junhui zhao, douglas a. maguire, douglas b. mainwaring, alan kanaskie
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Thinning mixed-species stands of Douglas-fir and western hemlock in the presence of Swiss needle cast. Junhui Zhao, Douglas A. Maguire, Douglas B. Mainwaring, Alan Kanaskie. Background. - PowerPoint PPT PresentationTRANSCRIPT
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Thinning mixed-species stands of Douglas-fir and western hemlock in the presence of Swiss needle cast
Junhui Zhao, Douglas A. Maguire, Douglas B. Mainwaring, Alan Kanaskie
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Background
• Young Douglas-fir plantations (≤40 yr) are tremendously important to the economic and environmental health of Oregon and Washington due to their extent and productivity (Campbell et al. 2004, Gray et al. 2005).
• Over the past 20 years, coastal forests in this region have been suffering from an epidemic of Swiss needle cast (SNC).
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Premature loss of older foliage,Needle longevity 1-4 years
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(Alan Kanaskie, 2011)
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Swiss Needle Cast affect Douglas-fir
Needle on the left showing rows of black fruiting bodies of Swiss needle cast.
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197019801983 1961
2008:1984
Direction of growth
The trees’ growth between 1984 and 2008 was packed into just a millimeter.
(Photo by Bryan Black)
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Current plantation strategy
• Due to its historically greater value, Douglas-fir continues to be an important component of planted stands.
• Increasing proportions of Douglas-fir are generally planted stands from west to east within the Coast Ranges of Oregon, with western hemlock making up most of the remainder.
(Beth Fitch, pers. comm)
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Pre-commercial thinning• Infected stands
respond positively to thinning.
• But Douglas-fir growth remains lower than its potential in absence of SNC.
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WH
DF
Growth market value
2000 2002 2004 2006 2008 2010 2012$200
$300
$400
$500
$600
$700
$800 Douglas-fir western hemlock
NO. 2 Saw log
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Aims of this study
1. to develop distance-independent individual tree diameter growth models for Douglas-fir and western hemlock growing in plots established across a gradient in SNC severity;
2. to compute the implied relative basal area growth of Douglas-fir and western hemlock trees of varying initial diameter as a function of foliage retention;
3. to develop a field chart to help managers select trees for removal and retention during thinning of mixed Douglas-fir and hemlock stands .
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Study plots• 10-30-yr old
Douglas-fir plantation
• 76 stands• 0.2 acre• Measured in
1998, 2000, 2002, 2004, and 2008.
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Method
• Develop diameter increment models for Douglas-fir and western hemlock by testing:– Tree size: DBH, CR, HCB– Competition: TPA, D40, H40, QMD, AGE, BA, CCF,
SDI, SI, BAL, CCFL– Site: ELEV, SL, LONG, LAT– SNC: FR
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The models
• Douglas-fir (R2=0.733)
• Western hemlock (R2=0.766)
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Residuals
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40.4% less
85.0% more
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Model application• TPA=400 ( DF250, WH150). CR=0.7.• Diameter of western hemlock: 2-12 inches• Diameter of Douglas fir: 0-5 inches larger than
western hemlock.• All Douglas-fir trees have the same DBH, and
all Western hemlock have the same DBH.
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Model application• The ratio of basal area growth of the Douglas-
fir and western hemlock trees was computed as a function of foliage retention and the difference between the diameters of the two species.
• For a given foliage retention, the diameter difference between the species where the growth ratio equals one implies a diameter difference threshold during a thinning.
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0 1 2 3 4 50.0
0.5
1.0
1.5
2.0
2.5
3.0D_wh = 4 inch
1.52.02.53.03.5reference line
i=DBHDF-DBHWH
BAGR
O_W
H/BA
GRO
_DF
FR
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0 1 2 3 4 50.0
0.5
1.0
1.5
2.0
2.5
3.0 D_wh = 2 inch1.52.02.53.03.5ref-er-ence line
i
BAGR
O_W
H/BA
GRO
_DF
0 1 2 3 4 50.0
0.5
1.0
1.5
2.0
2.5
3.0 D_wh = 4 inch1.52.02.53.03.5ref-er-ence line
iBA
GRO
_WH/
BAGR
O_D
F
0 1 2 3 4 50.0
0.5
1.0
1.5
2.0
2.5
3.0 D_wh = 6 inch1.52.02.53.03.5ref-er-ence line
i
BAGR
O_W
H/BA
GRO
_DF
0 1 2 3 4 50.0
0.5
1.0
1.5
2.0
2.5
3.0 D_wh = 8 inch1.52.02.53.03.5ref-er-ence line
i
BAGR
O_W
H/BA
GRO
_DF
0 1 2 3 4 50.0
0.5
1.0
1.5
2.0
2.5
3.0 D_wh = 10 inch1.52.02.53.03.5ref-er-ence line
i
BAGR
O_W
H/BA
GRO
_DF
0 1 2 3 4 50.0
0.5
1.0
1.5
2.0
2.5
3.0 D_wh = 12 inch1.52.02.53.03.5ref-er-ence line
iBA
GRO
_WH/
BAGR
O_D
F
i=DBHDF-DBHWH
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Conclusion
1. The foliar losses of Douglas-fir imposed by SNC diminish Douglas-fir crown density and diameter increment, thereby enhancing diameter increment of western hemlock, the most common associate of Douglas-fir in coastal forests of Oregon.
2. Application of Douglas-fir and western hemlock diameter increment models to simulate indicates that the relative basal area growth of the two species in young, mixed stands varies directly with foliage retention.
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Conclusion
3. When thinning in mixed stands where foliage retention is as low as 1.5 yrs, western hemlock trees will grow more in basal area than Douglas-fir tree that are 2-3 inches larger in diameter.
4. These results can be useful for forest managers who can prescribe “D+x” thinning where x represents the diameter advantage that Douglas-fir must have over an adjacent western hemlock to be selected as the leave tree. In this approach, “x” would be selected as a function of SNC intensity as measured by foliage retention.
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Acknowledgements
• This project was funded by the Swiss Needle Cast Cooperative (SNCC) hosted at Oregon State University.
• We gratefully acknowledge field work performed by many different field crews working for the SNCC and the Oregon Department of Forestry.
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THANK YOU FOR YOUR ATTENTION!