Ungrazed Conditions Research Articles

Effects of Summer Grazing by Caribou on Composition and Productivity of Vegetation: Community and Landscape Level

1 Changes in demography and studies on physical condition of the Riviere George caribou Rangifer tarandus herd have suggested that its size may be primarily regulated by the amount of forage available on the summer range. 2 We therefore document the impact of grazing and trampling on composition and productivity of two plant communities, the shrub tundra and stands of dwarf birch, within this range. Ungrazed sites were rare, but four previously located small areas were used as control sites. 3 For the shrub tundra, the lichen mat was absent in grazed sites and ground previously occupied by lichens was either bare, covered by fragments of dead lichens and mosses or recolonized by early succession lichen species. Ground cover of shrubs not eaten by caribou was lower in grazed sites than in ungrazed sites, and coverage of graminoids, forage shrubs and forbs did not differ significantly between grazed and ungrazed sites. 4 In stands of dwarf birch grazed by caribou, ground cover and leaf biomass of Betula glandulosa was significantly lower than in ungrazed sites. 5 Productivity of forage plant species over the summer range was estimated at 22.5 g m-2 year-l in an ungrazed condition compared to 10.3 g m-2 year' when grazed. 6 At the landscape level, caribou have fragmented the distribution of their food resource by reducing biomass of shrub tundra and stands of dwarf birch to a very low level. 7 The serious negative impact of migratory ungulates on plant productivity of their summer range may be explained by characteristics of the vegetation and the high carrying capacity of winter compared to summer ranges. Significant factors related to the vegetation are its low resilience and productivity and the absence of a response of vascular plants following removal of lichens.

Grazing Management and Rehabilitation of Degraded Rangeland in Western Australia

Rangeland in the arid zone of Western Australia has been degraded by sheep overstocking since the turn of the century. The Strategies available for restoring the productivity of such degraded rangelands are limited. In this paper optimal economic policies with respect to the choice of stocking rates and grazing patterns were derived for various starting states under a stochastic optimal control framework. Evaluation of these optimal policies was carries out by comparing their long run economic and ecological impacts on grassland with ungrazed conditions. All optimal policies call for a stnttegy of set stocking or destocking only. Rotational grazing is not economically viable at the specified cost levels. Optimal stocking rate increases with the level of forage biomass and adult plants, but decreases with the level of either young or old seedlings at the degraded nmge condition. The results indicate that under the criterion of maximisation of the long run average return, for slightly degraded range, rehabilitation through grazing management alone is possible. For· range which is modcrntely to severely degraded, rehabilitation to fair or good condition is not technically practical. On the other hand, under the criterion of maximisation of the net present value at a discount rate of 6 percent, the consequence of the long run impact on the range resource following the optimal policy is ecologically unsustainable, though economically viable. These findings suggest that if degraded ranges continue to be exploited for private profit, the range rcsom·ce may be driven beyond its capability to renew. If ecological sustainability is an Australinn social norm, economic rationality should subside in the decision criterion, and range management will require some willingness to forego short term profits for the sake of long term rewards or investment in regeneration measures.

Influence of cattle trampling on preferential flow paths in alkaline soils

Abstract. Preferential flow paths (PFP) are important in water and solute movement through soils, especially in regions where vertical water movements predominate, such as the flooding Pampa (Argentina). The impact of grazing on PFP and its interactions with other properties were studied in three soils with natric horizons in the flooding Pampa using an iodide colouring technique. In the soil with a mollic horizon (Typic Natraquoll), % PFP was decreased by trampling but was later restored by shrink‐swell. In the Typic Natraqualf, the most alkaline of the studied soils, % PFP was very small under both grazed and ungrazed conditions. In a coarser textured soil (Mollic Natraqualf) trampling did not affect % PFP. The % PFP of the Ah horizons increased with increasing organic carbon and sand contents and decreased as clay content, pH and sodium adsorption ratio (SAR) increased. The Bt horizons had small % PFPs and were not affected by cattle trampling.

