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I am curious, what people could do with a small piece of land like their home backyard (say originally it is a regular lawn smaller than 20m^2, in temperate continental climate (so pretty harsh)) to help fight climate change.

Intuitively, we might think fast-growing trees are the best carbon accumulator (e.g. hybrid poplar is a famous one). Wood is nonetheless very stable carbon but it may be an incomplete picture if we focus on the aboveground growth metrics only. As a matter of fact, most stable soil carbon as recent research has shown is root-derived (dead root as well as root exudates)[1][2][3]. Other things like mycorrhizae and dispersing litter also come into play which results in a larger radius of impact on soil carbon. Also, the backyard is preferably minimally managed with no synthetic products needed (which also come with its own carbon footprint).

I would be glad if someone can shed some light on this complicated matter. Answers with scientific evidence and an estimated amount of carbon sequestered (say per year) will be very appreciated :)

References:

[1]Sokol, Noah W., et al. "Evidence for the primacy of living root inputs, not root or shoot litter, in forming soil organic carbon." New Phytologist 221.1 (2019): 233-246.

[2]Lange, Markus, et al. "Plant diversity increases soil microbial activity and soil carbon storage." Nature communications 6 (2015): 6707.

[3]Treseder, Kathleen K., and Sandra R. Holden. "Fungal carbon sequestration." Science 339.6127 (2013): 1528-1529.

  • I'm not 100% sure I have a good enough picture of what you are working with. Where are you located? If you have question about what you can plant or grow above or below the surface I need a better understand of your landscape. Not just your weather, but the type of soil you have. If I had a region I could do a little more research into what is available to work with. – GardenGems Jan 6 at 21:59
  • I live in Quebec. The soil in my area ranges from sandy loam to loam. – y chung Jan 6 at 22:06
  • Quebec is a large province. What are the lowest temperatures, colder or warmer than -30°c? – GardenGems Jan 6 at 22:18
  • coldest can be around -20C – y chung Jan 6 at 22:28
  • Are you also considering mitigating climate change by restricting the use of gasoline (and battery) powered mowers, trimmers, etc? If yes, this would certainly affect any lawn you put in - you might want to consider something like buffalo grass or sedges like Carex pennsylvanica for their low-growing, no mow habits. They top out at about 15 cm or so, which could be tough for foot traffic. With fescues, ryegrass, and bluegrass, you can cut them with a reel mower at about 5 cm or so. – Jurp Jan 7 at 3:12
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It is a difficult question and I think you could do very little for storage of CO2. To directly combat climate change with storage, you should store CO2, so it means you need to create new organic matter in your soil, so probably lawn with very frequent mowing, and without removing cut herbs, but in your climate you will not get much storage. (or better, you can do much more with other methods and with much less time), a very good CO2 storage is peat, but you need a larger, wetter field, and possibly not near homes.

I would reframe your question and so I propose you two other options:

  • forget climate change and things nature, and so go for adding biodiversity. Is it good for you?

  • offset emissions: a vegetable garden could help you to consume less CO2: you will learn to use season vegetables, you learn more about classic vegetables, and you can remove some storage, refrigeration, CO2-preservetion, etc from vegetables you would buy from your supermarkets.

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I like your original idea. Sticking with your woodland trees with lots of underbrush. Poplars are fast growers. Not just above the surface, but below as well. They create a vast network of roots underground. Use native species. They will have better biodiversity. You can get them ungrafted, but your hybrid is probably grafted on different root stock. I would inoculate each with hardy mycorrhizal fungi. Using the Poplar with the native Bracken Fern. Bracken ferns are vigorous growers. Ferns make intensive roots. If there are any evergreen ferns you could add a few of these as well, but they will not spread as fast as the Bracken. Together you will have every inch covered in green during the growing season with what you know is a vigorous network below the surface. When you plant everything put down some clover seeds. Clover will keep the ground covered in green until your Bracken and Poplar fill in. (You can fit other native underbrush as well.)

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    You'll want to consider your neighbors, if you're in a town or city. Poplars are, as you noted, fast-growing, which also means that they'll be weaker in structure than slower growing trees. This can lead to falling branches in the future. This holds true with silver maple as well. The Populus genus is also relatively short-lived, which means your CO2 store is also short-lived (silver maples can live 150+ years). You could consider Catalpa speciosa, which is a fast-growing, longer-lived tree. As for undergrowth - you have an issue as the land will be in full sun for years before getting shady. – Jurp Jan 7 at 20:22
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    @Jurp One of the reasons with going with Bracken Ferns is they can handle the full sun. They are often planted under power lines to inhibit the germination of trees. Populus may have short lived trunks 30-40 years, but their massive root systems can live for thousands. They quickly replace any sunny spot with a new tree. They grow close together to create a natural wind barrier to protect themselves. Together the Populus & the Bracken can create that dense growth both above and below the surface. I don't know enough about Acer's root systems to say if they would accomplish the same. – GardenGems Jan 7 at 21:04
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    Aspen (Populus tremuloides) spreads rhizomatously and forms large clumps; not sure if the OP wants that. Female Cottonwoods (P. deltoides) are very messy and are not good urban trees. White Poplar (P. alba) is a cool tree but very weak (all would be fine rurally). In all cases, their leaves are leathery and don't decompose quickly. Bracken ferns are both invasive and toxic; from the US Dept of Agriculture: "Bracken fern is poisonous to cattle, sheep, and horses"; it's also poisonous to dogs. Also from USDA: "Research has indicated that bracken fern is also carcinogenic". – Jurp Jan 7 at 21:17
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    @Jurp I said this before, I don't want to argue. I don't have the energy. If want to answer the question then answer the question. If yours is different than mine, than so be it. But, stop trying to pick at mine for no reason than out of spite. You use the word invasive incorrectly anyway. A native plant is not invasive. It can be vigorous, and obnoxious, but not invasive. There are many plants that are poisonous to both human and some some animals, including many 'deer resistant' plants, that does not mean they do not serve a purpose in nature. Cattle are the invasive species. – GardenGems Jan 8 at 1:57
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    Whoa, slow down. Not trying to pick at you out of spite. Just trying to clarify your answer and, much more important in this case, tell the OP that your recommendation is toxic and possibly carcinogenic.I feel that it's important that our answers include potential solutions AND problems/issues (if any), ESPECIALLY health-related ones. I know you don't want anything bad to happen to the OP, but we need to include toxicity when it's an issue. The word "invasive" came directly from the USDA site, but I agree with your point. I would normally use "aggressive" or maybe "thug" for natives. – Jurp Jan 8 at 15:04

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