Eastern Forest Structure   Edward Frank
  Nov 24, 2004 19:20 PST 

Eastern Forest Structure

In the most basic terms we can describe the structure of a forest from
top to bottom to consist of a canopy level, understory level, brush and
shrub level, and herbaceous layer on the forest floor. Examinations of
real-life forests find them to follow this pattern in a general way, but
often show a great deal of diversity in how each of these aspects are
expressed. The challenge to be embraced by the Eastern Native Tree
Society is to determine how we can use our advanced measurement
techniques, our store of tree measurement data, and our knowledgeable
membership to provide a better view of the structure of these
magnificent forests than has ever been done before. We need to figure
out what questions to ask, and how to answer them. There can not be a
one size fit all approach to force fit the many different forests
across eastern North America into one tiny pigeonhole. There are
differences in tree species present, differences in the dominant tree
species at a site, differences in climate, different disturbance
histories, and differences in a host of other environmental factors.

An approach to begin this process at this point in time is to take more
detailed observations at the tree site we visit, to develop a list of
questions to be answered to guide these observations, and to provide
better descriptions of these sites including the additional observation
information. From there we can better tailor our numerical analysis of
the data to help answer these questions. I would suggest that initially
we try to develop a detailed description of some of our more measured
sites, and simultaneously try to add what detail we can along these
lines to other sites we visit. There have been a efforts along these
lines already. In particular I can cite the fine report on Mohawk Trail
State Forest by Bob Leverett, and the excellent detail provided in field
reports by Jess Riddle. Many others have made strides in this area as

Site Overview:

What is the basic climatic regime for a particular site? We can
collect data from the National Weather Service, and perhaps other
sources as well. Are there any special environmental characteristics of
the site that should be noted? What is the disturbance history of the
site? What evidence is there that sheds light on the sites disturbance
history? What is the general topography of the site? A section of a
topographic map showing the site would be useful to include with any
description. How are the boundaries of the site defined? And why were
these boundaries chosen? How is the water distributed at the site? Is
the site on a hillside? Mountaintop? Valley? Floodplain? Are there
seeps or streams on the site? Is the area relatively dry or swampy?
Soils information? (State Agricultural Agency?) What can you see that
tells you about the geology of the site? State Geological Survey
information is generally available to provide information on the
underlying geology of a site.

General Canopy Structure:

In the moist climates found in the majority of the eastern forests, the
forests typically have a closed canopy that is stratified with obvious
canopy, understory, brush and shrub, and herbaceous layers. In drier
climates, and in swampy areas there is generally a more open canopy and
the stratification is not as evident. Is the forest canopy at this site
closed, open, or somewhere in between? Are the openings present because
of fire, blowdowns, human activity, or some other cause? What
percentage of the site is made of closed canopy versus open areas?
Aerial photographs might be useful to quantify this information.


When you look across the treetops on a site, is it continuous, or are
there scattered treetops standing emergent above the general canopy
level? If these trees are present, how common are they? Of what
species are they? How much higher than the general canopy top do they
stand? Are these trees simply taller versions of trees making up the
general canopy level or are they representatives of uncommon species at
the site that are simply taller than the other species present? Will
Blozan mentioned these emergent tall trees in a post dated Nov. 21,
2003, “RE: Mount Peak/MTSF Is there any sense in discarding the tallest
tree in a Rucker Index if it is an emergent, like white pine, that may
tower over all other species, especially when pine is a dominant species
and all others fall well short of the maximum, such as Pine Flats in
Cataloochee? (Wm. Cullen Bryant?). Just a random thought. The Rucker
may be skewed by one dominant, and may not be the best indicator of the
site.”   I am not sure these trees need to be excluded from the Rucker
Index of a site, but it certainly makes sense that we develop an
understanding of what tree species and how many form this supra-canopy
level. How far do they extend above the general canopy? Why are these
trees taller than the others at a site?   How do these trees affect the
Rucker Index for the site? Should we break them out as a separate
Limited Rucker Index set? How can we compare them to trees that form
the mass of the tree canopy on a site?

