This I did not know:

The Friends of Shoreham Beach do a lot of work to help look after Shoreham Beach and to show people how special the vegetated shingle habitat is. They raise awareness about the damage people do to the plants without realising. For example, people throw garden rubbish on to the beach.
As these grass cuttings and other garden debris decomposes it makes soil. This means other plants and weeds from the gardens grow on the beach and can take up space that the shingle plants need.

From the informative blog of Ed the Bear.