Thanks for uploading it

GreatWhiteBear is right, trees will only grow on snow with dirt in it. If you open your map in the Remake map editor you can use the "view passability" option to see this. (select canPlantTrees)
But don't save the map using the Remake map editor! All of the tile data will be lost and you won't be able to use the terrain brushes in Krom's editor any more.
I think you will get better results if you think about where you place the objects, and make patches of flowers and mushrooms rather than just randomly scattered across the map. Obviously don't spend 10 minutes deciding where to place each one

but just think "hmm maybe a patch of mushrooms would look nice here".
My comments/suggestions:
- There is not much stone at all, especially for the top players. (remember it is only mined from the bottom, so some parts can't be mined) This means people won't be able to build long roads for mines, towers etc. You'd be surprised by how much stone is used in multiplayer games.
- There are some grass tiles along the very top row of the map
- Because of the ice, the top left position is very open and vulnerable. His village can be attacked from all sides and defending all his entrances will be almost impossible because they are so far away. I think you should put more water in the ice, and make it so there are only a few entrances where players can cross it to his village. You could sort of have a moat of water around his village so that players can walk around behind his village, but only attack at certain points where the ice connects.
- I think you could make the iron more dense in places. (use the tiles to do this, not terrain brushes) There is not much iron in the hills so it would almost not be worth mining it. Also I think dense iron looks better to start with. (it's like that in the original maps)
-
This iron hill is unusable because you can't build a road to the entrance. Also you shouldn't elevate the "reflection" in the water so much, I think it should be more like
this.
- Some of the water doesn't flow the right way, for example the bottom right pond and some water surrounded by ice.
- Tile transitions like
this which cannot be fixed should be covered by a rock or tree (use a tree that cannot be cut down, e.g. the biggest pine or a dead tree) Take a look around the map for more these, I saw a few.
- Your coal looks great! Well done.
- Some of the hills could look more interesting if you cut cracks and holes into them with elevation. Example:
Original;
Improved. (not the best example, I did it quickly. Take a look at some of the original maps too)
- A lot of the hills need more elevation. For example, 3 of the hills at the very center of the map, and the gold hills at the bottom left position could be a bit higher/more elevated.
- Experiment with using specific terrain tiles in some places, for example
bumpy sand which looks good instead of flat sand near hills. (but it is not used on the beach)
-
This flower cannot be walked or built on. (you can tell by the red X) There are two kinds of that flower, one can be walked on one can't.
Sorry for writing such a long list, but I hope some of it helps. I really like the map, these are just the things I noticed while looking at it.
Have you considered making an 8 player version of this map as well? (players grouped together in twos, similar to Warfare in the Wilderness 8P or The Northern Province) I think it would work well. There is certainly enough space.
Cheers,
Lewin.
P.S. I'll put this map in the new version if it's ready in time. We're planning to release next week (if all goes well)