Tree architectures adapted to efficient light utilization : is there a basis for latitudinal gradients ?

Simulation studies demonstrate that the angular distribution of sun elevations, as determined by latitude, has an effect on how efficiently different crown shapes of trees utilize direct photosynthetically active radiation (PARd) in uniform tree stands under favourable growth conditions. In particular, when potential net photosynthesis is considered, flat horizontally extended foliage displays are most efficient at low latitudes, while narrow vertically extended crowns are most efficient at high latitudes. At medium latitudes the crown shape appears to have a smaller effect on photosynthetic efficiency. The paper discusses the mechanisms and consequences of the interaction between direct solar radiation and forest structure as dependent on latitude, and addresses the possible effects of the differences in radiation geometry on structure and functioning of forest ecosystems at high versus low latitudes. T. Kuuluvainen, Univ. of Helsinki, Dept of Forest Ecology, Unioninkatu 40B, SF-00170 Helsinki, Finland.

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