Alseis blackiana: An Oxymoronic Shade-Tolerant Pioneer Tree Species

Tropical trees are often classified into two groups—that is, “shade-tolerant” species and “light-demanding” or “pioneer” species—based on their ability to persist as seedlings in the understory and their light requirements for seed germination and establishment. Although these classifications are largely robust, one exception exists on Barro Colorado Island (BCI). Alseis blackiana Hemsl. (Rubiaceae) couples the early life-history traits of a pioneer species—germination exclusively in high light—with one of the lowest sapling mortality rates in the tree community. High juvenile survival in the understory allows Alseis to achieve high abundance on the island. However, unlike other shade-tolerant trees that construct tough, nutritionally poor, and long-lived leaves that are unpalatable to most herbivores, Alseis achieves shade tolerance despite many of the opposite traits—thin, short-lived, nitrogen-rich leaves. Shade tolerance in Alseis is likely a consequence of high leaf display efficiency coupled with tolerance of damage and high resprouting capacity.