296
THE ESSEX NATURALIST
Method
I. In the field
To ensure that the survey at Wrabness would be based upon
accurately recorded information, each pair of students was
encouraged to collect and label representative specimens that
were subsequently used for reference. This essential preliminary
work was carried out in an area well away from the site selected
for detailed study and was accompanied by a brief description
of the salt-marsh and its flora.
Meanwhile, extending across the marsh and passing through
several features of interest, a line of bamboo canes was set up, each
of which was carefully lined-up with the tower of Royal Hospital
School clearly visible across the estuary. At the point where the
line passed on to the sea wall an iron pipe was driven into the
ground.
Although this pipe is at the origin referred to in Fig. 2 and,
together with the tower, identifies the line, an arbitary datum
on the general marsh served as a more convenient zero point by
which each sample was located. String was used to indicate the
line, and measuring tapes, pulled taut to avoid following the
surface contours, were held in position by fastening them to
the bamboo canes.
The sampling began with the first pair of workers placing their
quadrat on the ground, one edge in contact with the string and
one corner at the zero point. The second pair laid their quadrat
on the same side of the line and with the corresponding corner at
the 3-feet mark. The next pair began at the 6-feet mark and so
on down the line. This is illustrated in Plate 3.
A separate proforma, indentified by the position of the quadrat
(distance in feet "above" or "below" the zero point) and by the
names or code letter of the workers concerned, was used for each
and every sample. Two values were recorded against the name
of each species rooted within the quadrat.
(a) The number of smaller squares (0-25) in which the species
was present.
(b) The average number of plants in each smaller square (i.e., the
total number of plants divided by 25). For plants such as
Puccinellia maritima it was impracticable to count the num-
ber of tillers and no estimate of density was made.
Where necessary, the names of species not already listed were
added to the proforma and if no plants were present within the
quadrat, additional information (e.g., bare mud, water-filled
channel or path) was included by way of explanation.
The completed proforma was then handed in to the person in
charge who checked it for obvious errors and omissions. The
next unsampled position at the end of the double row of workers
was then allocated, a fresh proforma issued and the sampling
procedure repeated. By this means, a transect 840 feet long was
sampled at 3-feet intervals by twelve pairs of students in less