Simulated effects of precipitation and nitrogen on Serengeti grassland productivity

In the Serengeti National Park, Tanzania, precipitation and soil nitrogen vary greatly between northwestern tallgrass areas and southeastern shortgrass areas, with the tallgrass having higher total precipitation and lower soil fertility. We used a model of grassland productivity, carbon/nitrogen cycling, and abiotic factors to test the hypothesis that tallgrass productivity is limited primarily by nitrogen availability while shortgrass productivity is limited by water. Under observed grazing intensities and ungrazed conditions, precipitation exerted primary control over grassland productivity for both regions, with differences in soil texture mediating soil water availability to the grasses. Mineral nitrogen availability interacted with water availability to influence productivity at precipitation levels ⩾ 130% of the mean. Nitrogen mineralization and precipitation were positively related for each grassland type, however, nitrification varied both between grassland types and between grazed and ungrazed conditions. Combined mineralization and nitrification could not maintain soil mineral nitrogen levels in the face of plant nitrogen uptake stimulated by increased precipitation, thus providing the mechanism by which nitrogen becomes a secondary limiting factor for both grasslands. Model experiments indicated that the pattern of primary limitation by precipitation and secondary limitation by nitrogen was robust to model assumptions concerning ungulate deposition of urine and dung nitrogen to the soil.

Simulated Effects of Grazing on Soil Nitrogen and Mineralization in Contrasting Serengeti Grasslands

The roles of edaphic characteristics and grazing in regulating nitrogen cycling and belowground processes were simulated for the shortgrass and tallgrass regions of the Serengeti National Park, Tanzania, by coupling a model of grassland productivity with a model of belowground decomposition processes. Grasslands of each region were simulated under ungrazed and observed grazing intensities to establish reference points for sensitivity analyses using a wide range of grazing intensities and different microbial biomasses. The consequences of patchy carbon and nitrogen deposition were also simulated. Results indicate that nitrogen cycling processes are affected differentially by grazing in the shortgrass and tallgrass regions. Net nitrogen mineralized by the microbial biomass in the shortgrass simulations declined from the ungrazed condition at low grazing intensities, and proceeded to increase from moderate to high grazing intensities. Plant nitrogen uptake was significantly correlated with net mineralization, and soil mineral nitrogen levels were greatest at moderate grazing intensities. In tallgrass simulations, soil mineral nitrogen increased with grazing intensity; net nitrogen immobilization occurred over much of the grazing intensity range because of low decomposition substrate quality. Tallgrass plant nitrogen uptake responded to urine nitrogen input to the soil and was uncorrelated with net mineralization. The potential for nitrogen competition between grasses and microbes was greater in the tallgrass than in the shortgrass because of lower total system nitrogen and lower grazing intensity in the tallgrass. The ecosystem—wide soil nitrogen gradient of the Serengeti governs most properties of nitrogen cycling, while within—region edaphic conditions and grazing create significant variation in local ecosystem processes.

Effects of Selective Grazing by Snails on Benthic Algal Succession

Effects of ambient levels of snail grazing on rates and direction of benthic algal succession were investigated in experimental chambers located near two lakes. Benthic algal environments were manipulated by introducing snails (15 individuals/m²) to flow-through experimental systems (for 26-28 d) where clay tiles were colonized with algae from littoral lake water from Douglas Lake, Michigan, and Kentucky Lake, Kentucky. We found that algal succession was not always evident in ungrazed conditions; but when successional changes were evident, many different growth forms were observed among early and late succession species. Early succession species were typically non-motile unicellular or colonial growth forms, whereas late succession species were motile unicellular or filamentous diatoms and cyanobacteria. Grazing by the snail Elimia livescens arrested succession of non-diatom algae by selectively removing the overstory of filamentous cyanobacteria. However, grazing by E. livescens enhanced succession among diatoms by selectively grazing the early succession diatoms and leaving small motile late succession species. Whether grazing enhanced or arrested succession, or changed the direction of succession, was dependent upon growth forms of early and late succession algal species, which varied among habitats and corresponding species assemblages.

