• Age and body condition score and diets of grazing goats

      Mellado, Miguel; Rodríguez, Alvaro; Olvera, Abundio; Villarreal, Jose A.; Lopez, Ramiro (Society for Range Management, 2004-09-01)
      Diet selection by juvenile and adult non-pregnant, non-lactating goats and the diets of adult non-productive goats with low (≤ 1.5; grading scale 0-5) and moderate (≥ 2.5) body condition score (BCS) are described by microhistological analysis of fecal samples for a Chihuahuan desert vegetation in northern Mexico. In the rainy season, adult goats utilized more (P < 0.10) shrubs than juvenile goats (70.4 vs 58.6%), but, in the dry season, the diet of both groups contained equal amounts of shrubs. The proportion of forbs and grasses in the goats' diet also tended to vary (P < 0.10) between age groups in the rainy season. Juvenile goats generally had lower consumption of plants with spines than adult goats. Goats with low BCS selected more (P < 0.10) shrubs than goats with moderate BCS in the rainy season. Forbs were eaten in larger amounts by does with moderate BCS (38% of the diet) during the rainy season compared to goats with low BCS (30.9%). Regardless of age and body reserves, grasses formed less than 5% of goat diets in both seasons. Mean similarity index for juvenile and adult goats was 75, while mean similarity index for goats with low and moderate BCS was 78. For all classes of goats, Larrea tridentata (DC.) Cov., the dominating species in the plant community, was the only plant selected at proportions below those found in ground cover in the rainy season. These data indicate that, during the rainy season, juvenile goats mixed their diets to achieve more even use of forages than adult goats. These results also indicate that high utilization of shrubs, including resinous and fibrous forages, appeared to be an adaptive foraging strategy of goats with low fat reserves, when forage was readily available.
    • Book Review: Natural Enemies: An Introduction to Biological Control, Ann Hajek

      Metzger, C. W. (Society for Range Management, 2004-09-01)
    • Book Review: Origins of the Organic Agriculture Debate, Thomas R. DeGregori

      Metzger, C. W. (Society for Range Management, 2004-09-01)
    • Canopy spectra of giant reed and associated vegetation

      Everitt, J. H.; Yang, C.; Alaniz, M. A.; Davis, M. R.; Nibling, F. L.; Deloach, C. J. (Society for Range Management, 2004-09-01)
      This paper describes the spectral light reflectance characteristics of giant reed (Arundo donax L.) and the application of aerial color-infrared photography and videography for distinguishing infestations of this invasive plant species in Texas riparian areas. Airborne videography was integrated with global positioning system (GPS) and geographic information system (GIS) technologies for mapping the distribution of giant reed. Field spectral measurements showed that giant reed had higher near-infrared reflectance than associated plant species in summer and fall. Giant reed had a conspicuous pink image response on the color-infrared photography and videography. This allowed infestations to be quantified using computer analysis of the photographic and videographic images. Accuracy assessments performed on the classified images had user's and producer's accuracies for giant reed that ranged from 78% to 100%. Integration of the GPS with the video imagery permitted latitude-longitude coordinates of giant reed infestations to be recorded on each image. A long stretch of the Rio Grande in southwest and west Texas was flown with the photographic and video systems to detect giant reed infestations. The GPS coordinates on the color-infrared video scenes depicting giant reed infestations were entered into a GIS to map the distribution of this invasive weed along the Rio Grande.
    • Cervid forage utilization in noncommercially thinned ponderosa pine forests

