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A manager of a forestry company in Scotland has to decide which trees to plant. There are three main species to choose from, Sitka Spruce, European Larch or Lodgepole Pine.
Whatever trees are planted they have to be thinned after 10 and 20
years and the wood from the thinning is sold for a profit.
Each kind of tree has a different planting cost per hectare, a
different growth rate and a different value per hectare depending
on the age the tree is felled. All this information is given in the
table below.
Sitka
Spruce

European
Larch

Lodgepole
Pine


Planting cost per hectare (thousands of £s)  120  115  130 
Profit per hectare from 10 year thin (thousands of £s)  10  15  20 
Profit per hectare from 20 year thin (thousands of £s)  40  40  30 
After (years)  (thousands of £s)  (thousands of £s)  (thousands of £s) 
30  358  192  123 
40  513  469  366 
50  693  858  646 
60  834  1184  950 
70  1127  1158  1144 
80  904  1059  1311 
90  805  837  1476 
100  666  783  1360 
What strategy for planting and felling would you recommend to the manager in order to maximise the profit after 70 years, 90 years, more generally?