Grassland and Rangeland Science

Permanent URI for this communityhttps://hdl.handle.net/10413/7556

Browse

Now showing 1 - 20 of 86

A comparative classification of the sourish-mixed bushveld on the farm Roodeplaat (293 JR) using quadrat and point methods.
(1995) Panagos, Michael David.; Westfall, Ribert Howard.; Zacharias, Peter John Kenneth.; Ellis, Roger.
An area and a point-based technique were used together at each of the same 75 sampling sites (stands), on a Sourish-Mixed Bushveld farm, to collect data for the classification and mapping of the vegetation. Both sets of data were synthesized using the same computer program package and the efficacy of the resulting classifications as well as the efficiency of the two field sampling techniques was compared. Following this, a continuous 7 752 point (1 m apart) transect was carried out, traversing the farm, in order to determine the optimum scales at which to sample Sourish-Mixed Bushveld so as to increase classification efficacy and improve community boundary recognition. The results indicated that (1) the arbitrarily chosen sampling scale of 1:8 000 was too large for "farm-scale" studies; (2) the area-based method proved to be satisfactory in that the classification and vegetation map produced with this method were verified spatially and environmentally; (3) the point-based method was deficient as a classificatory and mapping tool at large scales, since too few species were recorded with this method to make any sense of the classification and mapping of the vegetation was not possible; (4) less time per species was spent using the area-based method but because more species per stand were recorded with this method, the point-based method was quicker per stand; (5) the area-based method was easier to use in dense vegetation and irregular terrain; and (6) the optimum sampling scales for Sourish-Mixed Bushveld, as indicated by the synthesis of the continuous transect data, are about 1:12 000, 1:50 000 and 1:250 000.
Production and economics of Arado and Barka cattle in Eritrea.
(2007) Tedla, Rezene Teweldemedhine.; Kirkman, Kevin Peter.; Ferrer, Stuart Richard Douglas.
Grazing lands in Eritrea are degraded due to decades of overstocking and consequent overgrazing. Since the rangelands are accessible to entire village communities, organisation and coordinated decision making regarding the management of these resources is not often achieved. Farmers are not motivated enough to make investments to improve a communally owned resource due to the prevailing common access grazing systems. A field survey was undertaken interviewing 12 farmers in the private access commercial and 80 farmers in the common access subsistence grazing using face to face interviews in the Barka and Arado cattle farming communities in four out of the six regions in Eritrea. Debub, Gash-Barka, S. Keih Bahri and Maekel regions were selected using stratified and simple random sampling methods. The regions were chosen based on various agroecological zones where the representatives of different grass species and the two most common cattle breeds in Eritrea (Arado and Barka) are found. The survey included the collection of data on village and household characteristics focusing on rangeland grazing management systems and additional sources of supplementary forage. The study uses several stages of analysis like principal component analysis accompanied by regression analysis together with descriptive statistics and ordination diagram. The commercial farmers addressed grazing constraints by investing in improved grazing through planting 258 ha per farmer of drought resistant seeds and 1767 vs. 8 cactus slices per farmer and covered 75% vs. 40% of forage requirements from grazing resources compared to the subsistence farmers, respectively, during 2002. These results were achieved because 78% of the commercial farmers adopted controlled stocking rates. In common access grazing, the costs of collective action to control cattle stocking rates are high, making imple mentation of stocking rate controls difficult. As a consequence, 65% of the subsistence farmers were forced to migrate their cattle looking for grazing forage in the dry season during the year. The outcomes of migration were evidenced by the results of severe overgrazing and degradation on the rangelands proximity to villages in Debub and Maekel regions and the populated area of Gash_Barka region. The increased number of animals resulting in high grazing pressure was the consequence of migration. Ten vs. six percent of mortality rates was reported for the subsistence systems compared to the commercial systems respectively. The lower results of milk yield, calving rates and off- take rate productivity indicated in the different stages of analysis for the subsistence farmers were the consequences of the lack of the adoption of controlled stocking rates primarily constrained by the migration. The Barka and Arado cattle farming systems are kept under common access grazing systems. Compared to the Arado cattle farming, the Barka cattle farming region had relatively better access to grazing forage. The better quality of grazing in this region is attributed to a naturally low stock density in the region. During 2002, the Barka cattle farming had 1087 vs. 721 Lit of milk yield, 63% vs. 53% of calving productivity and 9.3% vs. 10.9% of mortality rates than the Arado cattle farming regions respectively, due to access to a wider area of grazing lands and more labour inputs. The Barka cattle area farmers are agro pastoralists and usually focus on grazing dairy cattle farming than crop farming. They increased calving rate productivity and decreased mortality rates by increasing the proportion of lactating cows and decreasing the proportion of oxen compared to the Arado cattle farming. The Arado cattle farming had higher offtake rates and income from cattle sales compared to the Barka cattle farming region. The higher off- take rate, which is an index of percentage of cattle sold, for the Arado cattle was probably linked to the shortage of grazing forage and increased herding costs. The Barka and Arado cattle farmers had a shortage of quality and quantity crop residue winter forage during 2002. Farmers were dependent only on rain fed cropping. The application of crop rotation, fallow and chemical fertilizers were low to enhance soil nutrients. Out of the total crop residues forage produced, only 22% and 15% of legumes residue DM forage was produced for the Barka and Arado cattle farmers respectively. Agro- industrial and crop farming by-products supplementary feeds were also limited due to the shortage of feeds in the country during the year. In general, government intervention is important to bring institutional changes to promote the adoption of controlled stocking rates to alleviate the shortage of grazing forage.
Soil, herbaceous and woody responses to different methods of bush control in a mesic eastern Cape savanna.
(2000) Mapuma, Mathembekaya.; O'Connor, Timothy Gordon.
Bush encroachment is a major problem for the savannas supporting livestock in the Eastern Cape. Farmers employ chemical poisoning and mechanical clearing of woody vegetation to improve grass production. This thesis addressed the following questions. 1. Does soil fertility and hence, herbaceous production and/or quality increase beneath or between former bushclumps following woody clearing or poisoning? 2. Are chemical or mechanical control methods effective for all woody species? 3. Does bush density and height decline with increasing competition from the herbaceous layer? 4. Can fire and goats retard or revert woody re-establishment, thereby keeping these savannas open? A trial for assessing different methods of controlling bush was conducted near Kei Road. Initial treatments included chemical poisoning, mechanical clearing and a control, each replicated eight times in 0.36 hectare plots. Follow-up treatments were control, fire, goats, and the combination of fire and goats each replicated twice per primary treatment. Two additional mechanically cleared plots were oversown with Chloris gayana seeds. Herbaceous production, species composition, foliage quality and soil fertility, and mortality, recruitment, height increase and density of woody individuals were monitored for five seasons. Mechanical clearing of the woody vegetation increased soil fertility, except total nitrogen, and that explained the dramatic response in grass production that endured for the first four seasons since clearing. The periphery and ex-bushclump zones were characterised by increased colonization of Panicum maximum while there were no changes in frequencies of other key herbaceous species in all vegetation zones. Acacia karroo and woody "weeds" (Solanum incanum, Berkheya bipinnatifida) established from seed while all other woody species recruited mainly from coppicing. Seedling recruitment and resprouting resulted in high densities of woody stems and individuals by the second season after clearing when compared with the pre-clearing levels. Oversowing cleared areas with pasture grasses did not only increase grass production but also reduced the density of coppicing woody plants and "weeds". Chemical treatments mirrored the controls in terms of grass production, except during a very wet season, and species composition. Although encroaching woody species (e.g. Scutia myrtina, Maytenus heterophylla and Trimeria trinervus) were susceptible to poisoning, woody plant density was not reduced. Multi-stemmed woody individuals were resistant to poisoning. Fire and goats kept most coppicing woody plants short, less than half a metre, after three seasons of browsing and also improved grass production in the dense bushclumps suggesting that these clumps were being opened up. However, high browsing pressure forced goats to graze more hence this effect was masked. This study indicates that chemical and mechanical control of bush are economically unsustainable for beef and mutton production, at least in the medium term. Fire and goats are appropriate as a follow-up strategy for retarding woody regrowth, keeping bushclumps open, improving grass production and economic viability of mechanical clearing.
Grazing management in the communal rangelands of the Upper Thukela, Kwazulu-Natal.
(2005) Tau, Mahlodi Solly.; Everson, Theresa Mary.
