The Impacts of Logging on Carbon Stocks, Tree Diversity and Forest
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The impacts of logging on carbon stocks, tree diversity and forest recovery in Vietnam Suzanne Mathilde Stas Submitted in accordance with the requirements for the degree of Doctor of Philosophy The University of Leeds School of Earth and Environment June 2020 The candidate confirms that the work submitted is her own, except where work which has formed part of jointly authored publications has been included. The contribution of the candidate and the other authors to this work has been explicitly indicated below. The candidate confirms that appropriate credit has been given within the thesis where reference has been made to the work of others. Chapter 2 Stas, S.M., Le, T.C., Tran, H.D., Hoang, T.T.H., van Kuijk, M., Le, A.V., Ngo, D.T., van Oostrum, A., Phillips, O.L., Rutishauser, E., Spracklen, B.D., Tran, T.T.A., Le, T.T., Spracklen, D.V. 2020. Logging intensity drives variability in carbon stocks in lowland forests in Vietnam. Forest Ecology and Management 460, 117863. SMS, DVS, OLP, MvK and ER designed the study; SMS, TCL, HDT, TTL and DVS organised and/or conducted the fieldwork; DTN and AVL led the participatory mapping; TTAT and TTHH analysed the soil samples; SMS and AvO wrote the soil laboratory methods; BDS and DVS conducted the satellite analyses; SMS analysed the data, with the help of ER, and wrote the paper. Ngo, D.T., Le, A.V., Le, H.T., Stas, S.M., Le, T.C., Tran, H.D., Pham, T., Le, T.T., Spracklen, B.D., Langan, C., Cuthbert, R., Buermann, W., Phillips, O.L., Jew, E.K.K, Spracklen, D.V. 2020. The potential for REDD+ to reduce forest degradation in Vietnam. Environmental Research Letters 15, 074025. The paper was led by DTN and DVS. SMS provided the results of the forest plots and commented on the draft of the manuscript. II Chapter 3 In preparation. SMS, DVS, OLP, MvK and ER designed the study; SMS, TCL, HDT, TTL and DVS organised and/or conducted the fieldwork; SMS analysed the data, with the help of ER, and wrote the paper. Chapter 4 In preparation. SMS, DVS, OLP, MvK and ER designed the study; SMS, TCL, HDT, TTL and DVS organised and/or conducted the fieldwork; SMS analysed the data and wrote the paper. This copy has been supplied on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. The right of Suzanne Mathilde Stas to be identified as Author of this work has been asserted by her in accordance with the Copyright, Designs and Patents Act 1988. © 2020 The University of Leeds and Suzanne Mathilde Stas III Acknowledgements Looking back, I consider my PhD as a journey where several worlds came together: I worked with many new, inspiring people from the United Kingdom and Vietnam, while at the same time old colleagues from my time in Indonesia, Uganda and the Netherlands joined and helped during my PhD. This resulted in great collaborations with people with various expertise and I am very grateful for all the support I received. I was lucky to have Dominick Spracklen as my main supervisor, who is very approachable, committed and always willing to help. I learnt a lot from his attitude to think in solutions and to focus on the main objectives and I am very grateful for the freedom he gave me to make my own decisions about my research and to collaborate with various researchers. Dominick also visited me every field season in Vietnam, where he joined in measuring banana trees, was attacked by moi and vat and played werewolves with the locals. I was co-supervised by Oliver Phillips, who had always great ideas about alternative ways of analysing, literature suggestions and advices to improve my drafts. Thank you for sharing your knowledge and I really enjoyed the discussions we had with the three of us in Leeds. In Utrecht, I was co-supervised by Marijke van Kuijk, who helped a lot with developing research ideas, giving practical advices for the fieldwork and was always willing to provide feedback on drafts. I thank my “R hero” Ervan Rutishauser, for being “one click away” to solve errors in R, providing insightful literature suggestions and being always willing to help. I am also thankful to my previous supervisors Douglas Sheil and Yves Laumonier, who made me enthusiastic to persue a PhD and continued sharing their expertise and network during my PhD. IV I am very grateful to my “forest guys” Tinh Cong Le and Hieu Dang Tran, who always accompanied me to the forest and continued the fieldwork when I left Vietnam. Thank you for all your hard work and fun in the field. I thank Trai Trong Le, Anh Tuan Pham, Huong Mai Pham and other staff at Viet Nature Conservation Centre for their indispensable help with logistics, research permits and knowledge of the area. My PhD and fieldwork were financially supported by the World Land Trust, the University of Leeds and the Newton Fund Institutional Links programme of the British Council, for which I am very grateful. I sincerely thank