Morphological and physiological differences in Scots pine seedlings of six seed origins

One-year-old seedlings of Scots pine (Pinus sylvestris L.) offour native seed origins (Loch Maree Islands, Glengarry/GlenMorriston, Glen Affric and Abernethy), a commercial Britishseedlot, and a seedlot from Hedesunda, in middle Sweden, werecompared at monthly intervals from October 1993 to April 1994.Seedling morphology, root condition, root frost hardiness andbud dry matter were determined at each date. There were clear morphological differences among seed origins.Seedlings raised from the commercial seedlot (A70) were largerbut had a poorer root:shoot ratio than the other seed origins.Of the native pines tested, the Loch Maree Islands origin allocateda larger proportion of its photosynthate to fine roots and needlesand smaller proportion to woody structures. Seedlings raised from the commercial British seedlot tendedto have poorer bud lignification than the other origins andalso, in autumn, higher electrolyte leakage rates from its fineroots. During winter, the Swedish origin had the lowest fineroot electrolyte leakage. Seedlings of all origins showed aprogressive increase in fine root hardiness towards mid-winterwith maximum hardiness (–7°C) in January. Dehardeningoccurred over subsequent months reaching –3°C in April.Differences among origins were evident. The Swedish seedlotdeveloped greater frost resistance than the other origins, hardeningbegan earlier in autumn and dehardening began later in spring.The commercial seedlot hardened later than the other originsbut reached a similar level of frost hardiness by January. Ofthe native pines, seedlings of the Loch Maree Islands originwere slowest to develop root hardiness.     

How timing of stem girdling affects needle xylem structure in Scots pine

While needles represent a proportionally large fraction of whole-plant hydraulic resistance, no studies to date have investigated how source–sink disturbances affect needle xylem structure. In this study, we evaluated structural changes in xylem in current-year needles of Scots pine 227 and 411 days after stem girdling (hereafter referred to as DAG). Maximum and minimum tracheid lumen diameters and therefore also the size of tracheid lumen areas increased in needles 227 DAG compared to control needles. In contrast, tracheid dimensions were similar in needles 411 DAG as in the control needles, but smaller xylem area and lower number of tracheids resulted in the lower theoretical needle hydraulic conductivity of those needles. Several needle xylem parameters were intercorrelated in both control and girdled trees. These observed changes provide a new understanding of the processes that occur following a source–sink disturbance. Considering anatomical parameters such as the number of tracheids, tracheid dimension, or needle xylem area, which are rarely described in physiological studies, could be helpful, for example, in understanding to tree hydraulic systems or for modeling gas exchange. Finally, empirical equations were developed to calculate needle theoretical hydraulic conductivity and the number of tracheids in needles using an easily measurable parameter of needle xylem area.     

Dielectric spectroscopy of Scots pine

Dielectric properties of Scots pine (42 trees) were compared with density, moisture content (MC), and resin acid content (RAC) (of heartwood). The samples were measured in frozen, green, conditioned and non-conditioned dry moisture states to evaluate the potential of dielectric spectroscopy in determining the wood characteristics at different stages of wood processing. Heartwood and sapwood parts of each sample were measured separately, and through-transmission measurement was conducted in longitudinal and tangential direction at frequencies from 1 MHz to 1 GHz. The MC and density correlated significantly with the dielectric parameters in both measurement directions but especially in longitudinal direction. The RAC of the heartwood correlated significantly with tanδ and ε″/(ε′ ? 1) of the green samples measured in the tangential direction at frequencies above 200 MHz. The correlation at 1 GHz was ?0.56 for green samples, ?0.66 for conditioned samples and ?0.61 for non-conditioned samples (P < 0.001, for all). The study suggests that the extractives also affect radio-frequency dielectric responses, which might be used for extractive analyses of pine heartwood.     

