THE DISCRIMINATION OF COTTONWOOD CLONE? IN A MATURE POPULATION ALONG THE OLDMAN RIVER. ALBERTA LORI A. COM (Bachelor of Science, University ot Lethbridge, 1993) A Thesis Submitted to the Council on Graduate Studies of the University of Lethbridge in Partial Fulfilment of the Requirements for the Degree MASTER OF SCIENCE LETHBRIDGE, ALBERTA December, 1996 © Lori A. Gom, 1996 iii ABSTRACT: In the northwestern prairies, the cottonwoods Populus deltoides Bartr., P. balsamifera L., P. angustifolia James, and interspecific hybrids, form the foundation of the riparian forest ecosystem. The present project characterized the phenotype and phenology of each tree in a mature cottonwood grove (N=391) for the purposes of clone-delineation. In order of their utility, tree sex, general leaf-shape, six leaf dimensions, and phenology of flowering, leaf- flushing, senescence, and leaf-abscission were utilized. The population's 391 trunks represented only 115 individuals, 67 of which were clones which ranged from 2 to 58 trunks each. Thus, 88% of all trunks belonged to clones, and this high clonal content reflects the senior age of the population. Clone structure explained the population's apparent spatial-clumping, female- skewed sex ratio, differential spatial distributions of the sexes and species, and complexity in trunk-size classes. Trends suggest that P. balsamifera and P. angustifolia are more strongly clonal than P. deltoides, partially explaining their differences in environmental preferences. The observed extent of asexual regeneration has implications for riparian resource management and analyses of cottonwood reproductive ecology. Lori A. Gom - Cottonwood Clones of the Oldman River Floodplain iv ACKNOWLEDGEMENTS: My sincerest gratitude goes to everyone who has assisted me in this accomplishment. I would especially like to thank Stew for providing me this opportunity, my committee for their expert guidance, and my family for always being there. I would also like to thank my: Field Crew: (who persevered through muck and high water) Jennifer Wilmes Jennifer Ferries Andrea Kalischuck Chris Taboulchanas Mom Gom Brad Gom Technical-Support Crew: (always willing to lend an ear or hand) John Mahoney Karen Zanewich David Pearce Joanne Golden John Bain Andy Hurly Miscellaneous-Support Crews: the U of L Biology Department (for tolerating leaves in the photocopier and mud in the hall) the Single-Scientisf s Club (you know who you are) the River God (for sparing my site) Sid the Cat (for being soft and furry) Lori A. Gom - Cottonwood Clones of the Oldman River Floodplain V TABLE OF CONTENTS: TITLE PAGE i SIGNATURE PAGE ii ABSTRACT iii ACKNOWLEDGEMENTS iv TABLE OF CONTENTS v LIST OF TABLES viii LIST OF FIGURES xii 1.0 INTRODUCTION and LITERATURE REVIEW 1 1.1 Introduction to Riparian Cottonwoods 1 1.1.1 Native species in Canada and Alberta 1 1.1.2 The hybrid swarm in southern Alberta 4 1.13 Importance of the cottonwood forest 5 1.1.4 Present condition 6 Declining forests 6 Causes of forest decline 6 Management strategies 7 1.2 Overview of related research 8 1.2.1 Cottonwood Reproduction 8 Reproductive strategies 8 Seedling-based reproduction in cottonwoods 11 Clone-based reproduction in cottonwoods 12 Sexual vs. asexual replenishment in cottonwood groves 17 Lori A. Gom - Cottonwood Clones of the Oldman River Floodplain vi 1.2.2 Investigating ramet identity 18 Definition of terms 18 Clonal-connections and excavation studies 18 Methods for distinguishing clones from seedlings ... 20 -biochemical & genetic methods 20 -morphological & phenological methods 22 2.0 THE "PROBLEM" 26 2.1 Theoretical Framework of the Study 26 2.1.1 Is there evidence in mature cottonwood forests of asexual recruitment? 26 2.1.2 Delineating mature cottonwood clones using phenotype and proximity? 27 2.1.3 Trends in clonal nature and implications for cottonwood regeneration 27 2.2 Research Design 28 2.2.1 Study site selection 28 2.Z2 Census of phenotype 29 2.2.3 Analysis of similarity among siblings 34 2.2.4 Generating clone-groupings 35 3.0 METHODS 36 3.1 Study Site 36 3.2 Half-siblings 37 3.3 Data Collection 38 3.3.1 Physical observations 38 3.3.2 Morphological characteristics 38 3.3.3 Phenological characteristics 41 3.4 Treatment of the Data 43 Lori A. Gom - Cottonwood Clones of the Oldman River Floodplain vii 4.0 RESULTS AND DISCUSSION 44 4.1 Characteristics of the Population 44 4.1.1 General description 44 Spatial distribution of trunks 44 Trunk circumferences 45 Beaver impacts 52 4.1.2 Directly clonally-conserved characters 57 Tree sex 57 Leaf-shape (species-category) 60 Leaf dimensions 68 Timing of flowering 74 Timing of leaf-flush 78 Timing of leaf-senescence 86 Timing of leaf-drop 92 Occurrence of branch sacrifice 97 4.13 Indirectly clonally-conserved characters 97 Closely spaced trunks 102 Trunk architecture 102 Abundance of mite-galls 106 4.2 Half-Sibling Characteristics Ill 43 Identifying Clones 117 43.1 Constructing groups based on character similarity .... 