The imprint of the European metropolis remains in the vegetal landscape of its former colonies centuries later

Between the north of Australia, the south of South Africa and the east of Canada there are thousands of kilometers of distance.

As there are between the Mexican Pacific and the Canary Islands or between Southeast Asia and Suriname.

However, their floras are more alike than nature would dictate.

It is the still visible trace of European colonialism.

A group of researchers has overlapped the extension and duration of four great empires with the current distribution of thousands of plant species.

They have verified that many regions share a landscape decades and centuries after those empires fell.

The British was the one that most modified the environment and the Dutch, the least.

In between are Spanish (the second most transformative) and Portuguese.

In their travels, humans have always carried with them part of the flora of their homeland.

Whether for food, aesthetics, nostalgia for its landscape or accidentally, the introduction of exotic species that end up adapting to the new environment (naturalized) is a constant in human history.

But the transfer multiplied to scales never seen before with the beginning of the era of colonial empires when, from 1492, Europeans connected all corners of the planet with each other.

Expert ecologists in biological invasions have used the most recent information housed in GloNAF, a worldwide database with the distribution of naturalized plants, to determine their presence in almost 1,200 regions that in the past were colonies of one or more metropolises.

As expected in empires as large and diverse as the four studied (British, Dutch, Portuguese and Spanish), there is a great heterogeneity of landscapes.

The variable that most influences the diversity of the flora is the climate.

But they soon observed that when comparing different and distant regions belonging to the same empire, some have a greater degree of vegetal similarity than that indicated by climate, latitude or simple chance.

This similarity is greater between some of the former British colonies, followed by the Spanish, the Portuguese and, finally, the Dutch.

University of Vienna botanist Bernd Lenzner, the study's first author, says there are a number of explanations for this trend toward uniformity within empires.

"One, which we consider important, is that the British Empire was, on the one hand, very long-lasting, but also very recent."

Indeed, in the analysis of it, they observe that the longer a region belonged to an empire, the greater plant resemblance.

Imperial longevity would also explain much of the common landscape in various areas of the former Spanish empire.

Some, like various Mexican or Andean ecoregions, belonged to the Spanish crown for 290 years.

Rubber plantation in the Thai province of Nakhon Si Thammarat.

Originally from the Amazon rainforest, the English and Dutch introduced it to Southeast Asia. Surapan Boonthamon (Reuters)

The when of each empire also influences.

The Spanish empire began before the British.

The expansion of the first was made in wooden ships, that of the second, in ships and trains with steam engines, which facilitated the connection between the different parts of the British territory.

In the 16th and 17th centuries, led by the Spanish, there were hardly any plans for the conscious introduction and naturalization of species from one place to another.

It was not until the 18th and 19th centuries, the golden age of the English, that botanical gardens and acclimatization societies became popular, seeking to clone the English countryside in the colonies.

Also the governing style of each empire is relevant.

“The restrictive trade policies of European empires ensured that plants were predominantly traded between regions occupied by the same power.

Therefore, the set of species exchanged between regions was limited to the territory of the empire and, as a result, these areas became more similar in their flora compared to those outside”, says Lenzner.

Both Spain and Portugal and, to a lesser extent, England, only allowed trade within the empire, the rest was contraband.

The case of the Dutch empire, the one with the least floral similarity among its colonies, would show the opposite connection.

The Netherlands maintained more open trade policies, which would have facilitated greater heterogeneity.

“The restrictive trade policies of European empires ensured that plants were predominantly traded between regions occupied by the same power”

Bernd Lenzner, botanist at the University of Vienna expert in biological invasions

The work, which is based on network analysis, reveals that the central regions of each empire also have a greater similarity in their vegetal landscape.

In particular, the areas with commercial relevance, administrative capital status or important ports present more plant convergence within each empire.

This is the case of the coast of the current state of Guerrero, Baja California (Mexico) and Nariño (Colombia).

In the British Empire, eastern Australia and India stand out.

In the opposite direction, from the colonies to the metropolises, they barely observe significant modifications in the natural landscape of the ancient empires, beyond the gardens of exotic plants or agricultural species (not included in the study).

An exception would be the naturalization of various species of cacti, such as prickly pears, in much of Spain or southern Italy.

But they did work as repeaters.

Franz Essl, also from the University of Vienna and senior author of this research, comments on this: “They served as a center for the propagation of exotic plants, since in many cases new species were introduced from the colonies first to the mother country and, subsequently, to the mother country. they spread to other regions within the empire.”

Biological invasions carried out by animals, such as that of rabbits in Australia or that of cats on many islands, are well known.

But the impact of foreign flora can also be definitive.

“I agree that notorious cases of species well known to humans, such as rabbits, stand out for their harmful nature.

But non-native plants can profoundly alter habitats and ecosystems”, recalls Essl.

And he gives two examples.

On the one hand, the cat's claw (

).

Originally from South Africa, "it was introduced as an ornamental species in the Mediterranean regions of the world, where it has become very abundant along the coasts (also in Spain) and where it outcompetes specialized native plant species," he says. .

On the other hand, Essl also mentions the problem of many islands.

In previous work they showed that more than a quarter of all the islands studied have accumulated more exotic plant species than native ones.

Prominent examples are Hawaii or Mauritius, imagined by many as almost pristine paradises.

"There, exotic plant species have strongly transformed island ecosystems," warns the scientist.

One factor that aggravates the impact of plant colonialism is that plants are at the base of every ecosystem.

Another is time.

"We knew that alien species can take decades to establish and spread within a region into which they have been introduced, and that this process often takes place with a substantial delay," he recalls.

But he adds: “Detecting such legacies several decades, sometimes even centuries, after the collapse of European empires is something to reckon with.

This shows that we need to be very careful and aware of which species we move around the world."

The researcher at the Friedrich-Alexander University (Germany) Nussaibah Raja does not believe that the idea of ​​plant colonialism is new, but highlights the relevance of this research: “I think this work is the first to really recognize the impact of colonialism on the distribution global flora and how this radically changed the world as we know it.”

For her, she adds in an email, this type of research is indicating "a change towards the acceptance of how historical events have affected ecology."

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