Another interesting finding borne from these models is that there doesn't seem to be strong correlations between architecture and phylogeny. Although species within a specific genus often share similar architecture, there are often many exceptions. What's more, the same form can occur in unrelated species. For instance, Aubréville's model occurs in at least 19 different families. Similarly, the family Icacinaceae, which contains somewhere between 300 and 400 species, exhibits at least 7 of the different models. Alternatively, some families are architecturally quite simple. For instance the gymnosperms are considered architecturally poor, exhibiting only 4 of the different models. Even large families of flowering plants can be architecturally simplistic. The Fabaceae, for instance, are largely made up of plants exhibiting Troll's model.
So, at this point the question of what is governing these models becomes apparent. If most plants can be reduced to these growth forms at some point in their life then there must be some aspect of the physical world that has shaped their evolution through time. Additionally, how does plant architecture at the physical level scale up to the level of a forest? Questions such as this are fundamental to our understanding of not only plants as organisms, but the role they play in shaping the world around us.
Although many scientists have attempted to tackle these sorts of questions, I want to highlight the work on one individual in particular - Dr. Karl Niklas. His work utilizes mathematics to explain plant growth and form in relation to four basic physical constraints:
1) Plants have to capture sunlight and avoid shading their own leaves.
2) Plants have to support themselves structurally.
3) Plants have to conduct water to their various tissues.
4) Plants must be able to reproduce effectively.
Using these basic constraints, Dr. Niklas built a mathematical simulation of plant evolution. His model starts out as a "universe" containing billions of possible plant architectures. The model then assesses each of these forms on how well it is able to grow, survive, and reproduce through time. The model is then allowed to change environmental conditions to assess how these various forms perform as well as how they evolve.