Vegetation change in northern KwaZulu-Natal since the Anglo-Zulu War of 1879 Jennifer Mary ...

223 Pages·2014·6.37 MB·English

Vegetation change in northern KwaZulu-Natal since the Anglo-Zulu War
of 1879

Jennifer Mary Russell

Submitted in fulfilment of the academic requirements for the degree of
Master of Science

In the Discipline of Botany
School of Life Sciences
College of Agriculture, Engineering and Sciences
University of KwaZulu-Natal
Pietermaritzburg
2013
i

ABSTRACT
Historic photographs have been successfully used to compare landscape change over time. I
used photographs taken of the grassland biome during and just after the Anglo-Zulu War
(1879) in KwaZulu-Natal (South Africa), which are some of the earliest known available
landscape photographs. The study area encompassed Fugitives’ Drift, Isandlwana and
Rorke’s Drift and included communal and commercial rangelands, as well as conservation
areas. These fixed-point photographs showed a dramatic increase in woody cover (< 82.5%)
since the Anglo-Zulu War in all three land-use types. Floristic sampling showed that while
vegetation structure did not differ significantly, plant species diversity and richness differed
significantly for each land-use type. I also used a set of aerial photographs to give a much
wider perspective of the landscape changes for the study area from 1944 to 2005. These
images indicated that the increase in woody cover was progressive, with most of the woody
plant recruitment occurring prior to 1964. Thereafter, the increase in woody plant cover was
due to bush-clump thickening rather than recruitment into grasslands. This pattern did not
occur, however, in the commercial rangeland, where recruitment into open grassland
commenced in the 1980s.
Although the theory of patch dynamics is cyclical in nature, this model may fit the
patterns observed in the study area. Analysis of rainfall and temperature data showed that
there has been a decrease in average annual rainfall since 1902 and an increase in minimum
daily temperature since 1973. However, the decrease in mean annual rainfall is not consistent
with woody plant encroachment. While the increase in mean annual daily temperature
appears consistent with a shift to an environment typical of savannas, woody plant
encroachment started before the increase in daily temperature. A survey of long-term
residents in the study area with regard to livestock numbers, grazing patterns, fire and wood
harvesting was also inconclusive. I, therefore, speculate that increasing levels of atmospheric
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CO is driving bush encroachment, with the other drivers such as rainfall, temperature,
2
absence of intense fires, grazing patterns and land-use, playing a modifying role.
iii

PREFACE
The work described in this thesis was carried out at the School of Life Sciences, University of
KwaZulu-Natal, Pietermaritzburg, South Africa, from January 2010 to November 2013,
under the supervision of Professor David Ward.
This thesis is submitted for the degree of Master of Science in the Faculty of Science
and Agriculture, University of KwaZulu-Natal, Pietermaritzburg. It represents original work
by the author and has not been submitted in any form to another university. Where use was
made of the work of others, it has been duly acknowledged in the text.
Chapter 2 and 3 in this thesis were formatted in the appropriate journal style to which
they have been submitted.

………………………………………
Jennifer Mary Russell
November 2013

I certify that the above statement is correct.

………………………………………
Professor David Ward
Supervisor

26 November 2013
iv

College of Agriculture, Engineering and Sciences
DECLARATION 1 – PLAGIARISM
I, Jennifer Mary Russell, declare that
1. The research reported in this thesis, except where otherwise indicated, is my original
research.
2. This thesis has not been submitted for any degree or examination at any other
university.
3. This thesis does not contain other persons’ data, pictures, graphs or other information,
unless specifically acknowledged as being sourced from other persons.
4. This thesis does not contain other persons’ writing, unless specifically acknowledged
as being sourced from other researchers. Where other written sources have been
quoted, then:
a. Their words have been rewritten, but general information attributed to them
has been referenced.
b. Where their exact words have been used, then their writing has been placed
inside quotation marks and referenced.
5. This thesis does not contain text, graphics or tables copied and pasted from the
internet, unless specifically acknowledged, and the source detailed in the thesis and in
the References sections.

Signed:……………………………...
Jennifer Mary Russell
26 November 2013
v

College of Agriculture, Engineering and Sciences
DECLARATION 2 – PUBLICATIONS

DETAILS OF CONTRIBUTION TO PUBLICATIONS that form part of research present in
this thesis.

Publication 1 – submitted to the African Journal of Range & Forage Science
Russell J M and Ward D (2013) Vegetation change in northern KwaZulu-Natal since the
Anglo-Zulu War of 1879: local or global drivers?
Author contributions:
JMR conceived the paper with DW. JMR collected and analysed the data and wrote the
paper. DW contributed valuable comments to the manuscript and facilitated data analysis.

