IT’S NOT SPARTINA!
Firstly, we want to clear up a common misconception; that “the beach is covered in Spartina”.
Being able to identify the difference between these grasses is important to understanding what is happening on the beach at the moment. Next time you’re out on the beach go have a look and see if you can identify these two species. There are others, but Puccinellia is by far the most common.
Figure 1: This is Common Saltmarsh Grass (Puccinellia maritima), a native species that establishes naturally as a pioneer dune grass. It’s by far the most dominant grass on the foreshore. It is generallly an upper marsh species so it thrives ABOVE mean high water.
Figure 2: Common Cord Grass (Spartina anglica), an invasive species that is much less prevalent than in previous years, in large part because of the drier conditions on the beach as the beach level rises. As a lower marsh species it thrives only BELOW mean high water.
Figure 3: Common Saltmarsh Grass (Puccinellia maritima) after spraying in 2019. This would under normal circumstances quickly accrete windblown sand into "hummocks" which go on to form embryo dunes, but was not able to do so in 2019. However in the 2020 and 2021 growing seasons it has been able to trap large volumes of sand as the hummocks grow and join together.
Figure 4: Common Cord Grass (Spartina anglica); the only grass that survived the spraying aimed at eradicating it in August 2019. Spartina is a lower saltmarsh, not an upper marsh dune species. It does not survive well above mean high water. Suppression of dune formation prolongs favourable conditions for Spartina. Spartina has a very high Ellenberg (salt tolerance) value.
SPARTINA – PUCCINELLIA COMPARISON
Non native Common Cord Grass (Spartina anglica) has upright, spiky, dark green leaves with a 'v' shaped cross section profile if cut; a kind of supercharged lawn grass. Its strong, circular profile stems grow tall and straight and bear lightweight pale coloured flowers in late Spring / early Summer. Spartina has a high Ellenberg (salt tolerance) value and thrives in lower marsh conditions (BELOW mean high water).
The native Common Saltmarsh Grass (Puccinellia maritima), by contrast, has a round profile for both stems and leaves, like extended chives. Stems eventually become red; both stem and leaf are straggly, spreading horizontally across the sand. Both Spartina and Puccinellia are good sand accretors. Puccinellia has a much lower Ellenberg (salt tolerance) value than Spartina and thrives best in upper marsh conditions (ABOVE mean high water).
WHY THIS MATTERS
The shift from the dominance of lower marsh favouring Spartina anglica to the dominance of upper marsh favouring Puccinellia maritima is a clear indicator of accretion at the upper beach as it shifts from lower marsh to upper marsh conditions.
This is explained in figure 32 on the geomorphological survey page.
The presence of Puccinellia across most of the beach clearly shows that most of the upper beach is now above mean high water; this "tipping point" has been reached only very recently.
Since the gradient of the beach is very shallow (about 1 in 300) any rise in beach height leads to the mean high water retreating by a factor of 300 times that.
Since the beach rises vertically by around 2.5 cms per year, this means mean high water retreats by up to 7.5 metres per year. This estimate is confirmed to be accurate with LIDAR data shown on the beach profiles page.
The change in beach level and the resultant shift from fine, silty (muddy) deposit to larger grained dry sand is also a clear indicator of a shift from dominance of waterborne silt deposition to aeolian (windblown) sand deposition as a result of that accretion; and that has been accelerated by the relatively recent completion of the filling of the Hoyle Lake.
In other words, it is VERY significant and relevant that Spartina anglica is no longer the dominant species on the upper beach.
Furthermore, mean Ellenberg value decline across the beach is a further indicator and this is explained on the botanical survey page.
Now, more than at any time since the promenade wall was built, is the optimal time to allow Puccinellia maritima to colonise the upper beach: to monitor how much sand it traps; how and where dune succession takes place; and how then to balance the various needs of the environment and of the community.
Understanding and recognising this fundamental change is critical.
If we remove the Puccinellia maritima now, we not only remove the required baseline for meaningful studies, making them meaningless, we exacerbate windblown sand problems, and render it impossible to make any well informed future beach management decisions.