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Effects of Herbivory, Fire and N2-fixation on Nutrient Limitation in a Humid African Savanna

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Abstract

The quantities and spatial distribution of nutrients in savanna ecosystems are affected by many factors, of which fire, herbivory and symbiotic N2-fixation are particularly important. We measured soil nitrogen (N) pools and the relative abundance of N and phosphorus (P) in herbaceous vegetation in five vegetation types in a humid savanna in Tanzania. We also performed a factorial fertilization experiment to investigate which nutrients most limit herbaceous production. N pools in the top 10 cm of soil were low at sites where fires were frequent, and higher in areas with woody legume encroachment, or high herbivore excretion. Biomass production was co-limited by N and P at sites that were frequently burnt or heavily grazed by native herbivores. In contrast, aboveground production was limited by N in areas receiving large amounts of excreta from livestock. N2-fixation by woody legumes did not lead to P-limitation, but did increase the availability of N relative to P. We conclude that the effects of fire, herbivory and N2-fixation upon soil N pools and N:P-stoichiometry in savanna ecosystems are, to a large extent, predictable.

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Acknowledgements

This study was financed by the Swiss National Science Foundation grant No. 2-77502-04. We thank Prof. S.L.S. Maganga, Markus Schneider-Mmary and the authorities of Saadani National Park for their logistical support in Tanzania, and Benjamin Donald, John Williams and Hamis Williams for their assistance in the field. We also acknowledge comments provided by Michael Scherer-Lorenzen, D.A. Frank and two anonymous reviewers that helped to improve this manuscript.

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  1. Patrick G. Cech

    Present address: Swiss Tropical Institute, Socinstrasse 57, P.O. Box 4002, Basel, Switzerland

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  1. Institute of Integrative Biology, ETH Zurich, Universitätsstrasse 16, 8092, Zurich, Switzerland

    Patrick G. Cech, Thomas Kuster, Peter J. Edwards & Harry Olde Venterink

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  1. Patrick G. Cech
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Correspondence to Patrick G. Cech.

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P.C., H.O.V. and P.E. designed the study and wrote the paper. P.C. and T.K. performed the research and analyzed the data.

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Cech, P.G., Kuster, T., Edwards, P.J. et al. Effects of Herbivory, Fire and N2-fixation on Nutrient Limitation in a Humid African Savanna. Ecosystems 11, 991–1004 (2008). https://doi.org/10.1007/s10021-008-9175-7

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