Environmentally conscious consumers often ask me whether a real Christmas tree or an artificial one is the more sustainable choice. As ahorticulture and forestry researcher, I know this question is also a concern for the Christmas tree industry, which is wary of losing market share to artificial trees.

And they have good reason: Of the 48.5 million Christmas trees Americans purchased in 2017,45 percent were artificial, and that share is growing。许多因素可以影响这个选择,但bottom line is that both real and artificial Christmas trees have negligible environmental impacts. Which option “wins” in terms of carbon footprint depends entirely on assumptions about how long consumers would keep an artificial tree versus how far they would drive each year to purchase a real tree.

From seedling to wood chipper

Many consumers believe real Christmas trees are harvested from wild forest stands and that this process contributes to deforestation. In fact, the vast majority of Christmas trees are grown on farms for that express purpose.

为了估算圣诞树之类的总影响，研究人员使用一种称为生命周期评估的方法来开发“摇篮到严重”，对生产，使用和处置所需的投入和产出。对于天然的圣诞树，这涵盖了从种植幼苗到收获树木和处置它们的所有物品，包括设备使用，肥料和农药施用以及灌溉用水。

Life cycle assessments often will also estimate a system’s carbon footprint. Fuel use is the biggest source of greenhouse gas emissions in Christmas tree production. Using 1 gallon of gas or diesel to power a tractor or delivery truck releases 20 to 22 pounds (9 to 10 kilograms) of carbon dioxide into the atmosphere.

On the positive side, Christmas trees absorb and store carbon from the atmosphere as they grow, which helps to offset emissions from operations. Carbon represents about 50% of the dry weight of the wood in a tree at harvest. According to recent estimates, Christmas tree-sized conifers storeroughly 20 pounds of carbon dioxide in their above-ground tissueand likely store它们的根部下方的类似数量。

However, using 1 gallon of gasoline produces about the same amount of carbon dioxide, so if a family drives 10 miles each way to get their real tree, they likely have already offset the carbon sequestered by the tree. Buying a tree closer to home or at a tree lot along your daily commute can reduce or eliminate this impact.

And natural trees have other impacts. In 2009,科学美国人specificallycalled out the Christmas tree industry for greenwashing, because growers’ press releases touted carbon uptake from Christmas tree plantations while ignoring pesticide use and carbon dioxide emissions from plantation management, harvesting, and shipping.

Is synthetic better?

人造树具有不同的影响。尽管许多人认为从中国的工厂运送树木需要大量精力，但海洋运输实际上非常有效。人造树木中最大的能源用途是制造业。

产生用于制造人造树的聚氯乙烯和金属产生温室气体排放和其他污染物。中国正在努力reduce pollution from its chemical industry, but this may drive up the prices of those materials and the goods made from them.

Moreover, to consider sustainability from abroader perspective，真正的圣诞树的生产支持美国的当地社区和经济体，而购买人造树主要支持中国的制造商。

Going head to head

Recently the American Christmas Tree Association, which represents artificial tree manufacturers, commissioned a life cycle assessmentcomparing real and artificial Christmas trees。The analysis considered environmental aspects of sustainability, but did not examine social or economic impacts.

The report concluded that the environmental “break-even” point between a real Christmas tree and an artificial tree was 4.7 years. In other words, consumers would need to keep artificial trees for five years to offset the environmental impact of purchasing a real tree each year.

One major shortcoming of this analysis was that it ignored the contribution of tree roots – which farmers typically leave in the ground after harvest – to soil carbon storage. This omission could have a significant impact on the break-even analysis, given that increasing soil organic matter by just 1% cansequester 11,600 pounds of carbon per acre。

消费者不会影响农民如何种植自己的活树或制造商的生产方式，但是他们可以控制圣诞节后对他们购买的树木发生的事情。对于人造树，这意味着将它们重复多次。对于天然树，这意味着回收它们。

这对于优化真实树的碳足迹至关重要。磨二手的圣诞树并将其用于覆盖物，将有机物归还土壤，并有助于建造土壤碳。假期后，美国许多公共工程部门通常收集和筹码使用圣诞树。如果没有当地的树木回收，则可以将树木碎成并添加到堆肥中。他们也可以placed in backyards or ponds to provide bird or fish habitat。

In contrast, if a used tree is tossed into a bonfire, all of its carbon content is immediately returned to the air as carbon dioxide. This also applies to culled trees on tree farms. And if used trees are placed in landfills, their carbon content will ultimately return to atmosphere as methane because of the way materials buried in landfills break down. Methane is a greenhouse gas21 times more potent than carbon dioxide over a century, so this is the most environmentally harmful way to dispose of a used tree.

各种因素影响了关于圣诞树的选择，从新鲜树木的气味到家庭传统，旅行计划以及支持农民或在当地购买的愿望。无论您选择哪种选择，缓解环境焦虑的关键是计划重复使用或回收树。然后，您可以专注于将其放在其下的礼物。

Bert Cregg是密歇根州立大学的园艺和林业教授。该帖子最初出现在谈话。