The grazing management project in the Okhombe ward of the Amazizi Tribal Authority formed part of the National Department of Agriculture's LandCare program to address communal natural resource management issues. Okhombe land is communal whereby every member of the community is the legal owner of the rangeland with individual ownership of stock with the chieftaincy playing a major role in land allocation. In order to avoid critics of the past and address the top-down approach of the past interventions, a participatory approach was conducted in the planning and implementation of the grazing system. The service providers held a series of visioning workshops with the community in an effort to better understand community resource use patterns, needs, constraints and opportunities as part of the participatory approach. Issues identified by the community were the need for fencing grazing camps, animal health improvement, subdivision of rangeland and crop fields and the development of a rotational grazing system. The main aims of this study were to develop a participatory grazing plan with the community, develop and support institutional structures governing range management, and build capacity of the community in range management. The effect of the current grazing system on species composition was determined. In addition to these, the project investigated the potential different fodder trees has on alleviating feed and nutritional deficit, particularly during the dry winter months of the Upper Thukela. Among the main achievements of this study was the development and strengthening of local institutional structures and effective liaison by all structures with the Inkosi and the tribal council. The community developed a rotational grazing plan, marked the camp boundaries, produced digital maps and successfully built fence boundaries (approximately 20 kms of fencing) to divide their land. The fence boundaries separated the crop fields and rangeland, closed ward boundaries in the upland to prevent access by cattle from neighbouring wards, and divided the land into three camps. Six crush pens were constructed in each subward of the Okhombe ward. A communal herders fund opened and fence construction improved crop yields due to a decrease in crop damage by cattle. Okhombe ward, located in the Highland Sourveld region of KwaZulu-Natal, experiences feed and nutrition deficits to ruminants during winter. The prevailing species composition in Okhombe was investigated as part of the grazing plan. The veld condition of the sites ranged from poor (40.7%) in the bottomland to an averaged of 47.0% in upland sites. The most distinctive feature of the rangeland in this area was the loss of highly palatable Decreaser grass species (P <0.05), such as Themeda triandra in the bottom slopes « 1300 m) when compared to the upland (> 1800 m). The proportional abundance of Decreaser species accounted for an averaged of 1.02% of the bottomland and an averaged of 11.5% of the upland compared to the values of 49% in the benchmark (grassland in optimal condition). The composition of the less palatable Increaser Il species was very high at all elevations (1200 m -80.7%, 1400 m - 75.8% and 1700 m - 55.7%) when compared to the low benchmark composition of 19%. The dominant grasses of the bottom slopes were Increaser Il species, such as Eragrostis curvula, Eragrostis plana and Sporobolus africanus and unpalatable Increaser III species such as Aristida junciformis. A significant difference (P < 0.05) in the composition of Decreaser, Increaser I and Increaser Il species was found between the bottom and slopes compared to the upland region. However, the grass cover formed by these tufted species was generally high, making it more resistant to physical degradation. The bottom slope ranged from reasonable to excellent cover (16.9%), the middle slope ranged from reasonable (15.9%) to a good cover of 18.1%, averaging 16.7% and a range of 16.1% to 17.9% for the upland plateau. In the agroforestry trial the potential of different fodder species for supplementing fodder was examined. Leucaena leucocephala had the potential of being a suitable fodder tree species for use in alley cropping (P < 0.05) compared to Morus alba and Acacia karroo. Results from the partially intercropped treatments showed that L. leucocephala yield (665 kg ha-I) varied significantly (P < 0.05) from the A. karroo (378 kg ha-I) and M alba yield (345 kg ha-I). Treatments that were fully intercropped varied, but no significant difference (P > 0.05) were recorded. Morus alba produced the least yield of 345 kg ha-I, A. karroo yielded 378 kg ha-1 and 1. leucocephala recorded the high of 664 kg ha-I. Results from the second season showed similar trend in that 1. leucocephala yielded a significant (P < 0.05) fodder production of 1715 kg ha-I in comparison to M. alba (1101 kg ha-I) and A karroo (1140 kg ha-I). M alba yielded the least dry matter production (P < 0.05) but had high potential (P < 0.05) for addressing lack of firewood in rural areas. Morus alba yielded high fuel wood production from both two seasons. There were no significant differences in fuel wood yield (P > 0.05) from the partially intercropped M alba (507.9 kg ha-I) and 1. leucocephala (455.0 kg ha-I) but the yield from both species varied significantly from the A. karroo yield (103.kg ha-I). With regard to fully intercropped plots, fuel wood yield from all tree species varied significantly, A karroo resulting in low yield (63 kg ha-I), 1. leucocephala recorded 243 kg ha-l and M alba the highest yield of 444 kg ha-I. In the second season, M. alba yielded an averaged fuel wood production of 728 kg ha-l and a low of 439 kg ha-I from 1. leucocephala. Acacia karroo, a slow growing indigenous tree, might be preferred by farmers due to its less branches resulting in minimal light competition with crops. Leucaena leucocephala tend to grow slowly in its initial establishment stage, but once roots become well established, it grows fast and produces high quantity of fodder. The effect all fodder trees had on crop yield was not negative during the trial period and further research on long term effects of alley cropping is recommended. The conclusions drawn here were based on tree growth and their likely impact in alley cropping. Leucaena leucocephala was also recommended as a preferred species for rural ruminants based on the forage quality study. The results showed high content of crude protein (19.27%), low NDF content (50.38%) and very low tannin content (1.19%) from 1. leucocephala compared to A. karroo with a high tannin content of 5.69%. Acacia karroo had a crude protein content of 13.60%, NDF percentages of 44.16 and 34.64% of ADF content. Morus alba also had a recommended chemical composition of 11.71% of CP, 42.86% of NDF, 36.96% of ADF and a low tannin content of 0.65%. L. leucocephala foliage proven is readily degradable under different diet ranging within 24 hrs of intake (P < 0.001) compared to other feeds. L. leucocephala had high dry matter loss degraded from the rumen under Eragrostis hay diet with poor nutrients to high protein concentrates diet. Under the Eragrostis hay diet for instance, L. leucocephala tend to degrade rapidly with values of dry matter loss ranging from 32.2% to 39% at 4 hrs to 16 hrs, when compared to low dry mater loss of 26% at 4 hrs to 31.33% at 16 hrs. Feeds such as M alba tend to degrade slowly within 24 hrs of intake and rapidly degrades after the stated period. The ep content of maize stover was very low ranging from 1.60% in maize stalks to 2.63% in maize leaves. The fibre content in maize stover was very high when compared to lower values in fodder samples. The NDF content ranged from 77.92% in maize leaves to 81.60% in maize stalks. Maize leaves when compared to a combination of maize leaves and maize stalks sole tend to degrade better within 24 hrs of intake. This was due to low (P < 0.05) degradability rate of maize stalks compared to a combination of maize stalks and leave and leaves sole and least NDF content in maize leaves might have attributed to these results. Due to poor chemical compositions of these roughage samples, the study recommended the establishment of fodder banks and agroforestry systems to curb the nutrients deficit during winter. In conclusion therefore, this study highlight that the sustainability of rural systems to manage communal grazing land should be further explored. Most of the challenging issues in communal range management are social in nature rather than technical concepts. These include ways of improving social contributions from cattle to the community while maintaining cultural values of the use of cattle. The interventions in communal range management by service providers should understand the institutional arrangements within a community and an attempt to strengthen such existing structures is recommended. Further interventions by service providers in Okhombe ward should bring in the planning discussions, experts from social sciences, to deal with understanding of community dynamics. Complexities in communal range management involve dealing with non-stock owners within project boundaries. Communities from neighbouring wards should not be ignored and ways of improving communications and updating project details to them should be formulated. Shortage of land and closing of ward boundaries to prevent access to land by neighbouring wards is among community complexities to be explored. Communities in rural lands do share land and in most cases boundaries are known but invisible by an outsider to identify. It is important to strengthen and maintain every success in communal lands as that may form core of the project. Successes on grazing management by locals is far from being the improvement in veld but there are rather various factors to the successes of grazing projects in rural areas. Examples of successes based on Okhombe project are reduction in stock theft, improved in relationship between community and locals institutions, a reduction in stock mortalities during winter and improved animal health. Veld improvement is among successes but there are accomplishments phases to fulfil before focusing on improvement of species composition.
The role of fire and mechanical clearing in the management of Chromolaena odorata.
(2006) Wessels, Mathias Fittschen.; Kirkman, Kevin Peter.; Granger, James Edmund.
