Simulated Grazing Research Articles

Effects of Water Stress and Simulated Grazing on Leaf Elongation and Water Relations of an East African Grass, Eustachys paspaloides

Eustachys paspaloides was studied under conditions of water stress and simulated grazing (clipping) in the laboratory. Leaf and soil water potentials and leaf elongation rate (LER) were monitored during a 41-day drying period, and following rewatering. Water relations characteristics of tillers were derived from pressure-volume curves during the drought and recovery periods. Water stress developed more slowly in clipped than in unclipped plants; predawn water potentials declined at mean rates of 0.13 and 0.38 MPa day-1 in clipped and unclipped plants, respectively. Consequently, leaf elongation of clipped plants continued approximately a week longer during the drying period than when plants were not clipped. Following rewatering, LER increased from zero to steady levels over 4 days. Osmotic adjustment due to solute accumulation occurred in tillers of water-stressed plants. The difference in solute potential at full turgor between well-watered and stressed plants was 0.29 and 0.20 MPa for clipped and unclipped plants, respectively. The delay in permanent wilting afforded by lowered osmotic potential was about 1 day, indicating that osmotic adjustment is not a mechanism for reducing the effect of water stress on growth during long-term drought in Eustachys. However, osmotic adjustment may be an acclimation response to short-term drought during the growing season, and may aid in survival during the long dry season by limiting dehydration of the growing points.

THE IMPORTANCE OF SUBDIVISION AND MANAGEMENT PRACTICES IN IMPROVING HILL COUNTRY PRODUCTIVITY

The association between subdivision and other management resource inputs and levels of hill country sheep productive performance are reported in this paper. An analysis of computer simulated grazing systems and practices adopted by a sample of thirty farmers in North-East Wairarapa indicates that high levels of production were achieved with variable levels of subdivision. Appropriate grazing systems were often limited by poor planning and implementation rather than inadequate permanent fencing. Although subdivision was associated with higher autumn sheep liveweights on the survey farms, similar or larger increases could be achieved by refinmg existing management systems. Further increases in subdivision therefore may not lead to increases in productivity on many hill country farms. Keywords: Subdivision, hill country, management, computer simulation, survey, grazing systems.

DOES INTERFERENCE CAUSE NICHE DIFFERENTIATION? EVIDENCE FROM SUBALPINE PLANT COMMUNITIES

The effects of interference on community structure of subalpine meadows were investigated. Adults greatly reduced seedling survival in the greenhouse, and natural seedling survival was low. In fell fields, nurse plant effects were common, while survival was confined to gaps in productive meadows. A greenhouse experiment demonstrated that community dominants were strong competitors able to suppress subordinates. Simulated grazing of Festuca, a dominant, reduced its yield relative to most subordinates. Interference intensity appears to be a function of productivity and proximity. The proportion of negative species associations increased as productivity increased. Morphological similarity between species is least in the most productive community, but greatest where productivity is only moderate. Interference may permit only relatively dissimilar species to coexist unless it is ameliorated by factors such as grazing or heterogeneity. Spacing patterns suggest that minimal contact between dominants and other species is a characteristic of communities with intense interference. The evidence points to this hypothesis: interference acts contemporaneously to limit niche width in productive communities, but evolutionary changes are unlikely where complete dominance is possible and specialization is not a viable option. In contrast, species in unproductive communities, where abiotic stress is likely to have been an evolutionary force, appear genetically more niche differentiated. Where contemporary interference is moderate, evolutionary effects are possible because species may use resources not preempted by the dominants.

