Epsilon Open Archive

Abstract

Several different silvicultural treatments were studied in two experiments. In the first, mechanical scarification, slash removal, vegetation control, clear-cut age and seedling types were investigated with respect to frost injury to Norway spruce (Picea abies (L.) Karst.) seedlings. Frost damage was also related to near-ground minimum temperature. In the other experiment, the effects of Scots pine (Pinus sylvestris (L.)) shelterwood density gradients, ranging from dense, uncut forest to complete clear-cuttings, were analysed. Near-ground temperature and radiation were monitored close to planted Norway spruce cuttings with a mobile data acquisition system. Growth, frost damage and chlorophyll fluorescence were monitored and analysed in relation to microclimate. Budburst date was estimated and the nocturnal near-ground temperature during the period when the seedlings were most susceptible to frost was analysed in both experiments. The shelterwood moderated near-ground radiation fluxes and diurnal temperature varia-tions, while the daily mean temperature was unaffected. Near-ground minimum tempera-tures were lower, and vertical temperature inversions were more pronounced in clear-cuttings than in shelterwoods, during clear and calm nights. The effects were most pro-nounced during a dry period. Budburst was delayed in the shelterwood. Later budburst was shown to reduce the risk of exposure to frosts during the most frost-susceptible period, when cuttings of two clones, differing in budburst date, were compared. Mechanical scarification reduced frost damage to seedlings in the first growing season, but neither herbicide treatment, nor mowing affected the frequency of frost injury. The frequency of frost injury was higher amongst containerised seedlings than amongst bare-rooted seedlings, especially in the first growing season. Neither clear-cut age nor slash removal affected the frequency of frost damage. Frost injury to the cuttings was reduced by the shelterwoods, since 80% were damaged by frost in clear-cuts and low-density shelterwoods, 27% in moderately dense shelterwoods, and only 5% in dense shelter-woods. Of the climatic variables tested, the accumulated net and global radiation the day after a severe frost event were the most strongly correlated with the degree of frost injury among cuttings, and the variation in their Fv/Fm ratios, in the graduated shelterwoods. Frost injuries were rarely lethal, but reduced growth and increased the proportion of seed-lings with multiple leaders and spike knots, especially amongst seedlings that were re-peatedly injured over several years. Height growth was lower in the clear-cut area than in moderately dense shelterwoods during years with severe frost dama