Hi,
It's taken from the following system registry key:
Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Itoo Software\Forest Pack Pro\TexturePaths
by default set to:
C:\Program Files\Itoo Software\Forest Pack Pro\distmaps\images
Let me add, that if the plug-in doesn't find the keys in HKLM, it searches the same values on HKCU.
Best regards,