date: Thu Oct 1 18:05:02 1998
from: Keith Briffa <k.briffaatXYZxyz.ac.uk>
subject: increasing tree biomass results
I don't know if you remember , but some time ago you and Tom visited us at the Climatic Research Unit and you and I discussed some work I was doing with Fritz Schweingruber's tree-ring densitometric data base . It contains annual measurements of spring and summer radial tree growth and corresponding mean density values. The data represent nearly 400 sites, mainly around the northern boreal forest. I now have sufficient output to write up what I believe will be a very significant paper showing that growth has increased greatly during the 19th century - but perhaps more significantly it levelled off after the middle of the 20th century. To complicate issues it seems that this is not so for very young trees (under 50) . The replication of these young tree data is very low but it seems that basal area increment and maximum latewood density increase remarkably in the last few decades up to the 1980s when the data run out. The maximum density data decline steadily from 1950 onwards . So the picture is not simple but I believe the data show overall evidence of increasing tree biomass in the northern boreal forest from the middle of the last century to about the middle of this . Carbon sequestration probably did likewise in these regions. The question is : what are the implications for carbon uptake, atmospheric carbon dioxide concentrations, and past and future climate . The curves we have are relative indices. We also need to estimate absolute carbon fluxes associated with this phenomenon, probably by using published estimates of carbon in different components of the boreal forest. Also I would like to compare our Cross Sectional Mass (a combination of the Basal Area Increment and mean wood density) data timeseries (from A.D.1700 on) with reconstructed changes in the estimated northern terrestrial carbon sink, based on your carbon isotope interpretations. I am sending just a few plots and a Table by post to illustrate some of these points. I intend to write this up and would appreciate you opinion - and ideally your input. One or two joint papers is what I have in mind - perhaps one (with me and Fritz as first authors) showing the relative changes, one (with you first) dealing with the carbon implications (and perhaps another with Sarah Raper looking at the climate implications of the concentration changes we come up with, using a simple upwelling diffusion energy balance model). What do you think? At least look at the Figures I send but please treat them as confidential. I know you are a busy guy. If you can't do anything , I would still appreciate your opinion. Incidentally, though I will only send illustrations of overall geographically-averaged data, remember that different large sub-regions (e.g. central Siberia, Eastern North America etc.)all seem to show the general dramatic increase in radial growth in the last century. In one or two very restricted areas where we have long data (e.g. eastern Siberia ) the increase is unprecedented since 1200 or 1400 A.D.
I will post the Figures tomorrow. Best wishes