Despite the mountainous character of the Gesäuse, the major part of the National Park is not covered by high-alpine forests, but by montane and sub-alpine forests. A wide variety of forest types can be found depending on the soil and altitude – from riparian forests along the River Enns through to larch and Swiss stone pine forests at high altitudes. The forest inventory has identified 14 different forest types, which can be further divided into sub-types. The most important forest types to be found in the Gesäuse are briefly described in the following.
The riparian woodlands of the Gesäuse are found in the low-lying areas along the banks of the Enns and Johnsbach that are subject to regular flooding. They can be divided substantially into white willow and grey alder forests. Both types of riparian woodland are priority natural habitats of the EU Habitats Directive and therefore enjoy special protection across Europe. Drier locations that are not subject to flooding or only at longer intervals are often covered by maple-ash forests.
The white willow grows on soils that are subject to regular flooding, representing the first forest stage on young river sediment. Another dominant species in these riparian woodland systems is the hoary willow. Other species of the shrub layer include sycamore maple, ash, black cherry and grey elder. The grey elder and noble hardwoods can be regarded as the pioneers in the development towards more mature stages of riparian woodland.
Regular flooding has a powerful fertilising effect. The ground vegetation is provided with a high and regular input of nutrients, leading to vigorous and dense growth. Typical species of ground vegetation include horsemint (Mentha longifolia) and dewberry (Rubus caesius) as well as the small balsam (Impatiens parviflora) and Himalayan balsam (Impatiens glandulifera), both of which are neophytes, i.e. species introduced from other floral regions. The Himalayan balsam in particular is a strongly invasive species and poses a serious threat to native flora in riparian habitats. The National Park administration is therefore taking targeted management measures to prevent further spreading of this plant.
Grey elder stands typically develop on more elevated locations along the river banks than white willow stands. The tree layer is made up solely of grey elder, which grows to heights of about 16 meters. The dense understorey is dominated by nitrogen and moisture indicators such as balsam (Impatiens), stinging nettle (Urtica) and stitchwort (Stellaria). In locations with a lack of flooding dynamics the stands are often interspersed with spruce.
Maple-ash forests, also known as "noble hardwood" forests, settle locations up to the middle montane zone. This demanding forest type needs a rich nutrient and water supply, but without stagnant moisture. Favourable conditions enhance its productivity and lead to dense ground vegetation. In the Gesäuse National Park this forest type can be found on old gravel banks of the Enns and Johnsbach outside the floodplain and in cool, moist and nutrient-rich slope regions of the Hartelsgraben ravine.
WeiterlesenThe top canopy level is dominated by beech, maple and spruce, interspersed with elm and ash. A sufficient amount of light from the side or an open canopy will encourage the formation of a shrub layer of young trees, honeysuckle (Lonicera) and spindle (Euonymus europaeus).
The small-structured mosaic of crevices, less steep sections rich in fine soil and moss-covered rocks lead to a dense and highly diverse ground vegetation. The Gesäuse's only large ravine forest in the Hartelsgraben is home to conspicuous plants such as the hart's tongue fern (Asplenium scolopendrium) or honesty (Lunaria).
Winter Heath-Pine Forest
After the last ice age about 6,000 years ago (early postglacial period) the Gesäuse was densely covered with pine forest. Since then, the pine was largely replaced by spruce, fir and beech and can now only be found in extreme locations. This forest type requires warm conditions and therefore grows primarily on south-facing rock and gravel slopes in the lower montane zone.
These forest stands grow on shallow, steep slopes on solid Ramsau-Dolomite bedrock, which are among the most nutrient-poor locations in the National Park area. The dominating tree species in these slow growth stands is the Scots pine (Pinus sylvestris), which in mid-age develops a typical umbrella-shaped canopy. These pine stands are regularly interspersed with spruce trees. Other, more demanding tree species are seldom to be found. The underground vegetation typically consists of winter heath (Erica carnea) and hardy species such as white sedge (Carex alba), branched St. Bernard's Lily (Anthericum ramosum), thyme, rock thyme (Acinos alpinus) and swallow-wort (Vincetoxicum hirundinaria). The stands growing on gravel slopes, where the conditions are less extreme than on rock, are home to slightly more demanding species such as purple lettuce (Prenanthes purpurea) and European goldenrod (Solidago virgaurea).
