..the preimse behind the film is almost a metaphor of western world and 3rd world (i know it sounds really contrived but bear with me)
George is basically the western world, his love of all that he has and his comfort that these things bring him is escencially what is holding him back from really enjoying his life.
The trees are the 3rd world. They are not strong enough to support much and any extra weight put on the causes them to break.
When george decides that he does not need all the excess which he has and gives it away it makes him a happier person but it also makes the tree stronger and healthier and more able to sustain abundant life.
I know it sounds really tacky but theres not much i can do about it.
Another point of view is that george is just a fatman with too much chocolate, and the ground on which the forest sits simply does not hold enough nutrients to keep the trees strong and healthy.
still sounds like a metaphor to me though