Environmental Engineering Reference
In-Depth Information
Table 10.2
Three main storm events in Europe in the 1990s.
Dead wood (million m
3
)
Storm event
Area/country affected
Factor of annual cut
28 February-1 March 1990*
Switzerland
4.9
1.1
Southern Germany
65
2.0
Czech Republic/Slovakia
11.3
0.6
Great Britain
6.0
1.5
Belgium
5.5
1.8
Austria
4.8
0.3
Central Europe
100 -20
3 December 1999†
Denmark
3.6
>0.5
26 December 1999*
Western France
114.6
~4
Switzerland
12.3
2.6 (locally up to 10)
Baden-Württemberg
23.5
2.4-3 (locally more)
Bavaria
4.3
0.4
Austria
0.5
0.04
*Databases: several sources, see A. Fischer
et al.
(2002).
†Databases: Klitgaard (2002) and Brunner (2003, personal communication).
generalized. Forest transition and conversion mark a
way back to a higher degree of naturalness, lead to
an improvement of soil quality, and also result in a
higher degree of stability by reducing the danger of
specific pests (insects) and of fires and by anticipating
expected global climate change.
2002). Three main impact options were analysed:
(i) management-free stand development, (ii) clearing
the wind-throw area, followed by free stand develop-
ment and (iii) clearing and then establishing a new
tree layer, usually by planting.
All these studies show that species composition
(plants, animals and fungi) as well as the successional
trends are different in cleared and undisturbed wind-
throw areas. Plant species with a persistent seed bank
are promoted by the clearing procedure (mechanical
disturbances of the soil); after soil disturbance buried
seeds are stimulated to germinate. Without clearing,
soil seed-bank species are restricted to the pit and
mound systems around the bases of fallen trees.
Seedlings and saplings of trees present before the storm
event will grow up immediately after the event (due
to improved light conditions), whereas most young trees
will be destroyed by clear-cutting. Therefore natural
tree regeneration may work much better in uncleared
areas. Broad-leaved species may quickly dominate
under natural tree regeneration, if they are present in
the area (saplings) or in the close vicinity (mature trees).
Mycorrhizal fungi need living trees to survive; in
uncleared areas young trees are present, and they are
carriers of the suitable fungi. Survival rates of fungi
10.5.3 Forest-stand regeneration after
wind throw
Whereas in the boreal zone wildfire is an important
site factor of forest ecosystems, within the temperate
zone the most important disturbance impact influen-
cing forest structure are storms. Storm events may occur
during winter connected with intense low-pressure sys-
tems arriving from the Atlantic Ocean and crossing
central Europe, or during summer time as short but
strong thunderstorms, restricted to small areas. In
central Europe the 1990s were a period with several
strong winter storms; as Table 10.2 shows, the dam-
age was great. These storms caused a strong impact
on forestry and stimulated new scientific studies on
forest dynamics following disturbance (A. Fischer
1998, Mössmer & Fischer 1999, Schönenberger
et al.