117 43.2 Addressing the hypotheses 150 4.33 Description of putative clones and implications to population structure 151 4.4 Implications to Cottonwood Regeneration 181 5.0 SUMMARY OF CONCLUSIONS 186 5.1 Summary of conclusions for the hypotheses and queries . 186 5.2 Generalizations, Implications, Recommendations .... 187 LITERATURE CITED 190 Lori A. Gom - Cottonwood Clones of the Oldman River Floodplain LIST OF TABLES: Table 1-1. Comparing sexual (seedling) versus asexual (clonal) reproductive strategies in cottonwoods 9 Table 1-2. Review of publications reporting cottonwood asexual reproduction 14-15 Table 1-3. Characteristics for the field identification of aspen clones (from Barnes 1969) 24 Table 1-4. Characteristics for the field identification of cottonwood clones 25 Table 4-1. Deciding spatial pattern of distribution based on nearest neighbor distances (according to Clark and Evans 1954) . 47 Table 4-2. X2 Test for significance of occurrence of beaver damage in nearest neighbors of beaver damaged trees 54 Table 4-3. F and t-Test for significant difference between mean C.B.H. of beaver-damaged versus undamaged trunks 55 Table 4-4. ANOVA to test significance of difference between the mean C.B.H. from trunks of the three categories of beaver-damage 56 Table 4-5. X2 Tests to decide the population's sex ratio 59 Table 4-6. ANOVA to test significance of difference between the mean C.B.H. of male versus female trunks 61 Table 4-7. F and t-Test for significance of difference between mean distance to the river of male versus female trunks .... 62 Table 4-8. X2 Tests for significance of the occurrence of matching leaf-shape in nearest neighbors 67 Table 4-9. Deciding, based on amount of variation, whether to average the leaf measurements from the three leaves of each tree before or after standardizing 70 Table 4-10. Numbers of trees occurring in each flowering-stage during each observation date for males versus females 76 Lori A. Gom - Cottonwood Clones of the Oldman River Floodplain Table 4-11. X2 Tests for significance of difference between the flowering-stage distributions of males versus females during each observation date 77 Table 4-12. Numbers of trees occurring in each leaf-flushing stage during each observation date for males versus females . S3 Table 4-13. X2 Tests for significance of difference between the leaf-flushing stage distributions of males versus females during each observation date 84 Table 4-14. X2 Test for significance of difference between the occurrences of branch sacrifice in males versus females . 99 Table 4-15. X2 Test for significance of difference between the occurrences of branch sacrifice in the three species-categories 100 Table 4-16. X2 Test for significance of difference between the occurrences of branch sacrifice in the three trunk circumference categories 101 Table 4-17. Summary of the number of trunks belonging to each closely-spaced group 103 Table 4-18. Summary of occurrence of matched sex among the trunks in the closely-spaced groups 103 Table 4-19. Summary of occurrence of matched species-categories among the trunks in the closely-spaced groups 103 Table 4-20. X2 Test for significance of difference between the distributions of trunk architecture in the three species-categories ... 104 Table 4-21. ANOVA to test significance of difference between the means of trunk circumference in the three trunk architecture groups 105 Table 4-22. F and t-Test for significance of difference between the mean gall abundances of male versus female trunks ... 108 Table 4-23. ANOVA to test significance of difference between the means of gall abundance in trunks of the three trunk architecture groups 109 Lori A. Gom - Cottonwood Clones of the Oldman River Floodplain Table 4-24. Summary of groups generated by division according to sex and then leaf-shape category 118 Table 4-25. Characteristics of the hypothesized clone groupings made according to similarity in sex, leaf-shape, and phenology 123-130 Table 4-26. Summary of sex, species-type, and the distances between the ramets, for each hypothesized clone grouping .... 152 Table 4-27. Numbers of clones, ramets, and single trunks summarized according to sex and species-type 157 Table 4-28. F and t-Test for significance of difference in the mean number of ramets between male versus female clones . 158 Table 4-29. ANOVA to test significance of difference between the mean number of ramets per clone for the three species-categories 159 Table 4-30. X2 Test to determine if the ratio of clonal trunks to those occurring singly differs significantly between the sexes . 160 Table 4-31. X2 Test to determine if the ratio of clonal trunks to those occurring singly differs significantly between the species- categories 161 Table 4-32.