      Gibbs, Mary C.; Jenks, Jonathan A.; Deperno, Christopher S.; Sowell, Bok F.; Jenkins, Kurt J. (Society for Range Management, 2004-09-01)
      To evaluate effects of noncommercial thinning, utilization of forages consumed by elk (Cervus elaphus L.), mule deer (Odocoileus hemionus Raf.), and white-tailed deer (Odocoileus virginianus Raf.) was measured in ponderosa pine (Pinus ponderosa P. C. Lawson) stands in Custer State Park, S. D. Treatments consisted of unthinned (control; 22 to 32 m2/ha basal area), moderately thinned (12 to 22 m2/ha basal area), and heavily thinned (3 to 13 m2/ha basal area) stands of ponderosa pine. During June, July, and August, 1991 and 1992, about 7,000 individual plants were marked along permanent transects and percent-weight-removed by grazing was ocularly estimated. Sample plots were established along transects and plants within plots were clipped to estimate standing biomass. Pellet groups were counted throughout the study area to determine summer habitat use of elk and deer. Diet composition was evaluated using microhistological analysis of fecal samples. Average percent-weight-removed from all marked plants and percent-plants-grazed were used to evaluate forage utilization. Standing biomass of graminoids, shrubs, and forbs increased (P 0.05) from unthinned to moderately and heavily thinned stands. Utilization of graminoids and shrubs averaged less than 1% when measured as percent-weight-removed and percent-plants-grazed and did not differ (P 0.05) across treatments. Forb use averaged less than 5% within sampling periods when measured as percent-weight-removed and percent-of-plants grazed and did not differ among treatments. Results of pellet group surveys indicated that cervids were primarily using meadow habitats. When averaged over the 2 years, forbs were the major forage class in deer diets, whereas graminoids were the major forage class in diets of elk.
    • Defoliation increased above-ground productivity in a semi-arid grassland

      Loeser, Matthew R.; Crews, Timothy E.; Sisk, Thomas D. (Society for Range Management, 2004-09-01)
      In light of the continuing debate regarding overcompensation we studied the responses of above-ground biomass in a high-elevation, semi-arid grassland to defoliation, defoliation history, and livestock grazing. The above-ground annual net primary productivity (ANPP) was measured over 2 years in one-hundred twenty, 1-m2 plots that were exposed to single- and multi-year defoliation and grazing treatments. Plant communities showed an average increase in ANPP of 31%-45% due to a single defoliation event. The most conservative estimate of average ANPP of defoliated subplots was 29.4 g m-2 greater than the non-defoliated controls. A history of defoliation, due to clipping or grazing, lessened the magnitude of the compensatory response, but above-ground overcompensation of biomass was still observed, ranging on average from 17% to 26%. One dominant species, squirreltail grass [Elymus elymoides (Raf.) Swezeyi], accounted for nearly one-third of the community-level increases in ANPP. In contrast to above-ground patterns, below-ground root production of squirreltail did not increase in response to defoliation events. These results suggest that the above-ground production of high-elevation, semi-arid grasslands in the American Southwest may be temporarily increased through certain grazing events, and may help explain shifts in species dominance in grasslands exposed to long-term grazing by livestock.
    • Germination of seeds of Tamarix ramosissima

      Young, James A.; Clements, Charlie D.; Harmon, Daniel (Society for Range Management, 2004-09-01)
      The germination of seeds of saltcedar (Tamarix ramosissima Ledeb.) was compared at a wide range of constant or alternating temperatures from 0 through 40 degrees C. Germination temperature profiles were developed for seeds of saltcedar collected from the Walker River Delta in western Nevada over a 3 year period. Germination occurred over a wide range of temperatures. For 2 of the 3 years of testing, maximum germination observed was 98 or 100%, indicating the seed lots were highly viable. Germination ranged from 0 to 6% at very cold seedbed temperatures, but jumped to 39 to 43% at cold seedbed temperatures. There was very little difference in germination between moderate and warmer seedbed temperatures. No single temperature always supported optimum germination. The temperatures that most frequently supported optima were 10/20 (10 degrees C for 16 hours and 20 degrees C for 8 hours in each 24 hour period), 10/25, 15/20, and 35 degrees C. Mid summer collections of saltcedar seeds were much more variable in germination response compared to annually repeated late spring collections from the Walker River Delta. Available soil moisture apparently is an important factor in the germinability of saltcedar seeds collected in mid summer. Temperature regimes that supported optimum germination for the Walker River Delta accession of seed collected in mid summer, tended to occur at higher temperatures than for seeds collected from the same stand in late spring. Comparison of the saltcedar profile with germination temperature profiles of seeds of tree willow (Salix lutea Nutt.), coyote willow (S. exigua Nutt.), or Fremont cottonwood (Populus fremontii S. Watson) revealed that germination of saltcedar seeds was equal in the number of regimes with some germination, mean of optima, and maximum observed germination. For all other germination characteristics measured, saltcedar is lower and sometimes distinctly lower than for seeds of the native woody species.
    • Landscape use by cattle affected by pasture developments and season

