SPECIAL
PULPWOOD
SECTION
Logging on the shelterwood study area.
Sheltervvood harvesting:
tool for the vvoods manager
By RICHARD L. WILLIAMSON
Associate Mensurationist
Pac. NW Forest & Range Experiment
Station, U.S. Forest Service
Portland, Ore.
is the common harvest
method on all kinds of topography for
stands of western hemlock, the prin­
cipal pulpwood species in the Pacific
Northwest. Problems may arise with
this system though, usually in secur­
ing a new stand. But, suppose land
managers had assurance of an alter­
nate harvest method on ground suit­
able for selective cutting; one that
could assure reproduction; one with
no rotation time required for regen­
eration. Suppose this alternate method
could substantially increase growth on
trees near the end of a rotation. Then,
we would have a powerful tool for
the land manager-one enabling him
to circumvent anticipated regeneration
difficulties and possibly increase the
overall financial returns from his land
and timber capital.
An earlier article (PULP & PAPER,
December '62, pgs. 61-63) described
a shelterwood study in a 60 year old
western hemlock stand at the Hem­
lock Experimental Forest in Grays
CLEARCUTTING
Harbor County in western Washing­
ton. The experimental forest is main­
tained by the Pacific Northwest Forest
and Range Experiment Station in co­
operation with St. Regis Paper Co.
Shelterwood harvest, as related to its
effect on regeneration, is being ex­
amined as a possible means of boosting
productivity of coastal western hem­
lock forests in the Pacific Northwest.
These types cover about 4.2 million
acres and, in 1963, contained an esti­
mated volume of 29 billion cubic feet
of growing stock. The amount of land
in this type suitable for shelterwood
cutting is unknown, but is, no doubt,
substantial. Inferences from this study
can be applied only to this portion of
the type.
The U.S. Forest Service estimates
that 11 per cent of the total acreage
is nonstocked due to poor seed source,
competition from noncommercial spe­
cies and brush, deep logging debris,
and severe site conditions. There is
no estimate on the amount of land
poorly stocked for the same reasons.
Shelterwood harvest methods should
eliminate, or moderate, the influence
of these factors causing nonstocking
and poor stocking.
In
addition,
shelterwood
harvest
methods offer more complete site uti­
lization during the regeneration period
and have a positive value from the
esthetic standpoint. In some areas,
especially on public lands, partial cut­
ting methods may well be the only
ones acceptable to the public. The
time to find out if partial harvest
methods in these types are economi­
cally and silvicultnrally sound is now.
Logging on the 68-acre study area,
in 1960 and 1961, removed an aver­
age of 39 cords per acre and created
12 shelterwood stands of different
densities. This first part of a three­
stage harvest was designed to stimu­
late seed production through crown
release. The second cut, designed
primarily to leave sheltering trees for
established seedlings, and the third
cut, removing the last of the over­
story, were planned to follow at 5-year
intervals. A severe windstorm in 1962
disrupted this schedule. To salvage
windthrown trees, the second cut was
advanced 1 year to 1964 and removed
an average of 23 cords per acre. This
second harvest left stand densities
ranging from 17 to 156 trees per acre,
or approximately one-half the density
following the first cut. The third and
final harvest is now scheduled for
1969.
The following tabulation summa­
rizes the treatment schedule in terms
Dense stands like this .
More open stands .
The most open stands .
.
.
.
.
have a forest floor like this.
.
encourage seedling establishment.
.
support a mat of vegetation.
of number of trees per acre left after
each harvest cutting:
Treatment
number:
1
2
3
4
5
6
First
hamest
Secolld
harvest
328
185
135
134
145
90
156
104
97
60
56
40
7
54
25
8
58
18
9
68
28
10
64
21
11
32
17
12
42
20
Third
harvest
><
§
E-<
f2
g:
0
"
:g
riI
g:
Progress of regeneration, brush and
weed encroachment, growth of the
residual stand, and seedfall have been
measured annually since the first cut.
