Environmental Engineering Reference
In-Depth Information
period in spring favours species that develop their
leaves relatively late in the year, thus
Quercus liaotun-
gensis
is the dominant tree species of the potential
natural vegetation (PNV; see section 12.1), accompa-
nied by
Prunus
and
Pyrus
as well as deciduous shrubs
of the genera
Prunus, Lonicera, Euonymus, Rosa, Cra-
taegus, Forsythia, Syringa, Caragana
, and
Sophora
.
On dry south-facing slopes
Pinus tabulaeformis
and
Platycladus orientalis
(Chen
et al
. 2007).
The Loess Plateau is also the birthplace of Chinese
civilization and culture. In the heart of the region
resides the tomb of the legendary 'yellow emperor',
said to have reigned some 5000 years ago. Since that
time, the region has been intensively and continuously
used. In 221 BCE, Qin Shi Huang Di founded the
Chinese Empire and the capital city grew into the
modern city now known as Xi'an, located at the south-
ern edge of the Plateau. For the next 1100 years, this
was the epicentre of the Chinese Empire, resulting in
exceptionally high land use and resource pressure
and, therefore, in large-scale deforestation and devas-
tation of the formerly vast forests. Today, surviving
forest fragments are exceedingly rare, and the loess
soil surface is exposed and vulnerable. Approximately
50% of the region is badly affected by water and/or
wind erosion (Li & Fischer 2006). The sediment load of
the Yellow River, which passes through the Loess
Plateau, is on average 37.4 kg per cubic meter of
water, and may reach 500 or 600 kg per cubic meter
during fl ood periods (Zhu 1981). In the late 1990s,
repeated strong summer droughts and disastrous
fl oodings convinced the Chinese government in 1998,
to implement a
National Forest Protection Program
,
wherein the native forests of 17 provinces - covering
ca. 30 million hectares in the Upper Yangtze and
Yellow River basins - were put under a complete
logging ban. Together with the
Sloping Land Conver-
sion Program
, an integrated water and soil conserva-
tion programme for agricultural restructuring ('Return
Farmland to Forest'), implemented in 2001, two legal
instruments to fi ght against forest degradation and
soil erosion are now in place. Both are designed to
protect remaining forest stands and to encourage new
plantings of trees and shrubs.
The restoration efforts have led to the following
questions: Which tree and shrub species should be
planted and where should they be planted? Can other
services than erosion prevention be included in these
watershed conservation and afforestation measures?
(See Box 12.2.)
in Central China. It is the basis for understanding the
needs and options of forest restoration there.
Over the last few decades, not only changing forest
management practices but also soil
acidifi cation
,
eutrophication
and global
climate change
have
infl uenced species composition. All of these factors are
therefore relevant to the search for adequate and effec-
tive forest restoration measures. We now discuss them
in turn:
• Acidifi cation and eutrophication: The chemical com-
position of the planet's atmosphere has signifi cantly
changed over the last century, primarily due to indus-
trialization: increased H
+
concentration ( ' acid rain ' ) as
well as increased mineral-nitrogen concentrations in
the precipitation over much of the northern hemi-
sphere. The acidifi cation and eutrophication of the soil
resulted in change in fl oristic composition, which has
been detected by repeated recording of the species com-
position on permanent plots or by comparing sets of
phytosociological relevées from the same region and
the same vegetation type over a signifi cant period
of time (A. Fischer 1999, and references therein).
Although soil analyses showed decreasing pH, an
increase of plant indicators for acidic soil could in fact
only be found in a few areas with very strong, local
emission of industrial origin. As the most important
trend in forests, the representation of nitrophilous
species is steadily increasing (Figure 12.5). Also tree
increment has generally been increasing (R ö hle 1995 ).
• Global climate change: According to current knowl-
edge, most of the global warming observed over the last
50 years is caused by human activities (Intergovern-
mental Panel on Climate Change (IPCC) 2007b).
Anthropogenic increase of CO
2
content of the atmos-
phere from 280 ppm in 1750 to 379 ppm in 2005 is
well documented, and the processes forcing tempera-
ture increase - in the twenty-fi rst century, the mean
global surface temperature may increase between 1.1
and 6.4 K as extremes - seem to be rather well under-
stood. The growing season has lengthened from north-
ern Scandinavia to Spain and Greece by about 11 days
since the early 1960s (Menzel & Fabian 1999). First
migrations of shrub and tree species can be seen mean-
while:
Ilex aquifolia
in Scandinavia is spreading further
north, following the northward shift of the 0°C January
isotherm (Berger & Walther 2007); oaks in the Catalo-
nian Montseny mountains in the eastern Pyrenées,
northeastern Spain, are invading the beech forests of
