Collapse_ How Societies Choose to Fail or Succeed - Jared Diamond [156]
Thus, the impact of the Norse on the natural vegetation left them short of lumber, fuel, and iron. Their other two main types of impact, on soil and on turf, left them short of useful land. In Chapter 6 we saw how the fragility of Iceland’s light volcanic soils opened the door there to big problems of soil erosion. While Greenland’s soils are not as supersensitive as Iceland’s, they still rank as relatively fragile by world standards, because Greenland’s short cool growing season results in slow rates of plant growth, slow soil formation, and thin topsoil layers. Slow plant growth also translates into low soil content of organic humus and clay, soil constituents that serve to bind water and keep the soil moist. Hence Greenland soils are easily dried out by the frequent strong winds.
The sequence of soil erosion in Greenland begins with cutting or burning the cover of trees and shrubs, which are more effective at holding soil than is grass. With the trees and shrubs gone, livestock, especially sheep and goats, graze down the grass, which regenerates only slowly in Greenland’s climate. Once the grass cover is broken and the soil is exposed, soil is carried away especially by the strong winds, and also by pounding from occasionally heavy rains, to the point where the topsoil can be removed for a distance of miles from an entire valley. In areas where sand becomes exposed, as for example in river valleys, sand is picked up by the wind and dumped downwind.
Lake cores and soil profiles document the development of serious soil erosion in Greenland after the Norse arrived, and the dumping of topsoil and then sand by wind and running water into lakes. For instance, at the site of an abandoned Norse farm that I passed at the mouth of the Qoroq Fjord, downwind of a glacier, so much soil was blown away by high-velocity winds that only stones remained. Wind-blown sand is very common at Norse farms: some abandoned ones in the Vatnahverfi area are covered by sand ten feet deep.
The other means besides soil erosion by which the Norse inadvertently made land useless was that they cut turf for buildings and to burn as fuel, because of their shortage of timber and firewood. Almost all Greenland buildings were constructed mostly of turf, with at best only a stone foundation plus some wooden beams to support the roof. Even St. Nicholas’s Cathedral at Gardar had only the lowest six feet of its walls made of stone, above which the walls were of turf, with a roof supported by wooden beams and with a wood-paneled front. Although Hvalsey Church was exceptional in having walls entirely of stone up to their full height, it was still roofed with turf. Greenland turf walls tended to be thick (up to six feet thick!) in order to provide insulation against the cold.
A large Greenland residential house is estimated to have consumed about 10 acres of turf. Furthermore, that amount of turf was needed more than once, because turf gradually disintegrates, so that a building must be “returfed” every few decades. The Norse referred to that process of acquiring turf for construction as “flaying the outfield,” a good description of the damage done to what would otherwise be pastureland. The slow regeneration of turf in Greenland meant that that damage was long-lasting.
Again, a skeptic, on being told about soil erosion and turf cutting, might answer: “So what?” The answer is simple. Remember that, among the Norse Atlantic islands, Greenland even before human impact was the coldest island, hence the one most marginal for hay and pasture growth and most susceptible to loss of vegetation cover by overgrazing, trampling, soil erosion, and turf-cutting. A farm had to have sufficient pasture area to support at least the minimum number of animals required to breed back herd numbers after a long cold winter had reduced them, before the next long cold winter. Estimates suggest that the loss of only one-quarter of the total pasture area at Eastern