Prune

Witness branches compete for light. Drop them when too little is available. Evolve your trees into airy branching structures…

If a tree held on to every branch it grew, it would soon become a thick green ball that would collapse under its own weight. To escape this horrible fate, it drops all but the most successful branches. Dropping branches keeps the tree airy and allows light into the crown. This is the exact opposite to space colonization and yields far more natural results at the cost of more calculation time – but staying true to nature.

The Grove has 3 types of pruning:

  1. The tree itself drops shaded and low power branches all the time.
  2. Automatic pruning of the lower base will save you a lot of time.
  3. Manual pruning allows you to cut individual branches by hand, or to trim many branches at once by drawing cutting lines.

Shade

Most branches are dropped because of low light. To calculate shade, and to be able to grow sensitive trees, the Grove has its very own ray tracer for real shade. It works on the entire tree and can even include an environment. The results are smooth values from light to dark, calculated for each branch. The default values work well in most situations and you should rarely have to tweak them.

Real Shade

Ray Tracing

Let’s take a look at how shade is calculated. The first thing you should know is that branch tips are the eyes of the tree, and that they are looking for blue sky light. This is the light that makes trees grow into balanced shapes.

Shade Preview offers you a view behind the scenes. It shows you where The Grove distributes shadow casting areas and just how big they are. You will see that it places polygons at branch ends. When a branch gets increasingly vertical, the area’s center is shifted toward the branch end, matching the placement of real leaves around the branch. The size of each area is controlled by Leaf Area.

shadetab
Above: Shade parameters have moved from the Prune tab into their own Shade tab. The eye icon enables a 3D view preview of your settings.

Shade Preview also shows the ray tracing samples. This uses a phyllotaxic distribution of samples – the same natural distribution seen in sunflower seeds and pinecones. It’s only fitting to use this optimal distribution to sample the light environment. Increase Shade Samples for accuracy and smoothness, while fewer samples will introduce randomness.

Environment Shade

You can see the effects of To Light on single trees or multiple trees growing together. But it is best visible in trees avoiding buildings or natural obstacles. The Shade + Block environment type includes the environment’s polygons in shade calculation.

Drop

Alright, we’ve calculated the shade of every branch end. Now it’s time to drop the low performers. In the Drop tab you will find tools to drop Shaded, drop Relatively Weak and drop Low branches. Each of these tools control how many branches will be dropped.

Drop Shaded

By far most branches are dropped because of low light. A higher Drop Shaded will drop more branches, as simple as that. Drop Shaded only drops young branches (without child branches). Older branches can be dropped with Drop Relatively Weak.

Note that before the Grove release 5, Drop Shaded was called Shade Threshod and its behavior was inverted. When a branch had more shade than Shade Threshold, the tree would drop it.

Drop Obsolete

Some conifer trees drop their lower branches as they grow older. The process that caused this shedding of old branches was a mystery to me, and apparently also to everyone else. There is almost no research to be found on this, so I have come up with several theories of my own that I’ve tested in earlier releases. But forget about these earlier theories, because although they seemed to work in some cases, they had side effects and that told me that they just couldn’t be correct.

And then it struck me, while studying the formation of wood. The new theory is based on the formation of heartwood in the core of older branches. Young branches consist almost entirely of sapwood, with the important function of flowing water up to the leaves. Then the tree starts adding new rings around the old core, and year upon year the inner rings grow old and eventually die. This dead wood on the inside of thicker branches is called heartwood, and this wood stops flowing water – it’s dead. Some trees form heartwood faster than others, and some have almost none. Conifers do form a lot of heartwood and the layer of sapwood is especially thin.

Now, a young tree adds its side branches when the trunk is still thin and fresh. But then the trunk keeps adding new rings and keeps growing thicker. The side branch will also grow thicker, but at a much slower rate, again especially in conifers. So far all is fine, and the sapwood of the trunk will pass along water to the thinner side branch. But sapwood has a limited shelf life, and several years on the core of the trunk starts to “die”, forming heartwood. This dead tissue does not transport water anymore, and this is a serious problem for the side branch that has its water tubes nested in this inner tissue. If the side branch were very successful and had built up a lot of new thickness, there’s no problem, but otherwise it’s done.

This theory, when put into practice, gives very convincing results in conifers. I hope to further explore this and make improvements in coming releases.

Auto Prune

Drop Shaded and especially Drop Obsolete will clear the base of your tree when the tree grows older. But not enough. On the forest floor, animals eat the tasty green branches of your growing tree. They can only reach a certain height. In the city, trees are pruned to a certain height so they don’t hinder traffic. Auto Prune > Low is a handy automatic pruning tool that performs its work each year. Low lets you define a height up to where the base should be cleared. It gradually kicks in, when the tree grows higher than the set height. So a smaller tree will not be pruned. Only when the tree grows to twice the height, it’s base will be cleared to the full Low height. Keep Thick will keep thicker branches.

Prune by Hand

manualprune

Prune and Shape

The Prune and Shape tools are similar, in that they both cut off unwanted branches, but the long-term effects are different. Prune realistically cuts off branches and leaves thick and dead branch ends. A handy tool for cutting off larger branches.

Shape allows more artistic freedom. Cut ends have their thickness reset and they remain alive for further growth. The ends behave as new growth, as if they were never any longer to begin with.

Interactive pruning is fun to play with, extremely addictive, and gives rise to many more tree shapes, and even extremes like pollarded plane trees and pollarded willows.

To prune your tree, simply click Prune and draw cutting lines in the 3D view, then apply the cut with the Space-key.

To switch between Prune and Shape modes, press Tab.

Regenerate

When a tree crown is heavily damaged or pruned, its inner branches are once again exposed to light. The branches may still have unopened buds waiting for an opportunity like this to pop open.

Paired with the new Shape and Prune tools, trees will soon recover from the tyranny you impose on them. Gaping holes will soon fill up, all thanks to the new shade calculation!

Watershoots usually develop after damage caused by lightning, storms and falling neighbor trees. Although watershoots are natural, they are a common but unwanted sight on the trunks of city trees. The extreme pruning imposed on city dwelling trees is often the cause of many watershoots. The Grove has a handy tool called Auto Prune > Low for regular maintenance of your trunks.