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Mr. Smarty Plants - Compare Natives to Lawn for Carbon Footprint Benefits in Durham, New Hampshire

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Wednesday - September 22, 2010

From: Durham, NH
Region: Northeast
Topic: General Botany, Compost and Mulch, Soils, Turf
Title: Compare Natives to Lawn for Carbon Footprint Benefits in Durham, New Hampshire
Answered by: Marilyn Kircus

QUESTION:

Are there carbon sequestration rate tables for turf (lawn) and bushes, shrubs, trees? I want to compare the carbon footprint benefit of lawn versus the same area put into native plantings.

ANSWER:

This is a wonderful question and I’m excited that I will learn along with you about both carbon sequestration, greenhouse emissions from managing plants, and the carbon footprint benefit of non-native lawns versus native lawns and other plantings.

The short answer to this question is NO.  There are no tables you can consult.  This is because not all plants have been studied for carbon sequestration rates and there are many other factors, including the kind and condition of the soil, the climate, and the amount of water the plant receives, to name a few of the variables.

But we can look at trends in carbon sequestration.  Here are some things that will make it more positive:

Grow plants that have the best fit for the place.  This would select for native plants collected and grown from the same area, then the same species of native plants, but from slightly different areas, then non-native plants that grow in the same climate/soil conditions and finallly  the plants we have to coddle to get them to grow in the area.  This was from a study on Native Plants for Optimizing Carbon Sequestration on Reclaimed Lands .

Then it seems that native grasses and trees both have high sequestration rates for carbon. But is important to think about plant communities rather than  a single plant species as the interaction between plants as well as between plants and soil organisms factors into how well the plant system can sequester carbon.

Adding compost to soils, increases the ability of plants to sequester carbon.  The soil microorganisms themselves are both very important to carbon sequestration within the soil and aid the plants in giving them the materials they need to grow.

Having plenty of earthworms adds to the plants ability to sequester carbon.

The ratio of N:C must be correct. Need 100-200 pounds of N for each ton of C sequestered.

When we think about lawns, we have to also think about how we are managing them.  While they do sequester carbon, if we mow them with a gasoline-driven mower, blow the debris away and edge them with gasoline powered tools, fertilize them with chemical fertilizers, and water them with treated city water, we end up emitting up to three times the carbon dioxide that the plants can sequester.  (Reference 1) The assumptions made in this paper are being refuted in another study in which the amount of carbon dioxide generated by managing a lawn is calculated to be much less. But the study cited in reference 1 also checked for how much nitrous oxide was emitted by the grasses. Grasses emit this greenhouse gas after being fertilized with chemical fertilizers.  Release of nitrous oxide is dependent on the amounts and frequency of fertilization. But it should also be a factor when we are thinking of reducing greenhouse gasses in general.

Planting trees can help reduce your carbon foot print by letting you live comfortably on less energy while also sequestering carbon.

Another factor in whether native plantings or non-native lawns are going to sequester the most carbon is water.  In many places in the country, water is being rationed and one can not get enough water to allow the lawn to grow at a maximal rate and thus sequester the maximum possible rate of carbon.  And many cities are trying to educate people to catch all the water that falls on their property to reduce the energy costs of having to treat run-off water along with waste water since all of it goes through the sewage treatment plant. Land that has had the sod removed, and where a shallow depression, called a rain garden has been built and which has been planted with native plants that grow in the wet to dry conditions now available to them, and which is then mulched, is capable of retaining all the water that falls on the land, allowing it to fully permeate the soil and percolate down to the aquifer.  This, I think is another green reason to consider having a native garden rather than a lawn.

For general information, read Cropping super-sequestration options pack big carbon wallop.

Another interesting article on how native grasses fit better into the environment is Native grass could help fuel Bay cleanup.  It is also suggesting that switchgrass could replace corn in the production of ethanol as well as help prevent the chemical pollution of Chesapeake Bay.

This article, Landowners Guide to Carbon Sequestration Credits, is mostly useful for the plants the landowners are advised to use. They reiterate that a mix of grasses is best.

So while we won’t have the final answers in terms of numbers we can compare, we definitely can see the trends we need to follow to reduce our carbon footprint and sequester more carbon dioxide.  Growing plants that are adapted to our lands, not tilling the soils or using gasoline-driven engines to manage the plants, using compost and mulches to enhance our soils, having biodiversity and communities of plants that together, can work more efficiently to sequester carbon, and not adding extra water or chemical fertilizers will all help reduce greenhouse gases.

 

 

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