The spread of exotic plants bears the effects of colonialism

Photo above: Robinia pseudocacia is a tree native to North America that has been introduced to all continents. European empires often played an important role in its emergence and spread. (C: Franz Asel)

An international team of scientists has compared a database of exotic plants with models depicting the colonization of European countries. “In this data, we saw that the distribution patterns of plants correlate with colonial history,” says Bernd Lenzner, an ecologist who specializes in invasive species at the University of Vienna.

The similarities between the areas that were once part of the same colonial empire are significant, even today. The spread of plants throughout the colonial empires occurred in all possible directions, both between European centers and colonial lands, and between the colonies themselves. Varieties were often passed down by chance, but species were also introduced for economic reasons or out of botanical curiosity.

Each empire has its own distribution pattern

Colonial history is of course not the only factor that determines which exotic plants take root somewhere. Environmental conditions must first of all allow a new species to survive somewhere. Today’s population density, level of development and connectivity also play a role. “But belonging to a particular colonial empire turns out to be just as important as these contemporary factors,” Lenzner said.

What’s more, Lenzner said, is that all the different colonial empires had their own way of facilitating the spread of plants around the world. The similarities are greater within colonial empires than within empires. Most of the colonial powers pursued a restrictive trade policy. This meant that trade was primarily conducted within a colonial empire, rather than between the various colonial powers. The spread of plants through trade, transport, and deliberate introduction was therefore more intense within the colonial empire than among them, something that can still be seen today in exotic plants.

The impact of colonialism on the distribution of plants is related to the length of time the region was under European occupation, and its importance within the colonial empire. “We see more exchange of plant species between regions of significant economic or strategic weight within an empire such as the Indian archipelago, for example, the islands between Asia and Australia and an important area for the spice trade.”

Differences in the distribution pattern of exotic plants also have to do with the period in which the region was under European occupation. Lenzner argues that the height of the British colonial empire came later than its Spanish or Portuguese counterparts. In the period when Great Britain was the dominant colonial power, technology was much advanced. Transportation was easier, more frequent, and faster, which led to a more intense distribution of species.

Meanwhile, we live in a highly globalized world, and plants, animals, and microorganisms travel around the world on an unprecedented scale. The fact that the botanical imprint of colonialism is still clearly visible today is thought-provoking, Lenzner says. The spread of species by humans has an impact on biodiversity that can sometimes be felt centuries later. This should make us more cautious, because the movement of species around the world has long-term and profound consequences that will only become clear in the future.