• Viewpoint: Delineating ecological sites

      Creque, J. A.; Bassett, S. D.; West, N. E. (Society for Range Management, 1999-11-01)
      Both the Society for Range Management's (1995) Task Group on Unity in Concepts and Terminology (UCT) and the Natural Resources Conservation Service (1997) have recommended use of the ecological site as the fundamental land unit for evaluation of rangeland condition and trend. While the ecological site concept may be relatively straightforward. in practice the spatial definition of ecological sites within a management unit can prove problematic. This paper presents the use of readily available digital information in a GIS frame-work to delineate ecological sites within a pinyon-juniper/sagebrush semi-desert dominated landscape in Central Utah. An existing model of pre-Euroamerican pinyon-juniper woodland dynamics was combined with the site classification to evaluate landscape dynamics. We also created a map of landscape pattern of potential utility to land managers. The mapping capabilities of GIS offer a simple and remarkably adaptable technique for visual modeling of landscape pattern to assist in meeting a wide array of land management objectives. However. the "objective" delineation of ecological sites must be recognized as being necessarily based on a priori user-selected criteria.
    • Technical Note: Test of observer variability in measuring riparian shrub twig length

      Hall, F. C.; Max, T. (Society for Range Management, 1999-11-01)
      Measurement of riparian shrub twig length before and after use should yield a useful utilization index. A first step towards determining utilization is measurement of twig length. This study appraised variability between 15 observers for measuring dormant season twig length on riparian alder (Alnus incana (L.) Moench) shrubs. Ten streamside shrubs were selected on which 5 branches consisting of 5 twigs each were tagged below the fifth twig for a total of 250 twigs. Fifteen experienced people independently measured twigs on the same day after instruction in the method. Data were analyzed by hierarchical analysis of variance for length of twigs by branches, by shrubs, and by observers. Variation among observers within a branch was about twice the size of variability among shrubs and represented 20% of the total variation. Items contributing to observer variability were measurement of dieback, selecting the twig end or live bud for measurement, inclusion of short lateral leaf stubs in measurements, and selection of a crotch from where the twig is measured. These results clearly illustrate major difficulties in trying to measure riparian shrub utilization.
    • Technical Note: Nitrogen and phosphorus in runoff from 2 montane riparian communities

      Corley, C. J.; Frasier, G. W.; Trlica, M. J.; Smith, F. M.; Taylor, E. M. (Society for Range Management, 1999-11-01)
      It was hypothesized that the type and height of riparian vegetation would affect its ability to filter and retain inorganic nitrogen (nitrate-nitrogen (NO3(-)-N), ammonium-nitrogen (NH4(+)-N), and inorganic phosphorus (phosphate-phosphorus (PO4(-3)-P)). A rotating boom rainfall simulator was used to evaluate 2 montane riparian communities as filters for removing NO3(-)-N, NH4(+)-N, and PO4(-3)-P nutrients from sediment laden overland flow water. One riparian community was characterized by Kentucky bluegrass (Poa pratensis L.) and tufted hairgrass (Deschampsia caespitosa (L.) Beauv.), while the second community was dominated by beaked sedge (Carex rostrata Stokes) and water sedge (Carex aquatilus Wahl.). Three vegetation height treatments were evaluated: control (natural condition), moderate treatment (clipped to 10-cm height and clipped material removed), and heavy treatment (clipped to ground level, clipped material removed, and litter vacuumed up). A 10-m wide riparian buffer zone was an efficient filter as about 84% NO3(-)-N and 79% PO4(-3)-P was removed from the applied water and sediment. However, there were no consistent differences among specific vegetation height treatments or communities in the removal of N and P nutrients.
    • Spittlebug and buffelgrass responses to summer fires in Mexico

      Martin-R, M.; Cox, J. R.; Ibarra-F, F.; Alston, D. G.; Banner, R. E.; Malecheck, J. C. (Society for Range Management, 1999-11-01)
      Summer burning was used to reduce spittlebug (Aeneolamia albofasciata Lall.) populations in buffelgrass [Cenchrus ciliaris (L.) Link] on the Carbo Livestock Research Station in Sonora, Mexico. Five treatments included (1) an untreated control; (2) burning 7-14 days before the summer rains when the insect and the plant were inactive; (3) burning after the accumulation of 50 mm of summer precipitation during insect egg hatch or the second leaf stage; (4) burning between the second and third instars or early culm elongation; (5) and burning between the fifth instar and adult stages or active plant growth during the summer growing season. Summer burning after the accumulation of 50 mm of precipitation and between the egg hatch and the third instars or between the second leaf stage and early culm elongation reduced spittlebug nymph and adult populations by 100% and appeared to stimulate buffelgrass growth for 3 and 4 years post treatment. Burning at the peak of buffelgrass live biomass production effectively controlled spittlebug populations but reduced plant production by almost 50% for 4 years post-treatment. Equally detrimental was the untreated control where nymph and adult spittlebug populations killed more than 50% of the buffelgrass population. Summer fires conducted after 50 mm of precipitation were easier to control than fires conducted before the growing season when plant material was dry.
    • Soil compaction of forest plantations of interior British Columbia

      Krzic, M.; Newman, R. F.; Broersma, K.; Bomke, A. A. (Society for Range Management, 1999-11-01)
      Grazing cattle on forest plantations in the interior of British Columbia (B.C.) is a common practice, but its impact on soil compaction is not well documented. This study evaluated the effects of cattle grazing and forage seeding on soil compaction in lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) plantations near Kamloops, B.C. Grazing regimes consisted of ungrazed exclosures and pastures grazed to achieve 50% utilization of forage vegetation. Seeding treatments were 0 and 12 kg ha-1. Soil bulk density and penetration resistance were determined in 1996 and 1997, before and after the one-month grazing period on study sites grazed since 1989. Water infiltration rates were measured in 1997 after the one-month cattle grazing period. Bulk density was 6% higher on grazed pastures compared to the exclosures. Pastures seeded to domestic forage species had significantly greater soil bulk density at the 0-7.5 cm depth than unseeded pastures. Soil penetration resistance was higher throughout most of the soil profile in the grazed treatments than in the ungrazed exclosures. On pastures without grazing, seeding of the domestic forage species resulted in lower soil penetration resistance relative to unseeded pastures. This was especially true at depths below 6 cm. The rate of water infiltration was not affected by long-term grazing and forage seeding. The bulk density and penetration resistance data indicate that plantation grazing at 50% forage utilization does not lead to root-limiting increases in soil compaction.
    • Soil carbon and nitrogen changes following root-plowing of rangeland

      Teague, W. R.; Foy, J. K.; Cross, B. T.; Dowhower, S. L. (Society for Range Management, 1999-11-01)
      The effects of root-plowing on soil organic carbon and nitrogen were investigated by comparing paired undisturbed native rangeland with root-plowed sites in the southern Great Plains. Time since root-plowing ranged from 4 to 22 years. We hypothesized that following root-plowing (1) soil carbon would initially drop but recover to the level of untreated range within a 5-10 year period, and (2) the permanent removal of mesquite trees, which enhance ecosystem carbon and nitrogen and provide shade that lowers soil temperature, would result in a slow decline in soil carbon and nitrogen in this ecosystem. There were not significant differences due to treatment for either soil carbon mass (g m-2) (P=0.81) or nitrogen mass (P=0.62). There were significant differences in soil carbon mass (P=0.0014) with respect to elapsed time since plowing. The upper soil layer (0-100mm) had higher carbon levels (P=0.0001) than the deeper soil layer (100-200mm)(1422 +/- 210 g m-2 vs. 1111 +/- 206 g m-2). Differences in soil nitrogen were similar to those of soil carbon. There were significant differences in nitrogen among years-since-root-plowing observations (P=0.003) and the upper soil layer had higher nitrogen levels than the deeper soil layer 138 +/- 18 g m-2 vs. 107 +/- 18 g m-2) (P=0.0001). When the data were analyzed using paired native site values as covariate to account for site differences, the sites that had been root-plowed 4 years previously had higher soil carbon (p
    • Sequence grazing systems on the southern plains