Models for predicting microfibril angle variation in Scots pine

Context

Microfibril angle (MFA) is one of the key determinants of solid timber performance due to its strong influence on the stiffness, strength, shrinkage properties and dimensional stability of wood.

Aims

The aim of this study was to develop a model for predicting MFA variation in plantation-grown Scots pine (Pinus sylvestris L). A specific objective was to quantify the additional influence of growth rate on the radial variation in MFA.

Methods

Twenty-three trees were sampled from four mature Scots pine stands in Scotland, UK. Pith-to-bark MFA profiles were obtained on 69 radial samples using scanning X-ray diffractometry. A nonlinear mixed-effects model based on a modified Michaelis–Menten equation was developed using cambial age and annual ring width as explanatory variables.

Results

The largest source of variation in MFA (>90 %) was within trees, while between-tree variation represented just 7 % of the total. Microfibril angle decreased rapidly near the pith before reaching stable values in later annual rings. The effect of ring width on MFA was greater at higher cambial ages.

Conclusion

A large proportion of the variation in MFA was explained by the fixed effects of cambial age and annual ring width. The final model is intended for integration into growth, yield and wood quality simulation systems.     

Decomposition of Scots pine fine woody debris in boreal conditions: Implications for estimating carbon pools and fluxes

Litter quality and environmental effects on Scots pine (Pinus sylvestris L.) fine woody debris (FWD) decomposition were examined in three forestry-drained peatlands representing different site types along a climatic gradient from the north boreal (Northern Finland) to south (Southern Finland) and hemiboreal (Central Estonia) conditions. Decomposition (percent mass loss) of FWD with diameter ≤10 mm (twigs) and FWD with diameter >10 mm (branches) was measured using the litter bag method over 1–4-year periods. Overall, decomposition rates increased from north to south, the rate constants (k values) varying from 0.128 to 0.188 year⁻¹ and from 0.066 to 0.127 year⁻¹ for twigs and branches, respectively. On average, twigs had lost 34%, 19% and 19%, and branches 25%, 17% and 11% of their initial mass after 2 years of decomposition at the hemiboreal, south boreal and north boreal sites, respectively. After 4 years at the south boreal site the values were 48% for twigs and 42% for branches. Based on earlier studies, we suggest that the decomposition rates that we determined may be used for estimating Scots pine FWD decomposition in the boreal zone, also in upland forests. Explanatory models accounted for 50.4% and 71.2% of the total variation in FWD decomposition rates when the first two and all years were considered, respectively. The variables most related to FWD decomposition included the initial ash, water extractives and Klason lignin content of litter, and cumulative site precipitation minus potential evapotranspiration. Simulations of inputs and decomposition of Scots pine FWD and needle litter in south boreal conditions over a 60-year period showed that 72 g m⁻² of organic matter from FWD vs. 365 g m⁻² from needles accumulated in the forest floor. The annual inputs varied from 5.7 to 15.6 g m⁻² and from 92 to 152 g m⁻² for FWD and needles, respectively. Each thinning caused an increase in FWD inputs, up to 510 g m⁻², while the needle inputs did not change dramatically. Because the annual FWD inputs were lowered following the thinnings, the overall effect of thinnings on C accumulation from FWD was slightly negative. The contribution of FWD to soil C accumulation, relative to needle litter, seems to be rather minor in boreal Scots pine forests.     

Anatomical differences in the structural elements of fluid passage of Scots pine sapwood with contrasting treatability

