Improved quality of beneath-canopy grass in South African savannas: Local and seasonal variation

Questions: Do large trees improve the nutrient content and the structure of the grass layer in savannas? Does the magnitude of this improvement differ with locality (soil nutrients) and season (water availability)? Are grass structure and species composition beneath tree canopies influenced by soil...

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Bibliographic Details
Published in:Journal of vegetation science Vol. 19; no. 5; pp. 663 - 670
Main Authors: Treydte, Anna C., van Beeck, F. A Looringh, Ludwig, F., Heitkönig, I. M A.
Format: Journal Article
Language:English
Published: Oxford, UK Opulus Press Uppsala 01.10.2008
Blackwell Publishing Ltd
Opulus Press
Opulus Press AB
Subjects:
botanical composition
canopy
Carbon content
cattle
chemical constituents of plants
community structure
dry season
Dry seasons
ecosystem
Fixation
forage quality
Forest canopy
Grasses
Grazing
habitats
herbivores
Herbivory
leaves
Nitrogen
nitrogen content
Nitrogen fixation
nutrient content
nutrient uptake
Nutrients
open eucalypt woodlands
perennial grasses
phosphorus
Plant nutrition
Rainy seasons
Savanna soils
Savannas
seasonal variation
Seasons
shade
Soil fertility
Soil nutrients
Soils
South Africa
Species composition
species diversity
sward
Tree canopy
Trees
understory
vegetation
wet season
Wetland flora
wilting
South Africa
ISSN:1100-9233, 1654-1103, 1104-7402
Online Access:Get full text
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Summary:Questions: Do large trees improve the nutrient content and the structure of the grass layer in savannas? Does the magnitude of this improvement differ with locality (soil nutrients) and season (water availability)? Are grass structure and species composition beneath tree canopies influenced by soil fertility and season? Location: South Africa. Methods: We compared grass leaf nutrient contents and grass sward structure beneath and outside tree canopy areas in three savannas of different soil fertility during the dry and the wet seasons. Results: Grass nitrogen contents were twice as high during the wet season as compared to the dry season, being more strongly elevated underneath tree canopies during the wet season. Grasses had significantly less stem material and provided less dead material underneath trees on the high soil fertility site. Grass species composition differed significantly beneath and outside tree canopies, with more nutritious grass species found sub-canopy. Grass species richness was significantly lower beneath than outside of trees at the site of high soil fertility. Conclusions: Trees improve overall quality of savanna grasses by enhancing grass growth and nutrient uptake during the wet season, and by delaying grass wilting in the dry season. The positive effect of trees on the grass layer might attract grazing herbivores in otherwise nutrient-poor savannas. Hence, single standing large trees should be maintained to sustain high grass quality and, consequently, grazer populations in savanna habitats. Nomenclature: Trees: Palgrave (1983); Beentje et al. (1994) Grasses: Van Oudtshoorn (1999).
Bibliography:http://dx.doi.org/10.3170/2008-8-18435
ArticleID:JVS1091
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istex:5F1434E404165A318E5C37422751658A0159842B
Trees: Palgrave (1983); Beentje et al. (1994) Grasses: Van Oudtshoorn (1999).
Ackowledgements.
This study was funded by the German Research Foundation (DFG). SANPARKS and Scientific Services in Kruger Park gave permission to conduct field work, C.C. Grant, A. Delsink, S. Ronaldson, Y. Pretorius and C. van der Waal helped with logistics and stimulated fruitful discussions. We thank C.C. Grant and two anonymous reviewers for their comments on an earlier draft of this paper. Field technicians and lab assistants in South Africa and The Netherlands were of great support.
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content type line 23
ISSN:1100-9233
1654-1103
1104-7402
DOI:10.3170/2008-8-18435