D
unes are a world of constant
change and movement, and
must surely be the most
mobile of all the UK’s land
habitats. Peppered along
stretches of our coastline, with a distinct
westerly and northerly bias, they must also
represent one of our least modified and
therefore most ‘natural’ vegetation types.
Typically, dunes are characterised by
ridges or hillocks of sand beyond the reach
of the highest tides, and usually run in
bands parallel to the sea. Among them are
low-lying depressions, called slacks. Dunes
also tend to become progressively taller
and more vegetated the further from the
sea you go.
Britain’s oldest dune systems date back
9,000 years, but all coastal dunes form thesame way. Sand is bl wn onto the beach
before becoming trapped byeither
debris or plant material justabove
the high-water mark.The steadily
accumulating sand then begins
providing habitat fora limited
cast of tough, trailblazing
plants, such as sea saltwort,
sea sandwort and sand couch.
As these hardy, specialised
pioneers become ever more
engulfed by sand, they in
turn give way to classic dune
specialists such as marram
grass, which grows quickly
to ensure it doesn’t become
swamped, while also
stabilising the duneswith
its strong, stable root.As we move inland, further along the
‘duneconstruction conveyor belt’, we start
toseeolder, more stable dunes, known
asfixeddunes. Here, the slow build-up
oforganic matter from dead plant
material, and a corresponding drop
insalinity, results in finer grasses,
herbs and even bushes.
Tofurther complicate things,
‘blow-outs’ sporadically occur.
A blow-out forms when the
wind is able to exploit weak
points in the dune system,
scouring out sometimes
quite large areas, often right
down to the water table.
Ultimately, this can result
in the formation of low-
lying slacks with a diverse16 BBC Wildlife May 2020WILDLIFE WATCHING
In his series of great places to watch wildlife in the UK, the star of BBC
One’s The One Show this month shines a spotlight on why we should
all be fond of sand dunes and the ora and fauna they support.MIKE DILGER’S
SAND DUNES
IN MAY