Economics of Forest Thinnings and Rotation Periods for Finnish Conifer Cultures

In this study simultaneous optimization of thinnings and clear-cutting was investigated. The density-dependent whole-stand model was specified for all relevant Finnish Norway spruce (Picea abies (L.) Karst.] and Scots pine (Pinus sylvestris L.) site indices and solved by non-linear programming. Sensitivity analysis showed that in some cases and owing to endogenous thinnings the optimal rotation length may increase with the rate of interest and site fertility, and decrease with harvesting cost. The number of thinnings is more sensitive to changes in the rate of interest, logging conditions and site productivity for Scots pine stands than for Norway spruce stands. Economic optimization suggests that for both species the first thinning should be performed later than officially recommended. The last thinning should be heavier than officially recommended, especially at high rates of interest. This increases the optimal rotation length compared with solutions under restricted thinning intensity.     

Fine root morphological adaptations in Scots pine, Norway spruce and silver birch along a latitudinal gradient in boreal forests

Variability in short root morphology of the three main tree species of Europe's boreal forest (Norway spruce (Picea abies L. Karst.), Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth)) was investigated in four stands along a latitudinal gradient from northern Finland to southern Estonia. Silver birch and Scots pine were present in three stands and Norway spruce was present in all stands. For three fertile Norway spruce stands, fine root biomass and number of root tips per stand area or unit basal area were assessed from north to south. Principal component analysis indicated that short root morphology was significantly affected by tree species and site, which together explained 34.7% of the total variability. The range of variation in mean specific root area (SRA) was 51-74, 60-70 and 84-124 m(2) kg(-1) for Norway spruce, Scots pine and silver birch, respectively, and the corresponding ranges for specific root length were 37-47, 40-48 and 87-97 m g(-1). The range of variation in root tissue density of Norway spruce, Scots pine and silver birch was 113-182, 127-158 and 81-156 kg m(-3), respectively. Sensitivity of short root morphology to site conditions decreased in the order: Norway spruce > silver birch > Scots pine. Short root SRA increased with site fertility in all species. In Norway spruce, fine root biomass and number of root tips per m(2) decreased from north to south. The differences in morphological parameters among sites were significant but smaller than the site differences in fine root biomass and number of root tips.     

Estimation of nutrient removals in stem-only and whole-tree harvesting of Scots pine, Norway spruce, and birch stands with generalized nutrient equations

Whole-tree harvesting (WTH), where logging residues are removed in addition to stems, is widely practised in Fennoscandian boreal forests. WTH increases the export of nutrients from forest ecosystems. The extent of nutrient removals may depend on tree species, harvesting method, and the intensity of harvesting. We developed generalized nutrient equations for Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies Karsten), and birch (Betula pendula Roth and Betula pubescens Ehrh.) stands to be able to calculate the amounts of nitrogen, phosphorus, potassium, and calcium in stems and above-ground biomass (stem and crown) as a function of stand volume. The equations were based on Fennoscandian literature data from 34 pine, 26 spruce, and 5 birch stands, and they explained, depending on the tree species and nutrient, 61–99% and 56–87% of the variation in the nutrient amounts of stems and above-ground biomass, respectively. The calculations based on the equations showed that nutrient removals caused by stem-only harvesting (SOH) and WTH per harvested stem m³ were smaller in pine than in spruce and birch stands. If the same volume of stem is harvested, nutrient removals are, in general, nearly equal at thinnings and final cuttings in SOH, but larger in thinnings than final cuttings in WTH. If the principal aim is to minimize the nutrient removals per harvested stem m³, the harvesting should be done at mature pine stands. The effect of biomass removal on overall site nutrient status depends on site-specific factors such as atmospheric deposition, weathering of minerals, and the size of the nutrient pools in the soil.     

