Diversity and Structure of a Bird Community in a Logged Forest in South-East Côte D'ivoire
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Diversity and structure of a bird community in a logged forest in south-east Côte d’Ivoire Dissertation zur Erlangung des Doktorgrades der Mathematisch-Naturwissenschaftlichen Fakultäten der Georg-August-Universität zu Göttingen vorgelegt von Dipl. Biol. Matthias Waltert aus Tauberbischofsheim Göttingen 2000 D7 Referent: Prof. Dr. M. Mühlenberg Korreferent: Prof. Dr. R. Willmann Tag der mündlichen Püfung: 27.04.2000 Foreword Tropical rain forests constitute the most species-rich and ecologically complex terrestrial communities on earth. However, processes such as land conversion for agriculture, logging for timber or poaching put high pressures on tropical forests world-wide. Ecological changes at the turn of the 20th century were and continue to be so massive and rapid that biological science will not be able to assess even basic characteristics of forest ecosystems before their majority is lost. Hence, one of the most challenging tasks of tropical biology is to describe biodiversity in unmodified systems, where ecological processes relevant to the origin and maintenance of biodiversity are studied. In contrast, only few attention has been paid to the description of community patterns in faunas and floras already altered by man or presently subject to disturbance. However, human impact studies in tropical forests do and will play a very important role as most tropical forests can only persist as production forests (see Parren & de Graaf 1995). Questions concerning ecologically sound management plans cannot be answered without proper assessment in managed forest areas. Most studies on the alteration of forest fauna and flora due to fragmentation or timber exploitation are short-term approaches and are complicated by the fact that fragmentation, isolation or degradation processes often interconnect. Observed patterns often result from more than one process, making an analytical approach and the understanding of human impact more difficult (Crome 1997). Furthermore, as deforestation in the tropics is a very recent and still ongoing process, the dimension of fragmentation or habitat degradation effects will only be noticeable in the future, especially in longer-living organisms such as trees or vertebrates (Brooks & Balmford 1996, Brooks et al. 1999). Whereas wildlife biologists spent much time with difficulties of impact assessments in forest ecosystems, forest managers and economists could relatively easy claim sustainability for their operations. In contrast to biologists, they can more quickly present data, e.g. on the recruitment of commercial timber species (see discussion in Struhsaker 1997). Only in the last years and with the help of long-term research, biologists could document the adverse effects of disturbing processes such as habitat degradation or fragmentation on the forest fauna (e.g. Laurance & Bierregaard 1997, Struhsaker 1997). However, the ecology of tropical secondary forests is still far from being understood. Further research on ecologically sound management techniques and the appropriate size of managed forest areas is urgently needed. The establishment of forest reserves and management plans combining economy and ecology is often the only adequate strategy for developing countries to preserve a considerable proportion of their rainforest biodiversity. Economically inefficient reserves are not at all protected against irreversible land conversion, and are often rapidly cleared for other crops, e.g. cocoa and coffee. Acknowledgements The Kreditanstalt für Wiederaufbau (KfW) and the Gesellschaft für Technische Zusammenarbeit (GTZ) supported this project. I am especially grateful to Dr. H.J. Wöll, Dr. W.E. Waitkuwait, Dr. H. Fickinger (all GTZ), Mr. J.C. E. Anoh, Mr. Gbanzai, Mr. Bamba Singo, Mr. N’Dri Pascale and Mr. Aze N’Da (all SODEFOR). I am also grateful to the GTZ- team in Abidjan, especially Helga and Mamadou. Special thanks go to my supervisors Prof. Dr. M. Mühlenberg, Dr. J. Slowik and Dr. M. Louette, who appreciated and supported my work from the beginning. Also, I’d like to thank Prof. Dr. Mühlenberg and Dr. B. Steinhauer-Burkart for enabling visits to other parts of West Africa. During fieldwork, I particularly learned from the mist-netting skills of Mr. W. Jetz. Dr.Ugo Dall’Asta, Mr. Fane Adama, Mr. Aka Kouadio, Mr. Yaokokoré-Beibro K. Hilaire, Mr. Kouablan Tanoh, Mr. Djame Tanoh , Francis, D. Unger and H. Fermon also helped in many ways. For invaluable assistance with field identification I thank Dr. M. Louette (Royal Museum for Central Africa, Tervuren), Dr. C. Chappuis (La Bouille), Dr. L.D.C. Fishpool (Birdlife International, Cambridge) and Mr. R Demey (Den Haag). I also thank Dr. J.-M. Thiollay (Paris) and Dr. L.D.C. Fishpool for refereeing check-lists. For discussions, I thank Dr. M. Louette, Dr. U. Dall’Asta, Dr. R. Jocqué (all Tervuren), Dr. C. Chatelain (Genf), Dr. J. Fjeldså (Copenhagen), D. Nett (Hamburg), K. Barnes (Cape Town), Dr. L.H. Holbech (Accra), Dr. E. Gottschalk (Göttingen) and H. Fermon. I am also very grateful for the friendship and hospitality of Ekki and Solange in Abengourou. Special thanks for assistance in Appouesso to Beibro, Odile, Yvonne†, Ugo and Karim. My thanks also to the team of the Zentrum für Naturschutz: Prof. Dr. M. Mühlenberg, Dr. J. Slowik, Dr. E. Gottschalk, H. Hondong, M. Deseniß, S. Thies, P. Melchert and E. Opielka. Thanks to my parents Bruno and Vroni and also to Moe en Va for the wonderful times whenever we were togeher in Königheim or Aalst. The most special thank you goes to Heleen who read and corrected manuscripts and reports, prepared spot maps and vegetation data. Thank you for taking over organisation during my absences and while I wrote this thesis. Contents Foreword Acknowledgements 1. Introduction......................................................................................................................1 2. Background.......................................................................................................................3 2.1 Notes on species richness, endemism and ecology of the Upper Guinean forest avifauna...........................................................................................................................3 2.2 Status of Upper Guinean forests and possible threats to the avifauna ...................5 3. Objectives and hypotheses ...............................................................................................8 4. Study area.......................................................................................................................11 4.1 Geology, climate and soils.......................................................................................13 4.2 Vegetation, logging history and mammal fauna ....................................................15 4.3 Seasonality of insect abundance .............................................................................16 4.4 Management plan, silvicultural practices and biomonitoring...............................18 4.5 Study plot ................................................................................................................18 5. Methods ..........................................................................................................................21 5.1 Analysis of the vegetation structure .......................................................................21 5.2 Ornithological fieldwork .........................................................................................22 5.2.1 Preliminary surveys.........................................................................................22 5.2.2 Standardised mist-netting ...............................................................................22 5.2.3 Spot-mapping.................................................................................................25 5.3 Calculation methods and statistics .........................................................................26 5.3.1 Abundance .....................................................................................................26 5.3.2 Calculation of community parameters .............................................................27 6. Results.............................................................................................................................33 6.1 Vegetation structure of the Forêt Classée...............................................................33 6.2 Vegetation structure of the study plot: management effects .................................33 6.3 Avifauna of the region.............................................................................................36 6.3.1 General composition.......................................................................................36 6.3.2 Comparison of the Bossematié area with the Taï region..................................36 6.3.3 Comparison of the Bossematié Forest with Bia National Park.........................37 6.3.4 D-Diversity of understorey birds in the Bossematié and other forests...............38 6.3.5 The Bossematié forest compared to the surrounding area................................39 6.4 Avifauna of the study plot.......................................................................................40 6.4.1 Species richness and diversity.........................................................................40 6.4.2 Density patterns..............................................................................................42 6.4.2.1 Density and weight..............................................................................43