Crau
The Crau is a gravel steppe in southern France , northeast of the Camargue . Until the last century it was one of the many stone steppes that ran along the Mediterranean coast. All of them were created by the deposition of sediments from large rivers such as the Têt , Lèz, Arc , Gapeau and the Durance . After the last ice age , the gravel surfaces fell dry and the steppe-like landscapes, the Craus, emerged. Today, after the ongoing destruction of these areas, only the Crau d'Arles remains as a large, contiguous area. Much of the remaining area is in the triangle between Arles , Salon-de-Provence and Fos-sur-Mer .
Emergence
Until about two million years ago, the area of the Crau was still below the surface of the present-day Mediterranean Sea. The area was covered with waterproof, gray clays during this phase. After the sea had withdrawn, the Durance flowed into the sea with a large delta, the "Vieille Crau" was created by the slow pile of gravel and gravel that the Durance carried with it from the Alps. The Durance blocked its way through this gravel and shifted its course to the southeast. There the river enlarged its delta and, as before, again poured gravel and gravel from silicate rocks from the Alps, the "Crau de Luquier" and "Crau de Miramas" formed (120,000 and 70,000 years ago, respectively). The Durance changed course for the last time 12,000 years ago and continues to flow into the Rhone to this day . Through this "migration" of the river, as well as the accumulation of rock material, the 600 km² Crau was created over a long period of time.
ecology
There are various ecological influencing factors that have a lasting effect on the Crau.
water
Water has been an important factor right from the start. It applied the very water-permeable gravel so typical of the Crau. A special feature of the Crau, however, is that the gravel and pebbles form a concrete-hard conglomerate (taparas), some meters thick, at a depth of 40 to 60 cm using a calcareous binder . This geological feature is very important for the special water balance in the Crau. It means that the water from the groundwater reservoir is not accessible to the plants and animals of the Crau. Due to this limited water supply, hardly any tree growth is possible, only where the conglomerate layer is naturally weathered and holes appear. The groundwater can then reach the surface through these “laurons”. This geological peculiarity is also evident outside of the Crau. Where the taparas ends, there are strong pouring springs that cause large-scale swamping in the north. This can also be seen in the vegetation, which changes suddenly. The dry Crau is more like steppe-like, while the wet Crau is overgrown with trees and bushes, because there the taparas is deeper in the ground and more water can hold in the ground.
climate
A second important factor for the Crau is the climate. The Crau lies in the Mediterranean climate zone , which means hot summers and mild winters for this landscape. The average annual temperature is 14–15 ° C; there are partly frost-free zones in the Crau all year round. A special feature in summer is that the Crau is warmer than the surrounding areas, as the sun heats the stones during the day. This means that they serve as a heat store and release the stored heat again at night. This special microclimate is important for plants and animals as well as for agriculture. Nevertheless, because of the cold north winds, there is at least one cold month a year that is colder than 7 ° C on average.
wind
The wind is also a big factor in the Crau. The mistral is dominant here . It is caused by canalization effects in the Rhône Valley and is a cool and dry north wind that can reach speeds of 50–150 km / h. It blows up to 110 days a year and can cause temperature drops of up to 10 ° C. It also drives away the clouds and thereby increases the number of hours of sunshine (3000 hours per year) in contrast to Paris with 1780 hours of sunshine per year. The mistral also shapes the cultural landscape, as the farmers plant hedges to protect the fields, which are supposed to break the wind.
Precipitation
Due to the lack of groundwater, precipitation plays an important role in the Crau. The 500–600 mm precipitation per year falls mainly in autumn and winter, ie outside of the growing season . In summer there is only little precipitation and there is a high rate of evaporation, some of which exceeds precipitation. Therefore 3–4 months of the year are arid. This lack of water is a limiting factor for animals, especially when in some years only 300–400 mm of precipitation fall per year.
Use by humans
Sheep farming
The main cultivation of the Crau is sheep farming . The Crau was used as a sheep pasture by humans at an early stage . This began 10,000 years ago and is proven by bone finds. However, the shepherds stayed in the outskirts of the Crau, as they felt the stone desert was threatening. Therefore the Crau was hardly used until the 11th century. Sheep farming then became more and more economical. Especially after the irrigation has created green areas in the Crau. Since it is too hot for the sheep in summer, they were herded to pastures in the Alps . From this uplift, the shaft drive between the Crau and the Alps, the transhumance , which still exists today, arose . Nowadays sheep farming has largely been given up, the former shepherds are now farming in the Crau, with which they promote its destruction. The grazing of the Crau by sheep is still important today to keep the grass in the steppe short and thus to preserve the habitat for the Triel . Where the sheep do not or hardly graze, the grass grows tall. There you can find the habitat of the little bustard .
