ECO-PHYSIOLOGICAL STUDIES OF FACTORS DETERMINING THE DISTRIBUTION OF SUBALPINE EUCALYPTS AT SNUG PLAINS, SOUTHERN TASMANIA by Neil Jeremy Davidson A thesis submitted for the degree of Doctor of Philosophy in the University of Tasmania 1985 ( i ) CONTENTS Declaration (v) Acknowledgements (vi) Abstract 1 CHAPTER 1 - Introduction and Study Site Introduction 4 The Study Area 7 CHAPTER 2 - The Species Studied and Hybridisation Introduction 11 1. The Species Studied 11 2. Hybridisation Studies 15 Materials and Methods 15 Results 22 Discussion 28 Conclusion 35 CHAPTER 3 -Seedling Transplant Trials Introduction 36 Materials and Methods 38 1. Experimental Gardens 38 2. Meteorological Records 42 3. Soils 44 Results 44 Discussion 54 ( i i ) CHAPTER 4 - Frost Introduction 61 Materials and Methods 62 1. Temperature Records 62 2. Frost Damage to Natural Eucalypt Stands 64 3. Seedling Transplant Trials 66 4. Frost Chamber Trials 68 Results 71 1. Temperature Records 71 2. Frost Damage to Natural Eucalypt Stands 78 3. Frost Damage to Field Transplant Trials 85 4. Frost Chamber Trials 92 Discussion 97 CHAPTER 5- Waterlogging Introduction 104 Materials and Methods 105 1. Field Studies of Moisture Status 105 2. Field Transplant Trials 107 3. Glasshouse Waterlogging Trials 108 4. Glasshouse Nutrient-Waterlogging Trials 110 Results 111 1. Field Studies of Moisture Status 111 2. Field Transplant Trials 114 3. Glasshouse Waterlogging Trials 117 4. Glasshouse Nutrient-Waterlogging Trials 127 Discussion 130 ( i i i ) CHAPTER 6 - Drought Introduction 135 Materials and Methods 136 1. Preliminary Drought Trials 136 2. Field Studies 140 (a) Soils 140 (b) Stands Studied 143 (c) Plant Water Relations and Drought Damage 146 3. Seedling Root Pattern 151 4. Competition Trials 153 Results 157 1. Preliminary Drought Trials 157 2. Field Studies 164 (a) Soils 164 (b) Plant Water Relations 175 (i) During Drought 175 (ii) After Rains 185 (iii) Crown Damage and Recovery 190 3. Seedling Root Pattern 200 4. Competition Trials 200 Discussion 211 CHAPTER 7 - Conclusion 221 Bibliography 230 Appendices: Appendix 3.1 Height, Leaf Area and Stem Basal Area 274 Records Appendix 4.1 Literature Review: Frost Acclimation and 293 Freezing Injury ( i v) Appendices: (cont'd) Appendix 4.2 Temperature Records from Four Tasmanian 299 Weather Stations Appendix 4.3 Analyses of Variance 304 Appendix 5.1 Literature Review: The Effects of 308 Waterlogging Appendix 5.2 P.F. Curves 311 Appendix 6.1 Literature Review: Plant Water Relations 314 Appendix 6.2 P.F. Curves 321 ( v) DECLARATION Except as stated, herein, this thesis contains no material which has been accepted for the award of any degree or diploma in any university and to the best of my knowledge and belief, the thesis contains no copy or paraphrase of material previously published or written by another person, except where due reference is made in the text of the thesis. N.J. DAVIDSON (vi) ACKNOWLEDGEMENTS I would like to thank: Dr J.B. Reid, my supervisor, for his friendship, encouragement and criticism during the process of this project; Professor W.O. Jackson for the inspiration he engendered in the field of eucalypt ecology; and fellow students Dr Brad Potts, Dr Peter Minchin and John Davies for their lively and amusing company and discussions during this study. In particular, I would like to thank Brad Potts for his advice and assistance with statistical analyses. I am also indebted to the workshop and glasshouse staff, particularly Leigh Johnson and Charlie Pearson, who worked unerringly to assist in this project; and the friends and family wh? braved cold winters and long summers' days during dawn to dusk readings, to assist in field studies. My thanks to my two diligent proof readers Dr W.A. Loneragan and Sandra Davidson and dedicated typists May Lan Lee and Dawn Coelho. ABSTRACT An examination was made of the ecological factors causing the changes in dominance between six eucalypt species; E. delegatensis, E. coccifera and E. pulchella (subgenus Monocalyptus); and E. gunnii, E. unigera and E. johnstonii (subgenus Symphyomyrtus) which formed a mosaic within and surrounding a shallow depression on a subalpine plateau (approximately 600 m in altitude) at Snug Plains, southern Tasmania. The populations of the six species at the 1 square kilometre study area were in most cases lower altitude ecotypes of subalpine species. However, morphometric studies of foliar samples from field trees and glasshouse grown seedlings of the one lowland species, E. pulchella, suggested that the Snug Plains E. pulchella population was of hybrid origin ("phantom hybrid") with E. coccifera and E. pulchella as the putative parents. Reciprocal transplant trials established in six locations in the field at Snug Plains demonstrated that