Bend

Watch heavy branches bend under the weight they carry. The continuous interplay of growth and gravity is what creates some of the most beautiful tree shapes.

Bend feature illustration

Gravity has a big impact on the shape of trees. The shape of the crown is in constant change when its spreading branches continue to bend down with the added weight. Bending affects the distribution of branches – some get pulled apart, others get closer together – Drop Shaded will keep the branch distribution airy. Bending is a feature unique to the Grove and greatly improves tree realism.

Leaves and fruit pull down on branch ends, adding to the weight of a branch. On trees with relatively thin twigs, the combination of Leaf Weight and Fatigue causes dangling branches. Examples are weeping willow and silver birch. On other trees like ash, thick twigs can carry their leaves with ease. Add to this their strong tendency to grow away from gravity and branch ends all point up to the sky. Leaf Weight and gravitropism are in constant battle.

Let’s continue the example of the ash. Although it is quite capable of bending new growth up to the sky, gravity keeps pulling down on their thick branches year after year. Although adding new rings also adds weight, it also quickly strengthens branches, partially baking in the bending of that year. Control this with Bake Bend. This baking isn’t perfect, cells get tired and old oak trees tend to rest their biggest limbs on the ground. Weaken the effect of Bake Bend with Fatigue

Physical Bend

This is a snippet from the release notes of the Grove 4, which explains the way the Grove bends branches.
EulerBernoulliBend

For release 4, bending has been completely rewritten using the Euler-Bernoulli beam theory. By treating each internode as a cantilever beam with a force acting on the end, a branch is traversed from base to tip, bending each node along the way.

“It’s been a brain breaker from the start how even silver birches and weeping willows grow up before they let their branches dangle down.”

One of the puzzles to crack was how to realistically diminish bending when a branch grows thicker. Apparently, trees are amazingly effective at defying gravity. Each added ring very quickly adds strength to prevent further bending. The outer rings add so much extra strength that for bicycle frames, its designers chose to just leave out the core. Similarly, trees rotting on the inside can live on for decades without loosing structural integrity.

bendtab
Above: The Bend tab now has three very clear parameters.

Dangling branches form when an added ring is too thin to support the added weight of a branch. Each new ring bakes in part of the bending force and petrifies it. This adds up year after year.

Another initiator of weeping branches is Shade Elongation. The amount of bending depends on the weight, but also on the length of the internode. And we all know that plants in shade grow tall and slender shoots that are relatively weak. This allows sunny branches to slowly but steadily climb to the sky, while shaded branches grow fast and dangle down.

Bending now takes into account the real weight pulling on each node of every branch. A node’s weight depends on the thickness buildup over the branch. Tip thickness, Internode Gain and especially Branching Thickness Exponent have a big influence on how a branch bends. Internode Length and Shade Elongation define the Euler-Bernoulli beam length, longer nodes will increase bending.

Trees can grow high, very high. To get there, a tree has its ways to keep growing up and not down. Most importantly gravitropism – by growing more cells on the bottom of a branch and thereby effectively bending the branch upward. Simple but effective! But to keep these spreading branches growing up, it has to add structural thickness to keep if from collapsing under its own weight.

When tweaking bend parameters, keep thickness buildup and gravitropism in mind and try to create a balance with them.

Bending is interactive and fun to play with. Keep in mind one thing when tweaking the bending parameters when a tree is fully grown. In a growth cycle, the tree is first pruned, then grown, then bent. The distribution of the bent model determines the fate of branches when pruning. And as described above, bending changes the distribution branches and the tree’s ultimate shape. For optimal branch distribution you need to regrow your tree after changing bend parameters.

Next up, learn more about: Prune.