Dear all,

There is a correction factor used for estimating fine root biomass bellow 30 cm depth which is 0.39*fine root biomass from 0-30 cm depth. The CF is mentioned in this paper:

Galbraith D, da Costa ACL, Portela BTT, Levy PWM, Fisher

RA, Meir P. In review 2013. Effect of imposed drought on

root biomass and its distribution with depth in an Amazonian

rainforest. Global Change Biology.

I was wondering if any of you have the published version of this article?

Thanks in advance for your help,

Jhon

Thanks a lot.

Jhon

Hi Toby,

Thanks as always.

I was a bit confused because I found Jackson's value in the new version of RAINFOR-GEM manual. And before that I had read Galbraight's reference in Doughty's paaper (page 5): The production, allocation and cycling of carbon in a

forest on fertile terra preta soil in eastern Amazonia

compared with a forest on adjacent infertile soil. I thought that I could clarify it with Galbraight's paper.

Roots is always a tricky stuff. After all, I will take Jackson's value into account because it sounds like a average of several assessments. I was wondering if you have that paper and could share it with me, please. It would be good to take a look on it.

Thank you again.

Jhon

One more thing: I know that the difference between 39% and 31% is small and less than the natural variability between forests for this factor. The reason why I'm suggesting rather to use Jackson's 31% is because that paper also suggested estimates for other biomes (which I copied into the manual) so this factor becomes biome-specific if you follow that. For me, this is much more ecological. Toby

Hi Jhon,

There is the following rule of thumb in Malhi et al. ("The productivity, metabolism and carbon cycle of two lowland tropical forest plots in south-western Amazonia, Peru", Plant Ecol & Diversity). I imagine the Galbraith paper is referring to this '39% rule':

"We also estimated that there is an additional 39% fine root NPP beneath our 30 cm ingrowth core, by extrapolating to 1 m depth assuming an exponential decay of root biomass and productivity with depth"

this rule is equivalent to assuming 61% of all roots occur in the top 30 cm of the soil profile and may also be estimated from an equation used in the CLM model (as pointed out by Chris Doughty: see footnote p.58 of the Manual v3 and the same is encoded in rootbiomassf_s.m in the equation for dzz).

I asked Dan Metcalfe about this 39% rule in 2012 and he said it came from data collected by Rosie Fisher at Caxiuana. However I emailed Rosie F at that time and she said that this didn't come from her data so there has always been a bit of confusion over where the 39% rule originally came from.

After looking into this more deeply I found that Jackson et al. (1996) put the percentage of roots above and below 30 cm as 69%-31% rather than 61%-39% and that this is backed up by studies across tropical humid forests. That is why Jackson's estimate appears in the Table on p.58 of the Manual v3 and I recommend this to be used over the 39% rule.

Therefore, in answer to your question: that 39% rule is used by several references, but I suggest rather to use the 31% rule of Jackson (which is in the GEM manual section 2.3).

Hope this helps.

Toby