262
are those that reinforce other species through
nutrient cycles, aids to reproduction, control of
spatial diversity, population regulation and other
means (Odum 1989 ). On the other hand, ‘selfdesign’ relies on the self-organising ability of the
ecosystems; natural processes (wind, rivers,
tides, biotic inputs, etc.) contribute to species
introduction, selection of those species which
will dominate from this gene infl ow, etc. It is,
thus, said to be nature’s manifestation of ecosystem design. Further, in self-design, the presence
and survival of species due to the continuous
introduction of them and their propagules is the
essence of the successional and functional development of an ecosystem. This may be thought of
as analogous to the continuous production of
mutations necessary for evolution to proceed.
Summary
1. Wetland ecosystem has traditionally been
considered as transitional seres between
open lakes and terrestrial forests.
2. The accumulation of organic material from
plant production was seen to build up the
surface until it was no longer fl ooded and
could support fl ood-tolerant terrestrial forest
species (autogenic succession).
3. An alternative hypothesis is that the vegetation found at a wetland site consists of species adapted to the particular environmental
conditions of that site (allogenic succession). It is believed that both allogenic and
autogenic forces act to change wetland
vegetation.
4. A number of models have been suggested for
wetland plant developments.
5. The initial conditions at the site and the subsequent events generally characterise the
beginning and subsequent development of a
plant community.
6. In the classical view of succession, wetlands
are considered as transient stages in the
‘hydrarch development’ of a terrestrial forested climax community from a shallow lake.
According to autogenic versus allogenic view
of succession, lakes gradually fi ll in as organic
materials from dying plants accumulate
and minerals are carried in from upslope.
Eventually, the water becomes shallow enough
to support emergent marsh vegetation. This
continues to build a peat mat. Eventually,
shrubs and small trees also appear. They continue to transform the site to a terrestrial one.
7. According to community concept and the
continuum idea , the identifi cation of a ‘community’ is a conceptual issue. It is confused
by the scale of perception. A community
may be regarded as a population of living
organisms having homogeneity . A number of
other models of community change have
been developed, although a few have been
applied to wetlands.
8. According to centrifugal organisation concept , changes in species composition and
richness of herbaceous plants were related to
the gradients of disturbance and stress factors,
which reduce biomass and determine which
functional plant strategies would work best.
9. Historically, the community concept has
been of immense value in ecology. One
approach is to describe communities in
terms of functional ‘guilds’. According to
functional guild model , a ‘guild’ may be
defi ned as a group of functionally similar
species in a community.
10. According to environmental sieve model , the
presence and abundance of each species
depends on its life history and its adaptation
to the environment of a site.
11. The gap dynamic computerised model is an
individual-based model which tracks the
growth of each tree in a forest gap of defi ned
size, based on species-specifi c life history
traits and limitations of resource availability
on the individual. This model tries to simulate the growth and composition of a mangrove forest in South Florida.
12. Further, self-design and the related concept of
self-organisation are important concepts in
wetland ecosystem development. This concept states that natural processes (wind, rivers,
tides, biotic inputs, etc.) contribute to species
introduction, selection of those species which
will dominate from this gene infl ow, etc.
Further, in self-design, the presence and
survival of species due to the continuous
17 Wetland Ecosystem Development
are those that reinforce other species through
nutrient cycles, aids to reproduction, control of
spatial diversity, population regulation and other
means (Odum 1989 ). On the other hand, ‘selfdesign’ relies on the self-organising ability of the
ecosystems; natural processes (wind, rivers,
tides, biotic inputs, etc.) contribute to species
introduction, selection of those species which
will dominate from this gene infl ow, etc. It is,
thus, said to be nature’s manifestation of ecosystem design. Further, in self-design, the presence
and survival of species due to the continuous
introduction of them and their propagules is the
essence of the successional and functional development of an ecosystem. This may be thought of
as analogous to the continuous production of
mutations necessary for evolution to proceed.
Summary
1. Wetland ecosystem has traditionally been
considered as transitional seres between
open lakes and terrestrial forests.
2. The accumulation of organic material from
plant production was seen to build up the
surface until it was no longer fl ooded and
could support fl ood-tolerant terrestrial forest
species (autogenic succession).
3. An alternative hypothesis is that the vegetation found at a wetland site consists of species adapted to the particular environmental
conditions of that site (allogenic succession). It is believed that both allogenic and
autogenic forces act to change wetland
vegetation.
4. A number of models have been suggested for
wetland plant developments.
5. The initial conditions at the site and the subsequent events generally characterise the
beginning and subsequent development of a
plant community.
6. In the classical view of succession, wetlands
are considered as transient stages in the
‘hydrarch development’ of a terrestrial forested climax community from a shallow lake.
According to autogenic versus allogenic view
of succession, lakes gradually fi ll in as organic
materials from dying plants accumulate
and minerals are carried in from upslope.
Eventually, the water becomes shallow enough
to support emergent marsh vegetation. This
continues to build a peat mat. Eventually,
shrubs and small trees also appear. They continue to transform the site to a terrestrial one.
7. According to community concept and the
continuum idea , the identifi cation of a ‘community’ is a conceptual issue. It is confused
by the scale of perception. A community
may be regarded as a population of living
organisms having homogeneity . A number of
other models of community change have
been developed, although a few have been
applied to wetlands.
8. According to centrifugal organisation concept , changes in species composition and
richness of herbaceous plants were related to
the gradients of disturbance and stress factors,
which reduce biomass and determine which
functional plant strategies would work best.
9. Historically, the community concept has
been of immense value in ecology. One
approach is to describe communities in
terms of functional ‘guilds’. According to
functional guild model , a ‘guild’ may be
defi ned as a group of functionally similar
species in a community.
10. According to environmental sieve model , the
presence and abundance of each species
depends on its life history and its adaptation
to the environment of a site.
11. The gap dynamic computerised model is an
individual-based model which tracks the
growth of each tree in a forest gap of defi ned
size, based on species-specifi c life history
traits and limitations of resource availability
on the individual. This model tries to simulate the growth and composition of a mangrove forest in South Florida.
12. Further, self-design and the related concept of
self-organisation are important concepts in
wetland ecosystem development. This concept states that natural processes (wind, rivers,
tides, biotic inputs, etc.) contribute to species
introduction, selection of those species which
will dominate from this gene infl ow, etc.
Further, in self-design, the presence and
survival of species due to the continuous
17 Wetland Ecosystem Development