Grazing Capacity Research Articles

Bushclump-grass interactions: influence of bushclumps on their local environment in a south-east African savanna

The interaction between multi-species bushclumps and the herbaceous layer was investigated in a mesic Eastern Cape bushclump savanna. Bushclumps had a moderating effect on their microclimate when compared with the open grassland: lower maximum and higher minimum temperatures. higher humidity and 80-90% reduction in irradiance. Soils beneath bushclumps were more fertile than grassland soils with greater organic carbon. P, K and CEC. The importance of bushclumps in maintaining and recycling nutrients, especially on sandier soils, was highlighted as mesic savannas are threatened by complete bush clearing. Bushclumps were characterized by a sparse shade-tolerant herbaceous layer dominated by Panicum maximum and Helictotrichon capense which contributed little to grazing capacity. Grass production was greater in the grassland on the south-facing side of bushclumps than on other aspects. The size of the bank of woody seeds and seedlings beneath bushclumps, but not beneath grasslands, indicate a likely rapid re-establishment of woody individuals following bush clearing.

Mesocosm observations on the ecological response of an aquatic community to sediment contamination

Between 1992 and 1997 the effects of contaminated sediment on an aquatic community were studied in outdoor mesocosms (2m3), one filled with ‘naturally’ polluted sediment from the sedimentation area ‘Ketelmeer’, the other with relatively clean sediment from the shallow lake ‘Oostvaardersplassen’. Negative effects of the contaminated sediment were observed on the population development of the amoeba species Arcella megastoma and Difflugia accuminata, the mysid shrimp Neomysis integer, the microlepidopteran Cataclysta lemnata and the cladoceran community, whereas the biting midge Culex sp. showed a preference for the contaminated system. The reduction of the grazing capacity of the cladoceran community resulted in higher algal densities in the ‘Ketelmeer’ mesocosm despite the fact that nutrient concentrations in the water column of both mesocosms were comparable.

Sulphur fertiliser and sheep grazing capacity

Sheep grazing capacities over 15 years from two long-running high country trials in a moderate rainfall zone and under 30 different annual sulphur and phosphorus fertiliser combinations are presented. With time, the sheep grazing capacities became increasingly related to the rate of S fertiliser input, and largely independent of P fertiliser rate. The implication for grazing capacity, fertiliser purchase, transport and spreading costs is the very large cost benefit that could accrue from further development of methods for handling and spreading elemental S fertiliser. Keywords: fertiliser, grazing, high country, phosphorus, sulphur

Growth and abundance of Synechococcus sp. in a Mediterranean Bay:seasonality and relationship with temperature

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 170:45-53 (1998) - doi:10.3354/meps170045 Growth and abundance of Synechococcus sp. in a Mediterranean Bay: seasonality and relationship with temperature Nona S. R. Agawin*, Carlos M. Duarte, Susana Agustí Centro de Estudios Avanzados de Blanes, CSIC, Camino de Santa Bàrbara s/n, E-17300 Blanes (Girona), Spain *E-mail: agawin@ceab.csic.es ABSTRACT: In this study, we confirm the relationship between temperature and Synechococcus sp. experimental growth rates (r = 0.87, p < 0.005) and provide evidence of the existence of a general relationship. This link leads to a strong seasonality of abundance and biomass of Synechococcus sp. in the Bay of Blanes (NW Mediterranean), which was followed for 2 yr (1995, 1996), with high values in summer months (6 x 107 cells l-1) and low values in winter (5 x 105 cells l-1). The growth rate achieved in summer months (1.5 d-1) is close to or at the maximum possible at the in situ water temperature. As a result, Synechococcus growth may exceed the grazing capacity of its predators in summer, and this explains its significant contribution of >30% of the total gross autotrophic production and >20% of the total autotrophic biomass in summer. Thus, Synechococcus is an important source of organic C and nutrients for the coastal Mediterranean food web in the summer. KEY WORDS: Synechococcus sp. · NW Mediterranean Sea · Growth and abundance · Temperature Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 170. Publication date: September 03, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

Mesocosm observations on the ecological response of an aquatic community to sediment contamination

Between 1992 and 1997 the effects of contaminated sediment on an aquatic community were studied in outdoor mesocosms (2m3), one filled with ‘naturally’ polluted sediment from the sedimentation area ‘Ketelmeer’, the other with relatively clean sediment from the shallow lake ‘Oostvaardersplassen’. Negative effects of the contaminated sediment were observed on the population development of the amoeba species Arcella megastoma and Diflugia accuminata, the mysid shrimp Neomysis integer, the microlepidopteran Cataclysta lemnata and the cladoceran community, whereas the biting midge Culex sp. showed a preference for the contaminated system. The reduction of the grazing capacity of the cladoceran community resulted in higher algal densities in the ‘Ketelmeer’ mesocosm despite the fact that nutrient concentrations in the water column of both mesocosms were comparable.

