Restoration of dry grasslands and heathlands - Restoration Ecology - page 104

the limiting factor for plant production (van der
Woude et al . 1994). However, the plant communities
did not transform into the target communities of
heathland or oligotrophic grassland (Bakker 1989).
Adding carbon sources could be practised to
immobilize nitrogen as a means for accelerating the
restoration of grasslands on oligotrophic soils (Zink
& Allen 1998). Indeed, carbon addition decreased
nitrogen availability in laboratory microcosms. Short-
term field experiments revealed that immobilization
is possible in sites with relatively low organic matter
content and soil moisture. The method needs to be
evaluated over a period of several years (Török et al .
2000).

tion. After 25 years of haymaking in July, Festuca rubra
and Agrostis capillaris were dominant and several tar-
get species of oligotrophic grassland had established.
The latter were already present in the established
vegetation or in the soil seed bank. The long period
of haymaking did not result in the establishment of
target species present in a field nearby (500 m).
Dispersal for reaching regional target communities
seems to be a problem (Bakker et al . 2002a).
The decrease of standing crop from 800 to 200 g
of dry weight m −2 is not enough to create oligotro-
phic grassland. The nitrogen output by haymaking is
too low to compensate for the input by atmospheric
deposition (Table 8.1; Bakker et al . 2002a). The spread
of the moss Rhytidiadelphus squarrosus in dry grass-
lands in the Netherlands is supposed to be related
to atmospheric deposition (Londo 2002). A thick moss
carpet is disadvantageous for the establishment of
target species (van Tooren et al . 1987).
In the Netherlands, mulching seems not to be a good
practice to create oligotrophic communities. In con-
trast, it revealed similar results to haymaking in a
25-year experiment in southern Germany (Fig. 8.4).
The higher temperature in late summer is supposed to
better decompose the litter than in the colder Nether-
lands (Kahmen et al . 2002, Moog et al . 2002).

8.6.3 Mowing

A haymaking regime in July in the sandy uppercourse
of a brook valley in the Netherlands after intensive
agricultural exploitation showed transformation of
a community dominated by Agrostis stolonifera and
P. trivialis into dominance of Holcus lanatus and
Anthoxanthum odoratum after 25 years. The compar-
ison of different cutting regimes revealed that the best
result towards the target communities of oligotrophic
grassland was by haymaking twice a year as compared
to haymaking only once a year. Mulching annually
or once every 2 years showed a deviation into tall forb
communities (Bakker et al . 2002a). An adjacent field
that was acquired as a nature reserve some years
earlier had a shorter history of fertilizer application
(Bakker & Olff 1995), and hence a better starting posi-

8.6.4 Burning

Burning experiments are practised as a cheap way
to remove above-ground biomass and nutrients. Ini-
tial results from calcareous grasslands in Germany

Table 8.1 Average nitrogen content at peak standing crop (yield; mean S.D.) and nitrogen removal in the

first half of July in different cutting regimes and different years. Nitrogen content: 1975, n = 1; 1983, n = 3;
1999, n = 5; yield all years, n = 10. After Bakker et al . (2002a).

±

Yield (g of dw m − 2 ) N removal (kg ha − 1 ) Year Cutting regime N concentration (%)

1975 July 1.31 625 ± 92 82

July and September 1.39 810 ± 97 113

1983 July 1.49 723 ± 64 108

July and September 1.77 641 ± 69 113

1999 July 1.89 269 ± 23 51

July and September 1.41 291 ± 43 41

dw, dry weight.