Effects of Bud Demography and Elongation Patterns on Betula Cordifolia Near the Tree Line
1987
Maillette, Lucie
Because plants acquire their structure through the activity of their meristems, whether meristems die, remain dormant, multiply, or develop inflorescences has distinct morphological implications. Studies of bud demography have the potential to explain the form of many temperate—zone trees. In this paper, I present field data collected on tree—line mountain white birches (Betula cordifolia Regel) whose buds were censused over a period of 1—3 yr. Birches ranged in shape from fully erect trees (7—8 m tall) in sheltered forest sites, to low polycormic shrubs (< 1 m tall) in nearby exposed tundra sites. Three questions were asked. (1) Is size merely an expression of age? (2) Is shoot elongation limited by (a) environmental factors, (b) low levels of meristematic activity, or (c) excessive allocation to reproduction? (3) Do bud and branch mortality vary from site to site? If so, is that variation a result of (a) herbivory or (b) climatic factors? Reproduction and browsing were not significant factors contributing to the reduced size of tundra birches. These birches however, did produce smaller long shoots and suffered heavier bud mortality during winter than birches at the other sites, with important year—to—year fluctuations, and thus parts of questions 2a and 3b were answered. After exposure to an extreme winter, most birches can resprout from dormant buds in the root collar area and form polycormic individuals. Both the frequency and severity of winter injury were related to the degree of exposure to the elements, and appear to be key factors in the morphogenesis of tree—line birches.
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