Does Interference Cause Niche Differentiation? Evidence from Subalpine Plant Communities

The effects of interference on community structure of subalpine meadows were investigated. Adults greatly reduced seedling survival in the greenhouse, and natural seedling survival was low. In fell fields, nurse plant effects were common, while survival was confined to gaps in productive meadows. A greenhouse experiment demonstrated that community dominants were strong competitors able to suppress subordinates. Simulated grazing of Festuca, a dominant, reduced its yield relative to most subordinates. Interference intensity appears to be a function of productivity and proximity. The proportion of negative species associations increased as productivity increased. Morphological similarity between species is least in the most productive community, but greatest where productivity is only moderate. Interference may permit only relatively dissimilar species to coexist unless it is ameliorated by factors such as grazing or heterogeneity. Spacing patterns suggest that minimal contact between dominants and other species is a characteristic of communities with intense interference. The evidence points to this hypothesis: interference acts contemporaneously to limit niche width in productive communities, but evolutionary changes are unlikely where complete dominance is possible and specialization is not a viable option. In contrast, species in unproductive communities, where abiotic stress is likely to have been an evolutionary force, appear genetically more niche differentiated. Where contemporary interference is moderate, evolutionary effects are possible because species may use resources not preempted by the dominants.

Effects of Phosphorus Nutrition and Defoliation on C4 Graminoids from the Serengeti Plains

Kyllinga nervosa (Cyperaceae) and Digitaria macroblephara (Poaceae), C4 graminoids, were obtained from the Serengeti National Park of Tanzania. Kyllinga is most abundant on high pH, high calcium, low phosphorous, carbonatitic ash—derived soils, and Digitaria is more abundant on neutral, lower calcium, higher P soils. Both species come from intensely grazed grasslands. Plant responses to different nutritional levels and defoliation were measured to evaluate potential limiting interactions between energy and nutrient flows in grazing ecosystems. Plants were grown hydroponically at solution phosphorus concentrations of 10 and 100 μmol/L and were either unclipped or clipped weekly to a height of 3 cm for 5 wk. At that time, the kinetics of P uptake were measured with 32P, plants were harvested, and dry masses and the tissue concentrations of P and N were determined. Clipping and P concentration of the growth medium both had major effects upon yields of all plant components. Total yield of Kyllinga was highest in unclipped plants at high levels of P supply; yields under all other conditions were lower and indistinguishable from one another. In contrast, yield of Digitaria, which had been collected in areas with soils of higher phosphorus availability, was unaffected by defoliation but was almost 21/2 times greater when plants were grown at the higher P level. Root growth of Digitaria was stimulated by defoliation when P was abundant. Maximum yield to grazers from Kyllinga under conditions of this experiment would be achieved if grazers foraged only at the end of the period; maximum yield of Digitaria to grazers would be achieved if grazers defoliated plants at frequent intervals. A variety of morphological changes associated with maintaining similar leaf areas whether clipped or unclipped were associated with Digitaria's ability to compensate for simulated grazing. Yield to producers (the residual live biomass present at harvest) and yield to grazers were positively correlated, indicating that conditions promoting plant yield caused a proportional increase in yield to higher trophic levels. Maximum concentrations of P and N in the tissues of both species occurred in plants that were clipped and were grown at the high P level. N concentration was positively correlated with P concentration when plants were grown at high P, but was unrelated to tissue P concentrations when plants were grown at low P. That pattern reflects luxury N uptake of plants grown at low P. Nutrient uptake rate per unit root mass was higher in Digitaria than in Kyllinga. Defoliation stimulated nutrient uptake rate in both species, primarily due to decrease Km rather than changes in Vmax. Total P accumulation per plant (predicted from uptake rates measured with 32P, root mass, and nutrient mass, and nutrient solution P concentrations) was closely and positively correlated with measured P accumulation. However, P accumulation over the experiment fell far below predicted amounts. That disparity was likely due to low root biomasses early in the experiment and nutrient depletion between solution renewals.

