This report has been prepared by Carter Ecological Limited , with all reasonable
skill, care and diligence within the terms of the Contract with the client.
We disclaim any responsibility to the client and others in respect of any matters
outside the scope of the above.
This report is confidential to the client and we accept no responsibility of
whatsoever nature to third parties to whom this report, or any part thereof, is
made known. Any such party relies on the report at their own risk.
English Nature Contract Number 11 T4 00/01.
English Nature is grateful for the assistance of the Environment Agency and the
Medway and Swale Estuary Partnership in funding this report.
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1
Introduction............................................................................................................ 3
1.1 Purpose of the report .......................................................................................... 3
1.2 Aims and objectives of the scoping survey ....................................................... 3
1.3 Survey approach ................................................................................................ 3
1.4 Areas surveyed................................................................................................... 4
2 Methods ................................................................................................................. 5
2.1 General............................................................................................................... 5
2.2 Variables recorded ............................................................................................. 6
2.2.1 Division across the sea-wall ...................................................................... 6
2.2.2 Salt Marsh .................................................................................................. 6
2.2.3 Structural features ...................................................................................... 6
2.2.4 Management .............................................................................................. 7
2.2.5 Plant species............................................................................................... 7
2.3 Data processing.................................................................................................. 8
2.3.1 Network and survey files ........................................................................... 8
3 Results ................................................................................................................... 9
3.1 GIS product........................................................................................................ 9
3.2 Species occurrence............................................................................................. 9
3.2.1 Species groupings ...................................................................................... 9
3.2.2 Widespread species .................................................................................. 10
3.2.3 Local species ............................................................................................ 10
3.2.4 Rare species ............................................................................................. 10
3.3 Species distribution in relation to habitat ........................................................ 11
3.4 Categorizing walls according to species richness ............................................ 11
4 Discussion and recommendations for further survey........................................... 13
4.1 Confirming the scoping survey data ................................................................ 13
4.2 Vegetation ........................................................................................................ 13
4.3 Habitat niches .................................................................................................. 14
4.3.1 Physical niche .......................................................................................... 14
4.3.2 Community niche..................................................................................... 14
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1
INTRODUCTION
1.1
Purpose of the report
This report provides background information on a botanical scoping survey of sea
walls in the North Kent marshes, and discusses a recommended sampling strategy for
the second stage of the project. The survey area comprised the sea walls of three
SSSIs -The Medway Estuary and Marshes SSSI, The South Thames Estuary and
Marshes SSSI, and The Swale SSSI.
Fieldwork for the scoping survey was carried out by Carter Ecological Limited in
August and September 2000 under English Nature contract 11T400/01. The principle
output required was a report of the survey data as tables in MapInfo format, and this
GIS product was supplied in final form to English Nature on 24/11/2000. The other
output required was a written report on the recommended sampling strategy for the
second stage of the project, and this is addressed here. This report also provides
explanation of the methodology used in the scoping survey.
1.2
Aims and objectives of the scoping survey
The scoping survey aimed to relate the occurrence of scarce plant species to readily
observable aspects of the sea-wall environment using rapid surveying techniques.
Specific objectives may be summarized as follows.
1.3

To map boundary features and sea-wall types.

To map readily observable aspects of sea-wall vegetation and management.

To map readily observable aspects of salt-marsh condition outside the sea-wall.

To produce a preliminary map of the occurrence of scarce species characteristic of
the sea-wall habitat on the basis of conspicuous colonies only (the project brief
specified that time should not be spent on detailed searching for plants).
Survey approach
The survey was carried out by walking the sea-walls with a surveying wheel to
provide extremely accurate information on location. A range of variables were
selected for observation, including appropriate plant species, various aspects of sea
wall structure and management, and various aspects of salt-marsh condition.
Wherever the state of any variable altered (e.g. a scarce plant population ended, or
mowing management started) the chainage was recorded from the surveying wheel,
and the information was either entered directly into a hand-held computer or noted
more conventionally on paper. The computer software for field data entry required
the sea-walls to be divided into more or less straight sections up to 2-km long, so that
positional information from the surveying wheel could be correctly interpreted.
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1.4
Areas surveyed
All sea walls in the three SSSIs were surveyed as follows.

