Light responses of shade-tolerant tropical tree species in north-east Queensland: a comparison of forest- and shadehouse-grown seedlings

Abstract

Shadehouse design may have a significant influence on the results of shadehouse studies investigating the light responses of tropical seedlings. Shadehouse effects were investigated by examining the seedling growth and morphological properties of four shade-tolerant tree species from north-east Queensland in the forest and in neutral-density shadehouses for up to 1 y. Understorey plots were compared with 0.8% shadehouses, and single-treefall gaps were compared with 10% shadehouses. Seedlings of all species showed higher growth rates in the shadehouses compared with the equivalent forest treatments. Nonetheless, trends found between high- and low-light growth rates in the shadehouse seedlings were mirrored in forest-grown seedlings. Specific leaf area (SLA) values in the shadehouses provided a good approximation of SLA in the forest for species in both light treatments. In contrast, biomass allocation and leaf area ratios were only comparable for forest and shadehouse seedlings grown in the high-light treatment. Furthermore, seedlings grown in shadehouses differed significantly from forest-grown seedlings in terms of their root morphology. Despite the differences in absolute values of plant characters in the shadehouse and forest seedlings, 65% of significant differences detected between high- and low-light plant characters in shadehouse-grown seedlings were also found in the forest-grown plants.