The Effects of Fire Exclusion on Savanna Vegetation at Kpong, Ghana

Swaine, Michael; Hawthorne, W.D.; Orgle, Tetey Kwesi

doi:10.2307/2388670

Cited by 116 publications

(103 citation statements)

References 7 publications

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“…The majority of the woody savannas of Africa would, in the absence of disturbance, become forest: Sankaran et al (Sankaran et al 2005) show that if mean annual precipitation (MAP) is greater than 650 mm, then only disturbance (fire, herbivory, timber extraction) prevents canopy closure. This has been confirmed by the observation of rapid woody encroachment in long-term fire exclusion experiments in Ghana (Swaine et al 1992), Burkina Faso (Menaut 1977), and Ivory Coast (Vauttoux 1976).…”

Section: Introductionmentioning

confidence: 60%

Measuring Woody Encroachment along a Forest–Savanna Boundary in Central Africa

et al. 2009

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Changes in net area of tropical forest are the sum of several processes: deforestation, regeneration of previously deforested areas, and the changing spatial location of the forest-savanna boundary. The authors conducted a long-term ), whereas ,0.4% of the image showed a significant decrease in either period. The largest changes were in the lower canopy cover classes: the area with ,0.2 m 2 m 22 CAI decreased by 43% in 20 years. One cause may be a recent reduction in fire frequency, as documented by Along Track Scanning Radiometer-2/Advanced ATSR (ATSR-2/AATSR) data on fire frequency over the study area from 1996 to 2006. The authors suggest this is due to a reduction in human pressure caused by urbanization, as rainfall did not alter significantly over the study period. An alternative hypothesis is that increasing atmospheric CO 2 concentrations are altering the competitive balance between grasses and trees. These data add to a growing weight of evidence that forest encroachment into savanna is an important process, occurring in forestsavanna boundary regions across tropical Africa.

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Section: Introductionmentioning

confidence: 60%

Measuring Woody Encroachment along a Forest–Savanna Boundary in Central Africa

et al. 2009

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“…Studies in mesic tropical savannas elsewhere have also shown a tendency for increased cover of woody vegetation when fire is excluded from the system (Bond et al 2005, Hoffmann et al 2009). For example, after 32 y without fire, savanna in Ghana had developed into a forest thicket (Swaine et al 1992). In grassy woodland in Zambia, after 23 y sapling densities in the annual early and late fire treatments were 63% and 96% lower respectively than from an area in which fire was excluded (Trapnell 1959).…”

Section: Maintenance Of Savanna By Firementioning

confidence: 99%

Experimental evidence that fire causes a tree recruitment bottleneck in an Australian tropical savanna

2010

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Abstract:A fire-mediated recruitment bottleneck provides a possible explanation for the coexistence of trees and grasses in mesic savannas. The key element of this hypothesis is that saplings are particularly vulnerable to fire because they are small enough to be top-killed by grass fires, but unlike juveniles, they take several years to recover their original size. This limits the number of recruits into the adult size classes. Thus savanna vegetation may be maintained by a feedback whereby fire restricts the density of adult trees and allows a grass layer to develop, which provides fuel for subsequent fires. Here, we use results from a landscape-scale fire experiment in tropical Australia, to explore the possible existence of a recruitment bottleneck. This experiment compared tree recruitment and survival over 4 y under regimes of no fire, annual early and annual late dry-season fire. Stem mortality decreased with increasing stem height in the fire treatments but not in the unburnt treatment. Tree recruitment was 76-84% lower in the fire treatments than the unburnt treatment. Such fire-induced stem loss of saplings and reduced recruitment to the canopy layer in this eucalypt savanna are consistent with the predictions of the fire-mediated recruitment bottleneck hypothesis.

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“…Most studies have concentrated on species distribution within the forest (Eggeling 1947;Sheil et al 2000;Mwami and McNeilage 2003;Eilu et al 2004) or the woodland-savannah (Swaine et al 1992;Schwilk et al 1997;Schwartz and Caro 2003;Li et al 2004). Previous data of Budongo forest (Eggeling 1947) stimulated the emergence of the important Intermediate Disturbance Hypothesis (Connell 1978), which states that in a landscape, species diversity is highest in areas with an intermediate level of disturbance.…”

Section: Introductionmentioning

confidence: 99%

Composition of woody species in a dynamic forest-woodland-savannah mosaic in Uganda: implications for conservation and management

Nangendo¹,

Steege²,

Bongers³

2006

Forest Diversity and Management

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Abstract. Forest-woodland-savannah mosaics are a common feature in the East African landscape. For the conservation of the woody species that occur in such landscapes, the species patterns and the factors that maintain it need to be understood. We studied the woody species distribution in a forest-woodland-savannah mosaic in Budongo Forest Reserve, Uganda. The existing vegetation gradients were analyzed using data from a total of 591 plots of 400 or 500 m 2 each. Remotely sensed data was used to explore current vegetation cover and the gradients there in for the whole area. A clear species gradient exists in the study area ranging from forest, where there is least disturbance, to wooded grassland, where frequent fire disturbance occurs. Most species are not limited to a specific part of the gradient although many show a maximum abundance at some point along the gradient. Fire and accessibility to the protected area were closely related to variation in species composition along the ordination axis with species like Cynometra alexandri and Uvariopsis congensis occurring at one end of the gradient and Combretum guenzi and Lonchocarpus laxiflorus at the other. The vegetation cover classes identified in the area differed in diversity, density and, especially, basal area. All vegetation cover classes, except open woodland, had indicator species. Diospyros abyssinica, Uvariopsis congensis, Holoptelea grandis and all Celtis species were the indicator species for the forest class, Terminalia velutina and Albizia grandbracteata for closed woodland, Grewia mollis and Combretum mole for very open woodland and Lonchocarpus laxiflorus, Grewia bicolor and Combretum guenzi for the wooded grassland class. Eleven of the species occurred in all cover classes and most of the species that occurred in more than one vegetation cover class showed peak abundance in a specific cover class. Species composition in the study area changes gradually from forest to savannah. Along the gradient, the cover classes are distinguishable in terms of species composition and vegetation structure. These classes are, however, interrelated in species composition. For conservation of the full range of the species within this East African landscape, the mosaic has to be managed as an integrated whole. Burning should be varied over the area with the forest not being burnt at all and the wooded grassland burnt regularly. The different vegetation types that occur between these two extremes should be maintained using a varied fire regime.

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The Effects of Fire Exclusion on Savanna Vegetation at Kpong, Ghana

Cited by 116 publications

References 7 publications

Measuring Woody Encroachment along a Forest–Savanna Boundary in Central Africa

Measuring Woody Encroachment along a Forest–Savanna Boundary in Central Africa

Experimental evidence that fire causes a tree recruitment bottleneck in an Australian tropical savanna

Composition of woody species in a dynamic forest-woodland-savannah mosaic in Uganda: implications for conservation and management

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