A comparison of the stable isotopic ecology of eastern, western, and pre-human forest ecosystems in the South Island of New Zealand A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Environmental Science at the The University of Canterbury By Olivia Rose Johnston University of Canterbury 2014 ii iii Frontispiece Okarito Forest, Westland iv v Contents Acknowledgements.................................................................................................................... vii Abstract ...................................................................................................................................... ix List of figures and tables.............................................................................................................. xi Terminology used ..................................................................................................................... xiv Chapter 1: Introduction ................................................................................................................ 1 1.1 Vegetation history of the South Island ......................................................................................... 1 1.2 Stable isotope concepts and terminology .................................................................................... 3 1.3 C and N stable isotopes as tracers of ecosystem processes ......................................................... 4 1.4 Sources of foliar C stable isotopic variation .................................................................................. 7 1.4.1 Spatial variation ..................................................................................................................... 8 1.4.2 Temporal variation ................................................................................................................. 9 1.4.3 Species variation .................................................................................................................... 9 1.5 Sources of foliar N isotopic variation .......................................................................................... 11 1.5.1 Spatial variation ................................................................................................................... 11 1.5.2 Temporal variation ............................................................................................................... 13 1.5.3 Species variation .................................................................................................................. 13 1.6 Detection of changes in C and N cycling resulting from human activities .................................. 15 1.7 Fossil vegetation stable isotopic analysis.................................................................................... 18 1.8 Using C:N as a probe for N status at different sites .................................................................... 20 1.9 Objectives.................................................................................................................................... 21 Chapter 2: Study forest description ............................................................................................ 23 2.1 Introduction ................................................................................................................................ 23 2.2 West Coast forests ...................................................................................................................... 24 2.2.1 Climate ................................................................................................................................. 24 2.2.2 Geology and soils ................................................................................................................. 25 2.2.3 Vegetation ............................................................................................................................ 26 2.2.4 Saltwater Forest – a West Coast historically logged, disturbed forest. ............................... 27 2.2.5 Okarito Forest ‒ a West Coast unlogged forest, with limited human impacts. ................... 28 2.3 Eastern forests ............................................................................................................................ 29 2.3.1 Climate ................................................................................................................................. 29 2.3.2 Geology and soils ................................................................................................................. 30 2.3.3 Riccarton Bush ‒ an eastern lowland, unlogged, but highly disturbed and isolated forest.32 2.3.4 Pyramid Valley – fossil leaves from an eastern undisturbed, pre-human forest. ............... 34 2.4 Forest selection ........................................................................................................................... 36 Chapter 3: Methods ................................................................................................................... 39 3.1 Field methods ............................................................................................................................. 39 3.2 Mass spectrometer preparation and analysis of leaf stable isotopic composition .................... 43 3.3 Radiocarbon dating ..................................................................................................................... 44 3.4 Scanning electron microscopy .................................................................................................... 44 3.5 Data quality control .................................................................................................................... 45 3.6 Statistical analysis ....................................................................................................................... 47 Chapter 4: Description of leaf composition ................................................................................. 49 vi 4.1 Introduction ................................................................................................................................ 49 4.2 Modern forests ........................................................................................................................... 49 4.2.1 Eastern and western forest comparison .............................................................................. 55 4.2.2 Comparison between the logged Saltwater Forest and the unlogged Okarito forest ......... 56 4.3 North Canterbury fossil forest .................................................................................................... 57 4.3.1 Pyramid Valley foliar stable isotopic description ................................................................. 58 4.3.2 Comparison of fossil vegetation with modern vegetation .................................................. 64 4.4 Measurement uncertainty .......................................................................................................... 64 4.5 Summary ..................................................................................................................................... 68 Chapter 5: Discussion ................................................................................................................. 71 5.1 Introduction ................................................................................................................................ 71 5.2 Foliar δ13C values ......................................................................................................................... 72 5.3 Foliar δ15N ................................................................................................................................... 74 5.4 Foliar C:N ..................................................................................................................................... 76 5.5 Eastern and western forest comparison ..................................................................................... 76 5.5.1 Foliar δ13C in eastern and western forests ........................................................................... 77 5.5.2 Foliar δ15N and C:N in eastern and western forests ............................................................ 78 5.6 Historically-logged forest and unlogged forest comparison ....................................................... 82 5.6.1 δ13C in logged and unlogged forests .................................................................................... 82 5.6.2 Foliar δ15N and C:N in a logged forest versus, unlogged forest ........................................... 84 5.6.3 Species composition ............................................................................................................ 86 5.6.4 Summary of logging impacts to leaf stable isotopic composition ....................................... 87 5.7 Pyramid Valley extinct forest ...................................................................................................... 87 5.7.1 Age of fossil material............................................................................................................ 87 5.7.2 Integrity of fossil leaf stable isotopic composition .............................................................. 88 5.7.3 Comparison of fossil Pyramid Valley with Riccarton Bush vegetation ................................ 93 5.7.4 Summary of fossil data ........................................................................................................