      Zuo, Haitao; Miller-Goodman, Mary S. (Society for Range Management, 2004-09-01)
      Allowing cattle (Bos taurus L.) unrestricted access to streams can contribute to degradation of riparian and aquatic habitats. The objectives of this study were (1) to quantify the amount of time cattle spend using streams and associated riparian habitats when off-stream water and shade sources are offered and (2) to relate these patterns of habitat use to diurnal and seasonal changes in environmental conditions characteristic of the lower southeast. Diurnal (dawn-to-dusk) patterns of cattle location and behaviors were monitored between March 2000 and October 2001 in north-central Alabama at farms with pastures in which wooded streams were present. No significant decrease was detected in the length of diurnal periods cattle spent in riparian habitats after water and shade developments were in place. Grazing (7.8 hours) dominated daytime behaviors of cattle during the cool season when preference was for grassland habitat (7.6 hours). During the warm season, time spent lying increased to 4.7 hours versus 2.7 hours during the cool season; cattle consistently sought either riparian or other wooded habitat at midday and afternoon in comparison to morning and evening periods. Overall, grazing behaviors occurred predominantly (80%) in grassland habitat and lying behaviors occurred mainly (60%) in wooded habitat. Results suggested that comfort (relief from heat stress) appeared to be a major criterion in habitat use decisions by cattle during the warm season for the relatively small spatial scales (3.3 and 6.9 ha) studied. Therefore, dependence only on water and shade developments for alterations in livestock distribution may not be the most effective strategy for reduced degradation of many riparian habitats found in this region.
    • Mowing rights-of-way affects carbohydrate reserves and tiller development

      Nofal, Hisham R.; Sosebee, Ronald E.; Wan, Changgui; Borrelli, John; Zartman, Richard; McKenney, Cynthia (Society for Range Management, 2004-09-01)
      Intensive mowing has contributed to the loss of some climax grasses in Texas highway rights-of-way. The overall objective of this study was to evaluate the effect of different mowing heights and frequencies on total non-structural carbohydrate (TNC) concentration and tiller density in short and mid-grasses grown along highway rights-of-way. Shortgrasses were represented by blue grama [Bouteloua gracilis (H.B.K) Lag ex Steud.], and mid-grasses were represented by silver bluestem [Bothriochloa saccharoides (Sw.) Rydb], both of which are indigenous species. During 1999 and 2000, grasses were either non-mowed (control) or subjected to mowing heights of 5 and 10 cm, and 5 mowing frequencies (monthly, bi-monthly, tri-monthly, 1-time-only at the beginning or end of the growing season). Plants of both species mowed less frequently at either stubble height had higher TNC concentrations than plants subjected to more frequent mowing. Mowing produced fewer (P 0.05) tillers after 2 consecutive mowing seasons than after 1 mowing season in silver bluestem. Silver bluestem tiller growth was more susceptible to frequent mowing than blue grama. Mowing during periods of rapid inflorescence development reduced tiller density in both species after 2 mowing seasons. Mowing height and frequency guidelines are proposed to maintain roadside grasses in their most productive state through planning mowing practices around the target plant's natural growth habit and it's ability to respond to defoliation.
    • Nitrogen fertilization and row spacing effects on Digitaria eriantha

      Gargano, Alfredo O.; Adúriz, Miguel A.; Busso, Carlos A. (Society for Range Management, 2004-09-01)
      Crude protein (CP, %), yield of protein dry matter (YPDM, kg ha-1), nitrogen use efficiency (NUE, kg dry matter kg-1 N) and nitrogen recovery (NR, %) were evaluated in Digitaria eriantha after exposing this species to various field-treatments during 1998-1999 and 1999-2000 in Bahía Blanca (38 degrees 48′S, 62 degrees 13′W), Argentina. Treatments included (1) 3 N fertilization rates (0, 50 or 100 kg ha-1), (2) 2 row spacings (30 or 50 cm), and (3) 2 methods of fertilizer application (either split at the beginning of spring and summer or applied at once in early spring). Plants were cut leaving 5 cm stubble whenever they reached 26-28 cm. Studied parameters were determined on forage harvested in spring, summer or total annual. Crude protein increased (P < 0.05) as N fertilization increased in both seasons. Total annual CP averaged 9.7, 12.0 and 14.0%, respectively for the 0, 50 and 100 kg ha-1 fertilization rates, respectively. Crude protein was greater (P < 0.05) on forage which received split rather than bulk N fertilization, and mean values were 13.2 and 11.7%, respectively. Forage sown at different row spacings had a similar (P > 0.05) CP concentration. In general, YPDM responded positively (P < 0.05) to N fertilization and to a split application of N fertilizer. Although differences were not always significant, there was an inverse relationship between N fertilization rate and NUE and NR. Nitrogen use efficiency was 34.5 and 24.8 kg dry matter kg-1 N (P < 0.05), and NR was 98 and 79% (P < 0.05) when N fertilization rates were 50 and 100 kg ha-1, respectively. There was a positive (P < 0.05) relationship between rainfall and NUE or NR. Nitrogen fertilization in D. eriantha should be split with a N fertilization rate close to 50 kg ha-1, and using 30 rather than 50 cm row spacing.
    • Occupied and unoccupied sage grouse habitat in Strawberry Valley, Utah

