A habitat is an environment in which a species lives. There are many different habitats, often named after the plant communities that occupy them (e.g. Dinaric beech-fir forests). Habitat is essential for the existence of a species. Species are often adapted to one or several types of habitat, while they are unable to survive in others. Therefore, when looking for a species, it is useful to know which type of habitat it is adapted for. Likewise, if we know which habitats are present in an area, we also know which species can be found there. The greater the habitat diversity, the greater is the variety of species, which also means greater biological diversity and ecosystem health. If we want to conserve a species, we must first conserve its habitat, because no living creature can survive without a suitable living environment.
Velebit is a mosaic of diverse habitats - forests, grasslands, rocks, screes and rare aquatic habitats. No element of this mosaic is completely independent from the others, because many species use more than one type of habitat. In addition, the boundaries between habitats are not clearly delineated, but merge into one another in transitional areas, which are often the richest in life forms. It may seem to us that this landscape has always been like this, however, the reality is quite different. Its present appearance is the result of a long development process and a multitude of influences. The landscape is not static, but continually changes depending on a number of factors that are often difficult or even impossible to predict.
At the North Velebit National Park there are five main types of habitat:
The Park is predominantly covered by forest habitat (more than 80% of the total surface area). The main feature of mountain forest habitats is zonation - distribution in belts arranged according to altitude. With the increasing altitude, the climate becomes more severe, which is reflected in the plant cover or vegetation.
If you start climbing from the sea up the coastal slopes towards the peaks of north Velebit, you will first pass through the forest of downy oak and hornbeam. As you climb higher, the vegetation changes from hornbeam to hop-hornbeam and you find yourself in the downy oak and hop-hornbeam forest. The forests on the coast-facing slopes often take the form of a thicket, and are extremely important for conserving the soil that is exposed to strong bora winds.
Mountain Peak Region
On the highest peaks, you'll find dwarf beech trees or European mountain pines, with lumpy and curved branches hugging the ground. At such elevations, trees are exposed to extremely harsh conditions, with cold and short growing season preventing them from developing into full-grown trees. Instead, they develop stunted growth forms called krummholz. European mountain pine is a special pine species, characterized by longevity and resistance to harsh climatic conditions. This shrubby pine usually does not take the form of a tree, but develops close to the ground, without a central stem. Its branches lie low to the ground and are bent upwards. Thanks to its low, cushion-like shape, it is protected from wind and cold, with a layer of air trapped around it acting as an insulator. Moreover, European mountain pine can grow in a variety of soils.
At high elevations, when you start descending the slopes of North Velebit towards inland – the Lika plateau, you will again pass through sub-alpine beech forest. In this most unwelcoming habitats consisting of rocky precipices, sinkholes and closed depressions, you will encounter spruce trees. In north Velebit, several types of sub-alpine spruce forests can be found: the steep, rocky slopes, such as those of crags, are home to sub-alpine spruce forest. The steeper and rockier sinkholes and enclosed valleys are occupied by sub-alpine spruce forest with listera (Listero-Piceetum abietis), while the wetter and more humus-rich areas are occupied by sub-alpine spruce forest with Alpine adenostyles (Adenostylo alliariae – Piceetum). On warmer rocky slopes with more sun you may encounter the Dinaric fir forest on calcareous blocks, which is quite rare in north Velebit.
The species composition and distribution of trees in the Northern Velebit forests is similar to what you might find in a primary old-growth forest – forest that has never been cut down or exposed to other significant human influence. In addition, it contains a number of old and dead trees. This "deadwood" is not composed of mere tree carcasses, but soon becomes home to a wide variety of wildlife – countless species of insects, fungi and bacteria. They feed on old trees, turning them into fertile soil. The Park is home to as many as five out of the nine European woodpecker species that are dependent on dead and old trees – they feed on insect larvae found under the bark, and nest in cavities excavated in decaying trees. Thus, woodpeckers prevent insects that feed on the wood and damage the trees to multiply excessively. The old woodpecker nest holes are used for nesting by numerous other bird species, which makes them dependent on woodpeckers and old trees. Among the users of these cavities are six owl species and several species of forest bats, which use the cavities as refuge during the day, but also for raising the young. Among them are, for example, the barbastelle and lesser noctule bats, which also hunt in the forest.
Although grasslands are a common feature of a mountain landscape, the climate in Velebit, much like that of other Croatian mountains, is not suitable for the development of natural pastures. In high mountains, grasslands occur in areas above the "upper forest line", at about 2100 meters above sea level in the Alps region. Croatian mountains are too low for the development of grasslands due to the impact of climate in the peak regions. Natural grasslands which are called rudine, can sometimes be formed at lower altitudes as a result of specific local conditions such as the bora wind, which is what happens as well in the Northern Velebit National Park.
Unlike most modern human interventions in nature, creation of grasslands has improved the natural environment with a completely new habitat, that is inhabited by new grassland-specific species. Many plant species that are limited to very small areas of natural grasslands have thus obtained a much larger living space. Some of them arrived in the distant past with cattle herds from other areas, primarily the east Mediterranean region, and for some the grasslands have become the center of their evolution. Apart from increasing the total number of species, grasslands have become a feeding ground for the existing animals. For example, many birds of prey hunt on grasslands. As a result, the biodiversity of the entire area has increased, making the ecosystem more stable. Grasslands also speak of the past of the entire area, of how the people lived, worked and migrated, and form an integral and extremely important part of both the natural and cultural heritage.