South Thames Estuary and Marshes SSSI, 28 sections totalling 33km and 68m.

Medway Estuary and Marshes SSSI, 49 sections totalling 41km and 596m.

Swale SSSI, 54 sections totalling 54km and 898m.
The total length of wall surveyed was therefore 129km and 562m. Sea frontages
within the SSSIs that were clearly not sea walls were omitted as follows.

South Thames SSSI, frontage of Cliffe Fort and Jetties, frontage of Allhallows
Caravan Site and Leisure Park, and frontage of Grain village.

Medway SSSI, frontage of Kent Oil Refinery and east side of Colemouth Creek,
frontage of Stoke Creek Wharf from Bee Ness Jetty to western boundary of
Kingsnorth Power Station, frontage of Otterham Quay Wharf to Horsham Farm
Wharf, the western side of the Barksore Peninsula from Lower Halstow to
Barksore marshes, the southern Shore of Bedlams Bottom including Raspberry
Hill, Chetney Moat and Chetney Hill, and the northern end of Rushenden
Marshes.

Swale SSSI, frontage of Ridham Dock, frontage of Kemsley Marshes and Landfill
area, the Isle of Harty, and Elmley Hills.
Most of these are frontages modified by man, but a few (including Chetney Hill, Isle
of Harty and Elmley Hills) are natural frontages above sea level having intrinsic
nature conservation interest.
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2
METHODS
2.1
General
Fieldwork was carried out between 30/8/2000 and 6/10/2000 by Andrew Henderson,
Richard Carter, Andrew Cross and Elaine Dromey. Surveyors worked in pairs, though
at the beginning of the survey all four surveyors worked together to develop and
harmonize the methodology and set common standards for recording. Where
methodology was adjusted on the basis of this experience the trial stretches of sea-wall
were subsequently re-surveyed to the finally agreed standard.
The survey covered the flood defence embankment (i.e. the sea-wall proper) and the
habitats on either side of it, including the nearer part of the saltmarsh (if any) on the
outer side and the berm on the inner side. The landward boundary was set at the
seaward side of the borrow dyke or other boundary where there was no borrow dyke.
The width of the belt surveyed accordingly varied, depending on the width and
multiplicity of the various habitat features (e.g. trackways, second banks and berms).
It seldom exceeded 50m. In addition the character of land adjacent to the survey belt
on the landward side was recorded (e.g. pasture, arable).
The sea walls were walked in the direction that placed the sea on the left (i.e. chainage
increased in this direction). Besides avoiding possible confusion, this was
necessitated by the computer software. Recording sections were delimited on
pragmatic grounds including the following.

A requirement for easily recognizable start and end points determined by
recognizable physical features (allowing location on maps and facilitating future
relocation of the sections).

A software constraints setting the maximum permissible section length at around
2km.

A software constraint disallowing more than a very few sharp bends in any one
section (this would disrupt registration of data against base maps).
Owing to seasonality there were disparities in the ease with which different species
could be recorded. To find the less conspicuous species it was necessary to have one
recorder walking along the crest of the wall, while another ranged across the inner
face and berm, working in those places that appeared most promising for scarce
plants. This mode of working was adopted throughout the survey. Reasonably
comprehensive recording of the target species along the wall could be achieved,
though it was impossible to examine the whole width closely in places where there
were wide berms or multiple berms.
The majority of data were collected on a Husky field computer using specially written
software adapted by Data Collection Ltd from their highways surveying package.
Additional ecological data were recorded on paper. The sections were measured using
a Trumeter wheel with chainages recorded from accurately located start points. The
wheel is accurate to approximately 1%.
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2.2
Variables recorded
2.2.1
Division across the sea-wall
For data recording purposes the survey belt was divided into six parallel strips as
follows (from seaward side to landward side):
the salt marsh;
the outer face of the sea-wall;
the crest of the sea-wall;
the inner face of the sea-wall;
the berm; and
the edge of the borrow dyke.
The landward habitat use constituted a seventh recording location. The strips were
treated as recording locations numbered 1 to 7 from seaward to landward. At any
given chainage (or over any chainage interval) variables could be recorded in any or
all of these seven recording locations.
2.2.2
Salt Marsh
Characteristics of the salt marsh abutting the sea wall were recorded on the field
computer in recording location 1 as follows.
2.2.3

