European empires had a lasting impact on plant biodiversity worldwide

The global distribution of plants has been heavily influenced by the European empires that spread alien species across the world from the 15th century onwards

By Luke Taylor

The Azores were an important staging post for the Portuguese Empire

DaLiu/Shutterstock

European occupation and trade in the colonial era irreversibly transformed the global distribution of plants, leaving a legacy that can still be seen today.

The expansion of European empires from the 15th century onwards is known to have spread plant species around the world – for example, the common dandelion (Taraxacum officinale) was spread widely across the British Empire.

Bernd Lenzner at the University of Vienna and his colleagues studied a global database of alien plant species to quantify the impact that colonisation had on the distribution of plants for the first time.

The researchers studied the similarity of non-native species in 1183 regions of the former British, Dutch, Portuguese and Spanish empires.

The time that regions colonised by the same empire spent as colonies was as strong a predictor that they would share the same non-native species as modern social and economic factors were.

“The impact is almost equally important to the trade that we observe nowadays, so it’s really a strong signal still in this composition of flora,” says Lenzner.

The strongest predictors that countries would share the same types of non-native plants were proximity, common temperature and aridity, as climates dictate where alien species can survive.

But for non-natural causes, the time a country spent in the British or Spanish empires had more of an impact than GDP or human population density.

Regions of particular importance for the functioning of an empire were especially likely to share plant species with other regions in the same empire. Regions with major trading ports, such as Guerrero in Mexico and Port Curtis in Australia, had the strongest similarities with other locations in the Spanish and British empires.

The global spread of alien species was partly driven by the export of crops for agriculture in colonies, such as millet in the British Empire and sweet potato in the Portuguese Empire. But a fascination with exotic plants in the 18th and 19th centuries also played a key role, says Lenzner.

Countries that were part of the British Empire had the most foreign species in common, which may be partly because it had a strong botanical culture with many societies that imported exotic species for their gardens.

It is also possible that the commonality of species is related to how colonisation spread languages and established trade routes that continue to have an impact today.

The study highlights the lasting effect that the introduction of a foreign plant or animal species, intentionally or accidentally, can have.

Invasive species are increasingly disrupting ecosystems across the world as globalisation accelerates. With no natural predators or competitors, they often spread quickly and are hard to contain.

“We really need to think today about which species we are transporting across the world because we will see the consequences of that very far into the future, in the decades and centuries to come,” says Lenzner.

Journal reference: Nature Ecology & Evolution, DOI: 10.1038/s41559-022-01865-1