Treatability of wood is a function of anatomical properties developed under certain growing conditions. While Scots pine sapwood material normally is considered as easy to impregnate, great variations in treatability can be observed. In order to study anatomical differences in the structural elements of transverse fluid passage, wood material with contrasting treatability has been compared. Ray composition and resin canal network, membrane areas of fenestriform pits in the cross-field as well as dimension and properties of bordered pits were investigated. The results showed large anatomical differences between the two contrasting treatability groups. Refractory Scots pine sapwood samples developed more rays per mm² tangential section, while they were on average lower in cell numbers than rays found in easily treatable material. Easily treatable material had more parenchyma cells in rays than refractory material. At the same time, a larger membrane area in fenestriform pits in the cross-field was observed in the easily treatable sample fraction. Differences in the composition of resin canal network were not observed. Refractory samples developed on average smaller bordered pit features, with relatively small formed pit apertures compared to the easily treatable samples. In refractory Scots pine sapwood material, the structural elements of fluid passage such as bordered pit dimensions, fenestriform pits in the cross-field and parenchyma cells were altogether developed in smaller dimensions or number. Wood samples from better growing conditions and sufficient water supply showed a better treatability in this study.     

Stand Density Control Diagrams for Scots pine and Austrian black pine plantations in Bulgaria

Stand Density Control Diagram (SDCD) is a stand-level mathematical model, which describes the relationships between yield, density and mortality throughout all stages of stand development. The SDCD is primarily used to derive density control schedules by management objectives. The main objectives of the present study are to define a modified model of SDCD for application to Scots pine (Pinus sylvestris L.) and Austrian black pine (Pinus nigra Arn.) plantations in Bulgaria, to examine the fitness of the model with representative experimental data sets from plantations of both species and to present a way of direct application of the SDCDs for practical purposes. The constructed SDCDs characterize the spatial-temporal dynamics of the pine plantations in a broad range of densities, forest sites and growth stages from 4 to 26 (28) m of dominant height class. The full density lines were fixed with self-thinning exponents α = 1.69 and α = 1.75 for Scots pine and Austrian black pine, respectively, and the trajectories of natural thinning for 23 initial densities (444-40000/ha) were determined. A direct way for application of the SDCDs to the plantation management was designed to estimate the optimal initial densities for the maximum attainable final yield and large-size wood production by self-thinning stands.     

The effect of brown-rot decay on water adsorption and chemical composition of Scots pine heartwood

? The effect of brown-rot (Coniophora puteana) decay on the water adsorption capacity and concentration of extractives of Scots pine (Pinus sylvestris L.) heartwood were studied by comparing corresponding properties of decayed and undecayed wood samples.

? The samples derived from 39 felled trees having a large between-tree variation in the extractive concentrations, and subsequently in the mass loss in the decay test. The water adsorption capacity, expressed as equilibrium moisture content (EMC), was measured at a high relative humidity (RH ～100%, 21 °C).

? In contrast to the widely held belief, the water adsorption capacity of brow-rotted heartwood appeared to be significantly higher than that of undecayed heartwood.

? The chemical composition of heartwood was changed radically by the fungus: the concentration of stilbenes, resin acids and free fatty acids decreased, while the concentration of soluble sugars increased as a result of decay. In addition, fungal sugars were found in the decayed samples. The concentration of total phenolics increased, which obviously reflected chemical changes in cell wall constituents other than extractives.

? As a conclusion, the information concerning the hygroscopicity of brown-rotted wood might be valuable e.g. when carrying out repairs on buildings damaged by advanced decay.

     

Allometric equations for estimating the foliage biomass of Scots pine

The research described in this paper was performed in the Niepolomice Forest (Southern Poland) in 2001 as part of the Forest Environmental Monitoring and Management System (FOREMMS; 5FP IST) project. The material for the present study consisted of the measurement results of the biomass of Scots pine shoots with needles and needles alone carried out on 113 felled sample trees. The purpose of this study was to construct empirical equations for estimating the foliage biomass of Scots pine from easy to measure parameters. To achieve this aim, the dependence of the foliage biomass of Scots pine on stem diameter, height, age, crown length, basal area increment of the trees was analyzed. Using the biometric characteristics such as: tree diameter at breast height (dbh), basal area increment, age, height, and crown length empirical equations for estimating the foliage biomass of Scots pine reasonably precisely have been established. The created empirical equation gives accurate foliage biomass estimates. The explained variability varies between 65 and 85%, it depends on the number of variables applied in the equation. The equations presented in this paper were created with a view to their possible use in ecological studies where biomass quantity may be used, for example, in modeling carbon circulation in the forest ecosystem. From the point of view of forestry practice, these equations may help to assess biomass production in Scots pine stands.     

