I like to get a more in-depth understanding how to achieve large-scale nature scenes in Blender. Keeping it simple.
MTree helped me to create trees for the forest scene. After some fiddling, Particle Instance (on leaf) works with the leafs particle emitter.
I oriented to lolwel21’s feedback to rework the landscape scene.
Leafs are smaller then a fraction of a pixel. Asking myself … is it nescesary to keep leafs that small?
Basic Trees done with ModularTree addon. Blender 2.80.
Landscaping is like dancing with a freezer. Any wrong step, and Blender freezes in a loop, or GPU exhausted, or memory exhausted.
I keep particles in bounding box, and used child particles to reduce particle count on viewport and keep UI fluid.
Landscape is a dynamic sculpting.
Simple green texture.
Before I started with sculpting I watched timelapses on erosion.
Now, the trees …
There are strange artifacts. They do have polygon shapes. Not sure, what caused them, and how to get rid of them.
Mh … render artifacts on landscape related to particle children. I used thousands of render particle childs. (Interpolated children mode.)
After I reduced children count and set higher emitter count, artifacts got tamed a bit.
It seems, children mode ‘simple’ works better for large scale forest. Next image is done with ‘simple’ particle children mode.
Starting to look pretty good!
Are you specifically going for a super-dense forest, or do you think adding a few clearings here and there would look good?
Also, judging by the visual repetition on the close side of the image, it looks like you don’t have random rotation set up for your particles. Is there a reason for this? Adding random rotation really helps get much more visual variety out of a single tree model.
EDIT:
I just realized that a large ratio of child-parent particles will produce a similar effect to disabled rotation, even if rotation is enabled, because all nearby trees will share the same rotation. To remedy this effect, there are a couple options.
I personally used method 2 for my forest in the MTree thread.
I like to keep dense forests on hair particles. Like an etude, I try to focus on a technical problem. Its difficult to achieve both, variation in the forest and fluid blender.
Child particles do not vary in rotation. And child particle radius (Simple Mode) is limited to 10m. Thats 4 small to medium Trees, unless downscaled.
There might be workaround. I try to make single particle system not too dense, but layer several particle systems. I hope I could resolve repetive-children problem and keep blender fluid.
But I like to try your 2nd solution, too.
Happy blending.
Its a test … animated landscape, trees moving to wind. At least, they should do.
I try to render a 250 frame animation. Used Blender 2.8
Result:
Each frame consumes a bit more memory. after around 100 frames, 16G memory consumed. On around frame 120 stunning 32G memory were consumed. It was not possible to render all 250 frames in one render session without freezing my machine.
Killing blender process was a meditation session.
Now, remaining rendered frames glued into a video file. Video shows, that whole physics stopped working at some frame position.
Aaaah … grmpf … Donnerwetter! 
Another try.
Increasing memory consumption was caused by ‘Persistent Images’ setting. Without, memory consumption did not raise during frames rendering.
Still, little problem nibbled on the forest ani. You’ll see.
Your trees! They’re swiveling! (I think you’re using hair physics.)
Try just animating the tree mesh itself, and leaving the particles alone.
If you’re using random rotation, that saves you from the repeating tree artifacts, letting you use fewer tree models and saving RAM.
However, it also means you will only be able to model turbulent (non-directional) wind.
This is something Gooseberry had a huge problem with, and they never found a solution they were entirely satisfied with.
One potential idea is to do the wind animation procedurally with shader-based vector displacement (2.8 only). Not sure how good that’ll look, though.
Huh … yes. The trees roll. They spin around their own axis. I liked to understand if there is a way to use Blender Force Fields together with a particle forest.
It will be difficult to use animated Displacement with the forest. How to balance all the leafs to fit the tree with its branches? How the UV’s of maany twigs should be set to match the branches? I fear, this would be a tough one.
I hope, animation nodes will open new ways to animate a forest with force fields. For now, I will try animated tree mesh method.
I am still trying to understand Hair particles. Approaching for a solution, which combines animated single-trees and force-field acrobatics.
