• Predictive equations for biomass and fuel characteristics of Argentine shrubs

      Hierro, J. L.; Branch, L. C.; Villarreal, D.; Clark, K. L. (Society for Range Management, 2000-11-01)
      Predictive equations for estimating shrub biomass in semi-arid scrub ecosystems are essential for evaluating shrub encroachment, conducting ecosystem-level studies of net primary productivity (NPP) and nutrient cycling, and examining effects of different fire regimes. In this study, we developed predictive equations to estimate total aboveground biomass and biomass of foliage and stems of the 8most common shrubs in the semi-arid scrub (Monte) of central Argentina. We also examined the relationship between shrub size and proportions of these components for the dominant species, Larrea divaricata Cavanilles (creosotebush), and determined fuel characteristics (dead-to-live ratio, bulk density) of the 8 shrub species. Regression analyses were used to examine the relationships between aboveground biomass and 5 field measurements (diameter of the longest stem, shrub height, maximum crown width, crown width at right angles to maximum crown width, and crown volume). A natural log-log model based on a single variable best described this relationship in most cases. The easiest field measurement for 6 of the 8 species was diameter of the longest stem, and this measure was often the best predictor of shrub biomass. As L. divaricata increased in size, the proportional biomass of large stems increased, and bio-mass of foliage and small stems decreased. This pattern suggests productivity may decrease with shrub age. The mass of dead materialwas low in most shrub species. Bulk densities were comparable to those of shrubs in other semi-arid ecosystems. Equations developed here will allow rapid and accurate estimation of shrub biomass in the Monte of Argentina.
    • Protocol for monitoring standing crop in grasslands using visual obstruction

      Benkobi, L.; Uresk, D. W.; Schenbeck, G.; King, R. M. (Society for Range Management, 2000-11-01)
      Assessment of standing crop on grasslands using a visual obstruction technique provides valuable information to help plan livestock grazing management and indicate the status of wildlife habitat. The objectives of this study were to: (1) develop a simple regression model using easily measured visual obstruction to estimate standing crop on sandy lowland range sites in the Nebraska Sandhills, (2) provide sampling and monitoring suggestions in the use of visual obstruction on this grassland type, and (3) compare the visual obstruction technique to the standard clip and weigh procedure. Visual obstruction precisely predicted average standing crop dry weights for the sandy lowland range sites (r2=0.88). A prediction accuracy of ± 295 kg ha-1was found using a test data set. Two sampling options (A and B) were evaluated using a 2-stage sampling protocol. Option A (1 transect/quarter section) provided more precise estimates applicable to extensive grasslands than option B. However, option A was not applicable to a section (259 ha) or a few sections. Option B (3 transects/section) provided estimates applicable to each section and to the entire area, but it required more intensive sampling than option A to attain the same precision. The visual obstruction technique provided more precise estimates of standing crop than the standard clip and weigh technique when clipping and weighing up to 6 plots per transect. When 7 or more clipped and weighed plots per transect were sampled, standing crop estimates were more precise than using visual obstruction readings. However, since 20 visual obstruction readings/transect (25 minutes) can be sampled in about half the time spent clipping and weighing 6 plots/transect (45 minutes), visual obstruction in combination with a previously estimated regression model provides a simple, reliable, and cost effective alternative to the clip and weigh technique. Regression models should be developed for other grassland types following the methodology described in this paper.
    • Red deer and cattle diet composition in La Pampa, Argentina

      Pordomingo, A. J.; Rucci, T. (Society for Range Management, 2000-11-01)
      Presence of 2 large herbivores in the same rangeland makes assessment of proper stocking rates and management practices rather complex. This study evaluated composition and overlap of red deer and cattle diets in a semiarid, temperate rangeland of La Pampa province, Argentina. Deer and cattle diets were estimated by microhistological analysis of feces. Fifteen samples were collected for cattle and deer during fall, winter, spring, andsummer of 1994/95 (Period 1) and the same seasons of 1996/97 (Period 2). Red deer and cattle diets were different (P < 0.01) within each sampling season. Diets were also different (P < 0.01) among sampling seasons within each animal species. Red deer were better shrub users than cattle. Deer consumed more than 4 times the amount of shrubs than cattle during all seasons. Shrubs accounted for 28 to 50% of deer diets in most seasons, and from 6 to 12% in cattle diets. Forbs were a variable component of diets. However, red deer harvested more forbs than cattle in most sampling seasons (P < 0.05). Cattle were better grass users than red deer. Cows consumed more (P < 0.05) perennial graminoids in all seasons, and based their diet on cool-season perennial grasses. A trend for red deer to behave as an intermediate feeder, compared with cattle could be suggested. In the environment of our study, deer and cattle diet overlap varied greatly depending on availability of palatable fractions of forbs, shrubs, and grasses. Forb and shrub regrowth would reduce the diet overlap.
    • Response of incomplete Tifton 9 bahiagrass stands to renovation

