Succession and management - Ecological Applications: Toward a Sustainable World - page 221

a

Range of
natural
marshlands

b

c

1 10 100

Time (years)

Fig. 8.5 Recovery of different aspects of ecosystem functioning during active marsh restoration.
Curve a describes processes linked to hydrology (e.g. sedimentation, rates of carbon and
nitrogen accumulation in marsh soil) which are quickly restored. Curve b describes the slower
recovery of biological processes such as rate of production of biomass and decomposition. Curve
c describes marsh soil development (e.g. total amounts of carbon and nitrogen in the soil, as
opposed to their rates of accumulation) which recovers most slowly of all. (After Craft et al.,
2003.)

Thus, restoration of a natural tidal regime sets marshes on a path toward full
recovery of their ecological functioning, but this generally takes one or more decades.
Community recovery can be speeded up by actively planting salt marsh species, but
certain ecosystem properties (e.g. the carbon and nitrogen content of marsh soils)
do not recover as quickly as others (e.g. deposition of fi ne sediment) (Figure 8.5).

8.2.3 Invoking the
theory of
competition-
colonization
trade-offs

The late-successional stage of many successions is delayed because the more com-
petitive late-successional species are much slower to colonize than the pioneer
species (competition-colonization trade-off - Box 8.1). This knowledge can be used
by managers to speed up certain restoration projects.
An example comes from tropical forest, vast areas of which have been displaced
by agriculture. When the land is retired from production the early- and mid-
successional species tend to dominate succession for a century or more. Many of
the late-successional trees, still represented in distant forest fragments, have large
seeds that depend on animal dispersal by birds, bats or primates; they are in short
supply in the landscape and of the few that arrive after succession has started, most
die as seeds or seedlings. Martinez-Garza and Howe (2003) refer to the 'retarded'
community as a pioneer desert. But they note, in Panama and Costa Rica for
instance, that when large-seeded late-successional trees such as Dipteryx panamensis
and Genipa americana are planted by hand in pastures (before succession has really
got under way) they have a much higher probability of survival. It seems that the
competition-colonization trade-off can be circumvented by intervening to get late-
successional species off to an unusually good start. In this way up to 70 years of
succession can be bypassed.

8.2.4 Invoking
successional-niche
theory

The place of species in a succession does not invariably depend on their probability
of colonization. Many species are restricted to a particular moment in the succes-
sional timetable because their niche requirements (Chapter 2) are met only at that
time.