1 High elevation treelines ..................................... 1
1.1 The task ................................................ 1
1.2 Previous works .......................................... 4
2 Definitions and conventions ................................. 11
2.1 The life form 'tree' ................................... 11
2.2 Lines and transitions .................................. 13
2.3 Limitation, stress and disturbance ..................... 15
2.4 Altitude-related and other environmental drivers ....... 16
2.5 Treeline nomenclature .................................. 18
3 Treeline patterns ........................................... 21
3.1 Treeline taxa .......................................... 21
3.2 The summit syndrome and other treeline depressions ..... 23
3.3 Mass elevation effect .................................. 24
3.4 Treeline elevation ..................................... 25
3.5 Time matters ........................................... 29
3.6 Forest structure near treeline ......................... 30
4 Treeline climate ............................................ 33
4.1 Specific aspects of treeline climatology ............... 33
4.2 Criteria to define temperature regimes at treeline ..... 34
4.3 Treeline temperatures in different bioclimatic
regions ................................................ 38
4.3.1 Subarctic and boreal zone (45-68° N) ............ 38
4.3.2 Cool temperate zone (45-47° N, 44° S) ........... 40
4.3.3 Warm temperate zone (28-42° N, 36° S) ........... 43
4.3.4 Subtropical zone (19° S, 19° N) ................. 43
4.3.5 Equatorial tropics (6° N to 3° S) ............... 43
4.3.6 Mediterranean 'treelines' (38-42° N) ............ 44
4.3.7 The Nothofagus and Metrosideros case ............ 46
4.3.8 Treeline temperatures across bioclimatic
zones ........................................... 47
4.4 Seedbed and branch temperatures ........................ 51
4.5 Whole forest temperatures .............................. 55
5 Global mountain statistics based on treeline elevation ...... 57
5.1 Mountain geostatistics ................................. 57
5.2 Elevational belts ...................................... 59
5.3 Global treeline ecotones ............................... 60
6 Structure and stature of treeline trees ..................... 63
6.1 Foliage properties ..................................... 63
6.2 Wood properties ........................................ 70
6.3 Bark properties ........................................ 74
6.4 Root traits ............................................ 75
6.5 Tree stature ........................................... 78
6.6 Dry matter allocation in treeline trees ................ 80
7 Growth and development ...................................... 85
7.1 Tree growth near the treeline .......................... 86
7.1.1 In situ growth of seedlings ..................... 86
7.1.2 In situ growth of saplings and adult trees ...... 88
7.2 Xylogenesis at the treeline ............................ 91
7.2.1 In situ cambial activity ........................ 94
7.2.2 Apical growth dynamics .......................... 97
7.3 Root growth ............................................ 99
7.4 Phenology at the treeline ............................. 101
8 Evolutionary adjustments to life at the treeline ........... 105
8.1 Phylogenetic selection ................................ 105
8.2 Genotypic responses of growth and development ......... 106
8.3 Genotypic responses of physiological traits ........... 110
9 Reproduction, early life stages and tree demography ........ 113
9.1 Amount and quality of seeds at high elevation ......... 113
9.2 Germination, seedling and sapling stage ............... 119
9.3 Tree demography at the treeline ....................... 126
10 Freezing and other forms of stress ......................... 131
10.1 Stress at the treeline in a fitness context ........... 131
10.2 Mechanisms and principles of freezing resistance ...... 132
10.3 Freezing resistance in treeline trees ................. 137
10.4 Other forms of stress at the treeline ................. 145
10.4.1 Freeze-thaw cycles and hydraulic failure ....... 147
10.4.2 Winter desiccation ............................. 148
11 Water, nutrient and carbon relations ....................... 151
11.1 Tree water relations during the growing season ........ 151
11.2 Nutrient relations .................................... 156
11.3 Carbon relations ...................................... 161
12 Treeline formation - currently, in the past and in the
future ..................................................... 169
12.1 Causes of current treelines ........................... 169
12.2 Treelines in the recent past .......................... 175
12.3 Treelines in the distant past (Holocene) .............. 180
12.4 Treelines in the future ............................... 185
References ................................................. 191
Subject Index ................................................. 211
Taxonomic Index ............................................... 219
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