      Gates, R. N. (Society for Range Management, 2000-11-01)
      Establishment of warm-season grasses from seed is often impeded by slow germination and emergence, and low seedling vigor. Stand development can be further retarded by unfavorable soil moisture resulting from high temperatures and erratic precipitation. Management of poorly established stands of warm-season grasses has received limited research attention. Two- or 3-year old, poorly established stands (basal occupation < 61%) of ‘Tifton 9’ bahiagrass (Paspalum notatum Flügge var. saure) at a dry upland site and at a moist lowland site were reseeded (5.6 kgh a-1) in April of 2 different years either without tillage or after rototilling or light disking and compared to a non-seeded control. Our objective was to determine whether any combination of tillage and/or seeding would enhance stand coverage. At the upland site, basal occupation of the control increased from an initial 61 to 80%. No benefit was derived from interseeding, and both tillage treatments resulted in a stand reduction (P < 0.05) after 1 year. At the lowland site, basal occupation increased froman initial 28 to 59% for the control. Similar responses were observed with renovation treatments, but none were greater (P >0.05) than the control. Bahiagrass stands with at least a few plants per m2 should be managed to minimize weed encroachment, but introducing additional seed, with or without tillage, offered no benefit.
    • Stubble height as a tool for management of riparian areas

      Clary, W. P.; Leininger, W. C. (Society for Range Management, 2000-11-01)
      Stubble height, a measure of the herbaceous vegetation remaining after grazing, has been widely used in recent years to gage the impacts of grazing use in riparian areas. Stubble height is a short-term management guide that should only be applied to help attain long-term ecological objectives; it should not be thought of as a long-term management objective. Maintaining a minimum stubble height helps preserve forage plant vigor, retain sufficient forage to reduce cattle browsing of willows (Salix spp.), stabilize sediments, indirectly limit streambank trampling, maintain cattle gains, and provide an easily communicated management criterion. Based on limited specific research of riparian system response and on knowledge of the characteristics of how cattle graze, a 10-cm residual stubble height is recommended by the authors as a starting point for improved riparian grazing management. Monitoring should then be conduted to determine if an adjustment is needed. In some situations, 7 cm or even less stubble height may provide for adequate riparian ecosystem function, particularly when streambanks are dry and stable or possibly at high elevations where vegetation is naturally of low stature. In other situations, 15-20 cm of stubble height may be required to reduce browsing of willows or limit trampling impact to vulnerable streambanks. The recommended criterion would apply to streamside and nearby meadow sites with hydrophilic or potentially hydrophilic vegetation, but not directly to dry meadows or even to all wet meadows. Stubble height may have little application where the streambanks are stabilized by coarse substrates, or the channels are deeply incised. The effects of residual stubble height in riparian functions have received limited direect experimental examination. Consequently, much of the information in this review was derived from studies indirectly related to the questions raised and, to some extent, from observations of experienced professionals. The authors have identified areas of scientific investigation needed to improve our understanding of the effects of stubble height on riparian function and grazing management.
    • Suppression of grasshoppers in the Great Plains through grazing management

