date: Thu, 29 Mar 2007 18:11:37 +0200
from: Martin Wilmking <wilmkingatXYZxyz-GREIFSWALD.DE>
subject: [ITRDBFOR] biological mechanisms for "divergence"
your question is a good one! i have been struggeling with it for some time now.... the MS you saw is not submitted yet, since it is data from my PhD, which gets constantly put on the backburner. you know how that goes... there we did check for the influence of soil moisture on our findings of positive and negative responders (to temp that is). first results suggest that there is no clear relationship between soil moisture pattern and pattern of positive and negative responders. on regional scale it seems that the limiting factor in the negative responders has shifted from temp to precip, but on the plot scale we do not find this relationship, at least with our set-up.
and so i cannot predict negative or positive response. we are working on some other leads, but those are mostly the instability of the relationship between predictor and ring width, meaning we are looking at the results of the biological effects first to maybe then draw some conclusions on the mechanisms themself.
if anyone has some literature pointing that way, please let me know!
PS: check also with Rob Wilson and Rosanne D'Arrigo, they have a MS submitted on that topic, see Robs webpage
1. Thanks for the clarification. My question remains "what is the
biological mechanism behind these divergence patterns?" Any idea?
2. A weak correlation between temp & rw/mxd may well be the sum of a set
of positive and negative correlations. But that only begs the question:
how do you explain the divergent positive and negative responses to
temperature that you observe? Assuming that it is some aspect of
temperature that the tree is responding to, can you predict, a priori,
based on species, form, and site, whether a given sample is going to
exhibit a negative or positive response?
3. Checking your publication list I was intrigued by one title: "Drought
stress hypothesis in boreal forest not supported by field observations".
I have to ask: has this manuscript been submitted/accepted yet?
From: ITRDB Dendrochronology Forum
[mailto:ITRDBFOR@LISTSERV.ARIZONA.EDU] On Behalf Of Martin Wilmking
Sent: Thursday, March 29, 2007 8:09 AM
Subject: Re: Wikipedia on divergence
Divergence is happening on several "scales", which get mixed up quite
1) between width and density (?) the one you mentioned, i have no
2) between temperature and width
3) between growth trends of subchronologies at the same site
at least the two last ones might be related, i.e. 2) could be a result
also, when I looked at individual tree ring series (and not the site
chronology) in nearly all cases where i have worked (mostly northern
treeline) sensitivity to temperature increased in the second half of
the 20th century. and thus a closer relationship between temp and ring
width resulted (however, only in on of the two identified
subchronologies, the other showed an inverse relationship to temp). this
might, when averaged into a site chronology, translate into an apparent
breakdown, or divergence, between temp and ring width,
see some publications at
Martin Wilmking, Ph.D.
Working Group: Ecosystem Dynamic
Institute for Botany and Landscape Ecology
Grimmer Strasse 88
D - 17487 Greifswald, Germany
Tel: +49 (0)3834-864095
Fax: +49 (0)3834-864114