Partitioning of Understory Light Environments by Seedlings of Tree Species with Varying Shade Tolerance

Light availability significantly influences the survival, establishment, and distribution of naturally regenerated seedlings. This study evaluated light partitioning and range of partitioning across light gradients in tree seedlings (15-100 cm in height) of varying shade -tolerance in low elevation forests in Taiwan. Relative light intensity (RL) values, calculated by simultaneously measuring light quantum in the understory and in open field, are often used to quantify the understory light environment. However, RL values measured on high-light sunny days were lower than those measured on overcast days. To compensate for these differences, we established an empirical equation to convert RL values obtained on sunny days into a standardized understory RLadj value based on a light intensity of 500 μmol photon m-2 s-1. Results showed that seedlings of species of different shade-tolerance classes exhibited distinctly different patterns of light partitioning. In five forests of southern Taiwan, we found seedlings of highly shade-intolerant species were concentrated in areas with the highest light levels, with RLadj > 32%. Shade-intolerant species had more seedlings distributed in high- and intermediate-light environments, while seedlings of moderately shade-tolerant species tended to be distributed in intermediate- and low-light environments. However, shade-tolerant as well as very shade-tolerant species were predominately distributed in low light environments with RLadj © 2024 Taiwan Forestry Research Institute. All rights reserved.