1. Looking for the Plateau in Douglas-fir Annual Volume Increment
David M. Hyink, Ph.D. (retired)
Timberlands & Raw Materials R & D
Weyerhaeuser Company

2. Outline/Topics Context and Rationale for Growth and Yield Research
Biological First Principles
“Laws” of Self-Thinning
Langsaeter’s Hypothesis
Weyerhaeuser’s Langsaeter Study
Design
Results & Conclusions
Questions/Comments

3. Forest Growth & Yield and Wood Quality What do we want to know?
How stand management options…
Species, genotype, site preparation, planting spacing, non-crop competition & animal control, thinning, fertilization, pruning
Produce key properties of crop trees…
Dbh, height, crown ratio, stem form, branches & knots, specific gravity, micro-fibril angle, earlywood/latewood
That create value for specific end-uses.
Logs, lumber, fiber, engineered components
“Engineering-on-the-Stump”

4. Based upon “First Principles”
Forest Growth & Yield and Wood Quality Scientific Approach – Data and models
Based upon “First Principles”
Dominant Height / Age / Site Index
Landform / Habitat Type
“Laws” of Self-Thinning (Reineke, Drew and Flewelling)
Growth vs. Growing Stock Relationships (Langsaeter)
Continuously updated as new data and experimental results become available.

5. Biological First Principles / Langsaeter’s Hypothesis
The total production of cubic volume by a stand of a given age and composition on a given site is, … constant and optimum for a wide range of density of stocking. It can be decreased, but not increased, by altering the amount of growing stock to levels outside this range.

6. Biological First Principles / “Laws” of Self-Thinning
0.55
0.15
0.55
0.15
Reineke Stand Density Index Relative Density Index
Reineke (1933) Drew and Flewelling (1979)

7. The Langsaeter Study
Superimposed on an existing DF research plantation (SI=143)
Initial planting spacing: 5’x5’ (1742) and 8’x8’ (680)
4 reps of 4 treatments at each initial spacing (32 plots):
Non-thinned
Maintain Relative Density (D&F) 0.25 – 0.35
Maintain Relative Density (D&F) 0.40 – 0.50
Achieve RD (D&F) 0.50, then maintain at
Maintain 4 reps of initial 8’x8’ spacing 0.10 – 0.20 (4 plots)
Measurement ages: 13, 15, 16, 17, 19, 22, 25, 28 ,31, 34, 37

8. Self-Thinning / Reineke’s Stand Density Index
2440
1480
5’x5’
900
8’x8’
550
330
500
400
200
Quadratic mean dbh (in.)
Source: Husch, Beers & Kershaw, Forest Mensuration - 4th Edition

9. Self-Thinning / Relative Density Index (D&F)
116 39 28 13
1.4
0.5
Mean Tree Volume (ft3)
Maximum Size-Density
0.55
0.55
0.15
0.55
0.15
0.15
Trees Per acre

10. Growth vs. Growing Stock / Langsaeter’s Hypothesis5 4 3 2
Age 23
Source: USFS Research Paper PNW-RP-537 1
Volume (Cunits/acre)
Volume Increment (Cunits/ac/year) Volume Increment (Cunits/ac/year) 5 5
Volume Increment (Cunits/ac/year) 4 4 3 3 2 2
Age 17 1 1
Age 35
Volume (Cunits/acre)
Volume (Cunits/acre)

11. Growth vs. Growing Stock / Langsaeter’s Hypothesis
Age 23
Source: USFS Research Paper PNW-RP-537
Volume (Cubic feet /acre)
Volume Increment (Cu.ft./ac/year)
Age 17
Age 35
Volume (Cubic feet /acre)
Volume (Cubic feet /acre)

12. Langsaeter: Growth / Growing Stock – Age 23
Annual Volume Increment (Cubic feet / acre / year)
Volume (Cubic feet per acre)

13. Langsaeter: Growth / Growing Stock – Age 35
Annual Volume Increment (Cubic Feet / Acre / Year)
Volume (Cubic Feet Per Acre)

14. Yield Summary by Treatment: Total Age 37
Number of Thinnings
Cumulative Mortality (ft3) Total Volume Produced (ft3)
Quadratic DBH (inches) – Age Total Harvested Volume (ft3) 15 10 5
Quadratic Mean DBH

15. Langsaeter Study: Observations through Age 37
No firm evidence that a growth/growing stock “plateau” (phase III) was achieved.
Reductions in growing stock, due to thinning, initially resulted in reductions in periodic growth.
More aggressive thinning treatments captured mortality and concentrated subsequent growth on fewer, larger trees (as expected).
Douglas-fir does not stagnate (Phase IV/V) – loses growing stock through aggressive mortality!
No significant “bonus wood” was produced. (i.e. total production was either reduced or stayed the same -- but not increased -- by repeated thinning). Future growth on the thinned 40-50’s?
The 8’x8’ spacing, allowed to achieve RD 0.50 followed by thinning to RD 0.25 produced a nice combination of volume and QMD!
Self-thinning “laws” were validated as useful constructs!

16. Langsaeter Study: Shortcomings…
Limited (high) initial planting densities (680 & 1742 tpa)
Small plots
Final thinning treatment at total age 22
Most thinning strategies not economically viable (like LOGS)
Single installation on a high site

17. Questions / Comments