date: Thu, 29 Mar 2007 18:11:37 +0200 from: Martin Wilmking subject: [ITRDBFOR] biological mechanisms for "divergence" to: ITRDBFOR@LISTSERV.ARIZONA.EDU Dear Barry, 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! best martin 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? Barry Cooke -----Original Message----- From: ITRDB Dendrochronology Forum [mailto:ITRDBFOR@LISTSERV.ARIZONA.EDU] On Behalf Of Martin Wilmking Sent: Thursday, March 29, 2007 8:09 AM To: ITRDBFOR@LISTSERV.ARIZONA.EDU Subject: Re: Wikipedia on divergence Divergence is happening on several "scales", which get mixed up quite often: 1) between width and density (?) the one you mentioned, i have no experience there 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 of 3), 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 http://biogeo.botanik.uni-greifswald.de/index.php?id=publikationen martin -- Martin Wilmking, Ph.D. Working Group: Ecosystem Dynamic Institute for Botany and Landscape Ecology University Greifswald Grimmer Strasse 88 D - 17487 Greifswald, Germany Tel: +49 (0)3834-864095 Fax: +49 (0)3834-864114 http://biogeo.botanik.uni-greifswald.de