I saw Weight From Slope on the a.n.t. landscape generator panel and considered it’s use to distribute plants. It creates a weight map based on the slope of the ant terrain. A not thorough web search produced little information so I just played with it. Here is what I found.
This is the landscape and the weight map produced by Weight From Slope.
I added a particle system using the weight map for density to the terrain to distribute cubes on it . This had little effect. The cubes were not noticeably denser on the flat or sloped parts.
Inverting the weight map showed density variation by slope but the opposite of what is needed for plants.
I un-inverted the map and applied Levels in the weight map editor to exaggerate the map. The Offset value of Levels is what made a difference. You can see live feedback for the cube distribution as you change the Offset.
Using negative Offset created the desired effect with cubes favoring less slope.
With some negative Offset.
With strong negative Offset.
With Sapling trees.
The blend file.
TreesWeightMappedPlacement.zip (1.2 MB)