      Bunnell, Kevin D.; Flinders, Jerran T.; Mitchell, Dean L.; Warder, John H. (Society for Range Management, 2004-09-01)
      This study evaluated multiple aspects of spring/summer sage grouse (Centrocercus urophasianus) habitat in Strawberry Valley, Utah by measuring vegetation associated with nest, brood and adult use sites. In addition, 3 types of random habitats were measured including available habitat within core use areas, random sagebrush (Artemisia spp.)/grass habitat outside core use areas, and random sagebrush/grass habitat sites that had been converted to an understory of smooth brome (Bromus inermis Leyss) by past range management practices. Logistic regression was used to identify those habitat variables that discriminated between site types. Variables that discriminated adult habitat from brood rearing habitat included: 1) sagebrush height (P ≤ 0.01) and 2) forb diversity (P = 0.12) with sagebrush height being greater at adult sites and forb diversity greater at brood sites Variables that significantly discriminated occupied adult habitat from random habitat outside of core use areas included: 1) percent grass cover (P ≤ 0.01) and 2) area of sagebrush canopy (P = 0.03) with both variables having grater values in adult habitat. Variables that significantly discriminated occupied adult habitat from random habitat with a smooth brome understory included: 1) percent forb cover (P ≤ 0.01), 2) shrub canopy cover (P = 0.02), and 3) area of sagebrush canopy (P = 0.08) with all variables being greater in adult habitat. In addition, this study identified sagebrush age, sagebrush canopy area, and forb diversity as potentially important aspects of sage grouse habitat that have not been previously reported.
    • Pairing season habitat selection by Montezuma quail in southeastern Arizona

      Bristow, Kirby D.; Ockenfels, Richard A. (Society for Range Management, 2004-09-01)
      Montezuma quail (Cyrtonyx montezumae Vigors) are closely associated with oak woodlands (Quercus spp.). Livestock grazing and cover availability are considered important factors affecting Montezuma quail distribution and density. While habitat conditions during pairing season (April-June) are thought to be important to Montezuma quail survival and reproduction, information on habitat selection during that time is limited. We investigated habitat selection by Montezuma quail in grazed and ungrazed areas within the Huachuca and Santa Rita mountain foothills in southeastern Arizona. We used pointing dogs to locate quail during the pairing seasons of 1998 and 1999, and measured habitat characteristics at 60 flush sites and 60 associated random plots (within 100 m of flush sites). We recorded information on landform, substrate, vegetation, and cover. Montezuma quail selected (P < 0.10) areas with higher grass canopy cover and more trees than randomly available. Short (≤ 50 cm tall) visual obstruction (cover), usually associated with bunch grass, was greater (P < 0.10) at use sites than at random plots. Land management practices that reduce grass and tree cover may affect Montezuma quail habitat quality and availability in southeastern Arizona. Based on habitat selection patterns of Montezuma quail, we recommend that oak woodland habitats should contain a minimum tree canopy of 26%, and 51-75% grass canopy cover at the 20-cm height to provide optimum cover availability.
    • Ploidy, water, and nitrogen effects on Russian wildrye chemical composition

