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.     

Determination of mean diameter by basal area in stands of picea abies and pinus sylvestris in southeastern Norway by means of aerial photographs

Mean diameter by basal area (d_g) is an important stand variable for long‐term economic forecasts of forest holdings. In order to use stand‐by‐stand surveys based on aerial photo interpretation as the data basis for forecasts, d_g has to be determined. The objective was to develop and test a regression function for d_g in mature stands of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) applicable in southeastern Norway. A study of 700 plots was used to estimate a function for d_g . An additive model was found to be most suitable. The independent variables were potential yield capacity, Lorey's mean tree height, crown closure determined by ocular estimation by means of aerial photographs, and the product of potential yield capacity and crown closure. The R² value was 0.604 and the coefficient of variation was 10.8%. The regression fitted most parts of the calibration data quite well, but it may overestimate the mean diameter in pure spruce stands by 1–2%, and underestimate the diameter in pure pine stands by 3%. For mixed coniferous stands the regression seems satisfactory. Testing by means of an independent data set showed systematic errors of 3–23%. The systematic errors were due partly to calibration problems in connection with the ocular crown closure estimation.     

Distribution and yield of biomass from young Pinus sylvestris and Picea abies stands on drained and fertilized peatland

Above‐ground biomass has been measured on fertilized and control plots up to stand age 31 years. Each biomass fraction was estimated by two statistically coupled linear models with squared diameter at breast height as independent variable. All fractions except reproductive structures of pine and dead branches of spruce were estimated at high precision levels, R. between 0.93 and 0.99. The above‐ground biomass fractions per hectare could be precisely described by stem volume with bark. Application of the models for prognostic purposes is discussed. Annual above‐ground net biomass production in pine increased from 2.05 to 4.34 MT d.m./ha‐yr on control plots over 11 years, while plots given complete fertilizer mixture ranged from 6.75 to 9.09. Spruce stands with a nearly optimum water relationship and fertilizer programmes yielded from 9.50 to 11.86 MT d.m./ha‐yr. The combination of energy and timber production in highly productive peatland stands is discussed.     

Root growth capacity and field performance of Pinus sylvestris and Picea abies seedlings

Correlations between root growth capacity (RGC), at the time of planting, and field performance were studied for Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings. Before planting a gradient in seedling viability was generated through exposure to low root temperatures and different winter storage regimes. The hypothesis that high RGC values would improve field performance was to some extent verified for pine seedlings while no correlations could be registered for spruce. Reasons for these results are discussed.     

Induction of hairy and normal roots on Picea abies,Pinus sylvestris and Pinus cortorta by agrobacterium rhizogenes

Two‐ to three‐week‐old seedlings of Picea abies, Pinus sylvestris and Pinus contorta were inoculated with the supervirulent strain Agrobacterium rhizogenes R1600 2cm above the base of the hypocotyl; other treatments included inoculation with Agrobacterium tumefaciens strain A281 (pTVK291) or mock inoculation. Hairy or highly branched roots formed on 2–3% of seedlings of all 3 species that were infected by R1600 but on none of the other seedlings. Normal adventitious roots were also induced on 5–10% of Agrobacterium‐treated seedlings but none appeared on the other seedlings. Opine assays and growth rates of hairy and normal roots indicated that only roots with the hairy morphology were transformed.     

Timber quality after thinning from above and below in stands of Pinus sylvestris

Timber quality and logging damage after different thinning types in Scots pine (Pinus sylvestris L.) stands were studied in a field experiment in north Sweden. Thinning operations were mechanized and carried out according to normal Swedish practise. The treatments were thinning from below and thinning from above. The quality of the residual stand was evaluated using variables such as diameter of the thickest branch, stem taper, annual ring width, straightness and lean of trees. The only variables showing differences between treatments were lean of tree and stem straightness. No difference in the frequency of trees with logging damage was found. The conclusion of this study is that differences between thinning types in first thinning may be evened out when carried out as in commercial forestry due to extraction of strip road and damaged trees. Consequently, differences in timber quality and logging damage in the residual stand may be small.     