Boron retranslocation in Scots pine and Norway spruce

We previously traced 10B-enriched boric acid from shoots to roots to demonstrate the translocation of boron (B) in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings. To gain a more detailed understanding of B translocation, we sought: (1) to demonstrate B retranslocation directly, by showing that foliar-applied 10B is located in the new growth after dormancy; and (2) to assess whether shoot-applied B affects growth in the long term. We applied 10B-enriched boric acid to needles of Scots pine and Norway spruce seedlings. After a dormancy period and 9 weeks of growth, small but significant increases in the 10B isotope were found in the new stem and needles of both species. In Scots pine, the total B concentration of the new stem was also increased. Both species contained polyols, particularly pinitol and inositol. Boron-polyol complexes may provide a mechanism for mobilizing B in these species. To determine the long-term effects of applied B, seedlings were grown for two growing seasons after the application of 10B to shoots. In Norway spruce, the proportion of 10B in the root systems and current needles of the harvest year was slightly higher than in the controls, and in Scots pine root systems, marginally so. The B treatment had no effect on growth of Norway spruce seedlings. In Scots pine seedlings, the B treatment caused a 33% increase in total dry mass and significantly increased the number of side branches.     

Quantifying the effect of pine mistletoe on the growth of Scots pine

Mistletoe infection results in substantial growth losses in mistletoe‐infected forests. This study reports and evaluates the results of retrospective analyses of radial growth of Scots pine (Pinus sylvestris) in relation to the level of infection of pine mistletoe (Viscum album ssp. austriacum). A total of 43 Scots pine trees were destructively sampled from different sites. Of these trees, 14 were uninfected and 29 were infected. Infection classes were determined using six‐class dwarf mistletoe rating system (DMRS). All needle and mistletoe biomass were removed completely and weighed for each sampled tree. Subsamples from needles and all mistletoe biomass were taken to the laboratory for oven‐dried weight determinations. Five‐cm‐thick wood discs were cut from the stem at the breast height (1.3 m) to determine annual basal area increment for the last 25 years. In addition to DMRS, new infection classes were created using mistletoe‐to‐needle biomass (MB/NB) ratio. The results showed that the radial growth losses could be as much as 41% to 64% at different infection levels. The rate of growth loss in relation to DMRS and MB/NB ratio was similar, but with a larger variability in DMRS values. The results showed that both DMRS rating and MB/NB ratio seem to be important for quantifying growth loss on Scots pine trees infected with mistletoe. The results of this study can also be invaluable in modelling the effects of mistletoe on the growth of Scots pine trees.     

Predicting lumber grade and by-product yields for Scots pine trees

The purpose of this study was to develop models for estimating yields of lumber grades and by-products of individual Scots pine (Pinus sylvestris L.) trees using stem and crown dimensions as explanatory variables. Two separate data sets were used: (1) one simulated by the process-based growth model, PipeQual, which provides information about stem form and branch properties. The model was used to predict the 3D structure of Scots pine stems from thinning regimes of varying intensity and rotation periods and (2) an empirical data set with detailed 3D measurements of stem structure. The stems were sawn using the WoodCim sawing simulator and the yields and grades of the individual sawn pieces, as well as by-products, were recorded. The sawn timber was classified on A, B, C and D-grades for side and centre boards separately (Nordic Timber grading). By-products were pulpwood, sawmill chips, sawdust and bark.     