To ascertain which environmental con­
ditions favor establishment of western
hemlock regeneration, environmental
and topographic factors are also re­
corded for each sample point. These
variables are subjected to multiple
regression and graphic analyses.
Results to date indicate that satis­
factory regeneration is likely under
residual overstories ranging in density
from about 40 to 130 trees per acre.
In fact, overstocking may become a
problem. Success is less certain under
the more open stands (less than 40
trees per acre) or under the densest
(over 130 trees per acre). The densest
stands support little understory vege­
tation of any kind, an indication of
insufficient light for seedling growth.
In open stands, bracken fern, trailing
blackberry, salal, brush, and other
weeds seriously compete with small
seedlings and annually crush them
under a mass of litter. Heavy slash
combines with the dense brush in
open stands to further inhibit seedling
establishment. The amount of slash is
roughly proportional to intensity of
cut, but is in no way comparable, say,
to the slash resulting from clearcutting
an old-growth Douglas fir stand. Uti­
lization for pulpwood leaves very little
material except tops and branches.
The first cut apparently failed to
stimulate seed production, but this is
probably of little concern. The 1963
seed year was a failure over all treat­
ment areas, but in 1961 and 1962,
respectively, 531,000 and 2,513,000
viable seed were produced per acre
in the most open stand. Although this
stand was further reduced in 1964 by
the second harvest cut, it still pro­
duced 1,568,000 viable seed per acre
that year. Certainly, environmental
factors have exerted far more influ­
ence than amount of seedfall in suc­
cess of regeneration.
Regeneration for all treatments is
noticeably poorer on southerly and
westerly slopes than on northerly and
easterly slopes. The need for shelter
(amount of overstory retained ) , is
probably greater on poorer aspects
than on those more favorable.
Although 60 years old at the first
cut, trees in the more open shelter­
wood stands seem to have responded
to release remarkably. In stands with
less than approximately 80 trees per
acre, dominant and codominant trees,
ranging from 15 to 25 inches at breast
height, have grown twice as fast' in
diameter as have comparable trees of
equal diameter in lightly cut stands.
Windfall in 1962 disturbed com­
parisons of volume increment between
treatments. Available data, however,
suggest that increment suffered little,
if any, following light cuts. Even re­
moval of about 80 per cent of the
trees, leaving only dominant and co­
dominant ones, decreased volume in­
crement by only about one-half.
Reprinted from
PULP&.PAPER
January 3, 1966
Windfall losses in 1962 were spo­
radic, the average on all treatments
being 13 per cent by basal area, with
the range from 0 to 39 per cent. Per
cent loss was about inversely propor­
tional to density, though topography
exerted a modifying influence. The
heaviest blowdown occurred near the
upper end of lee slopes in stands
containing about 50 to 60 trees per
acre. A stand of 145 trees per acre
under this lee slope influence lost
about 26 per cent of basal area, but
otherwise, stands denser than about
70 trees per acre lost 9 per cent or
less of their basal area. Stands with
fewer than 50 trees per acre were all
on windward slopes and incurred
basal area losses of 28 per cent. All
merchantable windthrown material
was salvaged.
On the experimental forest, shelter­
wood logging costs (two different
operators over a four-year period)
have averaged around 75 per cent of
typical thinning costs in stands of the
same age, density, and size (14-in.
average dbh). Felling and bucking,
skidding, and loading costs in the
shelterwood operations have amounted
to $6.96 per cord. Skidding has been
by small tractors, track-type and rub­
ber-tired; loading, by small forklift
tractor.
In summary, results of the study,
at this time, suggest that, on ground
sl,litable for tractor skidding, adequate
regeneration of well-stocked stands
can be assured under any one of a
broad range of shelterwood densities;
that little volume growth need be
sacrificed in the residual stand; and
that no time in the rotation need be
allotted for regeneration. Final con­
clusions, however, will depend on how
presently established seedlings sur­
vive the final removal and how less
promising stands look in the future . •