• Overcoming dormancy in New Mexico mountain mahogany seed collections

      Rosner, Lee S.; Harrington, John T.; Dreesen, David R.; Murray, Leigh (Society for Range Management, 2003-03-01)
      Mountain mahogany (Cercocarpus montanus Raf) is a useful reclamation species because it can occupy and improve poor soils. Literature regarding seed propagation of this species is varied and often contradictory, recommending stratification durations of 14 to 90 days, and sulfuric acid scarification durations of none to 60 minutes. To assess variability in propagation requirements among seed sources, 8 New Mexico seed sources were tested with factorial combinations of scarification and stratification treatments. Sources were selected to encompass both a range of latitudes throughout New Mexico and a range of elevations at Questa, N. M. Seeds were scarified 5 or 10 minutes in concentrated sulfuric acid, tumbled 5 or 10 days in course grit, or unscarified (control). Seeds underwent subsequent stratification for 0 (control), 30, or 60 days. Averaged across scarification treatments, the 2 southernmost sources lacked a stratification requirement, while northern seed sources achieved their highest germination following the longest stratification duration (60 days). Improvement in germination due to stratification was greatest for the 2 highest elevation Questa sources. Scarification treatments were less effective in improving germination than stratification treatments, and produced more variable results. A 5-minute soak in sulfuric acid was the most effective scarification treatment, but for 2 sources, this treatment reduced germination. Variability in the stratification requirement appears to be an adaptation to macroclimatic differences among seed sources, whereas differential response to scarification may be a response to microclimatic differences.
    • Prescribed fire effects on dalmatian toadflax

      Jacobs, James S.; Sheley, Roger L. (Society for Range Management, 2003-03-01)
      Prescribed fires are important for rangeland restoration and affect plant community composition and species interactions. Many rangeland plant communities have been, or are under the threat of noxious weed invasion, however there is little information on how fire effects weeds. Our objective was to determine the effects of prescribed rangeland fire on dalmatian toadflax [Linaria dalmatica (L.) Miller] density, cover, biomass, and seed production. These plant characteristics, as well as density, cover, and biomass of perennial grasses and forbs were measured within burned and adjacent not-burned areas on 3 Artemisia tridentata/Agropyron spicatum habitat types in Montana. Areas were burned in the spring and measured in the fall 1999. Comparisons of plant characteristics between the burned and not-burned sites were made using t-tests and non-parametric Wilcoxon Rank Sum tests. After 1 growing season, fire did not affect density or cover of dalmatian toadflax. Burning increased dalmatian toadflax bio- mass per square meter at 2 sites, and per plant biomass at all 3 sites. Seed production of dalmatian toadflax was increased by fire at all 3 sites. Fire reduced forb cover at 1 site and increased grass biomass at 2 sites. The increases in dalmatian toadflax biomass and seed production suggest that fire used to restore healthy plant communities may increase dalmatian toadflax dominance. We recommend weed management procedures, such as herbicide control and seeding desirable species, be integrated with prescribed fire where dalmatian toadflax is present in the plant community.
    • Vegetation dynamics from annually burning tallgrass prairie in different seasons

      Towne, E. Gene; Kemp, Ken E. (Society for Range Management, 2003-03-01)
      Traditional perception of how tallgrass prairie responds to fire at times other than late spring is either anecdotal or extrapolated from studies that lack spatial or temporal variability. Therefore, we evaluated patterns of change in vegetation cover, species richness, diversity, and aboveground biomass production on 2 different topographic positions from ungrazed watersheds that were burned annually for 8 years in either autumn (November), winter (February), or spring (April). Topoedaphic factors influenced the response patterns of some species to seasonal fire, although differences were primarily in the rate of change. Annual burning in autumn and winter produced similar trends through time for most species. Big bluestem (Andropogon gerardii Vitman) cover increased with all burn regimes, whereas indiangrass [Sorghastrum nutans (L.) Nash] increased only with spring burning. Repeated autumn and winter burning eventually increased perennial forb cover, with the largest increases occurring in heath aster [Symphyotrichum ericoides (L.) Nesom], aromatic aster [S. oblognifolium (Nutt.) Nesom], tall goldenrod (Solidago canadensis L.), and legumes. Species richness increased (P < 0.001) through time with spring and winter burning, but was similar among all burn treatments after 8 years of annual fire. Average grass and forb biomass did not differ among burn seasons on either topographic position, although interannual biomass production fluctuated inconsistently with time of burn. Our findings contrast with many of the conventional views of how tallgrass prairie vegetation responds to seasonal fire and challenges traditional recommendations that burning should only occur in late spring.
    • Mineral concentration dynamics among 7 northern Great Basin grasses

