SMC Quar ter ly News
www.standmgt.org
Stand Management Cooperative
College of Forest Resources, University of Washington
2nd Quarter 2007
From the Director
The first quarter of 2007 has been busy and strange. Not only did
the field crew have some unusual weather to deal with but their
new truck was stolen from the parking lot of the motel where they
were staying in Longview. Perhaps more important than the truck
was the fact that the box with all of the gate keys, a data recorder
with recent data, and the field equipment were in the truck. Not all
Dave Briggs, SMC Director
was lost as computers and some equipment being recharged were
in the motel. Megan retrieved Bob and Bert who were stranded
with no transportation. Fortunately, the old truck that had just been
turned in to UW motor pool for the replacement was still available.
An arrest was made within a few days and the critical equipment
was found but a lot of personal field gear, chainsaws, and other
tools were never found. About a week after
the theft, the truck was found, drivable but
stripped of electronics and canopy. As a
result, we were able to weather this incident with relatively short time loss.
The other major event during the first
quarter was the sawmilling phase of the
inside:
From the Director
non-destructive testing study at the South
1
Jim Kniert Owner, Operator of the South Union
Sawmill
Union Sawmill near Elma, WA. Work in the log yard for log scaling,
Progress on the Tree to Log to
Product Non-destructive Testing
Study
1
to obtain acoustic velocity
Development of a hybrid modeling
approach for predicting intensively
managed Douglas-fir growth at
multiple scales
3
measure cookies was done on
Abstracts and Publications
7
Meetings
8
and knot data, buck logs, and
January 29-February 5. Log
yard procedures were the
South Union Sawmill
same as reported in the
previous issue for the veneer logs at the Weyerhaeuser
mill in Foster, OR; the only change was that the priority
Eini Lowell, PNW RS
marking lumber at the
South Union Sawmill
short log length was 16 feet. Sawing the logs
into 2x4 and 2x6 lumber took place over
March 5-16 with 4-5 SMC
and PNWRS personnel on
hand each day. The
lumber is currently being
South Union Sawmill
dried, will be planed and
graded, and then shipped to the US Forest Products
Laboratory for tests of mechanical properties. We anticipate shipment in early May. Currently, the Forest Products
Laboratory is testing the veneer that was shipped from Foster mill at the
beginning of the year. Tree
and log data from the earlier
phases is currently being
organized and checked and
Ramicorn branch in lumber
Masters Student Gonzalo
Thienel is starting an analysis
of the standing tree acoustic velocity
data from the plots.
Stacked green lumber at the South Union Sawmill
In this issue you will also find an
article by Aaron Weiskittle, Doug Maguire and Robert Monserud on “Development of a hybrid modeling approach for predicting intensively managed
Douglas-fir growth at multiple scales.”
Mark Your Calendars
SMC Spring Meeting will be on April 25-26 2007, at the Gifford Pinchot National Forest
Headquarters in Vancouver, WA. The agenda can be downloaded from the SMC website:
www.standmgt.org. Coffee and muffins will be offered at 9:00 on the 25th, the meeting will
start at 9:30 and go until 4:30. On the 26th, coffee will be offered at 8:00, the meeting will
start at 8:20 and go until 12:00.
Meeting fees are $30 per person which will include coffee/muffins the 25th and 26th, lunch
on the 25th and meeting handouts. Fees can be paid the day of the meeting, but be sure to
let Megan O’Shea know if you’re planning on attending, moshea@u.washington.edu or 206543-9744.
Rooms are available at the Comfort Suites in the Vancouver Mall, (877-874-5474) book
under the University of Washington, SMC.
2
Dev
elopment of a hhybr
ybr
id modeling approach
Development
ybrid
for predicting intensiv
el
ir
intensivel
elyy managed Douglas-f
Douglas-fir
gro
wth at m
ultiple scales
growth
multiple
Aaron Weiskitte, Doug Maguire, OSU, and Robert A. Monserud, PNW
Research Staton.
Introduction
Hybrid models offer the opportunity to improve future growth projections by combining
advantages of both empirical and process-based modeling approaches. Hybrid models have
been constructed in several regions and their performance relative to a purely empirical
approach has varied. A hybrid model was constructed for intensively managed Douglas-fir
plantations in the Pacific Northwest by embedding a hierarchy of components representing
fundamental processes into a spatially implicit individual-tree model.
