Stem growth of woody species at the Nkuhlu exclosures, Kruger National Park: 2006–2010

Koedoe - African Protected Area Conservation and Science

Field Value
Title Stem growth of woody species at the Nkuhlu exclosures, Kruger National Park: 2006–2010
Creator Scogings, Peter F.
Subject Ecology; Savanna; Plant-herbivore; Browse dendrometer; Dichrostachys; elephant; functional trait; herbivore; savanna
Description An important aspect of managing African conservation areas involves understanding how large herbivores affect woody plant growth. Yet, data on growth rates of woody species in savannas are scarce, despite its critical importance for developing models to guide ecosystem management. What effect do browsing and season have on woody stem growth? Assuming no growth happens in the dry season, browsing should reduce stem growth in the wet season only. Secondly, do functional species groups differ in stem growth? For example, assuming fine-leaved, spiny species’ growth is not compromised by carbon-based chemical defences, they should grow faster than broad-leaved, chemically defended species. Dendrometers were fixed at 20 cm in height on the main stems of 244 random plants of six woody species in three plots (all large herbivores excluded, partial exclusion, and control) and observed from late 2006 to early 2010. Average monthly increment (AMI) per dendrometer and season (dry, wet) was calculated and the interaction between plot and season tested per species, controlling for initial stem girth. AMIs of Combretum apiculatum, Dichrostachys cinerea and Grewia flavescens were zero in the dry season, whilst those of Acacia exuvialis, Acacia grandicornuta and Euclea divinorum were either positive or negative in the dry season. Wet-season AMI of D. cinerea and dry-season AMI of G. flavescens tended to be reduced by browser exclusion. Net AMI (sum of the seasonal AMIs) was tested per species, but results suggested that only D. cinerea tended to be affected by browser exclusion. The results also suggested that stem radial growth of some fast-growing species is more prone to reduction by browser exclusion than the growth of other species, potentially reducing their competitiveness and increasing their risk of extirpation. Finally, the usefulness of grouping woody species into simple functional groups (e.g. fine-leaved vs. broad-leaved) for ecosystem management purposes in savannas requires further consideration. Conservation implications: Growth rates of woody plants are important parameters in savanna models, but data are scarce. Monitoring dendrometers in manipulative situations over several years can help fill that gap. Results of such studies can be used to identify species prone to high risk of extirpation.
Publisher AOSIS Publishing
Contributor National Research Foundation University of Zululand Agricultural Research Council Swedish Research Council Swedish International Development Agency.
Date 2011-06-28
Type info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion — dendrometers; herbivore exclusion
Format text/html application/epub+zip text/xml application/pdf
Identifier 10.4102/koedoe.v53i1.1035
Source Koedoe; Vol 53, No 1 (2011); 8 pages 2071-0771 0075-6458
Language eng
Coverage Kruger National Park; Nkuhlu 2006-2010 stem girth
Rights Copyright (c) 2011 Peter F. Scogings