      Ganskopp, Dave; Bohnert, Dave (Society for Range Management, 2003-03-01)
      Livestock and wildlife managers must be aware of the nutritional dynamics of forages to sustain satisfactory growth and reproduction of their animals and assure fair value for pasture. Despite a history of livestock grazing in the northern Great Basin, annual and seasonal mineral concentrations of many of the region's prominent grasses have not been measured. We addressed this problem with monthly sampling (April-November) of 7 cool-season grasses at 6 sites during 1992, a drier than average year (86% of mean precipitation), and 1993 when precipitation was 167% of average (255 mm). Grasses included: Poa sandbergii Vasey, Bromus tectorum L., Sitanion hystrix (Nutt.) Smith, Agropyron spicatum (Pursh) Scribn. & Smith, Festuca idahoensis Elmer, Stipa thurberiana Piper, and Elymus cinereus Scribn. & Merr. Phosphorus, K, Ca, Mg, Mn, Fe, Cu, Zn, and Na were assayed, and initial statistical analysis was a split-split-plot with main effects of species, years, and months and all possible interactions. For a preponderance of the minerals, (Zn and Na excluded) the 3-way year x month x species interactions were significant (P < 0.05) indicating that main effects did not function independently. Generally, mineral concentrations averaged about 41% higher among the grasses for the drier of the 2 years (1992). Copper, Zn, and Na concentrations were below required levels for beef cattle (9.9, 28.8, and 672 mg kg-1, respectively) among all the grasses for all sampling periods. Seasonally deficient minerals included Ca, Mg, P, K, and Mn. Calcium and Mn were largely deficient (< 3.2 and 1.15 g kg-1, respectively) for beef cattle early in the growing season with levels rising as grasses matured. Seasonal patterns of Mg were variable among the grasses, increasing in some as the season progressed, remaining stable among others, and declining with maturity in yet others. Phosphorus and K levels were typically adequate (> 1.94 and 5.76 g kg-1, respectively) for beef cattle early in the growing season and declined to deficient levels by July and August. Iron was of no concern, because concentrations were more than adequate for cattle (> 48 mg kg-1) among all the grasses for all seasons. While a mixed stand of forages can extend the period of adequate mineral nutrition for cattle in some instances, we suggest that a supplement be available season-long on northern Great Basin rangelands and that the formulation include at least Ca, Mg, P, K, Cu, Zn, Mn, and Na in available forms and proper ratios.
    • Stocking rate effects on goats: A research observation

      Mellado, Miguel; Valdez, Raul; Lara, Laura M.; Lopez, Ramiro (Society for Range Management, 2003-03-01)
      Knowledge on the ecological effects of goat grazing on arid rangeland is far from complete, and specifically there is little scientific information on effects of heavy goat grazing on arid ecosystems. One objective of this study was to determine botanical composition of dairy-type goat diets on heavily (1.5 ha per goat) and lightly (15 ha per goat) grazed Chihuahuan desert range by fecal microhistological analysis. A second objective was to determine whether vegetation cover, some blood metabolites and mineral levels, as well as fertility of goats were sensitive to high grazing pressure. The lightly grazed site had more (P < 0.05) total foliage cover (38.6 vs 30.4%) than the overstocked pasture. Total shrubs in diets of goats was greater (86.4 vs 72.4 in the late-dry period, 78.6 vs 42.1 in late-wet period; P < 0.05) on the heavily stocked pasture than the lightly stocked pasture. Forbs in the diets were lower (P < 0.10) in the late-dry (11.4 vs 21.5%), early-wet (55.4 vs 64.0%) and late-wet period (15.0 vs 45.8%) on the heavily stocked pasture than the lightly stocked pasture. Substantially lower (P < 0.01) serum glucose, urea nitrogen, Zn and Mg concentration at the onset of the breeding period in goats on the heavily stocked pasture, compared to goats on the lightly grazed pasture resulted in a higher (P < 0.01) abortion rate (22 vs 12%) and consequently a lower (P < 0.05) kidding rate (42 vs 55%). We concluded that overstocking with goats greatly reduced shrub and grass cover. Also, decades of continuously high grazing pressure has forced goats to alter diet selection pattern by consuming more resinous, toxic, and coarse species. This switch was associated with a lower nutritional status, a negative daily weight gain, lower body condition score in the late-wet period, and lower fertility on heavily grazed range.
    • Woody vegetation response to various burning regimes in South Texas