Long-term Growth Effects Following Forest Nitrogen Fertilization in Pinus sylvestris and Picea abies Stands in Sweden

Forest nitrogen (N) fertilization induces changes in the soil and soil microorganisms that could hypothetically affect the long-term productivity of the soil. The tree growth response following a normal (i.e. 150 kg N ha^?1) single shoot N fertilization has a duration of 7–10 yrs. The aim of this study was to investigate whether any residual effects on tree growth persist, which could be attributed to previous N fertilization. The study included six Pinus sylvestris L. and three Picea abies (L.) Karst. experimental sites, sampled for growth parameters 14–28 yrs after the last fertilization. Residual growth effects were on average small, and not statistically significant. Negative residual growth effects of varying duration could be discerned, especially at low-fertility P. sylvestris sites. However, there was an overall tendency for growth to increase in the long term after N fertilization. The main conclusion is that operational forest N fertilization with a normal N dose should not be regarded as a threat to long-term forest production.     

Timing and intensity of precommercial thinning in Pinus sylvestris stands

The effects of timing and intensity of precommercial thinning were studied in three Scots pine artificially regenerated stands on Vaccinium forest sites in southern Finland. A two-level factorial design (3×3) was used in each stand: thinning at dominant height of 3, 6 and 9 m to 1000, 1600 and 2200 stems ha^?1. The effects of the treatments were analysed after a period of 23–25 yrs when the dominant height was 14–15 m. Early thinning resulted in the highest standing volume and amount of merchantable wood, and also in slightly accelerated height development. Thinning to 1000 stems ha^?1 caused a considerable production loss, but there were no differences between the densities of 1600 and 2200 stems ha^?1. Branches became thicker after early thinning, but the differences between the treatments were negligible for crop trees. Crown ratio was lowest as the result of early or moderate thinning (2200 stems ha^?1).     

Irradiance in young stands of picea abies (L.) karst. and pinus sylvestris L. and the possibilities to prevent suckers of broad‐leaved trees

Incoming shortwave global radiation (Q _g) and photosynthetically active radiation (PAR; Q _pa as a fraction of full daylight, relative irradiance (%Q), were measured at the same time in young stands of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.). Measurements were made on three levels above ground: 20 cm above ground and 50 and 15 % of stand height. Stands of three heights (75, 150 and 300 cm) were studied during two months. The stands were created by arranging young trees cut from natural stands, in nine quadratic spacings: 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 1.0, 1.4 and 2.0 m. The leaf area index (L) was estimated. Differences in %Q‐values for Q _pa and Q_g in the same species and at the same stand height and level of light measurements above ground were significant only in 150 and 300 cm stands. In 75 cm high stands of Scots pine, the %Q was <60% at spacings <0.2 m and in 75 cm high stands of Norway spruce, the %Q was <60% at spacings <0.3 m. Only at 0.1x0.1–0.3x0.3 m, %Q was <20% in Norway spruce stands. In 150 cm stands %Q<20% was measured at spacings <0.7 m in Norway spruce and <0.5 in Scots pine. In 300 cm stands of Norway spruce it was measured up to 1.2 and in Scots pine <1.1 m. Light extinction coefficients, K and K_g for spruce and pine stands were 0.17–0.40 and 0.16–0.31 respectively. Some practical implications of the study are presented. Lack of light (%Q<10%) as a single factor of seriously suppressed growth and development of broad‐leaved plants and suckers by competition in young stands of spruce and pine only occur in dense stands 0.3x0.3 m‐1.1xl.l m (8000–100000 stems/hectare). Competition by light on a regenerated area generally occurs in the level of 50% of tree height (150–300 cm) and higher due to the rapid growth of broad‐leaved trees (sprouts) compared with planted conifers but the light intensity at these levels %Q>10%.     

