Tree growth resources and the efficiency of resource-use for biomass production determine the productivity of forest ecosystems. In nutrient-limited forests, nitrogen (N)-fertilization increases foliage [N], which may increase photosynthetic rates, leaf area index (L), and thus light interception (I C). The product of such changes is a higher gross primary production and higher net primary production (NPP). However, fertilization may also alter carbohydrate partitioning from below-to aboveground, increasing aboveground NPP (ANPP). We analyzed effects of long-term N-fertilization on NPP, and that of long-term carbon storing organs (NPP S) in a Pinus sylvestris forest on sandy soil, a wide-ranging forest type in the boreal region. We based our analyses on a combination of destructive harvesting, consecutive mensuration, and optical measurements of canopy openness. After eight-year fertilization with a total of 70 g N m-2 , ANPP was 27 ± 7% higher in the fertilized (F) relative to the reference (R) stand, but although L increased relative to its pre-fertilization values, I C was not greater than in R. On the seventh year after the treatment initiation, the increase of ANPP was matched by the decrease of belowground NPP (78 vs. 92 g C m-2 yr-1 ; ~17% of NPP) and, given the similarity of I C , suggests that the main effect of N-fertilization was changed carbon partitioning rather than increased canopy photosynthesis. Annual NPP S increased linearly with growing season temperature (T) in both treatments, with an upward shift of 70.2 g C m-2 yr-1 by fertilization, which also caused greater amount of unexplained variation (r 2 = 0.53 in R, 0.21 in F). Residuals of the NPP S-T relationship of F were related to growing season precipitation (P, r 2 = 0.48), indicating that T constrains productivity at this site regardless of fertility, while P is important in determining productivity where N-limitation is alleviated. We estimated that, in a growing season average T (11.5 ± 1.0 °C; 33-year-mean), NPP S response to N-fertilization will be nullified with P 31 mm less than the mean (325 ± 85 mm), and would double with P 109 mm greater than the mean. These results suggest that inter-annual H. Lim et al. 3 variation in climate, particularly in P, may help explaining the reported large variability in growth responses to fertilization of pine stands on sandy soils. Furthermore, forest management of long-rotation systems, such as those of boreal and northern temperate forests, must consider the efficiency of fertilization in terms of wood production in the context of changes in climate predicted for the region.

-Effects of nitrogen fertilisation and thinning, 40% basal area removal, on annual ring width and ring density were studied in a 2 × 2 factorial field experiment in northern Sweden, in an even aged 56-year-old Scots pine stand twelve years after treatment. Each treatment was replicated six times. From four stem heights, wood specimens were measured using direct scanning X-ray microdensitometry. For the whole period, mean ring width increased by 14% following fertilisation and by 40% after thinning. Neither fertilisation (< 1%) nor thinning (-4%) significantly (p > 0.05) changed ring density during the twelve-year period. Based on four-year mean values at 1.3 m, ring width increased in all cases, except for fertilisation in the last four-year period. The only significant effect on wood density was a 5% decrease following thinning during the second four-year period. Linear regression showed negative correlation between ring density and ring width and no additional effects of treatments per se. growth / Pinus sylvestris / wood density / X-ray densitometry Résumé -Évaluation de la largeur et de la densité des cernes après fertilisation et éclaircie dans un peuplement de pin sylvestre. Les effets de la fertilisation et de l'éclaircie sur la largeur et sur la densité des cernes ont été étudiés dans un peuplement expérimental du nord de la Suède, 12 ans après traitement, dans un peuplement équienne de pins sylvestres, âgé de 56 ans. Chaque traitement était répété six fois. Des échantillons de bois représentant deux rayons opposés ont été prélevés à quatre hauteurs et analysés par microdensitométrie scanning direct. Au cours des douze années après traitement, la largeur moyenne du cerne a augmenté de 14 % après fertilisation et de 40 % après éclaircie. Ni la fertilisation (< 1 %), ni l'éclaircie (-4 %) n'ont eu d'effect significatif (p > 0,05 %) sur la densité des cernes durant la période de douze ans. La largeur du cerne à 1,30 m, basée sur des moyennes de quatre ans, a augmenté dans tous les cas, sauf lors de la fertilisation pour la période des quatre dernières années. Le seul effet significatif sur la densité de bois était une diminution de 5 % suivant le traitement d'éclaircie durant la deuxième période de quatre ans. Une régression linéaire a démontré une corrélation néga-tive entre la densité des cernes et la largeur du cerne et pas d'effet additionnel du traitement lui-même. accroissement radial / pin sylvestre / densité de bois / microdensitométrie Ann. For. Sci. 59 (2002) [29][30][31][32][33][34][35][36][37][38][39][40] 29

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Effects of combining lupin (Lupinus nootkatensis L.) establishment and soil scarification on stem volume and stem biomass yield of lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) were studied on a poor boreal site in Sweden 18 years after plantation. A field randomized block experiment was established with three different scarification techniques (disc trenching, moulding and ploughing) followed by establishment of lupins by either seeds or roots. There were three blocks without and two blocks with lupins. Overall, on average for the three soil scarification techniques, the lupin treatment significantly increased the volume per hectare by 102%.The lupin treatment significantly increased the stem volume per hectare by 236% for mounding and 139% for disc trenching, whereas the 55% increase for ploughing was not significant. The increase in the total stem biomass yield per tree was more pronounced for larger trees; 46% for average trees and 106% for dominant trees. However, there were no significant differences between scarification techniques for the lupin treatment in total stem biomass yield. Over the 18-year period, the increased growth rate following the lupin treatment resulted in a significantly decreased average stem basic wood density (on average 6%) for the sample trees. Because lupin is a nitrogen-fixing plant species, the large increase in tree growth following the lupin treatment was probably an effect of increased amount of nitrogen in the soil. The results indicate that use of lupin is a possible alternative to increase site productivity of lodgepole pine on poor boreal sites.