The chemical composition of needle and leaf litter from Scots pine, Norway spruce and white birch in Scandinavian forests

Needle litter from 14 stands of Scots pine (Pinus silvestris,L.), 13 stands of Norway spruce (Picea abies (L.) Karst.) andleaf litter from three stands of white birch (Betula pubescensEhrh.) were analysed for chemical composition. The concentrationsof the elements N, P, K, Ca, Mg and Mn as well as solid organiccomponents (lignin, cellulose and hemicelluloses) and solubleswere determined. When the average chemical compositions werecompared the Scots pine needle litter was clearly the most nutrient-poorlitter type. Of the solid organic-chemical components the ligninfraction dominated in the spruce and birch litter whereas thecellulose dominated in the pine needle litter. When Norway spruce and Scots pine were growing in adjacent standson soils with the same bedrock origin the spruce litter hadsignificantly higher concentrations of nutrients (N, P, K, Ca,Mg, Mn) than the pine needle litter. At sites where Norway spruceand white birch were growing in adjacent stands, the birch leaflitter had generally higher concentrations of nutrients. However, significant or nearly significant differences were onlyobtained for Mg (P = 0.002), K (P = 0.056) and N (P = 0.087),probably due to the few replicates of stands compared. Concerningorganic chemical components, the spruce needle litter had significantlyhigher concentrations of lignin and mannan than all the otherlitters and lower levels of ethanol-soluble substances, celluloseand galactan than the pine needle litter. Further, it had lowerconcentrations of water solubles, rhamnan and xylan than thebirch litter. No relationships were established between the nutrient statusof the conifer litters and the site index H100 (the dominantheight of the trees at a reference age of 100 years) of thestands. Concentrations of solid carbohydrates in the litterswere, however, positively correlated with site index (P <0.001). Further, the concentration of nitrogen in the pine needlelitter was negatively correlated with the latitude of the sites(P < 0.01). The influence of litter chemistry on the decompositionof litter and nutrient cycling of forests is discussed.     

Equations for estimating above- and belowground biomass of Norway spruce,Scots pine,birch spp. and European aspen in Latvia

This study aims to derive allometric functions to estimate the above- and belowground biomass components of the most important tree species in Latvia. The study material included a total of 81 Norway spruce (Picea abies [L.] Karst), 102 Scots pine (Pinus sylvestris L.), 105 birch spp. (mainly silver birch (Betula pendula Roth)) and 84 European aspen (Populus tremula L.) trees sampled in 124 forest stands. The suitability of three mathematical models for the prediction of total aboveground biomass, stem biomass, total live and dead branch biomass, belowground biomass and small root biomass was evaluated. Our analysis revealed that the use of the Intergovernmental Panel on Climate Change mean default values for the root-to-shoot ratio recommended for temperate and boreal ecological zones leads to the overestimation of root biomass of young trees, especially Scots pine and Norway spruce. Our findings indicate that biomass functions recommended for other Baltic Sea countries are not appropriate for the assessment of the biomass stock in Latvia’s forests because these lead to biased estimates. The biomass functions derived in our study are recommended for reporting the biomass stock in Latvia.     

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 response of remaining trees to harvesting intensity reliably, the post‐harvest period analysed must be longer than 5 yrs.     

Risk of Snow Damage in Unmanaged and Managed Stands of Scots Pine,Norway Spruce and Birch

The aim of this study was to assess the risk of snow damage to trees in unmanaged and managed stands of Scots pine (Pinus sylvestris L.), Norway spruce [Picea abies (L.) Karst.] and birch (Betula spp.) over a rotation. The risk assessment was based on the prediction of critical snow loads in interaction with the windspeed at which trees can be expected to break or be uprooted, and on the frequency of long-term extremes of precipitation and of suitable temperature conditions for the accumulation of snow on the tree crowns. The Scots pine stands were found to be more susceptible to snow damage than the others, and an unmanaged stand of Scots pine to be more susceptible to break and uproot than a managed one. Correspondingly, an unmanaged stand of Norway spruce was more susceptible to stem breakage than a managed one, but less susceptible to uprooting. Neither unmanaged nor managed birch stands were likely to suffer any kind of snow damage. The susceptibility of unmanaged stands is caused by low tapering of the trees. Based on the frequency of long-term extremes in precipitation at the temperatures needed for snow accumulation on tree crowns, critical snow loads of 10-19, 20-29 and 30-39 kg m^-2 occurred 19.3, 3.3 and 1.3 times in a decade in southern Finland. Critical snow loads of 10-19, 20-29, 30-39 and 60-69 kg m^-2 occurred in northern Finland 17.0, 6.3, 1.7 and 0.3 times in a decade.     

