there is an easy solution:
if there are enemy militarysites in range defeat them so you higher your territory size, if there are none simply build a militarysite to capture the land.
Now there is the part with the forest - in either way the most foresters will get destroyed because you occupied the area they stand on. some lumberjacks will now start to remove the trees and as soon as you can build a new militarysite the game goes on.
Of course it might take a bit longer to defeat the player but still it won't be a problem as long as the "lumberjack" player has a strong enough army (and yes I really talk about soldiers here not about lumberjacks)
When you discuss that much just because of the small time you get more through placing foresters at the borders in time - well you can see it as tactic and all tactics have disadvantages - in that case the disadvantages are:
- you can't build militarysites at frontier as well
- if you want to prepare the other land you need to create a BIG border of foresters on your borders. that will
1) cost a lot of resources as each forester costs one shovel (1 iron + one planks)
2) cost a lot of buildingspace which is normally needed to have a strong infrastructure for producing weapons...
and even those walls of trees are passable after some time - of course you get some more time, but only some more time
So YES there are some (and really just some) situations when such a tactic would be logical:
e.g. you have not yet reached a mountain, you already see the mountains, but must expand with at least two more militarysites, while the enemy already reached you on the other site of your area - in that case placing treees would be a good tactic to get a bit more time until the enemy reaches your headquarters.
Anyway I don't see a problem in it - actually it was never planned as feature, but the more I think about it, you can really see it as feature! What is wrong in having more ways for tactics than just placing militarysites at specific points? You know why Arminius won against Varus ?
I see no point for more discussion here!
It's a feature not a bug!!!