Fire and Its Effects on Vegetation in the Okavango Delta.Pdf

MICHAEL HEINL

Fire and its effects on vegetation in the Okavango Delta, Botswana

Feuer und sein Einfluss auf die Vegetation im Okavango Delta, Botswana

supported by Fire and its effects on vegetation in the Okavango Delta, Botswana

Feuer und sein Einfluss auf die Vegetation im Okavango Delta, Botswana

Diplomarbeit am Lehrstuhl für Vegetationsökologie Technische Universität München Freising-Weihenstephan Prof. Dr. Jörg Pfadenhauer - 25. August 2001 -

Autor: Michael Heinl ([email protected])

Betreuer: Dr. Jan Sliva ([email protected]) Prof. Jörg Pfadenhauer Dr. E. Veenendaal supported by PREFACE II

Fire and its effects on vegetation in the Okavango Delta, BoBotttswanaswana

Preface

The present MSc-Thesis (Diplomarbeit) describes the results of a one-year project about the effects of fire on vegetation, with special focus on the Okavango Delta region, Botswana. The study is based on a new initiated research co-operation between Harry Oppenheimer Okavango Research Centre (HOORC) in Maun, Botswana, part of University of Botswana and the Chair of Vegetation Ecology of the Technische Universität München (TUM), Germany funded by Stifterverband für die Deutsche Wissenschaft within their programme “Forschung für Naturräume“ for young scientists. Under the topic “Elements in Conflict - Anthropogenic fires in the RAMSAR-wetland Okavango-Delta (Botswana)”, prerequisites were set for future co- operative research projects between HOORC and TUM during August 2000 to August 2001. Besides the theoretical introduction to the ecology of the study area ‘Okavango Delta’, this period was primarily used to gain first practical experience on the vegetation and the fire ecology of the Okavango Delta during the stays in Botswana in October 2000 and March/April/Mai 2001. These were further used for getting in contacting with local and international researchers, NGOs and the authorities. The study can be used as a scientific basis for further research on fire ecology in southern African savannas, especially in the Okavango Delta region and was admitted to the international research initiative SAFARI 2000.

The structure of the present study describes indirectly the temporal development of the project. As a first step, a precise introduction to the study area Okavango Delta in Bot- swana was developed (part A). Because of the spatial and also the thematic distance to Central Europe, detailed studies were necessary both on large-scale relations and on local characteristics for getting an overall view of the ecology for this area. The understanding of ecological interactions is the basis for developing useful hypotheses for studies and interpretations of gained results. Therefore, part A deals besides climate, geology, vegetation and soil primarily with explanations on the hydrographic system of the Okavango Delta, which is probably the key for understanding ecological relations in this vast wetland. Unfortunately, this section is presented on German language omly, because at the time of its elaboration it was still unsure in which context this study will be used. An afterwards translation of this chapter would have meant to sacrifice the field-work, because of the time-limit of this study. Therefore, it is kindly asked to excuse the missing international understanding of this chapter. Part B of the present study describes the focus of the ecological research in the Okavango Delta on the topic fire and its effects on vegetation. Here again, a detailed evaluation of the present scientific knowledge was necessary to derive an ecological overview about fire, for interpretations of causes and consequences of fire on vegetation. PREFACE III

Part C describes the utilisation of the gained theoretical knowledge in the course of a field-study in April 2001, concerning the effects of fire on the vegetation in the Okavango Delta. But because of missing baseline-data, mainly about fire-events of the last years, the study is based on a simplified question (effects of the 2000/01 fires on vegetation). Besides, the vegetation surveys were used for developing and evaluating useful methods and approaches, as well as for gaining experience on the logistics. A kind of weakness of the results, as a consequence thereof, was expected and accepted in advance. Nevertheless some interesting ecological and methodical aspects referring to effects of fire on southern African savanna vegetation could be derived. VORBEMERKUNGEN IV

