Vincent,
Here is an example that will ignore all polygons tagged natural = "bare_rock" within landuse="forest" polys.
## ----------------------------------------------------------------------------------------------------------------------
# osm
ImportOGR|C:\Users\rgord\Desktop\Test_NATURAL\test_bare_rock.osm|*|*|NOREPROJ
# clear all 'bare_rock'
SubtractFeatures|landuse="forest"|natural="bare_rock"|1
# TREES
PlacePointsInPolygon|landuse="forest"|0.0001;0.0001|1.0;1.0
# this line generates a broadleaf tree for 2% of the tree coordinates with each tree between 58 to 65 feet tall
CreateAF2Plant|FRAND < 0.02|17.67;19.812|0|broadleaf|3
# this line generates a broadleaf tree for 18% of the tree coordinates with each tree between 40 to 55 feet tall
CreateAF2Plant|FRAND >= 0.02 AND FRAND < 0.2|12.19;16.76|0|broadleaf|0
# this line generates a broadleaf tree for 75% of the tree coordinates with each tree between 32 to 45 feet tall
CreateAF2Plant|FRAND >= 0.2 AND FRAND < 0.95|9.75;13.71|0|broadleaf|2
# this line generates a broadleaf tree for 5% of the tree coordinates with each tree between 20 to 30 feet tall
CreateAF2Plant|FRAND >= 0.95|6.096;9.144|0|broadleaf|12
# Export the AF2 TOC file
ExportTOC|C:\Users\rgord\Desktop\Test_NATURAL|test_bare_rock
## ----------------------------------------------------------------------------------------------------------------------
-- Rich