Nationalpark Thayatal

2082 Hardegg

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National Park Thayatal
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Nature | Habitat management

Neophytes in the Inter-National Park Thayatal - Podyjí

It is well known that river valleys represent a favored migratory corridor for many plant species. The fact that the habitats of the Thayatal are anthropogenically influenced is certainly conducive to the occurrence of neophytes in the International Park Thayatal-Podyjí. Utilisation of meadows used to be much more extensive, and some dry locations were used as pastures. Most of these uses were stopped a long time ago, but their long-term consequences are still existent. Another serious factor is the disruption of the ecology of the Thaya and its edges, which is linked to the water floods of the Vranov power plant. The construction of tracks and forest roads also facilitates the establishment of neophytes.

In its distribution atlas of the vascular plants of the National Park Thayatal (1997), Grulich gives an overview of the number of species and their distribution in the Inter-National Park Thayatal-Podyjí and its surrounding areas. The research area with its 227 km2 is much larger than the total surface of both national parks (77 km2). 116 of the 1288 plant species occurring in the research area are neophytes. Only a few are problematic.

Because of their ecology, dissemination and dissemination trend, the following species are considered as problematic in the National Park from a nature conservation perspective: Robinia pseudacacia, Impatiens glandulifera, Fallopia japonica and Heracleum mantegazzianum. They should be rated as invasive species in the Inter-National Park Thayatal-Podyjí, in particular as their populations grow constantly. As the dissemination of the plants leads to an extensive modification of the semi-natural vegetation, systematic control measures are carried out.

Robinias with peeled off bark

Robinia (Robinia pseudacacia)

In the National Park Thayatal, the robinia occurs sporadically. It cumulates only below the Max plateau and at the Burgberg mountain near Hardegg. These dry slopes were used as pastures until the 1950s. In the area of the Max plateau, robinias were already planted before World War II, the oldest tree are over 80 years old. The trees were planted to secure the steep slope and because of their appeal to bees. Both Hardegg forests spread widely mainly once the areas were no longer used as pastures. Another large population also exists near the Stony Wall (Steinerne Wand).

In 2001 robinias were girdled for the first time near the Max plateau and at the Stony Wall. It was carried out shortly after blooming time, as this is when energy levels of trees are at their lowest. Most of the time, trees react within a few weeks by shedding their leaves. Approximately two months after girdling, the buds at ground level started to sprout. Even root suckers several meters away from the trunk began to sprout. The shoots were chopped off - a measure which, since then, has been repeated every year.

Himalayan Balsam
Blooming Himalayan Balsam
Himalayan Balsam

Himalayan Balsam (Impatiens glandulifera)

In the Inter-National Park Thayatal-Podyjí Himalayan Balsam only grows on the banks of the Thaya. The side streams of the Thaya are not affected in the area of the National Park, however at the upper reaches of the Fugnitz river, the plant occurs frequently in some places. Himalayan balsam has only been found for a few years in the National Park: the species was discovered for the first time in 1995 on the banks of the Thaya. Since then it has been spreading rapidly. Preferred locations are wide bank areas with few or no wood stands, which used to be partly utilized as meadows. On the narrow shaded banks only few individuals were able to establish themselves. Likewise the plant also occurs in willow and alder floodplain forests, albeit only in small populations. The largest population was able to develop on river banks and the neighbouring meadow fallows at the Lange Grund. Until 2001 an almost closed population of varying width (2 to 20 m.) was able to develop here over a length of 1,300 meters. On the Czech side of the river the plant now only occurs very rarely due to many years of management. Upstream from the common border it was de facto possible to reduce the plant entirely.


In the Czech Národní park Podyjí measures have been taken against the plant since its appearance. However, the widespread populations on the Austrian side have lead to a regular resettlement in the Czech Republic. Therefore the two administrations decided on a coordinated approach. Following first measures in 2000, fighting measures were carried out in 2001 along the entire course of the Thaya. Individual plants and smaller populations were pulled out by hand between June and September, larger populations were mowed. Good results were achieved with the mowing of populations. In pulling them out, smaller and non flowering plants can be easily overlooked. As some parts of the river valley are hardly accessible on foot, the fighting measures in the NP Podyjí have been partly carried out by boat. So far management can be viewed as highly successful. Apart from some smaller populations, the plant has disappeared to a large extent from the National Park.

Japanese Knodweed (Fallopia japonica)

In the National Park Thayatal Japanese knodweed grows mainly near the towns of Hardegg and Merkersdorf. Only one population was found directly in the National Park at the edge of the Thaya. The populations are relatively small, between 4 m2 and 100 m2 . Regarding the populations close to towns, they are always road slopes which have ruderal vegetation.

Through the mowing of the plants, the populations could be reduced drastically. Moreover, one population near the Fugnitz in Hardegg was nearly eradicated due to floods. In the Czech Národní park Podyjí pesticides were also applied in some areas.

Gian hogweed in bloom
Umbel bloom of giant hogweed
Gian hogweed in bloom

Giant Hogweed (Heracleum mantegazzianum)

Dissemination and management
In 2006 individual plants of giant hogweed appeared for the first time in the National Park. Some plants were found next to the Thaya, others near a game feeding place. The plants were dug out before bolting and removed from the National Park.