|
| ||
|
|
||
Bush Encroachment (bush + encroachment)
Selected AbstractsBush encroachment under three contrasting land-use practices in a mesic South African savannaAFRICAN JOURNAL OF ECOLOGY, Issue 2009B. J. Wigley Abstract This study determined the effects of land-use practice had on the rate and extent of bush encroachment in a mesic savanna in KwaZulu-Natal, South Africa. Changes in woody cover were measured for 1 km2 sites in areas under communal, commercial and conservation land-use systems for the period between 1937 and 2000. Land users from each area were interviewed to gain the histories of each area and to determine how the changes in woody cover had impacted them and whether anything was being done to counteract the spread of trees and shrubs on their land. Bush encroachment occurred across all three of the land-use types in the 67-year period between 1937 and 2000. The results showed that land-use practice had enormous impacts on the process of bush encroachment. The communal site showed a decrease in grass (21%) and tree (5%) cover and an increase in shrub cover (13%). At the commercial site, there was a considerable decrease in grass cover (46%) and moderate increase in shrub cover (10%) and a massive increase in tree cover (36%). The area under conservation showed a substantial decrease in grass cover (47%), a slight decrease in shrub cover (19%) and a massive increase in tree cover (66%). The perceived causes of these changes were fairly similar amongst the different land users. The changes were mostly not perceived to be a problem for the communal land users. The main advantages mentioned were increased woody resources for building and firewood and increased browse availability. The commercial and conservation land users perceived the changes to have significant negative connotations including the loss of grazing land and biodiversity and secondary invasion of encroached areas by alien plant species. Despite these perceptions, very little has been done to combat bush encroachment in the commercial and conservation land use systems. [source] The impact of cattle ranching on large-scale vegetation patterns in a coastal savanna in TanzaniaJOURNAL OF APPLIED ECOLOGY, Issue 3 2003M. W. Tobler Summary 1The success of large-scale cattle ranching in African savanna vegetation has often been limited by problems of bush encroachment and disease (in particular trypanosomiasis spread by tsetse flies). Mkwaja Ranch, occupying an area of 462 km2 on the coast of Tanzania, is a recent example of a large ranching enterprise that failed within the savanna environment. It was closed in 2000 after 48 years of operation. In this paper we describe the main vegetation types of the area (excluding closed forest vegetation) and relate their patterns of distribution to the former use of the ranch for cattle. 2The study area comprised the former ranch and parts of the adjacent Saadani Game Reserve, which had not been grazed by cattle for many years and had never been used for large-scale ranching. Following field surveys, 15 distinct types of grassland and bush vegetation were defined and a vegetation map was created using a Landsat TM satellite image. A multispectral classification using the maximum likelihood algorithm gave good results and enabled all 15 vegetation types to be distinguished on the map. 3Two main spatial trends were detected in the vegetation. One was a large-scale decrease in the cover of bushland from the most intensively used parts of the ranch through more extensively used areas to the game reserve; this trend was attributed to differences in management history as well as to climatic and topographic factors. A second trend was a radial vegetation pattern associated with the enclosures where cattle were herded at night. High amounts of three bushland types [dominated by (i) Acacia zanzibarica, (ii) Dichrostachys cinerea, Acacia nilotica or Acacia mellifera and (iii) Terminalia spinosa] occurred in a zone between 300 and 2500 m from the paddocks, with a peak in bush density at about 900 m (mean value for 18 paddocks). In contrast, bushland dominated by Hyphaene compressa was scarce close to the paddocks and became more abundant with distance. There was also a radial trend in the grassland communities: close to the paddocks there was short grass vegetation containing many ruderals and invasive weedy species, while the tall grassland types with species such as Hyperthelia dissoluta and Cymbopogon caesius occurred further away in the areas less affected by cattle. 