THE RAPID SURVEY OF AN ESSEX SALT-MARSH 299
After completion, the figure was photographically reduced and
dye-line copies made available to all who had taken part in the
survey.
Discussion
The main advantages of this method lie in the following
features.
1. Subjective estimates of density and percentage cover are
avoided. Instead, for each sample of known area, the number
of plants, and the number of small squares occupied by those
plants, are noted. Small errors are of no importance.
2. The exact origin of each piece of information is known
and most errors and omissions can be corrected whilst still on
the site.
3. All original and partially collated data are entered on
printed proformae; individual note-books are not used.
4. Compilation of data is readily accomplished and each
student possesses a complete presentation of all relevant data.
The particular survey described yielded a substantial body
of information concerning the salt-marshes at Wrabness and
only the salient features are summarised here.
Spartina townsendii occupies the lowest zone of the marsh
which extends from, above mean tide level to mean high water.
It is the main marsh-building species. The next zone is that
of the general marsh just above mean high water of spring tides.
It is dominated by Puccinellia maritima, but Suaeda maritima
and Salicornia spp. are important constituents. Along the raised
edges of the channels Halimione portulacoides is the most impor-
tant species, and Agropyron pungens dominates the zone
immediately above the extreme high-water mark. With the
possible exception of one dominated by Festuca rubra, no other
zone can be recognised.
It must, however, be emphasised that, although the purpose
of the exercise was to obtain quantitative data that would
describe and perhaps typify the marsh under investigation, this
"typical" or "representative" area was in fact designated as such
by the author, and his judgement is necessarily subjective.
Nevertheless, the vegetation is self-evidently zoned and a care-
fully selected site will yield more information than will be
obtained from a series of "random" samples. Such a limitation
also prevents the indiscriminate and unsupervised collection
of information.