A special highlight of pine forests is the lady's slipper orchid (Cypripedium calceolus), Europe's largest orchid. This distinctive, limestone-dependent species can be found, with a little luck, in clearings of beech and pine stands as well as on gravel slopes in the dappled shade of dwarf mountain pines.
The beech-fir-spruce forest is one of the most widely spread forest types in the Gesäuse National Park. These carbonate gravel forests of the (high) montane zone are further divided into several sub-types. These include forests with tall herbaceous vegetation (loamy soil), mountain grasslands (on rock), carbonate gravel and high montane limestone forests on dry locations.
If left to develop on their own the competitive power of beech and fir leads to the formation of natural shady high forests largely lacking a shrub layer.
As the name suggests, spruce, fir and beech are the dominant tree species of this forest type, while the fir has become a rare sight in the region due to selective logging, the preference of spruce and heavy browsing damage. The existing stands mainly consist of spruce and beech, with spruce clearly dominating. The decomposition of spruce needles leads to a relatively high acid content in the soil (low pH value). The understorey thus houses typical acid indicators such as blueberry (Vaccinium myrtillus), twoflower violet (Viola biflora), chervil (Chaerophyllum) and Adenostyles (Adenostyles alpina). The Christmas rose (Helleborus niger), an early harbinger of spring, is also a characteristic plant of these forests. The dry locations lack tall forbs and ferns but are frequently colonised by species usually found on nutrient-poor grasslands such as hawkweed (Hieracium), plume thistle (Cirsium), betony (Stachys) and blue grass (Sesleria).
There are no pure beech stands in the Gesäuse National Park. The beech forests mentioned here are mixed spruce-fir-beech stands where the beech predominates over the other tree species due to favourable site conditions or forest management measures. Beech forests are further divided into two sub-types: those growing on limestone slopes and those growing on loamy soils, richly interspersed with maple and ash. These forest types can only be found at lower altitudes, in particular near Hieflau. An exception are dwarf beech shrub communities, a characteristic vegetation found in avalanche gullies, for example at the Tamischbachturm. Here beech may form pure krummholz stands, because other tree species are not able to withstand the impact of snow pressure and avalanches.
The limestone beech forests colonise locations on Dachstein limestone or Raumsau dolomite with a rich supply of water and nutrients. Spruce trees are also usually to be found in these forests.. In contrast to spruce-fir-beech forests, however, these forests are characterised by demanding understorey plants such as wood sedge (Carex sylvatica), bittercress (Cardamine) and yellow archangel (Lamium montanum). The loamy beech forests are rich in maple and ash and can be found on slopes with an optimal supply of nutrients and water on loamy terra fusca. In contrast to spruce-fir-beech forests on loamy soils, however, they lack acid-indicator species. Instead the ground vegetation is characterised by plants indicating good water and nutrient supply, such as hedge woundwort (Stachys sylvatica), balsam (Impatiens), lungwort (Pulmonaria) and Herb Robert (Geranium robertianum).
Spruce-fir forests can be found on deep carbonate-free locations in the National Park area with characteristic geological subsurface conditions, for example on ground moraines and soils overlying layers of the Werfen formation and rauhwacke. The more demanding beech is lacking due to the low lime content and temporary wetness of the soil. The undergrowth typically consists of acid-indicating species, especially ferns, which dominate the appearance of mature stands of this forest type. The dense vegetation cover includes among others lady fern (Athyrium filix-femina), mountain fern (Oreopteris limbosperma) and wood fern (Dryopteris).
Sub-Alpine Limestone Spruce Forest
The higher we ascend into the mountains or the deeper we go into the Alps, the less frequently we will find beech and fir. Spruce, which is better adapted to the cold climate of high altitudes, the short vegetation time and low (inner alpine) precipitation rates becomes more dominant and forms pure natural stands. In the Gesäuse the sub-alpine spruce forest belt generally begins at 1,300 to 1,450m, giving way to larch-Swiss stone pine forests from an altitude of about 1,650m. The natural spruce stands differ from each other depending on the bedrock, acid content of the soil and exposition.