Grazing levels – high, low or none.

Poaching levels – high, low or none.

Eroding edge – present or absent.

Spartina anglica – if present abundance was noted using the DAFOR scale.
Structural features
Structural features of the sea wall were noted as follows.

Outer wall (location 2 only) – construction type (e.g. concrete, concrete block,
other).

Outer wall (location 2 only) – vegetation cover (high, low, none).

Tracks (locations 3 and 5 only) – surface type (mud, gravel, asphalt etc.).

Saline areas (location 5 only) – rutted or other.

Landward boundary (location 7) – borrow dyke, fence or other.
6/15
2.2.4
Management
Walls were unmanaged, mown or grazed. Areas were recorded as grazed or mown,
not both. Management features of the sea wall were noted as follows.
2.2.5

Grazing (locations 3 to 5) – grass length to nearest 5cm.

Grazing (locations 3 to 5) – poaching level (high, low, none).

Mowing (locations 3 to 5) – grass length to nearest 5cm.

Mowing (locations 3 to 5) – cuttings left or not.

Weed control (locations 2 to 6) – if any, topping or chemical.
Plant species
Species were recorded as present or absent in 100m stretches of sea-wall. Precise
chainages were noted only for rare species (e.g. Lactuca saligna).
The following plant species were recorded wherever they were seen.
Astragalus glycyphyllos;
X Agropogon littoralis;
Bupleurum tenuissimum;
Carex divisa;
Hordeum marinum;
Inula crithmoides;
Lactuca saligna;
Lepidium latifolium;
Petroselinum segetum;
Peucedanum officinale;
Polypogon monspeliensis;
Puccinellia fasciculata;
Puccinellia rupestris;
Torilis nodosa;
Trifolium squamosum; and
Vicia bithynica.
The survey was carried out at an optimal time for the following species: Astragalus
glycyphyllos, Bupleurum tenuissimum, Hordeum marinum, Inula crithmoides, Lactuca
saligna, Lepidium latifolium, Petroselinum segetum, Peucedanum officinale and
Polypogon monspeliensis. There was no difficulty in spotting or recognizing these
species, though some are not conspicuous at the best of times (especially Bupleurum
tenuissimum). The sedge Carex divisa was less conspicuous than in June when the
flowering heads tend to stand erect, but was otherwise intact. The remaining species
were dead, but could mostly be recognized from dead remains (especially the
characteristic fruiting heads of Torilis nodosa and Trifolium squamosum). There is
however a danger that shattered material of these species was being overlooked.
Species not encountered included the following.
7/15

Alopecurus bulbosus which is conspicuous only at flowering in June. It can be
located at other times of the year, but could have been missed in rapid surveys
since close searching of turf would be required.

Trifolium ornithopodioides which grows on sea-wall paths and tracks, and is
virtually indistinguishable from trampled material of Trifolium dubium once
flowering is over.

