Engineered Properties of Wood, Wood Materials and Structures
FS-FPL-4714
Properties of Salvaged Dead Yellow-Cedar
Issue:
Yellow-cedar trees have been dying on over 1/2 million acres of forests
in southeast Alaska since the 1880's. The decline was apparently triggered
by warming to the climate in SE Alaska. Trees dead for 100 years stand
as snags, and appear to have sound wood. The number of dead trees may
compose up to 2/3 of the volume of cedar in some stands. Yellow-cedar
cut from live trees is the most valuable wood in Alaska, with most of
the wood being exported to Japan. Dead snags are primarily only used
for fire wood. There is considerable interest in removing these snags
to improve forest health, but this is not economically feasible unless
higher-value uses can be found.
Objectives:
The primary objective of this study is to determine if the mechanical
properties of dead yellow-cedar snags decline with the length of time
the snags have been standing dead. A secondary objective is to determine
if "black stain" in the standing tree effects properties.
Cooperators:
This study is a cooperative effort of the US Forest Service, Forest
Products Laboratory, Madison, Wisc., and US Forest Service, Region
10, Alaska.
Approach:
One hundred and eight trees were sampled from Wrangell Island in southeastern
Alaska. Trees were selected in 5 appearance classes, previously developed
by Paul Hennon. These classes were live (control), Snag Class II (mean
time since death of 14-yrs), Snag Class III (dead 26-yrs), Snag Class
IV (dead 51-yrs), and Snag Class V (dead 81-yrs). Material was shipped
to FPL and samples prepared for testing in bending.
Results:
A summary of the results at 12% MC is shown below. Equivalent values for
Coast Douglas-fir are given for comparison.
|
D.-fir |
Yellow-Cedar |
| Property |
|
Live |
Class 2 |
Class 3 |
Class 4 |
Class 5 |
| Specimens tested |
-- |
1586 |
155 |
879 |
146 |
667 |
| Specific Gravity |
0.48 |
0.48 |
0.49 |
0.49 |
0.46 |
0.46 |
| Modulus of Elasticity, 106 psi |
1.95 |
1.55 |
1.97 |
1.56 |
1.88 |
1.64 |
| Modulus of Rupture, 103 psi |
12.4 |
13.0 |
14.7 |
13.1 |
13.5 |
12.7 |
There is no indication of
a significant reduction in bending properties of wood from dead
yellow-cedar versus that from
live trees. The presence
of "black stain" did not reduce the MOE or MOR of wood from
either dead or live cedar. The high durability of yellow-cedar, coupled
with its potentially high economic value, make this a unique opportunity
to extend the available wood resource with the context of sustainable
forest practices.
Recommendations:
Results on the properties of dead cedar are very
encouraging. It is thus important to anticipate what additional information
will be needed.
One of the most pressing needs is for a more detailed survey
of the dead yellow-cedar resource in southeast Alaska.
Ultimately, volume
estimates by snag class and estimates of severe spiral grain by
snag class would
be invaluable to potential users of this resource.
Assessment of the environmental contributions, if
any, of the dead snags to the ecosystem.
Continue product yield studies
when use options and commercial interests become clearer.
Green, D.W.; McDonald, K.A.; Hennon,
P.E.; Evans, J.W.; Stevens, J.H.. Flexural properties of salvaged deadyellow-cedar
from southeast Alaska.
Submitted for publication, Forest Products Journal.
Hennon, P.E.; Shaw, C.G., III. 1997. The enigma of
yellow-cedar decline: what is killing those long-lived, defensive trees.
Journal of Forestry.
95(12):4-10.
Hennon, P.E.; Whittwer, D.T.; Stevens, J.H.; Kilborn,
K. 2000. Pattrerns of deterioration and recovery of wood from dead yellow-cedar
in southeast
Alaska. Western Journal of Applied Forestry. 15(2):49-58.
Contact:
For additional information, contact Dr. David Green, Forest Products Laboratory,
Madison, Wisc., at (608) 231-9261 or E-mail: dwgreen@fs.fed.us or
Paul E. Hennon, Pacific Northwest
Research Station, Juneau, Alaska (907) 586-8769 or E-mail: phennon@fs.fed.us.
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