The impact of tree removal on standing grass biomass, seedling establishment and growth of woody species
P. Monegi
A B * , N. R. Mkhize A B , T. J. Tjelele A , D. Ward C and Z. Tsvuura B
+ Author Affiliations
- Author Affiliations
A Agricultural Research Council, Animal Production, Range and Forage Sciences, Irene 0062, South Africa.
B School of Life Sciences, University of KwaZulu-Natal, Scottsville 3209, South Africa.
C Department of Biological Sciences, Kent State University, Kent, OH 44240, USA.
* Correspondence to: pmonegi@outlook.com
The Rangeland Journal 44(1) 25-32 https://doi.org/10.1071/RJ21003
Submitted: 19 January 2021 Accepted: 11 February 2022 Published: 6 April 2022
© 2022 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of the Australian Rangeland Society. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)
Abstract
The removal of trees in rangelands can create gaps and lead to increased grass production that could suppress subsequent tree seedling establishment and growth. However, gaps can also enhance the growth of remaining trees. We conducted a field experiment at two savanna sites with different soil texture and woody species. We used 24 plots at each site to determine the effect of tree-removal intensities (0%, 10%, 20%, 50%, 75% and 100%) on grass production, tree-seedling establishment and growth, and growth of the remaining large trees. Site 1 was on previously cultivated severely-eroded clay-dominated soils, encroached by a monospecific stand of Vachellia tortilis. Site 2 had never been cultivated, and was on sandy soils with several woody species. At Site 1, 75 and 100% tree removal significantly reduced standing grass biomass towards the end of the first growing season, with no differences towards the end of the second season. At Site 2, tree removal significantly increased standing grass biomass. There was no significant effect of tree removal on tree seedling establishment at Site 1, but at Site 2 tree removal had a significantly negative effect on overall tree seedling establishment. At both sites, there were no significant differences in tree seedling growth. Moderate (50%) to high (75%) removal of trees had a positive effect on the growth of remaining large trees at both study sites. We found that tree seedling establishment could be affected by the level of grass biomass following tree removal, but other factors including soil erosion are also important considerations. Reduced tree competition facilitates growth of remaining large trees. An implication of these findings is that, regardless of the substantial costs of woody plant control, the recovery of key ecosystem services such as an increased forage production may not be realised. However, we recognise that this may be system-specific.
Keywords: forage production, grass competition, rangeland management, restoration, soil erosion, tree clearing, tree competition, woody plant encroachment.
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