Unformatted text preview: 10.9 Forest Management 59 Let xi (i = l, 2, . . . . n) be the number of trees within the ith class that remain aftt
each harvestr We form a column vector with the numbers and call it the nonharve:
vector: Xi x2
x: xn For a sustainable harvesting policy, the forest is to be returned after each harvest to th
ﬁxed conﬁguration given by the nonharvest vector x. Part of our problem is to ﬁnd thos
nonharvest vectors x for which sustainable harvesting is possible. Because the total number of trees in the forest is ﬁxed, we can set x1+xz++x,1:s (l where s is predetermined by the amount of land available and the amount of space eacl
tree requires. Referring to Figure 10.9.2, we have the following situation. The fores
conﬁguration is given by the vector x after each harvest. Between harvests the tree:
grow and produce a new forest conﬁguration before each harvest. A certain number 0
trees are removed from each class at the harvest. Finally, a seedling is planted in place
of each tree removed, to return the forest again to the conﬁguration x. Trees
removed Forest aﬁer growth Trees not removed Gromh . .3 Same
forest
conﬁguration Plant seedlings .§\A§Ailii A Forest before growth Forest aﬁer harvest
(nonharvest vector x) (nonharvest vector X) A. Figure 10.9.2 l»
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~\. f“; Consider ﬁrst the growth of the forest between harvests. During this period a tree
in the ith class may grow and move up to a higher height class. Or its growth may be
retarded for some reason, and it will remain in the same class. We consequently deﬁne
the following growth parameters gi fori : I, 2, , n — 1: gr 2 the fraction of trees in the ith class that grow into
the (i + I)—st class during a growth period
For simplicity we assume that a tree can move at most one height class upward in one
growth period. With this assumption, we have
1 — g = the fraction of trees in the ith class that remain in the ith class during a growth period ...
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