The global distribution of plants has been heavily influenced by European empires that spread alien species throughout the world beginning in the 15th century.
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| The Azores served as a vital staging point for the Portuguese Empire. DaLiu/Shutterstock |
European colonial occupation and trade irreversibly altered the global distribution of plants, leaving a legacy that can still be seen today.
The expansion of European empires beginning in the 15th century is known to have spread plant species all over the world; for example, the common dandelion (Taraxacum officinale) was widely spread across the British Empire.
For the first time, Bernd Lenzner of the University of Vienna and his colleagues examined a global database of alien plant species to quantify the impact of colonization on plant distribution.
The researchers compared non-native species in 1183 regions of the former British, Dutch, Portuguese, and Spanish empires.
The time spent as a colony by regions colonized by the same empire was as strong a predictor of sharing the same non-native species as modern social and economic factors.
"The impact is almost equally important to the trade that we see today, so it's really a strong signal in this flora composition," Lenzner says.
Climate dictates where alien species can survive, so proximity, common temperature, and aridity were the strongest predictors of countries sharing the same types of non-native plants.
However, for non-natural causes, a country's time in the British or Spanish empires had a greater impact than GDP or human population density.
Plant species were especially likely to be shared between regions of particular importance to the functioning of an empire. Regions with major trading ports, such as Guerrero in Mexico and Port Curtis in Australia, bore the most resemblance to other parts of the Spanish and British empires.
The export of crops for agriculture in colonies, such as millet in the British Empire and sweet potato in the Portuguese Empire, contributed to the global spread of alien species. However, a fascination with exotic plants in the 18th and 19th centuries also played a role, according to Lenzner.
Countries that were part of the British Empire shared the most foreign species, which could be attributed to the fact that the British Empire had a strong botanical culture, with many societies importing exotic species for their gardens.
It's also possible that species' similarity is related to how colonization spread languages and established trade routes that still have an impact today.
The study emphasizes the long-term impact that the intentional or unintentional introduction of a foreign plant or animal species can have.
As globalisation accelerates, invasive species are increasingly disrupting ecosystems around the world. They spread quickly and are difficult to contain because they have no natural predators or competitors.
"We really need to think about which species we are transporting across the world today because the consequences will be felt for decades and centuries to come," says Lenzner.
Journal reference: Nature Ecology & Evolution, DOI: 10.1038/s41559-022-01865-1