In the autumn of 1996 research was carried out on vegetation and soils of 40 horse ranges in different condition in several parts of Iceland. The data was used in the development of the method presented on these pages. All the examples given are taken from the study. At each study site the work began by assessing the condition according to the classification table and determining the class for the site. Then a 30 metre transect was laid out for measurements of vegetation composition, sward height, herbage biomass, soil erosion and grazing mark.
T
he results showed a relatively good correlation between the classification scale used and the measured parameters, that indicated that the method could be used for assessing the condition of horse ranges. The highest correlation was found for spot erosion, sward height and herbage biomass and they are considered to be the best indicators of the range condition. The results for these parameters are given below.
 Results of measurements of spot erosion, sward height and herbage biomass in horse ranges in different condition in Iceland. |
Spot erosion develops in ranges of prolonged over-grazing. Under normal conditions they should hardly exist on good lowland ranges. The results showed that spot erosion was generally low in classes 0-2 (excellent-fair). It increased considerably in classes 3-4 (poor-very poor) and became very high in class 5 (not suitable for grazing), where it became as high as 47% of ground cover. Sward height showed a very good correlation with the classification scale. In classes 0-2 the sward height was always greater than 10 cm, whereas in class 4 it was always less than 10 cm. In class 5 the sward height was only about 5 cm. (Sward height was measured as the maximum upright height of leaves of grasses and sedges, excluding flowering shoots). Herbage biomass was found to be greatest in class 0 and it was also considerable in classes 1 and 2. In classes 3-5 herbage biomass was greatly reduced and was always less than 30 g/m2 dwt. In class 5 it averaged only 9 g/m2. Vegetation utilisation should generally not exceed 50%. A horse range in fair condition in Iceland should give at least 100 g/m2 of annual growth. The vegetation utilisation determined for classes 3-5 is therefore greatly over the 50% level. Under such conditions the plants are hardly able to build up the necessary carbohydrate storage in their roots for the winter. Growth in the spring will be reduced and under prolonged over-grazing the productivity and the general condition of the rangeland will worsen. |