Thanks so much for your insight Neil- that helps explain things quite a bit! Things are never quite as black and white as they first appear I guess! ~Eli
--- On Thu, 11/19/09, neil <[email protected]> wrote: From: neil <[email protected]> Subject: [ENTS] Re: Bristlecone Pines as signals of climate change To: "ENTSTrees" <[email protected]> Date: Thursday, November 19, 2009, 3:50 AM Hi Don, Eli, ENTS, I was able to see a preview of this paper. This paper is a limited gradient analysis. That is to say, the authors examined trees across a a small elevational gradient in the White Mountains. Tree ring theory predicts that only those trees at the top of the mountain, at forest tree line, will be mostly sensitive to temperature. Specifically, this theory predicts that the change in ring widths of these upper elevation trees will vary in a positive manner to changes in temperature. Because of cool summer temperatures, a short growing season and cold winters, rings in these trees will become wider when it is warmer annually or seasonally and narrower when it is colder. Eras of cooler temperatures ought to be reflected with longer-trends of narrower rings and vice-versa. This theory of site location also predicts that trees at lower elevations will be varyingly sensitive to temperature and precipitation and at the lowest elevations, trees will be mostly drought sensitive [positive correlation to precipitation and negative to temperature]. Trees at slightly lower elevations do not show the trend of wider growth rings over the last 50 years. The lower elevation trees are also shown in this paper to be more positively correlated to precipitation and negatively correlated to temperature, while the treeline trees in the White Mountains and two bristlecone treeline sites in the region are primarily positively correlated to temperature. Thus, these results indicate that temperature is a main factor in driving the increased ring widths over the last 50 yrs. Some might argue that elevated CO2 is responsible for the trends in this paper and it cannot be entirely ruled out. However, data presented here, though mostly circumstantial, indicates CO2 is not the most important factor of the recent growth trend. See, it is predicted that elevated CO2 will increase the ability of trees & plants to use water more efficiently and possibly grow higher than they might normally in similar droughty conditions, but at lower CO2 concentrations. Higher CO2 concentrations increases water use efficiency by allowing plants to keep their stomates more closed, which allows them to bring in the same amount of CO2 while losing less water through their stomates. As discussed above, lower elevation bristlecone pine are generally drought stressed - their ring widths are negatively correlated to temperature [like a panting dog] and positively correlated to precipitation [like that same dog walking across a desert - it needs water!]. Thus, these trees should benefit by the higher levels of plant food - CO2. Yet, in this study, the raw ring widths of lower elevational bristlecone pine do not show the same increase in growth. This result argues against CO2 fertilization. A test of isotopic ratios in the rings of these trees, a test that was not performed, will help determine if CO2 is an important factor of the main finding here. That test needs to be done so the role of CO2 can be better understood. Here is the NPR interview of Dr. Malcom Hughes on this research: http://www.npr.org/templates/story/story.php?storyId=120545587 neil On Nov 17, 5:41 pm, DON BERTOLETTE <[email protected]> wrote: > Eli- > > I think an even more interesting study would be gradient analyses of > moisture, temperature, UV at the geographic extents of the bristlecones > (lats, longs, elevations). > > One of the questions posed in a ecological restoration class I took was "How > will global climate change impact the geographic extents of > _____________(choose a species)". My choice was Quaking Aspen (Populus > tremuloides) in Northern Arizona on San Francisco Peaks...I predicted that > the aspen were somewhat less mobile, that they were likely to die out at > lower elevations due to increased predation by forest pathogens with rising > temperatures, and to stabilize at higher elevations. Lots more to it than > that, but the idea is that it just takes a few degrees (in this case > adiabatic temperature change) change to have significant impact on many > facets of an ecosystem. When enough of those subtle 'facets' accumulate, > major differences will be noticed. Particularly at the geographic extents, > where the natural limits already in place get exceeded. > > Attaching an image of bristlecones as they reach the edge of their > 'ecotone'... > > -Don > > Date: Tue, 17 Nov 2009 13:05:58 -0800 > From: [email protected] > Subject: [ENTS] Bristlecone Pines as signals of climate change > To: [email protected] > > Great article about how Bristlecone Pines near the treeline have grown more > rapidly in the 2nd half of the 20th century than in any other 50 year period > in the last 4600 > years:http://news.discovery.com/earth/oldest-trees-global-warming-growth.html > > Eli > > -- > Eastern Native Tree Societyhttp://www.nativetreesociety.org > Send email to [email protected] > Visit this group athttp://groups.google.com/group/entstrees?hl=en > To unsubscribe send email to [email protected] > > _________________________________________________________________ > Windows 7: I wanted simpler, now it's simpler. 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