Actual versus apparent size    Bob Leverett
   Jul 05, 2003 06:33 PDT 

Dale:

    Yesterday, Gary and I were discussing actual versus apparent size and all
the factors that enter into our making judgments based on visual cues. John
Knuerr and I often discuss the subject. I guess I'm trying to excuse myself
missing so many outstanding trees. Anyway, some conclusions are as followings.

1. Symmetry leads to the appearance of greater size/height. The vase shape of
the American elm is perhaps our best example. The pleasing curvature of the
species lifts the eyes upward and across the crown, giving an overall sense of
bigness. Asymmetry scatters the focus.

2. Dark-trunked trees generally appear larger than their lighter-trunked
counterparts.

3. Deeply furrowed bark imparts an appearance of greater size. The lack of
furrowing in combination with a light color accounts for sycamore's being
misjudged by many people.

4. Root bulges add measurably to the overall appearance of great size, even
when a tree slims down quickly.

5. Large light green leaves make a tree look shorter. One anticipates the tree
to be closer and thus shorter. This is my excuse for missing the cottonwoods.

6. Perception of greater value adds subconsciously to one's sense of tree size.
Conversely considering a species worthless diminishes one's sense of tree size.
The silver maple once fit into this class for me.


7. Lots of short, small twisted branches diminishes the perception of size. The
clutter provides an alternate focus that detracts from other physical
characteristics.

   Well, there they are - Burl-belly's 7 deadly rules. Now it is time for the
rest of you to rip them apart.

Bob
RE: Actual versus apparent size    Edward Frank
   Jul 06, 2003 20:56 PDT 

Bob,

I found your list amusing and generally on the money. There seems to be
three (perhaps 4) categories of reasons/excuses.

1) Background: Your comment about perceived value is interesting. Some
large examples of certain tree species are more noticeable than those of
similar heights in other species. Everyone tends to have some bias in
their observations. I wonder if your training in forestry - in which
cottonwoods have little economic value - was the pre-eminent cause of
you not noticing them before now? Do you think looking back on it you
started out focusing on trees of economic importance? More to the point
do people with other backgrounds have similar identifiable bias/ Would
an artist who has studied and values form perceive a broad canopied
symmetrical tree to be taller or shorter than a narrow canopied tree of
the same height/ How do different educational backgrounds affect the
perception of height or single out some species in preference to to others?
With my background in geology and geochemistry, I have learned that
these large vegetables are simply the organic scum that is covering up
the nice rocks.

2) Learned responses: There are a number of physical features in common
tree species that develop as the tree ages. You have touched on several
of them: Deeply furrowed bark, Root bulges, etc. Trees with these
features are through experience immediately perceived as being old, and
as being old is generally a precursor to being a tree of great size...
Deep inside is a Pavlovian response, and we salivate to the lure of BIG
TREE. Trees without these features do not generate the same
expectations deep in out medulla and fail to elicit the same 
emotional and physical response. They do not have the immediate
expectation of being something wonderful.

3) Illusions of perspective: You have cited symmetry and the presence of
"Lots of short, small twisted branches diminishes the perception of
size." There are other things that provide or distort visual clues to
the depth and the height of a tree I just can't think of any right now.

4) I am not sure about the idea that dark trunks look taller than light
trunked trees, or that light green leaves make the tree look shorter...
These are hypothesis that need testing...they could very well be true.
As for me I have yet to learn how to judge the height of tree
effectively, so I can add little more to the discussion.

Ed Frank
RE: Actual versus apparent size    Robert Leverett
   Jul 07, 2003 06:59 PDT 

Ed:

   Thanks for keeping the thread alive. It is an interesting subject
that intertwines human biases with professional judgments. Actually, I
had my tongue in cheek when talking about cottonwoods. I've always loved
the species as an attractive part of the landscape. In the western USA,
where the cottonwood dominates stream corridors, its charms are
magnified as often the only source of shade in an otherwise unrelenting
summer sun. But beyond its utilitarian value as shade, its charms
encompass the auditory. Cottonwood leaves rustling in passing breezes
provided the soothing sound that lulled my wife and I to sleep many a
night when we lived in South Dakota and Wyoming. And then there is the
cottonwood in autumn. Its brilliant yellow foliage in the fall rivaled
that of the aspens. Cottonwoods are cool trees.

   Nonetheless, you are on the money about money driving the attention
of lots of folks toward or away from a species. Until recently, my
perception of silver maple was tainted by the perspectives of folks who
make their living cutting or trimming trees. Landscape designers
correctly steer property owners away from planting silver maple and
lumbermen have little use for it. It wasn't always that way. In past
years tree aficionados wrote fondly of it. I think that it enjoyed its
heyday in New England in the early 1900s. We have many mature silver
maples in Massachusetts that date to that period.

   In terms of my failing to notice the cottonwood's ascendancy within
the valley, I've been frantically searching for more reasons (reqd that
excuses). My newest explanation is that the species wasn't so prominent
in the past. It has ascended since my moving to western Massachusetts in
1975. In truth, the cottonwoods have had 28 years to grow and grow they
have. Many have grown themselves into large trees since 1975. So they
were puny in '75.

   However, the cottonwood's large yellow-green leaves do give the
appearance of physical closeness. Have I convinced anybody?

Bob   
RE: Actual versus apparent size    Gary Beluzo
   Jul 07, 2003 07:44 PDT 

Bob:

Any idea what the psycho-physiological basis is for the yellow-green leaves
creating the illusion of closeness? A hypothesis begs a tentative
explanation...

Gary
RE: Actual versus apparent size    Lee E. Frelich
   Jul 07, 2003 10:01 PDT 

Bob, Gary and Ed:

People's eyes are more sensitive to green and yellow than other colors. We
can distinguish millions of shades of those colors. If you don't believe
it, you should see how many times people make mistakes while decorating and
have to repaint a green or yellow room. A tiny change in the color can make
a room feel totally different, whereas with red and blue, one can pretty
much pick out the right shade from a small color chip. This may or may not
have something to do with our perception of the yellow-green leaves of
cottonwood.

It seems likely that large leaves with a simple shape make a tree look
shorter from below, since one can still see whole leaves at the top of a
fairly tall tree, especially compared to ash, where the leaflets disappear
into the sky, fooling our sense of perspective (except for Will
Blozan) and making the tree appear taller than it really is. Cottonwood
leaves, at least in the Midwest, are often bigger at the top of the tree,
so they use an architectural trick to fool the sense of perspective, since
the leaves don't appear to get smaller as fast as they should with height.

Ed, regarding trees as scum that cover the rock, there are cases where I
agree. Three Mile Island in northern MN is one such case. Before the
prescribed burn last fall, the island was a bug-ridden sea of balsam fir
with millions of dead branch stubs to tear your clothes and poke your
eyes. Now it is a lovely landscape with undulating hills of pink granite
that were previously invisible. It is normal for about 20% of the boreal
forest to be in this post-burn state, so you can always see the rocks
somewhere.

Shade intolerant species maintain larger leaf sizes at the top of a tree
than shade-tolerant ones. Sugar maple and red oak, for example, have much
smaller leaves at the top than lower in the crown, where the big shade
leaves occur.

Intolerant species like cottonwood and aspen often have sucker-like shoots
at the top with huge leaves. I can see a 16' cbh cottonwood from my office
window, and although it is an old tree, it has 5-7 feet of new height
growth this summer with big leaves at the very top. It is in the process of
regaining its former height after being trimmed by a storm a few years ago.

Lee