The effects of fire and mechanical clearing were investigated for their potential in assisting with the eradication of Chromolaena odorata (previously Eupatorium odoratum). The study was divided into two focus areas, the first focused on mechanical clearing of dense stands of C. odorata on three sites and the second focused on the long term influences of a single burn on C. odorata plants in the different size categories. For mechanical clearing, two key issues were investigated; namely whether this type of clearing procedure was effective in dense C. odorata stands and whether rehabilitation was necessary in these cleared areas. The study was conducted from July 2002 to June 2004. The area was subject to a severe drought throughout the duration of the study. The severe drought had a large influence on the result in both focus areas. A bulldozer was found to be a very effective at clearing dense C. odorata stands. Results from the mechanical clearing study showed that there was still a large viable grass seed population in the areas that had been covered by a dense stand of C. odorata plants for over three years. Thus, indigenous plants were able to re-colonize the area after removal of C. odorata without human intervention, even thought the area was experiencing a severe drought. The density of C. odorata seedlings emerging in the cleared areas was far lower than expected. The C. odorata density in the permanent plots, for seedlings that germinated in the first season after clearing (SeptemberOctober 2002), was only 0.25,0.03 and 0.72 per 5 m2 in the three sites respectively by the end of the study in June 2004. For the C. odorata seedlings that germinated in the second season (September-October 2003) the density was, 0.5, 0.56 and 1.06 per 5 m2 in the three sites respectively by the end of the study in June 2004. It was suspected that the drought influenced seed germination. Unfortunately the number of C. odorata seedlings was so low, that no significant relationship could be found between grass and C. odorata seedling density. By the end of the study the grass fuel mass in all the rehabilitated sites was already over 3000 kg ha-1, even though the area was experiencing a severe drought. This grass fuel load, when burnt, will assist land managers in controlling C. odorata plants, especially seedlings. Very few other alien invasive plant species emerged in the cleared areas. At the Mhlosinga site, Senna pendula made up less than one percent of the herbaceous species composition and only a single Ricinus communis plant was recorded. No alien plant species were recorded on the other two sites. Results from the burning trials revealed that plants in all the size categories were affected by fire. Greater fuel masses and fire intensities were required to kill larger C. odorata plants relative to smaller ones. Fire was found to be very effective at eliminating small and medium size C. odorata plants. Fire applied as a once off treatment had a significant long-term effect on the C. odorata population. The following fuel loads were required to achieve 80% mortality in this 11 study: for small plants a fuel load of over 4000 kg ha-I, for medium plants a fuel load over 4200 kg ha-I and for large plants a fuel load over 4600 kg ha-I. Little difference could be detected between a head or a back burn, as both fire types had their own advantages and disadvantages. Although some of the C. odorata plants in the burnt plots had not perished by the time of the first investigation, following the burn (February 2003), by the time of the second investigation (June 2004), many of these plants had eventually succumbed. These results highlighted the fact that plants which are damaged by fire were more likely to persish during an extended droughts period, than plants which were not subjected to fire. Results from the control plots, in the burning trials, for medium and large plants showed dramatic increases in density over time. Tagged individuals from the control plots did reveal that some of the medium and large plants did die during the drought, although the amount was negligible when compared to the number of new plants growing into the new size categories. A large proportion of the small plants in the control plots also survived the drought with many of them even growing into the medium category. The difference between the control plots and the burnt plots was obvious and significant, especially once the fuel mass exceeded 3783 kg ha-I. Results from this study show that fire can be used as a very effective tool in assisting land managers to control C. odorata in open savanna bushveld.
Management of kikuyu (Pennisetum clandestinum) for improved dairy production.
(2007) Holliday, Jane.; Kirkman, Kevin Peter.
South African dairy farmers have generally used kikuyu pasture to tide them over from one ryegrass season to the next, and as a result of its resilient nature, have assumed careful management of it to be unnecessary. This has resulted in its mismanagement which is unaffordable in current times where the profitability of dairy farming is increasingly dependent on low input, pasture-based systems. Kikuyu pasture may play a larger role in supplying nutrients to dairy cattle over the summer months in future as the alternative home produced feed sources such as silage and perennial ryegrass become increasingly unaffordable. Improving animal production from kikuyu is difficult as there is little information relating kikuyu pasture management to dairy cow performance. Efficient utilization and quality of temperate pasture have been more comprehensibly researched. The relations discovered between the chemical compounds in temperate grass species have been applied to tropical pastures such as kikuyu with limited success and often confusing results. For example, crude fibre in kikuyu was found to be positively related to digestibility. In South Africa, much research has been done on the use of kikuyu in beef production systems. This information has been applied to dairy farming systems with limited success, owing to the higher metabolic demands of dairy animals. Pasture farming needs to become more precise to improve pasture quality and hence milk yields as research trials focussing on stocking rate and grazing system comparisons have yielded results that are too general with little application at the farming level. A need for integrated and flexible management of animals and pastures has been recognised. The grazing interval is a key aspect in improving pasture and animal performance and fixed rotation lengths and stocking rates have been identified as being detrimental to performance. The relation between growth stage and pasture quality has lead researchers to identify plant growth characteristics, such as pasture height and leaf stage, as signs of grazing readiness. At the four and a half leaves per tiller stage of regrowth, the chemical composition ofthe kikuyu plant is more in line with the requirements ofthe dairy cow, with the leaf to stem ratio at its highest. The primary limitation of kikuyu pasture is a lack of energy, particularly readily fermentable carbohydrate, which makes the fermentation of structural carbohydrates difficult and dry matter intakes are reduced. Other limitations to animal performance include high cell wall constituents, low calcium, magnesium and sodium content and antinutritional factors such as nitrate and insoluble oxalate. These deficiencies and antinutritional factors are in some cases unique to 5 kikuyu pasture, meaning that kikuyu specific supplementation may be the key to improving performance from dairy cattle grazing kikuyu pasture. The objectives are to evaluate current kikuyu management systems in South Africa and their impact on dairy cow performance and to evaluate the use of pasture height and burning as quality control tools.
Re-vegetation dynamics of land cleared of Acacia mearnsii (black wattle)
(2005) Glaum, Melanie Jane.; Zacharias, Peter John Kenneth.; Granger, James Edmund.; Everson, Theresa Mary.; Smith, M.
The overall aim of the study was to investigate re-vegetation of disturbed sites, using nursery grown plugs (from seedling trays) of Themeda triandra, Heteropogon contortus and Hyparrhenia dregeana in order to reach practical management guidelines for re-vegetation using indigenous grass plugs. A number of field trials were set up at Kamberg Nature Reserve (29°24'S, 29°40'E) on a site that was clear felled of A. mearnsii in October 1997. The trials were established in January 1998 and January 1999. A total of approximately 52 ,000 nursery raised plugs of T. triandra, H. contortus and H. dregeana were planted into an area of approximately 7,000 m2 . In the planting density trial , plugs of H. dregeana only and a combination of T. triandra/H. contortus were planted at 15 cm and 30 cm spacings. The T. triandra/H. contortus combination at 30 spacing showed the greatest survival and lateral plant growth (tiller number and basal area) and this combination is thus recommended. In the over-sowing trials, the H. dregeana and T. triandra/H. contortus combination at both 15 cm and 30 cm spacing were over-sown with E. curvula. The survival and lateral growth of the T. triandra/ H. contortus combination at 30 cm was again greater than the other treatments. Over-sowing with E. curvula suppressed the survival and lateral growth of the planted plugs across all treatments compared to not over-sowing. The over-sown conditions showed a significant decrease in the diversity of the plots, both in the number of species present and the Shannon diversity index. An area that had been cleared of A. mearnsii and sown to E. curvula 25 years previously was shown to have a lower number of species than the neighbouring veld. Nursery raised plugs of T. triandra were planted into the mature E. curvula in an attempt to improve the biodiversity of these areas. To re-introduce T. triandra into these E. curvula swards the plugs must be planted into the centre of a gap rather than around the base of an E. curvula plant. For improved survival of the plugs the E. curvula tufts must be clipped, while for best lateral growth the E. curvula tufts must be sprayed with a glyphosate herbicide three months prior to planting and clipping. However, the added expense of spraying and clipping is not warranted as the clipped treatments also showed good growth. Transplant shock is common when planting nursery raised plugs out into the field, as there is a relatively small root volume in the plug compared to the above ground leaf biomass. Alleviation of moisture stress at planting using a starch based polymer with high water holding capacity (Terrasorb®) and a white, needle punched geo-fabric (Agrilen®) to provide a seven day period of artificial shade after planting did not show significant improvements over the control with regards to survival or plant growth. Thus these methods of moisture amelioration are not recommended in revegetation through planting of plugs at this study site. A trial was established to investigate the biomass production of six different treatments to determine their potential to support a fire. The total biomass for the plots which were over-sown by E. tef and planted to only H. dregeana were on average sufficient for a fire, but there was a discontinuous fuel load across these plots, especially in the replications that had very low survival rates and thus these plots could not be burnt. The control and herbicide sprayed plots also showed sufficient fuel load for a fire, but this fuel load was made up of A. mearnsii saplings and bramble with very little grass cover and thus a fire would not have burnt through these plots either. The T. triandra/H. contortus combination did not produce sufficient fuel load, due to poor survival. Thus only the plots over-sown with E. curvula were able to burn in this trial and as a burning trial per se the trial was abandoned. Seed bearing hay (thatch) was collected in early summer (December 1997) and late summer (April 1998). Both times of year of harvesting proved to be successful in terms of grass cover, although the early harvested thatch had a greater number of species per plot. The Shannon diversity indexes of the two treatments were not significantly different. The multi-response permutation procedure technique confirmed that there was a compositional difference between the treatments. By the end of the trial Harpochloa falx and T. triandra and H. dregeana were indicators for the early and the late harvested thatch respectively. Comparing the thatching trial and the planting density trial indicated that the T. triandra/H. contortus combination at 30 cm spacing would be recommended to maximize biodiversity. The summer months have been shown to be the best time to plant the plugs, although the actual success will be dependant on the conditions within a particular year. The plugs should not be kept in the nursery for longer than three months and larger plugs (96 seedlings per tray) should be used. Nursery raised plugs of T. triandra and H. contortus were planted in an equal mix in an area that was cleared of A. mearnsii in 1996. By June 1998 661 H. contortus seedlings and 14 T. triandra seedlings had germinated naturally. The November 1998 population consisted of 418 H. contortus seedlings and 18 T. triandra seedlings. By May 2000 the June 1998 population showed a survival of 78.4% and the November 1998 population showed a survival of 91 .1 %. In the various trials, the ability of the nursery raised plugs used for re-vegetation to suppress the regrowth of A. mearnsii was investigated by determining the number of A. mearnsii seedlings per metre squared. The plant spacing and species of plugs used did not have a significant effect on the number of A. mearnsii seedlings per metre squared. Over-sowing with E. curvula did, however, significantly suppress the wattle re-growth. In the thatching trial the early harvested plots showed lower numbers of A. mearnsii per metre squared than the late harvest plots, as they were covered with a thick layer of thatch soon after the A. mearnsii was cleared which suppressed the A. mearnsii re-growth. Although E. curvula is able to produce a high biomass and suppress the A. meansii seedlings, it has a detrimental effect on the biodiversity of the area. Therefore, in conservation areas, where biodiversity is of great importance the planted plugs (at 30 cm spacing) or seed bearing hay must be used in preference to sowing E. curvula , although it must be remembered that greater follow up control is likely to be needed with planted plugs or seed bearing hay. The area must be planted or thatched as soon as possible after clear felling to provide competition for the A. mearnsii seedlings.
