i Allometry, biomass and litter decomposition of the New Zealand mangrove Avicennia marina var. australasica Phan Tran A thesis submitted to Auckland University of Technology in partial fulfilment of the requirements for the degree of Masters of Science (MSc) 2014 School of Applied Sciences i Table of contents ______________________________________________________________ Table of contents ..................................................................................................................... i List of Figures ....................................................................................................................... iii List of tables .......................................................................................................................... vi Attestation of authorship ...................................................................................................... vii Co-Authored Works ............................................................................................................ viii Acknowledgements ............................................................................................................... ix Abstract .................................................................................................................................. x Chapter 1. Introduction .......................................................................................................... 1 1.1 Mangrove ecosystems ................................................................................................... 2 1.2 Global patterns of mangrove forests ............................................................................. 3 1.3 Mangrove ecosystem services ...................................................................................... 4 1.4 Mangrove carbon studies .............................................................................................. 6 1.5 New Zealand mangroves .............................................................................................. 7 1.6 Research questions:....................................................................................................... 9 1.7 Outline of chapters: ....................................................................................................... 9 Chapter 2. Allometry and biomass allocation ...................................................................... 10 2.1 Introduction ................................................................................................................. 11 2.2 Methods and Materials................................................................................................ 14 Study areas .................................................................................................................... 14 Allometry and Leaf Area Index (LAI) ............................................................................ 15 Above-ground biomass: ................................................................................................. 16 Below-ground biomass .................................................................................................. 19 2.3 Results ......................................................................................................................... 20 Allometry and LAI of mangrove stands ......................................................................... 20 Biomass partitioning ..................................................................................................... 21 Vertical distribution of biomass .................................................................................... 23 2.4 Discussion ................................................................................................................... 24 ii Above-ground biomass .................................................................................................. 24 Belowground biomass ................................................................................................... 26 Allometric equation: ...................................................................................................... 27 Limitations ..................................................................................................................... 28 Chapter 3: Litter production and decomposition .............................................................. 30 3.1 Introduction ................................................................................................................. 31 Litterfall ......................................................................................................................... 31 Litterfall in mangrove forests ........................................................................................ 32 Litter decomposition ...................................................................................................... 33 Mangrove litter decomposition...................................................................................... 33 3.2 Methodology ............................................................................................................... 35 Site selection .................................................................................................................. 35 Litterfall ......................................................................................................................... 35 Decomposition ............................................................................................................... 37 3.3 Results ......................................................................................................................... 37 3.3.1 Litterfall ................................................................................................................ 37 3.3.2 Litter decomposition ............................................................................................. 42 3.4 Discussion ................................................................................................................... 45 Litterfall ......................................................................................................................... 45 Litter decomposition ...................................................................................................... 48 3.5 Conclusions ................................................................................................................. 49 Chapter 4. General discussion and implications for conservation and management ........... 51 4.1 Summary of main results ............................................................................................ 52 Allometry and LAI ......................................................................................................... 52 Biomass distribution ...................................................................................................... 52 Litterfall production ...................................................................................................... 52 Litter decomposition ...................................................................................................... 53 4.2 Conclusions and implication for conservation and management ............................... 53 References ............................................................................................................................ 56 iii List of Figures ______________________________________________________________ Figure 1. Major components of (mangrove) forest carbon pool and its cycle among ecosystems. Figure modified from Bouillon et al.(2008). ....................................... 6 Figure 2. Mangawhai Heads with five study sub-sites of Jack Boyd (JB), Molesworth (MO), Island (IS), Insley (IN) and Black Swamp (BS). ....................................... 15 Figure 3. Basal area against dry wood and leaf mass at Black Swamp, Mangawhai Harbour Estuary. The linear model Y = x * ba was used, with Y the wood / leaf dry weight and ba the basal area. R-squared is 0.94 for both plots. ........................................ 