      Ruthven, Donald C.; Braden, Anthony W.; Knutson, Haley J.; Gallagher, James F.; Synatzske, David R. (Society for Range Management, 2003-03-01)
      Responses of woody plant communities on native rangelands in the western South Texas Plains to fire are not clearly understood. Our objective was to compare woody plant cover, density, and diversity on burned and nontreated rangelands. Five rangeland sites that received 2 dormant-season burns, 5 rangeland sites that received a combination of 1 dormant-season and 1 growing-season burn, and 5 sites of nontreated rangeland were selected on the Chaparral Wildlife Management Area, Dimmit and La Salle Counties, Tex. Woody plant cover was estimated using the line intercept method, and stem density was estimated in 25-x 1.5-m plots. Species richness did not differ among treatments. Percent woody plant cover was reduced by 50 and 41 % on winter and winter-summer combination burned sites, respectively. Honey mesquite (Prosopis glandulosa Torr.), twisted acacia (Acacia schaffneri S. Wats.), Texas persimmon (Diospyros texana Scheele), lotebush [Ziziphus obtusifolia (Hook.) T. & G.], wolfberry (Lycium berlandieri Dunal), and tasajillo (Opuntia leptocaulis Cand.) canopy cover was greatest on nontreated sites. Woody plant density declined by 29 and 23% on winter and winter-summer combination burned sites, respectively. Density of guayacan (Guajacum angustifolium Engelm.), wolfberry, and tasajillo was less on all burning treatments. Percent cover of spiny hackberry (Celtis pallida Torr.) and density of Texas pricklypear (Opuntia engelmannii Salm-Reif.-Dyck) declined on winter burned sites. Inclusion of summer fire into the burning regime did not increase declines in woody plants. Fire created a post-fire environment which resulted in the decline of many woody plant species. It is unclear to what degree other environmental factors such as herbivory and competition between woody plants and among woody and herbaceous vegetation may have interacted with fire in producing woody plant declines. Fire may be a useful tool in managing woody vegetation on native south Texas rangelands, while maintaining woody plant diversity.
    • Hydrologic and sediment responses to vegetation and soil disturbances

      Giordanengo, J. H.; Frasier, G. W.; Trlica, Frasier (Society for Range Management, 2003-03-01)
      Soil erosion has been linked to stream sedimentation, ecosystem degradation, and loss of rangeland productivity. However, knowledge of soil loss, as it affects rangeland productivity or ecosystem sustainability is lacking. We evaluated the effects of 3 levels of vegetation cover reduction (0, 27%, and 43%) and soil removal (0, 12, and 24 tonnes ha-1) on soil surface runoff and sediment yield in a sagebrush [Artemisia tridentata var. vasseyana (Rydb.) Beetle] steppe under simulated rainfall. Time to runoff initiation was affected by the vegetation cover reduction treat- ments, but not by the soil removal treatments. The 43% vegeta- tion canopy reduction treatment resulted in a shorter time to runoff initiation than did the 27% and 0% canopy reduction treatments (p = 0.002). Results from analysis of covariance indicated that vegetation reduction and soil removal did not significantly affect sediment yield or runoff quantities in the first year following treatments. Multiple regression analysis revealed total sediment yield was related to forb cover, sand in the upper soil profile (0-5 cm), and the amount of bare ground. Time to runoff initiation was positively correlated with slope. Despite the lack of significant treatment differences, we do not conclude that these soil removal and vegetation reduction treatments had no affect on soil surface hydrology and sediment yield. There are numerous studies that show a strong relationship between vegetation reduction and soil erosion. Future research at this site may reveal long-term treatment effects that were not apparent in first year results.
    • An index for description of landscape use by cattle