Ngorongoro crater rangelands : condition, management and monitoring.
(2006) Amiyo, Amiyo T.; Kirkman, Kevin Peter.
The Ngorongoro Crater is a volcanic caldera located within the Ngorongoro Conservation Area in Tanzania. The Crater comprises a flat grassland plain surrounded by steep, bushy walls. It contains extremely high densities of animals and is ecologically the central feature of Ngorongoro Conservation Area. The management of the Ngorongoro Crater has changed significantly in recent times, with cattle being removed and fire excluded about 30 years ago. A detailed vegetation assessment was carried out in the Crater floor by Herlocker & Dirschl in 1972. Since then noticeable changes in vegetation structure and composition, with associated changes in wild herbivore numbers have occurred. The original vegetation survey was repeated in this study as accurately as possible using similar point-based techniques in order to quartify changes and form a baseline for management decision-making and future monitoring. In addition to repeating the vegetation survey, the standing biomass was estimated using a Pasture Disc Meter with associated calibration equations. Data were summarised using multivariate classification and ordination techniques in order to delineate six Homogenous Vegetation Units (HVUs) which can be used for management and management planning purposes, define transects and HVUs in terms of dominant species, describe the main species in relation to their occurrence in different associations and determine the fuel load of the standing crop. A key grass species technique was developed for rapid assessment of the Crater rangeland by the Ngorongoro Conservation Area staff who only need to be familiar with the dominant species. Bush surveys using a point centred quarter technique were conducted along transects in two distinct vegetation types, namely the Lerai Forest and Ngoitokitok Acacia xanthophloea forests and the lower caldera scrub vegetation. The data collected from these transacts were analysed to determine density and composition of the vegetation in the various height classes and the overall structure of the vegetation communities, A range monitoring system in conjunction with a controlled burning programme has been developed to provide an objective means of managing the- rangeland of the Ngorongoro Crater. Data revealed that changes have taken place in the vegetation, with a trend towards dominance by taller grasses and dominance by fewer species. Lack of fire has probably contributed to these changes. Reincorporating fire in the crater is recommended.
An assessment of the effect of season of grazing, stocking rate and rainfall on the dynamics of an arid rangeland on the west coast of South Africa.
(2005) West, James Alexander.; Kirkman, Kevin Peter.
A grazing trial investigating the effect of season of grazing and stocking rate initiated at the Nortier Experimental Farm in 1988 provided an opportunity to assess the response of the veld to both grazing and environmental influences in an arid environment. The trial allowed an assessment of the relative influence of internal (equilibrium) and external (non-equilibrium) forces on the dynamics of an arid rangeland. This study involved the analysis of a nine year data set stretching from 1988 to 1996 and served to provide evidence supporting the existence of an equilibrium/non-equilibrium continuum in rangeland dynamics. The most significant implication of this result is that rangeland systems should not be classified as either equilibrial or non-equilibrial, but rather according to a continuum extending between equilibrium and non-equilibrium poles. The exact position of any system on this continuum is a function of the relative influence of internal and external forces on its species dynamics. The dynamics of the veld at the Nortier Experimental Farm showed significant response to both grazing and environmental variables suggesting conformity to both equilibrial and non-equilibrial paradigms. Both ordination and analysis of variance highlighted the importance of rainfall particularly in the fluctuations of the predominant grass species, Ehrharta calycina, which increased in abundance with rainfall. Partial ordination enabled the assessment of species variation following the removal of variation associated with rainfalL Partial ordinations revealed the gradual, directional movement of samples through multivariate space in response to grazing treatments. Individual plant species were also shown to be responding to grazing, the extent of which was influenced by season of grazing and stocking rate. Both the partial ordinations and the ANOVA showed Melothria sp., Tetragonia fruiticosa and Hermannia scordifolia as increasing and Ruschia caroli as decreasing in absolute abundance in response to grazing. Season of grazing was shown to significantly influence the abundance of H. scordifolia over time. The 'shrublherb complex', which constitutes the 'key resource' at the Nortier Experimental Farm displayed an increase in absolute abundance over the duration of the trial. This increase in absolute abundance was accompanied by an increase in the relative abundance of the palatable component of this resource. The application of medium to heavy stocking rates during spring, summer and autumn and low stocking rates during winter resulted in elevated absolute abundances of palatable plants. Furthermore, low stocking rates, when averaged across all season of grazing treatments, resulted in a significantly higher absolute abundance of unpalatable plants. These findings provide the basis for the development of management principles for the Strandveld Vegetation Type. The application of medium to heavy stocking rates within a rotational grazing system, as recommended by the literature dealing with grazing systems in the Karoo, is supported by the results of the Nortier grazing trial. Medium to heavy stocking rates should be applied during spring, summer and autumn and low stocking rates during the winter months. Furthermore, it is recommended that rests of between 12 and 14 months should be afforded to portions of the veld periodically due to the variability in growth, flowering and fruiting times ofdifferent plants in the Karoo.
The use of various soil ameliorants and indigenous grasses, in the rehabilitation of soil from open cast coal mines in Mpumalanga, South Africa.
(2004) Webb, Christy Mary Winifred.; Granger, James Edmund.; Kirkman, Kevin Peter.; Laing, Mark Delmege.
A series of pot trials were undertaken to test the growth of indigenous grasses (Themeda triandra and Cynodon dactylon) on mine capping soil, treated with various soil ameliorants. The capping soils were obtained from open cast coal mines (Optimum Mine and Syferfontein Mine) in the Mpumalanga Highveld, south of Witbank. However, because mine soil was not available at the commencement of the project, the initial pot trial used soil from the Umlazi Landfill in Durban. The trials were the Umlazi Landfill Trial, Microbe Trial, Legume Trial and Fly Ash Trial. For the Umlazi Landfill Trial, landfill top and subsoil was used along with fertilizer, sewage sludge, K-humate, lime and microbes. The soil ameliorant treatments for the Microbe trial were Trichoderma harzianum (Eco'T), Bacillus subtilis Strain 69 (B69) and Bacillus subtilis Strain 77 (B77), for the Legume Trial, Medicago sativa, phosphorus and/or potassium were applied. For the Fly Ash Trial, lime and fly ash were introduced. From the Landfill trial it was shown that fertilizer and sewage sludge significantly increased the above ground, below ground and total biomass of T. triandra, further, there were no significant treatment differences between fertilizer and sludge. The lime treatment for this trial, surprisingly, significantly reduced below ground biomass but the application of microbes (B69 and BcoT) alleviated this negative effect. However, in the Microbe Trial the microbes (BcoT, B69 and B77) had a negative or no effect on the biomass of T. triandra and C. dactylon. In the Legume Trial it was shown that the above ground biomass of T. triandra was significantly reduced when grown with M. sativa. The Fly Ash Trial revealed that the lime and fly ash treatments had no effect on the biomass of M. sativa and T. triandra, and they did not maintain a reduction in soil acidity. The results therefore indicated that either organic fertilizer or sewage sludge could be used to significantly improve the growth of T. triandra. It was also suggested that lime not be applied to soils with an acid saturation of approximately 1%, as this could retard plant growth. The application of microbes and the growth of a legume with grass, although both have been recorded to have beneficial effects in aiding plant growth, in the short-term however, the application of T. harzianum, B. subtilis Strain 69 and 77 applied to the soil while growing T.triandra and C. dactylon and the growth of M. sativa with T. triandra is not recommended.
Determinants of grass production and composition in the Kruger National Park.
(2003) Zambatis, Nicholas.; Zacharias, Peter John Kenneth.; Morris, Craig Duncan.; Biggs, Harry Cawood.