Comparison of beta and weibull functions for modelling basal area diameter distribution in stands of pinus sylvestris and picea abies

The purpose of this study was to compare beta and Weibull distributions in describing basal area diameter distributions in stands dominated by Scots pine and Norway spruce. The material of the study consisted of 535 stands located in eastern Finland. Parameters for both two‐ and three‐parameter approaches of the Weibull distribution were estimated using the method of maximum likelihood. Models for these parameters were derived using regression analysis. For the beta distribution, regression models were formed for the minimum, maximum and standard deviation of diameters within individual stands. These models were used when the exponents of the beta distribution were calculated analytically. Also, some parameter models for beta and Weibull distributions from previous studies were compared with the measured diameter distributions. The distributions obtained were compared using diameter sums and an estimate of the proportion of sawtimber. The results did not reveal any major differences between the suitability of the beta and two‐parameter Weibull distributions. There are appropriate models available for both of the distributions and the more similar the original data is to the data of an application, the better are the results. The two‐parameter approach of the Weibull distribution gave better results than the three‐parameter approach. The poorest results for all the predicted distributions were obtained at the extremes of the distributions.     

Impacts of bucking and delimbing alternatives on pulpwood and energy wood yields in young thinning stands in Finland

The supply of energy wood from young forests could be enhanced by altering the harvesting methods in integrated pulpwood and energy wood thinnings. In this study, effects of different bucking and delimbing options on the biomass division into energy wood, pulpwood and logging residue were estimated in integrated thinnings of young stands dominated by Scots pine (Pinus sylvestris), Norway spruce (Picea abies) or birches (Betula spp.) in Finland. Thinning options were simulated in the harvestings of model stands created on the basis of forest inventory data. Increasing the minimum top diameter of pulpwood (MTDP) expectedly increased energy wood and decreased pulpwood yields. Depending on tree species, energy wood yield increased by 36–65% when the top diameter was increased from the regular level (6 or 7 cm) to 8 cm in whole-tree harvesting, and was more than doubled when the top diameter was increased to 10 cm. Delimbed energy wood yield was increased by 240–280% when the top diameter was increased to 10 cm. Total harvesting yield in whole-tree thinnings was slightly increased by increasing top diameter. These increments in harvesting yields and reallocations of tree biomass could have an impact on large-scale forest energy potentials.     

Between- and within-site variation of density and bending properties of Picea abies structural timber from Norway

This study provides an analysis on the variability of structural timber of Norway spruce (Picea abies) grown in Norway. Density, modulus of elasticity (MOE) and bending strength were measured on 1188 boards from 205 trees, sampled from 14 sites throughout Southern Norway, Eastern Norway and Trøndelag. The area represents the procurement area for the majority of Norwegian sawmills. The variability of the timber properties was analysed in a linear mixed model where the random variance was divided into variance due to site, variance due to trees and within-tree variance. Models describing variance due to site based on site index, altitude and latitude were developed, and combined with data from the Norwegian National Forest Inventory to estimate mean values and variability of the timber properties. The results showed that major parts of the variance due to site are explained by altitude and site index, and for density also by latitude. Major parts of the variance due to site and the variance due to trees in bending strength and MOE were explained by density.     

Photosynthesis and root respiration of Pinus sylvestris and picea abies seedlings after different root freezing and storage temperatures

Photosynthetic performance and root respiration were measured for seedlings of Scots pine and Norway spruce under constant conditions in an open gas exchange system in the laboratory. Measurements were carried out after root exposure to ‐20, ‐5 and 0°C and subsequent longtime storage in darkness at +1 or +4°C. Stomatal conductance in relation to net photosynthetic rates was also investigated after the same treatment of seedlings. Root respiration was low for seedlings whose root system had been exposed to ‐20°C, Scots pine showing lower rates than Norway spruce. This was probably an indication of root damage. At least for one provenance of Scots pine, respiration rates were higher for seedlings stored at +1 than at +4°C. Photosynthetic performance was also lowest for seedlings whose roots had been exposed to +20°C compared to higher temperatures, the difference being more clear‐cut for Norway spruce than for Scots pine. Storage at +1 gave slightly higher photosynthetic rates than at +4°C. There was a close relation between stomatal conductance measured on individual needles and photosynthetic performance measured on the whole seedling.     

