Journal of Range Management, Volume 44, Number 3 (May 1991): Recent submissions
Now showing items 21-26 of 26
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Defoliation effects on yield and bud and tiller numbers of two Sandhills grassesIntensive grazing strategies for the Nebraska Sandhills must be based on time and frequency of defoliation of key warm-season grasses. A 3-year field study was conducted in the Nebraska Sandhills to determine the effects of defoliation on yield and bud and tiller number of sand bluestem [Andropogon gerardli var. paucipilus (ash) Fern.] and prairie sandreed [Calamovilfa longifolia (Hook.) Scribn.]. Defoliation (7 cm) treatments imposed on a 1.5 X 1-m plot were: a single defoliation on 10 June, 10 July, or 10 August; 2 successive defoliations on 10 June and 10 August; or 3 successive defoliations on 10 June, 10 July, and 10 August. All plots were harvested in October to obtain aftermath yield. Control plots were harvested only at the end of the growing season (October). Defoliation treatments were initiated in 1986, 1987, and 1988 on different plots and the effect of year of initiation as well as the effect of 3 successive years of repeated treatment (1986 plots) was evaluated. Annual dry matter (DM) yield, and bud and tiller numbers were measured. Following the initial year of treatment multiple defoliations increased yield of both grasses while bud and tiller numbers were similar to those of the control plants. After 3 years of repeated treatment, annual DM yield of sand bluestem for all defoliation treatments was lower than the control. A single defoliation of sand bluestem in August or a June-July-August defoliation reduced bud number compared to other treatments and the control. A June-August defoliation of prairie sandreed over a 3-year period increased annual DM yield compared to all treatments and the control although defoliation treatments reduced bud number. The optimum time and frequency of defoliation for annual DM yield and bud and tiller number was a single June or July defoliation for sand bluestem and a June-August defoliation for prairie sandreed.
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Correlation of environment and root carbohydrate content to picloram translocation in leafy spurge14C-picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) absorption and translocation in leafy spurge (Euphorbia esula L.) was evaluated over 2 growing seasons and was compared to selected environmental parameters and root carbohydrate content. 14C-picloram absorption was greatest during the vegetative growth stage (52%) and increased directly with relative humidity but was not affected by the temperature at treatment. 14C-picloram translocation to leafy spurge roots generally was influenced more by the plant growth stage than the environment. The greatest translocation to roots occurred during the true-flower and seed-set growth stages. The water-soluble (monosaccharide and disaccharide) and water insoluble carbohydrate content in leafy spurge roots average across the growing season varied by depth with the lowest amount in the 0- to 8-cm depth, 35 and 53 mg/g, and the most in the 16- to 24-cm depth 84 and 221 mg/g, respectively. 14C-picloram translocation to leafy spurge roots was independent of either carbohydrate fraction when evaluated over the entire growing season. However, 14C-picloram content increased when the water-soluble fraction increased during the true-flower growth stage. 14C-picloram translocation to the roots did not increase in the fall, in contrast to the general hypothesis that herbicides move with photosynthates to the roots.
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Correcting estimates of net primary production: Are we overestimating plant production in rangelands?This paper addresses the issue of the effect of random errors in field estimates of net primary production (NPP). This is a critical subject in range management because field estimates of plant production are regularly used to determine stocking rates, range condition, and animal consumption. What we show in this paper is that random errors associated with field estimates of NPP can result in a positive bias and thus an overestimation of NPP. Depending on the case, this overestimation has been reported as high as 700%. We present examples with overestimations in the 200% to 400% range. The overestimation in NPP increases with increases in biomass variances, frequency of sampling, and number of taxonomic (species) and tissue (live, dead, etc) components sampled. We (1) outline in nonmathematical terms the reasons behind overestimation in NPP and the analytical solutions designed to correct them; and (2) present applications of the analytical solution for adjustments to concrete cases. The adjustments for overestimation outlined in this paper do not guarantee an accurate estimate of NPP but eliminate an unneeded source of error. A computer program (for IBM(TM) compatible) designed to implement the necessary adjustments is available from the authors free of charge (send a blank diskette).