The dynamics and complexities of climate-soil-vegetation relations in the Kruger National Park are poorly known. Although primary production and composition of the grass layer are very important components of the Park's ecosystem, equally little is known about the determinants of these parameters. A better understanding of these processes and relations will be of value to the management of this Park, as well as providing a better insight into these complex dynamics. A study was consequently undertaken covering a 14-year period to identify the most important determinants of above-ground grass production and composition. At the core of the study is the soil water balance. The use of evapotranspiration data in a study of this nature is however not absolutely essential, provided a variety of rainfall parameters are used, though it has the important advantage of providing a much more detailed and more complete insight into the relations of the grass sward with its environment. Stepwise and tree regression procedures were used to identify the important factors. It is concluded that rainfall in its various forms is the primary determinant of grass production, standing crop, and composition, the latter either as perennials or Decreasers. Secondary determinants, in varying degrees of importance, are the thickness and base status of the A horizon, distance to permanent drinking water, and competition by woody plants. Herbivore utilization is insignificant or at most, plays a relatively minor role. Herbivores appear to exert a negative influence on Decreaser abundance only when soil moisture stress exceeds a threshold level. When this is exceeded, relatively low herbivore densities are apparently sufficient to reduce Decreaser abundance. The definitions of Decreasers and Increasers consequently require revision to take into account the overriding influence of environmental factors, particularly those of soil moisture stress. The calibration of the disc pasture meter was re-evaluated. The relation between mean disc height and standing crop is non-linear. Up to a mean disc pasture meter height of 260 mm, the correlation between this parameter and above-ground standing crop is very strong (r2 = 0.95; P<0.0005). Beyond this height, the correlation is very poor (r2 =0.09; P<0.0005), apparently being strongly influenced by the structure of the grass plant, with tall grasses, or grasses with highly lignified culms resulting in a weaker correlation.
The responses of grasses to fire and bush clearing in the Hluhluwe Game Reserve.
(1992) Graham, Philip Mark.; Page, Bruce Richard.
Contemporary and historical studies of the flora of the Hluhluwe Game Reserve (HGR), have emphasised the woody component whilst little work has been performed on the herbaceous vegetation. This is particularly true with regard to the responses of grasses to historical fire and bush clearing. This study attempted to elucidate some of these responses. Of all the variables considered in this study, woody cover, altitude, the number of fire events, geological and soil parent material are the most important affecting the abundance of grasses in this reserve. Most of these variables are not independent in their effects on grass abundance, with varying degrees of correlation between each other. Certain species appear to be restricted to particular geological substrates. Along with successional changes in the composition and cover of the woody community, due to seemingly inevitable bush encroachment, there is a parallel change in grassland communities in this reserve. In the absence of clearing, numerous fires, higher altitudes, igneous geology and soils derived from igneous parent material delays this succession, whilst sedimentary geology at lower altitudes and fire frequencies accelerates the trend to high woody cover and associated grass species. The grass communities in HGR were shown to be significantly affected by bush clearing and fire. Specifically the number of clearings and fire events, physical bush clearing during 1957 - 1963 and chemical bush clearing during 1968 - 1978. From the responses of species in relation to the various key environmental variables, viz. geological substrate, woody cover and burning and clearing, a model of species response to these variables was developed. With increased fire and bush clearing frequency, the grass communities shift from closed woodland, shade tolerant species through to more open fire climax grassland. These are also more productive communities producing palatable grasses. Validation of aspects of the model were successful - the model having a relatively high predictive capability. Further testing of the model over different substrates and under different clearing regimes is necessary. With regular fires and re-clearing in some bush cleared areas, the vegetation of this reserve should be able to be maintained as productive and diverse grasslands. In the absence of this management, the grass communities will shift towards species associated with woodlands. Bush clearing activities would appear to be most effective over sites on igneous substrate, at higher altitudes, where successional rates are slowest. This is in comparison to sites at lower altitudes over sedimentary geology.
The effect of burning frequency on invertebrate and indigenous flowering forb diversity in a Drakensberg grassland ecosystem.
(2006) Arnott, Wendy Lynn.; Hamer, Michelle Luane.
The KwaZulu-Natal Drakensberg, South Africa, is predominantly a grassland ecosystem maintained by fire. The effect of the current burning regime on invertebrate and flowering forb diversity in this ecosystem is poorly understood. The overall aim ofthis study was to contribute towards the development of an effective burning regime for the KwaZulu-Natal Drakensberg that will conserve invertebrates and indigenous forbs, two major components of biodiversity. The objectives were to examine the effect of fire and fire frequency on flowering forb and invertebrate species diversity, to determine whether fire frequency, time since last burn or locality were influencing species composition, and to identify potential biodiversity indicators that reflect overall species richness for use in monitoring of invertebrates and forbs. Sampling took place in March, September and November of 2002 at Giants Castle Game Reserve. Invertebrates were sampled using sweep netting and targeted netting along transects, yellow pan traps and soil quadrats. Invertebrate taxa sampled were ants (Formicidae), butterflies (Lepidoptera), grasshoppers (Orthoptera), leafboppers (Cicadellidae), bees (Apoidea), bee flies (Bombyliidae), hover flies (Syrphidae), robber flies (Asilidae), spiders (Araneae), earthworms (Oligochaeta) and millipedes (Diploda). These were identified to species level with the assistance of taxon experts. Flowering forbs were sampled using five replicates of five by five metre quadrats randomly placed in each site. Overall flowering forb and invertebrate species diversity was higher in grasslands that were burnt for two consecutive years in 2001 and 2002 than in grasslands that were not burnt during those two years. Frequently (annual) and intermediately (biennial) burnt grasslands had significantly higher invertebrate and flowering forb diversity than infrequently (five years without burning) burnt grasslands. This, together with the fact that grasslands burnt during the year of sampling had higher species richness than grasslands burnt two and five years previously suggests that invertebrates and forbs are generally resilient to fire and many forb species appear to be stimulated by fire. However, each burn frequency had its own suite of unique flowering forb and invertebrate species. Invertebrate communities were influenced mostly by locality and the length of time past since the last fire and flowering forb communities were influenced mostly by the length oftime past since the last fire. Fire frequency had the least influence on both invertebrate and forb communities. Ecological succession occurred after each fire in the invertebrate communities but forb communities appear to need more than five years without fire for ecological succession to occur. The findings of this study therefore suggest that using a combination of three fire frequencies would result in patches of grassland in various stages of ecological succession, and would conserve species unique to each burning frequency, and would therefore conserve maximum diversity. Flowering forb species richness and certain invertebrate taxa (ants, leafboppers, spiders and bees) have the potential to act as indicators of overall invertebrate species richness for use in monitoring programmes.
Rangeland and animal performance trends in highland sourveld.
(2010) Short, Alan Douglas.; Du Toit, Justin Christopher Okes.; Kirkman, Kevin Peter.
Long-term trends in rangeland sward dynamics (species composition, structure, productivity) were examined on three trials established between 1989 and 1996 at Kokstad Research Station in the Highland Sourveld, while animal performance (average daily gain and gain per hectare) was examined on two of the trials. The region enjoys moderate rainfall of 782mm per annum, with hilly topography, and soil depths ranging from >1m to <20cm. The first trial was labelled the simulation trial, as it simulated a four-paddock rotational grazing system, in which animals spent two weeks in each of three paddocks while the fourth was rested for the entire season. The rested paddock was rotated each year. The trial tested two stocking rates (0.5 and 1.0 AU.ha-1) at five ratios of cattle to sheep, ranging from cattle only to sheep only. The trial was unreplicated, and was established in 1989 on flat topography with deep soils. The second trial (labelled the flat two-paddock trial) was established in 1992 adjacent to the simulation trial. The trial examined two stocking rates of sheep weaners (0.5 and 1.0 AU.ha-1 seasonally) in a continuous grazing two-paddock system, in which one paddock of each treatment was burned and grazed continuously while the second paddock was rested, to be burned and grazed in the following season. The trial was replicated twice. The third trial (labelled the steep two-paddock trial) mimicked the grazing system of the flat trial, but was located on a steep (c. 20%) West-facing slope with shallow soils. The trial incorporated two additional treatments: an intermediate stocking rate of 0.7 AU.ha-1 and an ungrazed treatment. Species composition of the sward was recorded biennially on all trials using the nearest plant-point technique with between 200 and 800 points per paddock. Sward standing crop was measured in the rested seasons of the simulation trial and at the beginning, middle and end of each season in one paddock of each two-paddock treatment of the two-paddock trials. In the two-paddock trials, sward standing crop was measured within and outside permanently placed exclosure cages. Animals were weighed fortnightly. The response of species to grazing pressure or animal type was mediated by soil depth and slope, as well as the grazing system. Tristachya leucothrix declined on all grazed treatments. The ungrazed treatments remained relatively stable over ten years. On the low stocking rate treatments of the steep trial, unpalatable species increased, but so did Themeda triandra. The heavily grazed treatment of the steep trial was surprisingly stable, with little significant change in relative abundance of key species other than an increase in the unpalatable Alloteropsis semialata and decline in T. leucothrix. The medium stocking rate treatment on the steep trial showed significant shifts in relative abundance of key species, with declines in T. triandra and T. leucothrix and increases in A. semialata and the unpalatable wiregrass D. filifolius. These trends were not repeated on the flat trial, however, with T. triandra and A. semialata increasing and all other key species declining or remaining stable. On the simulation trial, species responded largely unpredictably with species abundances often fluctuating considerably over time. Microchloa caffra and A. semialata increased substantially in both the low and high stocking rate sheep-only treatments, with a concurrent decline in T. triandra in the high stocking rate but not the low. Changes in composition over time, as measured by Euclidean distance, showed that shallow soils, high stocking rates and a high proportion of sheep caused greater shifts in species composition over time than deep soils, low stocking rates or more cattle. Three treatments, the sheep-only treatments on the simulation trial and the high stocking rate on the steep trial, showed an initial rapid shift in composition over about 6 years, before stabilising in subsequent seasons. The flat trial showed no substantial shift in composition over time. This general pattern of change was confirmed by Non-Metric Multidimensional Scaling. On the simulation trial, total standing crop was influenced by stocking rate and by the proportion of sheep in most seasons. On the two-paddock trials, increasing stocking rate significantly reduced sward vigour, and vigour declined over time. Stocking rate reduced total standing crop on both trials at the end of the 2004/05 seasons and the crop of unpalatable species on the steep trial. Total palatable plants were unaffected by stocking rate on both trials. The classic Jones-Sandland model of animal performance as influenced solely by stocking rate was not supported. Sheep performance was influenced by stocking rate and the interaction of stocking rate and seasonal rainfall. There was no difference in average daily gain between treatments over time, and hence cumulative animal production per hectare increased with increasing stocking rate. Animal performance was possibly influenced by many factors beyond the scope of this study, including the effect of predator attacks on surviving animals, and resource availability such as shade and shelter and high-production patches in some paddocks and not others. Scale effects on ecology are being increasingly investigated and a meta-analysis of this type shows that, even in one research farm, slight differences in management and environment can have significant effects on plant and animal responses to grazing.
