OUCH ! Quite amazing !! It seems to be really good !
To know how much polys are currently used in your scene hit "7" (not numpad).
You can change settings too to know how much triangles are used, this is the most important thing in Re-Volt.
You can put as much triangles as you want altough only ~16000 should be solid surfaces.
In any case, avoid more than 6000 viewable triangles at any time. This is subjective and variable but this would allow you to add some other polys in your scene for detail purposes.
Think about it, do not try to add details first unless if it's needed for setting up gameplay. Details can be added using instances too.
Try to put littles trees near to the roadway while huge ones could be placed far away. Then you can "cheat" to hide flat large places by adding some bushes, for example.
Polycount should be reduced a lot while your track will not lose anything.
Now my 2 cents :
I'll don't discuss the graphic style you've put in this track, but trees leafs seems to be so smooth while all the trunks are straights.
Also, try to put a transitional texture between trees and ground, something like this :

I know you'll probably don't change things so much in this track, just do it as you like to play around with 3ds, and keep it in mind for... next one ?
Good luck !!

PD : there is a way to set up 3ds so that your track will rendre as it will ingame. Just ask if you want to know more I could write a little tut.
