Sedona Canyon, AZ,  Old Growth?   Don Bertolette
  Sep 19, 2004 22:45 PDT 
Attaching an image from my most recent outing...perhaps it will serve as a
point from which to launch a discussion on just what constitutes old-growth,
and what makes a bush a bush (not intended to launch a political
discussion!) and a tree a tree.

The foreground is a manzanita (Arctostaphylos spp), the background the
redrocks of Sedona, and predictably enough, me on middle ground. I am
comfortable suggesting that this manzanita is pre-Euroamerican settlement in

I suggest that there is an analogy of this manzanita (and an oak of similar
stature and "soil" bank) to the more famous Bristlecones of the White
Mountains of Eastern Central California (attaining 3-4,000 years). Surely
they're old-growth? In my view, they belong to their own category, an
old-growth tree/forest that have attained their status from the "economy" of
their growth habit...they have adapted to conditions that are extraordinary
in their extremes - cold, minimal soil nutrients, incredible levels of
ultra-violet rays (10-14,000 feet, precious little atmosphere filtering out
the sun's rays), heat.

This probably opens up the bush/tree question, as there are those who
propose that the common creosote bush is among the oldest continuous
lifeforms (posited to create concentric "rings" as they allelopathically
force their growth outwards).

Back to manzanita, I have not yet seen one with a singular bole high enough
to have a dbh, but numerous examples yield trunk diameters of a foot or
more. This specimen here is growing in precious little soil and able to
survive on very little moisture. Taken during the second week in September,
the temps were in the low 80's. Not unusual for the area to rise into the
90's, occasionally in the 100's.


RE: Sedona Canyon, AZ,  Old Growth?   Robert Leverett
  Sep 21, 2004 07:39 PDT 


   Your make very important points. As I know you would agree, the
definitions we adopt for OG usually incorporate science, politics,
economics, and aesthetics. While our intent may be to restrict the
criteria to science, I think the exigencies of the situation usually
dictate otherwise. I'm struck by the practicality of Lee Frelich's
definition that for him old growth is whatever the resident authority
says it is. Lee then works within the context of that definition to
explore the natural processes that shape the forest environment - toward
a rapidly or slowly evolving system.

   Perhaps you should become the resident authority under the auspices
of WNTS. WNTS could become a repository for ideas, models, and debate.
One can hardly not be struck by the difference between environments that
cycle forests every 100 to 200 years as in flood plains to rock and ice
environments that can allow gnarled bristlecone pines to linger on for
5,000 years. Allowing for a 150 year cycle on a flood plain, one cycle
of the bristle cones equals 33 cycles of the flood plain environment. Of
course each environment has many cycles that play out beyond the obvious
seasonal ones, but sometimes it helps to consider how old growth
environments differ from one another as well as consider the points of

RE: Sedona Canyon, AZ,  Old Growth?   Edward Frank
  Sep 21, 2004 10:17 PDT 


Don presents a simple question about whether these manzanita are trees
and whether or not they constitute and old-growth forest. Behind this
simple question lies a variety of hidden questions:

1) Are these short manzanita considered to be a tree?

The hidden question is whether or not height is a dominant factor in
determining whether something is a tree or not. I don’t know. Is there
some structural or physiological difference between a tree and other
types of vascular plants? Does something become tree solely based upon
height? I know there are species of oak that are maybe a meter in
height, are these trees or not? Other members of the oak family reach
large size, so does it make sense that some are trees and others are
not? Does it really make any difference?

