Exercise 2 Thinning
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 __ years,
Max Volume @ age 30: __m3/ha, and maximum mean tree diameter at age 30
__ cm, Maximum Basal area =__ 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 ____ m3/ha and that present at age 30: ____ m3/ha.
F. How much regrowth occurred in Year 14? ____ m3/ha [______]
G. Record years required before stand volume to approach that at age 13:__ years
H. Record stand volume at 30 years: ____ m3/ha, mean stem diameter: ____ cm, and basal area ____ m2/ha
I. Calculate the harvested wood volume with and without thinning.___ w/o, ____ with thinning ( m3/ha)
J. Does the silvicultural thinning produce more wood over the rotation with larger diameter trees at rotation age, compared to the self-thinned forest?____ What is the difference? ___ m3/ha, diameters ____ cm _____ 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).