Western Wheatgrass Responses to Simulated Grazing

To evaluate responses of range grasses to herbage removal, removal patterns should simulate those under grazing. We compared responses of western wheatgrass (Agropyron smithii Rydb.) in mixed-grass range to no clipping, conventional clipping, and clipping which simulated continuous grazing. Two years of simulated grazing did not affect herbage production or tiller numbers, but both declined under conventional clipping. Belowground phytomass decreased as herbage removal increased. Total nonstructural carbohydrate concentration in rhizomes decreased when utilization exceeded about 40930, but that of roots and crowns decreased only when utilization exceeded 60-70%. Most clipping studies of range grasses make little effort to simulate herbage removal patterns which occur under grazing. Clipping studies usually include clipping at uniform heights, not random heights as occurs under grazing (Jameson 1963), and more severe defoliation than occurs under grazing (Heady 1961). Harris (1976) indicated that frequency, intensity, and timing of defoliation all influence plant responses. Lack of knowledge of these parameters has inhibited design of realistic clipping experiments. Hart and Balla (1982) photographed western wheatgrass (Agropyron smithii Rydb.) tillers at intervals during the grazing season and determined frequency, intensity, and timing of herbage removal. We used this information to design a clipping experiment ‘which simulated grazing more closely than ever before, and compared response of western wheatgrass under simulated grazing to that under conventional clipping and no clipping. Our objective was to provide better guides to grazing management than could be provided from responses to conventional clipping. thread (Stipa comata Trin. & Rupr.). Soils underlying the study plots were a fine-loamy Aridic Argiustoll of the Altvan Series. Stevenson et al. (1984) have given a more complete description of the range sites and vegetation of the research station. Twenty-four plots (25 X 40 cm) were established on an area of native range ungrazed since 1978 and containing450-600 tillers/m* of western wheatgrass. Each plot was bordered by aluminum lawn edging placed into the ground approximately 20 cm to eliminate rhizome spread between plots and between the plots and adjacent native range. Four replications of 6 treatments, in a randomized complete block design, were applied to the 24 plots. The 6 treatments included an unclipped control, clipping western wheatgrass to 2.5 cm 4 times during the summer, and 4 clipping treatments simulating 4 levels of continuous grazing of western wheatgrass. Frequency under simulated continuous grazing was defined as the percentage of tillers clipped 0, I, 2,3, or 4 times, while intensity was the percentage of clipping events at which I / 3,2/ 3, or all the aboveground herbage was removed from a tiller. Two frequencies (Table 1) times 2 intensities (Table 2) gave us 4 simulated grazing treatments.

A simulation model for managing perennial grass pastures. Part II—a simulated systems analysis of grazing management

A model for managing perennial grass pastures was used to simulate a grazing experiment on common bermudagrass pastures at Booneville, Arkansas. The experiment used sixteen years' weather data from this location. The management variables included number of fields, rotation period, and simulated grazing rate. The grazing season was from 1 June to 22 September each year, and simulated performance data were obtained for successive six-day periods throughout the grazing season. The attributes of performance data included: daily harvest rate, digestible dry matter and cell content nitrogen harvested, potential tissue production, reserve carbohydrates at the end of the year and the ratio of forage on offer to the simulated grazing rate. Analyses of these simulated performance data provided an inference base to support a recommendation concerning the management variables. The recommendation is as follows: a four-field system, a nine-day rotation period and 84 kg/ha/day simulated grazing rate. The results along with other simulated grazing scenarios will be used to plan field experiments at Booneville, Arkansas.

Grazing of Utetheisa pulchelloides Larvae on Its Host Plant, Argusia argentea, on Coral Cays of the Great Barrier Reef

