Environmental Engineering Reference
In-Depth Information
appeared to be in bad condition, tree increment has
often been increasing for more than two decades and
currently surpasses all expectations (Röhle 1995);
therefore, other effects seem to overcompensate for the
damaging effects (see section 10.4.2).
Altogether it can be stated that the floristic
composition of European forest vegetation is indeed
changing, but up to now this is only working on very
low levels of phytosociological hierarchy (subtype/
sub-association, not association). Nevertheless, it is an
effect working on a global scale since it could be shown
that intercontinental transport of NO
x
is possible and
significant (Splichtinger
et al.
2001).
minor increase
increase
no change
10.4.2 Global climate change
Fig. 10.3
Change in the representation of nitrogen-
indicating plant species in central Europe during the
last four decades. Modified from A. Fischer (1999).
Anthropogenic increases in CO
2
from 280 ppm in
1750 to 370 ppm in 2000 are well documented, and
the processes forcing temperature increase (in the 21st
century the mean global surface temperature may
increase by 1.4-5.8 K; IPCC 2001) seem to be rather
well understood. Indeed, it has been shown that - all
over Europe from northern Scandinavia to Spain and
Greece - the growing season has lengthened by about
11 days since the early 1960s (Menzel & Fabian 1999).
In northern and central Europe a floristic response
to such temperature increase and growing-season
extension up to now cannot be detected by using cur-
rent methods of vegetation ecology. In forests on the
southern edges of the Alps, however, an increase of
evergreen broad-leaved woody species has been
reported for the past few decades (Klötzli & Walther
1999: 'laurophyllization'), but although there is a close
correlation with climatic parameters, other causes
such as changes in land-use practices may also play an
important role in this change in species composition.
Altogether it seems evident that species composi-
tion in European forests will change within the 21st
century as a consequence of global climate change,
but beech will continue to be the dominating natural
tree species in central Europe (A. Fischer 1997).
general trends in European forest vegetation during
the past four decades can be seen (A. Fischer 1999).
1
As the most homogeneous trend in vegetation
dynamics in central European forests the representa-
tion (species number, frequency, cover/abundance
and mean ecological indicator value) of
nitrogen-
indicating species
is increasing (Fig. 10.3). This seems
to be a very strong reaction to the deposition of
nitrogen compounds like NO
x
and NH
x
as mentioned
above.
2
Although indicators of acidic soils were expected
to increase, such an increase could only be found
in a few areas with very strong local industrial
immissions. Usually, however, the effect of soil
acidification is overcompensated for by other eco-
logical factors such as N input.
Parallel to soil acidification, a tree decline
(
Waldsterben
) has been observed. While at first soil
acidification was discussed intensively as the main
driving factor for tree decline (Ulrich 1986), later on
evidence was found that
Waldsterben
is a multi-
causal phenomenon (Schulze
et al.
1989). Although
the crowns of many broad-leaved as well as needle
trees (e.g. beech, oak, spruce and pine) in Europe
10.4.3 Forest management
Forest management influences the forest ecosystem.
As shown in section 10.2.2
tree species composition