From planting to 26 years of age – actual growth and estimated volume scenarios for spruces and pines

The objective of this study was to compare the survival and volume of conifer stands at 26 years of age with their status at planting. Survival, growth and damage were studied in eight clear felled stands regenerated in 1972. Five of the areas were planted with Norway spruce (Picea abies (L.) Karst.) and three with Scots pine (Pinus sylvestris L.). The plantings were examined in 1972 and 1974. In 1974, the number of living undamaged planted seedlings was low (10–15%). However, the number of undamaged seedlings was supplemented by naturally regenerated conifer and birch seedlings. The total number of undamaged seedling in 1974 was equivalent to 20–30% of the number of seedlings planted. In 1998, the main species in three stands had changed from Norway spruce to Scots pine, and in one stand from Norway spruce to birches. Actual volume in 1998 for the stands was compared to stand volume generate according to five scenarios based on recommended and actual seedling number in 1972 and 1974. The actual volume was 64% of that expected if the recommended number of trees had been planted. Naturally regenerated Scots pine and Norway spruce increased stand density in 1998. The actual volume was 37% higher than the average volume in the surrounding county. On average, 36% of the trees were damaged. More than 50% of the total damage was caused by moose (Alces alces L.). For Scots pine, moose or other browsing animals damaged 30% of the trees. The results of this study indicate that the 1998 volume was higher than expected, considering the low number of undamaged seedlings in 1974. This was mainly due to the large amount of naturally regenerated plants. In addition, the results indicate that the volume could have been higher if the initial conditions had been better. Despite the low number of undamaged seedlings in 1974, seven of the eight studied stands produced a higher volume than the average stand for the region. In practise, high numbers of seedlings should be planted on scarified areas. In most cases there will be a supply of naturally regenerated seedlings.     

Infection experiments with Gremmeniella abietina on seedlings of Norway spruce and Scots pine

Conidia of Gremmeniella abietina infected and caused disease symptoms in annual shoots of both Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) seedlings. In Norway spruce shoots the infection remained largely latent, with only a few seedlings showing symptoms. Mycelial growth inside the shoots was faster in Scots pine than in Norway spruce and was favoured by low temperature in both hosts. The shoots of Norway spruce seedlings had higher endophyte populations than those of Scots pine, and the populations were decreased by low temperatures. Reductions in the normal epiphytic or endophytic flora by acid mist treatments seemed to favour the development of G. abietina.     

The spreading of the S type of Heterobasidion annosum from Norway spruce stumps to the subsequent tree stand

The occurrence of Heterobasidion annosum in stumps and growing trees was investigated on 15 forest sites in southern Finland where the previous tree stand had been Norway spruce (Picea abies) infected by H. annosum, and the present stand was either Scots pine (Pinus sylvestris), lodgepole pine (Pinus contorta), Siberian larch (Larix siberica), silver birch (Betula pendula) or Norway spruce 8–53 years old. Out of 712 spruce stumps investigated of the previous tree stand, 26.3% were infected by the S group and 0.3% by the P group of H. annosum. The fungus was alive and the fruit bodies were active even in stumps cut 46 years ago. In the subsequent stand, the proportion of trees with root rot increased in spruce stands and decreased in stands of other tree species. On average, one S type genet spreading from an old spruce stump had infected 3.0 trees in the following spruce stand, 0.5 trees in lodgepole pine, 0.3 trees in Siberian larch, 0.05 trees in Scots pine and 0.03 trees in silver birch stand. Although silver birch generally was highly resistant to the S type of H. annosum, infected trees were found on one site that was planted with birch of a very northern provenance.     

The effect of girdling on the moisture content of small-sized trees

In this study, the effect of girdling on the moisture content of small-sized trees for heat energy production was clarified. The moisture content was measured for Scots pine (Pinus sylvestris), Norway spruce (Picea abies), and Downy birch (Betula pubescens) during two growing seasons after girdling. The trees were girdled at breast height for around 30 cm by removing the bark, phloem, and cambium from around the stem. At the beginning of the growing season the mean moisture content of the living Scots pine (P. sylvestris) and Norway spruce (P. abies) was 60%, and for Downy birch (B. pubescens) it was 50%. During the first growing season the effect of girdling on the moisture content was low, but during the second growing season the moisture content decreased significantly. The moisture content of the Norway spruce (P. abies) (23%) and Downy birch (B. pubescens) (33%) was at its lowest point at 14 months after girdling. There were no significant changes in the moisture content of the Scots pine (P. sylvestris) in this study. The results of this study can be used in basic research and in the development of energy wood production.     

Impacts of changing climate on the productivity of Norway spruce dominant stands with a mixture of Scots pine and birch in relation to water availability in southern and northern Finland

A process-based ecosystem model was used to assess the impacts of changing climate on net photosynthesis and total stem wood growth in relation to water availability in two unmanaged Norway spruce (Picea abies) dominant stands with a mixture of Scots pine (Pinus sylvestris) and birch (Betula sp.). The mixed stands were grown over a 100-year rotation (2000-99) in southern and northern Finland with initial species shares of 50, 25 and 25% for Norway spruce, Scots pine and birch, respectively. In addition, pure Norway spruce, Scots pine and birch stands were used as a comparison to identify whether species' response is different in mixed and pure stands. Soil type and moisture conditions (moderate drought) were expected to be the same at the beginning of the simulations irrespective of site location. Regardless of tree species, both annual net canopy photosynthesis (P(nc)) and total stem wood growth (V(s)) were, on average, lower on the southern site under the changing climate compared with the current climate (difference increasing toward the end of the rotation); the opposite was the case for the northern site. Regarding the stand water budget, evapotranspiration (E(T)) was higher under the changing climate regardless of site location. Transpiration and evaporation from the canopy affected water depletion the most. Norway spruce and birch accounted for most of the water depletion in mixed stands on both sites regardless of climatic condition. The annual soil water deficit (W(d)) was higher on the southern site under the changing climate. On the northern site, the situation was the opposite. According to our results, the growth of pure Norway spruce stands in southern Finland could be even lower than the growth of Norway spruce in mixed stands under the changing climate. The opposite was found for pure Scots pine and birch stands due to lower water depletion. This indicates that in the future the management should be properly adapted to climate change in order to sustain the productivity of mixed stands dominated by Norway spruce.     

The effect of density after precommercial thinning on volume and structure in Pinus Sylvestris and Picea Abies stands

The interaction between stand density and dominant height and the development of volume, mean diameter, mortality and distribution of volume during a period from precommercial thinning to first commercial thinning was studied on permanent plots in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) stands in Sweden. The reciprocal equation of the yield density effect was used to level the volume yield. Higher density after precommercial thinning resulted in higher yield and smaller mean diameter. The mortality up to first thinning was low, but is also dependent on density after precommercial thinning. The positive skewness of the volume distribution was higher in denser stands.     

