above clearly shows the plant zonation patterns across the wetland.
There is a very narrow dry land zone on the eastern section
of this transect (1-6m mark). The plant species here are those which prefer drier
conditions. They include species such as Silver Birch and Rhododendron. Willow also grows
here, although it is mainly found in the marsh region. The Rhododendron, which originally
covered the entire area, still occurs in a narrow band down both the East and West sides
of the wetland and in the Northern dry land area. It is prevented from encroaching further
by the wet, marsh conditions in the adjacent areas.
The dry land areas grade very quickly into marsh
(6-28m). The marsh zone is characterised by water-logged sediments and levels of standing
water which vary with the topography of the zone. Dips and hollows fill with water, while
higher mounds are dry. It must be stressed that the water levels marked on the
diagram above were correct at the time of the survey. However, they will fluctuate
according to the amount of rainfall and stream water which is entering the wetland.
The marsh zone is characterised by species such as
Willow, Wood Clubrush, Greater Tussock Sedge, Reedmace, Yellow Iris, Marsh Bedstraw
and Branched Bur-reed. Water Mint is also very prevalent in this
area, but as an anomaly, due to the one metre recording interval, it has not been picked
up at all. The Silver Birch at the 16m mark was on a mound raised above the general level
of the marsh. It was therefore dry enough at this point for the Silver Birch to survive.
As the water level begins to rise (29m mark), the
marsh plants begin to die out. Water Mint and Branched Bur-reed are the last to die out.
As the marsh plants disappear and water depth increases, swamp plants such as Bog Bean
take over (35-38m).
The swamp ends adjacent to the incoming stream
channel. The western bank of the stream very abruptly marks the end of the deep water zone
(38m). The west bank of the stream is raised and Alder trees have grown up here. Marsh
species predominate to the west of this region. The species here are slightly different to
the marsh species in the centre of the wetland. Soft Rush and Pendulous Sedge are common
in this area.
The E/W continuous line
transect is valuable in that it picks up most of the species present in the
transect area (36 species in this case). However, the great number of plants which have to
be diagrammatically represented along the line makes the illustration quite difficult to
look at and extract information from. There is a great deal of 'clutter' taking the eye
away from general patterns of distribution.
Patterns of zonation are somewhat clearer in the
interrupted line transect pictured above, where records were taken every metre. This is
because a lot of the less dominant species have been removed from the picture. However,
this transect diagram does not show the patterns of zonation as clearly as the
corresponding transect diagram for the N/S transect. This is
because the 1m transect interval in this E/W transect picks up only about half of the
species present (19, as opposed to 36 for the continuous line transect). In other words,
rather too much 'clutter' has been removed.
There is an added disadvantage with this line
transect in that it is likely to underestimate the range of each species. This is the
total region through which the species can be found. As records are only being taken at
every metre mark, plants will only be recorded if they happen to touch the line at the
right point. This is illustrated by the apparent absence of Water Mint in the marsh zone,
when in fact it is very common there (see the continuous line
The range of a number of the more important plant species
distributed along the East/West line transect is shown here.
This diagram was derived from the continuous line transect data, for the reason noted just
Why use line transects? - the
merits of different types of line transect.
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