The Oklahoma Biological Survey defines the terms as follows: “There are
approximately 2,400 plant species in Oklahoma (Taylor and Taylor 1994)
and about 330 are trees, shrubs, or woody vines. For the purpose of this
document, a woody plant is defined as a plant that retains some living
woody material at or above ground level through the non-growing season
(several species of small cacti fit this definition, but are not
recognized trees or shrubs). Categorizing a woody plant as "tree",
"shrub", or "vine" is often difficult and can appear arbitrary.
Distinguishing between a tree and a shrub can be particularly difficult.
That is why it is not unusual to see descriptions such as "small tree or
large shrub." In this treatment we have adopted the following
definitions: a tree is a woody plant that is at least 10 cm (4 in ) in
diameter at 1.4 m (4.5 ft) above ground level; a shrub is less than 10
cm in diameter at 1.4 m above the ground and usually has multiple stems
or is clonal; a woody vine does not stand upright without support but
climbs on other vegetation or sprawls on the ground.”
So as far as the OBS is concerned the main difference between trees and
shrubs are their height. For the purposes of the WNTS and ENTS I would
lump both trees and shrubs together as a single category as the
separation between the two groups is arbtrary. Therefore this manzanita
(Arctostaphylos spp) is a “tree.”

2) Does this population of trees, including both manzanita and (oaks?)
Constitute a forest? 

Don says, “In my view, they belong to their own
category, an old-growth tree/forest that have attained their status from
the "economy" of their growth habit...they have adapted to conditions
that are extroardinary in their extremes...” I have been looking at
definition for various forest types.

Bob Leverett (Feb 10) wrote, “.. you raise some interesting points. The
most intriguing to me concerns how we actually define forests/forest
types especially today when so much human-created disturbance has taken
place that impacts what we can do. How might we define a floodplain
forest of say the Connecticut River at the latitude of Hatfield,
Massachusetts, given the massive ecological changes that have taken
place from the surrounding farms over many years? ...The answer to the
question of what we include in a definition probably depends on one's
profession. If so, what might be the differences in the requirements of
a definition as seen from the perspectives of the forester, forest
ecologist, plant ecologist, wildlife biologist, and conservation
biologist? Who would emphasize what as hard and fast requirements of a
definition. Like everyone else on the list, I've read plenty of
definitions of forest types/associations that are oriented to species
composition. Some hint at structural features, but usually only in a
very general way.”

Lee Frelich (Feb 10) wrote; “Minnesota Department of Natural Resources
recently switched to natural community-based definition for forest and
other vegetation. They used ordinations including trees, shrubs and
understory plants to separate communities within each region of the
state. The ordinations were based on thousands of plots where all trees
and plants were identified by Natural Heritage Ecologists. Those plots
that fell together in clusters in multi-dimensional ordination space
defined a natural community, and the characteristics of those plots were
used in the descriptions that have now been published (but its not on
the web yet).”

So clearly we can define this plant community as a distinct entity. Is
it a forest? It seems to me what we define as a forest or not a forest
depends on the density of trees in an area. In the eastern US trees
often grow like weeds. The density of trees in an eastern forests is
high. This is partially related to the age and species present, but if
talking about mature forests a major factor is the availability of
water. In drier climates there are savannah forests with more widely
spaced trees intermingled with grasses. A good example of this type of
forest is the cross-timbers area of Texas, Oklahoma, Kansas, and
Arkansas. You can see examples of this type of growth on the University
of Arkansas cross-timbers website:

It seems reasonable to say that what is a forest and what is not depends
on the environmental conditions. There is a spectrum between dense tree
population in wet areas, to more open savannah forests. Therefore under
the extreme conditions found in the arid areas of the southwest and
western United States, a sparsely populated community of woody plants
should be considered a “forest.”

There is little debate about whether these representative trees are old
or not. Their “forest” for the most part is relatively undisturbed by
human activities- they haven’t been timbered or cultivated. So these
forests should meet even the most strict definitions of an “old growth
forest” if you accept the first two propositions - that these are trees
and constitute a forest.

An important side issue is how do you measure these trees, since many of
them do not reach breast height? At what point should their 
circumference be measured? As for height, I would think the “pole
method” would be most appropriate.

Ed Frank

I have posted this comment thread and the picture of the manzanita tree
on the ents website at