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To conclude this chapter something must be said concerning the highly characteristic collection of ephemeral plants which often appear on the relatively bare sand of partially fixed sand-dunes. Very few of these species are confined to the coast and most of them are liable to turn up in waste ground anywhere. In marked contrast to the majority of perennial dune plants, these annuals have quite shallow roots, and a depth of more than 6 in. is unusual. A diagram of the root systems of some typical dune annuals is shown in Fig. 12 (N.B. 15 cms. = 6 in). These roots are devised to utilise the surface-water only, and it may be pointed out that such small amounts of humus as have accumulated at this early stage will be found near the surface.

FIG. 12.—Root-systems of dune-annuals (from Fritsch & Salisbury, 1946). a. Myosotis hispida; b. Cerastium semidecandrum; Phleum arenarium.

In this connection it is worth mentioning that these “ephemerals” often occur more thickly near rabbit droppings, which have locally provided some additional humus. The surface-sand rarely remains moist sufficiently long during the summer months to enable such shallow-rooting plants to exist, and they aim at completing their life-cycle while it is still damp from the winter and spring rains. They may be described as “drought-escaping” plants, but are more usually referred to as “winter annuals,” since they germinate in the autumn and persist as small seedlings through the winter. In early spring they start to grow quickly, then flower, and finally set their seed before the heat of the summer makes their habitat untenable. Their life-cycle comes to a rapid end with the setting of their seeds, and by the middle of the summer only their dried-up remains can usually be found.

Winter annuals are much more in evidence on the surface of dunes in some years than in others. Should an unusually long dry spell of weather occur in the late autumn, or should the surface be seriously disturbed by a series of especially violent gales when the seedlings have just germinated, most of next year’s population may well be blotted out. They are, however, mostly common plants with light seeds, which are widely distributed by the wind and, granted favourable conditions for their germination, can generally be found in abundance in a bare habitat like this, where there is little competition from taller plants. Typical examples are whitlow-grass (Erophila verna