4Synthesis and applications. The intensive modern livestock ranching as practised on Mkwaja Ranch proved to be unsustainable both economically and ecologically. In the end, the biggest problem faced by the ranch managers was not controlling disease, as had originally been feared, but preventing the spread of bush on pasture land. The results of our study demonstrate just how severe the problem of bush encroachment was, especially in areas close to paddocks. An important lesson for management is that grazing patterns need to be taken into consideration when determining the sustainable stocking rate for an area. To reduce the risk of bush encroachment in grazing systems with focal points such as paddocks or watering points, stocking rates need to be lower than in systems with a more uniform grazing distribution. [source] Effects of moisture, nitrogen, grass competition and simulated browsing on the survival and growth of Acacia karroo seedlingsAFRICAN JOURNAL OF ECOLOGY, Issue 4 2009Keletso Mopipi Abstract The effects of irrigation, nitrogen fertilization, grass competition and clipping were investigated for one growing season at the research farm of the University of Fort Hare in the Eastern Cape Province of South Africa. The aim of the experiment was to assess the short-term performance of Acacia karroo seedlings under different environmental conditions and the implications of such factors on the long-term recruitment of plant species in savanna rangelands. There were no significant treatment effects on the survival of A. karroo seedlings. Using stem length and basal diameter as growth parameters, it was observed that irrigation enhanced both variables, while nitrogen fertilization did not have any significant effects. Clipping, grass competition and their interaction greatly suppressed the growth of the seedlings. Clipping increased the mean stem length when they were irrigated and fertilized. Control and fertilized plants had the highest stem length in the absence of grass competition, while grass competition combined with clipping resulted in the lowest stem length in both irrigated and nonirrigated plants. It was concluded that in the presence of grass competition, controlled browsing could be a viable solution to the problem of bush encroachment in savanna rangelands. Résumé Les effets de l'irrigation, d'une fertilisation à l'azote, de la compétition avec l'herbe et de la taille ont étéétudiés pendant une saison de croissance dans la ferme expérimentale de l'Université de Fort Hare, dans la Province du Cap oriental, en Afrique du Sud. Le but de l'expérience était d'évaluer les performances à court terme de jeunes plants d'Acacia karroo dans différentes conditions expérimentales, et les implications de ces facteurs sur le recrutement à long terme d'espèces végétales dans des pâturages de savane. Il n'y a pas eu d'effet significatif des traitements sur la survie des plants d'A. karroo. En utilisant la longueur des troncs et le diamètre de la base comme indicateurs de croissance, on a observé que l'irrigation augmentait les deux variables, alors que la fertilisation à l'azote n'avait aucun effet significatif. La taille, la compétition avec l'herbe et leur interaction supprimait fortement la croissance des jeunes plants. La taille augmentait la longueur moyenne des troncs lorsqu'ils étaient irrigués et fertilisés. Les plants témoins et les plants fertilisés avaient les troncs les plus longs en absence de toute compétition avec des herbes, alors que cette dernière, combinée avec la taille, aboutissait à la longueur la plus petite des troncs, chez les plants irrigués ou non. On en a conclu qu'en cas de compétition avec des herbes, un pâturage contrôlé pourrait être une solution viable au problème de l'envahissement des broussailles dans les pâturages de savane. [source] Bush encroachment under three contrasting land-use practices in a mesic South African savannaAFRICAN JOURNAL OF ECOLOGY, Issue 2009B. J. Wigley Abstract This study determined the effects of land-use practice had on the rate and extent of bush encroachment in a mesic savanna in KwaZulu-Natal, South Africa. Changes in woody cover were measured for 1 km2 sites in areas under communal, commercial and conservation land-use systems for the period between 1937 and 2000. Land users from each area were interviewed to gain the histories of each area and to determine how the changes in woody cover had impacted them and whether anything was being done to counteract the spread of trees and shrubs on their land. Bush encroachment occurred across all three of the land-use types in the 67-year period between 1937 and 2000. The results showed that land-use practice had enormous impacts on the process of bush encroachment. The communal site showed a decrease in grass (21%) and tree (5%) cover and an increase in shrub cover (13%). At the commercial site, there was a considerable decrease in grass cover (46%) and moderate increase in shrub cover (10%) and