Environmental Engineering Reference
In-Depth Information
capacity to re-sprout quickly after damage and to pro-
duce a high number of propagules, and their seeds are
able to germinate on mineral substrate. These softwood
riparian forests are accompanied by the higher-elevated,
hardwood riparian forests. Flooding is less frequent
and there is sedimentation of loam, but no destruct-
ive power of the running water. Hardwood species
such as oak (
Quercus robur
), elm (
Ulmus laevis
and
Ulmus minor
) and ash (
Fraxinus excelsior
) are the most
frequent tree species. In general riparian forests are
characterized by a very high structural and species
diversity. As a consequence of riverbed corrections and
of the use of land for agriculture, infrastructure,
industrial complexes and buildings, this forest type is
today very rare in Europe and the remaining stands
are usually eutrophied.
10.3.7 Spruce forests
Outside the boreal forest zone spruce forests are
restricted mainly to the tops of high mountains of the
European highlands (e.g. Harz, Bavarian Forest, Ore
Mountains, Carpathian Mountains) and of the Alps.
Norway spruce (
P. abies
) settles on both acidic and
calcareous bedrock; nevertheless, it is usually accom-
panied by indicators of low soil pH, either because of
the acidic subsoil or because of the acidic organic mater-
ial that accumulates beneath the canopy of spruce trees.
10.3.8 Mediterranean evergreen
sclerophyllous forests
In the Mediterranean part of southern Europe the nat-
ural vegetation is formed by evergreen sclerophyllous
trees (mainly
Quercus ilex
or
Quercus suber
). Since
the intensive impact of humans (beginning with the
Greeks and Romans and including the Middle Ages)
most of the forests have disappeared, and intensive
soil degradation has taken place (see Chapter 14 in
this volume); forests were replaced by evergreen bush-
land (macchia) or evergreen shrub-land (garrigue).
10.3.5 Bolder field forests
This forest type of very limited extent is restricted to
natural bolder fields of steep mountain slopes. Maple
(
A. pseudoplatanus
,
Acer platanoides
), elm (
Ulmus
montana
) and linden (
Tilia platyphyllos
,
Tilia cordata
)
dominate the tree layer. Depending on geological
substrate, substrate structure, elevation and exposition
a high number of subtypes can be distinguished.
Because of the unfavourable position this forest type
can hardly be used and a remarkable number of
(small) stands still exists.
10.4 Causes of recent changes in forests
10.4.1 Acidification and eutrophication
The chemical composition of the atmosphere changed
remarkably due to industrialization. As a conse-
quence of acid rain significant soil acidification is
proven to occur in large areas of Europe (e.g. Wolff
& Riek 1997). According to calculations of the Euro-
pean surveying programme EMEP (1999) in most
parts of western Europe the immissions (wet and dry)
of oxidized nitrogen (N
ox
) amounts on average to 5-
10 kg ha
−1
yr
−1
, in addition to at least 5-10 kg ha
−1
yr
−1
of reduced nitrogen (N
red
) all over Europe.
The change of the floristic composition can be
detected by repeated recording of permanent plots (e.g.
A. Fischer 1993, Röder
et al.
1996) or by comparing
sets of phytosociological relevées from the same
region and the same vegetation type in the course of
time (e.g. Wilmanns & Bogenrieder 1986). Two main
10.3.6 Pine forests
While Scots pine (
Pinus sylvestris
) was very common
in Europe at the beginning of the post-glacial time
period (section 10.2.1), natural pine stands in central
Europe nowadays are limited to (i) wet areas in a land-
scape with mires and raised bogs, (ii) nutrient-poor, acidic
soils, usually quartz sands, and (iii) steep, south-facing
calcareous rock slopes with very shallow soil and there-
fore very limited water availability. Whereas in cent-
ral Europe Scots pine would only account for about
1% in the natural vegetation, it actually covers about
25% of the forest area (Fig. 10.2), due to more than
two centuries of intensive forest management.