Chenopodium chenopodioides which could have been overlooked among
depauperate plants of Chenopodium rubrum.
2.3
Data processing
2.3.1
Network and survey files
For each section, the start point and survey line of the field survey were drawn onto
OS digital maps using Fastmap GIS. The survey data were then laid over the
centreline and linked to its chainage. This process allocated a grid reference to all data
points. All data was collected according to centreline chainages, and displayed at the
appropriate chainages but offset to the left or right. In addition, each of the habitat
variables were offset to arbitrarily determined distances to enable clarity of display.
The offset distances are uniform throughout the survey, despite the real variation in
width of wall and berm.
8/15
3
RESULTS
3.1
GIS product
The survey produced MAPINFO overlays of the species and habitat variables on maps
of the sea-walls produced from OS line-data. Thus for any section of sea-wall it is
possible to call up a visual display of the incidence of plant species present, and
further to display this information in relation to the habitat variables recorded. This
GIS tool is the principle output of the survey. It is lodged with the Kent office of
English Nature to whom enquiries should be addressed. It allows interactive
probing of the data set, and in this respect cannot be summarized in a written report.
3.2
Species occurrence
3.2.1
Species groupings
Scarce species tend to occur in distinct parts of the sea-wall habitat complex as
follows.

General short grassland assemblage – short open grassland, often grazed and
poached, or else at the edge of trampled areas, supports an assemblage of scarce
species comprising Bupleurum tenuissimum, Torilis nodosa and Trifolium
squamosum. In one location Vicia bithynica was present. Several modestly
uncommon species not recorded in the scoping survey have their headquarters
here including Lathyrus nissolia and Lotus glaber.

Rutted saline areas – rutted saline areas on the berm support an assemblage of
grasses including Hordeum marinum, Polypogon monspeliensis, Puccinellia
fasciculata and Puccinellia rupestris. The very rare X Agropogon littoralis was
found in this assemblage in one place. More frequently flooded sites with
Polypogon monspeliensis may be the locus for Chenopodium chenopodioides not
found in the scoping survey.

Grassy berms – the only species generally confined to this habitat appears to be
Carex divisa, though Bupleurum tenuissimum and Trifolium squamosum are often
present as well. In one location Astragalus glycyphyllos was present. This may
be the locus for Alopecurus bulbosus not found in the scoping survey.

Outer faces of walls – The swash-bank at the top of walls and cracks in concrete
facings generally support few scarce species, though a number of the more
uncommon species occur mainly in this habitat, including Lactuca saligna and
Lepidium latifolium. Species found in other sea wall habitat components may
occur in small quantity, especially Hordeum marinum and Torilis nodosa.
Several modestly uncommon species not recorded in the scoping survey have
their headquarters here including Anthriscus caucalis and Carduus tenuiflorus.

Paths on wall crests – trampled paths on the crest of the wall often support
Puccinellia fasciculata and Puccinellia rupestris, while the edges of such paths
9/15
often support Torilis nodosa and Trifolium squamosum. This is also likely to be
the locus for Trifolium ornithopodioides not recorded in the scoping survey.
3.2.2

Salt marsh margins – the bottom of the wall is the main locus for Inula
crithmoides which may extend a short distance onto the salt-marsh where
elevations are high.