      Karn, J. F.; Frank, A. B.; Berdahl, J. D.; Poland, W. W. (Society for Range Management, 2004-09-01)
      Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski], a cool-season introduced bunchgrass, offers producers an alternative to crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schultes] for spring and fall grazing in the Northern Great Plains. Tetraploid Russian wildrye with improved seedling establishment may offer even greater potential for seasonal grazing. This study investigates how the concentrations of some nutritive quality components in leaf, stem, and inflorescence tissue of diploid and tetraploid Russian wildrye were affected by growing season water (50 and 150% of average precipitation) and fertilizer (10 and 134 kg N ha-1). Plants were sampled at vegetative, boot, anthesis, and anthesis plus 10-day stages of maturity in 1994, 1995, and 1996. Tetraploid plants had slightly (P 0.05) less crude protein (CP) in leaf, stem and inflorescence tissue than diploid plants. Plants grown at the 50% water treatment had higher CP and in vitro dry matter digestibility (IVDMD), and lower acid detergent fiber (ADF) and neutral detergent fiber (NDF) in leaf and inflorescence tissue, while in stem tissue only CP was affected by the growing season water treatment. Nitrogen fertilizer resulted in greater CP and IVDMD and lower ADF and NDF in all 3 plant tissues. Maturity affects were consistent over leaf, stem and inflorescence tissue, with CP and IVDMD declining and ADF and NDF increasing as plants matured. There were some differences in nutritive quality components between diploid and tetraploid plants, but overall their qualities were comparable and quite good. Crude protein at all stages of maturity in leaf and inflorescence tissue would have been adequate for most classes of beef cattle, while stem tissue CP would have only been adequate for lower producing animals.
    • Regrowth and production of herbaceous riparian vegetation following defoliation

      Boyd, Chad S.; Svejcar, Tony J. (Society for Range Management, 2004-09-01)
      Stubble height regulations are frequently used to manage livestock grazing of herbaceous riparian vegetation. The objective of this study was to determine the impact of stubble height, time of clipping and soil water status on production and regrowth of herbaceous riparian vegetation. We used a randomized block design with 4 study sites on each of 3 small ( 2m width) streams in northern Harney County, Ore. In June and July of 2000-2003, 40 × 50 cm experimental plots were clipped to stubble heights of 5.1 (2 inch), 10.2 (4 inch), or 15.2 cm (6 inch), and paired control plots were left unclipped. Complete treatment sets were located adjacent to the stream and 4 m from the stream at each site. All plots were clipped to 1 cm in October and regrowth was calculated by comparing clipped and control plots. Water table depth was measured weekly using PVC wells. Results indicate that height regrowth was associated positively with stubble height (P < 0.01) and was less with July compared to June clipping (P = 0.02). Weight regrowth was also positively related to stubble height (P < 0.01) and decreased with July compared to June clipping (P = 0.04) whereas annual aboveground production increased with July clipping (P = 0.02). Annual production values for clipped plots were higher than for unclipped plots, indicating compensatory production in response to defoliation. Plots distant from the stream had less water availability, but regrowth and production were not strongly influenced by distance from active stream channel. Timing and intensity of defoliation were reliable predictors of regrowth and production performance. Most clipping height × time combinations produced end of season heights sufficient to meet current federal stubble height requirements (i.e., 10-15 cm). Our results provide insight on the timing and intensity of defoliation that will allow for adequate regrowth to meet different management objectives. However, other factors such as stream channel morphology, animal selectivity, and annual weather variation will need to be considered.
    • Responses of desert grassland vegetation to mesquite removal and regrowth

      Tiedemann, Arthur R.; Klemmedson, James O. (Society for Range Management, 2004-09-01)
      The purpose of this study was to determine the long-term response of understory vegetation in the desert grassland of southeastern Arizona, USA, to removal and regrowth of mesquite Prosopis juliflora (Swartz) DC. var. velutina (Wooton) Sarg. trees. The study involved 3 treatments applied to mesquite in 1966; mesquite left intact (MI), mesquite removed (MR), and mesquite removed, sprouted, and regrown (MRS). Vegetation responses to 2 litter treatments, litter intact (LI) and litter removed (LR), also were examined. Cover of understory vegetation and juvenile mesquite ( 1.5 m height) were measured in canopy and open (intercanopy) locations. Major changes between 1967 and 1991 were increased cover of juvenile mesquite, shrubs, halfshrubs, bush muhly Muhlenbergia porteri Scribn., and Lehmann lovegrass Eragrostis lehmanniana Nees., and a decline in cover of Arizona cottontop Digitaria californica (Benth.) Chase, and plains bristlegrass Setaria macrostachya H.B.K. Arizona cottontop, plains bristlegrass, and bush muhly were more abundant in canopy locations; black grama Bouteloua eriopoda Torr. and Lehmann lovegrass were more abundant in open locations. Lehmann lovegrass cover was lowest in canopy locations of the mesquite intact treatment. Combination of the mesquite removed and sprouted and litter intact treatments favored increased cover development of native perennial grasses. Litter removal enhanced cover development of Lehmann lovegrass, most likely through increased amount of red light and increased soil temperature fluctuations. Low levels of understory cover (22% average) probably facilitated recruitment of mesquite and other woody plants. Our observation that the greatest cover of Arizona cottontop, plains bristlegrass, and bush muhly occurred in the canopy location of the mesquite intact treatment suggests a potential strategy for maintaining diversity of native perennial grasses. Mature mesquite should be examined as a refuge for native species.
    • Riparian vegetation response to different intensities and seasons of grazing

