Environmental Engineering Reference
In-Depth Information
large amounts of CaO are used to raise soil pH; a culti-
vable soil layer of at least 100 cm thickness may require
40 000 - 50 000 kg CaO ha
− 1
. Lack of nitrogen in the
initial soils is also an important limiting factor. Tradi-
tionally, inorganic fertilizers were used, whereas in
recent years there has been a trend towards the use of
organic waste materials and special humus material
(Katzur
et al
. 2001 ). The fi rst afforestation experiments
on bare post-mining 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 tree species such as alder, poplar, birch, red oak
and black locust. For pine-dominated ecosystems on
former lignite mine sites, for example, internal cycling
processes consisting of litter fall, decomposition of
litter and nutrient uptake by plants play an important
role in nutrient supply, as is also known for pine stands
on naturally developed soils (Rumpel
et al
. 1999 ; Fett-
weis
et al
. 2005). In pine stands of about 30 years of
age, roots were found below the amelioration horizon.
Chronosequence studies show that shortly after affor-
estation a forest biocoenosis develops spontaneously,
including soil fauna and symbiotic microorganisms
such as mycorrhizal fungi and nitrogen-fi xing bacteria
(W ö llecke
et al
. 2007 ).
In the case of afforestation of former arable land,
spontaneous succession may also be an option on post-
mining sites. 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 some decades or at least few centuries, these ecosys-
tems will change permanently into forest.
China, the focus is on afforestation of devastated land
as a means of erosion prevention.
In a time of intense global forest loss, and growing
attempts to mitigate anthropogenic climate change
due to greenhouse gas emissions, reforestation and
afforestation are important aspects of landscape
management. As the recent 'Global Forest Resources
Assessment' (FAO 2010) shows, the decline in global
forest area over the last decade was signifi cantly lower
than it was in the previous decade, mainly because of
reforestation and afforestation activities in Europe and
central Asia, especially China. To date, only a few fast-
growing species, often introduced from other parts of
the world, have been used for large-scale afforestation
projects. The pool of native woody species, however, in
all parts of the temperate zones is impressively large
(see Box 12.2 for the Loess Plateau). These species can
be used for the site conditions to which they are best
adapted (according to the PNV). Remaining forest
patches, even if they are small, are centres of local
biodiversity and therefore should be integrated into
afforestation measures.
Within the implementation phase of the EU directive
on afforestation of agricultural land, confl icts may
arise, since planned afforestation sites on marginal
soils often harbour the last remnants of historical
cultural landscapes valued by many people. These con-
siderations have to be taken into account to achieve
consensus on the objectives and implementations of
forest rehabilitation and reclamation projects.
The global environment today is changing funda-
mentally (see section 12.2), including the climate, the
chemical composition of the atmosphere and, as a con-
sequence, soils. Soil erosion in many parts of the world,
including temperate zones, is strong and ongoing. The
predicted environmental changes ('global climate
change') will also affect established forest ecosystems
and may exceed the capacity of forest tree populations
to adjust physiologically and developmentally. Uncer-
tainty in predicting the most likely scenario necessi-
tates special silvicultural responses (H. Fischer &
Wagner 2009): to safeguard a variety of tree species
with different ecological demands and mixed stands
with tree species resilient against environmental
changes and disaster occurrence, not only on forest
stand level but as a general strategy. Altogether it
seems evident that species composition in European
forests will change within the twenty-fi rst century as a
consequence of global climate change, beech never-
theless seems likely to continue to be the dominant tree
12.4
PERSPECTIVES
In many parts of the temperate climate zones, both
climate and soil conditions are excellent not only for
tree growth, and therefore timber production, but also
for food production. As a result, arable fi elds expanded
over recent centuries, and timber was over-exploited,
resulting in a decrease and fragmentation of the former
forest areas. Both in Europe (see section 12.2) and in
temperate Asia (see Box 12.1), this process started
several thousand years ago. The need for forest restora-
tion in these two regions is different: in Europe the
focus is on afforestation of abandoned agricultural
land and improving existing forests, while in central
