Environmental Engineering Reference
In-Depth Information
FOREST CONVERSION
Initial situation
Possible final situation
Silvicultural strategies to
improve horizontal structure
Acceptance of natural disturbance
Advance planting
Underwood planting
Regulation of mixture
Pure coniferous stand
Broad-leaved and/or
mixed stand
FOREST TRANSITION
Initial situation
Silvicultural strategies to
improve vertical structure
Possible final situation
Acceptance of natural disturbance
Consideration of site locality
Regulation of mixture
Selective cutting system
Continuous forest management
One-layered stand
Multi-layered stand
Figure 12.6
Silvicultural strategies to improve forest stands that are poor in structure.
that mixed-species stands are also more resistant to
both biotic and abiotic disturbance factors. In North
America, this topic is addressed as 'biocomplexity'
(Carey 2003) and is identifi ed as a leading goal in res-
toration of for example temperate coniferous forests.
Forests with such enhanced biocomplexity also show
better economic performance because of risk buffering
(Knoke
et al
. 2005) in a changing world.
The morphological and chemical properties of soil
organic matter and humus can be used as a sensitive
indicator
for the conversion capability of forest eco-
systems (Puhe & Ulrich 2000). While in pure Scots
pine or Norway spruce stands, the decomposition of
litter material is limited as a result of low mineraliza-
tion or bioturbation intensity, with increasing propor-
tion of deciduous tree species the thickness of this layer
decreases. Simultaneously a change of
humus forms
which are ecologically inactive (such as moder-like
humus) towards comparably active humus forms (such
as mull-like humus) took place (H. Fischer
et al
. 2002 ).
Furthermore, in the initial phase of forest conversion,
the total humus stock increases whereas in later stages
soil organic reserves continuously decrease (Figure
12.7). The easier the prevailing litter can be decom-
posed the faster humus integration occurs.
In conclusion, forest transition and conversion as
two steps of forest restoration and improvement repre-
sent a way back to higher naturalness, which also may
lead to improving soil quality, reducing the danger of
specifi c pests (insects, fungi) and of wildfi res (decidu-
ous trees instead of conifers) and anticipating expected
global climate change.
12.3.3 Rehabilitation: forest stand
regeneration after wind throw
Rehabilitation
in forestry includes two aspects
(Figure 12.1 ): (1)
reforestation
with native species
after clear-cutting or after disturbing events like wind-
fall, and (2)
afforestation
of land that had been used
for other purposes earlier, usually as agricultural fi elds
or pastures, transferred back into forest land for, for
example, soil erosion prevention, timber production or
CO
2
storage. First we discuss the tree recruitment after
wind throw (this section), then the afforestation of
former agricultural land (section 12.3.4).
From the point of view of economically oriented for-
estry, large-scale disturbances due to storms, fi res and
tree diseases are catastrophes: they disrupt long-term
