Fig 1.
Severely degraded landscape in South Iceland–a ‘desert’.
Remnants of deep soils (Andosols) and vegetation as an island on the right in the barren landscape. Glacial till surface from the Pleistocene glaciation left behind after soil erosion has removed the fertile dark-colored Andosols. The surface has been lowered by ~2.5 meters. The person to the left, inside the white circle, of the vegetation island provides scale. The area was previously fully vegetated with birch forests, which were utilized as fuel into the 17th century. The soils were coarse grained, near the active volcanic belt and susceptible to erosion.
Fig 2.
Distribution of the 500 sample areas (SA’s) in Iceland.
The lines separate geographical areas used in some of the statistical analysis. The Southern and Western region (S&W), the Northern region (N), Eastern region (E) and the Peninsulas (P). The peninsulas consist of the northernmost part of Iceland (NP) and the Westfjord Peninsula (WP).
Table 1.
List of variables extracted for each of the 500 sample areas (SA’s) in Iceland.
Further explanation is provided for each variable in the text.
Fig 3.
GroLind land condition (GL-value) map for Iceland.
The codes for the values are 1: very poor; 2: poor; 3: marginal; 4: good; 5: excellent (see also Table 2). © The Icelandic Soil Conservation Service/GroLind.is.
Table 2.
GL-values based on a land condition survey in Iceland.
The values are based on cumulative grade range for five factors: i) vegetation height, ii) proportion of bare ground, iii) proportion of vascular plants and iv), carbon content in soil surface horizons and v) soil erosion. Each grade range results in a GL-value, ranging from 1 (very poor condition) to 5 (excellent condition).
Fig 4.
Examples of land condition in Iceland.
A: Excellent, native birch forests (GL-value 5. B: Degraded, about 60% vegetation cover, marginal to poor land condition (GL-values 2 and 3). C: Very degraded area, vegetation islands remain, very poor land condition (GL-value 1). D: Desert area with vegetation remains in wetter depression. Mixture of good condition (wetland–GL-value 4) and very poor condition (desert–GL-value 1). Depending on how the sample area (SA) is selected, the land in figure D can have an average GL-value of 2–3.
Fig 5.
Map of dust deposition rates in Iceland from very low (1) to excessive deposition (7).
1: <50; 2: 50–100; 3: 100–150; 4: 150–250; 5: 250–500; 6: 500–1000; 7 >1000 g m-2 yr-1. Based on [39, 47].
Fig 6.
Such landscapes have long continuous and often steep slopes. Composition is commonly rhyolitic associated with extinct volcanic systems, in contrast to the basaltic lava flows making up most Icelandic rocks.
Fig 7.
A partial residual plot on the relationship between land condition values (GL-value) and A) Elevation (m.a.s.l.), B) Wetland index/Drainage, C) Dust deposit and D) Scree slop in Iceland, based on 500, 500 x 500 m sample areas. The black line is the regression line and and the gray area represent 95% confidence interval around the regression line.
Table 3.
Results from a regression model explaining the relationship between land condition and elevation, dust sedimentation rates, drainage/wetland, scree slope and slope angle for each region in Iceland.
Only results from the best model are shown. β st. is the standardized β.
Fig 8.
Comparison of land condition values (GL-values) for dryland sample areas and wetland sample areas in Iceland represented by boxplots.
Fig 9.
Relationship between GL-values (representing land conditions) and elevation in Iceland, separated by regions.
The GL-values for the Westfords Peninsula and the northern peninsulas (P) are more sensitive to elevation (line sitting lower) than the North and East regions (N and E respectively), with the South & West (S) being intermediate. The difference is more than 200 m in elevation between the regression lines where it intercepts with the GL-value of 3, and even greater for lower GL-values. The vertical lines indicate elevations limits where sample areas (SA’s) with GL-values >3 (marginal to excellent condition).