A prototype graphic landscape analysis system: Part 1. Predicting spatial patterns of grazing pressure using GIS

A prototype spatial graphic landscape system for use in PC-based micro-computers was developed. Spatial characteristics and attributes of a landscape were entered into a geographical information system to create a data base. A grazing pressure index was modelled using an algorithm which sequentially adjusts grazing capacity of response units for percentage lost to brush density, slope, and distance from water. The grazing pressure model was verified on a poorly watered homogeneous pasture (1302ha) and well watered complex pasture (2959ha). Response units were highly correlated to observed grazing (r 0.92-0.94) in the poorly watered, homogeneous pasture. However, correlations were poor in the complex, well-watered pasture. Circular barrier effects of slopes, intermittent watering sources and relative differences in ecological condition of adjacent response units were identified as the primary factors reducing model performance.

Description of a method for assessing veld condition in the Karoo

In the past, veld condition in the Karoo was assessed according to the ecological index method. This has recently been replaced by the grazing‐index method. The principles governing the method of botanical survey remain the same, but this methodology has not been described in detail. The objective of this paper is to address this shortcoming. The method is based on canopy‐spread‐cover strikes, and these strikes are assumed to represent mass as well as number of the species. Through the application of the individually estimated grazing‐index values of the different species, the index of veld condition is computed from either line‐point or clipped‐quadrat data. With appropriate data management, both the line‐point and the clipped‐quadrat data yield acceptable indices of veld condition, from which values, current grazing capacities, can be estimated for assessed sites.

Recent research on forage utilization by ruminant livestock in South Africa

An overview is given of pasture evaluation and improvement of existing germplasm in South Africa. The literature is reviewed from the perspective of upgrading the natural vegetation, reclamation of eroded soils, defining constraints, supplementation on cultivated pasture and improvement of low quality forages. Intake studies have also been emphasized because of the profound influence of intake on grazing capacity and as a distinguishing factor when screening cultivars and new introductions. Although temperate species which can be cultivated in the higher rainfall areas or under irrigation are discussed, the review largely concentrates on subtropical grasses and legumes that are drought tolerant and adapted to relatively poor soils.

Food resources and quality for the introduced Cretan wild goat or agrimi Capra aegagrus cretica on Atalandi Island, Greece, and implications for ecosystem management

A study of seasonal food availability and quality for Cretan wild goat or agrimi Capra aegagrus cretica introduced on Atalandi Island, Greece, was conducted during 1988–1989. The major portion of available forage consisted of Olea europaea var. sylvestris, Pistacia lentiscus and Cistus spp. The first two species are the main food resources in late summer and early autumn, the critical period for agrimi nutrition, and the only species with crude protein (CP) content exceeding maintenance requirements of agrimi. Grasses contained the highest level of neutral detergent fibre (NDF) and acid detergent fibre (ADF) among all plant categories in all seasons. Herbaceous species had the lowest level of lignin and shrubs the highest. In vitro organic matter digestibility (IVOMD) of herbaceous species was > 50% only in spring. During summer only Olea europaea produced sufficient forage with digestibility c. 50%. Future management must be directed toward maintaining a balance between vegetation productivity and grazing pressure. Maintaining the agrimi population at grazing capacity would allow an increase of productivity of palatable species. The seeding of palatable native herbs would provide nutritious feed for the agrimi and reduce the grazing impact. Continuous monitoring of the agrimi population, vegetation and soil trends is considered indispensable.

