[CzechTexan]

Well, this one is mere vodoo, but it works for me:

Reopen the map with the map editor. Do not touch any object. Add somewere a sole winter treeline. Do not add any other object. Save the map. Welcome the trees :-)

Off course a lone winter treeline can't influence anything, but it works. Never tried it with other types of objects, cause i was afraid to spoil the magic ;-)

This is some strange MOJO. I did a test by placing one object of winter trees onto my summer time map but it made all trees disappear.

I wonder if, since it is a winter object, somehow it affects the summer time trees by not making them show on the map.

Makes me wonder if Lowfighter accidentally placed some winter object or winter trees by accident to make his trees disappear.