The foraging behavior and grazing intensities of Utbetbeisa puLrbeLLoides (Lepidoptera: Arctiidae) larvae were examined on its host plant, Argusia argentea, a prostrate shrub commonly found on coral cays of the Great Barrier Reef. Larval abundance was greatest during summer (January-February), just after the major flush of Argusia leaves. The larvae were host specific, consuming approximately 2.9 cm2 leaf area/day (annually 2-5% Argusia leaf production of One Tree Island), and exhibited significant preferences for windward, shade leaves. Their diurnal activity w-as comprised of 53 percent feeding, 8 percent moving, and 39 percent resting. Displacement experiments showed greatest nonrandom tendency to relocate the host planr when navigating westward, but nonetheless involved a large time and energy investment. The turnover of Argusia leaf biomass through the grazing pathway is not high; presumably predators, physical environment. or factors other than food supply limit the Utetheisa populations on coral cays. ALTHOUGH HERBIVOROUS LARVAE ARE COMMONLY ASSOCIATED WITH FOREST COMMUNITIES, the dispersal and feeding behavior of individuals are difficult to determine in this habitat due to the logistic problems associated with the structural complexity and inaccessibility of the canopy. Because of these problems encountered in the field, most studies on feeding behavior of insect herbivores have been confined to the laboratory (Cates and Orians 1975, Scriber and Feeny 1979). Most defoliation studies rely on both controlled conditions and simulated grazing methods (e.g., Lee and Bazzaz 1980, Lowman 1982a). However, the isolation of individuals from their natural surroundings may influence feeding and development. The coral islands of the Great Barrier Reef provide isolated patches of vegetation that are rather simple both structurally and floristically. In particular, One Tree Island (23'30's latitude, 152'08'E longitude), has 2 1 permanent plant species (Heatwole et al. 1981) including approximately 128 shrubs of Argusia argentea, a prostrate, continuously-leafing shrub whose distribution extends throughout the Indo-Pacific from East Africa to the East Indies. On One Tree, Argusia argentea is the host plant to a monophagous Lepidopteran larva of the moth Utetheisa pulcbelloides (Arctiidae). The caterpillars are abundant, albeit with some seasonality, with cohorts staggered throughout the year. Argusia establishes on open beaches, usually just above the high tide line although sometimes extending into the island interior. This tendency to grow on exposed island edges may be a consequence of its oceanic seed dispersal (Guppy 1891). In fact, salt water exposure appears to be a prerequisite to germination (Lesko and Walter 1969).

The production and persistency of different grass species cut at different heights

AbstractThe effect of two heights of cutting (5 and 8 cm) on the dry matter harvested and persistency of a range of different grass species and varieties were monitored over a 3‐year period (1976 to 1978). Dry matter harvested was measured in the second and third harvest year and persistence of sown grass was assessed at the end of the first and third harvest year. The grasses were managed under a frequent cutting system, i.e. simulated grazing. Results showed that at the low cutting height tetraploid hybrid ryegrasses and diploid Italian ryegrasses in the third harvest year gave lower annual dry matter harvests of sown grass and were less persistent than at the high cutting height, whilst, in contrast, perennial ryegrasses gave higher annual harvests of sown grass but persistency was unaffected. In general at the low cutting height varieties of cocksfoot, meadow fescue and tall fescue gave comparatively higher annual harvests of sown grass in the second harvest year but lower yields of sown grass in the third harvest year. A notable exception was Cambria cocksfoot which in the second harvest year gave higher yields of sown grass and was more persistent at the low cutting height.However, at 5 cm cutting height, the proportions of weed grasses (mainly Poa spp.) in swards sown to tetraploid hybrid ryegrasses and diploid Italian ryegrasses were generally greater, particularly in mid‐season.

Effects of simulated grazing on foliage and root production and biomass allocation in an arctic tundra sedge (Eriophorum vaginatum).

Eriophorum vaginatum is a tussock-forming member of the Cyperaceae, widespread in the arctic tundra, and a common food item for grazing herbivores on the Alaskan North Slope. Populations of this sedge at Atkasook, Alaska, were subjected to a variety of simulated grazing experiments to determine tiller responses to frequent and intensive defoliation.The intial, short-term response of Eriphorum to defoliation was an increase in leaf production at the expense of belowground structures. Multiple defoliations, however, resulted in proportionately greater reductions in leaf weight than leaf area. Leaf blades of defoliated plants weighed 0.71 mg/cm of length, compared to an average weight/length ratio of 0.91 mg/cm in control plants. Declines in leaf production were accompanied by weight losses in stem base and sheath components and a curtailment of root growth. Root initiation was reduced by 28 and 63%, respectively, after one and two seasons of multiple defoliations, and the depth of penetration of these annual roots was reduced substantially. Total root biomass was reduced 24% in the least severe defoliation treatment and 85% in the most severe treatment. The allocation of dry matter into new tillers on defoliated plants, relative to new tiller production of control plants, was reduced by 75% after two seasons of defoliation, although equivalent numbers of tillers were initiated. The reduced biomass of daughter tillers was restored to levels observed in control plants during the season of rest following the season of multiple defoliation. Sexual reproduction was significantly depressed in the most severe defoliation treatment and stimulated by the least severe treatment. Defoliation treatments of intermediate severity had no significant impact on flower initiation.Over 80% of the tillers subjected to complete defoliation at 10-day intervals for one entire growing season survived, overwintered and initiated growth the following season. Recovery from multiple defoliations was partially achieved by the stimulated growth and extended longevity of older leaves on the tiller, although one season of rest was not enough to fully replenish weight losses of storage organs. Tillers were capable of withstanding more defoliation events when clipping was initiated early in the growing season. Biomass of storage organs of tillers subjected to multiple defoliations imposed at 10-day intervals for two entire growing seasons was 34% above the estimated minimum biomass necessary for tiller survival. The data suggest that Eriophorum tillers can survive 100% leaf removal at 10-day intervals for 50 to 75% of their estimated three to four year lifespan.