Karoobush Defoliation in the Arid Karoo

The relation was studied between the applied stocking rates and the degree to which sheep grazed stems of various karoobush species. A rule of thumb exists amongst farmers and research workers in the Karoo, that sheep graze stems of karoobushes with a diameter of 2 mm or less. This hypothesis was examined over a period of 3 years. The meetly grazed off stems of Pentzia spinescens Less. (doringkaroo) and Rosenia humilis (Less.) Bremer (blou perdekaroo), the most abundant forage species, were measured by sliding Vernier callipers. Estimates of grazeable dry matter, as used in the estimate of the current grazing capacity, is based on the separation of clipped dry matter into grazeable and non-grazeable material. This separation is based on the 2 mm criterion. The hypothesis that sheep voluntarily graze stems with a diameter of up to 2 mm was rejected. The stems of less palatable species are seldom grazed at 2 mm diameter, while grazed stems of paintable species are often thicker than 5 mm. It was established that sheep graze stems of the less palatable karoo bushes to a mean diameter of 1.4 to 1.6 mm. This impacts directly on the method in which dry matter production is estimated for the purposes of determining grazing capacity. The long term grazing capacity norm for this area is 30 ha large stock unit-1. Based on gain ha-1 data obtained from stocking rate trials, the grazing capacity is 33.4 ha large stock unit-1. The stocking rate: grazed stem relation yields an optimum grazing capacity figure of 32.5 ha large stock unit-1. This indicates that monitoring the grazed stems of appropriate species can be used to set grazing capacity limits or adjust stocking rates.

Objective `Safe' Grazing Capacities for South-West Queensland Australia: Model Application and Evaluation.

This paper describes the employment of two experienced graziers as consultants to apply and evaluate a model for calculating 'safe' long-term grazing capacities of individual properties. The model was based on ecological principles and entailed estimates of average annual forage grown (kglha) on the different land systems on each property and the calculation of the number of livestock (dry sheep equivalents, DSE) required to 'safely' utilise this forage. The grazier consultants applied and evaluated the 'safe' grazing capacity model on 20 properties of their choosing. For evaluation, model results were compared with; (a) the Department of Lands rated carrying capacities for those properties and (b) the grazing capacity assessed independently by the owners of those properties. For the 20 properties, the average 'safe' grazing capacity calculated by the model (21.0 DSE/kmZ) was 8% lighter than the average of the owner assessed capacities (22.7 DSE/kmZ), which in tum was 37% lighter than the average of the pre-1989 Department of Lands rated carrying capacity (31.0 DSE/kmZ). The grazing land management and administrative implications of these results and the role graziers played as consultants are discussed.

Objective `Safe' Grazing Capacities for South-West Queensland Australia: Development of a Model for Individual Properties.

Few tools are available to assist graziers, land administrators and financiers in making objective grazing capacity decisions on Australian rangelands, despite existing knowledge regarding stocking rate theory and the impact of stocking rates on land condition. To address this issue a model for objectively estimating 'safe' grazing capacities on individual grazing properties in south-west Queensland was developed. The method is based on 'safe' levels of utilisation (15%-20%) by domestic livestock of average annual forage grown for each land system on a property. Average annual forage grown (kglha) was calculated as the product of the rainfall use efficiency (kglhdmm) and average annual rainfall (mm) for a land system. This estimate included the impact of tree and shrub cover on forage production. The 'safe' levels of forage utilisation for south- west Queensland pastures were derived from the combined experience of (1) re-analysis of the results of grazing trials, (2) reaching a consensus on local knowledge and (3) examination of existing grazing practice on 'benchmark' grazing properties. We recognise the problems in defining, determining and using grazing capacity values, but consider that the model offers decision makers a tool that can be used to assess the grazing capacity of individual properties.

A comparison of some methods used to estimate the grazing capacity of a game ranch in Northern Province, South Africa

The grazing capacity of a game ranch in Northern Province was estimated in a number of different ways using rainfall and herbaceous composition and phytomass data. The results indicate that the grazing capacity under the present environmental conditions should be approximately 50 of the recommended agricultural grazer stocking rate. This is in agreement with recent literature, indicating that the methods used should be suitable for determining a first approximation of grazing capacity in the mixed bushveld of Northern Province.

