Watch heavy branches bend under the weight they carry. Bend fresh twigs to the sky, or droop them under leaf weight to create pendulous trees.
Gravity has a big impact on the shape of trees. The shape of the crown is in constant change when spreading branches continue to bend down with the added weight. Bending affects the distribution of branches – some get pulled apart, others get closer together. Because leaves cast shadow on branches beneath, bending determines the light each branch gets. It thus affects which branches are successful and which will drop. Bending is a feature unique to the Grove and greatly improves realism when you get it right.
Branch weight controls the bending of branches under their own weight. Bending at each node increases with the amount of nodes it carries. And it decreases with branch thickness and branch verticality. As branches grow in width, they strengthen and thereby Limit bending.
Leaves and fruit pull down on branch ends, adding to the weight of a branch. On trees with relatively thin twigs this 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 fresh twigs all bend up. Leaf Weight and Gravitropism (Turn Up) are in constant battle – Gravitropism is natures way to try and beat gravity.
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
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.
This is a snippet from the release notes of the Grove 4, which explains the way the Grove bends branches.
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.
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.