16 Fall 2012 Applegater
Thin for quality and health, not spacing
bY mAx bEnnETT AnD STEPhEn fiTzGERALD
Your chainsaw is revved up and • Poor form or has signs of
damage or internal decay
you’re about to sink the bar into a nearby
Douglas fir sapling. But which one? • Species not well suited to
the site
You’re surrounded by hundreds of them—
some smaller, some larger, all pretty close Crown ratio
Crown ratio is the percentage
together, but not uniformly spaced.
There are some madrone trees, too, and of the total height of the tree that
cedar, and a few spindly pine. You heard is occupied by the live green
somewhere that trees should be 10 feet or crown. For example, a tree that
12 feet apart…or was it 15 feet? You can’t is 75 feet tall and has crown on
quite remember. What to do?
the upper 25 feet of the tree has
The tree on the right has a sparse, thinning crown,
Many landowners ask about proper a live crown ratio of one-third
possibly
due to stress, insect attack, or root disease.
or optimum spacing when thinning trees. or 33 percent. Crown ratio is
Trees on the left have full crowns,
We’d suggest not getting too hung up important because the bigger the
indicating relatively better health.
initially on spacing, but instead focus on crown (the tree’s “food factory”),
tree quality and health (vigor). If you leave the better the tree’s growth. The rate from needle loss is another sign of stress.
primarily high-quality trees and take out of growth slows down in most species This can often be best determined by
mostly low-quality trees, it’s hard to go when the live crown ratio drops below comparing a thin or sparse crown with
wrong. You’re likely to have a healthier, 40 percent. Trees with crown ratios of 30 a denser crown on a nearby tree. An
more vigorous, more fire-resistant, and percent and greater often respond well to abundant crop of undersized cones (distress
more valuable stand in the long run.
release (removal of surrounding competing crop) is sometimes an indication that the
Is spacing between
trees), while trees with tree is severely stressed and likely to die in
t re e s u n i m p o r t a n t ?
crown ratios below 30 the near future.
Not at all. Trees need
percent often respond Tree form
adequate growing space
poorly. These trees may
The form of the tree trunk (stem) is
to thrive. However,
experience thinning an important consideration in thinning.
In a nutshell,
rigidly adhering to exact
shock or sunscald, or All other things being equal, trees with
spacing (e.g., 14 feet x 14
grow very slowly. Trees straight trunks and little taper that are
…“cut the sick,
feet) may lead you to cut
with very small crown free of defect are most desirable as “leave”
lame, and lazy,
trees that should be left
ratios may simply die trees from a timber perspective. However,
and to leave trees that
after thinning. This trees that are very tall for their diameter,
and leave the
should be cut. This is
often happens after especially conifers, tend to be unstable and
better ones.”
especially true in natural
diameter-limit thinning easily bent by the wind or snow, so some
stands where spacing
(removal of all trees above taper is important. Trees that have forked
between trees is highly
a certain diameter limit) or broken tops, crooked trunks or evidence
variable. In plantations
or high grading (“cut the of rot and defect may be candidates for
where spacing between
best and leave the rest”). removal. However, defective trees may
trees is more regular,
Gradual, light thinnings also make good wildlife trees, so aiming
using predetermined
are recommended for
spacing or stand density rules makes more very dense stands where few, if any, “leave”
sense. Remember that spacing guidelines trees have desirable crown ratios.
are just that—they are guidelines and, as Height growth
such, should remain flexible for leaving
Height growth can be determined by
the best trees. Also, remember that as examining the length of the leader if visible,
trees grow bigger, they progressively need or on many conifer species (including the
more space, so space trees out wide enough true firs, pines, Douglas fir), the length of
so that they will grow well until the next internodes, which is the distance between
thinning.
branch layers or whorls. Trees with good
So what makes a high-quality, height growth are preferred as “leave” trees.
vigorous tree? Following are some Crown shape/form
guidelines for “leave” and “cut” trees
Pointy-topped or A-shaped crowns
related to tree quality that you can use to indicate rapid height growth. Rounded
“eyeball” out in the woods. While these tops mean height growth has slowed.
points focus on conifer trees, the basic Good height growth is a sign of good vigor.
principles also apply to hardwoods.
However, as trees age, height growth slows,
Characteristics of “leave” trees
and trees tend to develop a round or flat
• Good live crown ratio (30% or
top. Full, symmetrical crowns are preferred
greater)
over ragged or lopsided crowns. Lopsided
• Good height growth for species
crowns develop when a tree is crowded on
and age
one or more sides. Trees with lopsided
• A-shaped crown (pointy top)
crowns are more vulnerable to blow down
• Abundant foliage with good color
or breakage in snow and ice storms.
• Good form (straight, without sweeps, Crown color/needle density
crooks, forks, etc.)
A dark green color indicates good
• Species is well suited to the site over
vigor. Light green or greenish-yellow
the long term
foliage (chlorotic foliage) is a sign of stress.
Characteristics of “cut” trees
This may be due to nitrogen deficiency,
• Poor crown ratio (less than 30%)
root disease, bark beetle attacks, or simply
• Poor height growth and crown form
moisture stress.
(flat or rounded top, lopsided)
Crown sparseness
• Foliage is sparse or off-color
A sparse or thinning crown resulting
For other informative woodland articles
Visit the online E-Newsletter of SW Oregon Woodland News at http://extension.
oregonstate.edu/sorec/small-woodlands-july-enews-2012. Check out the following
stories:
• The chain saw circle: Women of the woodlands
• Supreme Court to decide if logging road runoff is pollution
• Environmental groups say it will take 20 years to thin northwest forests
• Forest Capital Partners sells its timber portfolio
• The importance of burls and four other surprises from The Biscuit Fire
for a balance is important. For example,
large deformed black oak trees with broken
branches or heart rot are some of the best
habitat trees around. Unless they threaten
to demolish your house or barn if they
topple, consider leaving them alone.
Other considerations
These guidelines touch on a few key
indicators of tree quality. You should also
be on the lookout for evidence of insect
and disease problems, some of which
may warrant tree removal regardless of
other factors. Tree species should also be
considered. Many landowners like to leave
a mixture of tree species, both for esthetic
reasons and because a mixed-species forest
is often thought to be less vulnerable
to a pest problem that might devastate
a single-species stand (monoculture).
That’s generally true, but make sure that
the species is well suited to your site. For
example, hot, dry south-facing slopes in
the Applegate are good for pine and oak,
but aren’t so favorable for Douglas fir.
In a nutshell, these guidelines
follow the old adage, “cut the sick, lame,
and lazy, and leave the better ones.” As you
thin for quality, you will probably also be
reducing stand density to more desirable
levels. It may not be too scientific, but
forestry, after all, is a science and an art.
Max Bennett
541-776-7371 x221
Forestry/Natural Resources Agent
Oregon State University
Extension Service
Jackson-Josephine Counties
max.bennett@oregonstate.edu