Naked Science Forum
Life Sciences => The Environment => Topic started by: murf on 25/02/2010 19:55:12
-
From what I have read about dendrochronology the age of the tree is not taken into account when looking at tree rings. The assumption is that the ring size is dependant only on climate and it is valid to compare the width of a 10 year ring with that of a 100 year old ring. However, the question I am trying to answer is that given a constant climate - that is the same climate every year is there a variation of ring size throughout the lifetime of a tree? Would a ring from a 10 year old tree be the same width as one from a 100 year old tree if the trees were in identical climates and situations? Alternatively do younger trees make bigger rings than older trees?
-
The ring sizes would be different in most trees as they age. This is actually taken into account in dendrochronology by applying growth functions to the ring width chronologies. You are correct...a younger tree will generally produce wider rings than an older tree, and the decline in ring width is linear for some species, non-linear for others. As with anything, there are a couple of schools of thought on how these rings should be detrended...should each individual chronology be detrended, or should similar chronologies be detrended as a group? Both methods reproduce high frequency variability pretty well, but those rings that were detrended individually tend to lose their low frequency signals (much like the "hockey stick" graphs from the MBH papers). Those that were detrended as groups tend to keep their low frequencies, but there is the possibility that they are over/under estimated.
Then comes the frequency analysis...ugh. Im reading a paper now that shows different methods of spectral analysis amplifying slightly different signals in the higher frequencies. If this is the case, then there are some important proxy records that will have to be re-analyzed...but thats for another topic. Isnt climate science fun?
-
frethack, Many thanks for your insight into detrending.
It has put me onto the right road and got me reading more about the subject. I have now been wondering if there is a reference list of detrend functions and typical parameters for given genus or species of trees. For example, does the Platanus genus use a linear or non-linear function and what might be typical or average parameters for the detrend function e.g. in change in ring width/year? Is it possible to draw any conclusions regarding variations of these parameters? How might they vary between, say, an urban and a nearby forest setting (i.e so that climate variability is minimised)?
-
I have now been wondering if there is a reference list of detrend functions and typical parameters for given genus or species of trees. For example, does the Platanus genus use a linear or non-linear function and what might be typical or average parameters for the detrend function e.g. in change in ring width/year?
If you have access to Web of Science you should be able to search for peer reviewed articles that detail detrending methods for specific or groups of species. Im not sure what the cost is, but if youre a university student, you should be able to access it for free through the library system.
How might they vary between, say, an urban and a nearby forest setting (i.e so that climate variability is minimised)?
Most papers you will find (in fact, every one that Ive read...though Im not a dendrochronologist, so I havent read them extensively) will be from groups of trees in environmentally sensitive or stressed zones. Otherwise there is really no climate signal to pull from them. Happy trees produce fairly uniform rings, with the only general trends being those for growth (my guess is that these are the trees used to derive the growth functions, but I do not know that for sure.)