The North Thames Estuary & Marshes area was surveyed by RSK Biocensus Ltd in 2023 to determine the extent and type of saltmarsh habitat present and collect evidence to assess the case for designation as a Site of Special Scientific Interest (SSSI). The survey used the National Vegetation Classification (NVC) to identify and map vegetation types to sub-community level.
Natural England’s normal approaches to vegetation complexity were adopted, allowing mapping to NVC types and where necessary intermediate types or mosaics involving no more than two NVC types.
In the lower marsh, the principal NVC types were found to be ‘SM6 Spartina anglica salt-marsh community’ and ‘SM11 Aster tripolium var. discoideus salt-marsh community’. Communities with annual Salicornia species and Suaeda maritima were uncommon. There was often ‘SM10 Transitional low-marsh vegetation with Puccinellia maritima, annual Salicornia species and Suaeda maritima’ at the ecotone between the lower marsh and the middle marsh. In the middle marsh ‘SM13a Puccinellia maritima salt-marsh community, sub-community with Puccinellia maritima dominant’ was the only SM13 sub-community in any quantity, and its presence was localised.
Most of the middle marsh was occupied by ‘SM14a Halimione portulacoides salt-marsh community, sub-community with Halimione portulacoides dominant’ or by variants of SM14 close to SM14a with unusually large amounts of either Tripolium panonnicum var. flosculosus (towards the lower edge) or Atriplex prostrata or Juncus gerardii or Juncus maritimus or Elymus athericus (towards the upper edge).
The upper marsh was mostly ‘SM24 Elymus pycnanthus salt-marsh community’”.
On the landward side of the seawalls communities of halophytes and glycophyteswere described as non-NVC vegetation in the Puccinellio-Spegularion alliance are present. They contain scarce species including the grasses Hordeum marinum, Polypogon monspeliensis, Puccinellia fasciculata and Puccinellia rupestris.
The saltmarshes of the survey area provide a large resource of vegetation types that are typical of and in a significant degree special to the inner Thames estuary.