Exercise 2 Thinning [ANWSERS]
Problem: In a given environment, you wish to harvest trees before they die, and provide sufficient growing space so residual trees can grow to harvest at age 30 without further mortality.
Solution: 3-PG allows a comparison of yields with and without thinning
A.Open sheet labeled ‘Bariloche pi po’
B.With maximum weight of trees set at 100 kg when stocking is set at 1000 trees/ha (WSX1000), record at what age self-thinning begins 14 years,
Max Volume @ age 30: 474m3/ha, and maximum mean tree diameter at age 30
62.2 cm, Maximum Basal area =65.8 m2/ha
C. Under ‘Silvicultural Events’ create a thinning that begins (insert ’14’ beneath the heading ‘AGE’ and insert ‘500’ under ‘residual stemNo’.
D. Run model by clicking on the calculator symbol at the far left, bottom of the page.
E. Record volume removed at age 14 by thinning 108.5 m3/ha and that present at age 30: 414 m3/ha.
F. How much regrowth occurred in Year 14? 22.5 m3/ha [131-108.5]
G. Record years required before stand volume to approach that at age 13:6 years
H. Record stand volume at 30 years: 414 m3/ha, mean stem diameter: 54.3 cm, and basal area 65.6 m2/ha
I. Calculate the harvested wood volume with and without thinning.474 w/o, 522.5 with thinning m3/ha [(414+108.5) -474]
J. Does the silvicultural thinning produce more wood over the rotation with larger diameter trees at rotation age, compared to the self-thinned forest?yes What is the difference? 48.5 m3/ha, diameters 62.2-54.3 = 7.9 cm smaller with thinning.
K. If ‘WSX1000’ is set at 75 kg rather than 100 kg, self-thinning starts sooner on this site, with the result that mean tree diameters at age 30 will be larger than when thinning is imposed. One may assume in general that self-thinning should start at the age when maximum leaf area index is first attained.
J. You can thin from above or below, or defoliate, by changing the value 1 = average tree mass in foliage, stem and roots to 1.25 (larger), or 0.75 (smaller than average).