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Offwell Wetland Survey

Plant Zonation along the North/South Transect.

The diagram below shows the ranges of eleven of the most important species occurring in the wetland, along the N/S transect line. The range is the total area in which the species is found.

The diagram was drawn from data taken from the continuous line transect survey, which noted every plant to touch the line along its entire length. Data was not used from the interrupted line transects, which recorded plants touching the line at either 1 or 2 metre intervals. This is because this type of transect will tend to underestimate the range of species. They are only recorded as being present if they happen to touch the line at the right point and are otherwise missed.

The blue bars at the bottom of the chart represent the changes in water depth along the line.

The chart clearly illustrates the plant zonation patterns in the wetland. It also illustrates how the boundaries of zones become blurred where certain species overlap and occur in more than one zone. Only three plants of the plants illustrated (Alder, Wood Clubrush and Marsh Bedstraw) were confined to one zone. The rest overlap and it becomes difficult to draw a distinct boundary between zones. Increasing water depths, together with comparisons of the overall composition of the flora are the most reliable indicators of changes in zone.

Rhododendron is a species which prefers dry conditions. It is found in the northernmost region of the wetland where there is no standing water, but extends a little way into the marsh region. Plants such as Alder and Soft Rush are characteristic of the wetter conditions where dry land grades into marsh.

Soft Rush occurs at the edge of the marsh zone and also in the wetter woodland areas of the dry land zone. It does not extend far into the marsh region because plants such as Wood Clubrush, Marsh Bedstraw, Reedmace, Yellow Iris, Branched Bur-reed and Water Mint dominate this area.

As water depths begin to increase, the marsh species noted above begin to die out, except for Branched Bur-reed. This continues well into the swamp zone, where it is joined by floating Duckweed and Canadian Pondweed. Canadian Pondweed continues into the open water zone.

 

NORTH

SOUTH

.Dry Land

.Marsh

.Swamp

.Open Water

.

Rhododendron h

 

. . . . . . . . . ... ... . . . .
Soft Rush h

.

. . . . . . . . . . . . .. ... . . . .
Alder h . . . . . . . . . . . . . . . .. . . . . .
Wood Club Rush h . . . . . . . . . . . . .. . . . . .
Reed Mace h . . . . . . . . . . . . . . . . . . . .
Marsh Bedstraw h . . . . . . . . . . . . . ... . . . . .
Water Mint h . . . . . . . . . . . . . . .
Yellow Iris h . . . . . . . . . .. . . . . . .  
Branched Burreed h . . . . . . . . . . . . . .
Duckweed h . . . . . . . . . . . . . . . . .
C. Pondweed h . . . . . . .   .. . . . . . . . . .

.

.

Water depth 1-5cm h . ... .. . .. .. . .. .. .. . . . . .
6-10cm   . .. .. .. .. .. . .. .. .. . .. .. .. .. .. ................................
11-15cm   . .. . . . . . . . . . . . . . .. . ..

.

16-20 cm   . . . . . . . . . . . . . . . . . ..

.

21-25cm   . . . . . . . . . . . . . . . . ... .

.

26-30 cm   . . . . . . . . . . . . . . . . . .

 

31-35cm   . . . . . . . . . . . . . . . . . .

.

.
36-40cm   . . . . . . . . . . . . . . . . .. .   .
41-45cm   . . . . . . . . . . . . . . . . .. .

.

.
46-50cm   . . . . . . . . . . . . . . . . ... .

..

 
51-55cm   . . . . . . . . . . . . . . . . .. .

.

 
56-60cm   . . . . . . . . . . . . . . . . ... .

.

 

.

61-65cm   . . . . . . . . . . . . . . . . . .

.

.

 

.

 

The diagram above shows the ranges of the major species along the N/S line transect. However, it does not show how much of a particular species occurs at any one point. The range can include one small plant at either end, with a few in the middle or it may indicate a large stand,occupying a substantial area.

Within its range, each plant species will have an optimum zone where the environmental conditions suit it best. Its abundance will usually taper off at either end of its range, with maximum abundance occurring somewhere in between, in the optimum zone.

To access bar charts showing the changes in the percentage cover of each of the eleven major species charted above along their range, click here. The species are similarly colour-coded to aid comparison.


Plant Zonation diagram for the East/West Transect

 

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