The ecology of Pacific Northwest coastal sand dunes

can take two forms: either a long,
narrow trough with a moving pi1 e of
sand at its head (a possible incipient
parabola dune), or a
saucer- shaped bowl with sand pi 1 ed
along the lee side. The size of a
blowout varies considerably, from a
few square me&ters in area to several
hectares. As troughs or bowls enlarge
they may join wit11 other
blowouts, resu'l ting eventually in a
sand plain, or the blowouts may
sirlrply became revegetated. Where
there has been a history of blowout
fornation and stabil ization, the
grot~nd surface is very i rregul ar.
Sand Plain (Figure 21)
Sand plains are large, relatively
level or gently sloping
areas of sand, The surface may be
i rregular, but changes in re1 ief are
not great unless other dune forms
occur on the plain. Generally the
sand plain occurs between the beach
and the beginning of the icetention
ridge. It is a broad expanse of
sand on which other dune forms
(transverse ridges, sand hummocks,
etc.) develop if conditions of wind
and sand supply necessary to the
formati on a particular dune form are
present .
In general the sand plain is
dry with the water table some
distance be1 ow the surface. The
establishment of vegetation is a
slow process. Only if sand movement
is reduced will species tolerant of
some degree of sand covering become
established, leading eventually to
full vegetation cover. Reduction in
sand movement on a sand plain might
be due to the she1 tering effect of
nearby developing vegetation or to
the trapping of sand farther downwind
by developing vegetation.
Deflation Plain (Figures 13 and 22)
--
In certain areas, the wind
erodes the sand surface close to the
water table, resulting in a wet sand
surface very resistant to further
61'gure 21. Sand plain forfiled to
windward of orre of the large parabola
dunes at Sand Lake, Locality 9.
The red fescue--dune goldenrod cammunity
is stabilizing the area.
Note scattered lodgepole pine becmiwg
established in the open area.
Septmber , 1954 *
Figure 22, Deflation plain fomd
at the windward base of a large
parabola dune at Sand Lake, Locality
9. The lowest part of the deflation
plafn is on the right, where part of
a marginal ridge is visible. A
forested remnant of an earlier marginal
ridge is seen on the left. On
the horizon is Haystack Rock at Cape
Kiwanda April, 19M.