Force field tested with a basic object. Rendering done with workbench renderer. Objects quickly flips around their own axis. It wont do for trees, so I look for a way to fix it.
Fiddling for hours. Hair particle deforms still jerky. I think, hair particles are nice for static forests. But they wont work for forest animation.
After struggle with particles animation rotations, I decided to abandon particles.
Still using arrows instead of trees.
On animation nodes, I have to switch off “Auto Execution” in the ‘t’ tab, to prevent Blender from freezing.
To update whole Bunch, I hit “Execute Node Tree”
Thats how node tree looks like.
It almost replicates DupliFaces.
Now, look at instance count. 10000 instances. For a large scale forest, I would use around 100 times more instances. It took nearly 20 seconds to execute (19.28s, only single core used).
For large scale forest: this time, multiplied at least by 100. Around 30 minutes to execute node tree for a forest of just arrows.
Plane got more subdivisions.
Now, it seems there needs to be care about the Outliner. If “Animation Nodes Object Container” is opened, it slows down everything by a magnitude!
On 10000 instances, its 1.71 seconds if “Animation … Container” closed. If tis collection is open in outliner, 10000 instances take 18 seconds.
Trying 50000 instances. “Animation … Container” closed in outliner.
Blender freezes if I start “Executie Node Tree”.
What I like to do, I wont achieve with Blender at the moment. Need to simplify how forest is animated.
And I need to move on, to avoid too much frustration (running against walls for too long), protect motivation and strength.
A rough dynamic sculpt for mountains. Google Earth helps me to gasp shape of mountains.
Retopology
More details will be sculpted.
Sculpted landscape. Basemesh from last posting.
Sculpting texture brushes are combined with nudge brush or clay brush. (Stone structure.)
Multires seems WIP. A hat for diner!
“Delete Higher” on multires is dangerous atm.
Terrain without forest. Its WIP.
I did not count how often I destroyed landscape sculpting with a bug. I guess I have to do sculpting on 2.79b.
Now, after I did an apply base – and safed – whole landscape destroyed again.
I erased all multires data, and started again.
Same base mesh. Before any sculpting, I did 6 subdivisions on multi resolution in edit mode.
It helped me to avoid some artifacts, sculpt is cleaner now.
Texturing done in Krita.
Basic voronoi grunge.
I like to populate it with plants and keep everything animable.
Handmade tree. No particles used, but nested Collections, Instances (Dupli Linked) and Collection Instances.
Bounding Box seems to make problems with Collection Instances. A single Collection Instance creates a bunch of bounding boxes, cluttering the screen with its overlaping shapes.
Without proper bounding box, whole screen is full and its hard to orient. So I had to do some workaround to compensate and to keep work area clean.
But, Collection Instances did a good job to organize the tree. UI keeps fluid. All instances covered most of 34000 Objects. It is memory efficient too. Whole tree only consumed 50MB memory.
No particles used, just collection instances and ‘duplicate linked’ instances.
leafs -> twigs
twigs -> small branches
small branches -> large branches
There are some pros and cons.
Cons are mainly issues, because it is a young feature in Blender.
In the viewport, nested Collection Instances could become very cluttered. And, particles wont support collection instances atm. Particles would only be empties.
… munch munch … 
On the other side, there are pro’s. First, collection instances used together with ‘duplicate linked’ instances safe a lot of memory. This scene takes around 60MB ram. They render very fast. Finally, I believe we got a good foundation to create instancing based plants.
In future, I believe, addons could take advantage of this new part of Blender.
Manual Tree gets very fast very complex.
Base tree fist modelled as 2D shape, using skin modifier. Rotating stem branches from center of object creates a 3D tree.
Screenshot. Left area shows tree. Right area shows how ten thousands of Collection Instances clutter the screen.
Clutter is made from Empties-Axes of Collection-Instance-Children. To get further, I have to disable Display Overlays.
Leafs are hidden by hiding twigs. With twigs and leafs, the rendered tree looks like …
I guess, my branches are too planar. Its hard to fill whole space around tree with leafs and twigs.