18 Figure 4. Biomass allocation (%) estimated from the mean values of JB and MO sites in Mangawhai Harbour. ............................................................................................. 23 Figure 5. Vertical distribution of biomass estimated for compartments per players on Mangawhai Habour, with mean values and standard errors estimated among the sub-sites of JB, MO, IS and IN for wood and leaf biomass, JB,MO, and IS for pneumatophores and seedling, fine roots biomass and coarse roots under 40cm deep, and JB, MO and BS for coarse roots from 0-40cm deep. ............................ 24 2 Figure 6. Quadratic model Y = x * ba used for the regression of dry wood on basal area, with Y the dry wood mass, ba the basal area. Data from the Black Swamp site at Mangawhai Harbour Estuary. ................................................................................ 27 Figure 7. Basal area against total leaf mass (a) and leaf mass by height (b) at Black Swamp, Mangawhai Harbour Estuary. The linear model Y = x * ba was used, with Y the leaf dry weight and ba the basal area. R-squared is 0.94 for the relationship between ba and total leaf dry weight, and are 0.34, 0.54, 0.52, and 0.79 for the relationship between ba and leaf dry weight at 150-200cm, 200-250cm, 250- 300cm, and 300-350cm respectively. .................................................................... 28 Figure 8. Locations of litter traps and litter bags at JB (a), MO (b), and IS (c) at the Mangawhai Habour study area. ............................................................................. 36 iv -2 -1 Figure 9. Seasonal litter production at Mangawhai Harbour (gm day ), with the mean values for each litter component calculated from thirty traps across all sites. Error bars represent one standard error (n=30). .............................................................. 39 0 Figure 10. Site-specific seasonal litter production and monthly mean temperature ( C) measured at Mangawhai Harbour. Error bars represent the standard errors for the mean values of litter from ten traps (n=10) for each site Jack Boyd (JB), Molesworth (MO) and Island (IS). ........................................................................ 40 -1 Figure 11. Site-specific seasonal litter production and monthly max wind speed (kmh ) measured at Mangawhai Harbour. Error bars represent the standard errors for the mean values of litter from ten traps (n=10) for each site Jack Boyd (JB), Molesworth (MO) and Island (IS). ........................................................................ 41 Figure 12. Site-specific seasonal litter production and monthly total rainfall (mm) measured at Mangawhai Harbour. Error bars represent the standard errors for the mean values of litter from ten traps (n=10) for each site Jack Boyd (JB), Molesworth (MO) and Island (IS). ............................................................................................. 42 Figure 13. Mangrove leaf litter decomposition measured at Mangawhai Harbour, expressed as the percentage of initial dry weight remaining over time. Error bars represent the standard errors for the mean values twelve litter bags (n=10) collected each site Jack Boyd (JB), Molesworth (MO) and Island (IS). .............................................. 43 Figure 14. Asymptotic model fit y = Asym + (R0 - Asym) * exp(-exp(lrc) * x) with y the remaining weight over time), R0 the estimated intercept on the y-axis, Asym the asymptote parallel to the x-axis, and lrc is the estimated logarithm of the rate constant, applied generally for litter decomposition process at Mangawhai Harbour. ................................................................................................................. 44 Figure 15. Asymptotic fit model ysite = Asym + (R0 - Asym) * exp(-exp(lrcsite) * x, with y the the percentage of remaining weight over time, R0 the estimated intercept on the y- axis, Asym the asymptote parallel to the x-axis, and lrc the estimated logarithm of the rate constant applied site-specifically for IS (a), MO (b), and JB (c) at Mangawhai Harbour. ............................................................................................. 45 v -2 -2 -1 Figure 16. Carbon pools (kg C m ) and fluxes (kg C m y ) of A.marina with study results at Mangawhai Harbour ( black text) and assumed figures (red text) based on data from Suwa et al. (2006), Ray et al. (2011), and Alongi (2014). ............................ 54 vi List of tables ______________________________________________________________ Table 1. Traditional uses of mangroves ................................................................................. 5 Table 2. Allometric characteristics of the eleven sample trees at BS .................................. 17 Table 3. R-squared values for linear regressions between basal area and biomass of the individual layers ..................................................................................................... 19 Table 4. Measurement methods (cores/blocks) for below-ground biomass conducted at each sites of Jack Boyd (JB), Molesworth (MO), Island (IS) and Black Swamp (BS) . 20 Table 5. Allometry of Avicennia marina in the study transects at Insley (IN), Island (IS), Jack Boyd (JB) and Molesworth (MO) .................................................................. 21 Table 6. Leaf area index (LAI) and Specific Leaf Area (SLA) for the sites Black Swamp (BS), Island (IS), Jack Boyd (JB) and Molesworth (MO) ..................................... 21 Table 7. Biomass allocation in wood, leaf, roots and pneumatophores and seedlings for the sites Insley (IN), Island (IS), Jack Boyd (JB) and Molesworth (MO) ................... 22 Table 8. Biomass estimation for A. marina in Australia and New Zealand sites ................ 25 -2 Table 9. Total litter fall (gm ) at IS, JB, and MO from April 2013 to March 2014. ........... 38 Table 10. Litterfall production of A. marina presented in order of latitudes ....................... 46 vii Attestation of authorship ______________________________________________________________ “I hereby declare that this submission is my own work and that, to best of my knowledge and belief, contains no material previously published or written by another person (except where explicitly defined in the acknowledgements), nor material which to a substantial extent has been submitted to the award of any other degree or diploma of university or other institution of higher learning.” Signed Date: Aug 22, 2014 viii Co-Authored Works ______________________________________________________________________ The two main chapters of this thesis are in preparation to be submitted to the New Zealand Journal of Marine and Freshwater Research. To this work, although I am the principal author, I have received intellectual contribution from my supervisors through their valuable advice, which can hardly weigh. I identify authorship contribution as 85 % from myself, 10 % from Sebastian Leuzinger (primary supervisor), and 5 % from Andrea Alfaro (secondary supervisor). Signatures: Principal author: Phan Tran Co-Author Sebastian Leuzinger Co-Author Andrea C. Alfaro ix Acknowledgements ______________________________________________________________ I would like to express my deepest gratitude to my primary supervisor, Dr. Sebastian Leuzinger, for giving me the opportunity to complete this thesis. I could hardly have done without his devoted guidance and valuable advice. My sincere thanks are also to my secondary supervisor, Prof. Andrea C. Alfaro and my senior Jarrod Cusens for their helpful comments to make this study much better. I owe the Mangrove research team, especially Iana Gritcan, and other student peers for their dedicated help during my field work, which were highly labour-intensive. I also found myself indebted to the New Zealand Ministry of Foreign Affairs and Trade for their sponsorship for my study with AUT under New Zealand ASEAN Scholars Awards program. It would be difficult for me to finish this study without supports and encouragement from my family and especially my husband, Jobi George, for his sharing of family responsibilities during my academic years. Last but not least, I would like to reserve my thankfulness to AUT Applied Sciences LAB staff for their supports, which is also much important for me to complete my study.