Karst cliffs and rock shelters on the southwest coast of Madagascar. (Kristina Douglass/Penn State)

Satellite Data Shows Even Small Ancient Gatherer Communities Shaped The Landscape

24 OCTOBER 2021

Even when human societies do not grow crops, farm livestock, build permanent settlements, or burn fossil fuels, they can still shape the surrounding landscape in ways that persist for thousands of years.

 

In Madagascar, a new satellite study has highlighted several ways in which small, highly mobile foragers may have altered the ecology of the southwest coast.

In this corner of the island, archaeologists found evidence of foraging and fishing communities that persisted for close to two millennia.

The ancient humans that once lived here did not seem to farm or build permanent homes. Instead, they inhabited caves and rock shelters along the coast for certain parts of the year, likely moving with the wet and dry seasons.

Despite the 'low-impact' of their lifestyle, researchers were still able to demonstrate extensive alteration of the landscape by these ancient communities using satellite data.

Across all 300 square miles of the territory sampled, roughly 17 percent of the land showed lasting changes likely made by humans.

The impact is much fainter than what we are seeing currently due to human activity, but the environmental changes are surprisingly widespread for such a small, mobile society.

"We underestimate the impacts that non-agriculture societies have on shaping landscapes. These are subtle, but can be discovered," says archaeologist Kristina Douglass from Penn State University.

 

"Looking at landscapes across the world, we find that people modified more of the world than we thought before."

While today human activity has drastically changed the environment on a scale like never before, emerging research suggests humans have been producing "distinct, detectable and unprecedented transformations of Earth's environments" since foraging societies first emerged in the Late Pleistocene.

The Māori of New Zealand, for instance, were hunters, gatherers, and growers that also used fire to tame their landscape.

Recently, scientists have found evidence of soot from those very burns all the way down in Antarctica, which suggests human societies were polluting the atmosphere in minor ways long before the Industrial Revolution.

The new research from Madagascar further supports the idea that foraging communities can also be dominant drivers of landscape change. The impact of these changes on wider ecology, however, is yet to be understood.

Compared to areas of southwest Madagascar not inhabited by ancient humans, those areas that were once occupied held different soil and vegetation even to this day.

This could either represent direct human modification, or it could be that there was something special about the soil in these spots that was attractive to foragers.

 

Analyzing reflections in the satellite data, it appears the soil where human artifacts were found can absorb more water than soil elsewhere.

Further research on the ground in these areas will be needed to confirm whether that extra water-guzzling quality existed before humans arrived or was due to human interference.

Because the biggest difference between these locations was the presence or absence of archaeological artifacts, however, the authors suspect the differences are probably due to human activity.

"What we don't know is whether these types of changes in soil chemistry allowed people to occupy the areas in time of drought," says Douglass.

"Or whether it allowed the ground to retain moisture and grow different plants."

Such small increases in the soil's ability to retain moisture could have made a significant difference to the livelihood of the humans and the wildlife that sustain them in this arid region.

Regardless, the results of the current study suggest hunter-gatherers were fully capable of manipulating the environment around them for their own gains.

Wherever we go and whatever we do, it seems humans cannot help but leave a mark.

The study was published in Frontiers in Ecology and Evolution.