a massive increase in tree cover (36%). The area under conservation showed a substantial decrease in grass cover (47%), a slight decrease in shrub cover (19%) and a massive increase in tree cover (66%). The perceived causes of these changes were fairly similar amongst the different land users. The changes were mostly not perceived to be a problem for the communal land users. The main advantages mentioned were increased woody resources for building and firewood and increased browse availability. The commercial and conservation land users perceived the changes to have significant negative connotations including the loss of grazing land and biodiversity and secondary invasion of encroached areas by alien plant species. Despite these perceptions, very little has been done to combat bush encroachment in the commercial and conservation land use systems. [source] The production, storage and viability of seeds of Acacia karroo and A. nilotica in a grassy savanna in KwaZulu-Natal, South AfricaAFRICAN JOURNAL OF ECOLOGY, Issue 3 2003Michele Walters Abstract African Acacias are often major contributors to the progressive increase in the woody component of savannas, a phenomenon commonly referred to as bush encroachment. They produce large quantities of seed and may have large soil-stored seed banks. In Hluhluwe,Umfolozi Park, the number of adult Acacia nilotica trees per hectare far exceed that of A. karroo adults. The relative dominance is reversed in the juvenile stage with A. karroo outnumbering A. nilotica threefold outside closed woodlands. Acacia karroo trees were smaller than A. nilotica trees on average, but produced more seeds for a given basal diameter size class. Acacia karroo showed less bruchid infestation than A. nilotica at all stages of pod development. Unlike A. nilotica, a proportion of A. karroo seeds was able to germinate after bruchid attack. We detected no difference between the two species in the soil-stored seed bank or in the viability of seeds found in the seed bank. Résumé Les acacias africains sont souvent des contributeurs majeurs de l'augmentation progressive des composants ligneux de la savane, un phénomène connu comme l'envahissement du bush. Ils produisent de grandes quantités de semences et il peut y avoir de grands stocks de semences dans le sol. Dans le Parc de Hluhluwe-Umfolozi, le nombre d'Acacia nilotica adultes par hectare dépasse de loin celui d'A. karroo adultes. Cette dominance relative est inversée au stade juvénile, les A. karrooétant trois fois plus nombreux que les A. nilotica en dehors des forêts fermées. Les Acacia karroo sont en moyenne plus petits que les A. nilotica, mais ils produisent plus de graines pour une classe de diamètre donnée. Les A. karroo présentent une moindre infestation par les bruchidés que les A. nilotica, à tous les stades de développement de la gousse. Contrairement aux graines d'A. nilotica, une certaine proportion de celles d'A. karrooétaient capables de germer après une attaque de bruchidés. Nous n'avons décelé aucune différence entre les deux espèces en ce qui concerne le stock de graines dans le sol ou la viabilité des semences que l'on y trouve. [source] Movements and group structure of giraffe (Giraffa camelopardalis) in Lake Manyara National Park, TanzaniaJOURNAL OF ZOOLOGY, Issue 1 2000Henk P. van der Jeugd Abstract Movements and group structure of giraffe Giraffa camelopardalis were studied in Lake Manyara National Park, northern Tanzania. The giraffe population in Manyara had increased from 60 to 85 individuals between the early 1980s and 1991. This increase may have been the result of an increase in browse availability as a result of a dramatic decline in elephant numbers, and bush encroachment following a series of anthrax epidemics that killed impala. Giraffe densities in Manyara are high compared to other areas within the Masai ecosystem, and Manyara probably serves as a dry season refuge. Females were found in small, yet unstable groups, while males associated randomly with each other. Neither males nor females were confined to single localities, although home ranges were small compared with studies in areas with low giraffe densities. In one area within the park a more stable group was found, and resident males who were probably defending a temporary harem, engaged in necking contests with immigrant males. A comparison with other studies showed that giraffe density, home-range size, mobility and group stability differ across different habitats. The tendency that more stable groups are found in high density areas might be taken as evidence for the occurrence of resource defence polygyny in such areas. [source] Good or bad rangeland?LAND DEGRADATION AND DEVELOPMENT, Issue 3 2004Hybrid knowledge, local