Feuer und sein Einfluss auf die Vegetation im Okavango Delta, Botswana

Vorbemerkungen

Die vorliegende Diplomarbeit dokumentiert die Resultate einer einjährigen Studie über den Einfluss von Feuer auf die Vegetation, im Speziellen für das Gebiet des Okavango Deltas in Botswana. Die Arbeit basiert auf einer neu initiierten Forschungskooperation zwischen dem Harry Oppenheimer Okavango Research Centre (HOORC) in Maun, Botswana, einer Außenstelle der University of Botswana und des Lehrstuhls für Vegetationsökologie der Technischen Universität München, unterstützt durch das Nachwuchsförderungsprogramm 2000 „Forschung für Naturräume“ des Stifterver- band für die Deutsche Wissenschaft. Unter dem Thema “Elemente im Konflikt - anthropogene Feuer im RAMSAR-Feuchtgebiet Okavango Delta (Botswana)“ wurden während des Zeitraums August 2000 bis August 2001 primär die Grundlagen für weiterführende wissenschaftliche Arbeiten in Kooperation mit dem HOORC geschaffen. Dabei standen neben der theoretischen Einarbeitung in den aktuellen Forschungsstand zur Ökologie des Okavango Deltas vorwiegend die Aufenthalte vor Ort im Oktober 2000 und im März/April/Mai 2001 im Vordergrund, die die ersten Erfahrungen mit der Vegetation und der Feuerökologie ermöglichten. Sie wurden außerdem zur Knüpfung von Kontakten zu lokalen und internationalen Wissenschaft- lern, Behörden und NGOs genutzt. Die Studie soll als wissenschaftliche Basis für weiterführende Forschungen im Bereich der Feuerökologie der südafrikanischen Savannen, im Speziellen des Okavango Delta dienen und wurde in die internationale Forschungsinitiative SAFARI 2000 aufgenommen.

Die Struktur der vorliegenden Arbeit beschreibt indirekt den zeitlichen Ablauf und die Entwicklung des Projekts. Dabei bestand der erste Schritt zunächst in einer detaillierten Einarbeitung und Beschreibung des Untersuchungsgebiets Okavango Delta in Botswana (Teil A). Aufgrund der räumlichen und auch thematischen Distanz des Projekts zu Mitteleuropa waren ausführliche Studien nötig, um großräumige Zusammenhänge aber auch lokale Besonderheiten zu verstehen und in einen ökologischen Gesamtkontext stellen zu können. Das ökologischen Verständnis eines Raumes bildet die Grundlage für die Erstellung sinnvoller Arbeitshypothesen und die Interpretation der Ergebnisse. Teil A beschäftigt sich daher neben Klima, Geologie, Vegetation und Boden primär mit dem hydrographischen System des Okavango Deltas, dessen Verständnis als der Schlüssel zur Ökologie diese weiträumigen Feuchtgebiets angesehen werden kann. Leider liegt dieser Abschnitt nur in einer deutschen Fassung vor, da zum Zeitpunkt der Erstellung noch nicht abzusehen war, in welchem Rahmen die Diplomarbeit Verwendung finden soll. Einer nachträglichen Übersetzung wären aufgrund der zeitlichen Beschränkung der Diplomarbeit die Geländeuntersuchungen zum Opfer gefallen und so sei an dieser Stelle angesichts der fehlenden internationalen Verständlichkeit um Verzeihung gebeten. VORBEMERKUNGEN V

Teil B der Arbeit beschreibt die Konkretisierung der ökologischen Forschung im Okavango Delta auf das Thema Feuer und seinen Einfluss auf die Vegetation. Auch hier bedingt die thematische Distanz der Savannenbrände zu Mitteleuropa eine detaillierte Auseinandersetzung mit den bestehenden wissenschaftlichen Erkenntnis- sen, ebenfalls zur Erlangung eines ökologischen Überblicks, der es erlaubt, Ursachen und Folgen von Feuer auf die Vegetation abschätzen und interpretieren zu können. Teil C beschreibt die Anwendung der gewonnenen Erkenntnisse im Zuge einer Geländeuntersuchung im April 2001 zum Einfluss von Feuer auf die Vegetation des Okavango Deltas. Aufgrund fehlender Grundlagendaten, vorwiegend zu Feuerereignis- sen der letzten Jahre, liegt dieser Studie allerdings nur eine vereinfachte Fragestellung zugrunde (Einfluss der Feuer von 2000/01 auf die Vegetation). Parallel dienten die vegetationskundlichen Untersuchungen der Ausarbeitung und Evaluierung geeigneter Methoden und Ansätze sowie der Gewinnung logistischer Erfahrungen zur Vorberei- tung weiterführender Studien. Eine damit verbundene geringere Aussagekraft der Ergebnisse wurde bewusst in Kauf genommen. Nichtsdestotrotz konnte mit der vorliegenden Arbeit der Bogen von der Ökologie des Okavango Deltas über die Feuer in den Savannen des südlichen Afrika hin zu einer verbindenden Geländeuntersuchung gespannt werden und auch einige interessante Aspekte zum Einfluss von Feuer auf die Vegetation des Okavango Delta abgeleitet werden. INHALT / CONTENTS VI

