摘要:

This experiment evaluated the relationship between carrying capacity and veld condition. Goat browsing days were used as a measure of shrub productivity and cattle grazing days as a measure of the sward. Twigs on two shrub species were monitored to quantify utilization and recovery of the woody layer and a pasture disc meter was used to monitor grazing of the grass layer. Dense bushveld (high ecological status) had higher overall carrying capacity than open bushveld (low ecological status). Carrying capacity changed considerably depending on annual rainfall and this was complicated because the more degraded the veld the greater the variation. Maximum long‐term grass production occurred at intermediate tree densities. This was, however, extremely unreliable between years and a permanent grazer enterprise cannot be recommended. For total forage production and constant fodder supply, dense bushveld is optimum. Optimum, however, changes from season to season and with operator objectives. In wet seasons it will pay to have veld in the lower range of ecological status (i.e. open bushveld) whereas in other seasons veld with high ecological status (dense bushveld) will be more productive. Farmers with only cattle may aim to have veld in the mid‐range of ecological status but this conflicts with farmers who have browsers (e.g. goats and kudu) and with the conservation ideal, because bushveld, once thinned, does not regenerate, thereby limiting future management alternatives.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638314

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The patterns of grazing ofThemeda triandra, Tristachya leucothrixandHyparrhenia hirtaby cattle at two stocking intensities were examined within a rotational grazing system at two sites in the Southern Tall Grassveld of Natal. Species utilization data were collected by repeated measures at regular intervals on a sample of marked tufts during spring, late summer/autumn, and winter. Selection patterns were examined between and within species in terms of the number of plants defoliated, and the height and frequency of defoliation. Cattle selected forH. hirtain the post‐burn spring period, which was characterized by high quality and low quantity of available forage. As the availability ofH. hirtadeclined, selection forT. leucothrixandT. triandraincreased. These results have important implications for the management of extensive areas of old‐lands, which could provide a valuable source of forage in the early spring period following burning and reduce the grazing pressure on veld. The late summer/autumn period was characterized by low intensity of grazing and infrequent grazing of individual tufts. No clear species selection patterns were evident. It is proposed that increased herbage availability may accentuate the potential for area‐selective grazing.T. triandrawas the most preferred species during winter, with intermediate selection forH. hirtaand little selection forT. leucothrix.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638315

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The relation between above‐ground phytomass production and three independent variables, namely, seasonal rainfall, evapotranspiration (Et) and veld condition, were investigated using fourteen years’ data (1977–1991) from the dryThemeda‐Cymbopogongrassveld of the central Orange Free State. The data showed that rainfall and Ethave equivalent estimation value. The multiple curvilinear regression equation (r = 0.88) that was established, with seasonal rainfall and veld condition score as the independent variables, can be used with great success in this veld type to estimate seasonal production potential. In terms of the above‐ground phytomass production, it would appear that veld in good condition responds more efficiently to rainfall than veld in poor condition. Basal cover decreased linearly with a deterioration in veld condition.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638316

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Three expert systems (Wildfire, Standard Prescribed Burning, and Security Burning) were developed for a qualitative expert system shell to assist in the fire management of Pilanesberg National Park. A qualitative expert system is useful where knowledge can be categorized into a few classes, the data are either difficult to quantify, or do not yet exist. These expert systems are of value to the practising fire manager to ensure consistency in the implementation of fire policy, and to facilitate adaptive management. In other words, the management and the expert systems should be refined in the light of experience. The expert systems are valuable teaching and training aids.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638317

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We studied the relationship between herbaceous plant community composition and distance from water to test whether the provision of water in the Kruger National Park has an impact on community composition. Composition at watering points has shifted to disturbance related annual species (e.g.Urochloa mosambicensis, Tra‐gus berteronianus, Dactyloctenium aegyptium, Amaran‐thus thunbergiiandAlternanthera pungens)whereas perennial species (e.g.Digitaria eriantha, Themeda triandraandSporobolus fimbriatus)tended to increase in presence with distance from water. There was a significant relationship between the first axis coordinates of ordinations of community composition in transects and distance from water. Results show that permanent water troughs for large herbivores in the Kruger National Park have an impact on the herbaceous community composition. Community composition along transects radiating from watering points is satisfactorily described by the logistic equation and parameters derived from this equation may be built into ecological models. Sacrifice areas (where the herbaceous community consists mostly of annual plants), extending to 20–300 m from water, occur at watering points.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638318