      Gillen, R. L.; Berg, W. A.; Dewald, C. L.; Sims, P. L. (Society for Range Management, 1999-11-01)
      Eastern gamagrass (Tripsacum dactyloides (L.) L.) is a perennial warm-season bunchgrass that starts growth earlier in the spring than most other warm-season grasses. This suggests that combining eastern gamagrass with other warm-season grasses in a sequence grazing system could lengthen the period of rapid livestock gain. We studied sequence grazing systems consisting of eastern gamagrass and Old World bluestem (Bothriochloa ischaemum L.) (EG-OWB) as compared to native mixed prairie and Old World bluestem (Native-OWB) from 1993 to 1997. Crossbred beef steers averaging 239 kg grazed eastern gamagrass or native pasture from early May to early June and again from late July through August. Old World bluestem was grazed in mid season. We measured forage yield and nutritive value and steer gain. Standing forage of eastern gamagrass above a 15-cm stubble height averaged 895 kg ha-1 at the start of the first grazing period and 2,430 kg ha-1 at the start of the second grazing period. Dry, cold winter and spring weather reduced this amount to 80 kg ha-1 in May 1996 and precluded grazing the eastern gamagrass that season. Crude protein content of eastern gamagrass was greater than 14% and in vitro dry matter disappearance (IVDMD) was greater than 65% in May. By August, crude protein content had dropped to 5-8% and IVDMD was 45-50%. Peak standing crop of Old World bluestem averaged 4,580 kg ha-1 over years. Steer gain over the entire grazing season, 103 days, did not differ between forage systems, averaging 1.02 kg head-1 day-1 in both systems. Steer gain was higher on native pasture than eastern gamagrass in the late grazing season (0.91 versus 0.60 kg head-1 d-1, p=0.02). As a result of higher stocking rates, steer gain was 257 kg ha-1 for the EG-OWB system and 103 kg ha-1 for the Native-OWB system (p<0.01).
    • Relative costs and feeding strategies associated with winter/spring calving

      May, G. J.; Van Tassell, L. W.; Waggoner, J. W.; Smith, M. A. (Society for Range Management, 1999-11-01)
      Delaying calving season from late winter to late spring has been suggested as a way for producers in Wyoming and other high elevation areas of the West to reduce feeding costs. We hypothesized that shifting calving season to a later date would reduce feed costs by providing a closer match between cow nutritional requirements and nutritional quality of grazable forage. The objectives of this study were to estimate the cost of feeding a cow under 5 alternative calving month scenarios (February through June) and to identify alternative lower-cost forage practices that could replace feeding hay. Mixed integer programming models were constructed for each calving scenario with the objective of minimizing the cost of providing energy and protein to a mature cow. Objective function values from each model were compared to identify the low feed cost calving month. The ration was balanced for each month of the year, with requirements dependent on the interaction between the reproductive cycle and environmental conditions. Fat reserves were included as an alternative energy source and body condition was allowed to fluctuate. Under average weather conditions, June was the lowest feed cost calving month with a reduction in annual feed costs of 43 cow-1 over February calving. The cost reduction was a result of a shift from mechanical to stock harvested forage, with the cow being maintained at a lower average body condition during the winter.
    • Rangeland and steer responses to grazing in the Southern Plains

      Sims, P. L.; Gillen, R. L. (Society for Range Management, 1999-11-01)
      This investigation was to determine the carrying capacity of the Southern Plains mixed-grass prairie by measuring vegetation and yearling steer gain responses to 2 replicates of 3 different grazing intensity treatments between 1941 and 1951. The light, moderate, and heavy grazing treatments, set at 41, 53, and 82 animal-unit-days ha-1 (AUD ha-1), were grazed with straight-bred Hereford steers with an initial weight of 213 +/- 11 (SD) kg from about 13 November to 29 September each year. Basal cover of the individual herbaceous species and the canopy cover of the shrubs were measured along 1,289, 10-m line-transects in the 6 pastures (about 215 per pasture). All treatments showed recovery from a long history of severe grazing and the drought of the 1930's. Vegetation change was largely attributed to favorable precipitation during the study. The basal cover of all perennial grasses was about 5% in 1941 and increased to between 8 and 15% by 1951. The increases were greater in the heavily stocked pastures compared with the light and moderate grazing intensity treatments. Steer gains averaged 168 kg per head. Of this total, 134 kg or 80% occurred in the summer period (Apri1-September). Total live weight gain head-1 decreased as stocking rate increased. Stocking rate affected gain head-1 in both the winter and summer grazing periods. Live weight gain hectare-1 increased as stocking rate increased. Apparently, the maximum gain hectare-1 was not reached within the bounds of the experimental treatments. Net return hectare-1 increased as stocking rate increased. Based on this initial study, carrying capacity of this prairie was greater than 53 AUD ha-1. During extended periods of good rainfall, the carrying capacity of Southern Plains mixed-prairie may reach 82 AUD ha-1.
    • Plant responses to pocket-gopher disturbances across pastures and topography

