Grazing as a natural solution to suppress invasive alien species

December 23, 2020

Invasive alien plant species form a serious challenge in many areas across Europe, where their rapid spread can severely impact ecosystems. A natural solution may be present in the form of (natural) grazing, where herbivores can suppress or even eliminate the proliferation of invasive species. In this blog, we look in more detail at the case of Amorpha fruticosa, or false indigo-bush, which causes major problems, particularly in the Danube basin, and for which extensive grazing can offer a solution.

Bison prunes American black cherry
In areas where the European bison has been reintroduced, it has shown the ability to suppress invasive alien species such as American black cherry.
Leo Linnartz/ARK Nature


Field of giant hogweed destroyed by semi-wild cattle
A field of giant hogweed destroyed by semi-wild cattle.
FREE Nature

A cheap solution?

One of the least known aspects of herbivory is its influence on the occurrence of invasive plant species. A serious problem in various European regions, where native flora and fauna are outcompeted by species that are not native to the area. Measures to control these invasive alien species often take place with relatively expensive, mechanical interventions, with varying results. As some of these invasive species have colonized abandoned grasslands, this raises the question of whether the comeback of (more natural) grazing could play a role in reversing the process and eradicating these invasive species in favour of more diverse, natural ecosystems.


First hopeful signs

Free-roaming cattle on the floodplains of the Slikken van de Heen Nature Reserve in the Netherlands tackle giant hogweed.
Sabine Wolters / FREE Nature

For many invasive alien plant species, the effects of extensive grazing on their growth and abundance are still unknown. But for others, it becomes increasingly evident that grazing could play an important role in their control.

One example is the suppression of American black cherry (Prunus serotina) by European bison or by (high densities of) goat and cattle. Also, giant balsam (Impatiens glandulifera) and giant hogweed (Heracleum mantegazzianum) make up part of the diet of large herbivores in some areas and can be significantly suppressed through grazing. The latter species is very palatable to cattle and even appears to be a preferred part of the diet of free-roaming cattle in the rewilded floodplains in the Netherlands. There are other species, however, like the Canadian goldenrod (Solidago canadensis) that are avoided by these grazers and will spread further, if no additional measures are taken.


The Amorpha case

Dense groves of Amorpha on Tataru island
Dense groves of false indigo-bush (Amorpha fruticosa) on Tataru Island in the Danube Delta.
Sergey Podorozhny

One of the case study areas within GrazeLIFE is the Danube Delta. Here, the invasive false indigo-bush (Amorpha fruticosa) has widely dispersed along the Danube. This species, originally American, has spread over thousands of hectares, especially in the catchment area of the Danube and its tributaries like the Sava, Drava and Tisza rivers, with a major levelling influence on the indigenous flora and fauna.

In the Danube Delta, Amorpha grows in narrow belts on riverine bars. In places where there is no grazing, the species forms monotonous thickets which make natural regeneration of indigenous tree species impossible under their three to four metre-high canopy.

Efforts are underway across the Danube basin to combat this aggressive shrub species and here grazing appears to be an important part of a successful approach. In the Sava floodplains, the NGO BED (Ecological Society of Brod) has proven that the combination of cattle grazing and treading (by Podolian cattle) is the only permanent way to keep Amorpha under control on a large scale and enable the original flora and fauna to regenerate.


A significant role for cattle

Opening up of dense groves with Amorpha by cattle at Tataru island.
Dense groves of Amorpha opened up by cattle on Tataru Island. The plants show significant damage as a result of browsing and trampling.
Sergey Podorozhny

Another example can be found on Ermakov Island, where the plant has spread after agricultural abandonment. However, the reintroduction of horses and water buffalo on the island has seen the animals start to eat and trample Amorpha, especially in the winter. They inflict a lot of damage on the shrubs, giving a diverse range of indigenous vegetation more space to flourish.

Further upstream, on the island of Tataru, a herd of Ukrainian grey cattle suppresses Amorpha to the extent that this invasive species doesn’t have a chance to dominate the vegetation. Research on Tataru Island has shown the significant role of cattle in opening up the dense thickets of smaller willow species (Salix triandra and Salix fragilis), as well as suppressing the Amorpha fruticosa and opening up its groves.

Introduced in 2008, grey cattle had almost doubled the coverage of meadows on Tataru Island by 2010.


Concluding remarks

Natural grazing is not a panacea for all invasive species. But it appears that in many cases it can significantly suppress them and allow more complex native ecosystems to develop.

As such, extensive grazing systems should be supported as a relatively inexpensive way of tackling invasive species, particularly in regions strongly impacted by one specific species (for example, the false indigo-bush in the Danube basin and giant hogweed in some other areas).


Misha Nesterenko and Oleg Dyakov/Rewilding Ukraine

Wouter Helmer/Rewilding Europe

This blog is created as part of GrazeLIFE, a project to evaluate the benefits of various land management models involving domesticated and wild/semi-wild herbivores. The project is carried out at the request of the European Commission. The GrazeLIFE Consortium gathers information through literature reviews, interviews with more than 100 stakeholders, and field research in 8 European regions (encompassing 11 European countries). Through these blogs, the 10 consortium partners share experiences and insights that are intended to support discussion on grazing best practice.


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