Invasive and Expansive Plants
The current flora of the Czech Republic is composed of around 4200 vascular plant species. Of this total there are 1378 non-indigenous species. Of these non-native species we can classify 90 plants (6.5%) as “invasive species”, the further spread of which would be dangerous from a nature protection viewpoint (Háková et al. 2004). Invasive species are plants which are not native to our country and due to their highly competitive ability are able to colonise new localities, often at the expense of native species. The result of these invasions is that native species are lost from the natural vegetation as they are forced out by the more competitive invasive species (Háková et al. 2004). On the other hand, expansive species are our domestic species with similar abilities to spread into new areas.
In Podyjí NP we pay great attention to all invasive species. Their occurrence is regularly monitored by the NP Administration and management measures are proposed, when they are needed, in accordance with the Podyjí NP Management Plan. The main targets in the management of invasive species are (1) to protect valuable natural communities from the negative impacts of the invasion and (2) to prevent the spread of these species to further localities, or to prevent new species from entering the park. An important management toll is the liquidation of the most aggressive species, or at least to suppress their populations.
The Small Balsam (Impatiens parviflora) has penetrated into the forest stands in all parts of the national park, where it has become a common species in the herb layer, especially in forests with enough soil moisture. So far we do not have detailed information on the effects of the Small Balsam on the native vegetation in Podyjí. It is not technically possible to liquidate this species, so no measures are taken.
In the Dyje valley on the riverbanks we can find the Himalayan Balsam(Impatiens glandulifera). This balsam was first recorded during flora mapping work in Podyjí NP in 1990 – 1995. As there is a relatively strong population, we began to liquidate this species as early as the mid 1990s. After a 10-year fight against the balsams we have managed to reduce its population to a minimum, especially thanks to the co-operation with the Austrian Thayatal NP from 2000. Balsam is always liquidated by mechanical means – pulling it from the ground and then carrying the biomass out of the NP.
The occurrence of Knotweeds (Reynoutria spp.) has been recorded in the western part of the NP (Vranovsko) at several localities. This is especially the Japan Knotweed (Reynoutria japonica), but the Sakhalin Knotweed (Reynoutria sachalinensis) has also been recorded in the neighbouring Thaytal NP. By way of repeated interventions we have managed to reduce the occurrence of Knotweeds to a minimum. In recent years they have only been found occasionally. Liquidation is carried out in a combined manner – mechanically and chemically. First the overgrown biomass is cut back and removed and then after several months the regenerated plants are sprayed with chemical preparations.
The False Acacia or Black Locust (Robinia pseudoacacia) has the most serious effects among the woody species. False Acacia trees have a 2% representation in the Podyjí NP forest stands (forests under state ownership) and many False Acacias also grow on non-forested lands. The Podyjí NP Administration is carrying out a gradual transformation of False Acacia stands in to other community types according to the locality conditions. As this transformation work is very expensive and time-consuming in many places such as valuable steppe grassland biotopes our target is to prevent the spread of False Acacias to further localities. Acacias are liquidated by mechanical means (placing girdles or rings around the tree trunks and felling at a later date) and by chemical means (coating the tree stumps and spraying the regenerating acacias with pesticides). An equally aggressive tree species is the Tree of Heaven (Ailanthus altissima), but luckily this tree is almost unknown in Podyjí NP.
Several more invasive plant species have been recorded in small numbers along the Dyje river. These include the Giant Hogweed (Heracleum monteggazzianum), Jerusalem Artichoke (Helianthus tuberosus) and Coneflower (Rudbeckia laciniata), which were immediately liquidated and do not represent a serious danger for the riverbank growths in Podyjí NP. The Canadian Goldenrod (Solidago canadensis) and the Ashleaf Maple (Acer negundo) can be found in places along the riverbanks, but also by trails and buildings. The Canadian goldenrod can also be found on several uncultivated meadows. The Duke of Argyll’s Teaplant (Lycium barbarum) grows in places on rocks, terraces and stone walls, especially near human settlements (Hradiště terraces). Small numbers of the Bindweed Fallopia aubertii have been found repeatedly as well as the American Michaelmas Daisies (Aster spp.). However these species do not display strong invasive tendencies at the moment and are not considered dangerous. The occurrence of these species is occasionally monitored and measures are proposed when necessary.
Expansive species which deserve our attention include the grasses Wood Small-reed
(Calamagrostis epigejos) and False Oat-grass (Arrhenatherum elatius). The Wood
Small-reed is a branching and extremely vital grass which tolerates a wide range of ecological conditions, although
abandoned, uncultivated plots suit it the most. The Wood Small-reed’s role in the ecosystem on a given locality is to
establish such conditions, which allow for gradual succession and the formation of a new forest. The Wood Small-reed
occurs in Podyjí NP and especially its buffer zone in various biotope types – on meadows, grasslands, heathlands and
open forest. The degree of coverage of Wood Small-reeds on individual plots is variable. Some plots which have
suffered from long-term neglect (e.g. plots which the owners have not cut or grazed for a long time) are completely
overgrown with thick growths of Small-reed. Other plots only have small “outbreaks” of Small-reed in the middle of
valuable communities. In both cases the NP Administration is attempting to suppress the population of Small-reed and
to prevent their further spread. The most useful method is to cut affected areas several times per year. On trial
plots we have experimented with removing the Small-reed turf using mechanical excavators and also with burning the
The False Oat-grass is a tufted grass species, which is typical for mesophilic meadows. Some meadow types are even classified as oat-grass meadow. At present this grass is expanding widely in the countryside as a result of the overuse of nitrogen to fertilise soils (this nitrogen can come from fertiliser run off or from airborne deposits). Today this Oat-grass can be found in ditches along trails, in various types of meadows and grasslands and in open forests, and can even be found on the heathlands in Podyjí NP. These False Oat-grass stands are not as competitive as the Wood Small-reed, but it is a tall-growing grass which is capable of successfully colonizing large plots of land. Unfortunately we can hardly influence the main cause of its expansion (airborne deposits of nitrogen as a result of industrial pollution). The occurrence of False Oat-grass in Podyjí NP is suppressed by long-term management measures which include a combination of cutting and grazing.
Other species which are expanding strongly on previously neglected meadows include Tansy (Tanacetum vulgare), Creeping Thistle (Cirsium arvense) and the Common or Stinging Nettle (Urtica dioica).
Expansive woody species include the Dog Rose, Blackthorn and Wild Plum trees. In the south-eastern part of Podyjí NP and its buffer zone these shrubs are spreading very aggressively on the dry grassland biotopes or heathlands. The management target for both of these biotopes is to support a mosaic of grassland types or heathland with scattered individual shrubs or groups of shrubs. It is undesirable that these valuable communities should become overgrown with shrubs. Regular interventions are carried out to cut and remove these shrubs (during the winter period) and then to remove all new regenerating biomass.