Research press release





今回、Fiona Marshallたちの研究グループは、ケニア南西部のナロック郡にある3700~1550年前の新石器時代のものとされる牧畜地(5カ所)で化学分析、同位体分析、および堆積物分析を行った。その結果、この牧畜地で見つかった分解された畜糞堆積物には、周辺の土壌に比べて栄養素(カルシウム、マグネシウム、リンなど)と重窒素同位体が多量に含まれており、またこの肥沃化が最長3000年間継続したことが判明した。この結果は、マラ-セレンゲティのようなアフリカのサバンナが、「手付かずの」ままの景観では決してなく、牧畜民の影響を数千年間受けてきたことを示唆している。


African grasslands such as the Mara-Serengeti have been supported and enriched by mobile herders for thousands of years, reports a paper published online this week in Nature. This finding challenges the traditional view of the Mara-Serengeti as a pristine, wild savannah.

Grasslands play a vital role in supporting large wild mammal populations, along with herders and their livestock - although roaming herds have previously been implicated in landscape degradation. Recent studies have shown that livestock waste deposits in overnight pens can actually enrich the landscape by creating fertile hotspots that promote plant growth and grassland diversity. However, little is currently known about how long this effect persists.

Fiona Marshall and colleagues conducted chemical, isotope and sediment analyses of five Neolithic Pastoral sites in the Narok County of southwest Kenya that date back to between 3,700-1,550 years ago. They find that degraded dung deposits unearthed at these sites have high levels of nutrients (such as calcium, magnesium and phosphorus) and heavy nitrogen isotopes in comparison to nearby soils, and that this enrichment has persisted for up to 3,000 years. This suggests that, far from being a ‘pristine’, untouched landscape, African savannahs such as the Mara-Serengeti have been influenced by herders for millennia.

These findings add a historic perspective to ecological research into the significance of human-engineered nutrient hotspots, and further challenge the notion that the spread of pastoralism is inherently tied to environmental degradation.

doi: 10.1038/s41586-018-0456-9

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