Chemical composition and ultrastructural changes in Scots pine needles in a forest decline area in southwestern Finland

Tree decline and deaths have been observed among 15 to 20-year-old Scots pines (Pinus sylvestris L.) in a dry heath forest in southwestern Finland. The sudden decline in height growth, the dieback of leading shoots and the yellowing of needles in young shoots in the upper part of the tree are typical symptoms of the decline of these young pines. Needle ultrastructure and chemical composition of Scots pines with or without decline and fluctuations of them in different seasons were studied. Afflicted trees were found to suffer from a deficiency in calcium and magnesium with low concentration of foliar nitrogen and phosphorus observed in all the trees studied. Ultrastructural study revealed changes characteristic of different seasons and measured nutrient status of needles. A clear reduction of membrane system in chloroplasts, especially related to Mg deficiency, was observed in most samples. The symptoms related to N deficiency, the translucent appearance of the cytoplasm and chloroplast stroma, and the elongated chloroplasts, as well as swelling of mitochondria, indicating P deficiency, were also found in the needles sampled from this forest decline area. The present study showed that it is possible to detect specific nutrient deficiency symptoms in needle ultrastructure in field samples and for use as sensitive indicators of unbalanced nutrient status.     

The role of below-ground competition during early stages of secondary succession: the case of 3-year-old Scots pine (Pinus sylvestris L.) seedlings in an abandoned grassland

In abandoned or extensively managed grasslands, the mechanisms involved in pioneer tree species success are not fully explained. Resource competition among plants and microclimate modifications have been emphasised as possible mechanisms to explain variation of survivorship and growth. In this study, we evaluated a number of mechanisms that may lead to successful survival and growth of seedlings of a pioneer tree species (Pinus sylvestris) in a grass-dominated grassland. Three-year-old Scots pines were planted in an extensively managed grassland of the French Massif Central and for 2 years were either maintained in bare soil or subjected to aerial and below-ground interactions induced by grass vegetation. Soil temperatures were slightly higher in bare soil than under the grass vegetation, but not to an extent explaining pine growth differences. The tall grass canopy reduced light transmission by 77% at ground level and by 20% in the upper part of Scots pine seedlings. Grass vegetation presence also significantly decreased soil volumetric water content (Hv) and soil nitrate in spring and in summer. In these conditions, the average tree height was reduced by 5% compared to trees grown in bare soil, and plant biomass was reduced by 85%. Scots pine intrinsic water-use efficiency (A/g), measured by leaf gas-exchange, increased when Hv decreased owing to a rapid decline of stomatal conductance (g). This result was also confirmed by δ ¹³C analyses of needles. A summer ¹⁵N labelling of seedlings and grass vegetation confirmed the higher NO₃ capture capacity of grass vegetation in comparison with Scots pine seedlings. Our results provide evidence that the seedlings' success was linked to tolerance of below-ground resource depletion (particularly water) induced by grass vegetation based on morphological and physiological plasticity as well as to resource conservation.     

The effect of bark phenols upon mountain hare barking of winter-dormant Scots pine

Due to high numbers of mountain hares in recent winters in northern Finland the barking of winter dormant Scots pines was widespread. The hares fed selectively upon upper crown bark of grafted pines, nitrogen fertilized trees and trees in poor condition. Bark of preferred upper crown branches and physiologically mature scions contained less total phenols than lower parts. However, there were no differences between total phenols concentrations of graft bark preferred by hares and nearby unbarked juvenile phase Scots pine. Neither decrease in resistance after nitrogen fertilization n- or stress was correlated with bark total phenolic concentration. Thus, total phenolic concentration is not a reliable predictor of the susceptibility of Scots pine to winter barking by the mountain hare.     

Effects of drought and waterlogging on ultrastructure of Scots pine and Norway spruce needles

