INTERUNIVERSITY I C E PROGRAMME IN PHYSICAL LAND RESOURCES Ghent University Vrije Universiteit Brussel Belgium Relating tree growth to climate using tree ring analysis for the Congo basin forest Promoters : Master dissertation submitted in Dr. ir. Hans Verbeeck partial fulfillment of the requirements Prof. dr. ir. Kathy Steppe for the degree of Master of Science in Physical Land Resources Tutors : ir. Marjolein De Weirdt by Promise Simwinde Muleya Dr. ir. Hans Beeckman (Zimbabwe) Academic Year 2011-2012 Copyright This is an unpublished M.Sc dissertation and is not prepared for further distribution. The author and the promoter give the permission to use this Master dissertation for consultation and to copy parts of it for personal use. Every other use is subject to the copyright laws, more specifically the source must be extensively specified when using results from this Master dissertation. Gent, The Promoter(s), The Author, Dr. ir. H. Verbeeck (LA09) Prof. dr. ir. K. Steppe (LA09) Promise Simwinde Muleya Tutor: ir.Marjolein De Weirdt Dr. ir. Hans Beeckman i Acknowledgements I express my sincere and profound gratitude to all the people that helped me in this work. To my committed and kind tutor, ir. Marjolein De Weirdt, thank you a million times. Your patience, strength and encouragement will forever be the etched in my memories for as long as l live. Your tireless work and corrections made this thesis a success. To my promoter, Hans Verbeeck. It all started in the course of Meteorology and Climatology when l heard about climate reconstruction and the tiny seed of passion and interest in the subject grew. Thank you so very much for your comments and pointers. Your guidance has made me the richer. To Prof. Dr. ir. Kathy Steppe, thank you for affording me the opportunity to do this thesis in the lab of Plant Ecology, l must say, I am more ecological in my thinking now. To Dr. Hans Beeckman, thank you for introducing me to the world of wood! Never did it dawn upon me all those years growing up in rural Africa that a simple piece of wood could be a great archive and library of information. Thank you so very much. To ir. Maaike, thank you very much for your immense contribution to this work and the sacrifice of your time. You clarified the analysis with the wisdom of a seasoned dendrochronologist! To all the people at Tervuren, the likes of Lore, Sarah, Jöelle and many more, thank you very much. To all my classmates and friends in the Master of Physical Land Resources, you were a great company and will keep the memories alive. I would also like to extend heartfelt thanks to the VLIR UOS program for the financial assistance. And lastly Bedankt voor alles, merci, Belgium! ii Abstract Climate change is a real challenge that humankind has to face head on in order to prepare beforehand for many major effects that are yet to be fully known and understood. Rising global temperatures is expected to have an impact to our atmosphere and ocean circulation trends and hence rainfall patterns. Future scenarios predict marked precipitation decrease during the rainy season and also the annual precipitation totals. Forest ecosystems act as the key sources for sequestering carbon and also contain vast amounts of biodiversity. However the general lack of reliable data on the carbon stocks in Congo basin and the knowledge on how these forest ecosystems will respond to changing environmental factors still remain largely unknown and segregated. Tree ring analyses were carried out on 20 Pericopsis elata stems discs from Biaro, DRC at the Laboratory of Wood Biology and Xylarium, Tervuren. Growth was compared to rainfall and the above ground woody biomass from ORCHIDEE. The tree show annual rings marked by variations in vessel distribution and size, repeated pattern of alternating fibre and parenchyma bands, marginal parenchyma bands and density variations all with varying degrees of distinctiveness. Low threshold values were used in this study to improve cross-dating procedure (t ≥ 2 (p < 0.05) and GLK ≥ 50 %.). Incidence of wedging rings and missing rings, unclear distinction of rings in the sapwood and problems with the stitching process of images with Fiji ImageJ were encountered and may have given an underestimation of the actual tree ages. Raw ring counts ranged between 89 to 195 years and showed a relationship with mean annual radial growth. The highest mean annual radial growth of 3.7 mm year-1 was recorded and corresponded to the youngest stem disc (89 years) and lowest radial growth rate was 2.5 mm year -1corresponding to the oldest stem disc. The tree width index which formed a chronology (1912 to 2003) showed a marginal correlation with annual rainfall (r = 0.11). There was a significant correlation (r = 0.29; P < 0.01) between the ring width chronology and the previous rainfall sums of September and October. Comparison of the ring width index to the AGWB did not show explicit correlation (r = 0.08) but some synchronous peaks were observed. Pericopsis elata shows potential for dendrochronological analysis. More research can be done in relation to AGWB ORCHIDEE for longer time series. iii Table of Contents Copyright .................................................................................................................................... i Acknowledgements .................................................................................................................... ii Abstract .................................................................................................................................... iii Table of Contents ...................................................................................................................... iv List of figures ............................................................................................................................ vi List of tables ........................................................................................................................... viii List of abbreviations ................................................................................................................. ix 1 Introduction ............................................................................................................................. 1 2 Literature review ..................................................................................................................... 3 2.1 Tropical rainforests .......................................................................................................... 3 2.1.1 A general view .......................................................................................................... 3 2.1.2 The Congo Basin ....................................................................................................... 4 2.1.3 Pericopsis elata ......................................................................................................... 6 2.2. Global carbon dynamics ................................................................................................. 6 2.2.1 Carbon cycle ............................................................................................................. 6 2.2.2 Carbon stocks in tropical rainforest .......................................................................... 7 2.3 Tree growth ...................................................................................................................... 8 2.3.1 Wood anatomical features ......................................................................................... 8 2.3.2. Tree rings ................................................................................................................. 8 2.3.3. Factors influencing tree ring growth ........................................................................ 9 2.3.4 Dendrochronology: an overview ............................................................................. 10 2.3.5 Dendrochronology in the tropical areas .................................................................. 11 2.3.6 Development of tropical ring chronologies ............................................................ 12 2.3.7 Wedging rings ......................................................................................................... 12 2.3.8 Relationship between tree growth and rainfall ....................................................... 14 3 Material and methods ............................................................................................................ 16 3.1 Study site ........................................................................................................................ 16 3.2 Data collection ............................................................................................................... 17 3.2.1 Sampling and preparation of samples ..................................................................... 17 3.3.2. Tree Ring imaging ................................................................................................. 19 3.3.3 Stitching the images using Fiji ImageJ ................................................................... 19 3.3.4 Measurement of ring width ..................................................................................... 20 iv 3.4 Data treatment and analysis ........................................................................................... 20 3.4.1 Climatic effects analysis on radial tree growth ....................................................... 21 3.4.2 Average