The Col de la Pousterle (trail route no. 5)

The track rises gently up the right-hand bank of the Gyronde, on the "ubac" side. The "ubac" is the slope that is exposed to the north, so it is in shadow in winter when the sun is low in the sky.

The cliff is home to a variety of birdlife. The raven, not to be confused with the crow, frequently nests here. He makes an uncomfortable housemate with the peregrine falcon, a bird in sharp decline and still a vulnerable species. It, too, favours this cliff, which offers plenty of potential nesting holes. The wallcreeper, also known as the butterfly bird, also finds this a good nesting spot. Some climbing routes are closed during this bird's breeding season. 

A pousterle (in the local high-alpine Occitan language) is a small gate, a postern. It comes from the Latin posterula which means back door. This place name is sometimes given to a pass, which could be described as a gateway between two valleys! The glaciers carved out this gateway through which an arm stretched between the glacier occupying the Fournel valley and the glacier flowing down the Vallouise valley.

The symbol of the Southern Alps, this softwood tree loses its leaves in winter, and is swathed with gold and lights up the mountains in autumn. The larch forests are maintained by the grazing of flocks. Without them, other trees like the fir or other pine trees could grow, creating a different kind of forest. A pioneer species, the larch establishes freely in light conditions. Its solid rot-proof wood has always been used in the construction of houses. 

Bats don't just live in caves! In summer, some forest-dwelling species shelter in old hollow trees or woodpecker holes during the day. Sometimes, the females also form little colonies here, where their young will be born (one bat pup per female). In this forest, which is still young with very few old trees, artificial roosts have been installed to help the bats and to facilitate their study.

The call of this small, nocturnal bird of prey can be heard in the spring, and also in the autumn when it can utter some peculiar sounds. Active during daytime hours and at dusk, the pygmy owl is a predator of passerine birds and small forest rodents. But when they spot it, passerines will come together in large numbers to mob it, so as to prevent any attempted surprise attack. It is restricted to mountain forests where it seeks out trees with woodpecker cavities where it builds its nest.

The forest tracks are edged with great swathes of a tall plant which has purple flowers arranged in loose spikes. The rosebay willowherb is a pioneer plant and favours road embankments and disturbed ground. In late summer, its very numerous seeds, each with a little plume, float away en masse glowing in the advancing twilight…

A cousin of the common laburnum, this large shrub flowers in June-early July, producing beautiful drooping clusters of yellow flowers. Not very common and only found in the Alps and the Jura, it favours quite dry, airy woods. A beautiful surprise, and heavenly scent!

This small shrub which grows to 1 to 2 metres in light woods is characterised by three-lobed leaves on the flowering shoots which are sessile, that is to say without a stalk. It is easy to confuse with the scorpion senna, which has the same leaves but they are divided into 7 or 9 lobes. Both produce very beautiful yellow flowers in May to June.

The forest is home to roe deer, which can often be seen. This ungulate (hoofed mammal) is rather unusual because the rut does not take place in autumn, for births in May and June as is the case with other mountain-dwelling ungulates, but in summer. After fertilisation, however, egg development is suspended for 6 months (this is called embryonic diapause). Gestation then resumes so that the fawn (or twin fawns) can be born in spring, a period more favourable for its survival.