The lifeline of this alluvial landscape with its characteristic habitats is the Danube. The water regime and sediment load of the river form the basic parameters of landscape development through the rearrangement of substrate (erosion and sedimentation).

Depending on the nature of the substrate deposited by the Danube and its distance from the water body, an initial plant cover can establish itself on freshly deposited sand or gravel - and thus begins a development series characteristic of wetlands. The stages of this development series lead from herbaceous vegetation on freshly created pioneer areas to a phase with willow bushes to the establishment of the first wetland forest trees and the so-called softwood riparian forest.

Willows, black poplars and alders are among the characteristic species of the softwood riparian forest, which is flooded several times a year due to its proximity to the Danube or its branches. Species of this early wetland forest type are therefore particularly well adapted to floods and can recover quickly from damage after flood events.

If the river does not re-circulate the area, after a few tree generations, other tree species can establish themselves on the mature wetland soils. One of the first is often the white poplar, which can quickly take over new sites through root sprouts. White poplar forests therefore often form the transition between softwood and hardwood riparian wetlands. More demanding tree species such as oak, maple, ash and lime form the so-called hardwood riparian wetland.

This is no longer flooded frequently, but is still strongly influenced by the stream. Their locations are strongly influenced by the fluctuations of the groundwater flow that accompany the high and low water events of the Danube.

In the riparian forests of the National Park, highly endangered tree species are still locally very common, e.g. white willow and black poplar. Many specialised creatures also have their habitat here, such as beetles and their larvae in the deadwood of trees and shrubs. The stands of old trees are of great importance for bird life.

There is no longer any forestry use in the forests of the national park, only small-scale renaturation measures. These enable the forests in the protected area to develop rapidly into near-natural habitats again after decades of use and transformation by humans. The only woodcutter that is allowed to stay is the beaver.

A special feature of the wetlands are the steppe-type landscapes, locations on deep gravel accumulations where only drought-tolerant plants can survive due to the poor water supply. Typical plants are hawthorn, buckthorn, various orchids and feather grass. Extraordinary are lichens and mosses that tolerate water shortage - referred to by scientists as dry moss communities. A special feature is the occurrence of the praying mantis, an insect that is typical for extremely dry areas.

Centuries ago, humans created additional open areas for agricultural use in the wetlands, some of which are still maintained today as species-rich meadows in the National Park. Unique plant communities have developed on these regularly flooded, nutrient-rich floodplain meadows. As a result, rare animal species, such as the corncrake, found replacement habitats here for the biotopes destroyed by modern agriculture.

This diverse mosaic of different terrestrial habitats is still criss-crossed by a network of numerous ditches and watercourses, which are connected to the Danube depending on the water level. In the case of larger watercourses, a distinction is made between side arms with water flowing through them and former tributaries that have silted up.

As a result of river regulation, the watercourse network in the National Park area is now only inadequately connected to the Danube. In the natural river landscape, the process of the development of different wetland habitats always begins all over again, as after erosion by the force of the river, new areas of gravel or sand are created at different places, which can be newly conquered.

In addition to the regulatory intervention along the course of the river (bank stabilisation by block casts, separation of the tributaries), the protective dam on the north bank protects the Marchfeld against the floods of the Danube. It was built in the 1870s from Vienna to the mouth of the March.

Today, this artificially created, extremely dry habitat is home to extremely species-rich vegetation with over 400 plant species. Orchids in particular, such as spider's orchid, burnt orchid and helmet orchid, are represented here in large numbers. The European pond turtle finds similar conditions for its clutches on the artificial structure as on the hotlands, which are favourable egg-laying sites for it due to the warmth and dryness. The Marchfeld Protective Dyke is maintained and managed by viadonau.

On the south bank of the Danube, the National Park is bordered by the break-off of the Vienna Basin, which is colonised by a unique slope forest. The old impact slope of the Danube forms a 30 to 40 m high terrain step, which has an exceptionally humid-fresh microclimate due to its northern exposure. This makes it possible for tree species untypical of the relatively warm, dry Pannonian climate to grow in the lowland floodplains of eastern Austria.

The lowest-lying beech forests in Austria are located here. They mark the high-water line of the Danube on the slope, as they do not tolerate flooding. The character of this landscape is similar to that of the Vienna Woods. At the foot of the slope are chains of pools fed by spring outlets and seepage water from the slopes. They are particularly good spawning grounds for amphibians. Red deer like to move to these higher areas during floods.