      Carlson, J. M.; Crist, T. O. (Society for Range Management, 1999-11-01)
      Pocket gophers are important disturbance agents in rangelands, yet little is known about how plant responses to gopher disturbances vary with grazing and topography. We measured the spatial distribution of soil mounds created by the northern pocket gopher (Thomomys talpoides attenuatus Hall and Montague) in shortgrass steppe, and sampled plant cover and species composition on gopher mounds at 3 topographic positions within 2 pastures that were lightly and heavily grazed by cattle. Measurements were taken during 1996 and 1997 in each pasture along a 75 x 900-m transect that spanned the same topographic gradient: a south-facing slope, a north-facing slope, and an upland plain. Pocket-gopher mounds were more numerous in the lightly grazed pasture but mounds were larger in the heavily grazed pasture. An estimated 1-6% of the total area was disturbed on uplands and south-facing slopes, and <1% was disturbed on north-facing slopes. Plant cover on mounds was generally higher in the heavily grazed than in the lightly grazed pasture, primarily due to a greater cover of the dominant perennial grass, blue grama (Bouteloua gracilis [H.B.K.] Lag ex Griffiths). Detrended correspondence analysis also showed that pasture had a greater effect on plant species composition on mounds than topography or yearly variation. Our results demonstrate that topography affected the spatial distribution of pocket-gopher disturbances, and pasture influenced the pool of plant species colonizing mounds. It is therefore important to assess animal-disturbance effects and plant responses to disturbances on rangelands within the broader context of topography and grazing.
    • Nutrient dynamics of rangeland burns in southeastern Arizona

      Emmerich, W. E. (Society for Range Management, 1999-11-01)
      Burning of vegetation generally increases surface runoff and erosion and potentially can change the nutrient dynamics of an ecosystem with loss of nutrients. Nitrogen, phosphorus, and potassium nutrient status of soil and aboveground biomass were determined before fall and spring burns and 1 year later at 2 different soil and vegetation type locations in southeastern Arizona. The evaluations were repeated in subsequent years to evaluate a year effect. Potential nutrient loss in surface runoff and sediment was assessed with rainfall simulations conducted immediately after prescribed burns and after a second burn one year later. Nutrient loss in the runoff water and sediment from burned areas was compared to paired unburned. The soil contained >98% of the total nutrient and was not significantly influenced by the burn treatment. The nutrient concentrations in the regrowth biomass were generally greater. Immediately after the first burn, nutrient loss in surface runoff and sediment was not affected by the burn treatment, but one location was greater than the other. After 1 year and a second burn, nutrient losses on the burn treatment were significantly greater than the unburned treatment and similar between locations. The nutrient loss in surface runoff was primarily associated with the sediment and influenced by an interaction between biomass and soil. The nutrient loss in runoff and sediment was small compared to the nutrient in the aboveground biomass and insignificant compared to the soil nutrient. The implication is that increased surface nutrient loss from burning could take place for many years before a significant amount of nutrient would be lost from the large soil pool and change the nutrient status of the ecosystem. Year and season were also important factors influencing nutrients in the soil, biomass, and in runoff and sediment losses, irrespective of a burn treatment effect.
    • Nitrogen dynamics in stream and soil waters

      Stednick, J. D.; Fernald, A. G. (Society for Range Management, 1999-11-01)
      The mountainous riparian corridor performs important hydrologic functions including nutrient transfers between the terrestrial (upslope) and aquatic (stream) ecosystems. Nitrate-nitrogen and ammonium-nitrogen concentrations were determined on water samples collected in 1993 and 1994 from a montane riparian zone in Northern Colorado. Soil water samples were collected from the riparian corridor and upslope systems, under both losing (summer reservoir releases) and gaining (spring snowmelt runoff) streamflow conditions. Statistical analyses using least square means contrasts were made to identify spatial and temporal differences between: 1) the upslope system and the riparian corridor, 2) the upslope system and the stream, and 3) the riparian corridor and the stream. The Sheep Creek riparian corridor may serve as a sink for nitrate-nitrogen in both gaining and losing streamflow conditions, and as a source for ammonium nitrogen in gaining streamflow conditions. The length of the source or sink period is relatively short and is not meant to suggest differences in site productivity. Streamflow generation mechanisms help determine if the riparian corridor is a nutrient sink or source.
    • Modification of cattle grazing distribution with dehydrated molasses supplement

