Mikko Kukkola

Impact of whole-tree harvesting and compensatory fertilization on growth of coniferous thinning stands

Abstract A series of 16 field experiments was established to quantify the growth response of first-thinning stands of Pinus sylvestris and Picea abies to whole-tree harvesting (WTH), and to estimate the need for nutrient compensation. The experiments were undertaken in Finland, Norway and Sweden and represent a wide range of climatic and soil conditions. The biomass and nutrient amounts removed were estimated on the basis of felled sample trees. On average, WTH reduced tree volume growth in both pine and spruce stands (5% and 6%, respectively) during the first 10-year period. The growth reduction was counteracted by fertilization (NPK) and the results indicate that the reduction was an effect of reduced N supply. The inclusion of various site descriptive variables in the linear models did not explain variation in growth response to WTH. Since the growth reductions due to WTH after 10 years were still present, the observation period needs to be extended.

Effects of Nitrogen Inputs on Forest Ecosystems Estimation Based on Long-Term Fertilization Experiments

The material consists of 40 fertilization experiments in Scots pine and Norway spruce stands. The total amount of nitrogen applied during a 20-year period averages 315 kg ha- 1, which is equivalent to the total atmospheric nitrogen load in central Finland during a single rotation period according to current deposition levels.

Effect of wood ash fertilization on soil chemical properties and stand nutrient status and growth of some coniferous stands in Finland

The effects of wood ash or wood ash plus nitrogen (N) fertilization on soil chemical properties, needle nutrient concentrations and tree growth were studied in five coniferous stands, aged 31–75 yrs, after 5 and 10 yrs. In each experiment 3 t ha−1 of loose wood ash was applied to three replicated plots (30×30 m). In three of the experiments 120–150 kg N ha−1 was applied together with the same wood ash (WAN). These three experiments also included a stand-specific fertilization (SSF) treatment, which consisted of 120, 150 or 180 kg N ha−1. Five years after wood ash or WAN application the pH increase in the humus layer was 1–1.7 pH-units and in the 0–5 cm mineral soil layer 0.3–0.4 pH-units. The increase was approximately the same 10 yrs after application, and was also associated with an increase in pH in the 5–10 cm mineral soil layer. Wood ash or WAN significantly increased both the total and extractable calcium and magnesium concentrations in the humus layer on all the sites. Wood ash or WAN had an increasing effect on the boron concentrations, but a decreasing effect on the manganese concentrations in the needles. Wood ash had no significant effect on the volume growth. The trees on the WAN plots grew as well as or slightly better than those on the SSF plots.

Compensatory fertilization of Scots pine stands polluted by heavy metals

The results from four compensatory fertilization experiments located at different distances (0.5, 2, 4 and 8 km) along a heavy metal deposition gradient extending from the Harjavalta Cu-Ni smelter in SW Finland are presented. The experiments were established in middle-age Scots pine stands growing on dryish sites of sorted glaciofluvial sediments. The soil type in all the experiments is ferric podsol. The treatments in the experiments consisted of liming, a powdered slow-release mineral mixture and stand-specific fertilization which comprised at least methylene urea and ammonium nitrate.Monitoring of deposition and soil solution and studies on soil chemical and microbiological properties, on the nutrient status of trees and needle litterfall, on fine root dynamics and on the growth of the tree stands were carried out during a 5-year period.There was a severe shortage of exchangeable Ca and Mg in the organic layer of the most polluted stands. Although the uppermost mineral soil layer had relatively high exchangeable Ca and Mg concentrations, the trees were not able to utilize these nutrient reserves presumably due to the toxic effects of Cu and Ni on the plant roots and mycorrhizas.The treatments that included limestone markedly decreased the Cu and Ni concentrations in the soil solution and soil organic layer, presumably due to immobilisation through precipitation or absorption. The Ca and Mg concentrations correspondingly increased, which certainly contributed to the partial recovery of fine root and stand growth. The powdered mineral mixture and the combination of methylene urea and ammonium nitrate had no short-term effect on the microbial biomass and activity. All the fertilizer treatments increased volume growth in the most polluted stand. The stand-specific fertilization increased needle mass in heavily polluted stands, but the response of the needle mass to fertilizer treatments was low in the less polluted stands. No clear evidence was found to support the role of nutrient status in tree resistance.

Whole-tree harvesting at clear-felling: Impact on soil chemistry, needle nutrient concentrations and growth of Scots pine

Abstract The effects of logging residue removal on soil chemical properties and the needle nutrient concentrations and growth of Scots pine (Pinus sylvestris L.) were studied after clear-felling on two sites of different fertility in eastern Finland. Harvesting was carried out either conventionally, i.e. harvesting only the stems [conventional harvesting (CH)], or totally, i.e. harvesting all of the above-ground tree biomass [whole-tree harvesting (WTH)]. The seedlings were planted in ploughing tilts on 50×50 m sample plots. The number of replications was 24 on the more fertile site and 12 on the less fertile site. Compared with CH, WTH had no effects on either the survival or growth of Scots pine trees during the first 22 years. Apart from the statistically significant increase in needle nitrogen concentration in the WTH treatment on the less fertile site, the needle concentrations were not affected by the harvesting intensity. On the more fertile site, the total amounts of carbon, nitrogen and calcium, as well as exchangeable calcium and extractable phosphorus in the organic layer, were significantly lower on the WTH than on the CH plots. Although the pH remained unchanged, the exchangeable aluminium concentrations increased on the more fertile site, and on both sites the calcium/aluminium ratio was significantly lower on the WTH plots than on the CH plots.

