Succession is a process which operates through time. Because
this is a slow process, change in soil and vegetation at any one
location from bare sand to a late stage in the succession such as
dune heath will take 100s of years. However, because the dunes near
the coast are young and mostly become progressively older through
time it is possible to use distance as a surrogate for time.
As you walk from the strand line inland you will walk from young
to old dunes. Remember that you will not always find this simple pattern. Blowouts may occur and create new surfaces
within the dunes. On an eroding coastline, such as Formby Point, the dunes at the top of the beach
will not be newly formed; they might have a well-established vegetation
cover with a measurable soil organic horizon. Immediately landward
of these eroding dunes there may be newly deposited sand which the
wind has picked up from the eroding face of the seaward side of
the dunes. Dune slacks may be encountered;
these patches in the dune landscape are following a different successional
pathway to the dry dune succession. Dune slack succession starts
on wet sand. A transect is the best technique to use
for the study of dune succession. Starting from the strand line
a line is established at right angles to the shore. A compass can be used to take a bearing along the line. A tape is set
down along the line of the transect. The vegetation can be sampled
at intervals along the line by using a quadrat. You must
carefully decide the following in the design of your study of succession
along the transect line:
- How big should the quadrat be? (one metre squared is a suitable
size) What distance should there be between the quadrats along the
line of the transect? (the quadrats may be continuous along the
line, a belt transect, or they may be as much as 20 or
30 metres apart). Should the distance between the quadrats be the same every
time or might you, for example, increase the sampling distance
as changes become more gradual?
- What are you going to record in your quadrat? (this might be
percentage vegetation cover, percentage cover of each species
identified in the quadrat, amount of bare sand, colour of the
sand)
A clinometer or similar instrument may be used in conjunction
with the tape to record a profile of the dunes along the transect
line. Read about using a transect in your text books to help you
design your study of succession. |