Effects of water stress on needle ultrastructure of 2-year-old Scots pine (Pinus sylvestris L.) and 5-year-old Norway spruce [Picea abies (L.) Karst.] seedlings were studied in greenhouse experiments. Drought stress was induced by leaving seedlings without watering, and waterlogging stress was produced by submerging the seedling containers in water. Needle samples for ultrastructural analyses were collected several times during the experiments, and samples for nutrient analyses at the end of the experiments. In drought stress, plasmolysis of mesophyll and transfusion parenchyma tissues, aggregation of chloroplast stroma and its separation from thylakoids and decreased size and abundance of starch grains in needles of both species were observed. The concentration of lipid bodies around the chloroplasts were detected in pine needles. Calcium and water concentrations in spruce needles were lower by the end of the experiments compared to controls. In waterlogging treatment, swelling of phloem cells in pine needles and large starch grains, slight swelling of thylakoids and increased translucency of plastoglobuli in chloroplasts of both species studied were observed. The phosphorus concentration in pine needles was higher while phosphorus, calcium and magnesium concentrations in spruce needles were lower in the waterlogging treatments compared to controls. Typical symptoms induced by drought stress, e. g. aggregation of chloroplast stroma and its separation from thylakoids, were detected, but, in waterlogging stress, ultrastructural symptoms appeared to be related to the developing nutrient imbalance of needles.     

Growth and defence in young pine and spruce and the expression of resistance to a stem-feeding weevil

Defence in young trees has been much less studied than defence in older ones. In conifers, resin within ducts in bark is an important quantitative defence, but its expression in young trees may be influenced by developmental or physical constraints on the absolute size of the resin ducts as well as by differential allocation of resources to growth and resin synthesis. To examine these relationships, we used nitrogen fertilisation of 1- and 2-year-old pine and spruce to produce trees of different sizes and measured the effect on the number and size of resin ducts and the amount of resin they contained. All of these variables tended to increase with stem diameter, indicating a positive relationship between resin-based defence and growth of 1- and 2-year-old trees. In pine, however, the mass of resin flowing from severed ducts was much lower relative to duct area in 1- than in 2-year-old trees, suggesting that the older trees allocated a higher proportion of the carbon budget to resin synthesis. Resin-based defence in 1-year-old pines appears to be both positively related to growth and resource limited. In spruce, resin production was generally lower, and age-related differences were not observed, suggesting that resin-based defence is less important in this species. Bio-assays of 2-year-old trees with the pine weevil, Hylobius abietis, emphasised the importance of resin as a defence against this bark feeding insect. Nitrogen fertilisation had a limited influence on resistance expression. One-year-old trees remained susceptible because of their small size, low resin production and limited response to fertilisation. The strong growth response of 2-year-old trees to fertilisation increased resin-based defence, but most spruce trees remained susceptible, while most pines were resistant at all levels of fertilisation.     

Nitrogen metabolism of Douglas fir and Scots pine as affected by optimal nutrition and water supply under conditions of relatively high atmospheric nitrogen deposition

Nitrogen metabolism of the needles of 40-year-old Douglas fir and Scots pine trees, growing in two forest stands on cation-poor and acidic sandy soil with a relatively high atmospheric nitrogen deposition was studied. The composition of the free amino acid (FAA) pool, the concentrations of total nitrogen and soluble protein and the activities of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) were determined in the needles. An excessive nitrogen supply by a high atmospheric nitrogen deposition in both forest stands was indicated by the high concentrations of total nitrogen and the amino acids arginine, glutamic acid, glutamine and aspartic acid in control trees. In addition the effect of optimal nutrition and water supply (fertigation) on the needle nitrogen metabolism was evaluated. The total concentration of the FAA pool in needles of both tree species was lower in the fertigated than in the non-fertigated (control) trees, except for 1-year-old needles of Scots pine, in which the concentration after fertigation did not differ from the control. The lower total FAA concentration in the fertigated trees could be attributed to arginine, the concentration of which was on average 60% lower than in the control. Neither the concentration of soluble protein nor the activity of GS were influenced by fertigation. The activity of GDH in fertigated trees only differed significantly from the control in October. Scots pine needles had higher concentrations of protein (50%) and higher activities of GS (44%) and GDH (25%) than Douglas fir needles. Possible explanations for the lower vitality of Douglas fir compared to Scots pine are given.     

Chemical composition and biochemical changes in needles of Scots pine (Pinus sylvestris L.) stands at different stages of decline in Bulgaria

Water content was decreased in the needles of Scots pines (Pinus sylvestris L.) with moderate and slight levels of stress-induced decline. In pines with moderate decline a misbalance of foliar nutritional elements was observed. In 1-year-old needles of afflicted pines, the content of potassium and calcium was decreased, but the content of phosphorus, magnesium, iron, manganese and of the heavy metals cadmium and lead was increased. In 2-year-old needles of damaged pines, the content of calcium, iron and of the heavy metal cadmium was decreased, but the content of phosphorus, magnesium, manganese and zinc was increased. Potassium deficiency and zinc levels above toxicity tolerance characterized the nutrient status of declined Scots pines. In the same pines chlorophyll a/b ratio was diminished in 2-year-old needles and the protein content was increased in 1-year-old needles but was decreased in 2-year-old needles.In the second phase of the study 25- and 40-year-old pines with slight decline were examined. An increase in the protein content of 2-year-old needles of 25-year-old declined pines and of both 1- and 2-year-old needles of older 40-year-old pines was observed. A 280% increase of peroxidase activity in 1-year-old and a 178% increase in 2-year-old needles of 25-year-old damaged pines were shown. In older 40-year-old damaged pines a slight increase only in 1-year-old needles was seen. The observed age-related decrease in peroxidase activity in older 40-year-old symptomatic pines might be responsible for the lower resistance to decline in older pines. Our results show that clear but complex chemical and biochemical changes are observed in the needles of Scots pines in Bulgaria and that these changes hold promise for use as indicators of stress.     

The effect of shoot growth stage of Pinus contorta and Pinus sylvestris on the growth and survival of Panolis flammea larvae

Summary Young Panolis flammea (Lepidoptera: Noctuidae) larvae were unable to survive on the mature (one-year old) needles of Pinus contorta and Pinus sylvestris. Larval growth and survival on the current year's shoots of the 2 pine host plants first incresed, and then decreased as pine shoot development progressed, the effect on survival being more marked at 10° C that 18° C. The survival of larvae on lodgepole pine on field-grown plants transferred to 10° C rose from 26% in March to 87% in mid May, and rose from 3% to 82% on Scots pine in the same period. Larval survival exceeded 70% for about 8 weeks on lodgepole pine and about 6 weeks on Scots pine, this period starting and ending earlier on lodgepole than on Scots pine. The nitrogen, water and phosphorus contents of both pines were at a maximum in May and decline gradually thereafter; the soluble tannin content showed a more complex pattern. These results are discussed in relation to the possible importance of phenological coincidence on the population dynamics of P. flammea with emphasis on its greater abundance on lodgepole pine in Scotland.     

Simulated acid rain reduces the susceptibility of the European pine sawfly (Neodiprion sertifer) to its nuclear polyhedrosis virus

Summary The study dealt with the effect of simulated acid rain (both H₂SO₄ and HNO₃; acidities of pH 4 and pH 3) on the susceptibility of the larvae of Neodiprion sertifer to its nuclear polyhedrosis virus. Scots pines growing in a subarctic area with low ambient pollution levels were irrigated with simulated acid rain during two summers. Neodiprion larvae fed with foliage from the experimental trees were infected with a dilute virus suspension. The acid treatment of host trees had a significant effect on the proportion of virus-treated larvae alive 16 days after the virus application: there were almost no differences between the controls and the pH 4 irrigation group, but on the needles of pH 3-treated trees larval survival was twice as high as with other treatments. The direct spraying of acid water on the needles before they were fed to the larvae did not significantly affect the survival of virus infected larvae. Our results suggest that acid rain may reduce the susceptibility of Neodiprion larvae to virus disease via changes in the quality of pine foliage.     

The chemical composition of pine foliage in relation to the population dynamics of the pine beauty moth,Panolis flammea,in Scotland

Summary This paper reports part of a study to determine why damaging outbreaks of the pine beauty moth, Panolis flammea (D & S) (Lepidoptera: Noctuidae), in Scotland are frequent on lodgepole pine but do not occur on Scots pine, and why outbreaks on lodgepole pine are mainly confined to trees growing in deep unflushed peat. The elongation of shoots and the growth of needles of Scots pine occurred later in the season than did those of lodgepole pine. The foliage of Scots pine generally had a higher level of nitrogen, and consistently had a higher level of phosporus, but had a consistently lower level of tannins than that of lodgepole pine during the period when the larvae were feeding each year. The nitrogen content of the foliage of lodgepole pine growing in an iron pan soil was generally higher than that of lodgepole pine growing in deep peat during the same period but there were no general differences in the phosphorus or tannin contents of lodgepole pine in the 2 soil types. These findings suggest that Scots pine is a more suitable host plant than lodgepole pine and that the foliage of lodgepole pine growing in deep peat is not more suitable than lodgepole pine growing in an iron pan soil. On the basis of the chemical analyses used in this study, it is concluded that the abundance of pine beauty moth in Scotland is not strongly influenced by the nutritional suitability of its host plants.     

Evaluation of powdered pine bark for control ofMeloidogyne arenaria andHeterodera glycines on soybean

Commercially avaiable pine bark nuggets (composted) and fresh pine bark were ground into powders and added at rates of 0 to 50 g kg^–1 to field soil infested withMeloidogyne arenaria andHeterodera glycines. The treated soil was maintained moist in the greenhouse for 2 weeks, sampled, and planted with Davis soybean (Glycine max.). Eight weeks after planting, numbers ofM. arenaria andH. glycines in soil decreased with increasing amounts of composted or fresh pine bark. No juveniles were present in soil treated with 5% pine bark. The number of galls and cysts g^–1 root decreased in proportion to the amount of pine bark added to soil. Gall and cyst formation was completely eliminated at the 5% rate. Numbers of saprophagous nematodes were highest in soil with 4–5% pine bark. The activity of several soil enzymes was correlated with the addition of both composted and fresh pine bark. Fresh pine bark powder caused an increase in soil enzyme activity compared to composted pine bark, but did not provide consistent control of gall and cyst formation.Journal Series No. 18-933579 Alabama Agricultural Experiment Station     

Pine monoterpenes and pine bark beetles: a marriage of convenience for defense and chemical communication

Pine-feeding bark beetles (Coleoptera: Scolytidae) interact chemically with their host pines (Coniferales: Pinaceae) via the behavioral, physiological, and biochemical effects of one class of isoprenoids, the monoterpenes and their derivatives. Pine monoterpenes occur in the oleoresin and function as behaviorally active kairomones for pine bark beetles and their predators, presenting a classic example of tri-trophic chemical communication. The monoterpenes are also essential co-attractants for pine bark beetle aggregation pheromones. Ironically, pine monoterpenes are also toxic physiologically to bark beetles at high vapor concentrations and are considered an important component of the defense of pines. Research over the last 30 years has demonstrated that some bark beetle aggregation pheromones arise through oxygenation of monoterpenes, linking pheromone biosynthesis to the host pines. Over the last 10 years, however, several frequently occurring oxygenated monoterpene pheromone components (e.g., ipsenol, ipsdienol and frontalin) have also been shown to arise through highly regulated de novo pathways in the beetles (reviewed in Seybold and Tittiger, 2003). The most interesting nexus between these insects and their plant hosts involves the late-stage reactions in the monoterpenoid biosynthetic pathway, during which isomeric dimethylallyl diphosphate and isopentenyl diphosphate are ultimately elaborated to stereospecific monoterpenes in the trees and to hydroxylated monoterpenes or bicyclic acetals in the insects. There is signal stereospecificity in both production of and response to the monoterpenoid aggregation pheromones of bark beetles and in response to␣the monoterpenes of the pines. In the California fivespined ips, Ips paraconfusus, we have discovered a number of cytochome P450 genes that have expression patterns indicating that they may be involved in detoxifying monoterpene secondary metabolites and/or biosynthesizing pheromone components. Both processes result in the production of oxygenated monoterpenes, likely with varying degrees of stereospecificity. A behavioral analysis of the stereospecific response of I. paraconfusus to its pheromone is providing new insights into the development of an efficacious bait for the detection of this polyphagous insect in areas outside the western United States. In contrast, a Eurasian species that has arrived in California, the Mediterranean pine engraver, Orthotomicus (Ips) erosus, utilizes both a monoterpenoid (ipsdienol) and a hemiterpenoid (2-methyl-3-buten-2-ol) in its pheromone blend. The stereospecificity of the response of O. erosus to the monoterpenoid appears to be the key factor to the improved potency of the attractant bait for this invasive species.Dedicated to Professor David L. Wood on the occasion of his 75th birthday, January 8, 2006     

Root biomass and rooting profile of naturally regenerated beech in mid-elevation Scots pine woodlands

The natural establishment of shade-tolerant forest species such as beech (Fagus sylvatica L.) occurs in naturally regenerated Scots pine (Pinus sylvestris L.) woodlands that develop on former pastures and cultivated lands. To examine possible effects of underground competition in beech establishment, we studied the root biomass and the rooting profile of 53 mixed Scots pine-natural beech woodlands in French mid-elevation volcanic areas. Stands were arranged along a maturation gradient. Roots were sampled using the root-auger technique (0 to 75 cm depth every 15 cm). In addition, 23 young beeches were uprooted to study the entire root system. Total beech fine-root biomass was closely correlated with most beech aerial characteristics, (e.g., height, diameter and girth), and correlated moderately with tree age. However, it correlated poorly with basic competition indices such as stand density and basal area. Conversely, competition indices including vertical dimensions of competing trees were correlated with the underground biomass, probably as a result of redundancy with beech height. The rooting profile (fine roots, < 5 mm) of beech and pine were quite similar, and did not change significantly along the stand maturation gradient. Beech has a heart-shaped root system while pine is more plate-like and dimorphic. Beech fine-root biomass progressively surpassed pine biomass throughout the soil layers, thus confirming that it is dynamic and competitive in mature mixed stands. The coexistence of the root systems of beech and pine in the same soil layers presumably results in strong underground competition.     

Biomass allocation and growth responses of Scots pine saplings to simulated herbivory depend on plant age and light availability

This study experimentally analyses the response to simulated herbivory of juvenile Scots pine of two different ages in contrasting abiotic scenarios, focusing on the potential dual role of browsing ungulates: negative, by removing aerial biomass, and positive, by stimulating compensation capacity and providing nutrients by depositing their excrement. Compensation against herbivory was investigated by experimentally clipping a set of Scots pine (Pinus sylvestris L. nevadensis) juveniles, grown under different levels of light and nutrient availability. The responses analysed were survival, trunk-diameter growth, leader-shoot growth, increment in number of meristems, RGR, biomass of needles, shoots, root and whole plant, and root-to-shoot ratio. Clipping consistently resulted in a worse survival and performance of pines with respect to unclipped ones. From the factors analysed, light availability was responsible mainly for the variations in plant performance, while the addition of nutrients was much less important. Age was also important, with older pines showing in general better performance after clipping. Overall, clipping invariably had a negative effect on Scots pine, since none of the combinations of abiotic factors used resulted in overcompensation. However, the intensity on this negative effect proved quite variable, from almost an exact compensation in clipped older pines under full sunlight availability to very poor performance and high death probability in younger pines in shade. Scots pine cannot overcompensate after clipping, but, depending of the environmental conditions, the negative result of clipping varies from severe undercompensation to almost exact compensation. Also, small differences in sapling age can promote significant differences in sapling response to clipping and light environment.     

Changes in populations of soil microorganisms,nematodes, and enzyme activity associated with application of powdered pine bark

Evaluation of enzyme activities in combination with taxonomic analyses may help define the mechanisms involved in microbial decomposition of orgaic amendments and biological control of soilborne pathogens. In this study, powdered pine bark was added to nematode-infested soil at rates of 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, and 50 g kg^–1. Total fungal populations did not differ among treatments immediately after application of pine bark. After 7 days, fungal populations were positively correlated with increasing levels of pine bark. This increase was sustained through 14 and 21 days.Penicillium chrysogenum andPaecilomves variotii were the predominant fungal species isolated from soil amended with pine bark. Total bacterial populations did not change with addition of pine bark at 0, 7, and 14 days after treatment. At 21 and 63 days, total bacterial populations declined in soil receiving the highest rates of pine bark. Addition of pine bark powder to soil caused a shift in predominant bacterial genera fromBacillus spp. in nonamended soil, toPseudomonas spp. in amended soil. Soil enzyme activities were positively correlated with pine bark rate at all sampling times. Trehalase activity was positively correlated with total fungal populations and with predominant fungal species, but was not related to bacterial populations. The number of non-parasitic (non-stylet bearing) nematodes andMeloidogyne arenaria in soil and roots were not correlated with pine bark rate. However,Heterodera glycines juveniles in roots, and the number of cysts g^–1 root, declined with increasing levels of pine bark.Journal Series Series No. 18-933598 Alabama Agricultural Experiment Station     

Growth and nutrient characteristics in bog and fen populations of Scots pine (Pinus sylvestris)

Nutrient content in peat and growth rate, rate of nutrient accumulation and allocation patterns in Scots pine Pinus sylvestris L. from eleven natural Swedish peatlands were examined. The peatlands studied represented a wide range of climatic conditions and mire types. Whole and even-sized pines with intact root-systems were excavated to give the whole-pine budget for growth and nutrient accumulation. All samples originated from hummock communities.Pine growth and nutrient characteristics were much more variable in the minerogenous sites than in the ombrogenous sites, which indicates a larger environmental heterogeneity within the minerogenous sites. In the ombrogenous sites, rate of pine growth was constant, approximately 1 mg day^-1, and independent of latitudinal variation. There was either no relationship between latitudinal location and growth rate in the minerogenous sites, which suggests that pine growth is largely controlled by site-specific, very local conditions. The growth rate of pines was not correlated with any peat nutrient. The pines allocated a large proportion of their nutrient-pool to the metabolically active current year's growth. This is likely a trait that enables Scots pine to occupy a wide range of peatland types in which it experience a marked imbalance and shortage of nutrients.     

The ion concentration of dew condensed on Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) needles

Summary Dew droplets collected with pipettes from coniferous needles were analysed for their ionic composition. Almost all samples of dew taken from Scots pine trees (Pinus sylvestris) showed significantly higher ion concentrations than those taken from Norway spruce trees (Picea abies). This can be explained by the micromorphology of the needle surface. The higher microscale roughness of the wax layer of a pine needle causes a more efficient flux of atmospheric aerosol particles compared to the spruce needle surface. Dew on coniferous needles is shown to be capable of maintaining pH values below 3 for several hours.     

Two types of chemolithotrophic nitrification in acid heathland humus

Tree decline has been observed recently in 25–30 year old pine stands inCladina andCalluna-type heath forests in the Hämeenkangas and Pohjankangas areas of southwestern Finland. The trees had grown more or less normally for 15 years. During the following 7 to 8 years increased growth occurred. From 1982 to 1984, however, the trees revealed a sudden reduction in height increment. Additionally, some trees were marked by poor apical shoot dominance. Occasionally complete crown dieback was observed. The trees retained only one to three years' needles. These needles often were characterized by a brownish yellow discoloration.Chemical foliar and soil analysis indicate both a nitrogen deficiency and a deficiency in calcium and magnesium related to the relatively high aluminium levels in the soil. In the needles of affected trees phosphorus and especially potassium concentrations were higher than normally.The low content of nitrogen, calcium and magnesium in the soil is related to the acidic, nutrient-poor bedrock, and the low cation exchange capacity. Also the leaching of nutrients, the shallow and poor quality of the humus layer, and the removal of nutrients by tree harvesting may have effected on the nutritional disturbances.     

Effects of wood bark ash on the growth and nutrition of a Scots pine afforestation in central Finland

Results are presented from a fertilization experiment with wood bark ash (0, 1, 2, 5, 10, 20 Mg ha^-1) applied to prevent and cure visible nutrient disorders of young Scots pine established on a peatland field. 13 years after fertilization, dieback of trees and other symptoms of nutrient disorders were substantially reduced or even eliminated, especially where higher doses had been applied. The volume of the growing stock was more than 70 m³ ha^-1 for the highest dose while control plots produced less than 15 m³ ha^-1. Vegetation characteristics changed following ash treatments with high ash doses favouring grasses and low ash doses promoting mosses. Some major changes in soil and foliar nutrient concentrations were evident due to ash fertilization. K and B, however, were clearly the most limiting nutrients that could be cycled where high doses of ash were used. This was particularly the case with a dose of 20 Mg ha^-1. Decomposition of the topsoil was at its highest on plots with ash doses of 5 and 10 Mg ha^-1 ash and at its lowest when the dose was 2 Mg ha^-1. This was partly due to differences in the C/N ratio of the soil. All decomposition parameters indicated a high degree of humification in the topsoil. High N content (of organic material), low C/N in the soil and optimum levels of foliar N concentrations suggested sufficient N mineralization for tree growth to have occurred in the soil.     

Modelling the distribution of diameter growth along the stem in Scots pine

This paper presents an empirical model for the distribution of diameter growth along the stem in Scots pine (Pinus sylvestris L.) and for the consequent stem form over time. First, the distribution of annual mass growth in the stem is determined as a function of the total annual growth in stem mass, current stem mass and the distribution of the latter along the stem. Second, the distribution of diameter growth is obtained by converting the fraction of annual growth in the stem mass at a given height in the stem into the thickness of the annual ring at the same height. Application of the model to Scots pine data sets including both young and mature trees not used in parameter estimation showed that the model was capable of reconstructing the distribution of diameter growth from the stem butt to the apex and from the pith to the stem surface at any height in the stem in both young and mature trees. The resulting empirical model was also linked to a physiological, process-based model in order to study its performance in a simulated stand. Simulations representing trees grown in unthinned and thinned Scots pine stands with trees of different status (from dominant to suppressed) showed that the response in tree growth to thinning in terms of the distribution of diameter growth along the stem was quite realistic relative to measured data.