Effects on stem growth of Scots pine 33 years after thinning and/or fertilization in northern Sweden

Thinning and fertilization are two common and important stand treatments in forest management. In terms of area treated, thinning is the single most common form of stand treatment. The extent of forest fertilization on the other hand, has varied widely in recent decades and is currently not very common. Thinning is done primarily to promote stand properties while fertilization is done to increase growth before future final felling. After thinning stands of Scots pine, overall growth decreases, while growth of residual trees increases. An experiment was established outside Vindeln in northern Sweden where the long-term growth effects after thinning and/or fertilization were evaluated after 33 years. Experimental set-up was a randomized block design including 12 replications of four treatments. Treatments were control, fertilization, thinning, and thinning and fertilization combined. Thinning decreased overall and annual volume growth ha^?1, and increased green crown size and diameter growth at breast height (1.3 m, DBH) for the individual trees. No positive growth responses to fertilization could be seen after 33 years. In summary, this study showed that thinning can have long term effects on the growth of a Scots pine stand in northern Sweden. Possible reasons for the lack of positive response following fertilization are discussed.     

Effects of temperature and nutrient availability on plasma membrane lipid composition in Scots pine roots during growth initiation

We studied the effects of root zone temperature (RZT) and nutrient availability on free sterols and phospholipids in the plasma membrane (PM) and on PM-ATPase activity in roots of 1-year-old Scots pine (Pinus sylvestris L.) seedlings during growth initiation in the spring. Seedlings were grown for 6 weeks in hydroponic cultures with low (0.5 mM N; LN) or high (3 mM N; HN) nutrient availability. The root zone was subjected to slow warming (SW) and fast warming (FW) treatments while maintaining similar air temperatures in both treatments. Decreases in the amount of phospholipids and in the phospholipid/free sterol ratio, an increase in the degree of saturation of phospholipid fatty acids and changes in free sterol composition were observed during root growth initiation. Changes in lipid composition of the PM associated with the cold deacclimation process were detected at RZTs above 9 degrees C. Nutrient availability affected the lipid composition of the PM only when RZT was increased slowly. When RZT increased from 4 to 6 degrees C in the SW treatment, the degree of saturation of phospholipid fatty acids decreased, especially in HN seedlings. The sitosterol/stigmasterol ratio remained higher in HN seedlings than in LN seedlings. After an RZT of 9 degrees C had been reached in the SW treatment, HN caused increases in the saturation of phospholipid fatty acids and root PM-ATPase activity, and a decrease in the phospholipid/free sterol ratio. Possible effects of changes in PM lipid composition on root growth and PM-ATPase activity are discussed.     

Below-ground hydraulic constraints during drought-induced decline in Scots pine

Key message

Below-crown hydraulic resistance, a proxy for below-ground hydraulic resistance, increased during drought in Scots pine, but larger increases were not associated to drought-induced defoliation. Accounting for variable below-ground hydraulic conductance in response to drought may be needed for accurate predictions of forest water fluxes and drought responses in xeric forests.

Context

Hydraulic deterioration is an important trigger of drought-induced tree mortality. However, the role of below-ground hydraulic constraints remains largely unknown.

Aims

We investigated the association between drought-induced defoliation and seasonal dynamics of below-crown hydraulic resistance (a proxy for below-ground hydraulic resistance), associated to variations in water supply and demand in a field population of Scots pine (Pinus sylvestris L.)

Methods

Below-crown hydraulic resistance (r_bc) of defoliated and non-defoliated pines was obtained from the relationship between maximum leaf-specific sap flow rates and maximum stem pressure difference estimated from xylem radius variations. The percent contribution of r_bc to whole-tree hydraulic resistance (%r_bc) was calculated by comparing stem water potential variations with the water potential difference between the leaves and the soil.

Results

r_bc and %r_bc increased with drought in both defoliated and non-defoliated pines. However, non-defoliated trees showed larger increases in r_bc between spring and summer. The difference between defoliation classes is unexplained by differences in root embolism, and it is possibly related to seasonal changes in other properties of the roots and the soil-root interface.