Erklärung I

Preface II

Vorbemerkungen IV

Contents/Inhalt

A Das Okavango Delta - Lage, UmweltfaktorenUmweltfaktoren und Ökologie 1

1 Das ‚Okavango Delta‘ - Eine geographische Kurzeinführung 2

2 Klima 6 2.1 Die großklimatische Lage Botswanas 6 2.2 Das regionale Klima in Botswana 7

3 Geologie 10 3.1 Geologische Formationen 10 3.2 Tektonik und Oberflächenstruktur 12 3.3 Geologische Aktivitäten und landschaftliche Veränderungen im späten Quartär 14

4 Hydrographisches System 16 4.1 Das zeitliche Zusammenspiel von Niederschlag und Flut 16 4.2 Die räumliche Verteilung der Flut innerhalb des Okavango Deltas 21 4.3 Typisierung der ‚channels‘ 23 4.4 Die zeitliche Entwicklung der ‚channels‘ 26

5 Die Ökologischen Einheiten des Okavango Deltas und deren typische Vegetation 34

6 Boden 39 6.1 Die Böden des nördlichen Botswana 39 6.2 Die lokalen Böden des Okavango Delta 42

7 Zusammenfassung 44

Tafel 1 - 4 46 INHALT / CONTENTS VII

B Fire and its effects on vegetation in southern African savasavannnnasnas 47

1 Introduction 47

2 The ecology of semi-arid savanna vegetation in southern Africa 49 2.1 Describing ‘savannas’ 49 2.2 The coexistence of trees and grasses in savannas 51 2.3 Savanna dynamics 54

3 Fire in southern African savannas 57 3.1 Drought, fuel and ignition as prerequisites for fire 57 3.2 The fire behaviour 60 3.3 The fire regime in southern African savannas 62

4 Fire and vegetation responses 66 4.1 Plant responses for surviving fires 66 4.2 Plant responses to the post-fire conditions 69 4.3 Single fire related phenomena on the community-level 71

5 Summary 76

Plate 5 - 8 79

C Studies on the effectseffects of fire on vegetation diversity in the Okavango Delta, Botswana80

1 Introduction 80

2 The study area ‘Okavango Delta’ 82 2.1 Location and ecology 82 2.2 Conservation areas and land-use management of the Okavango Delta 83 2.3 The fire-use in the Okavango Delta region 85

3 Methods and critical remarks 87 3.1 The site-selection by using remote sensing data 87 3.2 The site investigations by applying the plant functional type (PFT) approach 95 3.3 Explanations on the measured parameters 101

4 Results and discussion of the field survey106 4.1 The preparatory work for evaluating PFTs 106 4.2 The results of multivariate analyses 107 4.3 The interpretation of linear correlation 109 INHALT / CONTENTS VIII

5 The discussion of the applied approaches 118 5.1 The selection and the quality of the study sites 118 5.2 The application of the PFT approach 119 5.3 The investigation of the study sites 121

6 Conclusion and future prospects 123

Plate 9 - 12 125

Acknowledgements 126

References 128 A DAS ‘OKAVANGO DELTA’- LAGE, UMWELTFAKTOREN UND ÖKOLOGIE 1

A Das Okavango Delta - Lage,Lage, Umweltfaktoren und ÖkolÖkolooogiegie

“Wetland ecosystems are among the most biologically productive in the world, but are disappearing globally at an alarming rate. The Okavango Delta is particularly significant as one of the largest remaining inland wetland ecosystems in the world today. While it is not known how many rare or threatened species of flora and fauna exist in the Delta, the wetland ecosystem as a whole is a critically Africa endangered environment of international significance. The Okavango is the habitat for between 2000 to 3000 species of plants, more than 65 fish species, over 162 arachnid (spiders, scorpion, ticks and mites) species, more than 20 species of large herbivores, and over 450 species of birds, including the endangered Wattle Crane.” (http://www.ramsar.org/cop7_doc_20.5_e.htm)

