Forest structure classes in central Finnish Lapland

Structure classes and changes in the vegetation attributable to the altitud e of the terrain were studied in the Hammastunturi virgin coniferous forest area. The area is located in Finnish Lapland, approximately 250-350 km to the north of the Arctic Circle (68 degrees 15'N; 68 degrees 45'N). The foll owing forest classes were formed on the basis of the ground Vegetation and stand coverage: (1) Pine stands, with birch admixture (n = 14), (2) Vaccini um-vitis-idaea-type pine stands (n = 24), (3) Vaccinium myrtillus-type pine stands (n = 17), (4) mixed stands, dominated by pine (n = 8), (5) mixed st ands, dominated by spruce (n = 18), (6) paludified spruce stands (n = 3) an d (7) vigorously growing spruce stands (n = 6). The forest structure classe s were depicted using DCA ordinates. The differences were more distinct tha n those between the normal forest type classifications of the same sample p lots. The basal area and volume of pine decreased with increasing altitude, while the proportion of spruce on those sample plots where it was present increased. Birch was present at an equal frequency at all altitudes. The fl oral composition and between-species abundance changed along with increasin g altitude. The change in floral frequencies could not be designated to a s pecific altitude zone.