Large herbivores may alter vegetation structure of semi-arid savannas through soil nutrient mediation

In savannas, the tree-grass balance is governed by water, nutrients, fire and herbivory, and their interactions. We studied the hypothesis that herbivores indirectly affect vegetation structure by changing the availability of soil nutrients, which, in turn, alters the competition between trees and g...

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Published in:	Oecologia Vol. 165; no. 4; pp. 1095 - 1107
Main Authors:	van der Waal, Cornelis, Kool, Ada, Meijer, Seline S, Kohi, Edward, Heitkönig, Ignas M. A, de Boer, Willem F, van Langevelde, Frank, Grant, Rina C, Peel, Mike J. S, Slotow, Rob, de Knegt, Henrik J, Prins, Herbert H. T, de Kroon, Hans
Format:	Journal Article
Language:	English
Published:	Berlin/Heidelberg Berlin/Heidelberg : Springer-Verlag 01.04.2011 Springer Springer-Verlag Springer Nature B.V
Subjects:	Analysis Animal and plant ecology Animal, plant and microbial ecology Animals biogeochemical cycles Biological and medical sciences Biomedical and Life Sciences bottom-up Bush encroachment calcium Calcium - analysis Competition Cycling Data processing Dung Ecology Ecosystem ECOSYSTEM ECOLOGY Ecosystem ecology - Original Paper ecosystems Feces Feedback fire Fires forage quality Fundamental and applied biological sciences. Psychology General aspects grass Grasses Grazing Herbivores Herbivory Heterogeneity Hot spots Hydrology/Water Resources kruger-national-park Life Sciences Livestock Livestock - growth & development Livestock - metabolism magnesium Magnesium - analysis nitrogen Nitrogen - analysis Nutrient availability Nutrient balance Nutrient cycle Nutrient cycles Nutrient hotspot Nutrients Nutritional Requirements phosphorus Phosphorus - analysis plant Plant production Plant Sciences Poaceae - growth & development Poaceae - metabolism Population Dynamics potassium Potassium - analysis Predation Recruitment Savanna soils Savannahs Savannas Seedlings Seedlings - growth & development Seedlings - metabolism soil Soil - analysis Soil - chemistry Soil fertility Soil nutrients Soil structure South Africa south-african savanna species recruitment Time Factors tree recruitment Tree-grass competition Trees Trees - growth & development Trees - metabolism Urine Vegetation Vegetation structure woody cover Tree–grass competition Bush encroachment Seedling Predation Nutrient hotspot Competition Herbivorous Savannah Hot spot Plant juvenile growth stage Shrub encroachment Tree-grass competition Soils Semi arid zone Tree Nutrient Herbaceous plant Vegetation structure
ISSN:	0029-8549, 1432-1939, 1432-1939
Online Access:	Get full text
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Summary:	In savannas, the tree-grass balance is governed by water, nutrients, fire and herbivory, and their interactions. We studied the hypothesis that herbivores indirectly affect vegetation structure by changing the availability of soil nutrients, which, in turn, alters the competition between trees and grasses. Nine abandoned livestock holding-pen areas (kraals), enriched by dung and urine, were contrasted with nearby control sites in a semi-arid savanna. About 40 years after abandonment, kraal sites still showed high soil concentrations of inorganic N, extractable P, K, Ca and Mg compared to controls. Kraals also had a high plant production potential and offered high quality forage. The intense grazing and high herbivore dung and urine deposition rates in kraals fit the accelerated nutrient cycling model described for fertile systems elsewhere. Data of a concurrent experiment also showed that bush-cleared patches resulted in an increase in impala dung deposition, probably because impala preferred open sites to avoid predation. Kraal sites had very low tree densities compared to control sites, thus the high impala dung deposition rates here may be in part driven by the open structure of kraal sites, which may explain the persistence of nutrients in kraals. Experiments indicated that tree seedlings were increasingly constrained when competing with grasses under fertile conditions, which might explain the low tree recruitment observed in kraals. In conclusion, large herbivores may indirectly keep existing nutrient hotspots such as abandoned kraals structurally open by maintaining a high local soil fertility, which, in turn, constrains woody recruitment in a negative feedback loop. The maintenance of nutrient hotspots such as abandoned kraals by herbivores contributes to the structural heterogeneity of nutrient-poor savanna vegetation.
Bibliography:	http://dx.doi.org/10.1007/s00442-010-1899-3 ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 14 ObjectType-Article-1 ObjectType-Feature-2 content type line 23 Communicated by Jason Kaye.
ISSN:	0029-8549 1432-1939 1432-1939
DOI:	10.1007/s00442-010-1899-3