The
working group set by the Forest and Park Service defines a key biotope
as "a habitat, where the occurrence of endangered species is
most likely". A key biotope differs from a commercial forest
by its more diverse or distinguished structure or tree species composition.
These are, for example, brook banks and pond sites, luxuriant forest
swamps and groves, old-growth stands and other dead wood concentrations.
In practice, these habitats are interpreted as key biotopes when they
are small of area, easily distinguished from their surroundings and
in their natural state.
Key
biotopes are also known as valuable ecological sites
. In the new forest legislation of Finland there are seven habitat
types the characteristics of which have to be preserved.
According
to a recent publication of professor Erkki Annila about half of the
threatened forest species occur in the key biotopes. Additional third
of the species are one way or another dependant on ded wood and thus
practically old-growth forest species.
The
amount of key biotopes and natural-state forest habitats left in the
commercial forests is crucial for the survival of rare species. Individual
key biotope patches cannot be left too small to live in either.
Species
will sooner or later disappear from a too sparse "archipelago"
of key biotopes. We have almost no information whether there is enough
key biotope patches left in the commercial forests today or not.
Old-growth
forest i.e. ancient forest means a natural-state (or close)
forest where the amount of dead wood is tens of cubic meters per hectare.
The succession of natural forests includes trees falling down individually
or in groups and big and small forest fires. Due to these the structure
of a natural forest is usually diverse.
Especially
moist spruce dominant forests regenerate through small size gaps.
A great share of Finnish old-growth forests are these kinds of spruce
dominant forests with a lot of big aspens and willows. Aspen is hardwood
of boreal forests with hundreds of associated species.