Human colonization causes changes in the vegetation of the islands eleven times more intense than the climate

A study published in ‘Science’ details the impact of the arrival of man to 27 islands around the world

CSIC/DICYT Iceland was colonized about 1,000 years ago by the Vikings, a navigating Nordic people with a strong negotiating character. The raw materials and resources offered by the remote North Atlantic island aroused strong interest from newcomers, who forever turned the economy of the area, northern Europe and most of the world upside down. But the Vikings left a mark on the natural environment that would never be erased again, like many other peoples who have colonized islands around the world. In Iceland, although the vegetation shows changes in the climate prior to human arrival, from the year 920 the activity of the first settlers accelerated changes in the vegetation, intensified erosion and destroyed forests in favor of pastures. The wood needed to build boats, stone and metal from such a resource-rich island were resources looted for years.

Now an investigation with the participation of the Higher Council for Scientific Research (CSIC) published in the journal Science indicates that the changes in the plant life of the ecosystem of an island produced by human colonization are eleven times more intense than those due to climate or effects such as previous volcanic eruptions. The research, led by an international team made up of scientists from the CSIC, has been carried out on 27 islands around the world. This is one of the first times that the human impact on a landscape has been quantified; in this case, thanks to the analysis of pollen samples from 5,000 years ago.

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Most of the world’s inhabited islands have experienced at least two different settlement waves, each with distinctive changes and increasingly complex legacies. This is due, this research indicates, to the “irreversible condition” of the changes that have occurred, which are increasingly rapid. This modification is also constantly reproduced, even centuries after human colonization.

The islands, ideal laboratories

The study constitutes one of the first times that the human impact on a landscape can be quantified, since until now in the continental masses it was difficult to separate the effects of climate and other environmental impacts from those caused by the first humans. The research team has studied fossilized pollen from 5,000 years ago, extracted from sediments of the 27 islands, which has allowed us to understand the composition of the vegetation of each one and how it changed from the oldest pollen samples to the most recent ones.

“The islands are ideal laboratories to measure human impact”, points out Sandra Nogué, a researcher at the University of Southhampton (United Kingdom) and first author of the article. “Most were colonized over the last 3,000 years, when climates were similar to today. Knowing when an isolated territory was colonized makes it easier to scientifically study changes in the composition of its ecosystem in previous and subsequent years, and provides insight dimension of its magnitude “, he emphasizes.

That is why it has been key to know that the population of the Polynesian islands arrived 3,000 years ago to remote areas such as Poor Knight (New Zealand, South Pacific Ocean) and also to Fiji (South Pacific); It is 2,800 years ago that they arrived in New Caledonia (Pacific), and 370 years ago that Europeans landed in Cape Verde (North Atlantic), considered the first tropical European colony in the Atlantic. And, for example, to some islands of the Canary archipelago (Atlantic) the European population arrived between 1,800 and 2,000 years ago, while in the Mauritius Islands (Indian Ocean) only 302 years ago after the arrival of the European colonizers.

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“The environment of those that were colonized by more modern populations, such as the Galapagos (Ecuador, Pacific Ocean, inhabited for the first time in the 16th century) or the New Zealand Poor Knight, received more impact,” explains Nogué. “On the other hand, those previously occupied received more primitive populations, which developed a life more linked to the natural rhythm and more sustainable and, therefore, the territory was more resilient to colonization.” For example, the study shows that islands reached by humans more than 1,500 years ago, such as Fiji and New Caledonia, experienced a slower rate of change.

“This difference in change could mean that previously populated islands were more resistant to human arrival. But it is more likely that land use practices, technology, and species introduced by later settlers were more transformative than those of the former “, explains the researcher.

Although ecosystems cannot be expected to recover their pre-settlement situation, the work can help “guide restoration efforts and understand the territory’s responsiveness to change”, in the words of another of the authors of the work, CSIC researcher Josep Peñuelas, from the Center for Ecological Research and Forestry Applications (CREAF).

From Fiji to Cape Verde

The trends were observed in geographic locations and climates as diverse as those of the South Pacific Ocean, the Indian Ocean, the South Atlantic or the Arctic Ocean, among others. Changes in ecosystems can also be due to various natural factors, such as earthquakes, volcanic eruptions, extreme weather conditions, and changes in sea level. However, the research team has found that man-made disturbances outweigh all these phenomena and the change is usually irreversible. Therefore, they advise that conservation strategies take into account the long-term impact of humans and the degree to which current ecological changes differ from those of pre-human times.

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The results show little evidence that ecosystems affected by man resemble the dynamics present before their arrival. Thus, anthropogenic impacts on islands are long-lasting components of these systems that often involve initial cleanup (for example, through the use of fire), and are exacerbated by the introduction of a number of species and the extinction of endemics. , in addition to continuous disturbances.

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