Seedling functional traits of tropical vs. cool-temperate trees

The dynamics of humid forests are thought to involve a trade-off between shade tolerance and growth in high light. Lusk et al. compare seedling growth and functional traits of tropical and cool-temperate Australian rainforest trees, and show that in contrast to the pattern found in the tropical species, seedlings of cool-temperate light-demanders are relatively slow-growing, and have smaller leaf area ratios, smaller xylem conduits and less-conductive stems than more shade-tolerant associates. These traits are consistent with selection for resistance to freeze–thaw embolism. They conclude that whereas competition for light favours rapid growth in light-demanding trees native to environments with warm, frost-free growing seasons, frost resistance may be an equally important determinant of the fitness of light-demanders in cool-temperate rainforests, as seedlings establishing in large openings are exposed to sub-zero temperatures that can occur throughout most of the year.