Influence of drought or elephant on the dynamics of key woodland species in a semiarid African savanna.
(2000) MacGregor, Shaun Donovan.; O'Connor, Timothy Gordon.
Extensive drought - and elephant-related dieback of Colophospermum mopane and Acacia tortitis, respectively, offered an opportunity for increasing understanding of the causes of drought-related patch dieback, the factors influencing elephant utilization of woody plants, and the response of woody plants to both aforementioned determinants of savanna structure and function. The dendrochronological analysis of both species was undertaken to estimate potential rates of replacement, following extensive mortality. Areas of discrete dieback were compared with adjacent paired areas of 'healthy' vegetation, which revealed, on average, 87% and 13% loss of basal area by mortality, respectively. 'Live' and 'dead' plots did not differ in soil type, topography or mean slope, but differed in vegetation structure, soil surface condition, and soil chemistry. Although there was evidence of self-thinning, neither inter - nor intra-specific competition explained dieback. 'Dead', by comparison with 'live' plots, had changed from functioning as sinks of sediment and water to sources, were less likely to retain water because of a poor soil surface condition, and were predisposed to drought effects because of a greater proportion of fines, and Na concentration. Dieback resulted from insufficient soil water for survival during a drought owing to the development of a dysfunctional landscape during 50 years of livestock ranching. Spatial heterogeneity within a landscape was suggested to enhance woodland resilience to severe droughts by ensuring the survival of plants in run-on sinks or 'drought refuge' sites. Stem sections were removed from 40 multi-stemmed C. mopane trees and prepared for examination under a dissecting microscope. It was impossible to age C. mopane, owing to a hollow and/or dark heartwood. Nevertheless, the distribution of stem diameters suggested a single recruitment event. Fire scars attributed to the last recorded fire in 1948 could explain the trees' multi-stemmed growth form and indicate that most trees of VLNR were > 50 years of age. Growth rings were identified in 29 A. tortilis trees of unknown age, but were not correlated with annual rainfall records. Growth rates varied between trees; mean ring width ranged from 1.4 to 3.5 mm (overall mean 2.4 ± 0.1 mm). A technique was proposed for predicting growth rate from annual rainfall, using selected data, and several factors potentially influencing ring width in semiarid environs were identified. Permanent ground-based transects were located within riparian (n = 16) and Acacia (n = 5) woodlands to monitor elephant utilization. Elephant had not changed the population structure of the woodlands by 2000, but had reduced stem density from 215.6 stems ha -1 (1996) to 84.4 stems ha -I (2000). Acacia tortitis trees in the woodlands had branches removed, were debarked, uprooted and broken. Acacia tortitis trees in the riverine had lower levels of utilization, whilst Acacia nilotica trees were mostly debarked. The method of elephant feeding varies within and between woody species, provided it is within the mechanical constraints of a certain size or species. Elephant behaviour is concluded to depend on spatiotemporal variation of forage abundance/quality, abundance of a preferred species, and species response (coppice or mortality). Elephant can cause a change of vegetation state, and increase spatial homogeneity of a plant population. The remnant population of woodland trees should provide the potential for recolonization, in which case the system would reflect the stable limit cycle. However, if browsing inhibits seedling recruitment, the system could reflect either a multiple stable state system or an artificial equilibrium imposed on a stable limit cycle.
Factors affecting savanna tree sapling recruitment.
(2013) Vadigi, Snehalatha.; Ward, David Mercer.
Savannas are globally important ecosystems characterized by the coexistence of trees and grasses. Woody plants, which are slow-growing dominant life forms, influence the physiognomic structure and function of savanna ecosystems. Their density and distribution provides sustenance to a vast and unique savanna biodiversity, by forming a major source of food material to large mammalian herbivores, sheltering them and through their facilitation of diverse plant species. Savanna tree existence is strongly affected by factors that determine their sapling recruitment. We defined „sapling‟ as a young tree, in the first season of its growth, which does not depend on cotyledonary reserves (=seedling stage) and relies on external resources to grow further. Sapling recruitment may strictly be defined as the progression of a young plant from seedling to sapling stage. However, we believe that savanna tree saplings, present within the grass layer in the initial years of their growth, are equally vulnerable to environmental stresses. This study examines the factors affecting tree sapling establishment in a humid savanna (1250 mm mean annual precipitation). Additionally, the effects of fire were tested in a greenhouse experiment. Dominant species from humid savannas (> 1000 mm MAP), Acacia karroo, Acacia sieberiana, Schotia brachypetala and Strychnos spinosa, and mesic savannas (approx. 750 mm MAP), Acacia nigrescens, Acacia tortilis, Colophospermum mopane and Combretum apiculatum, were studied. In this thesis I examined the effects of resource availability (water, nutrients and light), disturbances (fire and herbivory) and competition (grass) on the sapling ecology of these species. Sapling recruitment and growth were assessed in terms of survival and aboveground growth responses, i.e. total biomass, stem growth rates (used as proxy measures for assessing persistence) and leaf biomass proportion (important for producing root reserves necessary to resprout). I studied the effects of fire and a nutrient gradient on survival and growth of four Acacia species in the presence of grass competition, in a controlled greenhouse experiment. Generally, Acacias invest in defenses after herbivory. I also determined their physical and chemical defense investments in this experiment. Sapling survival was not influenced by nutrients but highly varied among the species due to fire, indicating that fires may have a differential effect on species composition at a landscape scale. Intermediate levels of nutrients were found to be beneficial for sapling growth than high and low levels. This may be due to an increase in grass competition at higher levels of nutrients. Fires did not have a positive influence on sapling defence investment. To evaluate the relative importance of resource availability on sapling tree recruitment and its interactions with grass competition, I tested the effects of water (frequent irrigation vs. rainfall), shade (presence vs. absence), nutrients (addition vs. no addition) and grass competition (presence vs. absence) on sapling survival and growth under controlled field conditions in a humid South African savanna. Treatments did not have an effect on sapling survival, indicating that mortality is not defined by resource availability and grass competition in humid savannas. Shade had the greatest negative effect on sapling growth, suppressing the beneficial effects of nutrients and absence of grass competition. Nutrient limitation and grass competition had a relatively small influence on savanna sapling growth. Frequency of water availability had no effect on sapling growth, perhaps owing to high rainfall experienced over the experimental period. Therefore, canopy shade can be considered to be an important driver of tree dynamics in humid savannas with some degree of influence by nutrient availability and grass competition. The effects of clipping (i.e. simulated herbivory of grass and tree saplings) as influenced by nutrient availability and grass competition were examined on sapling survival and growth of all study species in a humid savanna. None of the treatments had an effect on sapling survival. This signifies that herbivory alone cannot significantly decrease plant density in humid savannas. However, tree saplings grew taller with a reduction in diameter and overall biomass, implying that saplings may become more susceptible to fires after herbivory. Nutrient addition and grass competition in general had a positive and negative effect, respectively, on sapling growth. This response was prominent in the stem length growth rates of defoliated saplings of one humid and two mesic species. These results imply that clipping (or herbivory) is the major factor reducing sapling vigour to establish, but is affected by both grass competition and nutrient availability. This study shows that fire has a differential effect on sapling survival of different species, particularly between humid savanna species. Light interception among all other resources limits the recruitment of saplings into adult size classes. Clipping, nutrient availability and grass competition had a relatively small direct effect, but may interact with other factors to alter sapling establishment dynamics. Wet-season droughts in humid savannas are not a hindrance to tree establishment because sapling survival was not dependent on frequency of rainfall. Thus, in humid savannas, fires can have a major impact on tree species density and composition while canopy shade has a very high potential to alter tree distribution.
