How Much Carbon Do Different Forests Store & What Size Offsets Your Driving For a Year?


photo: Chor Ip via flickr.

As any TreeHugger worth his or her epiphytes knows, preserving tropical rainforests is a major part of preventing the worst of climate change--deforestation itself causing nearly as many carbon emissions as the entire transportation sector. But over the past year there have been a number of studies all essentially claiming that one particular type of forest or another stored more carbon than rainforests and why aren't we trying hard to protect them too? Which is a fair enough question to ask. So let's quickly sort it out a bit and provide some context:
Boreal forest, photo: peupleloup via flickr.

Before we even take one more step down this path, let's remember that preservation of forests (and indeed all ecosystems) is of the utmost importance, and the reasons for doing so extend well beyond just their ability to soak up the carbon emissions from human activity. Forests are intrinsically worth something far greater than their utility to humanity, full stop.

But within the boundaries of absorbing and storing carbon out of the atmosphere there are some major differences. Quickly scanning some of the headlines: Temperate Forests Beat Tropical For Capturing & Storing Carbon, Boreal Forests Store Twice as Much Carbon as Tropical, Mangroves & Coastal Wetlands Store 50 Times More Carbon Than Tropical Forests by Area.


Temperate rainforest in Oregon, photo: vis-a-v. via flickr.

All these make it seem we've got this save the rainforests thing kind of backwards, but when it comes down to it most of these headlines lead to stats parsing on the part of scientists to some degree. Sometimes calculations for above-ground and below-ground biomass are used; sometimes one or the other; sometimes its based on just the area of extant intact forest; all times its by area, and there just isn't that much area remaining, or even possible, when compared to other biome types.

Frankly the only one which makes across-biome comparisons is that first story, which details research done by the Australian National University. Let's use their data for reference.


Cool temperate dry forest, photo: Barry Solow via flickr.
Temperate Forests, Then Tropical, Then Boreal
Based on their calculations, for above- and below-ground biomass in metric tons of carbon stored per hectare, cool temperate moist forests store the most carbon, 625 tC/ha, with warm temperate moist storing slightly less, 500 tC/ha. Cool temperate dry forests stored 280 tC/ha. Tropical rainforests stored 250 tC/h. Boreal forests stored 100 tC/ha.

Remember those are averages and in some cases specific forests may be much higher--the researchers found that some temperate forests in Australia scored far higher. And combine any forest type with predominantly peat soils and you've got a natural carbon storage machine par excellence.


Tropical rainforest photo: Amanda Slater via flickr.
How Much Forest to Offset Your Driving for One Year?
But what do those numbers really mean? While I admit I'm not a huge fan of breaking down carbon storage into the number of cars taken off the road by a given activity, I frankly couldn't think of a more concrete example for this one.

In terms of the amount of emissions from cars that each type of forest could absorb, this is how it broke down. I'm using metric tons of carbon emitted by the average US car per year (1.5 tons based on EIA data; that's 5.5 tons of CO2 per passenger vehicle, by the way) absorbed by a hectare of forest. Which means...

A hectare of moist temperate forest offsets the yearly emissions of between 417 and 333 cars, depending on whether if that forest is in a cool or warm climate. The same area of dry temperate forest is 280 cars. Tropical rainforest is 250 cars, on average. Boreal forest is 100 cars per hectare.

Think of it another way, using the worst storage potential on this list: An area of boreal forest 10 meters by 10 meters in area is the amount needed to offset the carbon emissions of one year of your driving. At the other end of the scale, that's down to an area 4 meters by 5 meters.

Again, this is just one way of considering the importance of ecosystem preservation, and using one system of measuring, but hopefully it gives some perspective.

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Tags: Carbon Emissions | Conservation | Deforestation | Driving | Global Climate Change