Model Overview
The modeling approach emphasized a hierarchical treatment of multiscale processes with
predictions made at the individual branch-, tree-, and stand-levels. Three primary components comprise the model, corresponding to characterization of crown structure
(BCACS), estimation of annual net primary production (NPP), and allocation of carbon
and growth to different parts of the tree (ALOGRO).
BCACS
This submodel contains a set of empirical equations that predict the location, diameter, and
biomass of every branch on each tree on the sample plot being simulated. The input is a
tree list containing diameter at breast height (DBH), height (HT), height to crown base
(HCB; lowest live branch), and expansion factor (EXPF, in trees per ha) as well as estimates
of total age and site index (base age 50 years). Past height growth is reconstructed from
the dominant height curves developed by Bruce (1981) to determine the location of
annual whorls of branches. These attributes were then summed to estimate biomass and
surface area at the tree- and stand-levels.
Total stem and sapwood volume were estimated at the tree-level from existing stem
volume and sapwood taper equations (Maguire and Batista 1996; Walters et al. 1985).
Volumes were converted to biomass by applying regional values for total and sapwood
density (530 and 455 kg m-3, respectively). Belowground biomass at the stand level was
estimated from total aboveground biomass assuming the relationship presented by Ranger
and Gelhaye (2001).
Net Primary Production (NPP)
Inputs for this submodel were kept as simple as possible to capture the fundamental
physiological processes, and so included: (1) daily climate obtained from DAYMET (http://
www.daymet.org); (2) site physiographic features (elevation, slope, aspect); (3) stand
structural attributes from BCACS (LAI, biomass, canopy cover, etc.); (4) basic soils information (rooting depth, texture, rock content), and (5) foliar nitrogen concentration. The model
estimates gross primary production (GPP) five times daily. The model contains all the
necessary components for accurately estimating GPP, which include: (1) daily time step; (2)
3
separation of direct and diffuse radiation; (3) light extinction coefficients dependent on solar
geometry, canopy structure, and type of radiation; (4) separation of sunlit and shaded leaf
area; (5) photosynthesis estimates based on the Farquhar et al. (1980) biochemical equation
and modified by foliar nitrogen levels, (6) site slope and aspect effects on diurnal distribution
of radiation and fraction of sunlit leaf area (particularly in areas with complex terrain); (7)
estimates of stomatal conductance as a function of vapor pressure deficit and soil water
availability; and (8) canopy gas exchange linked to soil water and nutrition availability. Net
primary production was estimated as constant fraction of GPP (Waring et al. 1998).
Allocation and Growth (ALOGRO)
Figure 11. Location of SMC installations from
which the verification data were collected.
A modified 3-PG (Landsberg and Waring 1997) carbon allocation approach resulted in the
highest correlation between simulated above-ground NPP and observed stem volume
growth. The modifications to the 3-PG allocation approach involved estimation of the site
fertility rating from canopy N percentage (Swenson et al. 2005) and applying Duursma’s and
Robinson’s (2003) correction for inherent bias when estimating stand-level biomass (or its
allocation in this case) from stand-level mean tree size. Disaggregating of stand volume
growth to individual trees was based on weighted leaf areas estimated by a regression
model developed from the data of Brunner and Nigh (2003). Individual tree diameter and
height growth were predicted using differentiated allometric equations (Kirschbaum 1999),
pipe-model theory (Valentine and Mäkelä 2005), and transport resistance model (Thornley
1999). For comparison, predictions were also made with purely empirical equations
(Weiskittel et al. 2007) and the following hybridized form of these equations:
w
[1]
ΔYadj = ΔYEMP * (βij + βij*NPP + βij*ln(NPP))
where ΔYadj is the adjusted growth rate (diameter or height), ΔYEMP is the predicted
growth from the empirical equation, and the βij’s are annualized parameters to be estimated
from an independent dataset. Mortality in ALOGRO was assumed to occur when individual
tree growth efficiency (stem biomass increment/tree leaf area) fell below 0.10 kg m-2 yr-1.
Performance of this approach was compared to that from an empirical model for estimating
annual probability of individual tree mortality (Flewelling and Monserud 2002).
Model Simulations
Data from nine SMC installations in Oregon and Washington comprised the verification and
testing dataset (Figure 1). These installations covered a wide range of growing conditions
that are typical for the region. The plantations were established between 1971 and 1982 at
varying densities (905 to 1575 stems per ha) and levels of vegetation control. Several sets
of 0.2-ha permanent plots were established by the SMC at each installation between 1986
and 1992. Since establishment, the 56 plots have received a variety of silvicultural regimes
that have involved thinning, pruning, and nitrogen fertilization.
The model assembled from BCACS, NPP, and ALOGRO was evaluated by simulating leaf
area index (LAI) and growth on each of the 56 SMC plots and comparing the predicted
stem volume growth to observed current annual increment (CAI). The same plots were
also simulated in 3-PG after parameterizing for Douglas-fir with information presented by
Waring and McDowell (2002). To estimate the subjective soil fertility index for 3-PG, the
measured soil nitrogen percentage was converted to nitrogen content based on soil
4
W
This study
3-PG
35
depth and estimated bulk density (Kaur et al. 2002). This value for total nitrogen was then
converted to the soil fertility index with the equation developed by (Swenson et al.
2005). Climate information for the growth periods represented on the SMC plots was
obtained from DAYMET (http://www.daymet.org).
Results
Periodic annual increm ent (m 3 ha -1 )
(A)
30
25
20
15
10
5
0
[2]
[3]
ΔDBHadj = ΔDBHEMP * (0.5999 - 0.0149*NPP + 0.1742*ln(NPP))
5
10
15
20
25
30
35
40
35
40
Net primary production (NPP; kg dry matter ha-1)
35
Observed periodic annual increm ent (m 3 ha -1 )
At the stand-level the NPP algorithm described in this study performed significantly
better than 3-PG when LAI was estimated by BCACS (Figure 2). For individual trees, the
hybrid approach developed in this study produced a level of bias comparable to the
empirical approach, in large part due to its empirical basis (Table 1). The hybrid model
predictions modified empirical estimates as follows:
(B)
30
25
20
15
10
5
ΔHTadj = ΔHTEMP * (1.4197 + 0.0199*NPP – 0.3229*ln(NPP))
0
5
10
15
20
25
30
Predicted periodic annual increment (m3 ha-1)
15
(C)
where ΔDBHEMP and ΔHTEMP are predicted diameter and height growing using the
fell below the threshold produced final stand basal areas that were comparable to
predictions with an empirical mortality equation (Figure 3); however, both approaches
underpredicted mortality in stands with higher density.
Bias (observed - predicted)
equations of Weiskittel et al. (2007). Tree mortality imposed when growth efficiency
10
5
0
-5
-10
-15
5
Discussion
15
20
25
30
3
35
-1
Observed periodic annual increment (m ha )
Figure 2. Relationships between observed growth
and predictions from both the hybrid model and
3-PG: (A) observed current annual increment
(CAI; m3 ha-1) over simulated net primary
production (NPP); (B) observed over predicted
and CAI; and (C) bias (observed – predicted) over
observed CAI.
10
Bias (observed - predicted)
Hybrid models have been proclaimed as the next step forward for improving growth
projections for managed stands (e.g. Landsberg, 2003b). The hybrid modeling framework
combines the strengths of both empirical and process-based models. The hybrid model
constructed here for intensively managed Douglas-fir plantations in the Pacific Northwest
significantly improved predictions of LAI and CAI compared to other modeling approaches. At the individual tree-level, disaggregation of NPP and prediction of stem
diameter and height growth were improved. In addition, imposing mortality when growth
efficiency fell below a threshold value predicted mortality at a level of accuracy comparable to empirical approaches. These improvements resulted directly from: (1) more
detailed representation of crown structure and dynamics; (2) inclusion of key physiological mechanisms at an appropriate spatial and temporal resolution; and (3) application of
empirical equations modified by simulated NPP to predict diameter and height growth of
individual trees rather than relying on allometric or theoretical equations. Areas of future
improvement for these types of models include: (1) components that simulate the effects
of soil water and nutrients on physiological processes, particularly respiration and carbon
allocation, in a simple yet mechanistic manner; (2) components that account for the
effects of silvicultural treatment and environmental conditions on foliage age class
dynamics, so that seasonal variation in LAI and net photosynthesis can be simulated
more accurately; and (3) rigorous assessment of the relationship between growth
efficiency and probability of individual tree mortality.
10
Empirical equation
Growth efficiency
5
0
-5
-10
0
10
20
30
40
50
Observed basal area (m2 ha-1)
Figure 3. Bias (observed – predicted) in final stand
basal area (m2 ha-1) after four years of simulated
growth on 56 Stand Management Cooperative plots.
Predictions were made with two alternative tree
mortality models, the first an empirical mortality
equation and the second a threshold growth
efficiency.
