Carbon Capture

Tree Time

Many of us have an evergreen tree in our living rooms right now, and it’s an excellent time to reflect on the wonder of trees. I have come to do so every winter, which is why I call the few weeks when we have our tree for the holidays Tree Time. It is also a good time to plan what you are going to do with your tree once you are done displaying it. I hope to convince you to begin your carbon sequestration adventure by shoving it up your yard, so to speak. But more on that in a bit!

Our evergreen holiday trees are conifers, and they were some of the first land plants to evolve. They followed colonization of the land by mosses, ferns and other spore plants, and their partners fungi. Each new type of plant that evolved created opportunity for insects and other animals to evolve as well, and in that sense trees and plants are our progenitors.

Evergreen trees were probably first brought in the house for the holidays as a symbol of the ability of life to persist and renew itself despite the extreme dark and cold the winter brings. These days they could well be a symbol of the ability of life itself in the form of trees and plants to stabilize our climate and ecosystems.

Trees pull carbon (in the form of carbon dioxide) out of the air, and with the help of sunlight and water they turn it into glucose, which they use to build their bodies. Many people assume that the material in a tree’s trunk, branches, roots and leaves comes from the soil – but in fact, it comes from the air! Trees are powerful carbon sequestration engines, just like all plants. The mass of a large tree represents a huge amount of carbon sequestered for all of the time that a tree is alive. The more trees we have on the planet, the more carbon is safely tucked away from the atmosphere in tree bodies.

What happens when a tree dies? Well in the forests of the Pacific Northwest, where I grew up, the tree falls and slowly decomposes, while a horde of plants, fungi, and microorganisms use its carbon in myriad ways. During this long process, the fallen tree acts as a sponge, and holds tremendous amounts of water, helping the plant, fungal, and animal communities around it make it through the dry time. Some of the carbon from the decomposing tree becomes stable humus in the soil, where it will remain for hundreds or even thousands of years, again safely sequestered away from the atmosphere. We will talk more about soil humus and its awesome potential to save us from climate change throughout this blog.

What happens if a tree dies in a yard? Typically in the United States, it is cut up, raked up and hauled away. The soil near where the tree fell doesn’t get that gift of carbon. Most often, that tree will be hauled to a land fill, but sometimes it is chipped for mulch or burned for fuel. In later posts, I will examine these different fates in more detail. 

But for now I have a challenge for you. If you have a live Christmas tree, I challenge you to give it to your soil, as a regenerating gift of carbon. 

There are three basic options for shoving your Christmas tree up your yard without the use of a chipper. These options apply equally to other tree waste – fallen branches, trees you have to take down because they are diseased or likely to fall on your house, trees blocking a wonderful view, or whatever. 

The first option is to use the tree or parts of the tree as mulch. This is fairly easy – saw it into pieces, use loppers to cut up the branches, and lay it over the ground somewhere. The advantages are that it is easy to do, it will protect your soil from wind and temperature extremes, and over time it will undergo decomposition like the fallen tree described in the Northwest forest. Some of the carbon in the tree will return to the atmosphere and some will be turned into stable humus in the soil. The trunks and branches may even provide habitat to mushrooms during the process, and will for sure support beneficial fungal communities in the soil. Insects, birds and other small animals will appreciate the habitat, especially if you leave the whole thing as more of a brush pile. The disadvantage of this option is that it may not look the way you, your roomies, or your neighbors expect your yard to look.

The second option is to cut up the tree and use the pieces to define paths, create borders, fences, trellises or other supports for garden plants. It is surprising how useful wood can be in the garden, and it is much better to use wood you have on site than to buy wood from a store for many reasons. You can even get creative and use the wood to create garden sculptures. If you ever grow tired of your wood structures, they are all natural and can be placed on or in the soil to finish decomposition. 

The third option is to cut up your tree, dig an area where you would like a somewhat more raised garden bed, throw in the logs and branches and then cover them with the dirt you dug up. Ideally you would top the bed with mulch, and leave it until spring when it will be ready for planting. This is actually an ancient practice called hugelkultur, and I will write one or more extensive posts on hugelkultur later, but for now, bury your tree and you can’t go wrong. Your roomies and neighbors will notice nothing amiss, and your tree’s carbon will be safely sequestered where it will do you and your garden a lot of good for the next decade or more. As the wood underground slowly decomposes, it will begin to hold more and more water, getting your garden through dry times without such frequent watering. Microorganisms and fungi will feed off the carbon and then team up with your plants to help them grow. Your raised bed will warm up earlier in the spring, and will provide you with more surface area for growing more yummy and/or beautiful plants. Some of the carbon in your tree will become humus and will stay in the soil for centuries. Finally, no gasoline powered truck will have hauled your tree over to the landfill, spewing carbon dioxide into the atmosphere, and your tree won’t off-gas methane (a powerful greenhouse gas) as it undergoes anaerobic decomposition in the landfill.

There is no exercise more enjoyable to me after a feast filled holiday than digging a hole in the ground. I absolutely love it! I hope you will try it. If you have no yard, perhaps you can find a bit of soil somewhere in your neighborhood that can use some carbon.

If all else fails, many cities will pick up your tree on a certain date and will mulch it for use on yards, and that is nearly as good a fate for your tree. In my view, sending your tree off to be mulched will deprive you of some of the Tree Time fun to be gained by interning it in your own ground, but whatever you decide to do, Happy New Year! Let’s help make this a great year for our climate.

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8 thoughts on “Tree Time

  1. Great post Sandra.
    On the very general topic of trees, I highly recommend the following book.
    It is a fantastic and fresh perspective on the true nature of trees! It’s an easy, very enlightening and enjoyable read.
    The Hidden Life of Trees
    by Peter Wohlleben

    1. Thanks Tim I will check that out! I have been buying books during the pandemic like you wouldn’t believe – I now have a dozen or so I can’t wait to get to. It’s been a good time for study!

  2. I have the happy circumstance of having to leave my Christmas tree up until the end of January, as my husband is very nostalgic about the season. Thus, when my tree is ready to join the yard, it will be very dry. I plan to put the branches through my electric chipper, the SunJoe, and I love the idea of burying the bigger pieces in the ground. I look forward to creating my first hugelkultur bed! Thanks for the inspiration!

    1. Yay! I think our average Christmas trees will be good for a very small area Hugelkultur bed depending on how much you want the bed raised. Think in terms of about two feet by two feet to two feet by four feet.

  3. This may not be the most climate friendly use of our Christmas tree, but we always cut it up and burn in in our fire place or fire pit the following year. 🙂

    1. That makes sense! Wood heat is much more carbon neutral than natural gas or electricity from coal power plants as far as I know – and I like any treatment of home carbon that doesn’t involve hauling it off site!

    1. Hi Kate – I think thorny rose branches are great for hugelkultur IF you can put them way inside the mound, where you are not in danger of getting pricked when you dig around! I got a thorn scratch last fall that became infected and took months to heal! But inside a hugelkultur mound would be better than in your compost – that never works out in my experience!

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