      Onsager, J. A. (Society for Range Management, 2000-11-01)
      It was hypothesized that grazing management could mitigate grasshopper outbreaks on native rangeland in the northern Great Plains. Key practices would require deliberate variation in timing and intensity of grazing events, preservation of canopy during critical periods of grasshopper development, and reductions in areas of bare soil. The twice-over rotational grazing system appeared compatible with those requirements. Grasshopper population trends were monitored during 1993–1995 and 1997–1998 on commercial native rangeland under twice-over rotational grazing vs traditional season-long grazing. A ubiquitous pest grasshopper, Melanoplus sanguinipes (Fabricius), occurred at every sample site during each year in numbers sufficient to provide life history parameters for comparison between treatments. Under rotational grazing, the nymphs developed significantly slower and their stage-specific survival rates were significantly lower and less variable. Consequently, significantly fewer adults were produced signifi-cantly later in the season under rotational grazing.Seasonal presence of all grasshopper species combined averaged 3.3X higher under season-long grazing than under rotation-al grazing. Local outbreaks that generated 18 and 27 adult grasshoppers per m2 under season-long grazing in 1997 and 1998, respectively, did not occur under rotational grazing. The outbreaks consumed 91% and 168%, respectively, as much forage as had been allocated for livestock, as opposed to 10% and 23%, respectively, under rotational grazing. Of 9 important grasshopper species, none were significantly more abundant at rotational sites than at season-long sites. Three species that were primary contributors to outbreaks under season-long grazing remained innocuous under rotational grazing. It therefore appears that outbreak suppression through grazing management is feasible in the northern Great Plains.
    • Sward quality affected by different grazing pressures on dairy systems

      Mosquera-Losada, M. R.; Gonzalez-Rodríguez, A.; Rigueiro-Rodriguez, A. (Society for Range Management, 2000-11-01)
      The objective of the experiment was to examine the effects of different stocking densities (3.7, 4.6, and 5.5 cows ha- l) on tiller density, botanical composition, and chemical (crude protein [CP], acid detergent fiber [ADF], Ca, P, K, and Mg) quality of pasture and the seasonal (before flowering [spring], after flowering [summer], and autumn) distribution of these parameters. Percentages of sown [perennial ryegrass (Lolium perenne L. cv ‘Brigantia’) and white clover (Trifolium repens L. cv ‘Huia’)] and volunteer species were not significantly affected by stocking density, although as stocking density increased, tiller density also increased. This effect was more pronounced for volunteer species than sown species. Density was significantly higher before flowering than after flowering or autumn. Stocking density affected the chemical quality of herbage with ADF, CP, P, K, and Mg higher at high stocking density. The Ca/P relationship was lower at high stocking density, but the K/(Ca+Mg) relationship was not significantly affected by stocking density. Chemical quality of the pasture was higher before flowering than after flowering or autumn. The Ca/P ratio exceeded the upper limit recommended for dairy cows, but no osteomalacia was found in the presen texperiment. Low values of the K/(Ca+Mg) ratio were found in the spring. Therefore, on these pasture types it is advisable to use concentrates high in Mg or Mg supplements in the spring in order to avoid hypomagnesemia.
    • Technical note: Use of digital surface model for hardwood rangeland monitoring

      Gong, P.; Biging, G. S.; Standiford, R. (Society for Range Management, 2000-11-01)
      We built digital surface models (DSM) that contain 3D surface morphological information of the entire landscape using digital photogrammetry and aerial photographs. Changes in landscape components such as crown closure and tree height in hardwood rangeland were estimated using DSM. In comparison with manual interpretation results, errors of crown closure and tree hieght estimation using DSM were less than 0.7% and 1.5 m, respectively. This technique can be used for rangeland management, monitoring and ecological studies.
    • Tracked vehicle effects on vegetation and soil characteristics

      Prosser, C. W.; Sedivec, K. K.; Barker, W. T. (Society for Range Management, 2000-11-01)
      A 3-year experiment to evaluate tracked vehicle effects on vegetation and soil characteristics was established on the Gilbert C.Grafton South State Military Reservation (CGS) in North Dakota. Study objectives were to evaluate the effects of 3 tracked vehicle use intensity treatments on plant species cover and frequency, and soil compaction. The 3 treatments evaluated include heavy use (74 passes), moderate use (37 passes) and no use. The moderate use treatment represents a typical use of 1 battalion unit at CGS with the heavy use treatment classified as 2 battalion units. This land area comprised a 50 by 150 meter block subdivided into three, 50 by 50 meter blocks. Each 50 by 50 meter block was subdivided into three, 16.7 by 50 meter blocks with each block treated with 1 of the 3 treatments. Soil bulk density increased (P < 0.05) on the moderate and heavy use treatments in the 0 to 15, 30 to 45, and 45 to 60 cm soil depths. Kentucky blue-grass (Poa pratensis L.) cover (P < 0.05) decreased in 1996 on both the moderate and heavy use treatments but was not (P >0.05) different among all treatments in 1997. The tracked vehicle use on the heavy and moderate treatments did not change species composition or litter amounts after 2 years; however, bulk density and bare ground increased on both treatments in 1996 and 1997.