Tuesday, June 21, 2011

Day 21: Tree Ideas

This post will be very academic and filled with questions since I am trying to figure out how to set up the coring of the trees in the fen between my study lake, Larch, and the lake that feeds the inflow into Larch.

This may just reveal how my mind works as I try to research these questions and how I develop these questions. The first credit goes to the person who commented at the end of my PALS presentation that I could verify the age of the fen leading into Larch by sampling the tree rings.

So here it goes...

I'm interested in figuring out:
  1. Which species to core: Larch? Black spruce? White spruce?
  2. Where to core: Within the fen connection? Outside of the fen connection but still close to the study lake? Somewhere else in the region (or just compare to other cores taken in the region?)? We need to be able to determine if the growth rings during the time we are interested is due to the increased moisture (due to hydrological connection) or due to some other regional climatic factor.
  3. How many to core: How many to be statistically significant?
  4. How many cores in one tree? Two at about the same height but different angles to see the rings all the way around? One at chest height? What's the difference between base and chest height cores?
  5. How old are the trees?
    1. How do I find the oldest tree? Just by height and width of the trunk?
    2. Do I only core the oldest?
    3. If the oldest trees are still younger than the connection that we hypothesize occurred around 1960, will they be of any use at all?
    4. If the oldest trees are a lot older, is there a way to see a signal of increased moisture in the soil such as increased growth? Can I differentiate between increased moisture due to the melting of the snowpack at the beginning of the summer to increased moisture throughout the summer which could indicate the connection between the lakes? I will need to compare to trees that are in dry areas (how do I know that these areas are historically dry?). 
  6. What am I looking for in a core?
    1. Wide growth rings starting around 1960 in the trees along the fen, but not the trees outside of the fen
    2. continuous rings (discontinuous rings could indicate disease?)

Paper #1: Girardin et al., 2005 doi: 10.1657/1523-0430(2005)037[0206:RGOTLL]2.0.CO;2

Overview: Using tree cores from spruce and tamarack to determine the effects of the larch sawfly herbivory on the radial growth of tamaracks due to the defoliation of the trees. The study correlates the rings with the epidemic levels of the sawfly that slowed growth in the trees. Growth rings also correlate with the regional climate.
Larch sawfly
  • "Most variations in radial growth (highs and lows) were adequately predicted, with the exception of the 1940s and 1950s for which the prediction models underestimated the growth reductions in both tamarack and spruces." - where are these sites? Are any of the sites near my lake?
  • Less severe larch sawfly outbreaks in hydric site - does that mean that in the same tree and during the same outbreaks as other trees in the region, the damage will be less severe once the hydrological connection is made into Larch?
  • Should I use tamaracks if there seems to be a large larch sawfly epidemic right in the time frame I am looking at? Should I use white or black spruce instead? Which one?
  • How do I know the growth ring changes are due to regional effects, local effects, bugs and other catastrophes?
  • Statistical testing: Tree rings after the fen connection developed for the trees in the fen should differ significantly from the tree rings before the connection, which should be most similar to the tree rings outside of the fen (correcting for regional climate changes).
  • "This hypothesis is supported by the fact that the stand least susceptible to sawfly outbreak (LLA5) showed the weakest correlation with the nonhost chronologies and the highest percentage of affected trees in the outbreak analysis (Fig. 6) during the interval 1903–1912." - where is this stand? Would this be a stand that would look similar to the Larch inflow stand?
  • "Periodic flooding of bogs was reported to produce growth reduction which, were “indistinguishable” from those caused by larch sawfly defoliation (Nairn et al., 1962Ives and Nairn, 1966a)." and "Denyer and Riley (1964) reported important dieback and root mortality in tamarack growing in “treed muskeg” due to rising water levels."
    • Would this mean that instead of increased growth after 1960, I will actually find a period of supressed growth? 
    • Would black spruce (which grows better in wet soil) grow better in the fen or first establish itself in the fen when it is produced, outcompeting the tamarack?
  • What to try to correlate with? 
    • Trees outside of the fen
    • the larch core data
    • climate - regional temp during different months, precip during different months - how important is this for my study?
Paper #2: Tardif et al. 2008, Tree rings, δ13C and climate in Picea glauca growing near Churchill, subarctic Manitoba, Canada
  • "The climate signal contained in both ring-width and the δ13C residual chronologies suggests that warm early summers were conducive to larger rings whereas the δ13C best reflects the overall growing season temperature. Precipitation, relative humidity and/or drought index have little to no association with either chronology."
  • So this is looking at regional climate, not small scale locations and impacts, maybe that's why there is no correlation to the broad data - maybe the resolution of δ13C isn't strong enough
Paper #3: Camill DOI: 10.1007/s10584-005-4785-y
  • "Compressional growth rings formed as wide, lignified bands on the downslope side of the stem as a mechanism for restoring vertical growth, and the number of compression rings laid down indicated the number of years of leaning by each tree."
    • really interesting - an indication of permafrost thaw due to slump and figuring out when that slump began but not sure if it really helps
    • The writing of this study seems more like a personal write-up rather than a journal article. I'll have to remember that when I write mine
Paper #4: Ise and Moorcroft 2008, Quantifying local factors in medium-frequency trends of tree ring records: Case study in Canadian boreal forests
  • "In a Canadian continental boreal region, we compared synchronicity of medium-frequency tree ring patterns of open- and closed-canopy black spruce (Picea mariana (Mill.) B.S.P.) stands, and considered underlying mechanisms of spatial synchronicity."
  • Specifically looking for ecological interactions between individual trees that limit that tree's growth to determine stand history rather than the regional averages (where this sort of detailed information is filtered out)
    • I'm looking for this type of resolution! Not on the regional scale
  • So this study is looking at techniques to enhance the local "gap-scale" (the gap-scale refers to the space around a tree when the neighboring tree dies - there is more detail about the crown expansion and growth rate of the trees, but I don't think I need to get into that here) effects - through stratified sampling design which maybe I could implement.
    • "Medium-frequency signals were extracted with an index derived from exponentially weighted moving average (EWMA) in a continuous time series."
    • "Then, by using this index, local effects were quantified with an analysis of synchronicity in patterns."
    • "Our assumptions were that regional factors such as climatic variations are relatively homogeneous within the given stand, whereas local factors such as stochastic disturbance and competition occur in a less synchronous fashion in a mature stand (Tessier et al., 1997)."

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