Miscellaneous – other rarities including Petroselinum segetum and Peucedanum
officinale occur rather indiscriminately across habitat components in the few
places where they occur.
Widespread species
The following species were widespread throughout the three SSSIs – Bupleurum
tenuissimum, Carex divisa, Hordeum marinum, Inula crithmoides, Puccinellia
fasciculata, Puccinellia rupestris, Torilis nodosa and Trifolium squamosum.
3.2.3
Local species
Polypogon monspeliensis was locally common in disturbed saline ground (and to a
limited extent at the edge of adjacent arable fields) east of Gravesend, on the Barksore
Marshes, and especially on the Chetney Marshes.
Petroselinum segetum was encountered in very few places. It was not anticipated that
this species would be so uncommon.
3.2.4
Rare species
X Agropogon littoralis was encountered only on the Barksore Marshes. It was not
found near Kingsnorth where there are old records, though it could easily have been
missed in a rapid survey.
Astragalus glycyphyllos was recorded from mown grass on the berm on the eastern
side of the Motney Hill peninsula.
Lactuca saligna is a Red Data Book species that in recent years has been known only
from two sites at Fobbing in Essex (sea-walls) and Rye Harbour in Sussex (semiruderal habitats). Unconfirmed rumour has it that the plant is no longer to be found at
Rye Harbour, so this species is precarious in the extreme. It is reported that in
summer 2000 plants were recorded by Francis Rose from the Isle of Grain. In our
survey two populations, one large and one small, were recorded in sites over a
kilometre apart on the Isle of Grain, and a third population was located east of
Kingsferry Bridge on the Isle of Sheppey. This brings the count of UK populations
from one or two to four of five (depending on whether the Rye Harbour population is
extant). In this survey the plant was mainly found on the outer face of the sea-wall.
Lepidium latifolium is not generally rare, but was only encountered once in our survey
on the outer face of the sea-wall on the eastern side of the Motney Hill peninsula.
10/15
A single patch of Vicia bithynica was found among a sward consisting almost entirely
of annual legumes on the inner face of the sea-wall west of Seasalter.
3.3
Species distribution in relation to habitat
The data broadly support the impression gained by surveyors in the field that the
scarce species of sea walls are less frequent in two situations as follows.

Recently reconstructed walls, where recolonization appears to be slow even where
there are short open swards maintained by grazing.

Completely unmanaged walls, where swards of the tall grasses Arrhenatherum
elatius and Elytrigia repens exclude most other species.
A factor in the case of reconstructed walls may be the lack of saline areas on the berm
behind the wall (since topover and seepage are reduced) – this excludes the
complement of species associated with the Hordeum marinum community.
Beyond this definite patterns of occurrence in relation to observable current
management are obscure. This may be because factors such as grazing are routinely
varied from year to year according to the availability of grass and other accidents of
the agricultural economy. It may also relate to past periods of neglect or adverse
management leading to floristic impoverishment in some areas that appear suitable,
while elsewhere plants may persist in areas where management is currently adverse.
All of this may make simple relationships between species occurrence and current
management hard to discern.
3.4
Categorizing walls according to species richness
The tables in Appendices show the occurrence of species in 100m stretches of sea wall
throughout the areas surveyed. Walls may be categorized according to speciesrichness in various ways as follows.

The total number of species in each 100m stretch can be found, and parts of the
sea walls with high numbers of species in consecutive 100m stretches can be
identified by inspection.

The same approach may be refined by using the species groupings presented in
Section 3.2.1 to identify parts of the sea walls with high numbers of species in
particular habitat components, e.g. picking out areas that are important for rutted
berm species where short turf species are lacking, so that the areas do not stand
out on the basis of total numbers of species.

A rarity-weighted index may be computed for a section of sea wall using the
formula ‘number of records for species (all species or those in a specified species
group as in Section 3.2.1) divided by the number of 100m sections’.
On this basis the following wall sections (see Appendices) are exceptionally speciesrich across a range of species groups, often with five to seven scarce species per 100m
stretch: Elmley 03, Yantlet 05, Blacketts 01, Allhallows 01 and Allhallows 02. The
11/15
following are only marginally less species-rich: Yantlet 02, Horsham 02 and Murston
02. The following are moderately species rich across a range of species groups, often
with three to five scarce species per 100m stretch : Chetney 04, Minster 01, Yantlet
01, Yantlet 04, Spitend 03, Spitend 04, Horsham 01, Conyer 01 (part) and Teynham
02. Other wall sections may be important for particular species groups.
Some of the rarest species occur in the less species-rich sections, e.g. large Polypogon
monspeliensis populations near Gravesend and on Chetney Marshes, Peucedanum
officinale on Faversham Creek, X Agropogon littoralis on Barksore Marshes, Vicia
bithynica at Seasalter, and both Astragalus glycyphyllos and Lepidium latifolium on
the Motney Hill peninsula.
12/15
4
DISCUSSION AND RECOMMENDATIONS FOR FURTHER SURVEY
4.1
Confirming the scoping survey data
A first priority of the second stage of the survey should be to estimate how complete
the species information from the scoping survey might be. To this end some areas
should be surveyed closely, allowing estimation of the extent to which species may
have been overlooked in the rapid scoping survey. Recommendations for technique
include the following:

Stretches of sea-wall selected should contain sufficient 100m stretches for
adequate statistical comparison – 20 at least, perhaps 30, i.e. 2 or 3km stretches of
wall.

