Light is a key environmental factor limiting growth and survival of trees in the subcanopy of wet tropical forests (Davies 2001, Thomas 1996). Light availability varies both vertically and horizontally and affects tree height, crown shape and tree architecture (Bongers & Sterck 1998, Sterck & Bongers 2001, Sterck et al. 1999) in addition to growth and survival (Clark & Clark 1992, 2001). Although many studies of tree seedlings and saplings have shown that growth varies significantly with light availability in tropical wet forests (Clark et al. 1993, Iriarte & Chazdon 2005, King 1991, Kohyama 1991, Montgomery & Chazdon 2002, Oberbauer et al. 1988, 1993; Poorter & Werger 1999, Sterck et al. 1999, Welden et al. 1991), few studies have examined these relationships in size classes above 5 cm dbh (Sterck 1999). King et al. (2005) found that annual increment growth of trees in the 8–20-cm dbh size class in two Asian forests was positively dependent on an index of crown light interception, but no direct measurements of light availability were taken in this study. Due to logistical challenges, few direct measurements of light environments above tree crowns have been made in tropical forests (Sterck & Bongers 2001). To our knowledge, no measurements have been made in second-growth forests.
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