Good people don't extinguish life just for the pleasure of it. I'm not talking about meat eaters (that's fine), I'm talking about a population that is, ethically, much, much worse: Christmas lovers.
If Christmas itself is a consumerist disaster—and it is—Christmas trees are a moral one. A 2011 study found that the environmental impact between choosing a natural tree or an artificial tree is negligible, with fake trees being only slightly worse, likely because many of them get shipped over from China. Each year, between 34 million and 36 million Christmas trees are "harvested" (read: killed) in the United States, and 50 million to 60 million more are harvested in Europe. That's a lot of dead trees.
If we left them to grow into beautiful evergreen forests that provide wildlife habitat and carbon sequestration, I'd say, fine, go for it. Everyone could adopt a Christmas tree, visit it a couple times a year, and string some colored lights around a potted plant come Christmas. But we don't do that. We cut the fuckers down and hang fugly handmade ornaments on their dying limbs. And, when we're done abusing these thin-needled creatures, we dump their carcasses on the curb with the rest of the week's trash.
If you have chosen to murder a tree this Christmas, there are several options for January disposal: For one, you can burn it, which has been an annual tradition at Golden Gardens and is a really shitty idea. While massive flames licking the upper reaches of the atmosphere may look cool and apocalyptic, burning trees emits fine particulate matter that is bad for air quality and damages the respiratory tract. It's especially dangerous for the elderly, kids, and people with asthma, and it sends ash raining into the watershed.
Instead of burning your tree, you can leave it on the curb for the city to pick up, take it to a King County transfer and recycling station, or hire a private company to take it away for you. If you choose any of these options, your tree will be ground up and turned into mulch or compost that the city distributes among our many fine parks. As far as Christmas trees go, it's not a bad option, but it's still morally inferior to ditching the Christmas tree altogether.