      Bailey, D. W.; Welling, G. R. (Society for Range Management, 1999-11-01)
      A study was conducted in foothill rangelands during the fall to determine if livestock grazing distribution could be improved by strategic placement of dehydrated molasses supplement blocks (30% crude protein). Three pastures were categorized into inaccessible, easy, moderate, and difficult terrain. Moderate and difficult terrain was further divided into 27 to 55 ha subunits (n=32) and randomly assigned to control or supplement treatments. Every 7 to 10 days supplement and salt were moved; then the new supplement and control subunits were evaluated. Cattle use of the control and supplement subunits was compared by measuring forage utilization and fecal pat abundance both before supplement and salt placement and after removal. Measurements were collected near randomly selected sites within both control and supplement subunits. Salt was placed at half of the sites in both subunits while dehydrated molasses blocks were placed at sites only in the supplement subunit. Average daily supplement intake was lower (p<0.05) in the difficult terrain of 1 pasture (190 g) but ranged from 286 to 386 g in the other areas. Cattle consumed more (P<0.001) salt near supplement than in control areas. More (P<0.01) cattle were observed in areas with supplement (32 +/- 8%) than in control areas (3 +/- 2%). Increase in fecal pats was greater (P=0.01) in areas with supplement (3.3 +/- 07 pats/100 m2) than control areas (0.5 +/- 0.5 pats/100 m2) indicating greater use by cattle. Change in forage utilization was also greater (P>0.001) in areas with supplement (17 +/- 2%) than in control areas (-1 +/- 1%). For supllement areas, the incrase in forage utilization was greater (P < 0.05) in moderate terrain than in difficult terrain. Results from this study suggest that cattle can be lured to underutilizated rangeland by the strategic placement of dehydrated molasses supplement blocks.
    • Intrapopulation genetic variation for seed dormancy in India ricegrass

      Jones, T. A.; Nielson, D. C. (Society for Range Management, 1999-11-01)
      Indian ricegrass (Achnatherum hymenoides [Roem. &Schult.] Barkw. = Oryzopsis hymenoides [Roem. & Schult.] Ricker = Stipa hymenoides Roem. &Schult.) may buffer its seed banks over time via morphological (lemma and palea) and physiological (seed coat) seed dormancy. However, Indian ricegrass seed dormancy has usually not been examined from a genetic perspective. Because a positive relationship between seed dormancy and seed size has long been noted within Indian ricegrass populations we wanted to determine if genetic variation for seed dormancy was present among seed morphs. We also wanted to determine if genetic variation for seed dormancy was present in material without polymorphism. The T-593 population from McKinley Co., N.M., has 3 seed morphs produced on genetically distinct plants, 'elongate' (2.24 mg/seed), 'globose' (3.00 mg/seed), and 'jumbo' (8.70 mg/seed). Following a 3-week prechill, elongate seed showed higher germination (66%) than globose seed (20%) over 6 tests (pairs of seed lots), while jumbo seed did not germinate without scarification. Jumbo seed had thicker (181 microgram) lemmas than globose (93 microgram) or elongate (52 microgram) seed. Individual plants of the nonpolymorphic cultivar, Rimrock, were selected for high or low germination following a 3-week prechill. The spring following seed harvest, germination with prechill was greater for progeny lines of the high-germination selections (45.5%) than low-germination selections (3.8%) with Rimrock intermediate (11.8%). This heritable difference in germination was accompanied by only small differences in lemma and palea thickness and no difference in seed mass. Genetic variation in seed dormancy may be found both between morphs (interpreted as variation for morphological dormancy) and within morphs (interpreted as variation for physiological dormancy). Genetic variation for seed dormancy can be as great within a population as between populations.
    • Heavy stocking and early-season deferment of grazing on Mediterranean-type grassland

