Hyper carbon accumulator(s) for backyards

Question

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.

Answer 1

This article (and the "Part two" it links to) gives a lot of technical detail and some practical advice: Why Not Start Today: Backyard Carbon Sequestration Is Something Nearly Everyone Can Do.

In brief: you want plants which put nutrients into the soil so that you end up with a dark rich soil which contains a lot of nutrients, including carbon. And, of course, you do this by making a good choice of plants ... judging from the pictures you want native perennial flowers rather than trees.

Answer 2

While grass may capture carbon efficiently, the problem is keeping the carbon outside of the atmosphere permanently. If you grow grass, it will quickly grow to an equilibrium state, where every flow of carbon from the atmosphere is balanced by a flow of carbon to the atmosphere.

If you have some strategy of harvesting grass that has captured carbon and turning it into biochar for example, while making room for new grass to grow, in that case grass may be a good option.

However, if you don't, you are pretty much limited to trees. Trees have the benefit that they can easily grow for hundred years, and during that time, effectively capture carbon for the most of the 100-year period. While you can let a tree grow to as old as several hundred years, the carbon capture slows as the tree ages so it may be beneficial to chop down the trees at 100 years. Then you may use the trees to create lumber or biochar. Actually chopping down a tree and cutting it to pieces, if you put the pieces to some place that is sheltered from rain, it will keep the carbon captured for a very long time. So biochar production may not be necessity: whatever remains you have after creating lumber may be stored in a dry place, and it will keep the carbon captured.

Trees also have the benefit of needing very little care. Grass will grow to an equilibrium state very quickly, so you may need to cut the grass every 2 weeks or so and haul the cut grass into a biochar factory (and if you don't have a biochar factory nearby, if you leave the grass somewhere it will decompose and release its carbon).

Answer 3

GRASS, is an excellent carbon accumulator. But our mowing practices make it less practical. Grow your grass, let it grow to a high height then mow it. More time for growth permits longer, more thicker roots which stores more carbon.