the key factors influencing seedling survival in the low lying sites were: severity of frost, waterlogging and phytophagous insect attack. Differences in soil nutrition and texture had little influence on seedling growth and seedlings in elevated, well drained sites grew rapidly. There was also a strong tendency in the field transplant trials for the species naturally dominant at the site to become dominant or show greatest growth on a relative basis at its site of origin. A record frost, with an absolute minimum temperature of -22°C at the radiating surface, was recorded at Snug Plains in June 1982. Temperature measurements made in a transect across the study area indicated a marked vertical stratification of the air body occurred (up to 9°C/m) and a steep gradient in minimum temperature (7 .3°C over 200 m) was established between the base of the depression and the ridge top. The natural distributions of the six species studied were closely related to the minimum temperature recorded. Frost damage incurred by mixed pole stands on the margins of the. depressions was, in places, severe. Interspecific differences in frost hardiness were in the order (from greatest to least): E. gunnii > E. coccifera > E. johnstonii > f.: d~legatensis > E. pulchella. The severe frosts caused marked changes in dominance in mixed stands, even though they resulted in few deaths. Exceptional frosts like those of June 1982 may have an important effect on the distributions of subalpine eucalypts. In the reciprocal transplant trials, growing season frosts of -.5.5°C inflicted severe damage on the unhardened seedlings of all species except ~nnii, which exhibited outstanding frost resistance in the unhardened state. Winter frost of -10.5°C caused markedly less damage which 2 suggests that growing season frosts may play an important role in determining the distribution of subalpine eucalypts. Frost chamber experiments confirmed the importance of hardening pretreatment on relative frost resistance of the species studied, and demonstrated a significant interactive effect of waterlogging on frost resistance. The Monocalyetus species were more susceptible to frost in waterlogged soils, whereas no such relationship existed for the .sxmphyomyrtus species. Damage inflicted on seedlings in the transplant trials during a frost free period when waterlogged conditions prevailed, indicated that the sxmphxomyrtus species E. gunnii, E. urnigera and E. johnstonii were more waterlogging tolerant than the Monocalxptus species E. pulchella, E. coccifera and E. delegatensis. This was confirmed. by glasshouse based trials which showed marked differences existed between the subgenera in tolerance to waterlogging. After 30 days of waterlogging the sxmehxomyrtus species had significantly higher midday stomatal conductances and water potentials than the Monocalxpt~? species. Further, Sxmphxomyrtus species exhibited stem hypertrophy and developed extensive, aerenchymatous, adventitious root systems. The Monocalxptus species demonstrated no such morphological adaptations. The results suggest that the Monocalyetus species will be absent from waterlogged sites, which agrees with the distributions of the species and measurements of soil moisture-status in the field. Phytophagous insect attack which affected 3 transplant trials caused severe damage to E. gunnii, E. urnigera and E. johnstonii seedlings (up to 75% leaf' loss) but only slight damage to E. delegatensis, and E. pulchella (up to 10% leaf loss). This suggests that selective insect grazing may have an important effect on the dominance patterns in regenerating mixed eucalypt stands at Snug Plains. Glasshouse based drought trials suggested differences in drought resistance existed between the subgenera. The Monocalyptus species maintained higher relative water contents (R.W.C.) at low water potentials than the Symphyomyrtus species. Therefore, low tolerance to drought might b.e an important factor in explaining the absence of sxmphyomyrtus species from the ridge tops at Snug Plains. During the 1982-83 summer season south-eastern Tasmania was exposed to a drought of near record severity. As the drought developed dawn to dusk measurements of stomatal conductance and water potentials made in a mixed stand of the three Monocaly:ptus species on a ridge top at Snug Plains showed these species differed only slightly in water potential 3 down to -4.3 MPa. The leaf water potentials of all species reflected the soil water potential. However, measurements of R. W.C. demonstrated that E. 2_ulchella maintained a higher R.W.C. (61%) than either E. coccifera (55%) or E. delegatensis (48%) at these low water potentials. E. pulchella also exhibited less crown damage than the other two species during the drought and, after the first