ISSN:1022-0119    

DOI:10.2989/10220110009485729

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:1022-0119    

DOI:10.2989/10220110009485730

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:1022-0119    

DOI:10.2989/10220110009485731

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:1022-0119    

DOI:10.2989/10220110009485732

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:1022-0119    

DOI:10.2989/10220110009485733

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The need for an annual increase of 2% in global food production demands knowledge on how best to use natural grazing land resources. Taken with the requirement to protect resources, this need creates conflicting demands on grazing land management. Concerns for product quality, uniformity and continuity and for animal welfare will increasingly drive production processes. In this paper, the potential of mixed grazing for higher output of quality animal products, within these constraints, is assessed under both temperate and semi-arid conditions. Complementary behavioural patterns between domestic livestock types, particularly in their dietary selection, appear to be the primary basis for development of improved grazing ecosystems. Many of these processes operate at the landscape scale. In addition to increasing animal output, mixed grazing can be used to modify the vegetation. This is of particular importance for manipulating woody species cover in semi-arid areas and hence for improvement of range condition. For rural development, identification with the system and confidence in the purveyor sets the basis for success.

ISSN:1022-0119    

DOI:10.2989/10220110009485734

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Seed production and shrub association patterns of the two palatable shrubs.Tripteris sinuatumandTetragoma froticosawere investigated on heavily grazed communal and lightly grazed commercial rangeland in the succulent karoo, Namaqualand. Seed production in both these species was substantially reduced on the communal rangeland relative to the commercial rangeland. Seed production inT. sinuatumwas most severely affected, with seed production on the communal rangeland two orders of magnitude lower than on the commercial rangeland. The proportion ofT. sinuatumandT. froticosashrubs growing unassociated with other shrubs on the communal rangeland was reduced by approximately 50%.Lycium ferocissimumwas most effective as a refuge plant forT. sinuatumin terms of the mean seed production per plant.Ruschia robustawas however most important in terms of the overall amount of seed produced byT. sinuatumandT. froticosaon the communal rangeland, due to the large number of times this association occurred. Refuge plants did not appear to be particularly important forT. froticosain terms of seed production, but were important in terms of providing safe sites for recruitment. The results of this study suggest that unpalatable or thorny species such asL. ferocissimumplay an important role in providing refuge sites for palatable species that might otherwise become entirely lost from overgrazed rangelands.

ISSN:1022-0119    

DOI:10.2989/10220110009485735

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The non-selective rotational grazing system has undergone a long and controversial development. The merits of this grazing system, where relatively large numbers of livestock are herded into numerous small paddocks for short timespans with long rests between grazings, have not been formally evaluated in a long-term monitoring experiment in the Karoo. In this study we used exclosures (controls) on a 7 000 ha farm in the Central Lower Karoo, camped into approximately 50-ha paddocks, to evaluate the impact of this grazing system on certain vegetation parameters. We report on the first four years of monitoring, after each of four replicate paddocks had received four treatments (one treatment = 40 - 60 Large Stock Unit grazing days per hectare over a period of 2 - 16 days). Concentrated defoliation with concomitant trampling, dunging, and urinating did not influence the perennial species composition, and cover of this grassy, semi-arid shrubland. Changes over time in plant composition, and cover are explained by annual, and short-term (e.g. quarterly) rainfall rather than by grazing impacts. Ephemerals were not favoured by this grazing system, but litter was more abundant in the treatment than the control areas. The dominant grass,Eragrostis lebmanniana,and shrub,Pentzia incana, are resilient to this defoliation regime, and show signs of compensatory growth. As yet there is no evidence that non-selective grazing increases diversity, but the severe defoliation and trampling may enhance the biomass turnover rate, resulting in more vigorous, and productive plants in the grazed areas. Diversity is unlkely to change rapidly in response to grazing, largely because of the persistence of grazing-tolerant perennials. Concentrating mixed herds of livestock onto small areas with lengthy rests can be a useful tool for 'kick-starting' moribund karoo veld into greater productivity. Several of the impacts hold potential for restoring the rangeland quality of degraded areas, but this needs to be tested.

ISSN:1022-0119    

DOI:10.2989/10220110009485736

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We investigate the correlates of stocking rate in the Leliefontein communal reserve and attempt to provide a mechanistic explanation of the controlling factors. We further speculate on how high stocking rates are maintained in relation to the current state of the rangeland and grazing practices in the region. Stepwise regression revealed that over 80% of the variance in stocking rate could be explained by the mean maximum temperature during the hottest month, February. Deeper investigation revealed that the proximity of the West Coast played an important role in moderating temperature across the reserve. Areas further inland were not only hotter in summer, but were also colder in winter. We speculate that despite large differences in rainfall, the temperature gradient results in a shorter growing season and hence lower productivity of areas further inland. Mean annual rainfall was a very poor predictor of stocking rate and explained less than 5% of the variance in stocking rate across the reserve. Within a single village district, the stocking rate over time was, however, correlated with rainfall over the same period, indicating that stocking rates are determined by primary productivity and are at, or close to, the ecologioal carrying capacity. We further argue that continuous grazing of the lowlands during the growing season has resulted in the lowlands becoming dominated by annuals and unpalatable shrubs. Due to the shallow-rooted nature of annuals, the vegetation has become more sensitive to temperature effects. The reliability and seasonality of the rainfall in Namaqualand are seen as important factors contributing to the seasonal abundance of annuals and the viability of the current grazing system in the region.

ISSN:1022-0119    

DOI:10.2989/10220110009485737

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The effects of fire, bruchid seed beetles and soil type on the germination and seedling establishment ofAcacia drepanolobiumwere experimentally investigated. Seeds subjected to three seed treatments (bruchid damaged, bruchid-free burnt, and bruchid-free unburned) were germinated in three different soil types (black cotton, red sandy, and clay loam soils). Undamaged seeds had significantly higher germination (85.3%) than either beetle damaged (20.6%), or burnt seeds (3.4%). Soil type did not influence germination or seedling survival. Burnt seeds had an average germination of 2% in clay loams and 5.4% in red sandy soils, while beetle damaged seeds had an average germination of 15.6% in clay loams and 28.7% in black cotton soils. Treatment effects on seedling mortality or survival were not significant but seedlings from undamaged seeds had higher survival rates than those damaged by bruchid beetles.

ISSN:1022-0119    

DOI:10.2989/10220110009485738

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor