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Natural forests (4.3)
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| A typical boreal natural (undisturbed by man) coniferous forest at the end of its life span in southern Finland (Padasjoki). |
In the last twenty years, naturalness has developed into an international
indicator of forest biodiversity. Human activities change
the structure and species composition of forests. Naturalness
is thus an indication of human impact in forests, as well as an
indication of earlier, historical use of forests. When left unmanaged
or actively restored, forests grow into stands whose structure
resembles forests in their natural state. Unmanaged, strictly
protected conservation areas can be used to gain information
about the natural development of forests.
On the basis of their naturalness, forests are internationally (UNECE/
FAO 2002) roughly classified into three classes: 1) forests
undisturbed by man20, 2) semi-natural forests21, and 3) plantations22.
Due to differences in interpretation, there is as yet no
common, functioning European classification and measurement system for naturalness. The current classification allows also
planted stands to be classified as semi-natural forests if they
are left unmanaged for over 30–40 years. With the exception
of Austria, no country-specific assessments of naturalness have
been made so that they would correspond to the system of, for
example, national forest inventories.
Owing to long-term human intervention, no extensive natural
forests have survived in Finland, except for some small stands
in certain conservation areas.
According to the 9th National Forest Inventory, there were a total
of 170,000 hectares of old forests resembling natural forests
(forests over 140 years old with observed indicators suggesting
naturalness) in the hemiboreal, southern and middle boreal
zones. Of these, 40% were in conservation areas. In the northern
boreal zone there were 716,000 hectares of such forests, 56%
of them in conservation areas.
The structure of vegetation even in managed forests in Finland
has remained largely similar to natural forests, thanks to forest
management based on the natural site type classification and
the use of indigenous species in regeneration. Monocultures
are established only in the afforestation of fields (about one
per cent of all forests), but in them, too, the species and their
origin are Finnish. The total area of fields afforested during the
last 25 years is about 147,000 hectares.
The naturalness of forest sites has been altered by peatland
drainage. In wooded drained mires, however, the original tree
species composition generally remains unaltered. Altogether
55% of all mires, or some five million hectares, have been
drained. In the last 15 years, practically no new drainage projects
have been carried out. Some of the drained mires revert to natural
development, as it is not justifiable economically to maintain
the network of drains.
An increasing number of stands in Southern Finland remain
uncut. The number of forests exceeding 140 years of age and
where no fellings have been done in the last 40 years has grown
continuously.
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20 Undisturbed forests contain features belonging to the natural growth cycle
of forests. Such features include natural species composition, deadwood, natural
age structure and natural regeneration. The site is large enough to maintain
natural succession. There are no recognisable signs of human activity in
the area, or a sufficiently long time has passed from human intervention to
allow the re-emergence of natural tree species composition and its development
dynamics.
21 A semi-natural forest displays all those characteristics which are not included
in forests undisturbed by man and plantations.
22 Plantations are forest stands established by planting introduced species or
intensively managed stands of indigenous species which meet the following criteria:
one or two species at plantation, even age class, and regular spacing. The
exception is stands which were established as plantations, but which have been
without intensive management for a long time, allowing the stand to develop
naturally. In Finland, only afforested fields are classified as plantations. Sites of
normal forest regeneration are established at irregular intervals and, because
of supplementary natural regeneration and thinnings, they usually develop into
mixed stands containing a great number of naturally established trees. |