Standing Crop and Vigor of Defoliated Russian Wildrye in Southeastern Colorado

Standing Crop and Vigor of Defoliated Russian Wildrye in Southeastern Colorado

Effects of white amur ( Ctenopharyngodon idella) on a Florida lake: a model

The Lake Conway model predicts that stocking white amur will decrease lake productivity and respiration, increase epipelic algae biomass for two years, and increase biomass of benthic invertebrates and biomass and number of secondary predator fish for at least nine years. Water quality, as defined by submersed macrophyte abundance, phytoplankton biomass, orthophosphate in the epilimnion, and amount of dead particulate matter in the water column, increases during to 10-y simulation. Because of the nature of white amur growth and assimilation rates, simulated grazing impact is heaviest three years after stocking. Carbon flow through both grazing and detritus food chains increases in the simulation, in spite of decreased photosynthesis.

A model of resource allocation for savanna grasses

The model described in this paper provides a framework for simulating the transfer of reserves from stubble and roots to leaves throughout the growing season with repeated defoliations. In addition, the effects of changing phenology and its influence on the allocation of newly fixed and remobilized plant resources are simulated. The model is used to consider the effect of simulated grazing of various intensities and intervals on plant reserves.

Effects of grazing on cold desert shrubs: A simulation model based on relative growth rate

Abstract A generalized mathematical model for plant growth was developed to simulate primary productivity and response to grazing of cold desert shrubs. The model simulates root, shoot, and carbohydrate reserve biomass for periods of 5–20 y using a weekly time step and equations based on the principles of growth analysis. The effect of soil water on plant growth is simulated by an empirical relationship between average soil water content and annual production. A separate evaporation model simulates weekly soil water content using precipitation data. The plant model requires weekly average and maximum air temperatures. Other data requirements have been reduced so that the model can be adapted to different species and different sites. The effect of shoot removal on productivity of Atriplex confertifolia, Artemisia tridentata and Ceratoides lanata growing in the Curlew Valley in northern Utah was simulated. When productivity was simulated for 20 y with 25% removal in the spring or 50% removal in the winter, the shrubs were able to maintain themselves. But they were not able to maintain themselves when simulated removal in the spring was 50%. The response to simulated grazing appeared to be consistent with field observations of effects of defoliation on survival.

The effects of height of stubble left after simulated rotational grazing on regrowth of star grass

Abstract Star grass (Cynodon aethiopicus cv. No. 2) was grazed to leave stubble of 5, 15 or 25 cm in height after grazing. In the first year (1972–73) 350 kg N and 39 kg P per ha, and in the second year (1974–75) 500 kg N and 39 kg P per ha, were applied. Grazing was done at 15‐day intervals although in the first year this was not always possible because of poor rainfall which affected growth. In both years amounts of herbage harvested above the three stubble heights decreased as the height of stubble left after grazing increased. The relative proportions of green leaf, dead leaf and stem were similar with all stubble heights although there was slightly less green leaf in the 5 cm stubble.