Canopy Level:

What tree species make up the general canopy level of a site? How tall
are they on average? (Rucker Index) Is the canopy dominated by a single
species, a few species, or a wide diversity of species? What percentage
of the trees forming the canopy are of what species? (estimate) Does
the composition or the height of the canopy vary from location to
location on the site? If so, to what extent? What is the cause of this
variation? How thick is the canopy of the forest? (tree height -
height to lower living branches - Live crown measurements). In
extremely tall forests, and in tropical forests there can be multiple
layers within the canopy of a forest. Does the forest at this site
exhibit any of the characteristics of a secondary canopy layer? If so,
describe its characteristics and composition. If we were to break out
from the measurement data just the heights of trees that make up the
forest canopy, how many species would it include? Less than ten? More
than ten? Should we do a Limited Rucker Index only including the canopy
species? Larry Baum Nov 23, 2004 commented on this in a post, “Even for
the Northeast, 10 species sounds like quite a lot. Also, if we are truly
interested in growth potential, once you past the first 4-5 species, it
would seem that there might be a number of tracts where the remaining
5-6 trees would be hangers on and less adapted to the particular
microsite? Maybe a RI10 and RI4 should be kept for everything (where
possible), along with the HRI. ...An Appalachian mixed mesophyetic
forest might easily have 10 solid species, but otherwise, it seems
perhaps a stretch. I can think of some fabulous old-growth tracts in the
Adirondacks that are so sugar maple dominated, that beyond some
scattered white ash and yellow birch I don't recall seeing all that much
else, and yet the tract was tall and impressive, clearly OG, but I'm not
sure if it could qualify for the 10 species rucker, perhaps there are 10
species there, but I have my doubts, and even if so, it would surely
have its index unfairly cut down quite drastically.”


For these purposes the understory will refer to tree species that are
taller than the shrubs and bushes, but generally do not reach into the
canopy of a site. Occasional representatives of the species may reach
canopy levels. For ENTS these trees are greatly under-measured. I
understand why, the goal of most of the trips is to document the tallest
trees in a particular location and there is not enough time to
systematically evaluate and measure the understory species.   Many of
the trip reports post to the discussion list, and included on the
website, include exceptionally tall examples of what are normally
considered understory species. In particular in the GSMNP and some of
the other rich southern sites species restricted to the understory in
northern climes have been reported to great heights and can be canopy
species. I am not sure that these species need to be measured in great
detail, however any unusual specimens should be documented. Notes
should be made as to what understory species are present, how common
they are, and characteristics of the understory. Is the understory
layer present across the entire site? Is it patchy? Is it generally
absent?   Are the species making up the understory different from the
canopy species, or are they simply younger or smaller versions of the
canopy species? What about forest openings?

Shrub and Brush Layer:

The situation for the shrub and brush layer is much the same as for the
understory discussed above. The two may be intermingled to the extent
that they are indistinguishable. The same type of information should be
gathered for species in the shrub and brush layer. These species are
distinguished from herbaceous plants because they have a woody stem.
Grape vines are include in this layer regardless of the heights they
manage to climb in the trees on the site. One point to look for is
whether the site shows evidence of browsing by deer. At Cook Forest
State Park in Pennsylvania in many areas is an obvious browse line where
everything below 3 to 4 feet has been eaten by browsing deer, while
above that line the rhododendrons and other plants are green and living.

Herbaceous Layer

This layer consists of non-woody plants such as wildflowers, ferns,
mosses, grasses, and so forth. What species are present may provide
clues as to the fertility of the soils on the site. For example the
common Christmas fern typically grows on soils rich in calcium. I could
walk the boundary between the sandstone caprock and the underlying
limestone in the Mammoth cave area simply by walking the boundary
between where that fern grew and where it stopped. In areas subjected
to heavy browsing, by deer in particular, there will be few plants
growing on the ground. Test sites in the local area, at Cook Forest
State Park and Clear Creek State Park, PA where sections of the forest
are fenced to prevent the entry by deer, show a rich diversity of plant
sprouting, while outside the fence the ground is often all but bare.
Non-native invasive species were present are generally found in the
herbaceous layer or brush layer. Their presence should be noted.
Earthworms are another invasive that is disrupting the natural cycle of
the forest floor. Evidence of invasive species, diseases, or similar
health issues for the forest should be noted in whatever forest stratum
they are found.