Although grasslands are created by human activity, they are not all the same. As a rule, different altitude belts of forest vegetation are accompanied by different types of grassland.
The lowest, hop-hornbeam belt, has developed rocky grasslands of dwarf sedge and rock knapweed, abounding in sub-Mediterranean species – species that mainly inhabit the Mediterranean area, but can also be found in warmer regions of the southern part of the continent. Situated in protected locations and often surrounded by forest, to be found here on a relatively small area of land are also upright brome grasslands. They develop on deeper soils that are never rocky, and are probably of different origin. Upright brome grasslands were probably predominantly used as grazing land and, being located on level ground without protruding stones, they possibly also served as hay meadows. A small portion of these grasslands may have been created by overgrowth of agricultural land.
Mountain Peak Region
In protected areas of the peak region, especially those that are sheltered from strong gusts of bora winds, and often in places with deeper soils bosnian fescue grasslands can be found. The dominant grass, Bosnian Fescue, is a high-altitude endemic species of the Dinaric karst. In deeper, wetter soils east Alpine violet fescue grasslands occur in a mosaic pattern. They stand out very clearly being composed of dense stands of East Alpine violet fescue, often exceeding 1.5 meters in height. They are among the rarest types of mountain grassland in Croatia, and so far have only been found in the mountain plateaus of Šegotski padež, Bilenski padež and Tudorevo in the Northern Velebit National Park.
Former arable land on which predominantly potatoes and cabbage were grown, has now become completely abandoned and has eventually acquired the appearance of grassland. At first glance, they may appear as small exclaves of lowland pastures, because their composition is dominated by species typical of warmer areas with more nutritious soil. If grass is not a dominant species, such places may appear as tall herbs. Interestingly no foreign (invasive) species, have been found here, despite the fact that they usually occur, and are often dominant, in abandoned arable fields in lowland areas.
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, 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, Balkan snow vole, and Velebit leech, a deep pit dweller.
The subterranean areas have conditions completely different from those on the surface. The normal temperature is several degrees above zero, the moisture content is high and it is completely dark. All these conditions are very stable, which is the main feature of the underworld. The part of the subterranean area close to the entrance is a transitional zone influenced by the conditions on the surface, so the variations here are greater than in deeper areas.
Plants and other organisms that receive energy directly from the sun are not adapted to underground life. However, some plants, mosses and algae which do not require much light can be found underground close to the surface where some light enters the underworld. Since there are no plants underground, all food in subterranean habitats comes from the surface.
However, the true subterranean animal species live exclusively in caves and pits, and can be immediately recognized by missing or weak eyes and body colouration, because pigments and organs of vision are redundant in total darkness. At the same time, food is very scarce and it is therefore extremely important for underground animals not to squander food and energy on production of unnecessary molecules and organs. These animals often have very slow metabolism, which allows them to survive with minimal amounts of food and prolonged starvation. A slow metabolism leads to a long life and slow breeding. Subterranean animals are coping well in the dark thanks to a highly developed sense of smell and touch. These senses are often manifested in form of prolonged antennae and legs that carry more sensory hairs.
Almost all underground features discovered in the area of the Park are pits – vertical underground spaces. They are not as convenient for bats as caves, which is why no maternity colonies have been discovered here. However bats were found to hibernate in pits during the winter, although pits are not used as mass hibernation sites. Some of the recorded species are the lesser mouse-eared bat, the brown long-eared bat and the northern bat.
The majority of true underground animals are invertebrates. These are different groups of animals, often unfamiliar to the general public, such as beetles, earwigs, springtails, spiders, pseudoscorpions, isopods, polychaetes and others. They live in several different habitats within the underground: on land, in a thin layer of water that trickles down the walls and never dries out, in water, and on bat droppings or guano, a special type of underground habitat.
The Park is also home to some very rare aquatic habitats, which are of crucial importance for aquatic organisms. The most important and interesting aquatic environment in the Park is a network of streams and creeks at Štirovača, the only area in the Park with a water-impermeable ground layer, which contains the only source of drinking water and the only running water of the Park. There are several ponds (Borove vodice, Žive vodice, Lubenovačka ruja..) in the Park, either fully man-made or built around naturally occurring moist areas. Thanks to these ponds, water – a very sparse resource in Velebit, has become much more accessible to animals inhabiting the surrounding areas. As for aquatic residents in the waters of the Park, there is only a handful of fully aquatic algae, plants and very small animals, which can migrate on the bodies of birds and other animals that frequent the waters. Most of them spend only a portion of their life cycle in the water, while spending the remainder of their life on the ground or in the air, such as frogs and dragonflies, which allows them to inhabit these isolated habitats, "islands" of water in a "sea" of land of a very dry land habitat. Fish are not natural inhabitants of these tiny, isolated aquatic ecosystems, and if artificially introduced, they may significantly disturb, or even completely destroy, these delicate ecosystems.