The diagram above illustrates the plant zonation pattern across the wetland.
At the northern-most end of the transect, species which
prefer drier land predominate. This includes species such as Brambles, Alder, Silver Birch
and Rhododendron. The Rhododendron which used to dominate this area prior to restoration (Historical Background) still dominates this marginal dry land zone
(7-18m mark). The marsh area adjoining the dry land zone prevents the Rhododendron from
encroaching further, but it is easy to see that if the wetland were allowed to silt up to
any extent, the Rhododendron would once more rapidly cover the area. The trunks of
Rhododendron can stretch virtually horizontally, above ground level, for many metres. It
is therefore possible for the roots and main trunk of the plant to be on acceptably dry
land, while the rest of the plant canopy reaches well out into adjacent marshy areas. This
means Rhododendron plants are capable of extending their zone of dominance well beyond
suitable ground conditions.
The dry land zone grades into the marsh area beyond
the Rhododendron (22metre mark). 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
The marsh area closest to the dry land zone
(22m-30m) contains small Silver Birch seedlings. However, the area is too wet for them to
compete successfully here. Soft Rush is common in this region.
Further into the marsh area (approximately 31m -
43m), species such as Willow, Yellow Iris, Water Mint and Branched Bur-reed predominate.
As the water becomes deeper, most of these species begin to die out, leaving Yellow Iris
With increasing water depth, only the Branched
Bur-reed is left from the marsh flora (55m mark) and open water species such as Canadian
Pondweed begin to occur. This is the main species to be found in the open water zone.
The interrupted line transect, with records taken
every other metre, as pictured above, suffers from the disadvantage that it records too
few of the species which are present in the transect area. Only 10 of the 29 species
recorded by the continuous line transect are picked up by the transect.
The continuous line transect
is valuable in that it picks up most of the species present in the transect area.
However a great number of plants have to be diagrammatically represented along the line
for the continuous line transect. This 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.
In contrast, the interrupted
line transect where records were taken every metre, very clearly shows the patterns of
plant zonation. This is because a lot of the less dominant species have been removed from
the picture (16 species were recorded instead of 29). The disadvantage with this line
transect is that it is likely to underestimate the range of each species. This is the
total region through which the species can be found along the line. 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.
The Interrupted line transect, with an interval of 2
metres, pictured above suffers from oversimplification. Only about a third of the species
actually present (10 species)are recorded. While the patterns of zonation in the wetland
are still visible, the ranges of the major species present are very blurred. For this
habitat, this transect presents too little data to really understand the changes which are
taking place along the line.
The range of a number of the more important plant species
distributed along the North/South line transect is shown here.
This diagram was derived from the continuous line transect data, because the data from
this transect is the most complete.
Why use line transects? - the
merits of different types of line transect.
Back to Results