Spatial variation in canopy structure induces highly variable patterns of light availability for juveniles and understorey trees (Nicotra et al. 1999, Oberbauer et al. 1988, Tang et al. 1999). In the heterogeneous light environment, plasticity in resource use is essential for survival of juveniles and hence maintenance of populations (Valladares et al. 2000). One of the most striking characteristics of plants in their response to a given resource availability is their capacity to change morphological traits (Kiippers 1994). Previous studies have attempted to understand the significance of morphological adaptations in their contribution to competitive ability, focusing on crown form (Kohyama 1987, Sterck et al. 2003), branching pattern (King 1998), shoot architecture (Canham 1988) and leaf shape (King & Maindonald 1999, Takenaka 1994, Yamada et al. 2000). Several studies have investigated the changes in morphology of saplings or seedlings growing under different light availability across canopy gaps (Ackerly & Bazzaz 1995, King 1994, Valladares & Pearcy 1998). However, the phenotypic plasticity in morphology of saplings adapting to the fluctuation of light availability has been investigated less (Blundell & Peart 2001, Poorter & Werger 1999). We evaluated the morphological plasticity of Shorea parvistipulata (Dipterocarpaceae, a canopy species) saplings growing under different levels of canopy openness in the Kubah National Park, Sarawak, Malaysia (13 7'N, 110009'E). The mean annual precipitation is extremely high, 6000-7000 mm (Hazebroek & Marshidi 2000). The mean daily temperature during the period between February to July in 1999 was 26.7 C. The study site is covered by mixed dipterocarp forest. All saplings of Shorea parvistipulata in a 30 x 30-m study plot were investigated in March 1998 and March 1999. The saplings of S. parvistipulata showed two forms: unbranched and branched. Dependence of tree morphology, such as leaf shape and crown form, on life stage has been reported in previous studies (Osada & Takeda 2003, Yamada & Suzuki 1996). There were 80 saplings in the study plot in March 1998; 61 were unbranched (76%) and 19 were branched (24%). Fortysix unbranched (75%) and 18 branched saplings (95%) survived to the end of the research period. To quantify the light environment, hemispherical photographs were taken with a fish-eye lens (Nikon 8 mm F2.8, Tokyo, Japan) directly above each sapling, and at the corners of a 5 x 5-m grid at 1.5 m height within the study plot. The canopy openness above surviving saplings was significantly greater than the average condition on the forest floor (Figure 1). The canopy openness for the saplings that died during the study period was lower than that for the surviving saplings (medians 3.74% and 4.59%, respectively, U-test, U= 242.5, P 0.3 5). Branched saplings were taller than unbranched saplings (medians were 63.4 cm and 35.6 cm, respectively, U-test, U= 60.5, P 0.21). Logistic regression analysis was used to quantify the probability of a sapling dying (X2 = 13.6, df= 2, P < 0.005) versus size and light availability. For 1Corresponding author. Email: enoki@agr.u-ryukyu.ac.jp