“It offers great scenic beauty and sustains phenomenal numbers of wildlife, crocodile, hippo, water bucks and various fish species are among the many wild animals that could be viewed from safari vans and boats. With forests of palms, grasslands, islands, floodplains and lagoons to be seen, tourists seeking the pleasure of adventure are sure to have one of the best experiences of their life.” (http://www.gov.bw/tourism/okavango.html)

“Described as ‘the jewel’ of the Kalahari, the Okavango Delta is a tranquil and isolated oasis set in Botswana’s harsh and arid desert.” (http://www.zambezi.com/african/botswana/okavango.html)

“Put it in a bottle, label it ‘Okavangeau’ and you could make a fortune. It is crystal clear, cool and as natural as anything ever will be. And billions of gallons of the stuff annually pour into one of the world's largest inland deltas, where it transforms an age-old desert into a paradise of palms, papyrus and sparkling clear waterways.” (http://www.gorp.com/gorp/location/africa/botswana/birding.htm) INHALT / CONTENTS VI

please use seperate link for more details on part A!

(german version)

A Das Okavango Delta - Lage, Umweltfaktoren und Ökologie 1

1 Das ‚Okavango Delta‘ - Eine geographische Kurzeinführung 2

2 Klima 6 2.1 Die großklimatische Lage Botswanas 6 2.2 Das regionale Klima in Botswana 7

3 Geologie 10 3.1 Geologische Formationen 10 3.2 Tektonik und Oberflächenstruktur 12 3.3 Geologische Aktivitäten und landschaftliche Veränderungen im späten Quartär 14

5 Die Ökologischen Einheiten des Okavango Deltas und deren typische Vegetation 34

6 Boden 39 6.1 Die Böden des nördlichen Botswana 39 6.2 Die lokalen Böden des Okavango Delta 42

7 Zusammenfassung 44

Tafel 1 - 4 46

B 1 FIRE AND SAVANNAS - INTRODUCTION 47

B Fire and its effects on vegetation in southern African savasavannn-- nas

1 Introduction

The Okavango Delta was described as a vast wetland (about 25000 km2) composed of swamps, floodplains and drylands determined by strong fluctuations in the annual and long- term water supply, making it to a dynamic and almost unique ecosystem, explained more detailed elsewhere (chapter A). This followed by a chapter describing fire and its influence on the vegetation in southern African arid savannas sounds incoherent or contradictory; swamps and flooding have almost nothing in common with savannas and fire. But this is the particularity of the Okavango Delta region, showing a strong heterogeneity, as it consists not only of swamps, but also of numerous dry areas which are strongly influenced by savanna vegetation of the embracing Kalahari Desert (fig. 1 and 2 (chapter A); fig. 18). Hence many of the ecological factors controlling the savannas are also concerning the Okavango Delta wetland. And, however, looking at its geographic location on biome level, it is situated in southern African savannas, and it is thus just a question of scale, whether the Okavango Delta region is treated as a single wetland ecosystem or as part of southern African savannas.

The following sections devote to the latter, of- fering an overview about the more general e- cological frame of the Okavango Delta in contrast to the detailed ecological descriptions in the previous chapter A. Firstly, a characteri- sation of arid savannas in southern Africa is presented, with definitions, regional boundaries and explanations to tree-grass interactions, which determine the typical savanna appearan- ce, providing an impression of this vegetation type (chapter B 2 - savanna vegetation). Se- condly, because of the main focus of fire in this paper, general parameters of fire description and explanations to fire occurrences are B 1 FIRE AND SAVANNAS - INTRODUCTION 48

presented, to show in which different ways fire can behave and affect the vegetation in arid savannas (chapter B 3 - fire in savannas). Thirdly, some responses of vegetation to fire are presented, i.e. adaptations to certain fire regimes, advantages of different strategies and characteristics of fire-prone vegetation types are discussed (chapter B 4 - fire and vegetation responses). These chapters present an overview about the recent status of knowledge concerning the effects of fire on vegetation and savanna dynamics in general. But this knowledge is still far from comprehensive: “There is a need for more research into the effects of various aspects of patch and fire variables on biotic diversity, especially in savannas where our understanding is particularly poor.” (Parr & Brockett 1999: 117) Hence, many of the phenomena treated in the following can just be handled hypothetically or are based on single observations and thus, they can often just be described but not explained. But however, this raises and leaves lots of questions and should encourage for further research on this topic as demanded by Parr & Brockett (1999). INHALT / CONTENTS VI

please use seperate link for more details on part B!

