Environmental Engineering Reference
In-Depth Information
60
(a)
(b)
(c)
50
40
30
20
10
0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0
20
40
60
80
100
0
10
20
30
40
N
total
(%)
K (mg 100 g
-1
)
P
2
O
5
(mg 100 g
-1
)
Figure 14.7
Distribution of total nitrogen, percentage of soil-extractable potassium, soil-extractable phosphorus against the
number of species per 100 m
2
in 281 grassland sites in western Europe. (Modifi ed from Janssens
et al
. 1998 .)
(the undisturbed parent material) and to ' reboot ' with
oligotrophic soil conditions. The seed banks of target
species are depleted or removed, but so are those of the
nontarget species. The results after 10 years (Verhagen
et al
. 2001) show that nutrient removal is possible.
However, in some sites a considerable amount of phos-
phorus is found in the C horizon as a result of heavy
fertilizer inputs in the past (see Box 14.2 and Figure
14.6). Together with a continuous input of nitrogen
from atmospheric deposition, this may cause problems
for the future development of oligotrophic communi-
ties (Verhagen & van Diggelen 2006) through environ-
mental limitations (Figure 14.1; Baeten
et al
. 2009 ). A
high phosphorus level can be such a limitation. The
highest plant species diversity in grasslands over north-
western Europe is more related to low phosphorus
levels in the soil than to the levels of potassium and
nitrogen (Figure 14.7; Janssens
et al
. 1998 ).
After topsoil removal, vegetation studied by Ver-
hagen
et al
. (2001) revealed a range of 0-30% similar-
ity with target plant communities of oligotrophic
grasslands and heathlands. Many target species for res-
toration occurred within 1 km. However, after nearly
10 years, many target species were still absent. This
again indicates that dispersal is a limiting factor for
restoration. When host plants are lacking, the re-
establishment of target butterfl y species is also limited
(WallisDeVries & Ens 2010 ).
In a study of potential restoration techniques (Marrs
et al
. 1998) on a sandy soil that had been used for
arable production, at the Minsmere bird reserve in
Suffolk, United Kingdom, which was already men-
tioned above, a high available soil phosphorus concen-
tration and high soil pH were identifi ed as the most
diffi cult soil constraints for the restoration of heath-
land. Surface topsoil removal and burial were both
tested. Unfortunately, the site had been under agricul-
tural production for much longer than initially thought
and there had been substantial additions of lime and
marl. The result was that the soil properties did not
change over the upper 2 m, during the period of the
study, and surface topsoil removal would clearly have
been ineffective. Hence, we can conclude that the deci-
sion to carry out topsoil removal should be made with
care, as its potential usefulness differs between restora-
tion situations. This holds especially when the target
site has archaeological interest.
14.5
PERSPECTIVES
Restoration of communities on oligotrophic soil can be
achieved by reduction of nutrients, especially nitrogen,
in the soil. However, enrichment of nitrogen by atmos-
pheric deposition counteracts the intended reduction.
As the highest numbers of plant species in grasslands
in north-western Europe occur on soils very poor in
phosphorus, the latter must also be reduced. Even
when the appropriate abiotic conditons have been
restored, the restorationist may face the problem that
the target species do not re-establish without direct
assistance or intervention. Knowledge of the longevity
