- What is a temporary pond ?

A temporary Mediterranean pool or pond (scientific name: endorheic habitat) is an aquatic habitat whose identifying feature is that it dries up completely during the summer. It owes its existence to the whims of the Mediterranean climate, varying between the droughts of summer and the winter rains.(See first diagram, compare photos A and B) .
It sits in a shallow basin, with gently sloping sides. The impermeable nature of the hollow means that it stores the rain which falls on or trickles into it. It can take a variety of forms and surface areas (from 1m² up to 5 or 6ha). Other names for such ponds are: cupule, pool, brooklet or even lake. In the Roque-Haute Reserve, the largest temporary pond is about 2 500m², while the smallest is just 1m².

- Origin

A temporary pond can be formed in many ways: naturally, by undulations in a lava flow or erosion of impermeable soil, and artificially, say through old quarrying. At Roque-Haute, most of the hollows where ponds accumulate were hacked out by man, in the Middle Ages, to supply volcanic rock for building.

- The life cycle of a pond: from floods to drought (See second diagram)

Water supply :
The temporary ponds in the Reserve receive their water supply from rainfall alone. The water in some of the ponds drains off underground into adjacent ponds by trickling though cracks in the basalt, following the slope of the land. From autumn to the start of winter is the moment, then, when the ponds fill up. The spring rains may add a further supply, prolonging the period of submersion.
Water losses :
The temporary ponds then dry up in the summer. They lose their water in several ways :
- the water drains away into the soil at a rate determined by the nature and thickness of the sediment accumulated in the bottom of the pond; some of the ponds lose their water to other ponds by lateral seepage
- water starts to evaporate as soon as it gets warmer, with transpiration via the plants themselves contributing to the drying-out phenomenon
- the presence of trees in or around the edges of the ponds tends to encourage water loss via the root system and thence by transpiration through the leaves, though the shade they provide acts in the opposite direction.
It is this repeated sequence of submersion followed by drying out that makes the temporary pond habitat such an unusual one.