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?