The grazing index method of range condition assessment

Abstract Owing to the difficulty of examining succession theory in the Karoo, it is suggested the ecological index method (EIM), be replaced by the grazing index method (GIM), through the introduction of grazing index values (GIV) for Karoo plant species. The GIM may provide more acceptable range condition scores and more realistic estimates of the current grazing capacity. Using GIVs, arrived at by scoring the agronomic attributes of the plant species (productivity, forage value, perenniality), the estimated current grazing capacities are found to be closely similar to the grazing capacity norms established for the different agro‐ecological areas in the Karoo. The manner in which the range condition survey is conducted and the application of the grazing index method, ensures the computation of a figure representative of the agronomic potential of the area to support livestock. The cover figure and the range condition score determined for a sample site, can be employed in monitoring the trend in changes i...

Construction and evaluation of condition assessment and grazing capacity models for use in grazing management in the Eastern Mixed Bushveld of southern Africa

The Integrated System for Plant Dynamics (ISPD) is a comprehensive system in which new and existing data and knowledge are quantitatively or qualitatively used as a basis for range condition and grazing capacity assessments and for denning appropriate management options to maintain or improve the condition and capability of the range. This study was carried out to investigate the degree to which the qualitative approach in ISPD can be implemented, and to determine the amount and availability of data and expert knowledge in a specific area for the purpose of constructing a database in ISPD. Large quantities of information were available for the construction of vegetation condition and grazing capacity models for direct implementation in the grazing industry. The results generated by the models corresponded to the proposed grazing capacity values for the study area. The models furthermore enable any user to assess rapidly and accurately the range condition and grazing capacity for any vegetation unit in any stage of degradation.

The influence of rainfall on vegetation composition in different conditional states

The impact of ecological factors such as changes in rainfall could lead to large compositional changes in the diverse indigenous flora of southern Africa. A study was therefore initiated to determine the influence of rainfall conditions on species composition changes, which could serve as a basis for determining the long term influence of rainfall increase (e.g. cloud stimulation) and rainfall decrease (e.g. long term droughts). Certain species were found to occur in all the rainfall zones while others were limited to either the high or the low rainfall area. The reaction of species on the rainfall gradient also differs in vegetation representing different degradation stadia. The predictions of the reactions of key species on rainfall decrease or increase are of special importance for the eventual determination of grazing capacity.

Remote sensing, a tool for reindeer range land management

AbstractThe Finnish reindeer-herding area lies in the northern boreal forest zone. The herding area is divided into 57 reindeer management districts with a total area of 114,355 km2 (excluding water areas). The official number of reindeer in the year 1992 was 263,789, or 2.3 reindeer per square kilometre. In 1946 the density was only about one reindeer per square kilometre. The increased pressure on the mid-winter lichen pastures has reduced the volume of lichen. Also the decreased area of old coniferous forests with arboreal lichens has diminished the supply of food during the late-winter months. The lack of suitable winter pastures has led to the need for supplementary feeding with hay.The intention of this study was to develop and test methods for cost-effective reindeer range land inventory and to assess the present state of pastures in seven districts. Use was made of Landsat 5 TM satellite imagery that was processed with remote sensing and GIS software. The analysis of well-known field sites proved the image classification to be between 80 and 90% accurate. By comparing field data and classification results, estimates can be made on the available fodder reserves in the different pasture types. The results show that mid-winter pastures are both scarce and degraded in six of the seven areas investigated. Only one area (Muotkatunturi) has mid-winter pastures in reasonably good condition. Late-winter pastures with arboreal lichens are more widespread than mid-winter pastures and determine the amount of additional winter feeding required. Summer pastures are abundant in all seven reindeer-herding districts and are therefore not a limiting factor. The method used is objective, inexpensive, and fast when compared to conventional methods. Information can be produced on the quantity and quality of reindeer pastures. This knowledge can be used to make better estimates of the natural grazing capacity of reindeer districts in Finland.