Preliminary observations on the effect of removal of black bluebush (Maireana pyramidata) and Pearl Bluebush (M. sedifolia) on shrub regeneration, herbage production and erosion potential.

The effects of mechanical removal of shrub tops and grazing on two bluebush communities, one with Maireana pyramidata (black bluebush)and the other with M. pyramidata and M. sedifolia (pearl bluebush) as co-dominants, were examined on the western edge of the Riverine Plain in New South Wales Measurements were made on shrub regeneration, the relationship of shrub units to a critical value for an erosion index, the change in soil surface levels, and the growth of herbaceous plants over time Shrub regeneration was slower under grazed than ungrazed conditions and occurred mainly from basal shoots of established plants rather than from seedling establishment. Herbage yields Increased on the mounds previously occupied by shrubs, whereas production between shrubs was not affected by shrub removal. After four years there was sufficient shrub growth to prevent wind erosion, except on the cleared and grazed plot at the M. sedifolia site.

Spatial and Seasonal Variability of Field Measured Infiltration Rates on a Rangeland Site in Utah

This study was conducted to examine both spatial and temporal variability of infiltration rates on a rangeland site in west-central Utah. The experiment utilized a grid 20 m long and 18 m wide in both grazed and ungrazed sites with a sample spacing of 2 m within the grid. investigate the seasonal effect on variability of infiltration rates, data were collected for 3 seasons (summer, fall, and spring). Measured infiltration rates at 10 and 30 min during all seasons and under grazed versus ungrazed conditions were all found to approximate a two-parameter log normal distribution. Regionalized variable theory was applied to the data through the development of autocorrelograms and semivariograms, revealing a complete lack of variance structure among the infiltration rates. This finding excluded the possibility of using the Kriging technique for interpolation. Seasonal effect was found to be very important in influencing infiltration rates. The difference between the measured infiltration rates at both grazed and ungrazed sites was very significant for the 3 seasons under study. Variability is considered one of the most important aspects of the infiltration process. Many difficulties arise due to natural variability which is characteristic of all field studies. This characteristic complicates analytical expressions developed to describe and predict the infiltration process. In this matter, Vieira (1980) stated, To estimate the infiltration rate of a given field, the variance structure of the observations throughout the field must be identified in order to appropriately analyze each set of measurements, and obtain the best estimate of the expected mean Also, Nielsen et al. ( 1 973) emphasized that it is important to assess to some degree the confidence that can be attached to predictions made by models. Though many factors contribute to variability of infiltration rates, they can often be expressed simply in terms of time and space. The variation can be attributed to source combination of experimental error, time variations, and spatial variation (Campbell 1978). Several studies have investigated the spatial variability relationships among measured infiltration rates; however, there has been little attempt to investigate seasonal changes. In addition, most studies of spatial variability of infiltration rates have been conducted on agriculture lands. This study examines both spatial and temporal variability on a rangeland site in Utah. The study uses regionalized variable theory to assess the spatial relationships of field measured infiltration rates on a seasonal basis. The experiment had 4 objectives: first, to study seasonal infiltration rates; second, to determine the approximate frequency distribution of measured infiltration rates on a seasonal basis; third, to determine the spatial variability Authors are research assistant and professor, respectively, Watershed Science Unit, College of Natural Resources, Utah State University, Logan, 84322. Dr. Gifford is currently Head, Dept. of Range, Wildlife and Forestry, University of Nevada, Reno, 89506. This project was supported in part by the Food and Agricultural Organization of the United Nations and in part by the Utah Agricultural Experiment Station, Project 749 and 771. Paper Number 2783, Utah Agricultural Experiment Station, Logan. Manuscript accepted December 29, 1983. relationships among measured infiltration rates by using semivariograms and autocorrelograms; and last, to compare infiltration rates from grazed and ungrazed pastures. Concept of Regionalized Variables The term regionalized was proposed by Matheron (1971) to describe a phenomenon distributed in space (and/or time) which exhibits a specific structure. A variable which characterizes such a phenomenon is called a regionalized variable. Almost all variables describing subsurface water movement or atmospheric water movement may be considered regionalized variables (Delhomme 1976). From the mathematical viewpoint, a regionalized variable is simply a function x(z) which gives the value at point z (in a 1, 2, or 3-dimensional space) of a characteristic x of the natural phenomenon being studied. Regionalized variable theory is used for the analysis of the spatial variation of infiltration rates. Autocorrelograms and semivariograms are used to identify the degree of dependence (zone of influence) of infiltration rates on the distance between pairs of measurements. The Autocorrelogram If x(z) is the value of the regionalized variable x at a point z, and x (z+h) is the value of x at a point z+h at a distance h from z, the autocovariance between x(z) and x(z+h) for a given h is (Rendu 1978): o(h) = E { [x(z) E [x(z)] [x(z+h) E[x(z+h)]]} where E denotes expected value. The function a(h) is the autocovariogram of the regionalized variable x. Assuming o l to be the variance of x(z) and a2 variance of x(z+h): 2 a = E {[x(z) E (x(z))]2} 2 a2= E {[x(z+h) E[x(z+h)]]2} The coefficient of correlation between x(z) and x(z+h) is:

Chemical Water Quality of Runoff From Grazing Land in Nebraska: I. Influence of Grazing Livestock

AbstractThe chemical quality of runoff water from a 32.5‐ha cow‐calf pasture area at the Roman L. Hruska U.S. Meat Animal Research Center near Clay Center, Nebr., was determined over a 3‐year period. Runoff events from the grazed pasture were separated into those occurring while livestock were grazing and those occurring when no livestock were present. Grazing livestock increased by 52% the total solids concentration, but only increased total organic carbon and chemical oxygen demand concentrations by 11 and 7%, respectively, and decreased by 19% the total Kjeldahl nitrogen concentration. Concentrations of NH4‐N, NO3‐N, total P, soluble P, and Cl− were 6, 45, 37, 48, and 78% greater, respectively, when livestock were grazing. Runoff from an ungrazed control area within the pasture contained chemical concentrations that ranged from 1.94 to 10.8 times greater than those from an adjacent pasture under ungrazed conditions. We attributed these elevated concentrations to wildlife activity and decomposition of plant material.

Effects of Livestock Grazing on Infiltration and Erosion Rates Measured on Chained and Unchained Pinyon-Juniper Sites in Southeastern Utah

Effects of Livestock Grazing on Infiltration and Erosion Rates Measured on Chained and Unchained Pinyon-Juniper Sites in Southeastern Utah

Effects of five years of grazing on a salt-marsh vegetation

In a salt-marsh, which was ungrazed from 1958 to 1971, grazing was reintroduced in 24 out of 32 ha from 1972 onwards. Vegetation changes under these conditions were investigated. The area studied is part of a larger grazed area of ca. 110 ha, grazed with a stocking rate of 1.3–1.7 cattle, ha. from May to October. This allowed a comparison between vegetation development under continued ungrazed conditions and under the reintroduction of grazing. A quantitative comparison has been made, based on sequential detailed mapping in 1971 and 1976. The ungrazed area shows a progressive succesion. Because of the erosive coast this is not the succession of a developing salt-marsh but rather a ‘recovery’ succession, after grazing was stopped in 1958. Drift deposits appear to play an important role. The grazed marsh shows successional trends in some areas, but in others signs of retrogressive succession were seen. The vegetation becomes more open, alpha- and beta-diversity increase and the vegetation develops in a more intricate pattern while some vegetation boundaries seem to become more distinct, especially on the higher salt-marsh. The large extension of Saginion maritimae types is remarkable and is probably caused by a combined effect of warm, dry summers and grazing. Further investigation is required to test whether local qualitatively different changes in communities are caused by different grazing intensities. The ungrazed area becomes more rugged, a process that can be effectively reversed by grazing.

