A giant Himalayan lily in Sichuan, June 2004. The British introduced this flower from India to temperate regions of their other colonies. It has since escaped home gardens and become invasive in New Zealand. Photo: Ernst Gügel/Wikimedia Commons, CC BY-SA 3.0
- In a study, researchers in Vienna studied alien plants introduced by four major colonial powers: the British, the Spanish, the Portuguese and the Dutch.
- The team evaluated a database of naturalised alien plants called GloNAF to determine patterns of similarity or diversity in the distribution of these plants.
- According to the researchers, parts of the world colonised by the same power had more similar flora than those that were unoccupied or ruled by a different power.
- The study also found that alien flora in regions colonised by the British and the Dutch were also more similar than they were to those in other randomly selected regions.
- Although alien plants were naturalised for their economic value, the phenomenon has taken a toll on the biodiversity and economy of colonised countries.
The distribution of certain plants in different parts of the world is tied to their colonial history, according to a new study. These plants in places that the Europeans colonised are more similar to each other than to those in other random parts of the world.
An international team of researchers led by Bernd Lenzner and Franz Essl, a postdoctoral researcher and an associate professor, respectively, at the University of Vienna, conducted the study. Their findings were published on October 17.
Naturalised alien plants are plant species that aren’t native to a region, are introduced from outside, but adapt to the local climate and eventually grow there.
The introduction of alien plants to new regions dates back to the late Pleistocene age, when humans started migrating out of Africa, and the Neolithic age, when humans settled as farmers and agriculture spread from Asia to Europe.
The phenomenon gained momentum in the 15th century when Europeans started exploring and colonising. Although explorers initially brought food crops into the “new world” they discovered, colonial powers then introduced alien plants of economic and aesthetic value in the parts of the world they colonised.
Many such alien plants introduced centuries ago have now become household names in their new habitats. “We can hardly differentiate between native and alien flora,” Shyam Phartyal, an associate professor of forestry at Nalanda University, New Delhi, told The Wire Science. “For instance, imli, or tamarind, was introduced to India from tropical East Africa and named Tamarindus indica. We now think of it as native to India.”
Many garden plants and avenue trees we use today were brought here by the Europeans, he added.
In their paper, the Vienna researchers studied alien plants introduced by four major colonial powers: the British, the Spanish, the Portuguese and the Dutch.
They were quite surprised to still find the legacies of European empires in alien plants across the world echoing the world’s colonial history.
“Given the huge increase in plant introductions during the last decades, I find this quite remarkable,” Essl told The Wire Science. “Our study is the first that proves that colonial history is not only influencing cultural, linguistic and economic realities on the globe, but also the large-scale distribution of biota”.
The team evaluated a database of naturalised alien plants called Global Naturalised Alien Flora (or GloNAF) to determine patterns of similarity or diversity in the distribution of these plants in different parts of the world.
Using the 19,250 naturalised alien plant species on GloNAF, covering 1,183 regions, the researchers investigated the following aspects:
1. Whether naturalised plants occupied by the same European empire were more similar to each other than to those in random regions of similar size;
2. Whether regions colonised by the same empire for a longer period have more similar naturalised plants than other regions occupied by the same empire;
3. Whether certain regions that were strategically important for a colonial power had similar naturalised plants than in those that were less important strategically.
According to the researchers, parts of the world colonised by the same power had more similar flora than those that were unoccupied or ruled by a different power. For example, India, China and northern Australia have similar naturalised alien flora because of their shared colonial occupation by the British.
The study also found that alien flora in regions colonised by the British and the Dutch were also more similar than they were to those in other randomly selected regions. But plants in regions where the Portuguese and the Spanish ruled were not that similar when compared with those in other regions. This is because, Lenzner said in a press release, “The European empire’s restrictive trade policies ensured that plants were predominantly traded between regions occupied by the same power.”
“Hence, the set of species exchanged between regions was restricted to the extent of the empire and consequently the regions became more similar in their floras compared to outside regions – a process that intensified with the length of time a region was occupied by the empire.”
The study also found that the longer an empire colonised a region, the more similar their alien plants were to other regions colonised by the same empire for similar periods. This effect was not evident in regions that had been colonised for fewer than 140 years. The researchers speculated that this could be because of a general increase in the exchange of commodities in the late 19th century.
The climate and geographical distance between these places also drove this phenomenon. For example, alien flora introduced by the Dutch are predominantly seen in the Indo-Malay region as the area was a hub of trade activities of the Dutch in the 17th and 18th centuries. A critical reason for this, as the authors report, is because islands have a high success rate for naturalisation of alien plants because of their ecology and eco-evolutionary history.
Regions of administrative, strategic or economic importance for the colonial powers had very similar alien flora. For example, Australia and India emerged as important regions for the British empire. “The deliberate exchange of plants and plant materials across the British empire was well developed, with large networks of botanical gardens and acclimatisation societies,” the authors wrote in the paper.
As Phartyal said, the states of India that Britishers used as “summer vacation spots” – Uttarakhand, Himachal Pradesh, Maharashtra, Tamil Nadu, and Karnataka – had very similar naturalised alien plants as well.
Ecological and economic cost
Although alien plants were naturalised for their economic value, the phenomenon has taken a toll on the biodiversity and economy of colonised countries.
Phartyal recalled the shola grassland ecosystem of the Western Ghats, which the British degraded by introducing alien plants from Australia – acacia, eucalyptus, pine and cypress – because they considered the grassland to be ‘barren’ land.
“Often, Europeans who travelled to the global south in the 16th and 17th centuries romanticised tree-dominated landscapes and, therefore, wanted to plant trees on grasslands of the global south,” Phartyal said.
The giant Himalayan lily, which the British introduced from India to temperate regions of their other colonies, has now escaped home gardens and become invasive in New Zealand.
Apart from their effect on biodiversity, invasive alien species also have enormous economic implications. According to a 2022 study conducted by an international team of researchers led by Alok Bang, an assistant professor at Azim Premji University, Bengaluru, invasive alien species have cost nearly $183 billion dollars to the Indian economy between 1960 and 2020.
The Parthenium invasive species offers an illustrative example: it came to India as a contaminant with a wheat variety introduced in 1955. Since then, it has resulted in yield loss of up to 50% for different food crops, according to a 2016 study conducted by researchers at Bhagwati College of Management and Technology, Siwaya.
“These findings highlight the necessity of considering long-term consequences of the spread of alien species that are currently mainly driven by global trade,” Essl said.
Phartyal concurred: “I think this study can be used as a reference when our policymakers discuss open trade policies at different world stages, like the world economic forum.”
He added that intergovernmental fora like the G8, the G20 and the BRICS could design treaties to regulate the movement of alien plant species across borders, taking into consideration ways to minimise contamination of the native biodiversity.
Joel P. Joseph is a science writer.