Just playing aroung with the Ljolsalfar: They are just AWESOME at the Moment...
I think it is just TOO much that they can now build ANY improved under woods AND JUNGLE! This means very early Mines, even if there is Forest on them), with another later boost (ancient woods), being able to build gem-mines early under jungle, access to calender-resources like dyes, banana, even if there is jungle on them etc.
Any other civ has to trade produktion for Food (--> mines). But the Ljolsalfar can just build mines on a grassland hill and get 2 food (with ancient forest) and 4 Production. Simply just TOO good...i will continue the test and will try e.g. "Highlands". I am pretty sure that with this combination, the elves will almost outshine the dwarves concerning production, due to their larger an healthier cities...
And in former versions, the Ljolsalfar were quite slow to develop (beeing dependant on cottages, slow workers). But with this new jungle boost, their development should significantly improve...
Last point: A quite strong civ with an awesome world spell. I know the the game is balanced for standard sizes and normal speed...but i just achieved my earliest deity victory...arboria, duell...the treeants killed my oponent in turn 27...
For all other cardtypes: the ljolsalfar should be able to cripple or even eradicate ANY close opponent at almost any time...nobody can withstand an army of treeants by turn 100...i dont see any counter against this.
Furthermore, my elven workers were able to remove jungle just from the beginning, but thats probably a bug, so i will put it there.
I would recommend the follwing things:
I personally think that the Ljolsalfar are quite a strong civ, so the ability to build mines under woods and to build anything under the jungle should be removed.
Further i would tie some worldspells to certain techs (perhaps even if ANYBODY has this tech...) or scale them, e.g. with no tech the march of the trees summons SOME least treeants (about str 5) form SOME (not all, just too much, you never can afford SO many units at this time of the game), with another tech (be it FoL or anything other suitable) you summon some more lesser treeants (about str 7-8) and in the late game (with suitable tech) you have the current effect. This way the Ljolsalfar have some handy extra defenders on their hands, but not THAT EXTREMLY POWERFUL invasion army.
I admit, that this variant makes this worldspell more complicated, but i think it balances the spell quite well...
To add something: it might be an idea to allow GOBLIN/orcish workers to build something under the jungle...