Effect of Removal of Standing Dead Material on Growth of Agropyron spicatum

Agropyrorz spicatum (bluebunch wheatgrass), in the ungrazed condition, grows in clumps with a dense accumulation of dead culms and leaves, collectively known as standing dead. Standing dead modifies the environment of young leaves, and to a lesser degree older leaves, by intercepting sunlight and reducing air movement. Reduced light intensity may decrease photosynthetic activity. On the other hand, reduced air movement may favor a reduced vapor pressure deficit at the leaf surface and reduced water stress in plant tissues, compensating perhaps for the reduced light intensity. This report describes the effect on bluebunch wheatgrass of the removal of standing dead without the removal of live material. The results of this research are relevant to ecosystems studies focusing on the effect of standing dead on the growth of bluebunch wheatgrass. Grazing studies have dealt with the effect of removal of both live and dead material from rangeland grasses during the growing season (Rickard et al. 1975; Mueggler 1972, 1975; Wilson et al. 1966; Heady 1950). In contrast, this study addresses the effect of removing dead material early in the season before growth initiation of new leaves.

Population Dynamics of the Grass Anthoxanthum Odoratum on a Zinc Mine

'Our knowledge about the lives of individual plants and of their persistence in plant communities is very incomplete especially when perennial herbs are concerned.' This remark made by Tamm (1948) is still largely true today: very few studies have been made on the longevity of plants in natural populations. Tamm (1948, 1956) mapped individual plants of various species over a 13-year period, using permanent quadrats. Harper (1967) re-analysed some of Tamm's data to show that the decay rates of the different species differed yet remained relatively constant over the period of the investigation. Sagar (1959, data quoted by Harper 1967) in a 2-year mapping study of Plantago lanceolata showed that this perennial herb in permanent grassland had a rapid population turnover. Harberd (1961, 1962) studying the clonal patterns in Festuca rubra and F. ovina concluded that there was probably very little population turnover and that some of the genotypes were likely to be over 1000 years old. Parallel studies on twelve other nongraminaceous species (Harberd 1962), on clover (Harberd 1963), and subsequent studies on grasses (Harberd 1967; Harberd & Owen 1969) showed the presence of more restricted clonal patterns. Williams (1970), in the only direct study of the longevity of perennial grasses, showed that Danthonia cespitosa had a relatively rapid decay rate (half-life of 15-30 months), which was somewhat decreased by grazing. Chloris acicularis behaved quite differently: under ungrazed conditions its decay rate was generally very slow (halflife of about 24 years) whereas under grazed conditions it was rapidly eliminated (half-life of about 2 months). The present mapping study was undertaken between August 1964 and September 1970 to obtain data on the rate of population turnover and individual longevity in Anthoxanthum odoratum L., sweet vernal grass, on a derelict mine site.

Otlatmanın Yonca ve Korunganın köklerinde biriktirilen yedek besin maddelerine etkisi