irrigation
The irrigation of the Crau began in 1559 with the first large irrigation canal that led from the Durance into the Crau. It was planned by the engineer Adam de Craponne . A little later, extensions to the east and west were built. Until the 19th century, the extent of the Crau was only very slowly reduced by irrigation, there were still 500 km² of the originally 600 km² Crau available. At the end of the 19th century, the Compagnie Agricole de la Crau , which still exists today, is founded. Its aim was to drain 4000 hectares of swamps near Fos-sur-Mer and to make the Crau fertile with nutrient-rich water from the Durance. But it turned out that it was too expensive to fan the Crau with canals; the plan was rejected. Irrigation has advantages and disadvantages for the Crau. The species spectrum of the plants is increasing, they can grow better. The growth of plants creates new habitats for other animal species, which also benefit from irrigation. In addition, the new green spaces increased the profitability of sheep farming.
Agriculture
The first attempts at intensive agriculture began as early as 1965. The farmers planted large melon fields in the Crau and irrigated them with nutrient-poor groundwater . The soil was washed out and the farmers had to keep moving their fields. Thus, these areas of the natural Crau are destroyed because the taparas was partially blown away to get to the groundwater. In 1970, 26,000 hectares of the 53,000 hectares that could be irrigated were irrigated. Since the early 1960s, the irrigation of the Crau can no longer be rated positively. The sheep breeders are being displaced more and more by intensive fruit growers. Due to this massive destruction in 1980 only 150 km² of the original area were left. This remaining area is also at risk, as peaches are now grown instead of melons. Another problem is dry farming . It is used to grow feed grain for meat sheep and is limited to temporary cultivation areas. This type of agriculture does not irrigate, but removes stones and plows the soil. The microclimate of the soil, the soil structure and the water balance are severely disturbed. The only known dry field cultivation in the Crau that worked without major damage and also provided a habitat for birds was almond tree plantations .
Destruction of the Crau
There are many different aspects that drive the destruction of the Crau. In addition to irrigation and agriculture, there are many other causes of problems. For example the adjacent industrial areas. The industrial area of Fos-sur-Mer connects directly to the Crau in the south . Since land prices in the Crau are low, some see the Crau as a building land reserve. One example of this is the BMW test track that was built in the Crau. The area that was used for this was the breeding area of a calender lark colony that no longer exists.
It looks similar with the garbage dump in Marseilles . It is located in the middle of the Crau, because the land there is cheap and far from the city. However, it is not known whether the toxins from the landfill leachate get into the groundwater. In addition, the garbage is blown far into the Crau by the mistral and pollutes it widely. Another problem is that the area of the Crau is cut off from the surrounding area by roads, sometimes even cut up. As a result, the animals can no longer move freely in the Crau. In addition, they are severely disturbed by the noise from road construction and traffic noise. In addition, the taparas is destroyed during the construction of the roads, whereby the water balance along the road route is forever destroyed, even if the road is no longer used. Problems for the animals also arise from hunting. Traps that are actually set up against martens and rats are also dangerous for the protected animal species in the Crau. Also the tourism is disturbing, especially in the breeding season. The well-camouflaged eggs of ground-breeding birds can hardly be distinguished from their surroundings; the clutch can easily be trodden on.
natural reserve
After long work by various institutions, the Crau is now under the protection of UNESCO . Since 2001, ¾ of the remaining 10,000 hectares have been classified as “Reserve naturelle”. The Crau is important as a passage area for many migratory birds and as a habitat for endangered species such as the billy grouse , the little bustard , the triel , the red hawk and the pearl lizard . The nature reserve was created with the help of donors from Euronatur , donors from France and the local nature conservation association, the CEEP. The support is provided by the CEEP and environmentally friendly farmers in the region. The conservation activities are coordinated from the Écomuseé in Saint-Martin-de-Crau .
Mediated by Euronatur, Markgröningen in Baden-Württemberg and Saint-Martin-de-Crau entered into one of the first “environmentally oriented” town twinning in 1989 . There are large nature reserves in both municipalities. In addition, like Saint-Martin-de-Crau, Markgröningen was once a " Mecca " for regional shepherds. The city administration of Markgröningen has published a “NatUrlaub” travel guide for excursions around the twin city.
literature
- Andreas Megerle, Jürgen Resch: The Crau - stone steppe full of life . Verlag Jürgen Resch, Radolfzell 1987
- NatHoliday around Saint-Martin-de-Crau. Travel guide to the environmentally oriented city partnership . Ed .: City of Markgröningen (2nd edition), Markgröningen 2003
Web links
Coordinates: 43 ° 34 '14.9 " N , 4 ° 51' 15.9" E