The Dranse delta: moving with the waterflow

Summer Lilac (1) often confused with Common Lilac (2), Canadian Goldenrod, Himalayan Balsam, Black Locust, or even Japanese Knotweed colonize the banks of the Dranse river! Japanese knotweed, for example, spreads very quickly by little spots or even invades very large areas.

In this case we speak of invasive plants, growing to the detriment of the local flora and doing potentially harm to the fauna diversity! Humans are the main vector of these invasions. Asters CEN74, manager of the nature reserve, as well as the SIAC, in charge of river management, therefore carry out actions for the preservation of these ecosystems by limiting the invasion of some of these plants.

Acrobatic and hyperactive, tits never stop searching for insects in summer and seeds in winter. They need, every day, to find approximately the equivalent of their own weight in food!
The tit family includes many species, 5 of which are present in the nature reserve of the Dranse delta: the Great Tit, the Blue Tit, the Long-tailed Tit, the Coal Tit and the Marsh Tit.

Orchids implement selective strategies to attract insects that will ensure their pollination.

The flowers have various morphologies, adapted to the type of the targeted insect: the production of nectar attracts butterflies while a short spur is more intended for bees and bumblebees. Some orchids are even more specialized, taking, by mimicry, the shape of a female insect. A male will try to mate with the flower, attracted by the shape but also by the smell, perfectly imitating the female pheromones!

From May to July, you may observe the Bumblebee Orchid (Ophrys fuciflora) which imitates bees, the Military Orchid (Orchis militaris) which attracts and guides insects and the Midge Orchid (Gymnadenia conopsea) which attracts butterflies!

The nature reserve, a true haven for many migrating birds.

Mallards, Eurasian Coots and Tufted Ducks can be seen all year round and are joined by other species depending on the season. In winter, the pond welcomes Northern Pintails, Green-winged Teals, Little Brebes and Great Cormorants. In spring new visitors arrive such as Night Herons, and more specifically the Black Kite. The population of this raptor at the the lake of Geneva is the largest in Europe!

During the summer, the pond of Saint-Disdille is the only nesting location for the Black-headed Gull in the area around the lake of Geneva (including Switzerland).

Ecological corridors create connections between natural or agricultural environments, providing favorable conditions for movement and the fulfilment of life cycle. Hedges, grass strips or forests along rivers are essential for biodiversity.

An alluvial or riparian forest (ripi = bank; sylve = forest) is located along the Dranse river. This kind of ecosystem grows on alluvium deposited here and there by the river according to the floods. It is in permanent connection with the river and its groundwater(different from the water table) and is present at shallow depth. Disturbances (floods, erosion, water table fluctuations) play an essential role in the distribution of plant species.
Closer to the river, willows, alders, birches, black poplars don't always have time to grow as they please!

Wild black poplar is the dominant species in forest vegetation along river banks. It has many ecological benefits in these ecosystems, but it is threatened by the development of river banks and by potential hybridizations with cultivated poplars. The INRAE institute and the ONF organization coordinate the national program for the conservation of the genetic resources of this species, and the Dranse river is one of the major sites of the program.

A pioneer species, demanding in terms of water and light, the Black Poplar grows very quickly and has a great longevity (up to 200 years). It grows among riparian vegetation (alluvial forest) and is closely linked to river dynamics.

Did you know that the packaging of certain cheeses and fruits as well as crates are made from cultivated poplar?

You are facing the lake of Geneva, standing on a beach that is remodeled over the seasons. With its dimensions - 73 km long and 14 km wide -, it is the largest alpine lake in Western Europe. Of glacial origin, the lake occupies a depression created by the retreat of the Rhône glacier which was present a few thousand years ago.
This lake has affluents such as the Rhône river and... the Dranse river, which mouth is located here. The delta changes its appearance according to climat events, seasons, transport of sediment load and of course, the dams and other weirs upstream.
Did you know that lake of Geneva supplies drinking water to more than 850 000 people?

Two or three families, i.e. eight to fifteen individuals, live permanently in the nature reserve. The beaver leaves evidence of its presence: bevelled branches, burrows...

It leaves its lodge preferentially at dusk, watching over its territory on both riverbanks. Water is indeed an essential element for beavers: to protect the entrance to its burrow, to flee danger, to transport the branches used for building and to feed on. The largest rodent in Europe, the beaver is perfectly equipped for swimming: it can stay underwater for up to 15 minutes without breathing, translucent eyelids protect his eyes as if it had diving goggles and its webbed feet on the hind legs and its flat tail provide respectively thrust and rudder abilities.