THE VEGETATION AND SOILS OF THE THINGVALLAVATN AREA

Climatic conditions for plant growth are relatively favourable in the Thingvallavatn area compared with the conditions in Iceland as a whole. This is, however, only partly reflected in the characteristics and present state of the vegetation due to soil erosion and deterioration of the vegetation, which has caused tremendous reduction in the agricultural value of the land. The soils around the lake are mostly of aeolian origin, well drained, with a low content of clay and a mineral fraction consisting mainly of volcanic ash. These soils are verv susceptible to water and wind erosion. The vegetation of the area is characterized by absence of trees. Prior to the settlement of Iceland, the lowlands around Thingvallavatn, as well as most other lowland areas in the country, were covered with birchwood. Contemporary woodland around the lake is mostly confined to protected areas, indicating that in the absence of large herbivores, similar woodland vegetation would develop. The most extensive plant communities of the open rangelands of the area are moss heath, dwarf shrub heath, graminoid heath and wetlands. Heavy grazing of the rangelands over a long period has greatly reduced their carrying capacity through unfavourable effects on the flora and on plant production. Only a small part of potential arable land has been cultivated, mostly for hav production and pastures for livestock. Soil erosion is still a serious problem in the Thingvallavatn area. Improved grazing policies during the last decades have sofar, not resulted in a noticable improvement of the rangelands. An immediate, extensive land reclamation programme is needed in order to halt the erosion and restore the deteriorated vegetation.