Rocky Habitats
Rocky Habitats of Velebit
At first glance, rocky habitats appear naked and desolate, far from being a favorable habitat for wildlife. Plants need soil and water for life, and animals need food and shelter, none of which is provided by rocky ground. Nevertheless, rocks are inhabited. Even seemingly bare rocks are often covered with dry and hard lichens. A more careful look at the surface of the stone reveals, occasionally spotted, patches of gray, green, yellow, orange or pink. These are lichens, some of the toughest life forms on earth. Lichen is not a uniform organism, but a close community of two or more organisms, of which one is a fungus, and the others are algae or cyanobacteria. Algae produce nutrients through photosynthesis, while fungus builds the body of the lichen, which protects the algae. Lichens absorb moisture and other nutrients from the air, such as nitrogen, and need only air, sunshine and rain to survive. In addition, lichens are able to survive long periods in a dry, motionless state. Lichens can photosynthesize and grow only when they are wet, which is why their growth is very slow. This allows them to survive in hostile habitats such as the rocky ground or tundra. Since they depend on the quality of air, many species of lichens are important indicators of air quality – they serve as bioindicators. Lichens of the Northern Velebit National Park have not yet been systematically researched.
Nevertheless, rocky ground can provide more hospitable places for life than bare rock surface. Karst terrain abounds in rock crevices, where soil and water collect. Being partly protected against sun and wind, crevices provide home for many plant species. Some cracks are even big enough for a tree to set roots in. Rock plants growing under such conditions have to be extremely hardy and well-adapted to their environment. Apart for soil and water scarcity, plants in rocky mountain areas must be able to endure a number of adverse climatic conditions. Because the air is less dense at high altitudes, the sun is very strong in summer, and during inclement weather or at night temperatures drop close to, or sometimes below, zero even in summer. There are also strong winds which have a cooling and drying effect, and since at higher elevations the winter lasts almost six months, the plants have less time for growth and reproduction.
Therefore rock plants have developed special adaptations which allow them to resist adverse climatic conditions. Their surface is often covered with hairs that retain a layer of air near the surface of the plant, acting as thermal insulators and protection against dryness. The cushion-like, dense structure also contributes to thermal insulation. Many plants grow low to the ground, because air close to the surface of the soil is often much warmer than the surrounding air. Light color and thick hair protect the plants against sunburn. Some plants have hard, leathery leaves that resist drying out. To speed-up the development of seeds, many plants have flowers that are able to warm up to a higher temperature than the rest of the plant. Good examples are bell-shaped flowers. Warm air, which is less dense than cold air, moves upwards, and once it enters a bell-shaped flower, it cannot get out. A good example is bearberry, whose flowers have a very narrow bell opening. A completely different mechanism of warming is employed, for example, in the head-shaped blossoms of carline thistle. Its bright outer leaves direct the sunlight into the black center of the inflorescence which absorbs the heat.
Rocks host many animal species specially adapted to the life in this environment. These are typically smaller animals like snails, spiders, insects, reptiles or rodents, however, rocks are also inhabited by larger animals like chamois. Animals from surrounding habitats visit the rocks to feed on their inhabitants. Many birds use the rocks as a safe shelter to build their nests and feed on the rich surrounding grasslands.
Special habitats in rocky grounds are screes or rock creeps – loose and detached clusters of stones which fall from larger cliffs. Screes are usually formed on steep slopes or at foothills in places where the shape of the terrain channels the stone boulders. Stones that make up a scree can be of different size – from one meter stones, over stones the size of a ball or a fist, to small gravel-size stones. Beneath a layer of loose rock is wet soil. Screes are home to specialized plants, whose main adaptation consists in extremely long and branched out roots extending deep beneath layers of rock. The scree provides home to the most well-known Croatian endemic plant species, Velebit degenia (Degenia velebitica), which grows in central and south Velebit (but not in north Velebit).
Because rocky habitat requires special adaptations and is isolated from other similar habitats, it is home to many endemic species and subspecies. The denuded karst peaks of Hajdučki kukovi and Rožanski kukovi host the largest number of endemic plants in the Park, and some endemic animal species, can also be found in the rocky ground, such as Horvath’s rock lizard (Iberolacerta horvathi), Balkan snow vole (Dinaromys bogdanovi) and Velebit leech (Croatobranchus mestrovi), a deep pit dweller.
Izvor: NP NORTHERN VELEBIT