Effects of Simulated Grazing by Below-Ground Herbivores on Growth, CO 2 Exchange, and Carbon Allocation Patterns of Bouteloua gracilis

(1) A series of root-pruning experiments was performed to simulate the effects of grazing by root-feeding herbivores on Bouteloua gracilis. Approximately 37% (% 22 mg) of the root biomass of hydroponically grown plants was removed by clipping all roots 5 cm below the crown bases. (2) Total biomass of root-clipped plants (908 mg) was 20% lower than that of controls (1137 mg) 3 weeks after treatment. This biomass reduction was related to a 55% reduction in tiller production of treated plants. The mean rate of net photosynthesis of treated plants was 35% lower than in control plants for the first six days after treatment. For several days following root-clipping, the proportion of photosynthetically-fixed 14C allocated to roots was lower than in control plants, but this proportion increased until, by 3 weeks after treatment, the proportion allocated to roots of treated plants significantly exceeded that of controls. (3) Because of these effects on plant growth and metabolism, we suggest that below-ground herbivores may control primary production to a greater extent than would be predicted from their biomass or consumption rates.

Influence of Simulated Grazing (Clipping) on Pinegrass Growth

Influence of Simulated Grazing (Clipping) on Pinegrass Growth

A pasture production model for use in a whole farm simulator

Modular simulation models of crop and animal enterprises can be used in concert to simulate a particular whole farm operation and thus provide management information for individual farmers and farm advisers. This paper reports the development of a pasture module for such a whole farm simulator designed to study irrigation management in New Zealand. The model (CANPAS) describes the production of perennial ryegrass/white clover pastures under either dryland or irrigated conditions. Seasonal growth studies and the principles of ecological physiology form the theoretical base of CANPAS. Whenever possible, parts of other models were also used. With time steps of one day, CANPAS predicts the net above-ground yield of live and dead herbage, herbage digestibility, leaf area index and soil water supply. Harvested yields are also predicted for simulated grazing or cutting managements, assuming part of the above-ground yield of live and dead herbage is left as stubble. Field measurements of harvested pasture yields from the Canterbury Plains of New Zealand were used to validate the model. Validation procedure included the use of a simple set of statistical tests. The final version (CANPAS III) gave an overall r 2 of 0·83, but poorer performance was found under some test managements. Discussion covers the general aspects of this kind of modelling as well as the specific details of the pasture module.

Simulated grazing responses on the proposed prairies National Park

The tallgrass prairie version of the ELM Grassland Model was used to evaluate the potential impact of establishing a tallgrass prairie National Park in the Flint Hills region of Kansas. This total ecosystem model simulates (a) the flow of water, heat, nitrogen, and phosphorus through the ecosystem and(b) the biomass dynamics of plants and consumers. It was specifically developed to study the effects of levels and types of herbivory, climatic variation, and fertilization upon grassland ecosystems. The model was used to simulate the impact of building up herds of bison, elk, antelope, and wolves on a tallgrass prairie. The results show that the grazing levels in the park should not be decreased below the prepark grazing levels (moderate grazing with cattle) and that the final grazing levels in the park could be maintained at a slightly higher level than the prepark grazing levels.

Screening of legumes for veld reinforcementpeulgewastoets vir veld verbetering

Abstract In order to test their suitability for veld reinforcement, Desmodium intortum, D. sandwiceme, D. uncinatum,Glycine wightii, Listia heterophylla, Lotononis bainesii, Macroptilium atropurpureum, Stylosanthes fruticosa, S. humilis and three strains of S. guianensis were seeded in December 1970 in disced veld at Marandellas (sand) and near Mazoe (clay). Starting in December 1971 the legumes were grazed in common at two stocking intensities during the wet season only, the dry season only or year‐round, using a simulated rotational grazing system. Legume seedling mortality was high on the sand and only M. atropurpureum and the five Stylosanthes lines had plant densities in the second season greater than 1 plant/m2. On the clay establishment was better and all legumes except L. heterophylla had densities greater than 1 plant/m2. Oxley fine‐stem stylo was the only legume to persist and spread on the sand but on the clay a much wider range of legumes persisted, although all were adversely affected by a ho...