Environmental Engineering Reference
In-Depth Information
10
Restoration of forests
Anton Fischer and Holger Fischer
10.1 Introduction
infrastructural purposes (59.5% and 11.3%, respect-
ively, in Germany; BfN 1996). Compared with the PNV
the tree species composition of about two thirds of
the remaining forest stands changed fundamentally
due to the impact of humans (in central Europe needle
trees replaced beech). There are, however, remarkable
numbers of forest stands existing which, according
to their floristical composition, can be interpreted
as near-natural. Nevertheless, the stand structure is
usually intensively influenced by forest management,
and many groups of organisms depend especially on
stand structure; for example, many insects and fungi
live in dead wood.
The conversion of forests to open land implied
the establishment and expansion of vegetation types
characteristic of the historic cultural landscape, such
as unfertilized grasslands and heathlands, both dry and
wet, and many types of sedge wetland as well as weed
and ruderal communities. These vegetation types,
which are discussed in other chapters of this topic,
essentially depend on the management of humans.
Forest is the only (potentially) widespread ecosystem
type in large parts of Europe that is capable of per-
sisting without anthropogenic impact.
This chapter on
forest restoration
covers aspects of
(i) forest
improvement
in the sense of optimizing close-
to-nature forestry, (ii)
conversion
of tree plantations,
mostly Scots pine and Norway spruce, into (mixed)
deciduous forests, (iii) forest
stand regeneration
after
wind-throw, (iv)
reforestation
of areas used in the
past for agricultural purposes and (v)
afforestation
of
completely sterile new substrates in post-mining
landscapes. We focus on central Europe but reflect also
boreal and Mediterranean aspects.
In 2000 the world's forests covered about 3.87
billion ha, or about 29.6% of the world's total land
area. Between 1990 and 2000 there was a net loss of
forest area of about 9.4 million ha yr
−1
0.22% yr
−1
;
FAO 2001). These figures demonstrate clearly that
forests are an important natural resource that is
decreasing rapidly.
The concept of potential natural vegetation (PNV;
Faber 1937, Tüxen 1956) is a tool to indicate and
map sets of site conditions relevant for plant growth
in terms of vegetation types. The
Map of the Natural
Vegetation of Europe
(BfN 2000; scale 1 : 2.5 million)
is the most general PNV map for Europe. Its analy-
sis (Table 10.1) shows that - according to the site
conditions - forests represent the European natural
large-scale ecosystem, among which the boreal
coniferous and the temperate deciduous forests pre-
dominate. In central Europe (taking Germany as an
example; see Table 10.1) there are only very limited
areas which, according to recent abiotical site con-
ditions, cannot support forests, for example some
coastal and alpine areas as well as raised bogs. In
Europe, large-scale, natural open land only occurs
in the high north (arctic tundras) and the far east
(steppes). For Bavaria, situated in the core of central
Europe, Walentowski and Gulder (2001) calculated that
the three PNV units, namely
Luzulo-Fagetum
,
Galio
odorati-Fagetum
and
Hordelymo-Fagetum
, together
cover about 70% of the state forests.
Over two thirds of the potential (and former)
forest area, however, has been converted into either
agricultural land or land used for settlement and
(
−
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