DBH
(n = 8860)
HT
(n = 2805)
Approach
1. Empirical
Mean bias
-0.01
MSE
1.22
% bias
-0.61
Mean bias
-0.59
MSE
0.97
% bias
-3.84
2. Allometric
1.24
1.63
4.97
-0.42
1.30
-3.87
3. Pipe-model
3.07
3.25
13.04
-2.52
3.43
-19.78
4. Thornley (1999)
-3.75
3.91
-20.63
-0.06
1.28
-1.41
5. Hybrid
0.53
1.18
1.99
0.15
0.85
1.04
Tab
le 1. Mean bias, percent (%) bias, and mean square error (MSE)for individual-tree predictions of diameter and height
able
growth on 56 Stand Management Cooperative plots with thinning and fertilization treatments. Growth was estimated
with: (1) an empirical model (Weiskittel et al. 2007); (2) an allometric equation (Kirschbaum (1999); (3) equations based
on pipe-model theory (Valentine and Mäkelä 2005); (4) a transport resistance model (Thornley 1999); and (5) hybrid
equations developed in this study.
Literature Cited
Bruce, D. 1981. Consistent height-growth and growth-rate estimates for remeasured plots. Forest Science 4:
711-725.
Brunner, A., and Nigh, G. 2003. Light absorption and bole volume growth of individual Douglas-fir trees. Tree
Physiology 20: 323-332.
Duursma, R.A., and Robinson, A.P. 2003. Bias in the mean tree model as a consequence of Jensens’
inequality. Forest Ecology and Management 186: 373-380.
Farquhar, G.D., von Caemmerer, S., and Berry, J.A. 1980. A biochemical model of photosynthetic CO2
assimilation in leaves of C3 leaves. Planta 149: 78-90.
Flewelling, J.W., and Monserud, R.A. 2002. Comparing methods for modeling tree mortality. USDA Forest
Service Rocky Mountain Research Station.
Kaur, R., Kumar, S., and Gurung, H.P. 2002. A pedo-transfer function (PTF) for estimating soil bulk density
from basic soil data and its comparison with existing PTFs. Australian Journal of Soils Research 40: 847857.
Kirschbaum, M.U.F. 1999. CenW, a forest growth model with linked carbon, energy, nutrient and water
cycles. Ecological Modelling 181: 17-59.
Landsberg, J.J., and Waring, R.H. 1997. A generalized model of forest productivity using simplified concepts of
radiation use efficiency, carbon balance and partitioning. Forest Ecology and Management 95: 209-228.
Maguire, D.A., and Batista, J.L.F. 1996. Sapwood taper models and implied sapwood volume and foliage
profiles for Coastal Douglas-fir. Canadian Journal Forest Research 26: 849-863.
Ranger, J., and Gelhaye, D. 2001. Belowground biomass and nutrient content in a 47-year-old Douglas-fir
plantation. Annals of Forest Science 58: 423-430.
Swenson, J.J., Waring, R.H., Fan, W., and Coops, N.C. 2005. Predicting site index with a physiologically based
growth model across Oregon, USA. Canadian Journal of Forest Research 35: 1697-1707.
Thornley, J.H.M. 1999. Modelling stem height and diameter growth in plants. Annals of Botany 84: 195-205.
Valentine, H.T., and Mäkelä, A. 2005. Bridging process-based and empirical approached to modeling tree
growth. Tree Physiology 25: 769-779.
Walters, D.K., Hann, D.W., and Clyde, M.A. 1985. Equations and tables predicting gross total stem volumes in
cubic feet for six major conifers of southwest Oregon. Oregon State University, Forest Research
Laboratory.
Waring, R.H., Landsberg, J., and Williams, M. 1998. Net primary production of forests: a constant fraction of
gross primary production? Tree Physiology 18: 120-134.
Waring, R.H., and McDowell, N. 2002. Use of a physiological process model with forestry yield tables to set
limits on annual carbon balances. Tree Physiology 22: 179-188.
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Weiskittel, A.R., Garber, S.M., Johnson, G.P., Maguire, D.A., and Monserud, R.A. 2007. Annualized diameter and
height growth equations for Pacific Northwest plantation-grown Douglas-fir, western hemlock, and red
alder. Forest Ecology and Management in press.
Abstr
acts and Pub
lications
Abstracts
Publications
Assessing corewood acoustic velocity and modulus of elasticity with two impact based
instruments in 11-year-old trees from a clonal-spacing experiment of Pinus radiata D.