(english version)

B Fire and its effects on vegetation in southern African savannas 47

1 Introduction 47

2 The ecology of semi-arid savanna vegetation in southern Africa 49 2.1 Describing ‘savannas’ 49 2.2 The coexistence of trees and grasses in savannas 51 2.3 Savanna dynamics 54

3 Fire in southern African savannas 57 3.1 Drought, fuel and ignition as prerequisites for fire 57 3.2 The fire behaviour 60 3.3 The fire regime in southern African savannas 62

4 Fire and vegetation responses 66 4.1 Plant responses for surviving fires 66 4.2 Plant responses to the post-fire conditions 69 4.3 Single fire related phenomena on the community-level 71

5 Summary 76

Plate 5 - 8 79

C 1 STUDIES ON THE EFFECTS OF FIRE - INTRODUCTION 80

C Studies on the effects of fire on vegetation diversity in the Okavango Delta, Botswana

1 Introduction

This chapter describes and discusses methods, experiences and results of a four-week field study about the effects of fire on vegetation in the Okavango Delta, Botswana in March and April 2001. Burned and unburned sites of the fire season 2000/2001 have been selected by using remote sensing data (LANDSAT TM) and comparative investigations on vegetation diversity were carried out on these sites. For the author, it was the first stay in the Okavango Delta and in general in those lati- tudes during the vegetation period, so no practical knowledge about plant species and vegetation had been experienced for this region be- fore. Therefore, the main goals of the investigation besides the collection and interpretation of the field-data, was to get experiences about the field-work in the Okavango Delta in general and to validate the used techniques. As one will see, established theories and methods derived from European vegetation types could not be easily transferred to semi-arid savannas and logistic problems, like for example accessibility of the sites, determined the site selection often more than scientific criteria. These factors definitely relativize the quality of the field-data and have to be kept in mind constantly at their interpretation. But as this study should lead to further investigations and research projects, these experiences about limitations of methods and field-work are own important results. They are therefore described more precisely than usual in reports and can so be helpful to im- prove future projects.

The following section C 2 describes the general study area and provides a brief description of the Okavango Delta in terms of location, ecology and land-use; once more, because of the missing translation of chapter A. Chapter C 3 describes the used field-methods, i.e. the pa- C 1 STUDIES ON THE EFFECTS OF FIRE - INTRODUCTION 81

rameters measured (chapter C 3.3), but also the site selection by using remote sensing data (chapter C 3.1) and the plant functional type approach used for the vegetation surveys (C 3.2). Critical remarks on the methods are immediately added to each topic, in order to avoid repetitions in a separate discussion of these methods. The evaluation of the data and the interpretation of the derived results is presented in chapter C 4. In the final discussion (chapter C 5) the overall results are recapitulated and deficits of the study are shown. Chapter C 6 presents the conclusion and future prospects. INHALT / CONTENTS VI

please use seperate link for more details on part C!

(english version)

C Studies on the effects of fire on vegetation diversity in the Okavango Delta, Botswana 80

1 Introduction 80

2 The study area ‘Okavango Delta’ 82 2.1 Location and ecology 82 2.2 Conservation areas and land-use management of the Okavango Delta 83 2.3 The fire-use in the Okavango Delta region 85

4 Results and discussion of the field survey 106 4.1 The preparatory work for evaluating PFTs 106 4.2 The results of multivariate analyses 107 4.3 The interpretation of linear correlation 109

5 The discussion of the applied approaches 118 5.1 The selection and the quality of the study sites 118 5.2 The application of the PFT approach 119 5.3 The investigation of the study sites 121

6 Conclusion and future prospects 123

Plate 9 - 12 125

ACKNOWLEDGMENTS 126

Acknowledgements

The present study described in almost all chapters a lack of knowledge , of data and of research on fire in southern African savannas. This situation is probably not due to deficits in willing researchers or missing questions. Especially for ecological research, money is often the limiting factor, as long-term studies are required and no obvious short-term economic profit can be expected. Therefore, the primary thanks go to the ‘Stifterverband für die Deutsche Wissenschaft’, who funded this project unbureaucratically and offered the author an impressive first step not only to the Okavango Delta, but also to the international family of ecological researchers. The best was done to appreciate this support.

