Here are a couple like to help you out.
For the second part of the question, here: http://www.d20pfsrd.com/gamemastering/environment/environmental-rules#TOC-F alling-Objects
As to the first part... Well, I don't feel like doing the math, so here: http://www.metla.fi/silvafennica/full/sf44/sf444681.pdf
Basically, every tree is different (size, root structure, density, etc)
Unless he has put ranks in appraise, I would say he has to burn a ton of time trying out various trees before he finds one that he can pull out of the ground. The actual weight of it will be significantly less than his max lift load, as so much of that max weight was being consumed by overcoming the countering forces of the tree being firmly planted in the ground.
It may actually be more efficient to have a running search for fallen trees going on, set at your passive perception (take 10) value, and wait for the dm to say - oh, you spot a fallen tree. Even then, expect it to not weigh your max lift amount... Whatever level you are, the DM could roll a dX (where X = Level) to determine the weight of the tree.
Regardless of the weight, if it were a Collosal sized Tree (as big as a Tarrasque), if it fell 30 feet or less, it causes 2d6 damage (Ref DC 15 for half).
If the tree were dropped from between 31 and 150 feet in the air, it would do 5d6 damage (Ref DC 15 for half).
Lastly any height above 150 feet from which the tree was dropped, would cause 10d6 damage (reflex DC 15 for half)
Based on this: http://www.ncrs.fs.fed.us/pubs/ch/ch01%5CChvolume01page401.pdf
A character could be capable of lifting a colossal sized tree (64+ feet tall) by spending a point of burn - as early as first level. Though the probability of finding a tree that big and that light, is very unlikely. At 9th level, this shouldn't be a problem.
That said, it falls on the DM to say you have found the tree you were looking for.
The other thing to consider is, at 9th level, a point of burn only gets you 9 minutes of lifting.
So unless you have a way of carrying the heavy tree around when NOT dropping it on people, this is more of a cool theory than practical application