At the forest stand level the available energy for the considered forest, is considered globally, due to photosynthesis or due
to nutrients in the soil. This supplied energy makes it possible to ensure at the same time the maintenance and the growth of
the trees. The share reserved for maintenance increases with the tree height, therefore with time, which limits all the more
so the available part for growth. The energy left for growth is therefore a decreasing time function and allows the increase
of basal area of the forest stand. The increase of basal area of the forest stand at its peak of density r(n(t), s(t)) = 1 is given
by the function V(.). We assume that V(t) verify the following properties: