Models for Predicting Wood Properties in Stems of Picea abies and Pinus sylvestris in Sweden

To study and model the variation of wood properties, sample trees were selected from 42 Norway spruce and 20 Scots pine stands covering a wide variation in climatic and site conditions, stand maturation and tree sizes. Plot and tree measurements were followed by sampling wood from different heights in each sample tree and laboratory measurements of wood properties. Mixed linear and non-linear prediction models were developed using diameters, number of annual rings and climatic indices as explanatory variables. The variation in spruce properties explained by these variables was: basic density 50%, latewood content 52%, juvenile wood diameter 85%, heartwood diameter 94% and bark thickness 76%. The corresponding values for pine were 59, 54, 79, 92 and 85%. Random among-tree variance was an important contributor to the remaining variation for density and latewood. In general, only a minor part of the random variation was related to variance between stands. Predictions derived from the models for density and juvenile wood in both species, and heartwood in pine showed good agreement when validated with data sets from two other studies. The resulting models may be used for predicting wood properties in forest planning and in bucking computers in harvesters, provided that the essential information is available.     

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.     

Responses of Pinus sylvestris and Picea abies Seedlings to Limited Phosphorus Fertilization and Treatment with Elevated Ozone Concentrations

Scots pine ( Pinus sylvestris L.) and Norway spruce [ Picea abies (L.) Karst.] seedlings were exposed to high phosphorus (HP) or low phosphorus (LP) availability for one growing season in the open field, and to combined P availability and elevated ozone (O 3 ) concentrations (0, 55, 110 and 210 ppb for Scots pine and 0, 40, 75 and 150 ppb for Norway spruce, respectively) for 28 days in controlled laboratory chambers. Compared with HP, the LP treatment reduced Scots pine current-year (C) shoot and root dry masses and Norway spruce total dry mass, whereas the highest O 3 concentrations increased the magnesium concentration of Scots pine C needles and P concentrations of the C needles of both tree species. Chlorophyll a, a+b and carotenoid concentrations of Scots pine C needles were significantly higher in the LP treatment compared with HP under the highest O 3 concentration (210 ppb). In the mesophyll tissue of C needles of both tree species, LP treatment increased the size of mitochondria and elevated O 3 -induced granulation of chloroplast stroma and disintegration of cytoplasm. Exposure to elevated O 3 concentrations increased swelling of chloroplast thylakoids and reduced the amount of vacuolar tannin in the LP Scots pine C needles. The results suggest disturbances in needle photosynthetic machinery due to acute exposure to the combination of elevated O 3 and low P availability. However, clear additive effects were found only in needle P concentrations < 1 mg g -1 in short-term O 3 exposure.     

Effects of Previous High N Addition on Nutrient Conditions in Above-ground Biomass of a Picea abies Stand in Sweden

The effect of different thawing procedures on seedling quality in Norway spruce (Picea abies) was evaluated. Freezer-stored seedlings were thawed rapidly for 20 h by immersion in water with an initial water temperature of 8°C or thawed more slowly by gradually increasing the temperature in storage over a period of 8 weeks. Seedlings from these treatments were also compared with seedlings thawed rapidly overnight at 15°C. Frost tolerance, carbohydrate content and the time of bud break were used as indicators of the vitality of the seedlings. Seedlings thawed rapidly in water or air showed significantly better frost tolerance after storage than slowly thawed seedlings. The contents of sucrose and raffinose in seedlings thawed rapidly were also significantly higher than in seedlings thawed more slowly. Bud break occurred later in seedlings thawed rapidly than in slowly thawed seedlings. Rapid thawing in water may be a good method to ensure the delivery of high-quality thawed seedlings throughout the planting season.     

Patterns of Stem Damage by Moose (Alces alces) in Young Pinus sylvestris Stands in Sweden

The incidence of recent moose browsing of the main stem on young Scots pine (Pinus sylvestris L.) trees, and correlations with tree or stand characteristics, were examined using data from a large-scale survey in Sweden. On average, 10% of all Scots pine main stems showed one or more types of recent damage, with browsing of the apical leader accounting for about 75% of all damage recorded. Stripping of bark off the main stem occurred most frequently in the southern area, where site productivity is highest. Apical leader browsing was negatively correlated with height of the main stems, length of the apical leader and incidence of pre-commercial thinning, whereas bark stripping and stem breaking were positively correlated with the same variables. All types of recent stem damage correlated positively with the extent of previous stem damage and also with the extent of recent browsing of lateral shoots.     

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.     

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.     

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.     

Canopy density in stands of Picea abies and Pinus sylvestris after different thinning methods

Altogether 82 plots (261 estimations) of Picea abies (L.) Karst, and 193 plots (360 estimations) of Pinus sylvestris (L.) stands were estimated by a vertical tube. The “crown free projection”, CFP, of stands thinned in three methods with different thinning grades was measured: unthinned, heavily and very heavily thinned, heavily thinned delayed first thinning, extra heavily thinned and thinned from the top. Basal area (m²ha^?1) density (stems ha^?1) and diameter sum (m ha^?1) were plotted against CFP. Basal area was the best practical measure of stand in this study. Generally Scots pine stands have higher CFP and the curves are steeper than in Norway spruce stands. Depending on the grade of thinning, heavily and very heavily thinned spruce stands, delayed first thinning included, have CFP values of 10–15% and stands thinned from the top, 20–40%, compared with 30–80% and 30–60% respectively in pine stands. Extra heavily thinned stands have the highest CFP, 20–80% in spruce and 50–90% in pine stands. The CFP levels after thinning are too high in pine stands for avoidance of sucker and sprout production of aspen and birch. In dense Norway spruce stands thinned from the top or heavily and very heavily thinned, the CFP values are low enough (≤30%) to diminish the production of suckers.     

Radial,Height and Volume Increment Variation in Picea abies (L.) Karst. Stands with Varying Thinning Intensities

Variation in radial increment at different stem heights was compared with stem volume increment and height increment using thinning experiments of Picea abies (L.) Karst. in southern Finland. The magnitude of growth variation was similar on trees from different crown classes and stand densities. However, there was higher autocorrelation in the codominant and intermediate trees and trees on dense plots. The relationship between short-term volume increment and radial increment variation at breast height was not affected by thinnings. While short-term growth variation was similar at different stem heights, some evidence was found for differences in medium-term variation between radial increment at breast height and volume increment. Height increment reacted to unfavourable climatic events later than radial and volume increment. Radial and volume increments were negatively correlated to temperature and positively correlated to precipitation of the current summer. Height increment was positively related to current early summer temperature, but negatively to temperature of the previous summer.     

Morphological and Ecological Variation of Gremmeniella abietina var. abietina in Pinus sylvestris,Pinus contorta and Picea abies Sapling Stands in Northern Finland and the Kola Peninsula

The morphological and ecological variation of two types of Gremmeniella abietina var. abietina causing scleroderris canker on conifers was investigated in Pinus spp. and Picea sp. sapling stands in northern Finland and the Kola Peninsula. Small - tree type (STT or B type) of G. abietina was detected alone in 13 Scots pine, three lodgepole pine and two Norway spruce sapling stands out of 26 stands investigated, both STT and large - tree type (LTT or A type) were observed in six Scots pine stands, and LTT was detected alone in two Scots pine stands. For the first time, G. abietina was found to injure Norway spruce saplings in a respective plantation in northern Fennoscandia. STT isolates produced statistically significantly more conidia in vitro than LTT isolates. Morphological variation in conidia septation revealed that STT produced conidia with more than five septa more frequently than did LTT. There was a greater range in variation in septation in STT than in LTT, with overlapping between the types. Isolates of both types were equally associated with cankers, coloured wood, pycnidia or apothecia in the infected saplings.     

Natural Regeneration in Clear-cuts: Effects of Scarification,Slash Removal and Clear-cut Age

The effects of soil scarification (mounding), slash removal and clear-cut age on the natural regeneration in clear-cuts was evaluated using data from four sites in southern Sweden. The treatments were carried out during a good seed and establishment year for birch ( Betula pubescens Ehrh. and B. pendula Roth). Scarification had the strongest positive effect on the density of naturally regenerated seedlings, especially in birch, but also in pine ( Pinus sylvestris L.) and spruce [ Picea abies (L.) Karst]. Slash removal had a positive effect on birch density. No statistically significant effect of clear-cut age was found. In addition, no statistically significant interactions between clear-cut age and scarification or slash removal were found. The ingrowth of field vegetation was the fastest in areas that were not scarified, less rapid in areas scarified on old clear-cuts, and the slowest after scarification in fresh clear-cuts. In conclusion, it may be possible to control the density of birch during a good establishment year for birch. If birch is desired, the best combination of treatments is to remove the slash and scarify; otherwise, these treatments should be avoided.     

Retrospective Genetic Tests of Pinus sylvestris L. in Growth Chambers with Two Irrigation Regimes and Two Temperatures

The objective of this study was to estimate genetic correlations between stem volume in seven 19-30-yr-old field progeny trials and growth traits assessed in 1-yr-old Pinus sylvestris seedlings in growth-chamber treatments with optimal and limiting water availability at two temperatures. The seedlings in the growth-chamber experiment were open-pollinated families from two Swedish seed orchards. The field trials were established with full-sib families with the same parents. The genetic correlations between stem volume in the field progeny trials and height and biomass traits in the growth chamber were mainly low or zero. There was no clear pattern of juvenile-mature correlations with respect to combinations of growth-chamber treatments, field test site temperature and water availability. Periodic drought in the juvenile stage did not improve the juvenile-mature correlations, suggesting that at the juvenile stage, the mature stage, or both, the families used in this study do not appear to be specifically adapted to drought conditions.     

Pathogenicity of Thekopsora areolata from seed orchards in Finland on Prunus spp. and Picea abies

Pathogenicity of cherry‐spruce rust, Thekopsora areolata, was investigated by inoculations with aeciospores from seven Norway spruce, Picea abies, seed orchards that had suffered from successive severe rust epidemics in the 2000s in Finland. Detached leaves of Prunus spp. were inoculated in the laboratory using aeciospores from cones of various ages. In the greenhouse, live Prunus padus plants were inoculated, and possible autoecism of the rust was tested by inoculations of Picea abies seedlings. Thirty‐five spore sources from the seed orchards formed uredinia on Prunus spp. in the laboratory 2 weeks after incubation, but no telia developed. In the greenhouse, uredinia developed on live P. padus, but no rust symptoms, cankers or sporulation were detected on Picea abies. Thus, no evidence of autoecism was observed among the T. areolata populations and therefore all populations, suggesting all those tested from the Finnish seed orchards were heteroecious.     

The effect of tree architecture on conduit diameter and frequency from small distal roots to branch tips in Betula pendula, Picea abies and Pinus sylvestris

We studied the effect of tree architecture on xylem anatomy in three Betula pendula Roth., three Picea abies (L.) H. Karst. and three Pinus sylvestris (L.) trees (mean age 35 years). First, the analysis of conduit anatomy in different tree parts showed that conduits tapered and their frequency increased from roots (≥ 2 mm) to stem, from stem to branches and further to leaf petioles in B. pendula. Conduit anatomy in lateral and main roots, as well as lateral and main branches, significantly differed from each other in all the studied species. The increase in conduit diameter and decrease in frequency from the pith to the bark were clear aboveground, but variable patterns were observed belowground. In the leaf petioles of B. pendula, conduit diameter increased and conduit frequency decreased with increasing individual leaf area. Second, the results concerning the scaling of conduit diameter were compared with the predictions of the general vascular scaling model (WBE model) and Murray's law. The scaling parameter values at the tree level corresponded with the predictions of the WBE model in all the studied trees except for one tree of both conifer species. However, the scaling parameter values changed from one tree compartment to another rather than remaining uniform inside a tree, as assumed by the WBE model. The assumptions of the WBE model of a constant conductivity ratio, constant tapering and an unchanged total number of conduits were not fulfilled. When the conductivity ratio and relative tapering were plotted together, the results aboveground corresponded quite well with Murray's law: the conductivity ratio increased when relative tapering decreased. Our results support the theory that trees adjust both their macro- and microstructure to maximize their water transport efficiency, but also to prevent embolism and ensure mechanical safety.     

Structure of mixed Picea abies (L) Karst,and Betula pendula Roth and Betula pubescens Ehrh. stands in South and middle Sweden

Observed diameter distributions of forest stands are adapted to the Johnson S _b probability function. The stands investigated are untreated mixed stands of Norway spruce (Picea abies (L.) Karst.) and birch (Betula pendula Roth and Betula pubescens Ehrh.) aged between 20 and 32 years. The adaptation of the Johnson S_b probability function is made both on mixed spruce and birch, and on each species separately. Altogether 156 observations were tested with observed distributions against calculated distributions in the Kolmo‐gorov‐Smirnov test. The fractiles are predicted with multiple regression and two multivari‐ate techniques, simultaneous‐equation models (multivariate regression) and partial least squares with latent variables. The independent variables are characteristics of site and stand. Both multivariate methods predict diameter distribution well when tested.     

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.     

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.     

Biomass conversion factors (density and carbon concentration) by decay classes for dead wood of Pinus sylvestris, Picea abies and Betula spp. in boreal forests of Sweden

For estimating the amount of carbon (C) in dead wood, conversion factors from raw volume per decay class to dry weight were developed using three different classification systems for the species Norway spruce (Picea abies L. Karst), Scots pine (Pinus sylvestris L.) and birch (Betula pendula Roth and B. pubescens Ehrh) in Sweden. Also the C concentration in dead wood (dry weight) was studied. About 2500 discs were collected from logs in managed forests located on 289 temporary National Forest Inventory (NFI) sample plots and in 11 strips located in preserved forests. The conversion factors were based on an extensive data compilation with a wide representation of different site-, stand-, species- and dead wood properties and were assumed to represent the population of fallen dead wood in Sweden. The density decreased significantly by decay class and the range in density for decay classes was widest for the NFI decay classification system, suggesting this to be the most suitable. The C concentration in dead wood biomass increased with increasing decay class and in average Norway spruce (P. abies) showed a lower C concentration than Scots pine (P. sylvestris). The average dead wood C store of Swedish forests was estimated to 0.85 Mg C/ha.