NATURAL REGENERATION ON PLANTED CLEAR-CUTS IN BOREAL SWEDEN

Natural regeneration was registered on 97 clear-felled and scarified sites in northeastern Sweden ten growing seasons after planting. On each site, three fix plots were laid out at planting and the planted seedlings were mapped. Ten years later all healthy non-planted seedlings were registered in an annulus of size 15.7 m2. Non-planted seedlings were also observed in four 4 m2 squares on each fix-plot to estimate the zero-square frequency. Species were classified as Pinus sylvestris, L., Picea abies (L) Karst. and deciduous species (Betula pendula/pubescens Roth./Ehrh., Populus tremula L., Alnus incana (L) Moench.). On average, 7 133 non-planted seedlings ha-1 were found, of which 29% were conifers. Among the conifers, 71 % were P. abies. More than 2 500 conifer non-planted seedlings ha-1 were found on 27% of the plots. The number of non-planted seedlings was correlated to the presence of neighbouring seed-producing stands within 100 m and decreased with rising altitude. Pinus sylvestris seedlings were more frequent on dry soils while the deciduous seedlings were more frequent on wet sites. In the 4 M2 squares, the zero-square frequency was 29% if both conifers were and deciduous seedlings were considered and 63% if only conifers were considered. Mean height of the tallest seedling per species and square was 62 cm for P. sylvestris, 42 cm for P. abies and 107 cm for the deciduous seedlings.