Browse : quantity and nutritive value of evergreen and deciduous tree species in semi-arid Southern African savannas.
(2012) Penderis, Caryn Anne.; Kirkman, Kevin Peter.
Browse selection, intake, utilisation, palatability, quality and production are tightly linked and need to be considered together in trying to improve our understanding of browsing dynamics and the interactions between browsers and vegetation. Such an understanding is necessary in order to re-evaluate determinations of browser carrying capacities and evaluating actual and potential impacts of browsing animals on vegetation composition and diversity. Browser carrying capacity is determined by both the quantity and the nutritive value of forage. The measurement of browse quantity and nutritive value and the matching of browse supply to browser demand are central to sustainable utilisation and the monitoring of vegetation health. South African savannas are poorly studied with respect to tree canopy growth and browse production making it difficult to quantify the available browse biomass on which browsing capacity estimations are based, and consequently difficult to estimate levels of browsing that are sustainable. This study addressed these issues by investigating browse dynamics, broadly aiming to (1) explore factors affecting browse production, biomass and nutritive value; (2) develop models to assess and monitor these parameters across seasons and properties; (3) use the resultant models in improving our understanding of how to determine browser carrying capacities. More specifically, our study sought to examine the effects of plant physiognomy, forage nutritive value, canopy stratum, defoliation, temperature, rainfall and soil nutrient status on the browse production of evergreen (Carissa bispinosa, Euclea divinorum, Gymnosporia senegalensis), semi-deciduous (Spirostachys africana, Ziziphus mucronata) and deciduous (Acacia nilotica, Dichrostachys cinerea) savanna tree species from June 2003 – June 2005 in three sites along the northern Zululand coastline of KwaZulu-Natal. Available browse biomass, during the dry season, of four key savanna tree species (A. nilotica, E. divinorum, G. senegalensis, and S. africana) was estimated through the development of allometric regression equations. Non-linear regression was used to investigate the relation between the leaf dry mass (LDM) and canopy volume (CVol) of each of the four tree species. Exponential regression (y = a + brlnx) of the natural logarithm of CVol data provided the most accurate and precise description of the tree CVol – LDM relation. A study was undertaken to determine which factors may influence browse production in a southern African savanna. Regression tree models for the browse production identified that the dominant factors influencing browse production were CVol (m3), season, species and height to the lowest leaves of the tree canopy (HL) (m). The length of the growing season had a marked effect on the production potential of savanna tree species, suggesting that improved conditions for growth, i.e. greater rainfall, soil moisture content and improved soil nutrient availability result in a longer period of rapid sustained growth. Species was identified as an important contributing factor to differences in browse production rates, suggesting the need for the development of species or species group models. Mean annual browse production of evergreen trees was greater than that of deciduous and semi-deciduous trees. Mean quarterly (three monthly) browse production was highest, for all trees, during the wet season, with the greatest difference between wet and dry season production being observed in deciduous forms. Evergreen forms showed continuous growth over the whole study, with enhanced growth over the wet season. Deciduous forms, on the other hand, concentrated growth in spurts, when environmental conditions became favourable, with most production occurring during a short growing season. Browse nutritive value was found to be greatest during the wet season, when growth and photosynthesis are at their greatest. Further, browse nutritive value was greatest in deciduous species. Evergreen trees were found to have greater acid detergent fibre (ADF) concentrations than both the deciduous and semi-deciduous trees. By contrast, crude protein (CP) concentrations were greater in semi-deciduous and deciduous species than in evergreen species. The daily CP requirements for maintenance for an adult impala (45 kg) were met by all species over all three study areas and all seasons. Daily CP requirements for growth and lactation, however, were only ever met by deciduous and semi-deciduous species, though this result was not consistent over study areas and seasons. Predictive models for the production of browse on deciduous, semi-deciduous and evergreen trees in northern Zululand were developed using multivariate adaptive regression spline functions. The best predictors of growing season browse production in all three tree guilds (defined here as a group of trees having a characteristic mode of living) were primarily measurable tree dimensions, while the prevailing environmental conditions had little impact. Differences in the production, nutritive value and available browse biomass between the different tree forms and seasons have a profound effect on the determination of browser carrying capacities and need to be incorporated into any game or conservation management plan.
Effect of fire frequency on herbivore distribution and behaviour in the Kruger National Park, South Africa.
(2012) Chamane, Sindiso Charlotte.; Kirkman, Kevin Peter.; Hagenah, Nicole.; Smith, Melinda.
Fire plays an important role in structuring and maintaining savanna grassland ecosystems. Although regular fires are a characteristic feature of savannas, the effects of fire frequency on these systems are less well known, particularly with respect to how frequency of fire influences large herbivore distribution and behaviour. The expectation is that large herbivores should be attracted to frequently burned sites as a consequence of changes in forage quality and quantity, and/or vegetation structure and composition. The former could be driven by alterations in soil nutrients, such as N and P. Alterations in vegetation also could be important in determining risk of predation. For example, an increase in woody vegetation could decrease predator visibility making large herbivores more vulnerable to predation. The objectives of this study were to investigate the effects of long-term alterations in fire frequency on herbivore distribution and behaviour, as well as the mechanisms (soil nutrients, vegetation structure and composition, and forage quality and quantity) potentially driving the distribution of large herbivores. To address these objectives, I conducted large herbivore surveys on a bi-weekly basis from 2009-2010 in a series of plots in the Experimental Burn Plots (EBPs) burnt at different frequencies (annual, triennial and unburnt) over the last five decades at three study sites in the Kruger National Park, South Africa. Surveys also were conducted on new plots that were established adjacent to the long-term plots. These new plots have a fire return interval of 4 years which is similar to the triennially burned plots of the EBPs. They were established in the landscape adjacent to the EBPs to assess whether the responses of herbivores to fire observed in the EBPs reflected was at landscape level. The distribution of all large herbivore species combined and of grazers (e.g. zebra) or browsers (e.g. kudu) only were not affected by fire frequency. In contrast, the abundance of mixed-feeders, such as impala, was significantly higher in the unburnt (control) and annually burned plots than the triennially burned plots. Although season did not have a significant impact on the distribution of browsers and mixed-feeders, overall more grazers were recorded across all burn treatments in the dry season compared to the wet season. Similar patterns of herbivore distribution were observed between the new plots and the triennially burned EBP plots, suggesting that responses observed to the long-term fire frequency treatments reflects herbivore responses at the landscape level. The long-term fire frequency treatments significantly affected soil nutrients (N, organic C, P, and K were significantly lower with annual burning), vegetation structure (abundance of woody plants were greater in unburned plots), and forage quantity (unburned plots had higher biomass) but not quality. More frequent fires improved visibility by reducing tree height and density and herbaceous biomass, thereby potentially reducing predation risk, when compared to less frequent burning. As a result, herbivores selected sites with more frequent fires. The behaviour of the herbivore species investigated was predominantly influenced by seasonal-induced changes to their environment rather than fire frequency. In the wet season irrespective of the burning treatment visibility was low due to high rainfall that increases plant biomass, whereas in the dry season visibility was improved because there is little to no rainfall. This potential alteration in predation risk likely resulted in herbivores being more vigilant in the wet season than the dry season. Overall, results from this study suggest that the combination of fire frequency and season drive herbivore distribution and behaviour by altering mainly the vegetation structure which can influence predation risk.
The roles of competition, disturbance and nutrients on species composition, light interception and biomass production in a South African semi-arid savanna.
(2012) Mopipi, Keletso.; Kirkman, Kevin Peter.; Trollope, Winston Smuts Watts.; Morris, Craig Duncan.