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Black rhinoceros browse utilization was assessed at the woody plant species and community levels in western Itala Game Reserve, South Africa, using a semi‐quantitative, plant‐based method. Theis knowledge was used to hypothesize the possible effects of vegetation change on the black rhinoceros (Diceros bicornis). Acacia nilotica, Acacia karroo, andDichrostachys cinereacontributed most to the diet, andCassine transvaalensis, Rhus guenzii, andAcacia gerrardiiwere the most preferred species. Eighty‐six percent of the recorded browse was from plants <2.5 m, suggesting that a change from open woodland, with many trees, to a closed woodland, with a few small trees, would disadvantage black rhino. Plant communities ranged from highly utilized (bottomland scrub forest) to unutilized(Combretum apiculatumsparse woodland). The extremely patchy distribution of browse utilization within communities suggests that there are other important factors affecting browse utilization besides plant species composition. It appears that tall grass detracts from browse value, while factors that improve access, such as gentle slopes and paths, enhance habitat suitability. It is hypothesized that forest verges provide important black rhino feeding areas.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638319

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Braun‐Blanquet vegetation surveys are easier and quicker to undertake than point surveys. This paper reports on assessment of veld condition and calculation of grazing capacity of five plant communities of theEaland type of the northeastern Orange Free State using Braun‐Blanquet data. Veld condition scores were obtained by substituting Braun‐Blanquet cover‐abundance values for point cover values as required by the ecological index method. Grazing capacity was calculated using published procedures. Results indicated that grazing capacities (0.2–0.3 LSU ha‐1, mean = 0.2) fall into the range of current recommendations, and that the condition of the five communities can be classified as fair. This method shows promise for application in the grassland biome for the assessment of veld condition and the estimation of grazing capacity.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638320

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Five vegetation communities in the alpine catchments of Lesotho were identified by hierarchical classification of the botanical composition data. Discriminant analysis indicated that these communities occupy particular topographic positions. The community‐environment relationships identified in this study were similar to those reported from other alpine areas of Lesotho. Grasslands at high altitudes are temperate in nature, with a high proportion of C3grass species. Below 2 950 m on the warmer aspects and below 2 750 m on south‐facing slopes, subtropical grass species (C4) dominate the sward. Within the temperate and subtropical vegetation belts, slope orientation dictates the proportion of C3species present in the sward. It is proposed that topography acts to modify the factors that directly influence plant growth by modifying solar radiation patterns.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638321

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The Range Management Area (RMA) programme was implemented in 1982 to improve range condition and livestock productivity on Lesotho's rangelands by mobilizing collective management of communal grazing areas. Active local participation in management initiatives, equitable distribution of costs and benefits and popular support of the programme are prerequisites to collective management. These factors were assessed at the first two RMAs to be established in Lesotho (1 and 2, established in 1982 and 1985, respectively). In RMA 2 the residents were more systematically involved in developing the programme. In both RMAs active participation was largely confined to activities which were either mandated in RMA regulations and enforced, or voluntary but consistent with pre‐programme practices. In spite of possible regressive impacts on livestock distribution and supplemental feeding requirements, participants did not view equity as problematic. Popular programme support was high, particularly at the older RMA. These findings suggest that significant progress has been made in setting the stage for collective management but continued outside support is required at both RMAs.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638322

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The sexual reproductive system ofPortulacaria afrais characterized by the occurrence of gynodioecy; hermaphrodite and female plants occur in approximately equal proportions in all the populations studied. Female plants produce large quantities of viable seed whilst seed production in the hermaphrodite plants is limited. These modifications in the methods of sexual reproduction may have important implications for the future survival of this species.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638323

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor