Agriculture and Its Residual Effects

This chapter shows how detailed historical ecological research indicates that the impacts of historical agriculture are more widespread than previously thought, and often more subtle. Even apparently obvious connections, such as that between nomadic grazing and erosion, are now being questioned by historical analyses. Agriculture has not resulted universally in decreased biodiversity; in fact, grazing over millennia has in places increased biodiversity. Historical agriculture is also being implicated in millennial scale increases in CO2 and CH4 in the atmosphere, the former from deforestation and fires and the latter from paddy rice agriculture starting five thousand years ago. The discovery of hidden field systems under mature temperate and tropical forests and grasslands in Europe and the Americas are allowing reassessment of the impact of prehistoric agricultural systems on soils, species diversity, landscape patterns, and climate. The concept of "landnam" episodes proposed by Iversen for northern Europe may be applicable much more broadly. This has major consequences for considering human impact on global environments.