      Zuo, Haitao; Miller-Goodman, Mary S. (Society for Range Management, 2003-03-01)
      Understanding the role of landscape diversity in livestock distribution patterns is an important consideration for design of effective grazing systems. The objective of this study was to develop and evaluate a Distribution Evenness Index (DEI) based on the Shannon-Wiener index to characterize cattle distribution patterns for a heterogenous landscape within a given period of time. Observations of diurnal behavior of beef cattle (Bos taurus) were made in grassland, wooded, and riparian habitats within a fenced landscape from March to October 2000 at a farm in north-central Alabama. The DEI was calculated based on observation records at different time intervals (15-, 30-, and 60-min) and different levels of grassland habitat subdivision (18-, 9-, and 6-zones). Comparisons of calculated DEI values were made among different habitat types, observation intervals, landscape subdivision levels, and daytime periods. Annual DEI means indicated low evenness of cattle distribution in riparian (0.517) and wooded habitats (0.606), and consistently high evenness in the grassland habitat (0.860). Although grazing activity in the grassland habitat was uneven between different daytime periods (0.565 to 0.679), when combined for the total daytime period, grazing activity in the grassland habitat had a high evenness value (0.855). Relative stability of the DEI calculated between selected spatial and temporal scales in this study indicated that the index may be useful for comparison of evenness of livestock habitat use and grazing patterns between different studies at similar spatial and temporal scales.
    • A digital photographic technique for assessing forage utilization

      Hyder, P. W.; Fredrickson, E. L.; Remmenga, M. D.; Estell, R. E.; Pieper, R. D.; Anderson, D. M. (Society for Range Management, 2003-03-01)
      Changes in forage utilization have been difficult to measure non-destructively without some level of subjectivity. This subjectivity, combined with a lack of reproducibility of visual estimates, has made forage utilization measurement techniques a topic of considerable discussion. The objective of this study was to develop and test the accuracy and repeatability of an objective, computer-based technique for measuring changes in plant biomass. Digital photographs of target plants acquired before and after partial defoliation were analyzed using readily available image analysis software. Resulting data were used to develop a simple linear random coefficient model (RC) for estimation of plant biomass removed based on the area of the plant in the photo. Sample collection took approximately 20 minutes/plant for alfalfa (Medicago sativa L.). Analysis of images took another 60 to 90 minutes. Regression analysis gave an R2 of 0.969 for predicted vs. observed plant weights. Testing this model using 10 alfalfa plants yielded weight estimates of defoliated plants accurate to within +/- 8.5%. The advantage of the RC model is its ability to use easily obtained coefficients from simple linear regression models developed from each plant in a way that accounts for the lack of independence between samples within an individual plant. The technique described here offers an objective and accurate method for measuring changes in plant biomass with possible applications in ecology, botany, and range science. In particular, application of this technique for estimating forage utilization may improve accuracy of estimates and, thereby, improve range management practices.
    • Moderate and light cattle grazing effects on Chihuahuan Desert rangelands

      Holecheck, Jerry; Galt, Dee; Joseph, Jamus; Navarro, Joseph; Kumalo, Godfrey; Molinar, Francisco; Thomas, Milt (Society for Range Management, 2003-03-01)
      Vegetation changes were evaluated over a 13 year period (1988-2000) on moderately grazed and lightly grazed rangelands in the Chihuahuan Desert of south central New Mexico. During the study period, grazing use of primary forage species averaged 49 and 26% on moderately and lightly grazed rangelands, respectiely. Autumn total grass and black grama (Bouteloua eriopoda Torr.) standing crop were consistently higher on the lightly than moderately grazed rangeland throughout the study. Total grass standing crop declined on the moderately grazed rangeland when the last 3 years of study were compared to the first 3 years (10 versus 124 kg ha-1), but showed no change on the lightly grazed rangeland (320 versus 357 kg ha-1). Black grama, the primary perennial grass in the Chihuahuan Desert, increased in autumn standing crop on the lightly grazed rangeland, but decreased on the moderately grazed rangeland (97% decline) than on the lightly grazed rangeland (67% decline). Perennial grass survival following a 3-year period of below average precipitation was higher on the lightly grazed (51%) than the moderately grazed rangeland (11%). Severe grazing intensities on the moderately grazed rangeland during the dry period (1994-1996) appear to explain differences in grass survival between these 2 rangelands. Our study and several others show that light to conservative grazing intensities involving about 25-35% use of key forage species can promote improvement in rangeland ecological condition in the Chihuahuan Desert, even when accompanied by drought.
    • Hay-meadows production and weed dynamics as influenced by management

