2011-09-11 22:08:07Question: Are there easy to understand studies available about forests as carbon sinks?


Hi Folks,

a couple of days ago, I got into an argument with a colleague of mine who questions that rainforests are carbon sinks and just because of that would need to be protected (as an aside: he doesn't question AGW per se). He reasoned that rainforests don't have a lot of soil under the trees and that the sink would always need to be in the soil, the deeper the better. I was in a hurry to leave so didn't prolong the discussion but kept on thinking about his assertion. While I can understand the soil-argument as far as eg. the South American Rainforest goes, it doesn't sound quite right for - at least parts of - the Indonesian rainforest which grows on top of deep peats.

The big forests in the northern hemisphere are also a different story.

What I'm wondering is this: are there any easy to understand studies which show how big (or small) a carbon sink the different forests are and/or could be if left intact?

Thanks much and Cheers

2011-09-11 22:12:50


Isn't the carbon held in the actual material of the plant? The wood, stems and leaves?

So the forests serve as sinks when they are growing.

2011-09-11 22:48:32


Table 2.1 provides you with an estimate of the carbon held in the vegetation and soil separately for different forest types.  Unfortunately, this doesn't segregate each forest by country.  It seems reasonable that if a forest had deeper soils and/or peat then it should hold more carbon.


2011-09-11 22:58:22


This might be a starting point:


2011-09-11 23:01:55
Rob Painting

Baerbel, the rainforests are carbon sinks - for now. Whilst the carbon sink in boreal forests is down to regrowth of forest, primarily in the old Soviet Union countries and China, tropical forests are gaining mass through the CO2 fertilization effect & regrowth. 

I'm not sure I follow your colleagues train of thought. Yes a lot of carbon exists in the soils, but there are hundreds of thousands of trees in the RAINFOR network in the Amazon for instance, that are measured at regular intervals and are showing increases in above ground mass. And those woody vines, Lianas, in particluar are growing like crazy.

This is the most recent carbon forestry inventory I'm aware of:  A Large and Persistent Carbon Sink in the World’s Forests - Pan (2011)

The parts relevant to your query:

"When all tropical forests, both intact and regrowth, are combined, the tropical sinks sum to 2.9 T 0.6 and 2.7 T 0.7 Pg C year –1 over the two periods (Table 1), and on average account for ~70% of the gross C sink in the world forests (~ 4.0 Pg C year –1 )"

Sadly much of the (rainforest) natural carbon sink is being offset by rapid deforestation. IIRC there was a 15% jump in the rate of rainforest felling in Brazil in the last year.

2011-09-11 23:23:55
Rob Painting

Baerbel - Andy S linked to this excellent talk by Stephen Pacala in his post: Carbon Cycle Feedbacks. Worth a listen if you have time.

Perhaps a very good reason for saving the Amazon rainforest, not often thought of, is that the loss of the Amazon will throw the world's hydrological cycle into a tailspin. Over 20% of the world's freshwater flows from the Amazon, and the water recycling is largely a result of the rainforst itself. Who knows what it would mean for the world's weather patterns if the Amazon rainforest were lost?  

2011-09-12 03:42:17Thanks...

...for your quick replies! I'll check it out - try to understand it! - and pass it on to my colleague.
2011-09-12 09:26:16
George Morrison

I will second the recommendation of the Stephen Pacala video from Andy's "Carbon Cycle Feedbacks" post.

It seems to me that Baerbel and her friend may need to define what they mean when they refer to "sinks". Her friend is probably correct that there is relatively littel soil carbon - at least in the Amazon rainforest - relative to boreal forests, etc. (As I recall, anyway.) But as pointed out above, there is still a hell of lot of carbon in the forest, canopy, etc. Maybe he is referring to the ability of the forest to net sequester carbon and thinks it can only do so in the soils. I am not sure that is very good assumption, but as the Pacala suggests, the evidence seems to indicate that "missing sink" of terrestrial appears to be in the tropical forests themselves. The reason it appears to be in the tropical forests is that they do not seem to be as limited by nitrogen fixation versus temperate and boreal forests. So they may (presently) be net beneficiaries of "CO2 fertilization". I discussed that briefly here, pointing Andy to the video. Again, it's a good one.

And just a reminder that the resources of the Global Carbon Project, such as here, are always good sources for data on sources and sinks.