PARENT SESSION
Oral Session 7: GIS / Remote Sensing I.
Presiding: E Ellis and P Valko
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room B 116.
Land degradation in Iceland: Rates, patterns and processes.
THORSSON, JOHANN*,1, ARCHER, STEVE2, ARADOTTIR, ASA3, WU, BEN1, ARNALDS, OlAFUR4, 1 Texas A&M University, College Station, TX2 University of Arizona, Tucson, AZ3 Soil Conservation Service, Reykjavik, Iceland4 Agricultural Research Institute, Reykjavik, Iceland
ABSTRACT- In Icelandic lowlands, clearing and livestock grazing have transformed birch woodlands into grasslands with small bare spots formed by trampling and locally heavy defoliation. We hypothesize that soil freeze-thaw cycles are locally intensified on these bare spots and contribute to surface destabilization and increases their susceptibility to wind erosion. A positive feedback is thus initiated as new erosion spots appear on the landscape, and existing spots enlarge and coalesce. To test the validity of this hypothesized observation-based scenario and to determine rates and dynamics of change, vegetation cover and erosion spot properties (number, size, density and perimeter), were analyzed using sequential (1945-1997) aerial photographs. Field surveys in 2002 revealed that erosion spots occurred only in open grasslands and in woodland clearings. Total vegetated area and number of vegetated patches in grassland derived from woodlands changed little over the 52 year period. Although the total eroded area changed little, number of bare patches decreased 25% while the mean bare spot area increased 8% between 1945 and 1997. Patch shape complexity (measured as mean shape index) increased until 1977, then started to decrease. Results indicate that small erosion spots have been coalescing into larger entities, thus increasing the area of surface and perimeter exposed to erosive eolian processes. We predict that unless the current management regime is altered, erosion spots and patches on these landscapes will reach a critical structural threshold, whereby small additional increases in size will elicit disproportionately high losses of vegetation cover and soils.
Key words: remote sensing, andisols, land degredation, degredation processes