Restoration of forests - Restoration Ecology - page 138

removed from the seam and the overlying parent mater-
ial. A long-term pumping action greatly influences
both the ground and surface water (Hüttl & Bradshaw
2001). The overburden usually is translocated by the
use of conveyor bridges, which mixes different geo-
logical materials. While this technique homogenizes
the abiotic conditions on a landscape level, it leads
to large substrate heterogeneity on a small scale,
hence affecting the quality of the top-layer material
(Elgersma & Dhillion 2002). The small-scale spatial
variability of soil chemistry forms niches for the tree
roots and is the key to understanding the successful
establishment of forest stands on these - on average
- extreme sites (Weber 2000). Concerning mine
soils formed from carboniferous overburden, a high
acidity of sulphurous substrates caused by chemical
weathering and microbial oxidation of the ferric
disulphides pyrite and marcasite is usually the main
problem (Pugh et al. 1984, Pietsch 1998, Schaaf et al.
2001). This process starts immediately after contact
with atmospheric oxygen, it is irreversible (Katzur &
Haubold-Rosar 1996) and it causes pH values in the
extreme acid range down to 2.1. The sulphate con-
tent of post-mining limnic biotopes can be as high as
2000 mg l −1 (Grünewald & Nixdorf 1995). In addition,
most mine soils are characterized by an initial lack
of humus, an insufficient nutrient supply (Schaaf
et al. 1998, 1999), periodic and long wetting resistance
(Katzur & Haubold-Rosar 1996) and by preferential flow
which causes bypassing of water and nutrients in most
of the volume of the soil matrix (Gerke et al. 2001,
Hangen 2003). Another serious problem for forest plants
is the characteristic climate of wide-open land (intens-
ive light radiation, soil-lifting frost, late frost, wind
and erosion). Nevertheless, adapted species may grow
up and cause spontaneous ecosystem establishment and
succession, depending on site quality and diaspore
availability (Jochimsen 1991, 1996, Tischew et al. 1995,
Wittig 1998).
The first restoration step is a technical rebuilding
of the landscape, the creation and levelling of the sur-
face and the moulding of slopes. The subsequent
development depends on the dumped substrates. The
common sulphurous and carboniferous mine soils
remain barren of vegetation for decades if there is no
human interference (Felinks et al. 1998, Wiegleb &
Felinks 2001). In many cases soil amelioration is
needed, which requires detailed knowledge of site

conditions, in particular the identification of its lim-
iting soil nutrients (Heinsdorf 1992, 1996). Large
amounts of CaO are used to change soil pH value (a
cultivable soil layer of at least 100 cm thickness
needs 40 -50,000 kg of CaO ha −1 ). Traditionally, in-
organic fertilizers are used, whereas in recent years
there has been a trend towards the use of organic waste
materials (Leirós et al. 1996) and special humus
material (Katzur et al. 2001).
The first afforestation experiments on raw mine soils
in Europe were carried out and published in Germany
by Heuson (1929) and Copien (1942). Even then they
promoted mixed stands, and to date there are long-
term experiments with many species: pine, oak, lime
and larch as well as pioneer trees such as alder,
poplar, birch and black locust ( Robinia pseudoacacia ).
The establishment of forest stands by mechanical
planting after adequate soil amelioration shows sur-
prisingly good results. After afforestation soil devel-
opment first leads to the formation of regosols. The
results of Rumpel et al. (1999) and Fettweis et al. (2005)
indicate that in pine ecosystems on former lignite mine
sites internal cycling processes consisting of litter
fall, decomposition of litter and nutrient uptake by
plants play an important role in nutrient supply, as
is known for pine stands on naturally developed
soils. In pine stands of about 30 years of age roots
were found below the amelioration horizon. Chrono-
sequence studies show that shortly after afforestation
a biocoenosis develops spontaneously, including soil
fauna (Düker et al. 1999, Düker 2003) and symbiotic
micro-organisms such as mycorrhizal fungi (Golldack
et al. 2000, Wöllecke 2001) and nitrogen-fixing
bacteria (Kolk & Bungart 2000).
As in the case of reforestation of former arable land,
abandonment may also be an option in post-mining
landscapes. According to the high diversity of micro-
sites a high diversity of species, structures, ecological
niches and ecosystems will establish, and in the course
of time these ecosystems will change permanently
into forest as a final system. There are, however, a lot
of social, economic, aesthetic and ecological needs
connected with such landscapes and the develop-
ing vegetation; fast-growing tree species and alley-
cropping plantations as special forms of energy forests
have recently come into focus (Bungart et al. 2001).
The new forests will be evaluated by how well they
are meeting these demands as soon as possible, which