Understanding internode elongation in woody species is the basis of stable timber production. Although trees exhibit coordinated growth between leaves and internodes, it is unclear whether their coordinated growth occurs simply because both organs receive a common signal that triggers their growth or because the growth of one organ is regulated by the other. To test the latter possibility, we defined simple developmental stages and assessed the effect of leaves on the regulation of internode elongation at the phytomer level in the tropical tree Shorea leprosula, which is an important timber tree species in Southeast Asia. Our observation of phytomers showed that leaves and internodes grew coordinately in S. leprosula. A spatiotemporal analysis of internode elongation indicated that internode elongation occurred around young expanding leaves. Furthermore, the excision of expanding leaves significantly reduced internode elongation. These results suggest that expanding leaves positively regulate internode elongation. Therefore, the growth interactions between leaves and internodes must be considered in order to better understand the mechanism of internode elongation in S. leprosula. These results will also form the basis of future studies aimed at sustainable timber production using this species.