This study suggests a growth volume system for the efficient modeling of numerous trees for a real-time virtual ecosystem. To increase the efficiency of the real-time system and to allow natural tree generation, the basic tree modeling system obtains its growth rule by means of botany-based self-organizing under a recursive hierarchy structure. On the basis of this rule, growth volume was introduced and controlled to generate numerous trees in a virtual ecosystem more intuitively, which allows the generation of various trees. The reality of the expression was increased by including the effects of external factors, such as light, physical obstacles, and other trees. Finally, an instancing-based branch control procedure was added to enable an efficient rendering of the real-time ecosystem. Experiments were performed to verify whether various and natural trees could be generated and numerous trees in the virtual ecosystem can be easily modeled on the basis of the suggested growth volume, which shows the efficiency of the real-time ecosystem. Copyright © 2012 John Wiley & Sons, Ltd.