Cambialites, Tree Physiologists, and Foresters;
Given the recent thread of discussion on heartwood and sapwood (especially
the post of Barb Gartner - Oregon State) on the CAMBIUM email listserv and
my increasing interest in this area, I thought I might pose a question to
the combined groups that has been puzzling me for some time.
The question:
In terms of the "optimum" sapwood amount in a tree, does either the water
conducting capacity or the storage (of reserves - starch etc...) capacity
determine the width, area, or volume of sapwood?
Literature citations indicate that:
A given unit of foliage requires a given unit of sapwood area to supply
water [pipe model theory] (Huber 1928, Shinozaki et al. 1964).
Adequate volumes of sapwood are needed for storage materials (eg. starch)
(Bamber 1976 from Hillis 1987).
There is a plethora of information regarding the relationship between leaf
area and sapwood area (relating to transpirational demand and conducting
capacity). However, I wonder whether many individuals consider the role of
sapwood storage reserves as being crucial for tree fitness and survival.
According to Hillis (1987) the proportion of parenchyma varies between 5
and 40 percent of the total sapwood tissue (a moderate to considerable
sum). Further, some species (American elm, white oak, willow oak - off the
top of my head) have only ONE conducting sapwood ring (current annual ring)
yet maintain additional sapwood rings at carbon expense!
I'm interested in testing my idea/theory and have calculated ("back of the
envelope calculations" using Poiseuille's Law from Nobel [1991]
Physiochemical and Environmental Plant Physiology) that approximately 4% of
the cross-sectional sapwood area of sugar maple needs to be in vessel lumen
to support the transpirational demand of a 160 year old tree with a leaf
area of 243 m2. However, I digitized the sugar maple cross-section on page
603 in Panshin and DeZeeuw (1970 - Textbook of Wood Technology I) and
calculated that the lumen area was 21% of the cross-sectional area in the
figure. A large discrepancy that could be an error in calculation or the
result of only one digitized sample - which I am checking. However if this
is true, then is this evidence that the main determinant of the sapwood
amount is the storage of reserves?
I should also mention that this sugar maple tree is growing on my MAC
computer in the TREGRO simulation model and that I can proportion the
heartwood and sapwood amounts and the storage content (TNC). Current
parameterized values are:
Sapwood = 86% and heartwood = 14% - which I got from Chapman and Gower (1991).
I am in the process of varing these amounts and trying to determine if
there is an optimum sapwood (or heartwood) amount for sugar maple.
Comments, criticisms, and suggestions are welcomed!!! I will post the
entire reference list if you would like to peruse for yourself. I would
add here that I am not overlooking the support function of the sapwood, but
would argue (maybe not successfully) that in true heartwood trees/species
the heartwood could serve this function without the carbon cost (black
locust and catalpa as examples). Thanks in advance for your input...
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WA (Bill) Retzlaff
Boyce Thompson Institute for Plant Research
Ph. (607)254-1226
FAX (607)254-1242
email wr13@cornell.edu
homepage http://birch.cit.cornell.edu/profiles/WARprof.html
... I have lived temperately, eating little animal food. Vegetables
constitute my principal diet. I double, however, the doctors glass
and a half of vine, and even treble it with a friend. Thomas Jefferson
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