The optimal growth trajectory depends on the whole light environment and a critical threshold in sapwood area determines which trees can reach the canopy top. When the maximum light gradient, dQmax, is decreased and the height at maximum light gradient, HdQmax, is increased, the tree will invest more into crown size before switching to stem height and invest more in stem height before switching back to crown size growth. (a) The optimal growth paths and (b) the corresponding light environments for three different cases: reference canopy, lower canopy and higher canopy. For the reference canopy, the height at maximum light gradient is set to 10 m and the maximum light gradient is 0.25 m−1. For the lower canopy, the height at maximum light gradient is decreased to 9 m and for the higher canopy, it is increased to 14 m. The corresponding maximum light gradients are 0.27 and 0.17 m−1, respectively. The light condition (light level and gradient) at ground level is the same in all three cases. In the left figure a circle signals the end of a growth trajectory and when seed production starts. (c) The ontogenetic plane. The ontogenetic plane is divided into three areas, an area where the tree is able to grow (area of growth), an area where the tree cannot grow (area of no growth) and an area we call the ontogenetic trap (triangular area). Inside the ontogenetic trap which starts at a sapwood area (and associated crown size) indicated by (2), growth is possible, but the tree cannot reach a height larger than the critical tree height (marked (1)), and is unable to reach the canopy.