But research projects run not only because of money. Especially studies in foreign countries or even in foreign continents require a perfect co-operation with the partner institutes there. The Harry Oppenheimer Okavango Research Centre in Maun offered perfect conditions for the supposed research and supported the study not only by their knowledge about the Okavango Delta and their supply of equipment, but also by their great interest to the present study. Special thanks for the support go to Prof. Lars Ramberg, director of the HOORC, Prof. Susan Ringrose, for assistance especially on GIS and satellite imagery and to Dr. Elmar Veenendaal, the primary collaborator of this project in Maun.

Ecological research requires environmental baseline data for interpretation of e.g. vegetation responses to certain site conditions. These data are often just available at institutes or the authorities. Special thanks go therefore to the following contributors, who offered us help, data and experiences unbureaucratically:

• Sehenyi Tlotlepo (Conservation International, Maun) • Daniel E.C. Mughogho, Mr. Ntshebe, D.L. Sebotho (Department of Wildlife and National Parks, Maun) • Dr. Motshegwa (Department of Animal Health & Production, Maun) • G. Maposa (Agricultural Resource Board, Maun) • Ms. G.K. Ramothwa, Issac Kusane, Alfred Lefaphane, F. Modimoopelo (Depart- ment of Meteorological Services, Gaborone) • Ms. Nametso Monametsi (Department of Wildlife and National Parks) • David M.B. Stimela (Ministry of Agriculture, Gaborone) • Lennard Matlhodi (Ministry of Agriculture, Gaborone) • Malcolm K. Marks, (BRIMP; Ministry of Commerce and Industry) • Dipholo K. Dipholo, David Mmui (Ministry of Agriculture, Gaborone)

Special thanks go also to Thomas Gumbricht for the flooding data, derived from AVHRR satellite images and to Fred Ellery for providing the publications of the Okavango Research Group at the University of the Witwatersrand, Johannesburg and for sharing his experience on the Okavango Delta. Thanks also to Bob Swamp and Christelle Hely (both University of Virginia) for their support on fire research. ACKNOWLEDGMENTS 127

Although many weeks could be fortunately spent in the Okavango Delta, most work on this project was done at the Chair of Vegetation Science in Freising- Weihenstephan of the Technische Universität München. Thanks to all colleagues for scientific discussions on the PFT approach and savanna ecology. Special thanks go to Prof. Jörg Pfadenhauer and Prof. Wolfgang Haber, who supported this project from the very beginning by their knowledge and experience. Thank you also for your supporting letters of recommendation for the application of the PhD-project.

Finally there are two people, who accompanied me permanently through the whole study, and who deserve special consideration, as their efforts on this study were a main reason for its success. On the one hand, there is Budzanani Tacheba, the main research-collaborator from the HOORC, who worked on a parallel study on fire concerning species diversity in the Okavango Delta. His knowledge of the local ecology and plant species was a great help for the study and his experience in the local way-of-life gave me more as just an ecological impression of the Okavango Delta. He had the nerves to stay all days with me in the field, join me at the surveys and protect me from wild bufalloes and elephants, also on ‘Lariam-Days’. I guess, this collaboration became more than a pure scientific relation and this is probably what keeps this project on running. On the other hand, there is Dr. Jan Sliva, the supervisor, who initiated this project together with Dr. Elmar Veenendaal (HOORC). He offered me this chance to get in touch with research on the international level and to go to Botswana and see the Okavango Delta, which became one of my greatest experience in my life. It would be exhausting to stress all the details he initiated, organised and discussed for this project. All the methods, the approaches and the results of the present study were developed with his help and base on numerous debates. I think, here also more than just a pure scientific relation developed during the last months of collaboration and I am really looking forward for the expected joint project in the Okavango Delta region. REFERENCES 128

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