Tropical moist <Emphasis Type="Italic">Polylepis</Emphasis> stands at the treeline in East Bolivia: the effect of elevation on stand microclimate,above- and below-ground structure,and regeneration |
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Authors: | Dietrich Hertel Karsten Wesche |
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Institution: | 1.Plant Ecology, Albrecht-von-Haller Institute of Plant Sciences,University of G?ttingen,G?ttingen,Germany;2.Institute of Biology, Geobotany and Botanical Garden,Martin-Luther University Halle-Wittenberg,Halle/Saale,Germany |
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Abstract: | We studied Polylepis forests along an elevational transect between 3,650 and 4,050 m a.s.l. at the treeline of the moist eastern cordillera in
Bolivia to examine changes in above- and below-ground stand structure, leaf and root morphology, and regeneration in relation
to stand microclimate. Field measurements and model predictions indicated relatively cold growth conditions of the Polylepis forests. Tree height, stem diameter, and basal area of the stands decreased markedly while stem density increased with elevation.
Leaf morphology differed between the two occurring Polylepis species, and trees at the treeline had smaller leaves with higher specific leaf area. In contrast, fine root biomass increased
from 37 g m−2 at the lowermost stand to 234 g m−2 at the treeline. Trees of the uppermost stand had higher specific root surface area and a much higher number of root tips
per unit dry mass. Thus, root surface area and total number of root tips per unit ground area increased conspicuously from
the lowermost stand to the treeline. Density of young growth inside the forest increased towards the treeline, while density
in the open grassland decreased with elevation. Young growth originated from sexual reproduction at the lower forest but was
comprised exclusively of root suckers at the treeline stand. We conclude that both the marked change in carbon allocation
towards the root system, as well as the changes in root morphology with elevation indicate an adaptation to reduced nutrient
supply under cold conditions of these Polylepis stands at the treeline in E Bolivia.
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Keywords: | Fine root biomass Leaf morphology Reproduction Root morphology Temperature |
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