Conclusion

Our results highlight the importance of increasing below-ground hydraulic constraints during summer drought but do not clearly link drought-induced defoliation with severe below-ground hydraulic impairment in Scots pine.

     

Modelling stand structure in young Scots pine dominated stands

The purpose of this study was to construct models for predicting the structure of young Scots pine (Pinus sylvestris L.) stands. The two-parameter Weibull function characterized the height distribution of the stands. In young stands height was preferred to dbh as a random variable because of its continuous feature. Tree diameters were predicted using a multiplicative model, fitted as a linearized mixed-effect model. The modelling data consisted of repeatedly measured Scots pine dominated juvenile stands, carried out on a sub-sample of the 7th National Forest Inventory. The data covered a dominant height range from 0.2 up to 17 m. Two independent data sets were used to validate the models. The Weibull function was fitted using the maximum likelihood method. Four methods for predicting the distributions were compared: (1) parameter prediction models (PPM) consisting of seemingly unrelated regression equations, (2) a generalized linear model (GLM) which was a one-stage distribution and model fitting procedure, (3) a hybrid method including PPM for the shape parameter together with moment-based parameter recovery for the scale parameter, and (4) inclusion of moment-based parameter recovery for the scale parameter in the estimated GLM. Goodness-of-fit were tested in terms of Kolmogorov–Smirnov and error index statistics. Parameter recovery showed no improvement when used with PPM, but it improved GLM and gave the overall best performance for this new method. The constructed diameter–height model showed quite flexible and unbiased behaviour. Models are recommended as practical tools for Finnish forest management planning purposes.     

Tree stem diameter variations and transpiration in Scots pine: an analysis using a dynamic sap flow model

A dynamic model for simulating water flow in a Scots pine (Pinus sylvestris L.) tree was developed. The model is based on the cohesion theory and the assumption that fluctuating water tension driven by transpiration, together with the elasticity of wood tissue, causes variations in the diameter of a tree stem and branches. The change in xylem diameter can be linked to water tension in accordance with Hookea s law. The model was tested against field measurements of the diurnal xylem diameter change at different heights in a 37-year-old Scots pine at Hyyti?l?, southern Finland (61 degrees 51' N, 24 degrees 17' E, 181 m a.s.l.). Shoot transpiration and soil water potential were input data for the model. The biomechanical and hydraulic properties of wood and fine root hydraulic conductance were estimated from simulated and measured stem diameter changes during the course of 1 day. The estimated parameters attained values similar to literature values. The ratios of estimated parameters to literature values ranged from 0.5 to 0.9. The model predictions (stem diameters at several heights) were in close agreement with the measurements for a period of 6 days. The time lag between changes in transpiration rate and in sap flow rate at the base of the tree was about half an hour. The analysis showed that 40% of the resistance between the soil and the top of the tree was located in the rhizosphere. Modeling the water tension gradient and consequent woody diameter changes offer a convenient means of studying the link between wood hydraulic conductivity and control of transpiration.     

Needle polyamine concentrations and potassium nutrition in Scots pine

The response of free polyamines (putrescine, spermidine and spermine) in needles of Scots pine (Pinus sylvestris L.) to varying needle potassium concentrations was investigated in two potassium fertilization experiments on drained peatlands. A significant negative correlation was observed between putrescine and potassium concentrations in needles. Putrescine responded more sensitively to decreasing needle K concentrations during the growing season than during the winter. Putrescine accumulation started when needle potassium concentrations were above 5.5 mg g(dw) (-1) in summer and above 5.0 mg g(dw) (-1) in winter. A decrease in needle potassium concentrations below 4.3 mg g(dw) (-1) in summer and below 3.5 mg g(dw) (-1) in winter resulted in an exponential increase in putrescine concentrations. Putrescine accumulation was initiated well above the needle potassium concentrations generally considered indicative of deficiency. The exponential increase in putrescine concentrations in winter occurred within the range of needle potassium concentrations that has been identified as indicating severe potassium deficiency.