Just went back through the episode and they some artificial trees may have less environmental impact if used for at least 5 years. However, some other things to consider, first where do you think the plastics in the artificial tree come from? That's right, PETROLEUM! Also, artificial trees will end up in a landfill once they reach their end of life while a real tree is 100% biodegradable. Lastly, most artificial trees come from oversees (mostly China) whereas getting a live tree is a great way of supporting local businesses. Of course now that you have an artificial tree you're better off using that as long as possible to minimize the environmental impact.