Roger Wilson and other staff at World Land Trust for all their support to my PhD and the overall project. I thank Tue Van Ha and Tuan Manh Le for tree species identifications in our plots; Duc Tung Ngo and An Van Le for conducting the participatory mapping at our site; Tuyet Thi Anh Tran and Thi Thai Hoa Hoang for conducting the soil laboratory analyses; and Ben Spracklen for conducting satellite analyses at our project site. I am grateful to Nam Thanh Vu for his help and advice to arrange my fieldwork. I am thankful to Stephan Mantel, Imam Basuki and Yves Laumonier for their help in developing the methods for soil collection. Ad van Oostrum was indispensable for writing the methods for the soil analysis, thanks a lot for all your dedicated work and our nice collaboration. In Leeds, I was part of the Biosphere-Atmosphere group at the School of Earth & Environment and the Ecology and Global Change group at the School of Geography. I am very grateful for all the new friends I made, discussions, joined lunches and pub visits in Leeds: i.a. Bruno Cintra and Karina Melgaço (thanks so much for always offering me a warm home in Leeds and your friendship), Adriane Muelbert, Ana Julia Cabrera Pacheco, Jess Baker, Julia Tavares, Francisco V Diniz, Fernanda Coelho, Cat Scott and Carly Reddington. I thank Wolfgang Buermann for early discussions about my PhD and creating a map of our project site. I sincerely thank all members of the Ecology and Biodiversity group at Utrecht University for their support, shared lunches and coffee breaks, in particular George Kowalchuk for hosting me; Martin Droog for help with R; Rens Vaessen, Joeri Zwerts and Ana Patricia Sandoval for fieldwork discussions; Heinjo During for statistical advice; my office roommates for the nice working atmosphere and the “Dactylis guys” for lunch walks. I thank my dear family, friends and Sydney Sinkamba for all their support and interest during the course of my PhD. Above all, I am very grateful for all the support, trust and love I always receive from my parents Ben and Mariet Stas, my brother Rick Stas and his partner Jill Philipsen. Thank you for standing always by my side and for our memorable trip in Vietnam. I am only able to do this work because I have such a solid base back home. VI Abstract Tropical forests are important carbon (C) sinks and biodiversity hotspots. Yet, forests are seriously threatened by anthropogenic disturbances including logging, which is the main driver of forest degradation in Southeast Asia. Here, I analyse the impacts of logging intensity on C stocks, tree diversity and forest recovery in seasonal evergreen broadleaf lowland forests in north-central Vietnam. I established, measured and after two years re-measured twenty-four plots that vary in historical logging intensity, nine years after logging. Logging intensity, estimated by combining Landsat analysis and participatory mapping, was the main factor explaining the variability in aboveground carbon (AGC). Heavily logged forests stored only half the amount of AGC in stems ≥10 cm diameter as lightly logged forests, mainly due to a reduction in large trees. AGC of small trees, dead wood and belowground C stored small fractions of total C stocks, while the topsoil of 0–30 cm depth stored roughly half of total C stocks. Tree diversity did not differ significantly with logging intensity. Some compositional differences were observed with logging intensity, although the challenge of sampling at the species level sufficiently complicates interpretation. Community wood density decreased with logging intensity and timber species only occurred in small numbers in our plots, especially in the heavily logged sites. Vital rates and associated AGC fluxes did not differ with logging intensity during the two-year period. The forests suffered from typhoon-induced tree mortality and damage, with ~40% of plots experiencing a net annual reduction in AGC. This study shows the critical importance of reducing logging intensities to maintain high forest C stocks and community wood density and to prevent the depletion of timber species. Recent storm impacts retard the post-logging AGC recovery of these forests. VII Table of Contents Acknowledgements……………………………………......…………………………….......IV Abstract…………………………………………………………………………………..…VII Table of Contents………………………………………………………………………….VIII List of Tables……………………………………………………………………....………XIII List of Figures……………………………………………………………………….……..XIV Abbreviations…………………………………………………………………..………….XVI Chapter 1. General introduction ............................................................................................. 1 1.1. Tropical forests and ecosystem services .......................................................................... 1 1.2. Deforestation and forest degradation in Southeast Asia .................................................. 2 1.3. Selective logging and changing local environments ......................................................