Prediction of individual tree growth in managed stands of mixed Picea abies (L) Karst,and Betula pendula Roth & Betula pubescens Ehrh.

The individual tree growth in stands of mixed Norway spruce (Picea abies (L.) Karst.) and birch (Betula pendula Roth & Betula pubescens Ehrh.) is estimated using basal area and height growth functions for each species separately. The individual tree growth models are distant dependent and the number, size and proximity of neighbours are expressed as size‐ratio competition indices. The competition indices were calculated using a basal area factor gauge to define competitors. The tree growth functions are based on data from nine mixed stands of Norway spruce and birch. The recursive multivariate regression approach is used. The growth functions have standard deviation about the function/standard deviation about the mean (sf/sm) values between 31 and 61% and the evaluations made with root mean square error (rmse) give estimates which vary between 8 and 45 % of the observed mean value. These values are comparable with the precision reported in other studies. In the present investigation the distant dependent indices are important independent variables. It seems suitable to describe the change in growth conditions from retarded to released growth by means of size ratio competition indices. For birch, a positive effect on growth is obtained the more the total competition consists of Norway spruce. For Norway spruce a negative effect on growth is obtained the more the total competition consists of Norway spruce. The lower competitors have a positive effect on the growth of the spruce trees. The interpretation should be that it is better to have a small competitor than a larger one, not that small competitors as such have a positive effect on growth of Norway spruce.     

Effects of five tree-selection strategies when thinning spruce (Picea abies) stands: a case study in a field trail in southern Sweden

The aim of this study was to show the effects of five tree-selection strategies when thinning on quality and growth properties of Norway spruce stands, and their potential for improving quality in the stands. The five strategies were thinning to retain high-quality (HQ) and low-quality (LQ) trees, thinning from above (A) and below (B) and thinning to obtain an even distribution of residual trees (S). The study was conducted in two planted stands close to rotation age, located in southern Sweden, which had been thinned twice since the establishment of the thinning experiment. In the two quality-based treatments trees were selected for harvest on the basis of the following growth and quality traits: tree class, vitality, dbh, height, straightness, branch diameter and quality defects. The quality traits were found to be largely independent of tree size, thus the selection strategies based solely on dbh (A and B) did not improve quality within the stands. Thinning targeting HQ traits promoted the retention and growth of HQ trees, and improved overall quality of the stands compared to the other treatments. HQ thinning increased the share of straight trees by 15%, on average. Significant proportions of stem crooks and quality defects detected before the first thinning were invisible 21 years after it. All thinned stands had higher proportions of naturally pruned trees than unthinned stands. The selection method had no influence on periodic annual increment after thinning.     

A model for the relationship between branch number and biomass in Pinus sylvestris crowns and the effect of crown shape and stand density on branch and stem biomass

The branch biomass of young Scots pines (Pinus sylvestris L.) was inversely related to the branch number per projected crown area giving greater branch density and smaller branch biomass for narrow crowns than for broad crowns. In particular, in dense stands the small share of branches from the total biomass of narrow‐crowned trees was emphasized. The productivity of narrow crowned trees was, however, smaller than that of trees with broad crowns. The concept of the tree ideotype has been discussed on the basis of theoretical calculations.     

Epicuticular waxes,peroxidase activity and contents of chlorophyll,phaeophytin and carotenoids of needles from Pinus syivestris and picea abies as indicators of air pollution in the region of Stockholm

To trace any possible effects of air pollution stress and injuries on trees around a city centre, needles of Scots pine (Pinus Syivestris L.) and Norway spruce (Picea abies (L.) Karst.) from sites of different distances and directions from Stockholm were analysed. Comparisons were made between needles of different ages, a half to three and a half years old (C ‐ C + 3) for pine up to six and a half years old (C ‐ C + 6) for spruce. Epicuticular waxes, studied by scanning electron microscopy (SEM), showed age‐dependent but site‐independent changes. Different age‐patterns were found in the pine and spruce needles but no dust coverings or lesions were detected, irrespective of the sites. A proportionally increasing peroxidase activity (EC 1.11.1.7) with increasing needle‐age up to the third year was observed in both species. No certain indication of site‐effects, expressed by an unproportional increase of the enzyme activity with increasing needle‐age could be found. Chlorophyll a and b, phaeophytin a and b and carotenoid analyses on the corresponding materials only indicated disturbances in trees from some scattered sampling plots. Thus, neither could the pigment analyses reveal any signs of a general pollution stress in pine and spruce trees from the area in question.     