      Magda, Daniele; Theau, Jean-Pierre; Duru, Michel; Coleno, François (Society for Range Management, 2003-03-01)
      Managers of extensive livestock systems generally have 2 goals for permanent grassland management: to obtain sufficient dry matter to feed animals and to avoid the establishment and dominance of unpalatable species. Hay production to French Pyrenean meadows is dependant on the need to balance grazing and cutting dates to produce maximum biomass for hay stock and to prevent seed recruitment of Chaerophyllum aureum L., one of the major invasive unpalatable species. Experiments and observations on a set of meadows within farms show that optimal dates calculated from degree-days for cutting or spring grazing of C. aureum fitted to see production and apex development, respectively, decreases hay yield. This decrease is related to the earliness of the cut in regard to sward growth or to the biomass loss by senescence due to the vegetative regrowth of the sward after spring grazing. Compromises and choices have to be made for each meadow by the farmer according to its potential production, the risk of invasion by C. aureum, and its role in the forage system.
    • Development and use of state-and-transition models for rangelands

      Bestelmeyer, Brandon T.; Brown, Joel R.; Havstad, Kris M.; Alexander, Robert; Chavez, George; Herrick, Jeffrey E. (Society for Range Management, 2003-03-01)
      State-and-transition models have received a great deal of attention since the introduction of the concept to range management in 1989. Nonetheless, only recently have sets of state-and-transition models been produced that can be used by agency personnel and private citizens, and there is little guidance available for developing and interpreting models. Based upon our experiences developing models for the state of New Mexico, we address the following questions: 1) how is information assembled to create site-specific models for entire regions, 2) what ecological issues should be considered in model development and classification, and 3) how should models be used? We review the general structure of state-and-transition models, emphasizing the distinction between changes among communities within states (pathways) that are reversible with changes in climate and “facilitating practices” (e.g. grazing management), and changes among states (transitions) that are reversible only with “accelerating practices” such as seeding, shrub control, or the recovery of soil stability and historical hydrologic function. Both pathways and transitions occur, so these models are complementary. Ecological sites and the climatically-defined regions within which they occur (land resource units) serve as a framework for developing and selecting models. We illustrate the importance of clearly delineating ecological sites to produce models and describe how we have dealt with poorly-delineated sites. Producing specific models requies an understanding of the multiple ecological mechanisms underlying transitions. We show how models can represent and distinguish alternative and complementary hypotheses for transitions. Although there may be several mechanisms underlying transitions, they tend to fall within discrete categories based upon a few, fundamental ecological processes and their relationships can be readily understood. A knowledge of mechanisms is closely related to the use of ecological indicators to anticipate transitions. We conclude that models should include 1) reference values for quantitative indicators, 2) lists of key indicators and descriptions of changes in them that suggests an approach to a transition, and 3) a rigorous documentation of the theory and assumptios (and their alternatives) underlying the structure of each model.
    • State and transition modeling: An ecological process approach

      Stringham, Tamzen K.; Krueger, William C.; Shaver, Patrick L. (Society for Range Management, 2003-03-01)
      State-and-transition models hold great potential to aid in understanding rangeland ecosystems’ response to natural and/or management-induced disturbances by providing a framework for organizing current undersanding of potential ecosystem dynamics. Many conceptual state-and-transition models have been developed, however, the ecological interpretation of the model’s primary components, states, transitions, and thresholds, has varied due to a lack of universally accepted definitions. The lack of consistency in definition has led to confusion and criticism indicating the need for further development and refinement of the theory and associated models. We present an extensive review of current literature and conceptual models and point out the inconsistencies in the application of nonequilibrium ecology concepts. The importance of ecosystem stability as defined by the resistance and resilience of plant communities to disturbance is discussed as an important concept relative to state-and-transition modeling. Finally, we propose a set of concise definitions for state-and-transition model components and we present a conceptual model of state/transition/threshold relationships that are determined by the resilience and resistance of the ecosystems’ primary ecological processes. This model provides a framework for development of process-based state-and-transition models for management and research.