Age of tropical trees   Edward Frank   Oct 15, 2006 19:52 PDT  ENTS, I thought this was interesting.... http://www.sciencedaily.com/releases/2005/12/051213174230.htm Amazon Trees Much Older Than Assumed, Raising Questions On Global Climate Impact Of Region Trees in the Amazon tropical forests are old. Really old, in fact, which comes as a surprise to a team of American and Brazilian researchers studying tree growth in the world's largest tropical region. Using radiocarbon dating methods, the team, which includes UC Irvine's Susan Trumbore, found that up to half of all trees greater than 10 centimeters in diameter are more than 300 years old. Some of the trees, Trumbore said, are as much as 750 to 1,000 years old. Study results appear in the online early edition of the Proceedings of the National Academy of Sciences. "Little was known about the age of tropical trees, because they do not have easily identified annual growth rings," added Trumbore, a professor of Earth system science. "No one had thought these tropical trees could be so old, or that they grow so slowly."   Re: Age of tropical trees   Neil Pederson   Oct 17, 2006 18:51 PDT  Ed, A friend in the tropical tree - isotope biz says the errors are not as large as I thought. But, the says dating over the past four hundred yrs is difficult. Interestingly, he says the report you forwarded might be the exception for finding tropical trees that old so far: two other locations in the tropics show ages younger than expected. So much to discover yet! Here is an excerpt from his email: "Tropical tree ages: Good question, and there are at least 2 scientific schools of thought, I'd say. One is represented by Jeff Chambers and Susan Trumbore, and is summarized pretty well by the press release you have below (paper attached, too). They do indeed find tropical trees (1 or 2) in excess of 1000 years old, and quite a cluster from 400 to 600 years old. So, it seems that tropical trees might well be quite old. On the otherhand is the paper by Worbes and Junk (also attached) with their article 'How old are tropical trees? The persistence of a myth' -- ouch. Essentially, they are saying that, while there are indeed old Methuselahs, they don't represent well the dynamics of tropical tree populations as a whole. Their populations in Costa Rica tend to cluster from 200 to 400, but they didn't chose trees like Chambers' group did. Interestingly, both groups found a relationship between diameter and age, which I have to say has NOT held up at my sites in Costa Rica so far. So, radiocarbon probably works fairly well at about 1000 years, all other things being equal (its more problematic at around 400 BP to A.D. 1950, actually) -- who knows if those few old ages could be outliers or have contamination or analytical problems, I suppose, but there is nothing a priori I would say that suggests they are necessarily problematic. So, yeah there are probably really old individual tropical trees. It probably depends heavily on site and species, nutrient dynamics, stand dynamics, etc. So far in Costa Rica though, trees that people thought were old have tended to turn out not-so-old." John K. asked about growth increments in tropical trees: tropical trees form growth bands, but the periodicity of these bands is porly understood to date in most trees sampled. It is hard to say if they occur twice a year, 3X/yr, and so on. Teak grows fairly reliable rings; reliable for traditional dendro. I've heard of one forest that is flooded 6 mo out of the yr; trees in this forest produce rings that are usable for traditional dendro methods. Anyhow, this lack of understanding [to date] on the periodicity of growth bands in tropical trees is a reason why people are using isotopes to age these trees. John E. asked about fossil fuel C14 signal in today's atmosphere. Yes, it is detectable. Last I heard, this old carbon, they call it dead carbon, is just about to or has swamped the natural C14 signal, much like the 300th+ American being born today, I suppose. Hope this helps, Neil   Home