Figure 12: a Tree Model with Branches Competing for Access to Light, Shown without the Leaves

Figure 13: A climbing plant growing on the tree from the previous figure is above a threshold Nmin. If these conditions are not satisfied, production p11 removes (sheds) the branch from the tree using the cut symbol %. Simulations. The competition for light between tree branches is manifested by two phenomena: reduced branching or dormancy Figure 14: A model of deciduous trees competing for light. The trees are shown in the position of growth (top) and moved apart (bottom) to reveal the adaptation of crown geometry to the presence of the neighbor tree. of apices in unfavorable local light conditions, and shedding of branches which do not receive enough light to contribute to the whole tree. Both phenomena limit the extent of branching, thus controlling the density of the crown. This property of the model is supported by the simulation results shown in Figure 11. If the growth was unlimited (production p6 was always chosen over p7 and p8), the number of terminal branch segments would double every year. Due to the competition for light, however, the number of terminal segments observed in an actual simulation increases more slowly. For related statistics using a different tree architecture see [52]. A tree image synthesized using an extension of the presented model is shown in Figure 12. The key additional feature is a gradual reduction of the branching angle of a young branch whose sister branch has been shed. As the result, the remaining branch assumes the role of the leading shoot, following the general growth direction of its supporting segment. Branch segments are represented as texture-mapped generalized cylinders, smoothly connected at the branching points (cf. [6]). The bark texture was created using a paint program. As an illustration of the flexibility of the modeling framework presented in this paper, Figure 13 shows the effect of seeding a hypothetical climbing plant near the same tree. The plant follows the surface of the tree trunk and branches, and avoids excessively dense Figure 15: A model of coniferous trees competing for light. The trees are shown in the position of growth (top) and moved apart (bottom). colonization of any particular area. Thus, the model integrates several environmentally-controlled phenomena: the competition of tree branches for light, the following of surfaces by a climbing plant, and the prevention of crowding as discussed in Section 6. Leaves were modeled using cubic patches (cf. [46]). In the simulations …