Impacts of savanna trees on forage quality for a large African herbivore |
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Authors: | Fulco Ludwig Hans De Kroon Herbert H T Prins |
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Institution: | (1) Department of Environmental Sciences, Wageningen University, Droevendaalsesteeg 4, 6708 PB Wageningen, The Netherlands;(2) Department of Ecology, Radboud University Nijmegen, Toernooiveld, 6525 ED Nijmegen, The Netherlands |
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Abstract: | Recently, cover of large trees in African savannas has rapidly declined due to elephant pressure, frequent fires and charcoal
production. The reduction in large trees could have consequences for large herbivores through a change in forage quality.
In Tarangire National Park, in Northern Tanzania, we studied the impact of large savanna trees on forage quality for wildebeest
by collecting samples of dominant grass species in open grassland and under and around large Acacia tortilis trees. Grasses growing under trees had a much higher forage quality than grasses from the open field indicated by a more
favourable leaf/stem ratio and higher protein and lower fibre concentrations. Analysing the grass leaf data with a linear
programming model indicated that large savanna trees could be essential for the survival of wildebeest, the dominant herbivore
in Tarangire. Due to the high fibre content and low nutrient and protein concentrations of grasses from the open field, maximum
fibre intake is reached before nutrient requirements are satisfied. All requirements can only be satisfied by combining forage
from open grassland with either forage from under or around tree canopies. Forage quality was also higher around dead trees
than in the open field. So forage quality does not reduce immediately after trees die which explains why negative effects
of reduced tree numbers probably go initially unnoticed. In conclusion our results suggest that continued destruction of large
trees could affect future numbers of large herbivores in African savannas and better protection of large trees is probably
necessary to sustain high animal densities in these ecosystems. |
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Keywords: | Acacia tortilis Nutrients Plant– animal interactions Tree– grass interactions Wildebeest |
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