Succession and management - Ecological Applications: Toward a Sustainable World - page 220

On the other hand, the recovery of intensively grazed English pasture to species-
rich meadow is a slow and unreliable process (Pywell et al., 2002). But recovery can
be speeded up by sowing a species-rich mixture of seeds of desirable plants adapted
to the prevailing conditions (also discussed in Sections 3.2.1 and 4.3).

8.2.2 Restoration
timetable for animals

Restoration involves recovery not just of plants but of animals too. After opencast
mining of coastal sand dunes in northeastern South Africa has ceased, the sand
dune communities slowly recover to the characteristic dune forest vegetation. This
can be considered a primary succession (Box 8.1) because mining leaves no trace
of the previous community. However, since 1978 regeneration has been accelerated
in some locations by actively reshaping dunes to resemble their predisturbance
topography, and by covering them with topsoil containing seeds of early-succes-
sional plants. In effect, the managers convert the slow primary succession to a more
rapid secondary succession (Box 8.1). Millipedes perform an important ecosystem
role by feeding on dead organic matter and thus contribute to the decomposition
process. They colonize spontaneously regenerating sand dunes, gradually approach-
ing the species composition of unmined dunes, but the process is very much more
rapid in the rehabilitated dunes (Figure 8.4).
Tidal salt marshes are now much rarer because many have been drained for agri-
culture or because tidal cycles have been obstructed by tide gates, culverts and
dykes. The restoration of tidal action, and thus of links between the marshes and
the wider coastal ecosystem in Connecticut, USA, leads to recovery of salt marsh
vegetation (an allogenic succession - Box 8.1). These restored marshes take at least
10 -20 years to achieve 50% coverage of their salt marsh plants (principally Spartina
alternifl ora , S. patens and Distichlis spicata) and characteristic salt marsh animals
follow a comparable timetable (Warren et al., 2002). For example, the high marsh
snail Melampus bidentatus reaches densities comparable to intact marshes after 20
years and the bird community also takes 10-20 years to reach a characteristic
marshland community composition. Marsh 'generalists' that forage and breed in
upland areas as well as tidal wetlands, such as song sparrows Melospiza melodia and
red-winged blackbirds Agelaius phoeniceus , feature early in the restoration sequence.
But these are replaced later by marsh 'specialists' such as marsh wrens Cistothorus
palustris , snowy egrets Egretta thula and spotted sandpipers Actitis macularia . Typical
fi sh communities recover more quickly, within 5 years.

Fig. 8.4 A measure of
similarity in the
composition of
millipede communities
(Bray-Curtis index) is
used to compare
regenerating sand dunes
and natural undis-
turbed sand dune
forests in South Africa.
Triangles represent
spontaneously
regenerating sites, and
squares represent
actively rehabilitated
dunes. The millipede
community achieves
50% similarity in
species composition
compared to unmined
dunes after about 15
years on rehabilitated
dunes, but in the case
of spontaneously
regenerating dunes this
takes 50 years or more.
Twent y-t wo species of
millipede were
identifi ed in the study.
Between 12 and 19 are
found in undisturbed
dune forest, while 12
species occurred after
24 and 54 years in
spontaneously
regenerating and
rehabilitated dunes,
respectively. (After Redi
et al., 2005.)

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Site age (years)