To start with...what is a Christmas tree (not going to assume anything here)? The typical
Christmas tree is an evergreen tree (Pinophyta or Conifera), typically a fir, brought inside and
decorated with all kinds of shiny bright objects. According to the NRCS...er, actually the U. of Illinois Extension Office, there are 36 million Christmas trees sold every year, and 73 million planted yearly. That's a lot of Christmas trees, and they are planted at an initial density of over 2,000 per acre. For comparison, in the state of Kansas, tree mitigation plantings are typically
done at 640 trees per acre. So we are talking some really high initial densities. Of course anything sold by the millions will have government oversight. Feel free to peruse the absolutely tedious USDA Christmas Tree Grades. (pdf warning...not that anyone's going to read that!) Wow.
About 95% of the real trees purchased come from farms. According to the National Christmas Tree Growers Association, a few are allowed to be harvested from National Forests. And let's take a moment here to appreciate that yes, there is a National Christmas Tree Growers Association and yes their 'Mythbusting' article is just as ridiculously snarky as anything I've ever read by a glorified PR firm. The article is actually about the "Great De-Myth-ification Campaign". I'll offer a quick summary: Fake trees suck. Although I'd prefer this message
wasn't coated in a thin vaneer of hazy logic and silly attacks at the fake tree industry, I tend to think that environmentally, a real tree is probably a lot better.
Why? Well...As stated above, the real trees are grown on farms, and although it sounds like there are a lot of pesticides and other petroleum products used in their management, at least we're not talking about a completely manufactured product. Of course, this is all a straw
man...the real question is why have one in the first place? Oh, you know, lots of culture and stuff. Didn't I say I was going to talk biology?
I usually refer to conifer trees as evergreen trees. Can anyone in the class tell me why that's not really a good term? Yeah, that's right, because not all 'evergreen' trees are conifers. Consider plants in the tropics: None of them drop their leaves seasonally. So let's stick with conifers.
Conifers are typically distinguished by their leaves and reproductive organs. The leaves are usually thin and waxy, allthough some are more like scales (see examples). These leaves minimize water loss and maximize light absorption (especially in cold and dry climates). As expected, almost all of them keep their leaves year-round even in temperate or northern climates, but a few do not. Conifers tend to do better in cold or arid climates (i.e., northern or high altitudes) and can get really really big (Giant Sequoia). I don't know anything about the evolutionary history of conifers, and nobody on the web is really giving me a lot of info on this.
The best I can say is that conifer-like plants emerged around 300 million years ago. There are currently ~700 species of conifers, which is actually a really small number for such an
ecologically important group of plants. By comparison, there are estimated to be 250-400,000 species of angiosperms. Wow.
A typical Christmas tree takes about 7-10 years to grow. Out of the 2,000 per acre planted, only between 750 and 1000 per acre will survive, which is still a heck of a lot. Keep in mind that just because a plant is chopped off at the base and stuck in your living room it is still alive. That tray at the bottom of the tree isn't just for the dog and cat to drink out of, its to keep your tree living. Firs tend to not lose their needles easily even after dying and drying, but other species will, and keeping the trees well-watered will reduce that. You'll also get more of the 'tree smell' that so many people (myself included) find awesome.
I know that was a sorta non-sciency post, but I've been busy and its Christmas. Merry Christmas!