Response of litter decomposition and soil C and N transformations in a Norway spruce thinning stand to removal of logging residue

Increasing demand for production of bioenergy has led to an interest in forest management which uses logging residue from both clear-cuttings and thinning stands. The aim of this study was to investigate the effects of removal of logging residue in a thinning Norway spruce stand on (1) litter decomposition and (2) soil microbial processes in C and N cycling and the quality of soil organic matter. The study site was a 40-year-old Norway spruce stand growing on a relatively fertile site. During thinning, logging residue was either removed (whole-tree harvest) or left on the site (stem-only harvest). Different types of material in the logging residue, from main branches to needles, were weighed separately into mesh bags. The bags were placed above the moss layer in the whole-tree harvest treatment and in the logging residue layer in the stem-only harvest treatment, and decomposition was monitored for 5 years after treatment. From the humus layer, samples were taken 10 years after treatment. Harvest method affected the mass loss of the litter material very little but the C-to-N ratio of the remaining material was slightly higher in whole-tree harvest than in stem-only harvest, particularly in the needle material. In the humus layer samples, taken 10 years after treatment, the rate of C mineralization was lower in whole-tree harvest than in stem-only harvest; also the rate of net N mineralization and the amounts of C and N in the microbial biomass tended to be lower, although not statistically significantly. Removal of logging residue had no effect on pH (pHH₂O$\text{p}{\text{H}}_{{\text{H}}_2\text{O}}$ 3.9 in both treatments) or C-to-N ratio (28 in both treatments) in the humus layer. The concentrations of total water-soluble phenols and an important group of phenols, condensed tannins, were both lower in the humus layer of whole-tree harvest than in that of stem-only harvest. Concentrations of sesqui-, di- or triterpenes in the humus layer were similar in both treatments. In conclusion, 10 years after harvest, soil microbial activities and organic matter characteristics in whole-tree harvest differed from those in stem-only harvest.     

Determination of the optimal rotation age: A theoretical analysis

This paper systematically analyzes the problem of the determination of the optimal rotation age. Using the land expectation value model, it shows that at the optimal rotation age $\text{t}{}^1$, the marginal revenue product (MRP) of letting the stand grow one more year must equal the marginal input cost (MIC) of doing so. The relationships between regeneration cost (C), interest rate (r), stumpage price level P(t) and the optimal rotation age are then analyzed graphically. The relationships between the land expectation value model, the present net worth model, the forest rent model and the traditional biological model are also examined. It is shown that the last three models are special cases of the land expectation value model.     

The impact of forest fertilization on growth of mature Norway spruce affected by Sirococcus shoot blight

The effects of forest fertilization and Sirococcus shoot blight on growth of mature Norway spruce (Picea abies (L.) Karst.) were studied in a field experiment. The single tree fertilization experiment was established with 144 sample trees in the year 2000. These trees were selected among the dominant and co-dominant trees of the stand in a way that half of the trees exhibited symptoms of Sirococcus shoot blight and the other half did not. One-third of the sample trees were fertilized with dolomitic lime, one-third with kieserite and gypsum and one-third were left unfertilized as control. The treatments were randomly assigned to the sample trees. As the experimental design became unbalanced due to tree mortality caused by bark beetle infestation final analyses were performed with the volume growth data of 125 sample trees only. An analysis of covariance was used to evaluate the effect of fertilization and Sirococcus shoot blight on volume growth. The average volume increment of the period 1977–1980 was used as a covariate attribute, assuming that during this period growth was not yet affected by Sirococcus shoot blight. Indeed an effect of Sirococcus shoot blight on growth turned out to start after 1980 and the analysis revealed that over the whole period 1981–2006 trees with shoot blight symptoms had a significantly lower increment. The increment reduction of the nonfertilized trees by Sirococcus   was 7.46±2.90$7.46\pm 2.90$% in 1981 and was continuously increasing with time to 37±3.78$37\pm 3.78$% by the year 2000. A significant positive effect of fertilization was only found for the kieserite+gypsum$\text{kieserite}+\text{gypsum}$ variant from 2002 to 2006, with the highest surplus increment in 2004 with 31.6±15.2$31.6\pm 15.2$%, calculated as average over the diseased and healthy group. However, a mitigation of the Sirococcus-caused increment loss via fertilization with kieserite and gypsum was statistically significant only for the year 2003. A moderate relationship between basal area increment and disease severity was found, indicating decreasing basal area increment with increasing disease severity.