date: Thu, 29 Mar 2007 12:23:30 -0400 from: "Trevor J. Porter" subject: Re: [ITRDBFOR] Wikipedia on divergence to: ITRDBFOR@LISTSERV.ARIZONA.EDU This is definitely a very intriguing question in circumpolar dendro at the moment. I am working in the Mackenzie Delta, Canada, where we have also observed these divergent climate-growth trends at the sub-site chronology level (see Pisaric et al., 2007, Geophys. Res. Lett., vol. 34). I don't know about MXD in the delta yet, but I will be developing several MXD site chronologies this summer. Our 13C and 18O isotope records seem to be time stable for the one site we have developed these records from. The answer to the question "what is the biological mechanism behind these divergence patterns" remains elusive. It is very peculiar that a dichotomy in growth patterns can exist within a given site, which do not appear to be driven by microtopographic or age-related differences. In the delta, approximately 70% of the trees at a given site can share a common growth response, with the remaining 30% exhibiting a different common response. I do not have an answer to Barry's question, but I'm curious if genetic differences might help answer it? Trevor Porter Cooke, Barry wrote: >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 >