      Gutman, M.; Holzer, Z.; Baram, H.; Noy-Meir, I.; Seligman, N. G. (Society for Range Management, 1999-11-01)
      An experiment with beef cows grazing Mediterranean-type grassland was conducted to study the effect of grazing deferment at the beginning of the growing season on pasture productivity and animal performance under intensive herd management conditions. The grazing trial was composed of 4 treatments (deferred grazing at stocking rates of 0.83 and 0.67 cows per ha and continuous grazing at 0.67 and 0.5 cows per ha) replicated in 2 blocks and continued for 5 consecutive years. The herds were given low-energy supplemental feed during deferment and during the dry summer. At the intermediate stocking rate, at which both deferred and continuous grazing were compared, herbage production was significantly reduced by grazing during the 'deferment period' and calf weaning weights without deferment were significantly lower than in the deferred grazing treatments. Weaned live weight per cow was significantly lowest in the continuous intermediate treatment. Weaned weight per hectare was greatest at the highest stocking rate (with deferment). Utilization of supplementary feed per unit weaned live weight was significantly greater in the deferred treatments. Only about a third of the herbage production was grazed, even at the heavy stocking rates. Herbage production varied more between years than between treatments. It is concluded that in the system studied, deferment with supplementary feeding becomes important for both animal and vegetation production as stocking rate approaches and exceeds 0.67 cows ha-1. With deferment, herbage production during the main growing season can be maintained even under heavy grazing pressure. This result can be explained with a simple dynamic growth and grazing model.
    • Grass defoliation intensity, frequency, and season effects on spotted knapweed invasion

      Jacobs, J. S.; Sheley, R. L. (Society for Range Management, 1999-11-01)
      Preventing the invasion of uninfested rangeland is central to managing spotted knapweed (Centaurea maculosa Lam.). Intensity, frequency, and season of grass defoliation determine the ability of grasses to tolerate grazing and resist weed invasion. We hypothesized that as grass defoliation intensity increases, spotted knapweed cover, density, and biomass would increase, that increasing defoliation frequency would increase the intensity effect, and that spring defoliation would cause a greater increase in spotted knapweed than summer defoliation. We hand clipped grasses in 1 m2 plots at 2 spotted knapweed infested Idaho fescue (Festuca idahoensis Elmer) sites in western Montana. Clipping treatments were 4 intensities (0, 30, 60, and 90% of the foliage), 3 frequencies (1, 2, and 3 at 14-day intervals), and 2 seasons (spring beginning in mid-May and summer beginning in mid-July), factorially arranged in a randomized-complete-block design with 4 replications for a total of 24 treatments per replication. Treatments were applied in 1995 and 1996. By 1997 grass cover and density were reduced by defoliation intensity of 90%. Defoliation frequency greater than once caused a reduction in grass cover and density at the 60% intensity. Spring defoliation caused a greater reduction in grass cover and density than summer defoliation. Grass biomass was reduced by the 30% defoliation treatment. Grass defoliation intensity greater than 60% caused an increase in spotted knapweed cover and density. Defoliation more than once increased spotted knapweed cover. Spring defoliations increased spotted knapweed cover compared to summer defoliations. Spotted knapweed biomass was not affected by defoliation treatments. Our study suggests that an annual single grass defoliation of 60% or less, regardless of the season, will not increase spotted knapweed invasion on rangeland.
    • Forage quality of 10 Eastern gamagrass [Tripsacum dactyloides (L.) L.] genotypes

