Dispersal, migration and management - Ecological Applications: Toward a Sustainable World - page 91

Again they calculated a mean of the three components and scaled between 0 and 1
to provide a relative index (Figure 4.5).
Not all plants have wind-dispersed propagules: some are capable of dispersing by
water (assessed experimentally as the proportion of seeds still fl oating after 72
hours) or via animals (those with fl eshy fruits). Once again, immigration potential
of wind- and animal-dispersed plants was estimated by also taking into account
fecundity and relative plant abundance adjacent to abandoned peat workings. Figure
4.6 plots the percentage occurrence of plant species in abandoned peatbog workings
- a measure of their ability to recolonize naturally - against estimated immigration
potential for plants in all the dispersal categories.
The recolonization of many vascular plants is quite well predicted by their esti-
mated immigration potential - those with a dispersal index above 0.9 predictably
occur in abandoned bogs. For these species, it seems that physicochemical condi-
tions in the abandoned bogs are adequate. On the other hand, mosses have high
immigration potential but are very poorly represented, strongly suggesting that
adverse physicochemical conditions are limiting their successful re-establishment.
Put another way, the physicochemical conditions of the abandoned peatbog work-
ings encompass the fundamental niches of many of the vascular plants but not of
the mosses (Box 2.1 defi nes fundamental niche). Campbell's team concludes that
restoration efforts should concentrate on actively introducing species with low
immigration potential. In addition, microenvironments should be created that are
suitable for the establishment of the mosses and other species with relatively high
immigration potential but poor representation in abandoned bogs.

4.3.3 Wetland forest
restoration

Next I turn to a case of restoration that contrasts with the peatbogs because exten-
sive seed-banks remain and many species (but not all) can recolonize by means of
'time travel'.
A very large proportion of the world's forested wetlands were lost when people
drained and converted them for agriculture. Ironically, however, market changes
have led to abandonment of vast areas of the wettest of this agricultural land, espe-
cially in Europe and North America. In the southeastern USA, for example, 89,000
hectares of fl oodplain land is due for reforestation in the early years of this century
(King & Keeland, 1999). Restoration faces two major problems. The fi rst is that some

Fig. 4.6 Relationship
between mean
occurrence of study
species in abandoned
peatbog workings in
eastern Canada and
their immigration
potential by wind
(circle s), water
(squares) or animal
dispersal (triangles).
(After Campbell et al.,
2003.)

20

15

10

5

0

0 0.2 0.4 0.6 0.8 1.0

Dispersal index