Open the FSX.CFG File, and add this entry, just below the [TERRAIN] section in FSX.CFG
TERRAIN_MAX_AUTOGEN_TREES_PER_CELL=4500
TERRAIN_MAX_AUTOGEN_BUILDINGS_PER_CELL=3000
The figures above are the default and you should set them to a lower amount. Setting to 0 for instance will mean that you see no objects in the simulation. Please note that the maximum setting for each item is 6000 and it is suggested that you use a minimum of 10 to avoid issues within the game.
The suggested settings to set initially are:
TERRAIN_MAX_AUTOGEN_TREES_PER_CELL=1000
TERRAIN_MAX_AUTOGEN_BUILDINGS_PER_CELL=800
