typical dry matter is ~50% carbon by mass there are 10,000 m2 per hectare fast-g

Question

typical dry matter is ~50% carbon by mass

there are 10,000 m2 per hectare

fast-growing trees will produce ~10 metric tons of dry matter/hectare-year (with optimal placement and areal density)

slow-growing trees will produce ~1 metric tons of dry matter/hectare-year (with optimal placement and areal density)

Finally, suburban house offsetting

a) Can the average suburban house offset its fossil fuel CO2 emissions (direct energy and electricity) with fast-growing trees onsite?

b) Is there enough space? If not, how much more is needed?

Some key factoids:

Average household emits ~10 metric tons carbon per year

o Assume a 0.5 acre parcel as the average lot size

o Assume 50% is occupied by building

Explanation / Answer

Here average lot size is given as 0.5 acre, of which 50% is occupied by the builiding itself. Therefore, land left for planting tress would be 0.25 acre.

Now, we know 1 acre = 4000 m2. therefore, land that is available for avaerage household to plant trees- = 0.25*4000m2 = 1000m2.

Since it is given that 10 metric tons of dry biomass is produced by fast growing trees in on hectare of land, and one hectare = 10000m2. Therefore, 10 metric tons of biomass is produced in 10000m2.

a) Now, since area available for avg. household for planting trees = 1000m2, therefore, dry biomass produced by houshold will be = 10*1000/1000= = 0.1 metric ton per year. Of this 0.1 metric ton, only 50% is carbon. Therefore, an average suburban houshold can only produce 0.5*0.1 = 0.05 metric ton of C per year by planting fast-growing trees.

We see that avg household emits 10 metric tons of carbon per year but produces only 0.05 metric tons of carbon per year. Therefore, it can NOT offset its fossil fuel emission by planting trees onsite.

(b) To offset its fossil fuel emission an average house hold needs to produce 10 metric tons of carbon per year, which can be done by planting fast-growing trees on 2*1 hectare or 2*10000m2 of land. (please note that 1 hectare of land can produce only 50% of 10000 metric tons of C).

But avg. household has only 1000m2 of land to plant trees, therefore, additional land that will be required can be calculated as 20000/1000 = 20. It means an average household will require 20-fold more land to offset their fossil fuel emission.

Thanks!

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