      Lucas, Richard W.; Baker, Terrell T.; Wood, M. Karl; Allison, Christopher D.; Vanleeuwen, Dawn M. (Society for Range Management, 2004-09-01)
      Sustainable management of riparian ecosystems depends on our understanding of these complex systems. Thus far, the scientific literature has not adequately addressed the effects of livestock grazing on riparian areas in the American southwest. Most available information is observational, anecdotal, based on unreplicated experiments, or compares heavily grazed areas to areas from which livestock have been completely excluded. This study, in the Black Range of western New Mexico, compared effects of different seasons of use (cool season, warm season, and dormant season) and grazing intensities (light, moderate, and none) of cattle on young narrowleaf cottonwood (Populus angustifolia James) populations, and herbaceous vegetation in 2 adjacent southwestern riparian areas. Cottonwoods in lightly grazed and moderately grazed plots received significantly greater use than cottonwoods in ungrazed plots which experienced negligible grazing pressure. Increased grazing pressure did not have significant impacts on cottonwood populations. Effects of season of use were significant on both herbaceous species richness and diversity. We conclude that no single riparian area management approach is best in all situations, but the grazing treatments used in this study appear to have been successful at maintaining riparian communities.
    • Seasonal diet selection of cattle grazing a montane riparian community

      Evans, Steven G.; Pelster, Andrew J.; Leininger, Wayne C.; Trlica, M. J. (Society for Range Management, 2004-09-01)
      Cattle-grazing in riparian areas has become increasingly controversial. More information is needed about cattle use of these areas to develop Best Management Practices. This study was designed to determine seasonal changes in diet selection of cattle in a montane riparian community in northern Colorado. Previous cattle diet studies in riparian zones have not separated the interaction between seasonal preference and biomass utilization. The experiment was conducted within large exclosures that had not been grazed by livestock since 1956. Vegetation biomass estimates and diet samples from 5 esophageally fistulated steers were taken during 4 grazing periods (spring, early-summer, late- summer, and fall) in 1995. Vegetation measurements and diet samples were also collected during the late summer and fall of 1994. One of the 3 paddocks in each grazing period of 1995 had been grazed in 1994. Steer diets in 1995 were found to contain 15% more Carex spp. from paddocks that had been ungrazed until 1995 as compared with paddocks previously grazed in 1994. Kentucky bluegrass (Poa pratensis L.) and forbs were consumed about 13 times and 5 times greater, respectively, in previously grazed paddocks as compared with ungrazed paddocks. Carex spp. were the most preferred component of cattle diets throughout the study. Willows (Salix spp.) were not preferred in any grazing period of either year, and consisted of less than 4% of cattle diets in any season. However, a trend towards increased consumption of willows was found from spring to fall, 1995. Information obtained in this study should help managers develop grazing systems that allow for a desirable combination of herbaceous and woody species in a riparian community while still affording grazeable forage.
    • Soil texture and tree coverage influence on organic matter