Another point to note is whether or not there are downed trees lying on
the forest floor, or whether they have been removed. These downed trees
provide a critical link in the growth of many species in the forest.
Salvaging these logs can disrupt these natural processes and life
cycles. So their presence or absence is worth noting.

Well, I have rambled enough for now. I am sure I have forgotten things
I wanted to say, and missed some obvious ideas. I am looking for
discussions by members of the group on what we can do with our accurate
height measurements and through site descriptions, or other methods, to
better characterize our forest sites.

Ed Frank

Forest Structure   Edward Frank
  Nov 24, 2004 20:13 PST 


I wanted to forward this note from Colby regarding forest diversity as it
applies to the forest structure discussion:

From: "Colby Rucker"
To: "Edward Frank"
Subject: Re: Diversity Index
Date: Wed, 26 May 2004 00:24:18 -0400


I agree. We get more and measurements on big trees, but little to tell us
anything about the site. Essentially no one's measuring small trees,
developing forest profiles, or recording indicator species such as ferns,

Although large sites have more diversity than the smaller components,
dividing by acreage would result in high numbers for very small
gerrymandered sites. Overall numbers for trees, shrubs, ferns, etc. by
county might be more meaningful - how would Sevier County compare with

After entering all the new info from Will and Jess, I'm a bit hesitant to
start another list unless it's going to do something. I'd like to see
people constructing forest profiles and descriptions like the ones I did for
Chase, Belt, Corcoran and Cook.

It would be nice, but I don't expect we'll ever see it.


----- Original Message -----
From: "Edward Frank"
To: Colby Rucker
Sent: Tuesday, May 25, 2004 10:41 PM
Subject: Diversity Index


People are always proposing new indexes of one thing or another. I would
be interested in seeing some sort of a diversity index for forest
trees/shrubs/ I am thinking some value for each different species divided
by the acreage of the site or per 100 acres of a site. Is there anything
thing like that out there? Any thoughts about the idea? I would be
interested in seeing a greater variety of trees be measured at various
localities to facilitate more expanded forest profiles. Some value to
represent species diversity might spur some progress in that area.

Ed Frank
RE: Eastern Forest Structure   Ernie Ostuno
  Nov 26, 2004 01:35 PST 


I've always thought about ways of quantifying the level of human
disturbance to a forest and how it differs from natural disturbance. One
thing that I've been most impressed by in remnant old growth stands,
besides the awesome forms that the big trees assume, is the large volume
of decaying wood, both standing and fallen. The standing snags and
prostrate trunks add their own special contribution to the old growth
ecology (and aesthetic) as well as being a pretty good indicator of the
level of historical human disturbance at that site. 

I wasn't always thus
impressed, however. It's funny to think back several years ago when I
was trodding over the many fallen, moss-covered, giant hemlocks at
Snyder-Middleswarth Natural Area in Pennsylvania and my thoughts were
more along the lines of "wow, there's a lot of wasted wood here". Once
my mind evolved away from that way of thinking, it became possible to
appreciate that the less sign of human disturbance, the more impressive
the site is. It's especially evident here in lower Michigan where the
handful of old growth sites are usually more "topographically
accessible" than in Pennsylvania, which means they often have lots of
trails crisscrossing through them, sometimes paved roads and
campgrounds, too. It's really exhilarating when you find a remote site
with pits and mounds and minimal signs of unnatural disturbance.

Anyway, I like the idea of your list of items that can be noted as an
individual site is explored. This would be a way of more thoroughly
describing a site in terms of its ecology, along with the height and
girth of individual trees there. I think Pennsylvania old growth sites
were given a letter rating such as "A" or "B" several decades ago, but I
don't know what criteria was used. I'll have to track down the