      Bidlack, J. E.; Vaughan, J. E.; Dewald, C. L. (Society for Range Management, 1999-11-01)
      Ten eastern gamagrass [Tripsacum dactyloides (L.) L.] entries from Kansas, Oklahoma, and Texas, were evaluated for in vitro dry matter digestibility (IVDMD), protein concentration, lignin concentration, and phenylalanine ammonia lyase (PAL) activity. Whole plants were harvested in Spring 1992 and 1995 from 4 replicates of each entry and divided into leaf and stem (plus sheath) components for analyses. Entry significantly affected all measurements except PAL; whereas the entry by year interaction significantly affected stem IVDMD, protein, and PAL. Across entries, stem IVDMD in 1992 (56.3% to 66.4%) and 1995 (55.9% to 64.9%) demonstrated greater variation than leaf IVDMD in 1992 (62.2% to 68.0%) and 1995 (66.7% to 71.0%). In 1992 and 1995, average leaf IVDMD and protein concentration were generally higher than average stem IVDMD and protein concentration. In 1992, lignin concentration was generally higher and varied more in stems (3.27% to 4.99%) than in leaves (3.54% to 4.11%). In 1995, lignin concentration was about the same and varied more in leaves compared with stems. Stem IVDMD was significantly correlated with lignin concentration in 1992 (r = -0.92) and 1995 (r = -0.83) as well as with protein concentration (r = 0.83) in 1995. Activity of PAL in 1995 was correlated with stem IVDMD and protein. When all data were combined, IVDMD was significantly correlated with protein concentration (r = 0.82). These results indicate that gamagrass entries demonstrate significant variation in forage quality, particularly in stems. Potential exists for development of new gamagrass cultivars with high IVDMD and protein.
    • Fire history and western juniper encroachment in sagebrush steppe

      Miller, R. F.; Rose, J. A. (Society for Range Management, 1999-11-01)
      The recent expansion of juniper into sagebrush steppe communities throughout the semiarid Intermountain West is most frequently attributed to the reduced role of fire, introduction and overstocking of domestic livestock in the late 1800s, and mild and wet climate conditions around the turn of the century. This hypothesis has, however, limited quantitative support. There are few studies of fire history in the sagebrush steppe and none that examine the chronosequence of changes in mean fire intervals, introduction of livestock, and coincident climatic conditions with the initiation of post-settlement juniper expansion. This study was undertaken to test the hypothesis that the postsettlement expansion of juniper was synchronous with the introduction of domestic livestock, reduction in fire frequency, and optimal climate conditions for plant growth. We documented the fire history and western juniper (Juniperus occidentalis Hook). woodland chronology for a sagebrush steppe in a 5,000 ha watershed in south central Oregon. Regional tree ring data were used as proxy data for presettlement climatic conditions. Western juniper age distribution was determined by coring trees across the study area. Fire history was constructed from several small clusters of presettlement ponderosa pine (Pinus ponderosa Laws.) scattered across the study area. Samples were crossdated to determine fire occurrence to the calendar year. Mean fire intervals were computed for each cluster based on cumulative fire history of each tree sampled within the cluster. Fire events in low sagebrush (Artemisia arbuscula Nutt.) were documented by determining death dates of fire-killed western juniper trees. Records dating the introduction and buildup of livestock during the late 1800s and dates of initial fire suppression were summarized. Western juniper expansion began between 1875 and 1885, with peak expansion rates occurring between 1905 and 1925. The fire record spans 1601 to 1996. Before 1897, mean fire intervals within individual clusters ranged from 12 to 15 years with years between fires varying between 3 to 28. Nearly one third of the fires in the basin were large and usually proceeded by one year of above-average tree ring growth. Two fire events were recorded in the sparsely vegetated low sagebrush site, 1717 and 1855. The last large fire occurred in the study area in 1870 and the last small fire in 1897. The time sequence of wet climatic conditions between 1870 and 1915, introduction of livestock, and the reduced role of fire support the hypothesis that these factors contributed to the postsettlement expansions of western juniper.
    • Economics of redberry juniper control in the Texas Rolling Plains

      Johnson, P.; Gerbolini, A.; Ethridge, D.; Britton, C.; Ueckert, D. (Society for Range Management, 1999-11-01)
      Redberry juniper (Juniperus pinchotii Sudw.) is a common invasive brush species that reduces rangeland productivity over vast acreages in the Rolling Plains and Edwards Plateau regions of Texas. The objectives of this study were to evaluate the economic feasibility of redberry juniper control and determine the optimum treatment cycle for maintenance burning. A response equation was used to estimate the relationship between herbage production and redberry juniper canopy. Data to estimate the relationship was obtained for a site in the Texas Rolling Plains. The analysis used chaining as the initial treatment and periodic prescribed burns as maintenance treatments. Additional livestock production resulting from brush treatments and the costs of treatments were estimated and used to calculate net present values of the investment in brush control over a 30-year time horizon. Net present values indicated that juniper control was economically feasible across a wide range of economic and environmental conditions. Prescribed burn intervals were found to be optimal at 7-year intervals under most conditions.