Regulate growth by controlling the flow of juice. Favor current or sub branches, with a bias to the base or crown.
Trees regulate growth with hormones. Different parts of a tree synthesize these hormone molecules. Hormones get distributed through the branches and have an effect on each cell they reach. They are a means of communciation, the smart parts of the tree tell the rest of it what to do.
Branch tips produce such a hormone, called auxin. It tells side branches down the branch to lay low. Suppressing side branches helps the tree expand and win the race for light. The scientific name for this is Apical Dominance. Simulate this effect with Favor Current. The hormones travel down the branch, but at some point the concentration will be too low to stop side branches from growing, the Favor Current Reach.
Each single branch of a tree competes for light with all other branches through Shade Avoidance. This value is added to Favor Current according to how much a branch is shaded. So a shaded branch will shoot out, further suppressing its child branches in order to find light.
Favor Current helps the tree get a good start in getting toward light. But when the tree grows older a different effect shows up. The hormone that suppresses side branches only travels a limited distance from the branch tip that created it. After that side branches can freely grow, and the tree now needs to favor the best performing branches, those with most leaves and those harvesting most light. These are the branches that will keep the tree healthy.
A tree knows which branches to favor through a brilliant physical phenomenon. Leaves continually consume water for photosynthesis, and they even purposefully evaporate water just keep the flow going, for a steady flow of soil nutrients. At a branching point, this now causes the branch with most demand and thus suction to have precedence over the branch with a lower leaf area. On top of that, the leaf area is multiplied by its shade. Combined with the now accurate shade calculation, the suction is therefore actually dependent on the photosynthesis of the branch.
The crown of the tree is generally a bright place and a healthy part of the tree, therefore Favor Healthy naturally also favors the crown of the tree.
On older branches, only a thin layer just beneath the bark is alive. This layer keeps keeps growing out, leaving layer after layer of dead tissue within. This dead core acts like a sponge – sucking up water as high as possible until it can’t beat gravity. When a branch reaches Peak Height, its tip will be out of water and its power to grow will be gone.