— It's that time of year when even environmentalists committed to saving trees proudly display a massive tree carcass in the living room, bejeweled and topped with a star. American cities are rarely greener than during Christmastime, when every other street corner can seem to be occupied by a tree peddler.
Christmas trees play into a wider debate among environmentalists: Are tree farms better or worse at carbon sequestration than untouched forests?
The pro-tree-farm argument goes like this: When you plant a tree, it goes from seedling to full-grown plant by rapidly extracting carbon from the atmosphere, including carbon that humans have emitted by burning fossil fuels and raising cattle. (When a climatologist looks at a tree, he sees a leafy pillar of solidified greenhouse gases.) Once the tree reaches maturity, though, it slows its consumption of carbon. By way of comparison, think of the appetites of a growing teenager and a senior citizen. When you're done growing, you stop consuming as many calories. The best move, according to some tree-farm advocates, is to replace the mature tree with a new sapling and start the growth process over again.
Tree farmers have been making this claim for more than two decades, but many climate experts think it's bunk. The most obvious objection to the theory is: What becomes of the trees once they're cut? According to research out of Oregon in the 1990s, 58 percent of felled trees are used for paper, mulch, firewood or other short-term purposes. In those cases, the tree's sequestered carbon quickly reenters the atmosphere after decomposing or burning. The remaining 42 percent is used in ways that keep the wood intact more than five years, such as homebuilding and furniture production. Even in those cases, though, the carbon doesn't stay sequestered forever.