The enviromental costs of Christmas trees: real vs. artificial

I'm guessing this is the big question in environmental economics. Timothy Taylor takes a look at the issue at his Conversable Economist blog. He writes,

One artificial tree used for one year has greater environmental impact than one natural tree. However, an artificial tree can also be re-used over a number of years. Thus, there is some crossover point, if the artificial tree is used for long enough, that its environmental effect is less than an annual series of trees. For example, the ellipsos study finds that an artificial tree would need to be used for 20 years before its greenhouse gas effects would be less than those of an annual series of natural trees. The PE Americas study offers a wide range of scenarios, and summarizes, but here is the situation "for the base case when individual car transport distance for tree purchase is 2.5 miles each way. Because the natural tree provides an environmental benefit in terms of Global Warming Potential when landfilled, and Eutrophication Potential when composted or incinerated, there is no number of years one can keep an artificial tree in order to match the natural tree impacts in these cases. ... For all other scenarios, the artificial tree has less impact provided it is kept and reused for a minimum between 2 and 9 years, depending upon the environmental indicator chosen."

But a full analysis of the issue needs to look at effects across all the full life-cycle of the tree, whether natural or artificial. And things get complicated right about here.

Under what conditions is the tree manufactured or cultivated, with what use of energy, fertilizer, and logging methods? By what combination of transportation mechanisms is the finished tree moved to the home? A substantial share of artificial trees are manufactured in China and then shipped to North America. What are the different issues in use of the tree, including use of water and emissions of fumes? What is the end-of-life for the tree? For example, the carbon in a natural tree will be stored for some decades if the tree goes into a landfill, but not if if is composted or incinerated.

In short, its difficult being green!