Below are some tips, tricks, and recommendations for using Forest Pack with Arnold
We only can make each Forest update compatible with one Arnold version. When we compile a new version of the plugin, we always use the latest Arnold SDK available, therefore we recommend you use the latest Forest update from our website, and the latest MaxToA package available for your 3DS Max version. Please be aware that Autodesk doesn't provide MaxToA updates to all Max versions. In this case, you can search the latest MaxToA for your Max version in the archive
Edge Mode and Forest Color
To use Forest Color and/or Forest Edge maps with Arnold, you will need to turn on Legacy 3ds Max Map support in Render Settings->System.
To use edge clipping mode, a Forest Edge map needs to be applied to the opacity slot for all the materials of the scattered objects. This can be automated by launching the Material Optimiser script from the Material rollout
Geometry and Scene Setup
Polygon Count: Handling fewer objects with more polygons is generally easier on the renderer than the opposite.
Scene Origin: Ensure your scene is not too far from the origin point, especially for models imported from other software like AutoCAD or Revit.
Background Trees: For trees in the background, consider using larger leaves and disabling opacities and 2 sided materials to lower the polygon count. ForestLOD can be used to switch items based on distance from the camera