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Author

Feetham Banyikwa

Bio: Feetham Banyikwa is an academic researcher from University of Dar es Salaam. The author has contributed to research in topics: Regional planning & Environmental change. The author has an hindex of 2, co-authored 2 publications receiving 1586 citations.

Papers
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Journal ArticleDOI
08 Dec 2005-Nature
TL;DR: It is shown, using data from 854 sites across Africa, that maximum woody cover in savannas receiving a mean annual precipitation (MAP) of less than ∼650 mm is constrained by, and increases linearly with, MAP.
Abstract: Savannas are globally important ecosystems of great significance to human economies. In these biomes, which are characterized by the co-dominance of trees and grasses, woody cover is a chief determinant of ecosystem properties1–3. The availability of resources (water, nutrients) and disturbance regimes (fire, herbivory) are thought to be important in regulating woody cover1,2,4,5, but perceptions differ on which of these are the primary drivers of savanna structure. Here we show, using data from 854 sites across Africa, that maximum woody cover in savannas receiving a mean annual precipitation (MAP) of less than ,650mm is constrained by, and increases linearly with, MAP. These arid and semi-arid savannas may be considered ‘stable' systems in which water constrains woody cover and permits grasses to coexist, while fire, herbivory and soil properties interact to reduce woody cover below the MAP-controlled upper bound. Above a MAP of ,650mm, savannas are ‘unstable' systems in which MAP is sufficient for woody canopy closure, and disturbances (fire, herbivory) are required for the coexistence of trees and grass. These results provide insights into the nature of African savannas and suggest that future changes in precipitation6 may considerably affect their distribution and dynamics.

1,740 citations

01 Jan 2003
TL;DR: Henschel et al. as discussed by the authors developed the Environmental Long-Term Observatories Network of Southern Africa (ELTOSA), a network of long-term observatories in Southern Africa.
Abstract: CITATION: Henschel, J., et al. 2003. Developing the Environmental Long-Term Observatories Network of Southern Africa (ELTOSA). South African Journal of Science, 99(3-4):100-108.

10 citations


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Journal ArticleDOI
14 Oct 2011-Science
TL;DR: Tree cover, climate, fire, and soils data sets are used to show that tree cover is globally discontinuous, and only fire differentiates between savanna and forest.
Abstract: Theoretically, fire–tree cover feedbacks can maintain savanna and forest as alternative stable states. However, the global extent of fire-driven discontinuities in tree cover is unknown, especially accounting for seasonality and soils. We use tree cover, climate, fire, and soils data sets to show that tree cover is globally discontinuous. Climate influences tree cover globally but, at intermediate rainfall (1000 to 2500 millimeters) with mild seasonality (less than 7 months), tree cover is bimodal, and only fire differentiates between savanna and forest. These may be alternative states over large areas, including parts of Amazonia and the Congo. Changes in biome distributions, whether at the cost of savanna (due to fragmentation) or forest (due to climate), will be neither smooth nor easily reversible.

1,043 citations

Journal ArticleDOI
14 Oct 2011-Science
TL;DR: Empirical reconstruction of the basins of attraction indicates that the resilience of the states varies in a universal way with precipitation, and this results allow the identification of regions where forest or savanna may most easily tip into an alternative state.
Abstract: It has been suggested that tropical forest and savanna could represent alternative stable states, implying critical transitions at tipping points in response to altered climate or other drivers. So far, evidence for this idea has remained elusive, and integrated climate models assume smooth vegetation responses. We analyzed data on the distribution of tree cover in Africa, Australia, and South America to reveal strong evidence for the existence of three distinct attractors: forest, savanna, and a treeless state. Empirical reconstruction of the basins of attraction indicates that the resilience of the states varies in a universal way with precipitation. These results allow the identification of regions where forest or savanna may most easily tip into an alternative state, and they pave the way to a new generation of coupled climate models.

945 citations

Journal ArticleDOI
TL;DR: It was revealed that encroachment had mixed effects on ecosystem structure and functioning at global scales, and that shrub traits influence the functional outcome of encroachment.
Abstract: Encroachment of woody plants into grasslands has generated considerable interest among ecologists. Syntheses of encroachment effects on ecosystem processes have been limited in extent and confined largely to pastoral land uses or particular geographical regions. We used univariate analyses, meta-analysis and structural equation modelling to test the propositions that (1) shrub encroachment does not necessarily lead to declines in ecosystem functions and (2) shrub traits influence the functional outcome of encroachment. Analyses of 43 ecosystem attributes from 244 case studies worldwide showed that some attributes consistently increased with encroachment (e.g. soil C, N), and others declined (e.g. grass cover, pH), but most exhibited variable responses. Traits of shrubs were associated with significant, though weak, structural and functional outcomes of encroachment. Our review revealed that encroachment had mixed effects on ecosystem structure and functioning at global scales, and that shrub traits influence the functional outcome of encroachment. Thus, a simple designation of encroachment as a process leading to functionally, structurally or contextually degraded ecosystems is not supported by a critical analysis of existing literature. Our results highlight that the commonly established link between shrub encroachment and degradation is not universal.

896 citations

Journal ArticleDOI
TL;DR: To understand the potential negative and positive contributions of soil microbes to land–atmosphere carbon exchange and global warming requires explicit consideration of both direct and indirect impacts of climate change on microorganisms.
Abstract: There is considerable interest in understanding the biological mechanisms that regulate carbon exchanges between the land and atmosphere, and how these exchanges respond to climate change. An understanding of soil microbial ecology is central to our ability to assess terrestrial carbon cycle–climate feedbacks, but the complexity of the soil microbial community and the many ways that it can be affected by climate and other global changes hampers our ability to draw firm conclusions on this topic. In this paper, we argue that to understand the potential negative and positive contributions of soil microbes to land–atmosphere carbon exchange and global warming requires explicit consideration of both direct and indirect impacts of climate change on microorganisms. Moreover, we argue that this requires consideration of complex interactions and feedbacks that occur between microbes, plants and their physical environment in the context of climate change, and the influence of other global changes which have the capacity to amplify climate-driven effects on soil microbes. Overall, we emphasize the urgent need for greater understanding of how soil microbial ecology contributes to land–atmosphere carbon exchange in the context of climate change, and identify some challenges for the future. In particular, we highlight the need for a multifactor experimental approach to understand how soil microbes and their activities respond to climate change and consequences for carbon cycle feedbacks.

884 citations

Journal ArticleDOI
TL;DR: The extent of this climate mismatch has been revealed by physiologically based global vegetation simulations and by large empirical data sets, and the implication is that ecosystem structure and function depend on demographic transitions.
Abstract: Though the distribution of global vegetation can generally be predicted from climate, grasslands are an exception. C4 grassy biomes cover vast areas that are warm enough and wet enough to support closed forests. The extent of this climate mismatch has been revealed by physiologically based global vegetation simulations and by large empirical data sets. Reasons for the existence of grassy biomes have long been debated, polarized into bottom-up (resources) or top-down (fire, herbivory) arguments. Recent studies indicate that both are important, especially in suppressing woody recruits. Grasses are formidable competitors belowground, create highly flammable fuels, and can support large herbivore densities. The net effect on trees is rare and episodic recruitment of adults in tree-fall gaps. The implication is that ecosystem structure and function depend on demographic transitions. Tree cover is increasing and grass/forest boundaries are changing. These changes can have large feedbacks to the earth-atmosphere...

857 citations