Hostname: page-component-586b7cd67f-2brh9 Total loading time: 0 Render date: 2024-11-24T15:56:38.681Z Has data issue: false hasContentIssue false
  • English
  • Français

Microhabitat variation in an African savanna: effects of woody cover and herbivores in Kenya

Published online by Cambridge University Press:  10 July 2009

Nicholas J. Georgiadis
Nicholas J. Georgiadis
Affiliation:
Biological Research Laboratories, 130 College Place, Syracuse, NY 13244USA
Get access Rights & Permissions [Opens in a new window]

Abstract

Effects of extreme livestock pressure on the abundance and distribution of a drought-deciduous shrub Sericocomopsis pallida, and effects of the shrub canopy on microclimate, soil fertility and grass production, were studied in savanna grasslands of southern Kenya. Canopy volume declined with increasing herbivore pressure, but shrub density was not systematically affected, suggesting strong resilience against destruction by herbivores. However, shrubs became more aggregated with increasing herbivory, suggesting that clumps of individuals are more resilient to destruction than are isolated individuals. Grass production was three times greater under the canopy of S. pallida than in the open. Comparisons of physical-chemical properties among soils derived from four microsites revealed far higher nutrient levels in sub-canopy soil than in soil derived from open ground between canopies, and radically different properties compared to soil heavily enriched with livestock dung and urine. Higher nutrient levels beneath the canopy most likely resulted from Utter decomposition.

A pot experiment, designed to simulate shading and soil conditions in the field, showed that grass growth promotion was largely due to a substantial increase in soil fertility beneath the canopy of S. pallida, comparable to grass productivity in soil enriched with livestock excreta. However, this increase in sub-canopy grass production did not significantly increase regional grass layer production.

Keywords

Africagrass productionherbivoryKenyasavannashadesoiltrees
Type
Research Article
Information
Journal of Tropical Ecology , Volume 5 , Issue 1 , February 1989 , pp. 93 - 108
Copyright
Copyright © Cambridge University Press 1989

