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I wonder how much carbon dioxide does grass sequester, compared to trees. Moreover, is grass still efficient in absorbing pollution? It seems to me that grass would be more efficient in storing carbon in soil than trees.

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    There probably isn't really an answer to this question. "Grass" and "trees" aren't two uniform, globally constant processes. They're two very large branches of life that can exist under a wide range of conditions (including different human management systems). Aug 5 '19 at 19:09
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I found this article regarding lawns. It suggests that lawns could be regarded as carbon sinks only if they are not (frequently) mowered, and do not use pesticedes.

Also:

An acre of established temperate forest can hold from 2,000 lbs. up to 6,000 or more lbs. of carbon per year, depending on the age of the trees and other conditions. Mature grasslands sequester 2,400-3,600 lbs. per acre each year.

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    Also, my understanding is that applying nitrogen fertilisers to anything tends to accelerate growth and cause carbon to be lost from the soil. Such fertilisers are commonly applied to lawns, and to pasture. Jun 12 '15 at 23:10
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I believe its all about mass, biomass is effectively sequestered CO2.

In year one a lawn probably has a greater mass than a one year old tree, and so more CO2 sequestered. But in year twenty the tree has a greater mass about 1 tonne which is 3 tonnes of CO2, and the lawn, if its been regularly mowed still only has the same biomass as it did in year one.

Of course by year twenty there is a twenty years worth of lawn clippings somewhere which has either returned to the air or broken down into soil somewhere, its in some other lifecycle.

That said the tree might lose its leaves every year which would join the same lifecycle as the lawn clippings.

In conclusion, the lawn is more efficient for carbon sequestration in the first year or so, but over the long term the tree is more efficient in locking up the Carbon in a more permanent manner.

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    This analysis is incomplete because it only includes above-ground biomass. It also doesn't consider the complete lifecycle of the biomass. Where does the carbon from the above-ground portion of a tree end up at the end of its life? Typically, released into the atmosphere. So over the complete life of a tree it is often close to carbon neutral. Aug 5 '19 at 13:23
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I wonder how much carbon dioxide does grass sequester, compared to trees. Moreover, is grass still efficient in absorbing pollution? It seems to me that grass would be more efficient in storing carbon in soil than trees.

Where I live, trees grow 7 cubic meters per hectare per year. One cubic meter is 0.5 tonnes so this is 3.5 tonnes per hectare per year.

1 acre is 0.404686 hectares so it's 1.42 tonnes per acre per year.

If grass grows 10,000lb per acre per year then that's about three times as fast as tree growth.

However, consider what happens to the carbon after the tree or grass is cut down.

Trees can be for example be used to construct houses. The carbon stays sequestered for 100 years.

Grass will usually biodegrade after cutting it, if exposed to ambient air.

So, to cause the carbon in cut grass to stay sequestered, you will need to dig a hole to the ground, store the grass there and cover it in such a manner that oxygen can't reach the cut grass. Then the cut grass will become the fossil fuel reserves of the future.

All of this however is only of academic interest. In reality, we are using fossil fuels at such a great rate that the CO2 created will never be captured this way. The problem needs to be fixed at the source, by using alternative forms of energy production, not by attempting to store cut grass underground.

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Two things you need to consider:

  • Storing more CO2 in the soil means you want to have more life in there. This points to the avoidance of fertilizer and pesticides in your lawn.

  • Peat has a huge capacity to store CO2, so you may consider turning your lawn into wetland if possible ;)

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Grass is more efficient at capturing carbon from the atmosphere. If it is used productively, ie, used to feed animals or the clippings mulched or composted, this locks away the carbon very effectively. When grass is mowed or grazed, the roots—which store a significant proportion of the plant's carbon deposits—are shed by the plant and become part of the organic matter in the soil, providing nutrition and habitat for bacteria, fungi, worms and other creatures. This all locks away carbon in the soil.

Over 20 years, a hectare of grass, properly managed, will produce more vegetative mass than a hectare of trees. Because the biomass is harvested throughout the year it may seem that there is less in a meadow than in a forest but if you consider all of the clippings that have been usefully produced, the mass is greater from the meadow (all other things being equal).

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    Hello and welcome! That's quite the claim -- can you provide a reference?
    – LShaver
    Dec 8 '20 at 1:42
  • Check out Joel Salatin's Ted talk: youtube.com/watch?v=4Z75A_JMBx4 He mentions that his fields produce 10,000lb of grass per acre each year. There is plenty of other similar data out there as well as life experience that is impossible to provide a reference to. Dec 9 '20 at 11:53
  • Conduct a thought experiment; consider a piece of ground, think about how tall the grass will grow in, say, 2 months, multiply that by the cuttings you could get per year and multiply that by, say, 20 years. Compare than to the trees that could be planted on the same ground and how tall they would be after 20 years. Dec 9 '20 at 11:59
  • But trees take decades to biodegrade (releasing captured CO2 back to the air). Grass takes... a few months?
    – LShaver
    Dec 10 '20 at 20:11
  • So after capturing the carbon, the next question is what you do with it! You can sequester the carbon captured by the grass in the soil or feed it to cows or other animals—which is a great way to store the carbon. Peat is one of the richest carbon stores that we have. Trees can either be turned into timber—a great store of carbon—or burned—which releases the carbon back into the atmosphere very quickly. Dec 14 '20 at 11:54

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