II Light gl 5 A Cont I Terrestri I hid istributi nln ealand University of Canterbury Christchurch A thesis presented in fulfilment for the degree of Doctor ofPhilosophy in Botany By Angela Abernethy 2002 This thesis examines how, and to what extent, do light regimes control the distribution of terrestrial orchids, through field studies of orchid populations under difTerent forest types, manipulated light environment trials, and seasonal studies of orchids growing under different light environments. The significance of understorey light environment as a determining factor on terrestrial orchid occurrence and distribution is examined. A survey is performed over two primary (Nothofagus and Podocarp) and two secondary (Broadleaf and Manuka) forest types at selected South and Stewart Island sites. Hemispherical photography is used to record canopy architecture. Four parameters are used to represent canopy and understorey light characteristics. Broadleaf sites are significantly darker than the other three forest types. Of the 23 orchid species identified at these forest sites, the thirteen most abundant are classified into three categories based on the four light parameters. Pour species are considered to be low-light plants, all of which are of the genus Pterostylis. A further three species are classified as occurring under medium light conditions, with the remaining six species assigned to a high-light group. Light environment is a key factor controlling orchid occurrence under the sampled forests (R2 = 0.37 - 0.74). Even stronger correlations are identified for plant density (R2 = 0.73 - 0.93). The adaptability of Pterostylis banks ii, P. graminea, Thelymitra longifolia and T. pauciflora to different light environments is examined using transplanting trials. Plant occurrence, morphology and physiology is compared under three different light regimes, with comparisons made to the original field populations. P. banksii is able to successfully adapt from the low-light Broadleaf environment to significantly higher enclosure light regimes. T. longifolia specimens are able to successfully adapt to both higher and lower light regimes than the field conditions. These plants also exhibit modified metabolism with leaf efficiency (P",a/Rdark) of T. longifolia enclosure plants significantly lower than field plants. Morphological changes are also evident with the production of multiple replacement tubers in enclosure individuals. Results for P. graminea and T. pauciflora are inconclusive due to high mOltality rates. It is believed that P. graminea is unable to adapt to the significantly higher light conditions, with T. pauciflora intolerant of transplanting. The relationship between understorey light environment and the morphology and phenology of natural populations of P. banks ii, graminea, T. longifolia and T. pauciflora is examined. Dry weight and total non-structural carbohydrate concentrations of organs are recorded over a 12 month period. The two Pterostylis species have a similar phenology and morphology, with biomass and carbohydrate allocation patterns generally following similar trends. Inflorescence production precedes replacement tuber development, suggesting that floral induction is based on cues from the previous season. Replacement tuber development occurs late in the growing season, only two months prior to plant senescence, making November and December key months for carbohydrate acquisition. The two Thelymitra species have similar morphology and phenology, with equivalent biomass and carbohydrate allocation patterns. Photosynthetic characteristics vary significantly with plant age for T. longifolia, but not T. pauciflora. Inflorescence production occurs several months after replacement tuber initiation. The results of this study demonstrate that understorey light environment is a key environmental factor for terrestrial orchids, inducing changes in orchid morphology and physiology. The influence of light regime on orchid occurrence and density is significant, but only fully apparent when understorey conditions are represented using multi-parameter models. Acknowledgements Many people have been involved throughout the course of this thesis. My supervisors, Ashley Sparrow and Matthew Turnbull, I thank you for your expertise, guidance and patience. I would like to thank my grandmother (Bernice) for first introducing me to the 'fairies' (Corybas macranthus) which lived in the bottom of the garden. Also my grandfather (Ken) for allowing 'Kalua' to be sailed down to Stewart Island. My greatest thanks goes to my husband (Tristan) whose love, support and faith in me has never wavered through stressful times. I would also like to thank him for his ability to debug S-plus manuals and cryptic error messages for which I am gratefuL I would also like to thank the departmental technicians, especially Maggie Tish. Finally I would like to thank the inhabitants of our fish tanks for much needed stress relief. This project was supported by a Forest and Bird Society grant, of $1000, awarded in 1997. 1. Introduction ................................................................................................................ 1-1 1.1. Understorey Light Environments ........................................................................ 1-1 1.1.1. Spatial Variation .......................................................................................... 1-1 1.1.2. Temporal Variation ...................................................................................... 1 1.1.3. Spectral Variation ......................................................................................... 1-2 1.2. Light and Species Occurrence ............................................................................. 1-3 1.3. Plant Adaptations to Light Environments ........................................................... 1-3 1.3.1. Morphology .................................................................................................. 1-3 1.3.2. Physiology .................................................................................................... 1-4 1.4. Orchid Research .................................................................................................. 1-4 1.5. New Zealand Orchids .......................................................................................... 1-6 1.6. Rationale and Overview ...................................................................................... 1-7 2. Light Environments of Four New Zealand Forests Types ......................................... 2-1 2.1. Introduction ......................................................................................................... 2-1 2.2. Hemispherical Photographs - Theory .................................................................. 2-3 2.2.1. Estimation of Canopy Characteristics .......................................................... 2-6 2.2.2. Estimation of Understorey Light Environment.. .......................................... 2-9 2.3. Methods ............................................................................................................. 2-12 2.3.1. Study Sites and Sampling ........................................................................... 2-12 2.3.2. Photographs and Image Processing ............................................................ 2-12 2.3.3. Light Analysis Program .............................................................................. 2-13 2.3.4. Data Analysis ............................................................................................. 2-16 2.4. Results ............................................................................................................... 2-16 2.4.1. Observations of Indigenous Forests Types ................................................ 2-16 2.4.2. Forest Canopy Characteristics .................................................................... 2-17 2.4.3. Forest Floor Light Environment. ................................................................ 2-22 2.4.4. Principle Component Analysis of Forest Light Environments .................. 2-25 2.5. Discussion ......................................................................................................... 2-27 2.5.1. Forest Characteristics ................................................................................. 2-27 2.5.2. Successional Changes ................................................................................ 2-29 2.5.3. Heterogeneity ............................................................................................. 2-30 2.5.4. Sunflecks .................................................................................................... 2-30 2.5.5. Identification of 'Key' Parameters ............................................................. 2-3l 2.6. Summary ........................................................................................................... 2-32 3. Light Environments of Forest Orchids ....................................................................... 3-1 3.1. Introduction ......................................................................................................... 3-1 3.2. Methods ............................................................................................................... 3-3 3.2.1. Study Sites and Sampling ............................................................................. 3-3 3.2.2. Photographs and bnage Processing .............................................................