Acacia Woodland Research Articles

A preliminary assessment of some immediate and long-term effects of aerial spraying of endosulfan on Glossina pallidipes (Austen) in the Lambwe Valley, Kenya

In 1981 an attempt was made to eradicate a 300 km2 fly-belt of Glossina pallidipes (Austen) in the Lambwe Valley of western Kenya by means, principally, of sequential aerial application of endosulfan aerosol spray. The progress of spraying operations was monitored entomologically by surveying for fly with biconical traps sited in main habitats of thicket, Acacia woodland and coniferous plantation, and by age-grading females caught between spray cycles. Although nine spray applications of relatively heavy dosages of insecticide were carried out, the campaign ultimately failed to accomplish its objective. Females which had clearly survived and bred in the intervals between spray cycles were found throughout the area. By the end of operations, the tsetse population appeared to have been reduced by 99.9% in thicket and woodland, and by 99% in coniferous plantation. Nevertheless, on the basis of a crude estimate of total fly numbers in the Lambwe Valley, several thousand flies possibly remained after spraying. Monthly post-spray monitoring showed that the population in thicket fully recovered in about 12 months, but to only 20–30% of its original level in woodland and plantation two years after spraying. The population in thicket maintained an approximate equilibrium density after recovery, indicating that density-dependent processes had re-established a regulatory effect. There was some evidence that this was brought about in part by fly movement. Calculations of the population growth rate gave a value for r, the instantaneous rate of increase, of 0.015 per day; equivalent to a finite rate of increase of 1.610 per month, and a population doubling time of 45 days. Some possible ecological reasons for failure to achieve eradication are discussed.

Joint use of habitat by red kangaroos and shorthorn cattle in arid central Australia

Abstract The distribution of cattle and red kangaroos among the major communities of a 170 km2 paddock in central Australia was determined from 108 and 82 air surveys respectively over a four and a half year period. Fifty‐nine surveys of each species were used in this report. Changes in use of the communities by the two species were analysed in relation to forage conditions using linear regression techniques. The two species showed trends in time of use of the open and wooded communities. Kangaroos used the mulga‐perennial community (groved Acacia woodland with a shrub and perennial grass understorey) during good forage conditions and moved to the drought refuge open communities when forage conditions deteriorated. Cattle, on the other hand, used the open communities during good forage conditions and tended to move to the mulga communities and the hills when drought began. Mulga‐annual (ungroved Acacia woodland with short grass and forb understorey) was the only major community which showed no clear linear relationship between kangaroo use and forage conditions. This might be a buffer area from which kangaroos come and go as other areas become more attractive as feeding areas. Cattle, however, show some preference for mulga annual during medium forage conditions. There appears to be little spatial interaction by the two species except during drought when kangaroos concentrate on the open communities and some cattle continue to feed in these communities. Community selection seems to be determined mainly by forage conditions, as there is no evidence that one species attracts or repels the other in spatial terms. In the conditions observed, the two species successfully coexisted with some control of numbers of cattle by man.

Parallel dunefield ecosystems: southern Kalahari and central Australia

The central Australian and southern Kalahari dunefields resemble each other closely in climate and geomorphology. In addition, and presumably in consequence, there are parallels in soil patterns, vegetation structure and plant life-forms, and the herbivorous fauna. The main differences appear to be the presence of acacia woodland in most interdune valleys in central Australia but not in the southern Kalahari, and the relatively greater importance of fire in Australia and of large grazing animals in the Kalahari. Overall, the resemblances are closer than between sand deserts in general, reflecting similarities in latitude, geological and climatic history, and present atmospheric circulation patterns. As yet there is insufficient information on catenary soil and vegetation patterns on the southern Kalahari sandridges to assess whether their functional relationships parallel those on the central Australian ridges; such catenary patterns are predicted, but remain to be tested.

Occurrence of birds in acacia woodland in Northern Botswana related to endosulfan sprayed for tsetse fly control

The occurrence of birds was monitored in Acacia woodland during tsetse fly Glossina morsitans control operations in northern Botswana. These involved sequential applications of endosulfan applied as an ultra-low volume aerosol at rates of 6–12 g ha −1. During the spraying season bird species diversity increased along two sprayed and two unsprayed transects. No species suffered catastropic decline. Changes in the occurrence of insectivorous species were similar along the sprayed and unsprayed transects.