Don. Jean-Pierre Lasserre, Mason, Euan G. and Watt, Michael S. Forest Ecology and
Management,Volume 239, Issues 1-3 , 15 February 2007, Pages 217-221.
Outermost wood and whole stem modulus of elasticity (E) was measured acoustically from trees
within an 11-year-old Pinus radiata experiment, which included six clones grown at two contrasting
stand densities (833 and 2500 stems ha-1). This study examines the effect of bark removal on whole
stem E as measured by resonance (Eres) in the lower log (0–2 m) and how branch removal influences
Eres in the upper log (2 m to 70% tree height). An additional objective was to develop relationships
between E of the outer part of the wood made on standing trees, using time of flight (Etof), and whole
stem E measured using resonance (Eres).
Both branch and bark removal significantly influenced Eres, increasing values by an average of 8.3% and
5.4%, respectively. The influence of bark on Eres was relatively constant across the E range examined,
ranging from 8.0% at low values of Eres (2.6 GPa) to 8.6% at high values of Eres (5.5 GPa), with bark. In
contrast, increases in Eres induced by branch removal ranged from 24% at low values of Eres (3.4 GPa)
to 0% at high values of Eres (6.5 GPa).
There were strong positive linear relationships between Etof and Eres, both when bark was present (r2
= 0.94) and removed (r2 = 0.92), from the whole stem. Values of Eres measured with and without bark,
were respectively on average 38% and 33%, lower than Etof (with bark). Although stand density and
tree diameter did not significantly influence these equations the relationship between Etof and Eres logs
with bark attached was significantly influenced by clone (P < 0.05). The percentage of stems correctly
reallocated by time of flight back to whole log modulus of elasticity classes (high, medium and low),
was significant (P < 0.0001) and high, averaging 80% across the three classes. These results highlight
the utility of Etof measurements on standing trees in predicting whole stem Eres, and also suggest that it
is important to account for the effect of bark and branches when measuring whole stem E using
acoustic methods.
The role of species mixtures in plantation forestry. Matthew J. Kelty. Forest Ecology
and Management. Volume 233, Issues 2-3 , 15 September 2006, Pages 195-204.
Nearly all forest plantations are established as monocultures, but research has shown that there are
potential advantages to be gained by using carefully designed species mixtures in place of monocultures. This paper reviews recent studies that compare stand development and productivity of mixed
and pure plantations. Higher stand-level productivity in mixtures has been found with two kinds of
species interactions: (1) complementary resource use between species that arises from development
of a stratified canopy (and possibly root stratification); (2) facilitative improvement in nutrition of a
valuable timber species growing in mixture with a nitrogen-fixing species (but only if combined with
complementary resource use as well). These mixtures can also improve economic return through
greater individual-tree growth rates and provision of multiple commercial or subsistence products.
More complex plantation mixtures of 5–70 species have been used for ecological restoration of
degraded lands; these large numbers of species of different successional stages are combined to
reduce the need for a series of sequential plantings. Future research needs to examine many more
tree species across a wider range of sites. Innovative planting designs have been developed to reduce
the land area needed for mixed-species plantation experiments, by focusing on individual-tree analysis
rather than plot-level analysis.
7
Upcoming Meetings and Ev
ents
Events
Apr
ual Spr
ing Meeting at the Gifford Pinchot National Forest Headquarters in Vancouver, WA.
Aprilil 25-26, 2007, SMC Ann
Annual
Spring
For more information visit: http://www.standmgt.org.
Apr
m Forestr
ual Meeting, Red Lion Hotel and Conference Center,
Aprilil 26-28, 2007, Washington Far
Farm
Forestryy Association Ann
Annual
Kelso, WA. For more information contact Rick Carter, 360-978-4434.
June 24-26, 2007, Meeting of the Wester
estern
Mensurationists,
n Forest Mensur
ationists, Lake Okanagan Resort, Kelowna, British Columbia.
For more information please visit http://www.westernforestry.org/wmens/
August 7-10, 2007, Inter
national Scientif
ic Conf
erence Forest Gro
wth and Timber Quality: Cro
wn Models and
International
Scientific
Conference
Growth
Crown
Sim
ulation Methods ffor
or Sustainab
le Forest Management, Doubletree Hotel, Portland, OR. For more information please
Simulation
Sustainable
visit http://www.westernforestry.org/crownmodels/crownmodels.htm.
College of Forest Resources
University of Washington
Box 352100
Seattle, WA 98195
9