Instead of palm trees only stone gardens

Whe car driver must have seen it as a brown wall, the cloud that suddenly enveloped them as they drove at full speed. The pile-up on the A 19 near Rostock in April 2011 was one of the most serious accidents on German motorways. Strong winds had blown the upper soil layer of dried out fields over the road on both sides of the accident site.

When humans intervene in nature, this often has undesirable consequences. So also on Easter Island in the Pacific. When Polynesians reached the island – between 400 and 800 AD, after more recent findings not even until around AD 1200 – it was covered by a subtropical palm forest. According to pollen analyzes, a plant community flourished on different floors – dominated by mighty honey palms, around 20 million of which could have been on the island. But a thousand years after the Polynesians arrived, there wasn’t a single one left. The island was now a barren steppe strewn with black stones.

Greed for timber and palm sap

Why? “There can only be guesses as to the fact that written sources are completely absent and scientific findings are also rare,” says Hans-Rudolf Bork from the University of Kiel, who has been working on Easter Island for 20 years with his colleague Andreas Mieth. He rules out clear-cutting to create agricultural land: “The palm trees were several meters apart, and horticulture was excellent in between. It is possible that the Polynesians needed the palm trunks to roll their huge stone sculptures, the “Moai”, onto the coasts. Bork thinks it is more likely that they were after the sweet sap inside the palm.

Soil erosion in northwestern Madagascar on the Betsiboka River (“Red River”)

Image: Nasa

However, the depletion had dire consequences. Without the protection of the palm roof, the wind dried up the fertile crumb and carried away its finer particles, the rest was washed away by the rain. “Horticulture ended where the floors were rinsed,” says Bork. Large parts of the east of the island became sterile. People were forced to look for new acreage.

Stone mulch as an adaptation service

However, Bork believes that this did not lead to a collapse of society, because the Polynesians were a resourceful people. “They laid more than a billion stones the size of a fist or head in their gardens.” There were more than enough of these on the volcanic island. This so-called stone mulch protected the fertile soil from rain and wind, and they even reduced evaporation. At the same time, the mineral weathering products of the rock fertilize the soil, and its dark color stored warmth into the evening hours. Man had adapted to his environment, which he had changed so much.

The large-scale cultivation of turf, as here in Ginsheim am Altrhein, is a cause of soil erosion.  After the sward has been scraped off, as can be seen here, hard, dry topsoil remains.

The large-scale cultivation of turf, as here in Ginsheim am Altrhein, is a cause of soil erosion. After the sward has been scraped off, as can be seen here, hard, dry topsoil remains.

Photo: Manfred Lindinger

In this country, too, and not just with the onset of industrialization, environmental changes brought about devastating natural disasters. The traces of an event in the summer of 1342 can still be seen in many places in Germany today. The rains on the day of St. Magdalena went down in history as the Magdalene Flood. Even then, a large number of protective trees had disappeared in Central Europe. Of the forest areas that had dominated the country around the turn of the first millennium, 85 percent had already been cleared by 1300. “Back then, the landscapes of Central Europe were more scarce than ever before,” says Bork, who also deals with the events of the Magdalene flood. “Every usable area had become arable land by the 13th century,” explains Bork.

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