Wolf plant effects on water relations, growth and productivity in crested wheatgrass

When improperly managed in pastures, crested wheatgrass (Agropyron desertorum (Fischer ex Link) Schultes) develops wolf plants because of the long-term persistence of inflorescences. The objective of this study was to test the hypothesis that the wolf plants have no effect on the growth and water relations of grazed or subordinate plants in crested wheatgrass. Treatments applied to wolf plants included killing with glyphosate, mowing to a 10-cm stubble, killing with glyphosate + mowing to a 10-cm stubble, and a control. Rates of vegetative and reproductive development, tiller and whole plant weights, tiller replacement and xylem water potentials of leaves were determined for subordinate plants for 2–3 yr following treatment. The presence of wolf plants had no consistent effect on the water relations or on growth of subordinate plants of crested wheatgrass. Because they play no apparent beneficial role in the water status and productivity of crested wheatgrass, management techniques should be implemented to exploit the forage produced by wolf plants. Accessing this forage can substantially increase the grazing capacity of crested wheatgrass pastures. Key words:Agropyron desertorum (Fischer ex Link) Schultes, grazing management, pasture improvement, plant water relations

Does the impact of nutrients on the biological structure and function of brackish and freshwater lakes differ?

The effects of nutrients on the biological structure of brackish and freshwater lakes were compared. Quantitative analysis of late summer fish, zooplankton, mysid and macrophyte populations was undertaken in 20–36 shallow brackish lakes of various trophic states and the findings compared with a similar analysis of shallow freshwater lakes based on either sampling (fish) or existing data (zooplankton, mysids and macrophytes). Special emphasis was placed on differences in pelagic top-down control. Whereas the fish biomass (CPUE, multiple mesh-size gill nets) rose with increasing P-concentration in freshwater lakes, that of brackish lakes was markedly reduced at P-concentrations above ca. 0.4 mg P l-1 and there was a concomitant shift to exclusive dominance by the small sticklebacks (Gasterosteus aculeatus and Pungitius pungitius); as a result, fish density remained relatively high. Mysids (Neomysis integer) were found at a salinity greater than 0.5‰ and increased substantially with increasing P-concentration, reaching levels as high as 13 ind. l-1. This is in contrast to the carnivorous zooplankton of freshwater lakes, which are most abundant at intermediate P levels. The efficient algal controller, Daphnia was only found at a salinity below 2‰ and N. integer in lakes with a salinity above 0.5‰. Above 2‰ the filter-feeding zooplankton were usually dominated by the less efficient algal controllers Eurytemora and Acartia. In contrast to freshwater lakes, no shift to a clearwater state was found in eutrophic brackish lakes when submerged macrophytes became abundant. We conclude that predation pressure on zooplankton is higher and algal grazing capacity lower in brackish eutrophic-hypertrophic lakes than in comparable freshwater lakes, and that the differences in trophic structure of brackish and freshwater lakes have major implications for the measures available to reduce the recovery period following a reduction in nutrient loading. From the point of view of top-down control, the salinity threshold dividing freshwater and brackish lakes is much lower than the conventionally defined 5‰.

Range Condition Influences on Chihuahuan Desert Cattle and Jackrabbit Diets

Knowledge of comparative diet selection by cattle and black-tailed jackrabbits (Lepus californicus) would permit better estimation of grazing capacity on Chihuahuan desert ranges. Cattle and black-tailed jackrabbit diets were evaluated seasonally on good and fair condition ranges over a 2-year period. Fecal samples analyzed by the microhistological technique were used to determine diets of both animals. Key forage species in cattle diets were dropseeds (Sporobolus sp.), black grama (Bouteloua eriopoda Torr.), leatherweed croton (Croton pottsii Lam.), and bush muhly (Muhlenbergia porteri Scribn.). Key forage species in jackrabbit diets were honey mesquite (Prosopis glandulosa Torr.), cactus (Opuntia sp.), dropseed, broom snakeweed (Gutierrezia sarothrae Pursh.), and black grama. Overall diet botanical composition data showed cattle consumed 58% grass compared to 22% for jackrabbits (P < 0.05). Forb consumption was similar between the 2 animals and averaged about 31%. Shrub consumption averaged 47% and 12% for jackrabbits and cattle, respectively (P < 0.05). Range condition did not influence total grass consumption by either animal. Both animals, however, had lower forb and higher shrub consumption on fair compared to good condition range. Overall dietary overlaps between jackrabbits and cattle were 40 and 42% on good and fair condition ranges, respectively. Poisonous plants contributed up to 14 and 36% of cattle and jackrabbit diets, respectively. Data from this study show little forage competition occurs between cattle and jackrabbits when stocking rates and jackrabbit numbers are moderate. Several plants poisonous and unpalatable to cattle were important jackrabbit foods. These plants were more prevalent on the fair compared to the good condition range.