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Accueil du site → Doctorat → États-Unis → 1991 → Factors controlling the elevational positions of pines in the Chiricahua Mountains, Arizona : Drought, competition, and fire

University of Michigan (1991)

Factors controlling the elevational positions of pines in the Chiricahua Mountains, Arizona : Drought, competition, and fire

Barton, Andrew Marder

Titre : Factors controlling the elevational positions of pines in the Chiricahua Mountains, Arizona : Drought, competition, and fire

Auteur : Barton, Andrew Marder

Université de soutenance : University of Michigan

Grade : Doctor of Philosophy (PhD) 1991

Résumé
Recent models suggest that a tradeoff between water and light use results in changes in dominant species over productivity gradients of increasing soil moisture and decreasing light. The hypothesis predicts a negative correlation between drought resistance and shade tolerance and control of more productive limits by competition for light and less productive limits by water stress. With increasing elevation (1568-2296m) in the Chiricahua Mountains, soil moisture increased and light available to seedlings decreased, but fire frequency and litter depth also increased and soil temperature decreased. I tested the tradeoff hypothesis and the role of these three additional factors in controlling upper elevation limits in three pine species distributed along this gradient. Consistent with the tradeoff hypothesis, results suggested that water stress strongly influenced lower elevation limits of all species. Lower species exhibited better survival and CO$\sb2$ uptake than upper species during a greenhouse drought. At low elevation, seedlings occupied field microsites high in soil moisture relative to available microsites. Species differences in lower limits appeared to result from differences in seedling maintenance of water potential during drought. In small-seeded P. leiophylla, reduction of emergence by deep litter in otherwise favorable microsites under vegetation also influenced its lower limit. Inconsistent with the tradeoff hypothesis, upper elevation limits were not controlled uniformly across species by light limitation. The most drought resistant and lowest elevation species, P. discolor, was the most shade tolerant in a greenhouse experiment. Field experiments, age structure, and microsite preferences suggested that light limitation did not control upper limits of this species or P. engelmannii, but was important in P. leiophylla, a fast-growing species with apparent fire-associated regeneration. Instead, mortality from more frequent fires at high elevation probably limited P. discolor, which lacks fire adaptations exhibited by the other two species. This limitation may have resulted, in part, from constraints imposed by drought resistance on maximum growth rate and height. These results suggest that fire, or other agents of selective mortality correlated with productivity, can exert strong control over plant distribution and community composition, and should be incorporated into general models relating plant strategies to community structure.

Mots clés : Biology, Botany, Biology, Ecology, Agriculture, Forestry and Wildlife

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