New Thinning Research - Implications for Forest Management

Transcription

1 New Thinning Research - Implications for Forest Management Dr. Niall Farrelly Irish Forestry Woodland & Bio Energy Show, Fri 10 th May 2013, Stradbally, Co. Laois

2 Potential Hectares of First Thinning Private Estate

3 Focus of Thinning Research - Teagasc Why Thin? Compare Thin V S No thin, When to thin? Especially for productive plantations YC 24+ How much to thin? - Volume How to thin? Reduce rotation lengths Increase EUR Grow to what the market requires target volume Develop protocols for thinning

4 WHY THIN? Forest premium running out - provide periodic income Salvage material that will ultimately die Provide increased growing space for trees Remove less valuable material in thinning Maximise productive potential of site increase by 10% Increase revenue returns Thin V No Thin Maximise sawlog potential

5 Funded by the Irish Government under the National Development Plan Provision of Adequate Growing Space 25 years weakest trees die, stronger trees increased competition 20 years TIME 15 years Thinning to remove suppressed trees. Vigorous trees take up best position 10 years Competition for light, moisture and nutrients. 5 years Planting 2,500 stems per hectare,

6 Timing of thinning? Avoid supressed Diameter growth Supressed Diameter growth Vigorous Diameter growth Supressed Diameter growth

7 When does Serious Competition take place? For fully stocked stands of Sitka spruce Onset of competition 8 11 cm Site Occupancy 9 13 cm Lower limit of Self thinning cm Threshold Basal Area Top Ht (m) Basal Area Fully stocked after

8 Suppression in Plantations Trees in a forest plantation are typically differentiated into 4 canopy classes as follows (Figure) Dominant trees larger than average trees, growing vigorously with large crowns above the general level of the canopy, 21 cm + Co-dominant trees with medium sized crowns at or below the general level of the canopy and are more or less crowed on the sides cm Subdominant trees receiving little light, usually with small crowns and crowded on the sides cm Suppressed - trees with crowns below the canopy, receiving no direct light from above or on the sides cm Figure: Crown differentiation in forest stands into dominant, co-dominant, subdominant and suppressed classes (Kraft crown classification)

9 Ready Reckoner - timing of thinning DBH SPH Not yet suitable Suitable for YC <16 crops Suitable for YC crops Suitable for YC 24+ crops Ready reckoner* for thinning based dbh & SPH (1) Not yet suitable these are not yet ready for thinning (2) Suitable for YC<16 crops (3) Suitable for YC crops (4) Suitable for yield class 24 and above *modified from Rollinson (1999) to include higher yield class crops

10 Growth in Unthinned and Thinned stands UNTHINNED Age 42 years P. spacing: 3421 Mortality: 1405 SPH: 1994 Av. DBH: 21.8 cm Height 25.1 m Unthinned stand age 42 years high mortality THINNED Age 42 years P. spacing: 3421 SPH: 706 Mortality: 0 Av. DBH: 35 cm Height 24.5 m Thinned stand age 42 years no mortality

11 Volume Assortments Thin V s No Thin

12 How Much to thin? Can remove 70% of the Yield Class annually YC 22 = 22 * 0.7 * 5 years = 77 m3/ha/yr local level variations and v. confusing for growers is there another way Yes

13 The Thinning Response Hypothesis Maintain an unthinned control plot of uniform stand characteristics to regulate thinning Yield reference plot Rule: Removing more than 50-65% of control plot at any thinning will decrease volume prod by 5%

14 Testing the Hypothesis Two Experiments 1. Frenchpark, Sitka spruce age 15 years, GYC Abbeyshrule, Sitka spruce age 17 years, GYC 30 Four Treatments 1. No thinning 2. 20% of Basal Area Grade B (remove subdominant tree) 3. 32% of Basal Area Grade C (remove subdominant and some co-dominant) 4. 49% of Basal Area Grade D (remove subdominant and many co-dominant)

15 Response to thinning (Vol. Increment - 3 Years) Frenchpark

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17 Effect on DBH after thinning (Frenchpark & Abbeyshrule) B 0 cm increase 0.8 cm increase C 1.3 cm increase D 2.3 cm increase

18 Rotation & Revenue Analysis Comparison of thinning Objective: 1. Use IDYM to grow to target volume of between m3 2. Determine if thinning can shorten rotation(s) 3. Determine if thinning is the most profitable treatment Four Treatments on two sites (Abbeyshrule & Frenchpark) 1. No thinning 2. 20% of Basal Area Grade B (remove subdominant tree) 3. 32% of Basal Area Grade C (remove subdominant and some co-dominant) 4. 49% of Basal Area Grade D (remove subdominant and many co-dominant)

19 Thinning significantly reduces the rotation length years (thinned) versus years (unthinned) D treatment has shortest rotation length ~ 24 years Thinning increases profitability ~ 35-60% versus no thinning Increased annual payments of between 100 to 900/ha with thinning. D treatment is most profitable Findings Thinning sig. reduces top height versus no thin treatment ~ 7 m implications for areas where there is a critical height issue / concern. The impact of short rotations on timber quality and sawing outturn is an unknown

20 Thinning Take home Messages Thinning is more profitable than no thinning crops > YC 14 To achieve 2 cm increase thinning to grade C/D is necessary Largest returns arise in grade D thinning D treatment suitable (stable sites or stands thinned on time) Thinning early reduces rotation length NO benefit in thinning late (stands overstocked) Rotation lengths to 0.8 m3 possible after years (YC 26-34) Unthinned stands have sig. longer rotation lengths (windthrow risk)

21 Seeing is believing

22 Thank You!