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Growing plant trade may spread invasive species – but help ecosystems adapt to climate change
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Growing plant trade may spread invasive species – but help ecosystems adapt to climate change

A large adult bison in a forest clearing.


To ensure healthy ecosystems, plants seeds must travel long distances. Travelling seeds are carried on the wind, in the fur and dung, or in the fur of animals. They help clear forest patches regrow and infuse rare species with diverse genetics, making them more resilient to extinction.

It is important to understand how plants disperse. It is becoming more importantThe human impact on natural habitats is increasing. As commerce and tourism become global businesses, humans are intentionally or unintentionally moving many plants, or their seeds or cuttings at an unprecedented pace.

This can, on the one hand help species adjust their range to suit their climate requirements. Many of their former habitats have become too dry or hot, so it is important to move. ensure plants persistChanges in landscapes are rapid. Options for survival have already been severened by the loss large wild herbivores and herded livestock, as well as fruit-eating wildlife. long-distance dispersal. In their absence, humanity can act the main dispersal agent, transporting many species over very large distances.

A large adult bison in a forest clearing.
Bison herds once helped to disperse plant seeds throughout Europe.
Michael Gäbler/Wikipedia, CC BY

However, human activity can increase the spread of potentially invasive and alien species. These plants can cause disruptions in whole ecosystems, and can also crowd out native species.

The dispersal of cultivated soil and the growing global trade in cultivated crops has been linked to an increase in global trade. Species that could be contaminant. However, the accidental dispersal of seeds is often overlooked. Very few studies have examined how many seeds are buried in these soils. Given the fact that many of these growing mediums are made in large quantities (more then a million), it is not surprising that they are so expensive. 30,000,000 cubic metresIt is produced every year in the EU) and ready to use potting soils are Regularly importedThe importance of this dispersal pathway to distant countries is likely underestimated.

Accidental human dispersal

In Research in progressWe also studied the effects of this process. We purchased three bags of 11 different commercially available potting soils from Debrecen (Hungary) from several different producers. From March 2019 to November 2019, we germinated each bag with samples. We weighed each seedling and identified its species. Then, we calculated how far each species could have spread.

Plastic trays of potting soil with germinating seedlings in a greenhouse.
The potting soil samples are used to grow plants.
Judit Sonkoly, Author provided

One litre of potting dirt contains on average 13 seeds of six species. A 20-litre bag of soil purchased from a garden center could contain approximately 265 viable seeds. Each potting soil had a different seed content. Soils with manure contained more species and seeds than soils that did not have it. This suggests that long-distance dispersal occurs due to grazing livestock passing seeds and people adding seed-rich manure potting soils which they transport and use over long distances. The dispersal ability of a species of plant depends on its diet.

A map of Europe with diamonds depicting the places of production and purchase for potting soils.

Peat from Lithuania had to travel thousands of kilometres in order to reach its destination.
Judit Sonkoly, Author provided

The distances the seeds travelled in the potting soils, from where they were produced to where they were purchased in Debrecen, ranged from 171km (originating in Lučenec, Slovakia) to 1,117km (originating in Münster, Germany). Some potting soils can be transported and sold further. Each seed has a very slim chance of establishing itself in a new place, but the large number of seeds that are dispersed this way makes up for the low probability.

Five of the species that germinated out of soil samples weren’t native to Hungary. However, four of them (redroot amaranth., Canadian horseweed., daisy flyabane. and tall goldenrod) are already well-known in Hungary. Only fringed willowherb is still in existence. Meanwhile, several native but sparse species were found in the samples: small-flowered bittercress, St. Peter’s wort and blunt-flowered rush.

A clutch of daisy-like flowers.
Daisy fleabane, an invasive species that is widespread in Hungary.
Contri/Wikipedia, CC BY – SA

This means that the global trade in plants is capable of spreading and introducing new species. It also represents a general dispersal pathway to many species. It can help genes flow between isolated populations, shift ranges in response to changing climate and landscape, or other large-scale ecological processes that are of great conservation concern. This pathway of long distance dispersal can have both negative and positive effects on plant communities.

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