Enhanced use of beneath-canopy vegetation by grazing ungulates in African savannahs

Abstract The cover of large trees in African savannahs is rapidly declining, mainly due to human land-use practices. Trees improve grass nutrient quality and contribute to species and structural diversity of savannah vegetation. However, the response of herbivores to trees as habitat features is unknown. We quantified the habitat use of wild and domestic ungulates in two eastern and southern African savannahs. We assessed grazing intensities and quantified dung depositions beneath and around canopies of different sized trees. Grasses were eaten and dung was deposited twice as frequently beneath large (ca. 5 m in height) and very large trees (7–10 m) than in open grasslands. Small trees (

[1]  I. McDonald,et al.  Nutritional studies on East African herbivores , 1975, British Journal of Nutrition.

[2]  Kelly K. Caylor,et al.  Determinants of woody cover in African savannas , 2005, Nature.

[3]  S. Milton,et al.  Large trees, fertile islands, and birds in arid savanna , 1999 .

[4]  L. Isbell,et al.  Ants on swollen-thorn acacias: species coexistence in a simple system , 1997, Oecologia.

[5]  Ignas M. A. Heitkönig,et al.  Trees improve grass quality for herbivores in African savannas , 2007 .

[6]  D. Ward,et al.  Effects of Large Mammalian Herbivores and Ant Symbionts on Condensed Tannins of Acacia drepanolobium in Kenya , 2002, Journal of Chemical Ecology.

[7]  E. Witkowski,et al.  Harvested and standing wood stocks in protected and communal miombo woodlands of eastern Tanzania , 2002 .

[8]  F. Ludwig,et al.  Modelling ungulate dependence on higher quality forage under large trees in African savannahs , 2009 .

[9]  M. A. Zavala,et al.  Delayed effects of fire on habitat use by large herbivores in Acacia drepanolobium savanna , 2005 .

[10]  A. Watkinson,et al.  Dynamics of shrub encroachment in an African savanna: relative influences of fire, herbivory, rainfall and density dependence , 2001 .

[11]  S. Archer,et al.  Tree-grass dynamics in a Prosopis-thornscrub savanna parkland: Reconstructing the past and predicting the future , 1995 .

[12]  S. McNaughton,et al.  Promotion of the cycling of diet-enhancing nutrients by african grazers , 1997, Science.

[13]  A. Ash,et al.  Forage quality and feed intake responses of cattle to improved pastures, tree killing and stocking rate in open eucalypt woodlands of north-eastern Australia , 1998, The Journal of Agricultural Science.

[14]  Fulco Ludwig,et al.  The influence of savanna trees on nutrient, water and light availability and the understorey vegetation , 2004, Plant Ecology.

[15]  J. Grace,et al.  Local versus landscape‐scale effects of savanna trees on grasses , 2009 .

[16]  H. Beentje,et al.  Kenya trees, shrubs, and lianas , 1994 .

[17]  Fulco Ludwig,et al.  Impacts of savanna trees on forage quality for a large African herbivore , 2008, Oecologia.

[18]  P. V. Wyk,et al.  Field Guide to Trees of Southern Africa , 1997 .

[19]  F. Keesing,et al.  Consequences of herbivory by native ungulates for the reproduction of a savanna tree , 2007 .

[20]  D. Western,et al.  Woodland loss and restoration in a savanna park: a 20-year experiment , 2004 .

[21]  O. V. Auken Shrub Invasions of North American Semiarid Grasslands , 2000 .

[22]  D. E. Buffington,et al.  Physiological and Production Responses of Dairy Cattle to a Shade Structure in a Subtropical Environment , 1977 .

[23]  B. Campbell,et al.  Changes in Miombo woodland cover in and around Sengwa Wildlife Research area, Zimbabwe, in relation to elephants and fire , 2002 .

[24]  James B Grace,et al.  Savanna tree density, herbivores, and the herbaceous community: bottom-up vs. top-down effects. , 2008, Ecology.

[25]  T. Groen,et al.  Herbivores as architects of savannas: inducing and modifying spatial vegetation patterning , 2008 .

[26]  R. Ostfeld,et al.  Impacts of large herbivorous mammals on bird diversity and abundance in an African savanna , 2008, Oecologia.

[27]  Harry Biggs,et al.  Trends in woody vegetation cover in the Kruger National Park, South Africa, between 1940 and 1998 , 2000 .

[28]  A. J. Belsky,et al.  Influences of Trees on Savanna Productivity: Tests of Shade, Nutrients, and Tree-Grass Competition , 1994 .

[29]  Kirk A. Moloney,et al.  Modelling the impact of small‐scale heterogeneities on tree—grass coexistence in semi‐arid savannas , 1998 .

[30]  S. McNaughton,et al.  Grazing Lawns: Animals in Herds, Plant Form, and Coevolution , 1984, The American Naturalist.

[31]  M. Tobler,et al.  The impact of cattle ranching on large-scale vegetation patterns in a coastal savanna in Tanzania , 2003 .

[32]  R. Scholes,et al.  Tree-grass interactions in Savannas , 1997 .

[33]  F. Ludwig,et al.  Improved quality of beneath-canopy grass in South African savannas: Local and seasonal variation , 2008 .

[34]  M. Firestone,et al.  Influence of tree canopies on grassland productivity and nitrogen dynamics in deciduous oak savanna , 1990 .

[35]  F. V. Oudtshoorn Guide to Grasses of Southern Africa , 2012 .

[36]  S. McNaughton,et al.  FEEDBACKS BETWEEN SOIL NUTRIENTS AND LARGE HERBIVORES IN A MANAGED SAVANNA ECOSYSTEM , 2003 .

[37]  Gunnar Köhlin,et al.  Woodfuels, livelihoods, and policy interventions: changing perspectives , 2006 .

[38]  C. Stuart,et al.  A Field Guide to the Tracks and Signs of Southern and East African Wildlife , 1994 .

[39]  Mark West,et al.  Carbon dioxide enrichment alters plant community structure and accelerates shrub growth in the shortgrass steppe , 2007, Proceedings of the National Academy of Sciences.

[40]  R. Biggs,et al.  The impact of the African elephant on marula trees in the Kruger National Park , 2002 .

[41]  T. Palmer,et al.  KLEE: A long‐term multi‐species herbivore exclusion experiment in Laikipia, Kenya , 1997 .

[42]  J. Powell,et al.  Nitrogen and phosphorus transfers in a crop-livestock system in West Africa , 1987 .

[43]  G. Schaller The Serengeti Lion: A Study of Predator-Prey Relations , 1972 .

[44]  F. J. Pierce,et al.  Contemporary Statistical Models for the Plant and Soil Sciences , 2001 .

[45]  Nutrient limitations on understory grass productivity and carbon assimilation in an African woodland savanna , 2008 .