The effects of mulch and scarification on the establishment and growth of six clones of Norway spruce [ Picea abies ( L.) Karst.] were examined in a study in southern Sweden. Mulch and scarification reduced the amount of competing vegetation and tended to improve soil moisture and soil temperature. Budbreak occurred earlier for cuttings planted in the scarification treatment in comparison with the control and mulching treatment. Scarification increased survival and the combination of scarification and mulch resulted in the best growth. Gas exchange and the number of new roots were higher in planting spots covered with mulch. Clonal differences regarding gas exchange and growth were significant. Clones with a poor height growth also had a low gas exchange and a small number of new roots. In contrast, the clone with the best height growth had high gas exchange and a large number of new roots. Clonal effects on growth were greater than site preparation effects.

Specific leaf area (SLA), nitrogen and chlorophyll concentrations and photosynthetic characteristics were studied in upper and lower canopy leaves of Salix viminalis and S. dasyclados grown at two nutrition levels. Fertilization increased SLA and leaf mass-based nitrogen concentration in most cases. Positive effects of fertilization on leaf light-saturated photosynthetic rate (A(max)(A)) and maximum carboxylation rate (V-cmax) were not detected. Significant differences between the leaves from upper and lower canopy layers in area-based nitrogen, A(max)(A), SLA, mass-based chlorophyll, V-cmax and stomatal conductance were found for most plots. We attempted to estimate the fraction of non-photosynthetic nitrogen and found that it tended to be higher due to fertilization. Thus, the insensitivity of leaf photosynthesis to fertilization could be caused by higher proportion of non-photosynthetic nitrogen in the leaves of fertilized plots. Though leaf-level photosynthesis was not increased by fertilization, considerably higher leaf area index of fertilized plots still resulted in increased canopy carbon gain.

Within the last 10 years, computer simulation software for several individual-tree growth simulators has been developed. Using these simulators, long-term prognoses and scenario analyses for the development of forest stands can be conducted. However, during the growth of forest stands trees have to be removed from the stands for reasons like thinning or harvesting. In order to simulate the various types of thinning and harvesting, and for reasons of automatization of these interventions in the simulation process, algorithms are needed to clearly describe which individual trees have to be removed from the forest stand. This paper provides a description of existing thinning and harvesting algorithms of five European individual-tree growth simulators—SILVA, MOSES, PROGNAUS, STAND and BWINPro—which are involved in the EU-project ITM (Implementing Tree Growth Models as Forest Management Tools, QLRT 1999-31349). How these algorithms can be classified is proposed as well. Finally, it provides an overview of several possibilities of application and software implementation of these algorithms. This paper enables developers of individual-tree growth simulators to decide which existing thinning or harvesting algorithm could be implemented in their simulation software.

Seasonal courses of light-saturated rate of net photosynthesis (A360) and stomatal conductance (gs) were examined in detached 1-year-old needles of Scots pine (Pinus sylvestris L.) from early April to mid-November. To evaluate the effects of soil frost and low soil temperatures on gas exchange, the extent and duration of soil frost, as well as the onset of soil warming, were manipulated in the field. During spring, early summer and autumn, the patterns of A360 and gs in needles from the control and warm-soil plots were generally strongly related to daily mean air temperatures and the frequency of severe frost. The warm-soil treatment had little effect on gas exchange, although mean soil temperature in the warm-soil plot was 3.8 degrees C higher than in the control plot during spring and summer, indicating that A360 and gs in needles from control trees were not limited by low soil temperature alone. In contrast, prolonged exposure to soil temperatures slightly above 0 degrees C severely restricted recovery of A360 and especially gs in needles from the cold-soil treatment during spring and early summer; however, full recovery of both A360 and gs occurred in late summer. We conclude that inhibition of A360 by low soil temperatures is related to both stomatal closure and effects on the biochemistry of photosynthesis, the relative importance of which appeared to vary during spring and early summer. During the autumn, soil temperatures as low as 8 degrees C did not affect either A360 or gs.