      Buschiazzo, D. E.; Estelrich, H. D.; Aimar, S. B.; Viglizzo, E.; Babinec, F. J. (Society for Range Management, 2004-09-01)
      Soil organic matter (OM) is an important factor for maintaining the productivity and the stability of the so-called caldénal woodland ecosystem of central Argentina. Little is known about the influence of tree coverage and soil texture on OM accumulation in soils of the study region. The relationships between OM content, silt + clay content, and the percent of tree coverage were studied in a 25 × 25 m grid in 2 sites. Results showed that OM was lower (P < 0.05) at Site I (2.86%) than at Site II (6.41%). The OM was positively correlated with the percent of tree coverage in Site I (OM = 0.0156 trees cover + 1.97, R2 = 0.29, P < 0.001), but not in Site II. Conversely, a positive correlation with silt + clay was observed in Site II (OM = 0.17 silt + clay - 6.79, R2 = 0.41, P < 0.05) but not in Site I. A multiple regression analysis [OM = - 16.64 + 0.71 (silt + clay) + 0.04 (tree coverage), n = 78, R2 = 0.55, P < 0.001] tended to confirm these results. Although they differed in their relative weight both silt + clay and tree coverage affect OM accumulation at both sites. The larger influence of trees on OM variability at Site I was attributed to the lower, but highly variable, tree coverage, and the stronger influence of silt + clay on OM variability at Site II can be attributed to the lower variability of tree coverage, and the higher variability of soil texture. According to our results, (a) 41% of OM variability is explained by silt + clay content when tree coverage is dense and uniform, and (b) a 29% of OM variability is explained by tree coverage when such coverage is sparse and heterogeneous. The influence of tree canopy on OM distribution could be explained by its effect on the temperature regime. The influence of soil texture on OM could be attributed to its effect on the water retention capacity of soils. While forest clearing increases the maximum temperature and the temperature amplitude of soils, erosion in cleared areas affects soil texture, and consequently, its water retention capacity. The deterioration of both temperature and soil water regimes deteriorates, in turn, the capacity of the soil to accumulate OM.
    • Steer diets in a montane riparian community

      Pelster, Andrew J.; Evans, Steven; Leininger, Wayne C.; Trlica, M. J.; Clary, Warren P. (Society for Range Management, 2004-09-01)
      Diets of fistulated steers that grazed a montane riparian community were determined throughout a growing season. The objective was to determine if willow (Salir spp.) consumption by steers was related to the season of use and the residual stubble heights of herbaceous forae species. Diet samples were collected at 4 levels of herbaceous utilization throughout 4 grazing periods that were based on willow phenology. Results suggested that spring grazing of riparian pastures was preferable to late-season use to minimize browsing on willows. Willow consumption increased substantially as herbaceous stubble height approached 10 and 18 cm during the spring and early- summer grazing periods, repectively. Stubble heights greater than 20 cm were needed to reduce willow consumption when they were most preferred during the late- summer and fall grazing seasons in this tall sedge (Carex spp.)/willow riparian community. Sedge and rush (Juncus spp.) composition in steer diets declined, while willow composition increased in steer diets, in response to decreasing stubble heights. Grass consumption by steers was little affected by stubble height, while forb consumption was directly related to forb availability. Although grazing activity has the potential to negatively impact riparian willows, these results suggested that timing of use and carefully controlled levels of herbaceous utilization could be used to minimize the consumption of willows by cattle in a montane riparian community.
    • Stocking rate and grazing frequency effects on Nebraska Sandhills meadows

      Voleski, Jerry D.; Schacht, Walter H.; Richardson, Devyn M. (Society for Range Management, 2004-09-01)
      Nearly one-half million ha of the Nebraska Sandhills is comprised of highly productive wet meadows. A study was conducted from 1998 to 2001 to evaluate the effects of stocking rate and grazing frequency on herbage dynamics, disappearance, and composition of a wet meadow dominated by cool-season vegetation. Defoliation characteristics were measured on 2 key species. Stocking rates were 148, 296, and 444 AUD ha-1 combined with a grazing frequency of 3 (F3) or 5 (F5) times. Cumulative standing crop disappearance and height reduction increased linearly with increasing stocking rate. Disappearance was 1,920, 2,700, and 3,090 kg ha-1 for the 148, 296, and 444 AUD ha-1 stocking rates, respectively. Greater disappearance at the highest stocking rate was expected based on calculated intake estimates for that stocking rate. Percentage of tillers grazed and percentage height reduction increased with stocking rate for both key species. Percentage of tillers grazed was greater under F3 compared to F5. This likely was caused by higher grazing pressures under the F3 treatment at each grazing period. Frequency of occurrence of the primary plant species or groups was not affected by stocking rate or grazing frequency during any year of the study (P > 0.05); however, frequency of occurrence of legumes and Kentucky bluegrass (Poa pratensis L.) was higher in grazed pastures compared to the control. The abundance of soil moisture in these meadows appeared to mitigate the effects of heavier defoliation associated with higher stocking rates. However, defoliation of the taller grasses and sedges resulted in a more open canopy allowing shorter-statured species to increase. Overall, stocking rate affected more response variables than grazing frequency and the productivity of our wet meadow site would potentially support a stocking rate of 296 AUD ha-1.