Environmental Engineering Reference
In-Depth Information
clearing the wind-throw area, followed by free stand
development and (3) clearing and then establishing a
new tree layer, usually by planting. Species composi-
tion (plants, animals and fungi) as well as the succes-
sional trends are different depending on the intensity
of mechanical impacts, the pre-storm stand history
and, as a result, the specifi c species pool of the affected
forest stands (Brang
et al
. 2004). Plant species with a
persistent seed bank are promoted by the clearing pro-
cedure: after soil disturbance, buried seeds are stimu-
lated to germinate. Without clearing, soil seed-bank
species are concentrated to the pit and mound systems
around the bases of fallen trees. Many young trees will
be destroyed by cutting and clearing. Therefore natural
regeneration of late-successional tree species may
work much better in uncleared areas (Fischer & Fischer
2009). These species may quickly dominate under
natural tree regeneration, if saplings are present in the
area or mature trees occur in the close vicinity. Mycor-
rhizal 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 are therefore
rather high (see in A. Fischer 1998).
Summarizing, wind throw not only causes problems
for forestry but also offers options to improve the eco-
logical quality of the forests:
• Windfall in artifi cial spruce or pine stands may
induce a change back to a higher proportion of decidu-
ous trees (see section 12.3.2), either via natural regen-
eration or via planting native, site-adapted tree species.
• Free stand development (without clearing) in a
number of forest stands is an option to create a small-
scale patch mosaic, leading to a variety of ecological
niches (biocomplexity; see section 12.3.2) and there-
fore to increase biodiversity in managed forests.
• Using the natural regeneration potential may reduce
costs (for seeding and planting) and prevent root defor-
mations (causing bad tree growth). Nevertheless, pest
outbreaks in managed forests have to be prevented.
Altogether it is an ecologically valuable possibility to
include natural regeneration processes into reforesta-
tion strategies, while at the same time saving money.
100
HUMUS COVER
80
60
40
20
MINERAL SOIL
(0-100 cm)
0
400
300
200
100
0
Pine 84 years
Pine 76 years
Beech 34 years
Pine 114 years
Beech 57 years
Beech
91 years
Figure 12.7
Accumulated humus stock and relative
distribution of soil organic matter in forest fl oor and
mineral topsoil (to 100 cm) in a chronosequence of four
study sites in northeastern Germany. These parameters are
used as indicators of forest conversion. (From H. Fischer
et al
. 2002 .)
management plans, reduce timber value and thus
affect wood markets. However, they can also be consid-
ered as opportunities to improve the degree of natural-
ness in managed forests in the near term.
Whereas in the boreal zone wildfi re is the most
important large-scale cause of disturbance in forest
ecosystems, windstorm is more important in the tem-
perate zone. In central Europe, the 1990s were a period
with several strong winter storms (e.g. 28 February to
1 March 1990), producing 100-120 million cubic
meters of dead wood. The memorable storm that hit
western Europe on 26 December 1999, produced
about 115 million m
3
dead wood in western France
alone (data summarized in A. Fischer
et al
. 2002 ).
These storms caused a strong impact on forestry and
also stimulated new scientifi c studies on forest dynam-
ics following disturbance (A. Fischer 1998; Schönen-
berger
et al
. 2002). Should foresters wait for natural
tree regeneration or should they plant trees? Three
main management options for
reforestation
were
analysed: (1) management-free stand development, (2)
12.3.4 Rehabilitation: afforestation
of former agricultural land
Afforestation
of abandoned pastures or arable fi elds
plays an important role in landscape planning, since
abandonment in the 1980s and 1990s was common in