Publication 2 – submitted to the International Journal of Remote Sensing
Russell J M and Ward D (2013, in review) Remote sensing provides a progressive record
of vegetation change in northern KwaZulu-Natal, South Africa, from 1944 to 2005.
Author contributions:
JMR conceived the paper with DW. JMR collected and analysed the data and wrote the
paper. DW contributed valuable comments to the manuscript and facilitated data analysis.

Signed:………………………………
Jennifer Mary Russell
26 November 2011
vi

ACKNOWLEDGEMENTS

This project would not have been possible without the support and guidance of many
professionals, friends and strangers, for which I am truly grateful.

Firstly, I must thank Prof. David Ward for accepting me as a student. His patience, advice,
expertise and vast knowledge are all highly appreciated. My thanks, too, go to Prof. Timm
Hoffman and James Puttick for their guidance on repeat fixed-point photographic techniques
and to Dr Tim O’Connor for his encouragement and advice. I am grateful to the seven
vegetation ecologists who assessed my fixed-point photographs for bush encroachment:
W. Bond, K. Botha, K. Kirkman, T. O’Connor, J. Puttick, the late R. Scott-Shaw and
Z. Tsvuura. Invaluable assistance was given by Brice Gijsbertsen of the Geography
Department (UKZN), Clement Adjorlolo of Natural Resources (Cedara) and Olivier Harrison
with analysis of the aerial photographs.

I also wish to thank the staff at KwaZulu-Natal Museum Services and at the Killie Campbell
Africana Library for their help in accessing historic photographs; the Chief Directorate of
National Geo-spatial Information, Mowbray, for providing the aerial photographs; SA
Weather, Agricultural Research Council and the Talana Museum for rainfall and temperature
data; South African Environmental Observation Network for technical assistance (in
particular, Sue J van Rensburg and Beate Holscher for their unstinting efforts through hail
and heat wave) and financial help; and the Rattray family at Fugitives’ Drift Lodge for
accommodation during field trips. I am also grateful to National Research Foundation for
funding DW, the Gay Langmuir Bursary Fund for funding JR and Ideaswild for donating
field equipment.
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To my fellow students at UKZN, thank you for welcoming me into your midst and helping
me find my feet. To Nicki von der Heyde of Campaign Trails, thank you for introducing me
to the fascination of the battlefields all those years ago. To William Bond, thank you for the
idea of this project. And lastly, but by no means least, to Peter Russell, friend, husband, goad
and true pillar of support – thank you.
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TABLE OF CONTENTS
ABSTRACT .......................................................................................................................... i
PREFACE ............................................................................................................................ iii
DECLARATION 1 – PLAGARISM ................................................................................... iv
DECLARATION 2 – PUBLICATIONS ............................................................................... v
ACKNOWLEDGEMENTS.................................................................................................. vi
TABLE OF CONTENTS ................................................................................................... viii
LIST OF FIGURES ........................................................................................................... xiv
LIST OF TABLES .............................................................................................................. xv

CHAPTER 1 ......................................................................................................................... 1
Literature review ................................................................................................................... 1
Introduction .......................................................................................................................... 1
Savannas ............................................................................................................................... 4
An overview of the dynamics of savannas ............................................................................. 5
Competition- or resource-based models ............................................................................. 6
Disturbance-based models ............................................................................................... 10
Potential mechanisms that determine the tree:grass ratio of savannas .................................. 12
Climate ............................................................................................................................ 13
Soil moisture ................................................................................................................ 13
Temperature ................................................................................................................. 14
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Fire .................................................................................................................................. 15
Fire and its effect on bush encroachment ...................................................................... 15
Fire intensity and return frequency ............................................................................... 16
Fire and the life-sages of trees ...................................................................................... 16
Timing of fires ............................................................................................................. 17
Effects of fire exclusion ............................................................................................... 18
Herbivory ........................................................................................................................ 19
Direct effects of herbivory ........................................................................................... 19
Indirect effects of herbivory ......................................................................................... 20
Competition and facilitation ............................................................................................. 21
Competition ................................................................................................................. 22
Facilitation ................................................................................................................... 24
Soils ................................................................................................................................ 25
Carbon dioxide and C plants ........................................................................................... 26
4
Nitrogen enrichment ........................................................................................................ 28
Land-use .......................................................................................................................... 30
Woody plant encroachment in KwaZulu-Natal grassland and savannas ............................... 32
Long-term monitoring of vegetation change ........................................................................ 33
Fixed-point photography .................................................................................................. 33
Remote sensing................................................................................................................ 35
The study area – an historical overview ............................................................................... 36