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

LITERATURE CITED

Agnew, A. D. Q. 1974. Upland Kenya wild flowers. Oxford University Press, London.Google Scholar
Bell, R. H. V. 1982. The effect of soil nutrient availability on community structure in African ecosystems. Pp. 193–216 in Huntley, B. J. & Walker, B. H. (eds). Ecology of tropical savannas. Springer-Verlag, Berlin.CrossRefGoogle Scholar
Booysen, P. de V. & Tainton, N. M. (eds). 1984. Ecological effects of fire in South African ecosystems. Springer-Verlag, Berlin.CrossRefGoogle Scholar
Braun, H. M. H. 1973. Primary production in the Serengeti: purpose, methods and some results of research. Annates Universite de Abidjan, Serie E (Ecologie) 6:171–188.Google Scholar
Bremen, H. & de WIT, C. T. 1983. Rangeland productivity and exploitation in the Sahel. Science 221:1341–1347.CrossRefGoogle Scholar
Charley, J. L. 1972. The role of shrubs in nutrient cycling. Pp. 182–203 in McKell, M., Blaisdel, J. P. & Goodin, J. R. (eds). Wildland shrubs - their biology and utilization. USDA Forest Service Gen. Tech. Report INT-1.Google Scholar
Charley, J. L. & West, N. E. 1975. Micro patterns of nitrogen mineralization activity in soils of some shrub-dominated semi-desert ecosystems of Utah. Soil Biology & Biochemistry 9:357–365.CrossRefGoogle Scholar
Cole, M. M. 1982. The influence of soils, geomorphology and geology on the distribution of plant communities in savanna ecosystems. Pp. 145–174 in Huntley, B. J. & Walker, B. H. (eds). Ecology of tropical savannas. Springer-Verlag,, Berlin, Heidelberg, New York.CrossRefGoogle Scholar
Cumming, D. H. M. 1982. The influence of large herbivores on savanna structure in Africa. Pp. 217–245 in Huntley, B. J. & Walker, B. H. (eds). Ecology of tropical savannas. Springer-Verlag, Berlin, Heidelberg, New York.CrossRefGoogle Scholar
Dye, P. J. & Spear, P. T. 1982. The effect of bush clearing and rainfall variability on grass yield and composition in south-west Zimbabwe. Zimbabwe Journal of Agricultural Research 20:103–117.Google Scholar
Fireman, M. & Haywood, H. E. 1952. Indicator significance of some shrubs in the Escalante Desert, Utah. Botanical Gazette 114:143–155.CrossRefGoogle Scholar
Frost, P., Menaut, J -C., Medina, E., Solbrig, O. T., Swift, M. & WALKER, B. 1985. Responses of savannas to stress and disturbance. International Union of Biological Sciences News Magazine, Special Issue.Google Scholar
Georgiadis, N. J. 1987. Responses of savanna grasslands to extreme use by pastoralist livestock. Ph.D. Dissertation, Syracuse University, New York.Google Scholar
Grieg-Smith, , P. 1983. Quantitative plant ecology. University of California Press, Berkeley and Los Angeles.Google Scholar
Hatton, J. C. & Smart, N. O. E. 1984. The effect of long-term exclusion of large herbivores on soil nutrient status in Murchison Falls National Park, Uganda. African Journal of Ecology 22:23–30.CrossRefGoogle Scholar
Hirose, T. & Tateno, M. 1984. Soil nitrogen patterns induced by colonization of Polygonum cuspi-datum on Mt Fuji. Oecologia 61:218–223.CrossRefGoogle ScholarPubMed
Huntley, B. J. & Walker, B. H. (eds) 1982. Ecology of tropical savannas. Springer-Verlag, Berlin.CrossRefGoogle Scholar
Le Houerou, H. N. 1985. Rain use efficiency: a unifying concept in arid-land ecology. J. Arid. Env. 7:213–247.CrossRefGoogle Scholar
Knoop, W. T. & Walker, B. H. 1985. Interactions of woody and herbacious vegetation in a southern African savanna. Journal of Ecology 73:235–253.CrossRefGoogle Scholar
Mack, R. N. 1977. Mineral return via the litter of Artemisia tridentata. American Midland Naturalist 97:189–197.CrossRefGoogle Scholar
Mcnaughton, S. J. 1976. Serengeti migratory wildebeest: facilitation of energy flow by grazing. Science 191:92–94.CrossRefGoogle ScholarPubMed
Mcnaughton, S. J. 1979. Grassland-herbivore dynamics. Pp. 46–81 in Sinclair, A. R. E. & Norton-Griffiths, M. (eds). Serengeti: dynamics of an ecosystem. University of Chicago Press, Chicago, Illinois, USA.Google Scholar
McNaughton, S. J. 1983. Serengeti grassland ecology: the role of composite environmental factors and contingency in community organization. Ecological Monographs 53:291–320.CrossRefGoogle Scholar
Mcnaughton, S. J. 1985. Ecology of a grazing ecosystem: the Serengeti. Ecological Monographs 55:259–294.CrossRefGoogle Scholar
McNaughton, S. J., Coughenour, M. B. & Wallace, L. L. 1982. Interactive processes in grassland ecosystems. Pp. 167–94 in Estes, J. R., Tyrl, R. J. & Brunken, J. N. (eds). Grasses and grasslands. University of Oklahoma Press, Norman, Oklahoma, USA.Google Scholar
Montgomery, R. F. & Askew, G. P. 1983. Soils of tropical savannas. Pp. 63–78 in Bourlière, F. (ed.). Tropical savannas. Elevier, Amsterdam.Google Scholar
Norton-Griffiths, M. 1979. The influence of grazing, browsing and fire on the vegetation dynamics of the Serengeti. Pp. 310–352 in Sinclair, A. R. E. & Norton-Griffiths, M. (eds). Serengeti: dynamics of an ecosystem. University of Chicago Press, Chicago, Illinois, USA.Google Scholar
Olsvig-Whittaker, L. & Morris, J. W. 1982. Comparison of certain Nylsvley soils using a bioassay technique. South African Journal of Botany 1:91–96.CrossRefGoogle Scholar
Pellew, R. A. P. 1983. The influence of giraffe and fire upon the Acacia woodlands of the Serengeti. African Journal of Ecology 21:41–74.CrossRefGoogle Scholar
Radwanski, S. A. 1969. Improvement of red acid sands by the neem tree (Azadirachta indica) in Sokoto, north-western state of Nigeria. Journal of Applied Ecology 6:507–511.CrossRefGoogle Scholar
Radwanski, S. A. & Wickens, G. E. 1967. The ecology of Acacia albida on mantle soils in Zalinger, Jebel Marra, Sudan. Journal of Applied Ecology 4:569–579.CrossRefGoogle Scholar
Rickard, W. H. 1965. Sodium and potassium accumulation by greasewood and hopsage leaves. Botanical Gazette 126:116–119.CrossRefGoogle Scholar
Rickard, W. H. & Keogh, R. F. 1968. Soil-plant relationships of two desert steppe shrubs. Plant and Soil 29:205–213.CrossRefGoogle Scholar
Roberts, R. C. 1950. Chemical effects of salt-tolerant shrubs on soils. Fourth International Congress on Soil Science 1:404–406.Google Scholar
Tothill, J. C. & MOTT, J. J. (eds) 1985. Management of the world's savannas. Australian Academy of Sciences.Google Scholar
Touber, L. 1983. Soils and vegetation of the Amboseli-Kibwezi area, van der Pouw, B. J. A. & Van Engelen, J. (eds). Kenya Soil Survey, Ministry of Agriculture, Government of Kenya Press.Google Scholar