Rocky grasslands on basic soils – gravel bars
Alysso-Sedion albi
Rocky grasslands proliferate on weathered rocky surfaces or on sandy substratum on carbonate or silicate soils with frequently occurring erosion. In the lowlands, this habitat type is manifested largely in the form of gravel bars. These are shingly or alluvial river sediments (pebbles of different sizes, rough and fine sand) carried and deposited by the river with its transportation power. Gravel bars are temporary and distinctly dynamic habitats, given that rivers carry away material during high waters and deposit new materials in the same place. In spite of the occasional plenitude of water, natural habitats are extremely dry, warm and sunny, with meagre nutrients and shallow soil as a rule. Consequently, plant communities consist of annuals and succulents. The majority of gravel bars are formed on the inner parts of meanders, whereas on the outer parts the material is carried away by the river flow. As soon as material is deposited in the middle of the river channel, the river flow splits into a few smaller courses.
Threat factors
Currently, the river’s dynamics is totally transformed owing to the greatly reduced bed load caused by consolidation of its banks and erection of hydroelectric power plants. The flow of gravel over the dams has practically stopped. Consequently, gravel bars are being increasingly overgrown with vegetation and several animal and plant species have already lost their habitat. The situation has been additionally aggravated by the illegal and uncontrolled misappropriation of gravel.
Project activities
The gravel bars’ conservation status is to be improved by measures to stimulate hydromophological processes as well as by removal of overgrowth from the bars and reestablishment of gravel mobilization. To raise people’s awareness regarding the significance of preserving gravel bars and natural river processes, educational interpretation point is to be set up.
How can we contribute towards the conservation of habitat types and their species diversity?
- By not misappropriating gravel from gravel bars.
- By not disturbing birds breeding on gravel bars in spring and early summer.
Did you know?
- Removing of overgrowth from gravel bars not merely restores valuable habitats for several animal and plant species, but also contributes towards greater flood safety by greatly increasing the riverbed’s flow-through capacities.
- Alluvial gravel functions as a filter that purifies water both mechanically and chemically.
- The Drava’s gravel bars are the most important breeding grounds for the following two endangered bird species in Slovenia: Little Ringed Plover and Common Sandpiper. These birds lay their eggs in a little hollow in the midst of gravel and line it with remains of woody plants. The Little Ringed Plover builds its nest near a large stone or a small plant, which function as signposts for the parents to find it easier over and over again.