Environmental influences on juvenile shoot growth in Picea abies

Under certain environmental conditions, juvenile shoot growth characters might give early indications of adaptability and growth potential. Therefore, the reaction patterns of predetermined and free shoot growth were studied on Picea abies (L.) Karst, plants, which at different times during the growth period were treated by (1) application of nutrients, (2) defoliation, and (3) short days. Fertilization caused an increase in both predetermined and free growth, while defoliation and short day treatment caused a decrease in both forms of shoot growth and short days did not allow any free growth to occur. In the growth period following the treatments, fertilization caused more predetermined and less free growth to occur, while defoliation caused less predetermined and more free growth. Predetermined growth is explainable by the finite number of predetermined needle primordia. Free growth is initiated thereafter. It is influenced strongly by the environmental conditions and seems not to be influenced by the amount of preceding predetermined growth. Free growth enables young plants to utilize favourable growth conditions in summer for height growth precociously, which might increase their adaptability and competitive value. However, predetermined growth is the preferable mode of shoot growth because favourable conditions in successive growth periods induce more predetermined than free growth. Predetermined and free growth are well integrated forms of shoot growth giving no supporting evidence to the hypothesis that free and predetermined growth are inherited independently of each other. Rank changes in provenance development are probably not explainable by a loss in height growth when free growth occurs no more due to age, but by other causes.     

Outdoor exposure of untreated Scots pine (Pinus sylvestris L.) and Norway spruce [Picea abies (L.) Karst.] wood samples

Abstract

Untreated Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) samples were exposed above ground in a durability test for 6 years. The samples consisted of three pieces of wood, 22×95×500 mm, screwed together; two pieces lengthwise with a third piece overlapping. Weight was measured, to calculate moisture content (MC), and samples checked regularly for cracks and fungal growth. Parameters investigated were heartwood/sapwood (pine), annual ring orientation (spruce), stand site, annual ring width and density. Stand site, annual ring width and density had no influence on MC or fungal growth for either pine or spruce. Spruce samples with vertical annual rings had fewer cracks than samples with horizontal annual rings. Pine sapwood samples had a high MC and a large amount of rot fungi, while heartwood had a lower MC and no rot. Most spruce samples were similar to pine heartwood, except from a few samples that had high MC and fungal growth. Those were all sawn from the outer part of the log. Therefore, it can be stated that spruce sawn from the inner part has almost the same properties as pine heartwood, while spruce from the outer part of the log has similar properties to pine sapwood.     

Current growth differences of Norway spruce (Picea abies), Scots pine (Pinus sylvestris) and birch (Betula pendula and Betula pubescens) in different regions in Sweden

Abstract

The choice of species in forestry is important, and a real issue as large areas of wind-damaged forest land in southern Sweden need to be regenerated. To compare the growth potential between the most common tree species in Sweden, ratios between site quality derived from site index values determined with site properties were used. A regression function to determine site index for birch from site properties was used to complement the known relationships between site properties and site index for spruce and pine. In large regions of Sweden the distribution of site quality classes was calculated to compare the special characteristics and demands of the three species. On average, the growth difference for pine compared to spruce was about 60% in southern Sweden and 95% in northern Sweden. Corresponding figures between birch and spruce were 40% and 60%. Birch was expected to produce around 60% of pine in northern Sweden and about 70% in southern Sweden. However, it must be stressed that the comparison is based on survey data encompassing mainly naturally regenerated birch, whereas spruce and pine are mainly planted.