The National Christmas Tree Association has this to say
about using natural trees
Real Christmas Trees: The Best Choice
Each holiday season, shoppers find themselves confronted with a choice: celebrate with a fresh, real tree, or one that is artificial plastic or aluminum. What most people don't realize is that the best choice has always been the traditional and natural choice - a Real Christmas Tree.
Real Christmas Trees Benefit the Environment
While they're growing, Real Christmas Trees support life by absorbing carbon dioxide and other gases and emitting fresh oxygen. The farms that grow Christmas Trees stabilize soil, protect water supplies and provide refuge for wildlife while creating scenic green belts. Often, Christmas Trees are grown on soil that doesn't support other crops.
Real Christmas Trees Are Renewable
Real Christmas Trees are grown on farms just like any other agricultural crop. To ensure a constant supply, Christmas Tree growers plant one to three new seedlings for every tree they harvest. On the other hand, artificial trees are a petroleum-based product manufactured primarily in Chinese factories. The average family uses an artificial tree for only six to nine years before throwing it away, where it will remain in a landfill for centuries after disposal.
So what does this have to do with heating with wood pellets?
When wood lots and forests are managed as a farm just like those of Christmas tree farms or other agricultural crops we are working in a sustainable manner that is better for the environment then using petroleum based sources for heating our homes.