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

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

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”

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.

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.

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)

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

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

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 0.15 384 665 1153 1998 Trees Per acre

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 1 1 Age 35 Volume (Cunits/acre) Volume (Cunits/acre) 0 20 40 60 80 100 0 20 40 60 80 100

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)

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

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

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

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!

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

Questions / Comments