The sub-alpine limestone spruce forests are the most widespread type of natural spruce forests in the Gesäuse National Park. They are characterised by an unusually low acid content for spruce forests, which is clearly reflected in the species community found in the undergrowth. The ground vegetation is usually much more diverse than in spruce forests on acid soils and partly also consists of base-loving species such as Christmas rose, Adenostyles, primula or dog's mercury (Mercurialis perennis). This makes for a colourful mixture of ecological species groups such as lime indicators and deciduous forest types along with typical species of acid-soil spruce forests. Experts differentiate between four site types of limestone spruce forests in the Gesäuse National Park: dry spruce forests on limestone slopes, tall forb spruce forests with mountain grassland species, lush tall forb spruce forests and spruce boulder forests on pseudogley.
Acid-Soil Spruce Forest
Acid-soil spruce forests grow on soils overlying greywacke slate, Jurassic clay and lime-free layers of the Werfen formation. These soils are characterised by a low pH value (acid), which has a strong effect on the vegetation. The undergrowth of this forest type is generally relatively poor in species. Spruce is the dominant tree species, interspersed with larch.
Acid-soil spruce forests can again be divided into three groups. The first type, sphagnum moss spruce forests, occurs in the Greywacke zone. The soils there are very wet, favouring the growth of sphagnum moss. The sites are characterised by higher acidity and lower nitrogen levels than in other spruce forest types. An even higher soil moisture is found in sphagnum moss spruce forests with cottongrass (Eriophorum), which are characterised by boggy soil conditions. Typical vegetation includes cottongrass and bog bilberry (Vaccinium uliginosum). The last group is spruce forest with wood sorrels (Oxalis), which can be found in less extreme locations with a larger number of more demanding forest plants in the undergrowth.
Pure larch forests tend to be the exception rather than the rule in the Gesäuse National Park, as they are commonly interspersed with varying admixtures of spruce. The larch is, however, very competitive on shady rocky slopes poor in fine soil and dominates at altitudes between 1,400 and 1,600m. The vegetation found in larch forests consists mainly of species adapted to rocky conditions and include for example dwarf alpenrose (Rhodothamnus chamaecistus), Alpine rock-cress (Arabis alpina) or Austrian bellflower (Campanula pulla).
Larch-Swiss Stone Pine Forest
The highest tree level in the Gesäuse is the larch-Swiss pine forest, which can be found mainly on the old plateaus and south of the Hochtor chain. The National Park is the easternmost edge of the range of this tree species in the Alps. The forests are characterised by scattered stands with varying proportions of Swiss stone pine and larch, with the larch dominating in many places. Other tree species such as spruce or fir can only compete in secondary stands due to the tough climatic conditions prevailing at these high altitudes.
WeiterlesenThe larch-Swiss stone pine forests in the Gesäuse National Park usually occur on Dachstein limestone. It shows a higher proportion of larch than its silicate counterpart. This forest type is completely lacking north of the River Enns due to the extremely steep terrain morphology. The range south of the river can be divided into three areas: the rocky "Zirbengarten" east of the Hüpflinger-Hals, the former grazing grounds on the northern slopes of the eastern Zinödl massif towards the Wolfbauernhochalm pasture, and finally the high valley north of the Hesshütte Alpine hut over the steep slopes of the Planspitz and Zinödl mountains.
Detailed information about the larch-Swiss stone pine forests in the Gesäuse National Park can be found in the following publication (in German) "Lärchen-Zirbenwälder im Nationalpark Gesäuse sowie pflanzensoziologische Diskussion des Carbonat-Lä-Zi-Waldes in Österreich" by Anton Carli (2013).
Dwarf Mountain Pine Shrubs
At high altitudes, where the forest reaches its limits, the landscape is dominated by dwarf mountain pines forming a continuous krummholz belt above the timberline. In scree and avalanche tracks they descend down to the valleys. The dwarf mountain pine is ideally adapted to the extreme conditions of its habitat. It can withstand heat and draught as well as frost and extended snow cover and even thrives on steep rock faces.
The dwarf mountain pine forms dense stands in less exposed and steep areas, encouraging growth of other tree species such as sycamore maple (Acer pseudoplatanus), mountain ash (Sorbus aucuparia), larch and Swiss stone pine. If left undisturbed, dwarf mountain pine stands below the timberline may develop into another forest community, depending on the dominant tree species.
Detailed information about the forest types and their different appearances can be found in the relevant forest site survey (in German) "Forstliche Standortserkundung für das Gesäuse" by Anton Carli (2007).