattle diets in the Chihuahuan desert. Botanical composition of cattle diets on Chihuahuan desert ranges in excellent and good condition was studied by microhistological analysis. Cattle feces were analyzed seasonally from fall 1991 through fall 1992. Excellent condition and good condition ranges supported 86% and 72% of the climax vegetation, respectively. Key species in cattle diets on the excellent condition range were black grama (Bouteloua eripoda Torr.) and threeawns (Aristida spp.). On the good condition range the key species were dropseeds (Sporobolus spp.), threeawns and black grama. Total grass and black grama content of cattle diets were greater on the excellent condition range. Seasonal trends occurred in cattle diets on good condition but not on excellent condition range. Low availability of forbs and shrubs explained the high diets similarities among seasons on the excellent condition range. Cattle on good condition range readily used forbs and shrubs when green grass was unavailable. Nitrogen and phosphorus analyses of fecal samples indicated diets were nutritionally superior on the good compared to the excellent condition range. Our research and other studies show consumption of forbs and shrubs permits cattle to maximize their nutritional welfare when grasses are dormant. The excellent condition range in our study had a different(P<0.05) mean grass standing crop (999 kg/ha) across periods compared to on the good condition range (659 kg/ha). Based on our research and other studies excellent condition Chihuahuan desert range maximizes forage quantity for cattle but good condition range appears better from a nutritional standpoint in the spring and early summer. Our research and other studies indicate Chihuahuan desert ranges dominated by black grama are most effectively used in winter while ranges with a high dropseed component are best suited for use in summer and early fall.