EFFECTS OF REMOVING ACACIA MEARNSII ON THE WATER TABLE, SOIL AND VEGETATION PROPERTIES IN THE TSOMO VALLEY OF THE EASTERN CAPE PROVINCE, SOUTH AFRICA By Hloniphani Peter Mthunzi Moyo A thesis submitted in partial fulfillment of the requirements of the degree of Master of Science in Agriculture (Pasture Science) in the Faculty of Science and Agriculture at the University of Fort Hare January 2010 Supervisor Dr. Sikhalazo Dube PERMISSION FOR USE This thesis is presented in partial fulfillment of the requirements for a Masters degree in Pasture Science at the University of Fort Hare. The library of this University may keep the copy for inspection and reference. The permission for copying part or the whole of this thesis in any manner for scholarly purposes or any other reason may be granted by my supervisor or in his absence by the Head of Department of Livestock and Pasture Science or the Executive Dean of the Faculty in which this work was done. Use of part or the whole of this thesis for financial amplification shall not be permitted unless done in writing by myself. The recognition shall be given to me and to the University of Fort Hare in any scholarly consumption that may be made of any material from this thesis. ii DECLARATION I declare that The effects of the removal of invasive Acacia mearnsii on the water table; soil and vegetation properties in the Tsomo valley of the Eastern Cape, South Africa is my own work, that it has not been submitted for any degree or examination in any other university, and that all the resources I have used or quoted have been indicated and acknowledged by complete reference. Hloniphani P.M. Moyo January 2010 iii ABSTRACT Invasion of rangelands by trees such as Acacia mearnsii threaten native vegetation and their habitats because invasive trees compete with native vegetation for resources such as water, nutrients and the sun. The non-indigenous trees have higher evapotranspiration rates that eventually lead to reduction in stream and river flows. Acacia mearnsii also have inhibitory effects on growth of underneath vegetation through exudates from either their roots or leaves that prevent either the germination or the full establishment of native vegetation. The purpose of this study was to investigate (1) the effects of Acacia mearnsii on water table; and (2) the effect of Acacia mearnsii on soil and vegetation properties in the Eastern Cape Province, South Africa. Water table was measured using HOBO data loggers in plots where A.mearnsii was cleared and where it was not. There was significantly higher (p < 0.05) recharge in plots where trees were cleared (-8.7m) compared to where they were not (-9m). Soil samples were collected from inside and outside Acacia mearnsii canopies and analyzed for pH, soil organic carbon, soil aggregate stability, electrical conductivity and nitrogen content. Soil from under A.mearnsii canopies was more acidic (3.05) compared to that from outside (5.47). Nitrogen content was significantly higher in soils from under the canopies (0.52 mg kg-1) compared to those from outside (0.21 mg kg-1). Soil aggregate stability was not significantly different (p > 0.05) between soils from inside and those from outside canopies. iv Total herbaceous production was measured using the dry-weight method. Total herbaceous production was significantly higher (p < 0.05) in the plots that were cleared (290 kg ha-1) than in those that were not (22 kg ha-1). Soil samples were collected from inside and outside canopies, incubated in the greenhouse to determine the seed bank botanical composition and the seed bank size. Soils from outside canopies had higher seed bank size (p < 0.05) (59% of total seedling emergence) than soils from under the canopies (41%). Acacia mearnsii contributed 5% of total seedling emergence in trays while forbs contributed 50%, showing that in the absence of A.mearnsii, germination increases. It is concluded that Acacia mearnsii significantly reduces groundwater recharge, soil pH, biomass production and native vegetation seed bank whilst increasing soil nitrogen and soil organic carbon under its canopies. v ACKNOWLEDGEMENTS For the gift of life, ability and strength for this research work to be possible all thanks and praise to the Lord God above. I thank my supervisor Dr Sikhalazo Dube who gave me the opportunity to carry out this research and work with him. Thank you for the advice and patience throughout the course of the research; it was a pleasure working with you. Thank you Dr Luthando Dziba (ARC) for your advice and encouragement during this work. During the course of the study I had the opportunity to work with the farm owner, Mr Nelson Mdlungu, who sheltered and allowed us to have our way during data collection; my sincere thanks go to him and his family. I thank the farm workers who helped with data collection. I thank the colleagues in the Department of Livestock and Pasture Science, especially Bethwell Moyo, Lesoli and Thulani, for their assistance through statistical analyses, data sorting and for moral support. Thank you Bra Welly for your patience and assistance in those days when we were climbing those mountains. Dr. Fatunbi, thank you so much for your patience with me specifically when I felt reluctant to do some of the things. Last but not least a big thank you goes to my family who were with me, spiritually and emotionally. vi DEDICATION This work is dedicated to my late mother, Miss Winnie. vii TABLE OF CONTENTS PERMISSION FOR USE ............................................................................................................... ii DECLARATION ........................................................................................................................... iii ABSTRACT ................................................................................................................................... iv ACKNOWLEDGEMENTS ........................................................................................................... vi DEDICATION .............................................................................................................................. vii TABLE OF CONTENTS ............................................................................................................. viii LIST OF FIGURES ....................................................................................................................... xi LIST OF TABLES ........................................................................................................................ xii LIST OF PLATES ....................................................................................................................... xiii LIST OF ABBREVIATIONS ...................................................................................................... xiv 1. INTRODUCTION ...................................................................................................................... 1 Objectives .................................................................................................................................... 2 2. LITERATURE REVIEW ........................................................................................................... 4 Effects of controlling invasive trees on vegetation structure ...................................................... 9 Effects of invasive trees on soil properties................................................................................ 11 Effects of invasive trees on grass seed bank ............................................................................. 14 Causes of invasion ..................................................................................................................... 15 Environments prone to invasions .............................................................................................. 17 The ecology of Acacia mearnsii................................................................................................ 18 Acacia mearnsii in South Africa ............................................................................................... 22 Uses of Acacia mearnsii ............................................................................................................ 23 Positive effects of invasion ....................................................................................................... 25 Detrimental effects of invasive trees ......................................................................................... 26 Invasive plant control and management .................................................................................... 29 The control of Acacia mearnsii ................................................................................................. 30 viii 3. STUDY SITE ............................................................................................................................ 33 4. EFFECT OF ACACIA MEARNSII REMOVAL ON THE WATER TABLE ........................... 35 Introduction ............................................................................................................................... 35 Experimental layout and data collection ................................................................................... 37 Data analysis ............................................................................................................................. 38 Results ......................................................................................................................................