PARENT SESSION
Oral Session #52: Plant Ecology: Light and Carbon Allocation.
Presiding: T. Day
Wednesday, August 7. 8:00 AM to 11:30 AM. Gila Meeting Room, TCC.

Determinants of juvenile tree shade tolerance in a temperate rain forest.

Lusk, Chris^*,1, ¹ Departamento de Botánica, Concepción, Chile

ABSTRACT- This study relates growth, allocation, foliage turnover, biomass distribution and gas exchange to low-light survival of juveniles (20-100 cm tall) of eight temperate rainforest evergreens. Taxa which suffered no mortality in low light during the 14-month study are referred to as “shade-tolerant” species, and those which did are referred to as “light-demanding” species. In low light (2 - 5 % canopy openness), shade tolerant species had slightly lower light compensation points than light-demanders. Light-demanding species had more plastic aboveground allocation patterns, allocating less to foliage production than shade-tolerant associates in high light (>10 % canopy openness), but more in low light. Foliage turnover was much slower in shade tolerant species than in light-demanding associates. As these differences in leaf retention outweighed variation in allocation, shade tolerant species displayed higher leaf areas. Furthermore, all shade-tolerant species gained leaf area in low light during the study period, whereas light-demanding taxa showed leaf area declines. Higher leaf area ratios, plus differences in compensation points, indicate that large seedlings of shade-tolerant evergreens enjoy net carbon gain advantages over light-demanding associates in low light. However, minimal growth rate differences in low light imply higher storage allocation in shade tolerant species. This study illustrates the long-term consequences of foliage turnover differences for biomass distribution, and suggests that shade tolerance in juvenile evergreens is associated with traits which enhance carbon gain, but not growth, in low light.

KEY WORDS: Allocation, Gas exchange, Leaf area ratio, Leaf longevity