Height growth of planted conifer seedlings in relation to solar radiation and position in Scots pine shelterwood

Seedlings of different provenances of Scots pine (Pinus sylvestris L.), lodgepole pine (Pinus contorta Dougl., var. latifolia Engelm.) and Norway spruce (Picea abies (L.) Karst.) were planted in three Scots pine shelterwoods (125, 65 and 43 stems ha⁻¹) and a clear-cut, all in northern Sweden. The sites were mounded and planting took place during 2 consecutive years (1988 and 1989). The solar radiation experienced by the individual seedlings was determined using a simulation model. Height development of the seedlings was examined during their first 6 years after planting. During the final 3 years of the study, height growth of Norway spruce was relatively poor, both in the shelterwoods and the clear-cut area. Height growth of lodgepole pine was significantly greater than that of Scots pine, both in the shelterwoods and the clear-cut. In contrast to Norway spruce, Scots pine and lodgepole pine displayed significantly greater height growth in the clear-cut than in the shelterwoods. For all three species in the shelterwoods, regression analyses showed that height growth was more strongly correlated with the distance to the nearest tree than with the amount of radiation reaching the ground, i.e. growth was reduced in the vicinity of shelter trees. Therefore, we conclude that the significant reduction in height growth of seedlings of Scots pine and lodgepole pine in Scots pine shelterwoods was partially caused by factors associated with the distance to the nearest shelter tree. Because the substrate was a nitrogen-poor sandy soil, we suggest that root competition for mineral nutrients, especially nitrogen, accounts for the reduction in height growth.     

Assessment of bias due to random measurement errors in stem volume growth estimation by the Swedish National Forest Inventory

Abstract

We evaluated the performance of two methods for estimating stem volume increment at individual tree level with respect to bias due to random measurement errors. Here, growth is either predicted as the difference between two consecutive volume estimates where single-tree volume functions are applied to data from repeated measurements or by a regression model that is applied to data from a single survey and includes radial increment. In national forest inventories (NFIs), the first method is typically used for permanent plots, the second for temporary plots. The Swedish NFI combines estimates from both plot types to assess growth at national and regional scales and it is, therefore, important that the two methods provide similar results. The accuracy of these estimates is affected by random measurement errors in the independent variables, which may lead to systematic errors in predicted variables due to model non-linearity. Using Taylor series expansion and empirical data from the Swedish NFI we compared the expected bias in stem volume growth estimates for different diameter classes of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.). Our results indicate that both methods are fairly insensitive to random measurement errors of the size that occur in the Swedish NFI. The empirical comparison between the two methods showed greater differences for large diameter trees of both pine and spruce. A likely explanation is that the regressions are uncertain because few large trees were available for developing the models.     

Optimal management of uneven-aged Norway spruce stands

An optimization model is specified to analyze forest management without any restrictions on the forest management system. The data on forest growth comes from unique field experiments and is used to estimate a nonlinear transition matrix or size-structured model for Norway spruce. The objective function includes detailed harvesting cost specifications and the optimization problem is solved in its most general dynamic form. In optimal uneven-aged management, stand density is shown to be dominated by limitations in natural regeneration. If the goal is volume maximization, even-aged management with artificial regeneration (and thinnings from above) is superior to uneven-aged management. After including regeneration and harvesting costs, the interest rate, and the price differential between saw timber and pulpwood, uneven-aged management becomes superior to even-aged management. However, in the short term the superiority is conditional on the initial stand state.     

Effects of growth regulators on germination of picea abies and Pinus sylvestris seeds

Nine seed lots each of Norway spruce (Picea abies L.), and Scots pine (Pinus sylvestris L.) were treated with combinations of the growth regulators: Indole‐3‐acetic acid, indole‐3‐butyric acid, etephone, kinetin, fusicoccin, and the gibberellins A₁ A₃ A_4/7, and A₉. GA₉ GA_4/7 and fusicoccin significantly promoted the germination of five Norway spruce, and three Scots pine, seed batches. Independent of species, the germinability of seeds treated with auxins, etephone, kinetin, GA₁ and GA₃ were unaffected or reduced. The rate of germination was stimulated for both species when treated with GA₉ or GA_4/7. The germination percentage for Scots pine seeds was enhanced by GA₉ but not by GA_4/7. Neither of the two GAs enhanced the germination percentage of Norway spruce seeds.     