understandings of vegetation dynamics in the Kalahari, science Abstract Using data from field studies in the Kalahari rangelands of Southern Africa, the relationships between ,scientific' and ,land user' interpretations of land degradation and change in nonequilibrium savanna ecosystems are explored. Scientific and land-user views are often regarded as distinct, and even opposed, knowledges. We contest that a more constructive view can be taken through the concept of hybrid knowledge, whereby value is attached to both approaches and through which a more useful and meaningful assessment of environmental change, and its implications for development and natural resource use, can be made. We find that in both the southwestern and northwestern Kalahari, pastoralists have a complex understanding of the patchiness of ecosystem variability, and that they utilise elements of this patchiness of change, notably dimensions of bush encroachment and grass species change that have commonly been regarded as degradation in scientific understandings, within livestock management strategies, especially at times of environmental stress. We urge caution in the application of the term degradation, and a more widespread recognition of the multifaceted dimensions, including benefits, of change within the scientifically recognized variability of nonequilibrium rangelands. Copyright © 2004 John Wiley & Sons, Ltd. [source] Rangeland degradation is poised to cause Africa's first recorded avian extinctionANIMAL CONSERVATION, Issue 3 2009C. N. Spottiswoode Abstract Rangeland degradation by livestock threatens several restricted-range species, but is largely overlooked by conservation biologists. The Sidamo lark Heteromirafra sidamoensis, confined to the Liben Plain grassland in southern Ethiopia, is critically endangered by bush encroachment, permanent settlement and agricultural conversion. Its global range was previously estimated at 760 km2, but in 2007,2008 available habitat covered<35 km2. Density estimates from multi-model inference analysis of distance transect data provided a global population estimate of 90,256 adults (possibly with a serious sex-ratio bias towards males). Logistic regression models of habitat selection showed that males preferentially occurred in areas of grassland with greater cover of medium-length grass (5,15 cm), less cover of bare ground and fewer bushes. Habitat transects extending outward from its core range revealed massive and rapid bush encroachment, corroborating information from semi-structured interviews. The survival of both local Borana pastoralism and this species , mainland Africa's likeliest first avian extinction , depends on restoring seasonal patterns of grazing, resisting agricultural conversion of grasslands, reversing fire suppression policies and clearing bush. [source] Managing the matrix for large carnivores: a novel approach and perspective from cheetah (Acinonyx jubatus) habitat suitability modellingANIMAL CONSERVATION, Issue 1 2006J. R. Muntifering Abstract Effective management within the human-dominated matrix, outside of formally protected areas, is of paramount importance to wide-ranging carnviores. For instance, the largest extant population of cheetahs Acinonyx jubatus currently persists on privately owned Namibian ranchlands, and provides an excellent case study to examine and design matrix conservation approaches. Although human-caused mortality is likely the principal threat to this population, ancedotal evidence suggests that ,bush encroachment', the widespread conversion of mixed woodland and savannah habitats to dense, Acacia -dominated thickets, is another probable threat. A better understanding of cheetah habitat use, outside of protected areas, could be used to directly influence habitat management strategies and design local restoration and conflict mitigation efforts. To identify specific habitat characteristics associated with cheetah use, we used radio-telemetry locations to identify areas used intensively by cheetahs on commercial Namibian farms. We then compared the habitat characteristics of these ,high-use' areas with adjacent ,low-use' areas. A binary logistic regression model correctly categorized 92% of plot locations as high or low use, and suggested that cheetahs may be utilizing ,rewarding patches' with better sighting visibility and greater grass cover. We discuss the possible reasons for kudu Tragelaphus strepsiceros, Namibian cheetahs' preferred prey, exhibiting significantly lower abundance in high-use areas. Using habitat characteristics to identify areas intensively utilized by cheetahs has important implications for guiding future habitat restoration and developing effective predator conflict mitigation efforts. [source] | ||||||||||