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Comparison of four methods of grassland productivity assessment based on Festuca pallescens phytomass dataThe relative utility of 4 methods for grasslands above-ground net primary productivity (ANPP) assessment were evaluated. These methods, applied to a set of phytomass and litter data collected at about bimonthly intervals for 2 years in a Festuca pallescens (St. Yves) Parodi grassland steppe of southwestern Chubut, Argentina, were: (1) summation of positive increments of green (live) biomass between harvests, (2) summation of positive increments of total phytomass between harvests, (3) summation of positive increments of green biomass between harvests plus correction factors which accounted for the concomitant increases in dry, old dead, and litter, respectively, and (4) mathematical model of simultaneous differential equations which fitted the values of phytomass data obtained in the field. Method 1 gave consistently (p less than or equal to 0.05) the lowest ANPP values in both years. Productivity values obtained with methods 2, 3, and 4 were highly correlated and did not differ significantly (p less than or equal to 0.05) with each other. Their estimates varied from 94.9 to 105.3 g of dry matter per m2 for the first year and from 73.0 to 149.4 g of dry matter per m2 for the second year. These values are within the range of productivity given for other climatologically and physiognomically similar semiarid grasslands of North America. Each method except 1 provided reliable estimations of ANPP for the grassland studied. Methods 2, 3, and 4 can also be used to assess ANPP in any other grassland with similar characteristics. Each one, however, might have particular applications according to the specific objectives pursued.
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Cattle grazing behavior on a foothill elk winter range in southeastern WyomingCattle at a light stocking rate of 0.17 to 0.18 AUM/ha over a 35-day grazing season in summer preferred to graze on lowland range sites, while elk in winter preferred upland range sites. We changed stocking rates on the same pastures to a moderate rate of 0.28 AUM/ha and a very light rate of 0.034 AUM/ha to determine the effects of stocking rate on cattle preference for range sites and possible habitat overlap between cattle and elk. At all stocking rates, cattle spent significantly more time grazing on loamy range sites and less time on other sites than would be expected on the basis of area occupied by the sites. When grazing pressure was increased from light to moderate, cattle grazing time on loamy sites increased. When grazing pressure was decreased from light to very light, cattle grazed only loamy and shallow sites to the complete exclusion of other sites. Cattle grazed farther from water as stocking rate increased and as the grazing season progressed. They also grazed on steeper slopes as stocking rate increased, and as the season progressed under the highest stocking rate. Even at the highest stocking rate studied, there was little habitat overlap between cattle and elk.
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Beef cattle distribution patterns on foothill rangeA 3-year experiment designed to quantify the spatial and temporal utilization patterns of range sites by beef cattle on summer foothill range was conducted on the Wick Brothers Management Unit of the Wyoming Game and Fish Commission, 8 km w. of Arlington, Wyo. The grazing seasons, in replicate pastures, were from 15 July-9 August, 15 June-26 July, and 15 June-2 August in 1980, 1981, and 1982, respectively. Daily observations were made of radio-telemetry collared cattle (3 per pasture). Cattle dispersion was constrained by the spatial distribution of water and slope. Across 3 seasons, 77% of observed use was within 366 m of water. Approximately 65% of the land area was beyond 723 m from water and sustained only 12% of observed use. Cattle concentrated use (79%) on slopes less than 7%. Consequently 35% of the area, on or surrounded by slopes > 10%, received only 7% of observed use. Loamy, grazable woodland and wetland/subirrigated range sites were most preferred and accounted for over 65% of observed use while occupying less than 35% of the land area. Overall, coarse upland, very shallow and shallow loamy sites were not preferred; however, site preference varied as areas further from water were utilized. Observed use was significantly (P < 0.10) correlated (r 0.41 to 0.69) with standing crop and crude protein standing crop over various growth form characteristics of the forage component. Associated stepwise regression models accounted for 44 to 73% of the variation in observed use over the 1982 grazing season. As the forage complex became more similar, in terms of standing crop and crude protein content, significantly less (P < 0.05) variation in use was accounted for by the forage variables (0-37%).