Effect of long-term fertilization on the biomass production and nutrient status of Scots pine stands

The effect of repeated fertilization on soil properties, nutrient status of the stand and the biomass production of the above-ground components of the trees are examined in the study on the basis of material from three fertilization experiments. Two of the experiments were established in sapling stands, and the third in a pole-stage stand. The stands had received repeated doses of fertilizer totalling N 597–776 kg ha−1 and P 69–80 kg ha−1 over a 26 to 30-year study period in accordance with a factorial experimental design.Nitrogen fertilization increased the amount of organic matter in the humus layer of two of the experiments by 25–35%, and the amount of total nitrogen by about 50%. The C/N ratio of the humus layer in all three experiments decreased as a result of nitrogen fertilization by 11–18%. No decrease in soil pH was detected.At the end of the experimental period, i.e. 5–6 years after the most recent fertilization, the nitrogen concentration of the current needles on the nitrogen-fertilized plots was clearly lower than that of the older needle age classes. Fertilization did not have any marked effect on the concentrations of other macronutrients in the needles.Of the above-ground components, stemwood production was affected the most by nitrogen fertilization. The range of the relative growth response was 22–36%. The effect on branch biomass was 25% on the least fertile site, but there was no effect on the most fertile site. The effect of nitrogen fertilization on the needle biomass component was least, from −8 to 18%, owing to the 5 to 6-year time lag between the preceding fertilization and biomass sampling. A negative response was found on the least fertile site, where six years had elapsed since the most recent fertilization. However, on this site the proportion of over one-year-old needles was greater on the nitrogen-fertilized plots (24%) than on the others (19%). Phosphorus fertilization had only a slight effect on stemwood production.In general, nitrogen fertilization decreased the crown biomass per unit volume of stemwood.

Growth response of coniferous stands to whole‐tree harvesting in early thinnings

A series of 15 field experiments was established to quantify the growth response of first‐thinning stands of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst) to whole‐tree harvesting and to estimate the need for nutrient compensation. The experiments were undertaken in Finland, Norway and Sweden and represent a wide range of site conditions. The site index (H 100) of Scots pine stands varied from 19 to 29 m, and that of Norway spruce stands from 28 to 36 m. Total amounts of biomass and nutrients removed were calculated based on data obtained from felled sample trees. During the first 5‐yr period the growth response to the removal of logging residues varied considerably in both pine and spruce stands. Regression analyses did not reveal any functions that explained the variation in results satisfactorily. In cases where whole‐tree harvesting influenced tree growth negatively, this effect was counteracted by compensatory fertilization. It was concluded that to determine the respons...

Logging residue removal after thinning in boreal forests: long-term impact on the nutrient status of Norway spruce and Scots pine needles.

The aim of this study was to compare how conventional stem harvesting (CH) and whole-tree harvesting (WTH) in the first, and in some cases also in the second, thinning affect the needle nutrient status of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) stands in Finland. A series of 12 long-term field experiments was studied. The experiments were established during 1978-86. The effects of logging residue removal after thinnings on the needle nutrient concentrations were generally minor and without any overall trends, but there were differences between experiments. Trees tend to maintain their current needle nutrient concentrations at the same level by re-utilizing the nutrients stored in the older tissues and by changing C allocation in the whole tree. Thus, needle analysis should be combined with stem growth data in order to achieve a more comprehensive understanding of the effects of WTH on the nutrient status of trees.

Functioning of Forest Ecosystems under Nitrogen Loading

Reducing anthropogenic emissions of nitrogen seems to be a difficult task to carry out in practice. In the nitrogen budget of forest ecosystems, the proportion of atmospheric input may therefore even increase in the near future. In Finland nitrogen deposition comprises approximately 30 % organic and 70 % inorganic nitrogen, about half of the latter being ammonium and half nitrate nitrogen (Jarvinen and Vanni 1990). Most of the nitrogen in forest soils is in an organic form. Annual nitrogen mineralisation has been estimated to account for 0.5–3.0% of the total amount of nitrogen in forest soils, depending on the soil layer, and the variation between sites is large (Persson and Wiren 1995). Because the rates of decomposition and nitrogen mineralisation are low in boreal coniferous forest soils, the availability of mineral nitrogen is normally the factor restricting tree growth in mineral soils (Kukkola and Saramaki 1983).

Effects of nitrogen fertilization on carbon accumulation in boreal forests: Model computations compared with the results of long-term fertilization experiments

Abstract Computations with a gap-type forest simulation model indicate that net primary production increased by 20% in a mesic site and 44% in a dry site due to an increased nitrogen input of 600–750 kg N/ha over a 26- to 30-year period. In addition to enhanced carbon sequestration by the vegetation, the nitrogen input increased carbon storage in the litter and humus layers. The results of these model computations were similar to those of the long-term field experiments. Thus, it can be assumed that the model can be used for assessing the effect of nitrogen input on the biomass production and carbon balance of forest ecosystems.