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. 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” Forest Growth & Yield and Wood QualityWhat do we want to know?

4. Forest Growth & Yield and Wood QualityScientific 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 Reineke Stand Density Index Relative Density Index Reineke (1933) Drew and Flewelling (1979) 0.55 0.55 0.15 0.15

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 0.25 - 0.35 • 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 3.5 5.2 7.8 11.6 17.3 Quadratic mean dbh (in.) Source: Husch, Beers & Kershaw, Forest Mensuration - 4th Edition

9. Self-Thinning / Relative Density Index (D&F) Mean Tree Volume (ft3) 116 39 28 13 1.4 0.5 Maximum Size-Density 0.55 0.15 0.55 0.55 0.15 0.15 • 384 665 1153 1998 • Trees Per acre

10. Growth vs. Growing Stock / Langsaeter’s Hypothesis 5 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 Age 35 1 1 Volume (Cunits/acre) Volume (Cunits/acre) 0 20 40 60 80 100 0 20 40 60 80 100

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 3 4 3 3 1 3 1 0 0 Cumulative Mortality (ft3) Total Volume Produced (ft3) Quadratic DBH (inches) – Age 37 Total Harvested Volume (ft3) 15 10 5 Quadratic Mean DBH 19.0 13.1 13.5 10.2 11.2 12.5 13.0 9.3 11.0

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