Interspecific variation in the response of growth, crown morphology, and survivorship to light of six tree species in the conifer belt of the Bhutan Himalayas

Authors:
  • GGGeorg Gratzer
    Georg Gratzer
  • PCPurna B Chhetri
    Purna B Chhetri
  • PRPrem Bahadur Rai
    Prem Bahadur Rai
  • OEOtto Eckmüllner
    Otto Eckmüllner
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Abstract
The responses of radial and height growth, plant architecture, and the probability of mortality of saplings to varying light levels were quantified for six tree species in temperate,conifer forests of the Bhutan Himalayas. Increases in growth,with increasing light were comparable,with those of high latitude tree species but lower than those of tropi - cal tree species and temperate,species in North America. The shade-tolerant species Tsuga dumosa,(D. Don.) Eichler showed,the strongest increase in radial growth,at low light and reached asymptotic growth,early. It had the deepest crowns in low light and a low decrease of leader growth with decreasing light. It represents a continuous growth type, which,invests in height rather than lateral growth,under low light conditions. Betula utilis D. Don. showed,greater in- creases in radial growth and a higher mortality at low light than the more shade-tolerant Abies densa Griff., in keeping with the trade-off between survivorship and growth at low light. Picea spinulosa Griff, Larix griffithiana Carriére, and Pinus wallichiana A.B. Jackson showed,small increases in growth,at low light levels. The latter two species showed,no capacity to adapt their morphology in response to changing light levels, which resulted in higher probabilities of mor- tality at lower light levels. Differences in the probability of mortality at different light levels were more,pronounced than differences in the light–growth response, underlining the importance of survivorship at low light for successional dynamics. Résumé : Les effets de différents niveaux de lumière sur la croissance radiale et la croissance en hauteur, sur l’archi-

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