A sample of stretches should be selected on a stratified random basis, so that
different sea-wall types and management types are equally represented in the
sample.

Sample stratification should also ensure that species-poor and species-rich
sections of wall are included in the sample.
Within selected areas, an exhaustive search for scarce species should be made, using
smaller recording sections than in the scoping survey – perhaps 25m. A fuller
description of the habitats present should also be attempted (see Section 4.3.1).
In addition to recording data from a stratified random sample of walls, it would also be
advisable to collect similar data from the places that were in fact richest, according to
the findings of the scoping survey.
There would be some advantage in carrying out the second stage surveys earlier in the
year than the scoping surveys. Surveys conducted during June and July would be
better for several species, especially the widespread species Puccinellia fasciculata,
Puccinellia rupestris, Torilis nodosa and Trifolium squamosum, and worse for very
few (though Bupleurum tenuissimum would be less conspicuous). There might be
some loss of direct comparability with the scoping survey results, but there would be
large gains in respect of the first priority of estimating how complete the species
information from the scoping survey might be. However, if for any reason it were
necessary to conduct the second stage surveys later it would not be a major problem.
4.2
Vegetation
Vegetation may be a better indicator of where scarce plants are likely to occur than
management type, even though management may ultimately control the vegetation. A
possible objective of the second stage could therefore be to identify the vegetation
types in which scarce species occur. It might equally be of value to know what types
they do not occur in. It may well be easier to determine how to manage vegetation
types that provide the locus for scarce species, than to determine what the species
require individually.
13/15
Unfortunately sea wall vegetation is a recognized gap in the coverage of the National
Vegetation Classification (Rodwell et al. 2000). It is probably beyond the scope of a
study on these SSSIs to remedy this. It may however be possible to erect an ad hoc
classification, perhaps identifying types by means of indicator species and
physiognomy, e.g. tall MG1 Arrhenatherum elatius grassland with Anthriscus
sylvestris , ditto without Anthriscus sylvestris, swash-bank community with Anthriscus
caucalis etc. This would give an initial indication of where the scarce species occur in
phytosociological terms.
It is to be hoped that JNCC will urgently support a project to provide sea-wall
relevees for consideration in relation to the National Vegetation Classification.
The findings of the scoping survey could assist in providing justification for such a
survey.
4.3
Habitat niches
4.3.1
Physical niche
Another objective of the second stage could be to identify more closely the precise
niche occupied by each scarce species in the sea-wall habitat complex, and to identify
localities of importance for each species. This may in the first instance be possible
from in-depth analysis of the scoping survey data, provided that further work suggests
that species were not extensively overlooked.
Beyond this it will be necessary to devise improved ways of characterizing the habitat
conditions on the basis of experience from the scoping survey. Matters that especially
need to be addressed include the following.
4.3.2

Characterization of grazing and mowing regimes which cannot always be inferred
from a site visit. Consultation with site managers is required, and better ways of
describing the conditions at the time of survey are also required – perhaps more
objective indices of poaching and dunging and rutting.

A wider range of wall types and structures could be recorded in more detailed
surveys, e.g. double berms, unusual facing types, scrub.
Community niche
For the scarcest species it would be worth identifying the community type by
recording species cover in quadrats targetted on the locations containing the scarce
species.
Appendices:
Appendix 1
Excel spreadsheet of sections surveyed.
1. South Thames
14/15
2. Medway
3. Swale
Appendix 2
Excel spreadsheet of species distribution.
1. South Thames
2. Medway
3. Swale
15/15