Do stem form differences mask responses to silvicultural treatment

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Do stem form differences mask responses to
silvicultural treatment?

• Doug Maguire
• Department of Forest Science
• Oregon State University

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Typical responses monitored during silvicultural
trials

• Dbh
• Height
• Height to crown base?
• Upper stem diameters??
• Branch diameters??

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Monitor Dbh and Ht (perhaps crown size), but do
regional or subregional volume/taper equations
adequately estimate tree volumes? How would you
test statistically for silvicultural treatment
effects on stem form?
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Lennette thesis Effects of stand density regime
on stem form in larch Garber thesis Effects of
initial spacing and species mix on tree and stand
productivity Scott Ketchum, Robin Rose Does
relative stem profile respond to early control of
competing vegetation? Mark Gourley et al. Are
Swiss needle cast and/or nutrient amendments
changing stem form in Douglas-fir?
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Wider spacing ?
(increasing dbh)
(same relative stem profile?)
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Wider spacing ?
Larger crowns (length and width) ?
Influence on distribution of bole increment ?
Change in relative stem profile?
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Are any responses in stem form accounted for by
monitoring treatment effects on crown size
(length)?
Andy Lennette. 1999. Twenty-five-year response
of Larix occidentalis stem form to five stand
density regimes in the Blue Mountains of eastern
Oregon. M.S. Thesis, Oregon State University
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Lexen (1943) bole surface area as measure of
growing stock (Approximation of cambial surface
area on which wood accrues) Measurement of bole
surface area to regulate stocking
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Catherine Creek Levels-of-growing-stock
study Stocking regulated by bole surface
area Accomplished with Barr and Stroud optical
dendrometer Many upper stem measurements over
time
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Growing stock levels 1 5,000 ft2/ac 2 10,000
ft2/ac 3 15,000 ft2/ac 4 20,000
ft2/ac 5 25,000 ft2/ac
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35 yrs old in 1966 at start of study Thinned
twice, ages 45 and 65 (last thinning in 1965 Last
measurement in 1991 upper stem diameters
retrieved for 25-29 trees per treatment On
average 10 d.o.b.s per tree
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GSL Dbh (in) Ht (ft) I 16.1 83.6 II 12.
2 74.1 III 11.4 73.7 IV 10.7 72.6 V
9.5 74.8
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Increasing thinning intensity
Height on tree
dob
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Crown ratio
Increasing thinning intensity
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Analysis Kozak variable exponent model Dob/DBH
XC where X 1-(h/H)0.5 / 1-(4.5/H)0.5
C a1sin-1(h/H) a2(h/H)2 Fitted to each
individual tree, then SUR for a1 f( GSL or
tree attributes (eD/H) ) a2 g( GSL or tree
attributes (CR) )
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Increasing thinning intensity
Height on tree
dob
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Light thinning
Heavy thinning
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Light thinning
Heavy thinning
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Light thinning
Heavy thinning
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Conclusions Relative stem profile was
significantly different between the 2 most
intensive thinning treatments, and these 2 were
significantly different than the 3 least
intensive thinnings There was no marginal effect
of treatment beyond its effect on D/H and crown
ratio
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Production analysis requires development of
taper/volume functions (without attempt at
explicit test of treatment effects on stem
profile)
Sean Garber. 2002. Crown structure, stand
dynamics, and production ecology of two species
mixtures in the central Oregon Cascades. M.S.
Thesis, Oregon State University
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Ponderosa pine/lodgepole pine mixed species
spacing trial, planted in 1967 Grand
fir/ponderosa pine mixed species spacing trial,
planted in 1974 Both sampled in fall 2001 (34
and 27 yrs old, respectively)
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Upper stem measurements from trees felled outside
of permanent spacing trials Analysis based on
Kozak variable exponent model Dob/DBH
XC where X 1-(h/H)0.5 / 1-(4.5/H)0.5
C f(h, H, and D)
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Objective was NOT to test for spacing and species
effects on stem form, but rather on relative
productivity. BUT needed a reliable volume or
taper function for the site. Rather than
two-stage approach, can a mixed-effects model be
applied ? Is a random tree effect sufficient to
eliminate autocorrelation among observations
within a tree?
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Nonlinear residuals
NLME with two random tree effects
NLME CAR(1)
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Average tree in each spacing
Subtle spacing effects on relative stem profile
(but estimated adequately from D/H)
Lodgepole pine Ponderosa pine
Grand fir Ponderosa pine
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Spacing effect was not tested explicitly in taper
model since trees were felled off the
plots Instead profiles were plotted for the tree
of average dbh and height within each
spacing-species combination Effect of species
composition was even more subtle
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Conclusions Random tree effect dramatically
reduced the order of autocorrelation, but did not
eliminate it. A first-order continuous
autoregressive error process eliminated the
remaining autocorrelation.
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Conclusions (continued) The taper functions had
equations (Cochran 1985) differed from the taper
equation estimates by 20-30 for grand fir,
20-60 for lodgpole pine, and 2-10 for ponderosa
pine.
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Rose, Ketchum, Hanson. 1999. Three-year
survival and growth of Douglas-fir seedlings
under various vegetation-free regimes. Forest
Science 45117-126.
8 treatments, 3 reps/trt _at_ each of 2 sites Area
of herbaceous and woody control (1st two growing
seasons) 0, 4, 16, 36, 64, 100 ft2 100 ft2
woody only 100 ft2 herbaceous only
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3-ft
1-ft
2-ft
4 ft2
16 ft2
36 ft2
4-ft
5-ft
64 ft2
100 ft2
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Planted in February 1993 with 11
Douglas-fir Rose et al. (1999) present 3-yr
results Maximum growth response under the
largest (Summit) or 2 largest (Marcola) areas of
treatment (height, D2H, basal diameter) Greater
growth under herbaceous only, not under woody
only, relative to controls
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Winter 2001-2002, stem d.o.b. measurements Does
the intensity of early weed control affect stem
profile beyond the effect on diameter and
height? Do existing volume equations accurately
predict stem volume of weeded plantations?
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• Potential for systematic bias by treatment
• To test for treatment effects on stem profile,
• mixed-effects linear
• and non-linear models

finish
start
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Analysis Kozak variable exponent model Dob/DBH
XC where X 1-(h/H)0.5 / 1-(4.5/H)0.5
C b1(h/H) b2(h/H)2 Fitted to each individual
tree, then SUR for b1 f( site, treatment, tree
attributes ) b2 g( site, treatment, tree
attributes )
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Tentative conclusions No treatment effects, but
significant site effects. Relative stem profiles
similar even without accounting for differences
in height and diameter.