Habitat preferences of ungulates in closed savanna of central Africa

AbstractHabitat preferences of fifteen species of ungulate were studied between July and September 1975 in dry savanna woodland of Mwabvi Game Reserve, Southern Malawi, Central Africa.Thirteen vegetation types were recognized using vegetation transects and plotless sampling techniques (but three of these are omitted from further analysis here either because of the difficulty of sampling in a representative manner or because of their infrequency). A combination of six methods was used to study habitat preferences since each had particular advantages or disadvantages, although quadrat sampling of fresh pellets/spoor counts was the most satisfactory and so used predominantly.The most common and widely distributed species was the Greater kudu, although abundance estimates in different habitats varied according to the method used. Pellet/spoor counts showed heavy use of open grassland by kudu which was not detected by daytime drives. Temporal patterns of activity indicated that the species was moving into more closed woodland during the day and only coming out into open grassland at night. Relative abundance estimates of a species may also be affected by changing group size. The mean group size of kudu increased in more open vegetation, although group size in warthog did not show this relationship. Some species, e.g. impala, reedbuck, and klipspringer showed narrow habitat preferences, occurring in only one or a few vegetation types, whilst others, e.g. kudu, sable, duiker, suni, and grysbok showed much broader preferences.Mixed Colophospermum mopane /Acacia woodland had the highest species diversity but rather low abundance. Open grassland and Acacia/Albizia woodland had high species diversity together with the greatest abundance of ungulates. Open Julbernardia/Diplorynchus, Brachystegia/Julber‐nardia woodland, and particularly Pterocarpus/Diplorynchus/Combretum hill woodland had the lowest species diversity and abundance of ungulates. Ready access to cover and availability of suitable food plants probably account for the preferences of certain vegetation types over others, whilst the different behavioural ecology and food preferences of each species account for individual species differences. Access to water probably also determines habitat preferences in particular species, and studies during the wet season may show different distributions.

Desertification of rangelands in arid Australia

Desertification means a long term decline in biological productivity of drylands. The case of arid Australia gives an example of the relationship between society and natural environment. The proofs of desertification are numerous (vegetational and physical deteriorations) , especially in the low acacia Woodlands and in the tussock and hummock grasslands, under grazing pressure. Different measures to combat desertification are possible : limitation of stocking levels to match the safe yield of the pastures ; efforts to improve productivity ; limitation of rabbit numbers...

Browse production and utilization in Tarangire National Park

SummaryA survey of the vegetation was undertaken in order to ascertain the browse production and its utilization by the existing community of animals in the park. The most prevalent types of woody vegetation are Acacia woodlands in the drainage lines and Commiphora‐Combretum deciduous woodlands on the uplands. As these formations are considered to provide the bulk of the available browse, the animal impact on the woody plants (mainly shrubs and young trees) in relation to replacement growth and regeneration, is the principle theme of the present paper.The method used for collecting field data is explained. The intention was to collect meaningful information on the composition and dynamic status of the vegetation in relation to the course of plant succession and possible causes of disturbance.For the present purpose, the data are treated so as to elucidate the effect of browsing on growth and growth on browsing. The main factors considered include, the distribution, status and structure of the vegetation; possible disturbances that may have caused changes from the state of naturalness; the distribution, frequency and density of the commoner species of shrubs and trees; the intensity and effect of browsing on woody plants, and the influence that utilization may have on the course of plant succession or decline.Conclusions are discussed in the light of conservation. On the one hand it is accepted that browsing animals have to be catered for. On the other, that the productivity and diversity of the vegetation should be maintained.A balanced situation is one in which utilization is replaced by growth. In these circumstances, both the primary and secondary productivity of the ecosystem is maintained. Both over‐utilization and under‐utilization would indicate an imbalance as a result of which productivity will be lowered.The survey indicates that only about half the available browse is currently utilized, and of this amount, most is replaceable by growth. On the average, not more than 1 % of any common species is so damaged that recovery is unlikely. Most of the species that are severely damaged are deciduous; those that are least damaged, but at the same time sustain the highest overall impact, are evergreen. Furthermore there is no conclusive evidence that the course of succession is impeded by utilization.The results of the survey do not, therefore, indicate that there is over‐utilization of the available browse. Other conditions being equal, the browse potential in the park should be sufficient to support the existing community of animals. However, the environment is not stable. The rainfall is low and variable. The vegetation is degraded and because grassy types of vegetation are extensive, the fire hazard is high. Undoubtedly there has been over‐burning for years and a programme of fire management is overdue.In these circumstances, the following recommendations are made. (1) Further field data should be obtained by using the method explained in this paper. (2) A programme of fire management should be initiated and carried out. (3) Utilization, replacement growth and the progress of plant succession should be monitored in order to ensure that the productivity of the area is being maintained or increased. In this way the goals of management in the park will be assured and it is expected that the browse potential in the park will be able to support a healthy and varied community of animals.

Analysis of a Collection of Barn OwlTyto AlbaPellets From Warmbaths, Transvaal

Barn owl Tyto alba pellets were collected regularly at a roost in a maize loft on the farm Sandfontein, 8 km east of Warmbaths, Transvaal. The farm embraces a mosaic of Acacia and Combretum woodland. The roosting site was not used for nesting during the time that pellets were collected, though it has been used for breeding in the past (P. Rissik: pers. comm.). The loft is situated near the homestead bordering open cattle paddocks with some big trees, mostly Sclerocarya birrea and Acacia tortilis.

Bush-Control Studies in the Drier Areas of Kenya. IV. Effects of Controlled Burning on Secondary Thicket in Upland Acacia Woodland

Bush-Control Studies in the Drier Areas of Kenya. IV. Effects of Controlled Burning on Secondary Thicket in Upland Acacia Woodland