Plants are the major source of food or energy required to sustain life on the planet, but humans are grappling with the deteriorating conditions of natural ecosystems such as compositional change, desertification, invasive plants and soil erosion. In the face of global climate change and growing demands for agricultural productivity, future pressures on grassland ecosystems will intensify, therefore sustainable utilization of all plant resources is of vital importance to enhance food security within the limits of good conservation. The semi-arid grasslands of southern Africa represent major grassland resources for grazing. Herbage production in these areas is determined not only by water and nutrient availability, but also by controlled and uncontrolled fires. Since fire is regarded as a natural factor in savannas, it is essential to develop a deeper understanding of the role of fire in community structure and function for the development of appropriate burning regimes. A study was conducted in the Eastern Cape of South Africa where the rural communities are faced with the challenges of rangeland degradation in the form of encroachment by unacceptable bush, karroid, macchia and less desirable grass species, as well as soil erosion. The main objective of this thesis was to investigate the roles of competition and disturbance regimes (fire and simulated non-selective grazing) on species composition, habitat productivity and the performances of selected species from this semi-arid savanna. Long-term effects of burning frequency on herbaceous species composition, Leaf Area Index (LAI), Photosynthetically Active Radiation (PAR) within the herbaceous canopy, biomass production and soil chemical properties were investigated. These studies were conducted on a fire trial set up in 1980 at the University of Fort Hare research farm in the Eastern Cape, South Africa. The treatments comprise an annual, biennial, triennial, quadrennial, sexennial and no burn control, all replicated twice in a Complete Randomized Design. The data from the trial collected between 1980 and 2008 were used to determine compositional variation for herbaceous species using the Non-metric Multidimensional Scaling and Bray-Curtis Dissimilarity tests. The PAR ceptometer was used to determine LAI and intercepted PAR, while random samples were harvested from 1m² quadrats from each plot. Soil samples were taken at four depths (0-2 cm; 2-4 cm; 4-6 cm and 6-8 cm) from each plot and analyzed for pH, Ca, K, P, total C and total N. The Resin-Bag technique was used to determine nitrogen mineralization. Burning frequency caused significant variation in herbaceous species composition over time. The species were distributed along gradients of increasing burning frequency, and these responses were in three categories: Those that increased with burning frequency such as Themeda triandra; those that decreased with burning frequency such as Melica decumbens, and those that showed little response such as Panicum maximum. The three-year burn resulted in the highest compositional variation, light interception, Leaf Area Index, aboveground biomass production, while the annual, biennial and no burn treatments resulted in the lowest. The fact that infrequent burning resulted in higher species variation, improved habitat productivity due to increased leaf area for light interception shows that appropriate use of fire can maintain a more diverse and productive savanna system. Burning frequency had significant effects on the soil properties, while soil depth did not show any significance. Frequent burning increased soil pH, K, Ca, and Na, but reduced C, N, P and N mineralization. There was a negative correlation between burning frequency and N mineralization, but no correlation existed between N mineralization and total N, total C or the C:N ratio. These results imply that frequent burning can cause nutrient losses and a greater nutrient limitation to plants in the long-term, especially soil C and N loss from combustion of organic material in the soil top layer. The ability of shade-tolerant plants to persist under shade and regular defoliation such as in burnt and grazed systems may be of greater importance for long-term productivity and sustainability of forage crops. It is therefore imperative to explore the mechanisms by which some species were favoured by frequent burning which created low shade conditions, while others were favoured by high shade conditions where burning is infrequent or absent. A pot experiment was conducted to investigate the shade tolerances of seven grass species that were abundant in the long-term fire trial. The test species were Cymbopogon plurinodis, Digitaria eriantha, Eragrostis curvula, Melica decumbens, Panicum maximum, Sporobolus fimbriatus and Themeda triandra. Individual grass tillers of each species were collected from the natural vegetation, propagated in separate seedling trays and transplanted into individual pots, and were grown under five shading treatments: full sun (0 % shading), 55 %; 70 %; 85 % and 93 % shading respectively. Shading significantly reduced the dry matter production of all the species. Biomass production of all the species decreased linearly to varying degrees with an increase in shade intensity. Digitaria eriantha and Eragrostis curvula were most adversely affected by shading, hence are classified as shade intolerant, while Melica decumbens was the least affected by shading, and is hence classified as shade tolerant. Cymbopogon plurinodis, Panicum maximum, Sporobolus fimbriatus and Themeda triandra are classified as moderately shade-tolerant. From the results it was apparent that some species could perform optimally in partial shade than in full sunlight, and these results lead to a conclusion that for satisfactory natural regeneration and seedling growth of this savanna vegetation would require a gap large enough to provide at least 30 % of ambient light. Investigating patterns in competitive effects and responses of species in these communities may not only explain the abundance of each species, but may also provide insight into the nature of forces that affect the structure and function of that community. Since fire, herbivory and soil nutrients are natural drivers of savanna community structure and function, their influence on competitive interactions of selected species were investigated. Two experiments were conducted to investigate the competitive effects and responses of eight selected common species in the area. The test species (phytometers) included one woody shrub, Acacia karroo and seven grass species namely: Cymbopogon plurinodis, Digitaria eriantha, Eragrostis curvula, Melica decumbens, Panicum maximum, Sporobolus fimbriatus and Themeda triandra. In an outdoor plot experiment the responses of the phytometers to competition from neighbours (0; 2 and eight neighbours respectively), fertility (fertilized, unfertilized) and clipping (clipping, no clipping) were investigated. The second comprised a pot experiment where the competitive effects of the species were investigated. Each species was grown under 3 levels of fertility (0 %; 50 % and 100 % Hoagland‘s solution) and clipping (clipping, no clipping) in pots filled with fine river sand and 4 neighbours. Competition intensity, soil fertility and clipping had significant effects on the biomass production of the phytometer species. Acacia karroo and Melica decumbens, exhibited the weakest competitive effects and responses, and incurred the highest mortalities after clipping and with 8 neighbours. Digitaria eriantha and Panicum maximum exhibited the strongest competitive effects and responses, especially in high fertility, and experienced the lowest mortalities. T.triandra exhibited stronger competitive effect after clipping in low fertility, while A. karroo and C. plurinodis exhibited stronger competitive effects in moderate (50 %) fertility. Cymbopogon plurinodis, Eragrostis curvula and Sporobolus fimbriatus ranked between these two extreme groups in terms of competitive effects and responses. Relative Competitive Interaction increased with soil fertility and number of neighbours in the absence of clipping. These results indicate that in general, taller or broad-leaved grass species outgrow the shorter ones, and this gives them a competitive advantage over light and soil resources. One of the range management objectives in the False Thornveld of the Eastern Cape is to promote the abundance of Themeda triandra, which is of high forage value and an indicator of rangeland that is in good condition. The general situation under livestock farming conditions in this area is that if the grass sward is optimally grazed and rested then there is a great potential for Themeda triandra to dominate.The results of the competition experiments indicated that the species exhibits strong competitive interaction, and also exhibited stronger competitive effect after clipping in low fertility. These results imply that it has a low response and a high effect, an attribute that would enhance its performance if it is moderately grazed or the area is burnt. The species is also moderately shade tolerant, and this may explain why it thrives in burnt and moderately grazed areas. These studies have demonstrated the important role that competition and disturbance in the form of fire and herbivory play in the maintenance of this savanna grassland. Through natural selection species are able to occupy different niches in the same area and coexist in a heterogeneous environment and minimize their chances of extinction.
Dry woodland and savanna vegetation dynamics in the Eastern Okavango Delta, Botswana.
(2012) Tedder, Michelle Jennifer.; Kirkman, Kevin Peter.; Bonyongo, Mpaphi Casper.; Morris, Craig Duncan.; Trollope, Winston Smuts Watts.
The Okavango Delta is an extremely dynamic system with variable vegetation comprised of permanent swamps, seasonal swamps, dry islands, floodplains and dry grassland, savanna and woodland. The system is largely driven by the interaction between fire and the annual flood, which filters down from the Okavango River catchments in Angola. While extensive research has been conducted on the flood-driven vegetation little is known about the dry woodland and savanna regions bordering these flood-driven habitats. A taxonomic classification of woody species composition resulted in eleven vegetation types. These data were then reanalyzed in terms of woody species morphology allowing these eleven vegetation types to be grouped into four functional response groups in order to provide a platform for improving the understanding of how dry woodland and savannas interact with the environment. These four groups were the savanna group mixed thornveld and the three woodland groups; mixed broadleaf woodland, shrub mopane woodland and tall mopane woodland. Burning in mixed thornveld and mixed broadleaf woodland was found to decrease woody species density and grass fuel loads and could be used for grazing management to remove unpalatable growth and improve grass species composition, while burning in shrub mopane woodland and mixed mopane woodland merely decreased the woody understory and is not recommended. Utilization dominated by grazing livestock resulted in overutilization of the grass sward leading to bush encroachment in both mixed thornveld and shrub mopane woodland, while utilization by goats alone resulted in underutilization of the grass sward and a dominance of herbaceous annuals. Livestock utilization had no effect on the occurrence of Pecheul-loeschea leubnitziae, a shrubby pioneer previously thought to be an indicator of overgrazing, however extensive P. leubnitziae cover was associated with a sward dominated by shade-tolerant grasses with low forage quality. Shrub mopane woodland and tall mopane woodland appear to be more stable vegetation states than mixed broadleaf woodland and mixed thornveld being less vulnerable to colonization by pioneer species and alteration as a result of utilization or environmental factors. For this reason management and monitoring of mixed thornveld and mixed broadleaf woodland is essential to prevent vegetation degradation and to ensure optimal forage availability for both livestock and wildlife.

Browse

Browsing Grassland and Rangeland Science by Date Accessioned