The natural environment
The Haute Vallée de Chevreuse Regional Natural Park is part of the sedimentary unit of the Paris Basin. Its ecological and landscape characteristics are closely linked to its specific geological features, but also to past and present human activity.
A bit of Geology
The sands of Fontainebleau represent the most important visible deposit, which sometimes can reach a thickness of more than 70 metres. They rest on impermeable layers; sandstones have formed on top of these deposits. Thus, the region has known several flooding periods that lead to these different deposits. The limestone deposits from the end of Tertiary (the last sea recession) and the clay deposits have resulted in characteristic formations on top of the sandstones, millstone clays and millstones. In Quaternary, this flat landscape was cut by important erosions into becoming the present relief: a line of plateaus deeply cut by narrow valleys. The northern versant is steeper than the southern, the first been fully exposed to south and subject to frosting and defrosting, while the later remains longer in the shadows. The sandstones thus freed by erosion crumble in great chaos. Vegetation developed on these formations according to preferences (light, temperature, soil, humidity, etc.), or influenced by humans!
Water and valleys
With 160 hectares of closed water (ponds and wallows) and about 90 kilometres of river, water is omnipresent on the territory. Mérantaise, Rhodon, Yvette, ru des Vaux, Rémarde, Gloriette, Rabette, are winding through the country side. Steep ravines, valley bottoms with linear afforestation, wetlands, wallows, grasslands and reed beds inhabited by birds form so many ecosystems, so precious in Île-de-France.
Forests
The forested areas represent 40% of the Park's territory. Close to two thirds are private forests, constituting mainly large production properties but also hunting grounds. The forests of the plateaus are exploited, while the versant and ravine forests are natural habitats for wild landscapes.
Agricultural plateaus
The agricultural plateaus, resting on a layer of sand covered by silt, create wide horizons enlivened by built shapes. The plateaus, not too stretched, penetrate the Park's territory through all sides. Agricultural space covers about 40% of the Park's territory. 115 sites of ecological interest were defined depending on diversity and sparsity of inhabiting animal and plant species. In total, more than 950 superior plant species were counted.
Natural habitats
Geology, hydrology, and the relief have created the most remarkable natural habitats. Presently, we believe that the wetland and aquatic areas, and the open spaces of not overexploited prairies accommodate the majority of patrimonial fauna and flora of the territory. Humans, by their acts and eco friendly usages are guarantors of this inheritance.
Species
The Park has made an inventory of its territory's natural environment in 1995, which resulted in a map of ecological units. This shows a great variety of open and forested environments. Presently, the Park has, among others: More than 950 superior plant species
• 111 nesting bird species out of 273 counted in France
• 21 batrachians species out of 28 present in Ile-de-France
• 44 dragonfly species
• 46 mammal species
• 21 reptile species
• more than 700 coleopteran species
115 sites of ecological interest were defined depending on diversity and sparsity of the inhabiting animal and plant species. Thus, regarding vegetation,
• 200 plant species of patrimonial value:
• 45 protected species (10 at national level and 35 at regional level)
• 20 very rare species in Ile-de-France
• 57 rare species in Ile-de-France
• 98 quite rare species in Ile-de-France
This considerable natural patrimony places the territory of the Park among the first of ecological interest sites of Ile-de-France, with the Fontainebleau forest, Seine's loops towards Moisson, and the Vallée de la Bassée.
