After getting cats we were still determined to keep getting live Christmas trees. I can't really remember much about the first year, because they were still pretty small kittens, so they didn't seem to care much about the tree itself other than the ornaments. Last year we only had the one cat for the first time, and being a little more bored (but happy) having no playmate, Jaypeg seemed to show a greater interest in the tree in the form of eating the needles.
We have gotten white pine the past couple years because I loooove the appearance of the longer needles, and because I heard internet horror stories about how evergreen needles can be deadly to cats if ingested (puncture intestines and the like). I figured the softer pine needles would be a little easier on her internal organs than fir needles, if she happened to eat any.
And eat them she did, which led to vomiting on a fairly regular basis as pine needles are mildly toxic to cats. By the time Christmas was over I was so ready to be rid of the tree so we wouldn't have to deal with all the vomiting.
This year I kind of forgot about that and we picked up another gorgeous white pine (for $30 at Sobeys, who else thinks it's insane that a live tree that took years to grow doesn't cost $5000???) and she promptly started eating the needles before we'd even put the tree in the stand. And of course started vomiting.
Last year I googled high and low to try and figure out how to keep her away from the tree but nothing seemed to work, including putting a compressed air motion sensor under the tree (she could just work around it). But this year I had a stroke of genius/luck the day after we set up the tree.
I was standing at the kitchen counter next to an empty wire cooling rack that I'd just taken a loaf of bread off of, one of these:
Jaypeg is not supposed to be on the counter which naturally means she is always on the counter, but I noticed her try to step on the cooling rack and then decide against it. Eureka! I put the three wire racks we have around the tree, and sure enough, combined with the compressed air sprayer she pretty much completely avoids the bottom of the tree now. The only eating of needles and vomiting now is when our Roomba pushes the racks away a couple times a week but I can deal with that frequency (or maybe place the Roomba barriers better).
There you have it, internet - a surefire method for keeping your cat away from the Christmas tree: wire cooling racks!