Leaf characteristics and growth response to light of understory Rhododendron hodgsonii in the Bhutan Himalayas

Specific leaf area (SLA), leaf area index (LAI) and leaf area ratio (LAR) of Rhododendron hodgsonii were characterised across size classes. Responses of radial and height growth and plant architecture of saplings to varying light levels were quantified. Growth history of and light levels at recently died-off saplings were characterised. Average SLA was 52 cm super(2) times g super(-1). It was less in the upper crown half and decreased with plant size. Average leaf size was negatively correlated with plant size. Over 90 percent of the variation in number of leaves, leaf area, aboveground biomass and crown projection area were explained by allometric functions from collar diameter. Mean LAI of individual canopies was 0.96, mean LAR was 8. Fifty percent of the maximum radial and shoot growth were reached at 6 and 7 percent of full sunlight, respectively. No decline in diameter growth prior to death could be observed while shoot lengths declined steadily from the fifth year to the last year before to death. Self shading is minimised by arrangement of leaves at the end of branches. Costs for this architecture are high; larger plants are assumed to be close to their ecological compensation point.