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18.9 Riparian Ecosystems
Riparian ecosystems are those ecosystems in
which the soil and soil moisture are infl uenced by
the adjacent stream or river. In other words, the
riparian zone of a river, stream or other body of
water is the land adjacent to that body of water,
which is, at least periodically, infl uenced by
fl ooding. The riparian zone could be described as
‘an interface between man’s most vital resource,
namely , water, and his living space, namely , the
land’ (E.P. Odum 1981). Further, riparian ecosystems could also be defi ned as the ecosystems
with a high water table because of proximity to
an aquatic ecosystem or sub-surface water.
Riparian ecosystems usually occur as an ecotone
between aquatic and upland ecosystems, but have
distinct vegetation and soil characteristics
(Johnson and McCormick 1979).
These are unique because of their linear form
along rivers and streams and also because they
process large fl uxes of energy and materials from
upstream systems. Major expanses of riparian
ecosystems are called bottomland hardwood
forests. These are found in the eastern USA.
However, many have been drained and cleared
for agriculture. Less extensive but ecologically
critical riparian systems in the western USA,
especially in the arid SW, have nearly all been
greatly modifi ed as a result of water management
practices, logging and use by livestock. Riparian
zones respond to structures and processes operating at continental scales (climate, geology), river
system (intra-riparian), scales (elevation, timing,
magnitude, duration of fl ooding, stream valley
landform dynamics) and local trans-riparian
scales (slope and moisture gradients, sediment
sorting, biotic processes).
Minshall et al. (1989) incorporated the US
Fish and Wildlife Service wetland defi nition
(Cowardine et al. 1979 ) into their defi nition of
riparian zones. Gregory et al. (1991) had emphasised on landscape pattern in their characterisation of the riparian zone as follows.
Riparian zones are the interfaces between
terrestrial and aquatic ecosystems. As ecotones,
they encompass sharp gradients of environmental
factors, ecological processes and plant communities. The riparian zones are not easily delineated,
but are composed of mosaics of landforms,
communities and environments within the larger
landscape.’
In general, riparian ecosystems are found
wherever streams or rivers, at least occasionally,
cause fl ooding beyond their channel confi nes or
where new sites for vegetation establishment
and growth are created by channel meandering
(e.g. point bars). In deserts, riparian vegetation
may be found along ephemeral streams as well
as on the fl oodplains of perennial streams
(Leopold et al. 1964).
Notwithstanding the above, the riparian ecosystems could be broad alluvial valleys which
may be several tens of kilometres wide in the
southern USA. Conversely, they could be narrow
strips of stream bank vegetation in the arid
western USA. Brinson et al. (1981) described the
abundance of water and rich alluvial soils as
factors which make riparian ecosystems different
from upland ecosystems.
The differences between riparian ecosystems
and other ecosystems could be broadly summarised below:
(a) Riparian ecosystems generally have a linear
form as a consequence of their proximity to
rivers and streams.
(b) Energy and materials from the surrounding
landscape converge and generally pass through
riparian ecosystems in much greater amounts
than those of any other wetland ecosystems,
i.e. riparian systems are open systems.
(c) Riparian ecosystems are functionally connected to upstream and downstream ecosystems and are laterally connected to upslope
(upland) and downslope (aquatic) ecosystems.
Riparian wetlands occur in different parts of the
world. Estimation revealed that there is a total of
1980 forested riparian region covering an area of
375,000 ha in the Rocky Mountain State and 1.25
million ha in the pacifi c coastal states of Washington
and Oregon (Abernethy and Turnner 1987).
It may be mentioned here that Western riparian zones in the USA have been extensively
18.9 Riparian Ecosystems
18.9 Riparian Ecosystems
Riparian ecosystems are those ecosystems in
which the soil and soil moisture are infl uenced by
the adjacent stream or river. In other words, the
riparian zone of a river, stream or other body of
water is the land adjacent to that body of water,
which is, at least periodically, infl uenced by
fl ooding. The riparian zone could be described as
‘an interface between man’s most vital resource,
namely , water, and his living space, namely , the
land’ (E.P. Odum 1981). Further, riparian ecosystems could also be defi ned as the ecosystems
with a high water table because of proximity to
an aquatic ecosystem or sub-surface water.
Riparian ecosystems usually occur as an ecotone
between aquatic and upland ecosystems, but have
distinct vegetation and soil characteristics
(Johnson and McCormick 1979).
These are unique because of their linear form
along rivers and streams and also because they
process large fl uxes of energy and materials from
upstream systems. Major expanses of riparian
ecosystems are called bottomland hardwood
forests. These are found in the eastern USA.
However, many have been drained and cleared
for agriculture. Less extensive but ecologically
critical riparian systems in the western USA,
especially in the arid SW, have nearly all been
greatly modifi ed as a result of water management
practices, logging and use by livestock. Riparian
zones respond to structures and processes operating at continental scales (climate, geology), river
system (intra-riparian), scales (elevation, timing,
magnitude, duration of fl ooding, stream valley
landform dynamics) and local trans-riparian
scales (slope and moisture gradients, sediment
sorting, biotic processes).
Minshall et al. (1989) incorporated the US
Fish and Wildlife Service wetland defi nition
(Cowardine et al. 1979 ) into their defi nition of
riparian zones. Gregory et al. (1991) had emphasised on landscape pattern in their characterisation of the riparian zone as follows.
Riparian zones are the interfaces between
terrestrial and aquatic ecosystems. As ecotones,
they encompass sharp gradients of environmental
factors, ecological processes and plant communities. The riparian zones are not easily delineated,
but are composed of mosaics of landforms,
communities and environments within the larger
landscape.’
In general, riparian ecosystems are found
wherever streams or rivers, at least occasionally,
cause fl ooding beyond their channel confi nes or
where new sites for vegetation establishment
and growth are created by channel meandering
(e.g. point bars). In deserts, riparian vegetation
may be found along ephemeral streams as well
as on the fl oodplains of perennial streams
(Leopold et al. 1964).
Notwithstanding the above, the riparian ecosystems could be broad alluvial valleys which
may be several tens of kilometres wide in the
southern USA. Conversely, they could be narrow
strips of stream bank vegetation in the arid
western USA. Brinson et al. (1981) described the
abundance of water and rich alluvial soils as
factors which make riparian ecosystems different
from upland ecosystems.
The differences between riparian ecosystems
and other ecosystems could be broadly summarised below:
(a) Riparian ecosystems generally have a linear
form as a consequence of their proximity to
rivers and streams.
(b) Energy and materials from the surrounding
landscape converge and generally pass through
riparian ecosystems in much greater amounts
than those of any other wetland ecosystems,
i.e. riparian systems are open systems.
(c) Riparian ecosystems are functionally connected to upstream and downstream ecosystems and are laterally connected to upslope
(upland) and downslope (aquatic) ecosystems.
Riparian wetlands occur in different parts of the
world. Estimation revealed that there is a total of
1980 forested riparian region covering an area of
375,000 ha in the Rocky Mountain State and 1.25
million ha in the pacifi c coastal states of Washington
and Oregon (Abernethy and Turnner 1987).
It may be mentioned here that Western riparian zones in the USA have been extensively
18.9 Riparian Ecosystems