OZET Mevsim boyunca otlatmamn sun'i mer'a kansimindaki baklagil bitkilerinin koklerinde depo edilen yedek besin maddelerini ne sekilde etkiledigini saptamak uzere girisilen bu denemede Kayseri yoncasi ve yerli korunga bitkilerinin koklerinden 4 tekrarlamali olarak alinan iimekler, O.2N H iOS 4 ile hidrolize, Heinze ve Murneek'in tarif ettigi Shaffer Somogyi metoduyla glikoza diinusturulerek miktarlari titrasyonla bttlunmustur. Otlatilan ve otlatilmayan sU/i' i meralardaki yonca ve korunga bitkilerinin yedek besin maddeleri bakimindan karsilastirmalari yapildiginda; yoncanin genellikle korungadan daha fazla elverisli karbonhidrat ihtiva ettigi, gerek otlafilan ve gerekse otlatilm/yanda mevsim boyunca cok onemlifarkliliklarmeydana getirmesine karsilik; korunga bitkilerinin ihtiva ettigi elverisli karbohnidrat seviyesinin yoncadan dusuk oldugu ve elverisli karobonhidrat trendinin buyuk olcude degisiklikler gostermedigi ve netice olarak kapasite dahilinde otlatmanin yonca ve korunga bitkilerine mevsim sonu haric menfi etki etmedigi sonucuna vanlmistir. SUMMARY THE EFFECT OF GRAZING ON THE TOTAL AVAIBLE CARBOHYDRATE IN THE ALFALFA AND SAINFOIN ROOTS. This experiment was conducted at Ataturk University farm in Erzurum. Kayseri Alfalfa and Commen sainfoin which were grown in the alfal fa x grasss and sainfoin x grass pastures used by Randomized block design with four replication. Plant sampling for carbohydrate analyses began on May 25, i 970, shortly before the animals put the pasture and was repeated at 15 days intervats during the grazing season. Twenty to 30 plants of each legume were dug from each treatment on each sampling date. The top growth was remowed at the junction of root and stern, and the roots clipped to 15 cm. in length. The roots were washed, dried at ioOoc for one hour and drying was completed at 700C. Total avaib1e carbohyodrates in the root tissue were extracted from duplicate 1/2 gram samples using 0.2 N H2S04. An aliquat was analysed for g1ucose by the Shaffer-Somogyi method described by Heinze and M urneek and the result experessed as percent total avaible earbahydrates on a dry weight basis (700C). During the growing season, it may be concluded that the change of Ibrahim MANGA total avaible carbohydrate Ievels of alfalfa roots which were grown under grazed and ungrazed pastures were not related to grazing but they were effected by climatic contitions and physiologcal reations of plants. The total avaible carbohydrate levels of sainfoin roots were Iower at grazed pasture than ungrazed. Except two samples which were taken on 31. 7.970 and 1.9.970, there were no statistical differences between sainfoins grown under grazed and ungrazed pastures, during the growing season. Co.mparing the total avaible carbohydrate levels in sainfoin and alfalfa roots which were grown at grazed and ungrazedpasture, in general, alfalfa level is higher than sainfoin and also there was a significant ~hange during the grazing season. In enontrast this, the total amount of ava.ib1e earbohydrate is lower than alfalfa and there were not significant differences between grazed and ungrazed conditions during the grazing season. The results showed that grazing at the carrying capacity levels of pastures were not affected on sainfoin and alfalfa plants.

STUDIES OF THE DIFFERENCES BETWEEN THE FAUNA OF GRAZED AND UNGRAZED GRASSLAND IN TIREE, ARGYLL

The Reef machair on the south side of the airfield in Tiree, Argyll is a highly uniform type of grassland which has never been tilled. The airfield was built in the locality during the 1939‐45 war and the perimeter fence constitutes an ecological discontinuity of at least twelve years' standing, between grazed and ungrazed grassland. The differences in the soil fauna on either side of the fence are demonstrated by two similar batteries of pit‐fall traps over a period of twelve months.The catches of the traps consist mainly of arthropods. Over eighty species of invertebrate were identified and some of these were used for quantitative analysis. The numerical differences between catches on grazed and ungrazed plots are great, and the taxonomic groups are classified into those which are favoured by grazed and ungrazed conditions. The abundance peaks of the two plots are compared. Most of the groups have a single peak in autumn, a few in early summer and a few in both early summer and autumn. Numbers caught at times of climatic extreme are discussed. This habitat of highly uniform appearance is found to be heterogeneous and the reasons for this are given.Fencing is an important technique in forestry and wildlife management in Britain. The finer consequences are unknown, and this paper demonstrates what these are likely to be in a simple situation in uniform natural grassland in Tiree.