Environmentally conscious consumers often ask me if a real Christmas tree or an artificial tree is the most sustainable choice. As a researcher in horticulture and forestry, I know that this issue is also of concern to the Christmas tree industry, which is worried about losing market share to artificial trees.
And they have a good reason: of the 48.5 million Christmas trees bought by Americans in 2017, 45% were artificial, and this share is increasing. Many factors can affect this choice, but the bottom line is that Christmas trees, whether they are artificial or not, have negligible effects on the environment. The "winning" option in terms of carbon footprint is entirely dependent on the assumption that consumers will keep an artificial tree in relation to the distance traveled each year to buy a real tree.
From the plantation to the shredder
Many consumers believe that 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 this purpose.
To estimate the total impact of something resembling a Christmas tree, researchers use a method called life cycle analysis to develop a "cradle-to-grave" accounting of the inputs and outputs needed to produce it, its use and disposal. For natural Christmas trees, this covers everything from planting to harvesting trees through their disposal, through the use of equipment, the application of fertilizers and of pesticides and the consumption of water for irrigation.
Life cycle assessments often also estimate the carbon footprint of the system. The use of fuels is the main source of greenhouse gas emissions in the production of Christmas trees. The use of a gallon of gasoline or diesel to operate a tractor or delivery truck frees up 20 to 22 pounds (9 to 10 kilograms) of carbon dioxide in the truck. atmosphere.
On the positive side, Christmas trees absorb and store carbon from the atmosphere as they grow, helping to offset emissions from operations. Carbon represents about 50% of the dry weight of a tree's wood when harvested. According to recent estimates, conifers the size of a Christmas tree store about 20 pounds of carbon dioxide in their tissues located above the ground and probably store similar amounts underground in their roots.
However, the use of 1 gallon of gasoline produces roughly the same amount of carbon dioxide. Therefore, if a family travels 10 kilometers in each direction to get its real tree, it has probably already offset the carbon sequestered by the tree. The purchase of a tree closer to home or on a wooded ground along your daily commute can reduce or eliminate this impact.
And natural trees have other impacts. In 2009, American scientist specifically called on the Christmas tree industry to launder the heat, as producer press releases touted carbon uptake by Christmas tree plantations, while ignoring pesticide use and greenhouse gas emissions. carbon dioxide resulting from the management, harvesting and shipping of plantations.
Is the synthesis better?
Artificial trees have a different set of impact. Although many people think that the shipping of trees from factories in China consumes a lot of energy, shipping is actually very effective. The greatest energy consumption in artificial trees is in manufacturing.
The production of polyvinyl chloride and metals used in the manufacture of artificial trees generates emissions of greenhouse gases and other pollutants. China is employing to reduce pollution from its chemical industry, but this could drive up prices for these materials and products made from them.
In addition, to consider sustainability in a broader perspective, the production of real Christmas trees supports local communities and the US economies, while the purchase of artificial trees mainly supports manufacturers in China.
Go head to head
The American Christmas Tree Association, which represents makers of artificial trees, recently commissioned a life cycle assessment comparing real and artificial Christmas trees. The analysis took into account the environmental aspects of sustainability, but did not examine the social or economic impacts.
The report concluded that the environmental "breakeven" between a real Christmas tree and an artificial tree was 4.7 years old. In other words, consumers should keep artificial trees for five years to offset the environmental impact of buying a real tree each year.
One of the major drawbacks of this analysis is that it ignored the contribution of tree roots – which farmers generally leave in the soil after harvest – to storing carbon in the soil. This omission could have a significant impact on the break-even analysis, as a 1% increase in soil organic matter can sequester 11,600 pounds of carbon per acre.
Reuse or recycle your tree
Consumers can not influence how farmers grow their live trees or how manufacturers produce artificial versions, but they can control what happens after Christmas for the trees they buy. For artificial trees, this means reusing them as many times as possible. For natural trees, it means recycling them.
This is essential to optimize the carbon footprint of a real tree. The grinding of used Christmas trees and their use for mulching brings back the organic matter to the ground and can contribute to the formation of carbon. In the United States, many public works departments routinely collect and crush used Christmas trees after the holidays. If local tree recycling is not available, trees can be shredded and added to compost piles. They can also be placed in backyards or ponds to provide habitat for birds or fish.
On the other hand, if a used tree is thrown into a bonfire, all of its carbon content is immediately returned to the air as carbon dioxide. This also applies to trees felled on forest farms. And if the trees used are placed in landfills, their carbon content will eventually return to the atmosphere as methane due to the degradation of materials buried in landfills. Methane is a greenhouse gas 21 times more potent than carbon dioxide over a century. It is therefore the most harmful way for the environment to get rid of a used tree.
All sorts of factors influence the choice of Christmas trees, from the scent of fresh trees to family traditions, travel plans and the desire to support farmers or buy local products. Regardless of your choice, the solution to relieve environmental anxiety is to reuse or recycle your tree. Then you can focus on the gifts to put below.
Bert Cregg is professor of horticulture and forestry at Michigan State University. This article was originally presented on The Conversation.