Functions for Biomass Estimation of Young Pinus sylvestris,Picea abies and Betula spp. from Stands in Northern Sweden with High Stand Densities

New silvicultural regimes with high within-stand competition require new functions for estimation of standing stock and growth of biomass components, since the allometry of trees is changed by light competition. This paper presents functions for estimation of the aboveground biomass dry weights for stem wood, stem bark, branches and leaves of young (diameter at breast height <10 cm) Scots pine (Pinus sylvestris L.), Norway spruce [Picea abies (L.) Karst.] and birch (Betula pendula Roth. and Betula pubescens Ehrh.) trees growing in dense mixed stands. The functions were derived from a sample consisting of 84 Scots pine, 43 Norway spruce and 66 birch trees from six stands in northern Sweden with high stand densities (>10000 st ha^-1). The logarithmically transformed power function displayed a good ability to stabilize the variance of dry weights and showed a good fit to the material (0.37< R ² <0.99). A comparison with the most commonly used biomass functions in Sweden today showed that they overestimated the weight of stem wood and branches, while the weight of foliage was underestimated. The nature of these discrepancies suggested that the precision of biomass estimations might also be improved for young trees at wider spacing.     

Growth in supplementarily planted Picea abies regenerations

Abstract

An experiment was established in 1978 in two Norway spruce [Picea abies (L.) Karst.] plantations in southern Sweden to study yield after mortality in patches with and without supplementarily planted (SP) seedlings. Gaps of different sizes were created by removing the originally planted seedlings. The gaps were either left unplanted or a supplementary planting was performed with one of four species [Norway spruce, Scots pine (Pinus sylvestris L.), lodgepole pine (Pinus contorta Dougl.) or hybrid larch (Larix deciduas Mill×L. Leptolepis Gord.)] 2 (at Knäred) or 6 years (at Ullasjö) after the original plantation. In 2002, most of the SP Scots pine, lodgepole pine and hybrid larch seedlings were dead or severely damaged by roe deer and moose. Survival was high among SP Norway spruces, but they had slower growth than the originally planted spruces. Growth was lower at Ullasjö than at Knäred. In Ullasjö, growth was lower in small gaps than in large gaps. Trees in original regeneration in areas surrounding unplanted gaps were larger than trees surrounding gaps with SP seedlings, which in turn were larger than originally planted trees in plots without gaps. In conclusion, because the original plantation surrounding unplanted gaps used a large part of the open space and growth of SP seedlings was slow, supplementary planting resulted in an insignificant growth increase. However, supplementary planting may increase the timber quality of trees surrounding the gaps, although this effect remains to be quantified.     

Phosphorus supply and cycling at long-term forest monitoring sites in Germany

In this study, the supply and input–output balances of phosphorus (P) were investigated for a 10-year-period at 85 long-term monitoring sites in German forest ecosystems under the European Level II programme. These sites encompass 23 European beech (Fagus sylvatica L.) stands, 9 oak stands comprised of common oak (Quercus robur L.) and/or sessile oak (Quercus petraea Liebl.), 20 Scots pine (Pinus sylvestris L.) and 33 Norway spruce (Picea abies H.Karst.) stands. We quantified P concentrations in needles and leaves, P inputs from the atmosphere, P outputs through leaching and harvesting, and total P in the soil and humus layers. The P concentrations in European beech leaves from two sites (>1 mg P g⁻¹ dry weight), and in Norway spruce needles from four sites (>1.2 mg P g⁻¹ dry weight), were deficient over several years. In contrast, the oak and Scots pine sites were well supplied with P. When P removal through harvesting was disregarded, P balances were positive or stable (median 0.21 kg P ha⁻¹ a⁻¹). With harvesting, balances were mostly negative (median −0.35 kg P ha⁻¹ a⁻¹), with long-term P removal from the forest ecosystems.