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.     

Effects of climate and site characteristics on Scots pine growth

Scots pine is a highly diverse species, extended across Europe from Scandinavia to Spain, Italy, Greece and Turkey. It is also a valuable species, used in many commercial monoculture plantations in Great Britain and particularly in Scotland. Because of the diversity of growing environments and its commercial importance, it is necessary to identify the combination of significant factors affecting the observed variability of growth. Temperature, mainly during the growing season, is quite commonly considered as the most important factor in knowledge-based or empirical models. However, in highly oceanic climates like that of Scotland, the impact of temperature may have a less significant impact on growth. Here we argue that other factors, such as incoming winter solar radiation, frost, drought and management also have a significant effect on the growth of Scots pine. In addition, we argue that the already developed Ecological Site Classification knowledge-based model, used as a forest management tool in Great Britain, should be updated to incorporate our findings. Furthermore, we discuss the need to include management impact and possibly more physiological based components in its growth modelling routines, as these would allow the introduction of the effect of winter solar radiation.     

The effects of pine mistletoe (Viscum album subsp. austriacum) on the growth of Scots pine and Crimean pine in Turkey

In this study, the effect of pine mistletoe (Viscum album subsp. austriacum) on basal area increment of Crimean pine and Scots pine was investigated. Dendrochronological data were collected from 223 (71 uninfected and 152 infected) Crimean pines and 195 (77 uninfected and 118 infected) Scots pines located in Kastamonu province of Turkey in 2014. Infected sample trees were classified as light, moderate or severe infection levels. Growth trends and basal area increment loses were compared between uninfected and infected trees for the periods of the last 10, 20 and 30 years. In addition, infection status of forest stands was investigated using temporary sample plots; 27 plots in Crimean pine stands and 26 plots in Scots pine. Results demonstrated that basal area increments were negatively affected by pine mistletoe for both species. Mean basal area increment losses of infected trees for the last decade were determined as 24% for Scots pine and 26% for Crimean pine. Basal area increment losses varied by infection levels (light, moderate and severe) as follows: 25%, 20% and 28% for Scots pines and 20%, 32% and 9% for Crimean pines. Scots pine stands were more severely infected by pine mistletoe than Crimean pine stands. There were negative correlations between number of infected trees and stand density for both species, while positive correlation was detected between the number of infected trees and mean diameter for Scots pine. The results of this study indicate that the pine mistletoe infection has negative effect on radial growth of Scots pine and Crimean pine trees. The results can be an important contribution to the forest management and protection activities in mistletoe-infected stands.     

Radial growth of Norway spruce and Scots pine: effects of nitrogen deposition experiments

The growth patterns of annually resolved tree rings are good indicators of local environmental changes, making dendrochronology a valuable tool in air pollution research. In the present study, tree-ring analysis was used to assess the effects of 16 years (1991–2007) of chronic nitrogen (N) deposition, and 10 years (1991–2001) of reduced nitrogen input, on the radial growth of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) growing in the experimental area of Lake Gårdsjön, southwest Sweden. In addition to the ambient input of c. 15 kg N ha^?1 year^?1, dissolved NH₄NO₃ was experimentally added to a 0.52-ha watershed at a rate of c. 40 kg ha^?1 year^?1. Atmospheric N depositions were reduced by means of a below-canopy plastic roof, which covered a 0.63-ha catchment adjacent to the fertilized site. The paired design of the experiment allowed tree growth in the N-treated sites to be compared with the growth at a reference plot receiving ambient N deposition. Nitrogen fertilization had a negative impact on pine growth, while no changes were observed in spruce. Similarly, the reduction in N and other acidifying compounds resulted in a tendency towards improved radial growth of pine, but it did not significantly affect the spruce growth. These results suggest that spruce is less susceptible to changes in the acidification and N status of the forest ecosystem than pine, at least in the Gårdsjön area.     

Identifying the biological effects of pre-commercial thinning on diameter growth in young Scots pine stands

Data from seven Scots pine (Pinus sylvestris L.) stands in central Sweden that had undergone pre-commercial thinning (PCT) were used to investigate the biological effect of PCT on the diameter at breast height (DBH) growth of the remaining trees. Two treatments were considered: a PCT treatment and a control (C) with no PCT. The DBH of the trees in each stand was measured on up to four occasions over 15 years. We examined mean DBH and DBH growth of the largest 300, 600, 900 and 1200 trees ha^?1. Two methods of selecting the trees used to calculate the mean DBH values for each measurement occasion were considered: the actual mean DBH (Dma), which is based on the DBH distribution of the trees on the measurement occasion in question, and the genuine mean DBH (Dmg), which is based on the DBH distribution of the trees on the final measurement occasion of the study and therefore focuses on the same set of trees for all measurement occasions. There was no clear difference between the Dma- and Dmg-based DBH increments, but the Dmg values tended to be somewhat larger both for the C and PCT treatments. Over a 15-year period, the relative mean yearly increments (Dma/Dmg) for different tree size classes ranged from 0.91 to 0.98, with lower values for the C treatment and larger DBH size classes. We found that PCT promotes DBH growth: over a 15-year period, the increased growth amounted to about 2.0 mm year^?1 compared to the trees in unthinned plots.     

Thinning intensity and growth response in SW-European Scots pine stands

The effect of different thinning intensities on growth and yield was studied in Pinus sylvestris L. stands at the south-western limit of its distribution area (Central Spain), using five long-term thinning trials. Data were analysed collectively considering several factors (trial, block, plot and period) as random effects. Total volume and volume increment decreased with thinning intensity, this loss being more significant in the case of moderate and heavy thinning. No difference was found among treatments for total basal area or the increment in basal area. The results revealed an optimum basal area (Assmann’s definition) between 85 and 100% of the basal area in unthinned plots. Volume growth loss associated with heavy thinnings (reduction of 18% in volume increment) was smaller than that reported in Central and Northern European regions (greater than 25%). Height increment was not influenced by thinning, whereas dominant and quadratic mean diameter increments increased with the thinning intensity. The response of diameter growth to thinning was greater at younger ages (less than 50 y) and in medium-sized trees.     

Long-term effects of stump harvesting on soil properties and tree growth in Scots pine and Norway spruce stands

Abstract

Effects of stump harvesting on the properties of surface soil and on the density, structure and growth of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) stands were estimated in a field trial in western Finland. The experiment was established in 1977 and measured in 2010. Stems and logging residues were harvested after clear-cutting, and stumps were lifted and removed from half of the experimental area. Sixteen plots were planted with pine seedlings and 16 with spruce. The main effects of stump harvesting were improved survival of planted trees and an increase in natural regeneration. No clearly negative effects were noted in the stand development. Stump harvesting had no or minimal effects on the properties of the organic layer and those of the 0- to 10-cm mineral-soil layer. Soil properties did not differ between tree species. Pine production was higher on plots with stump removal compared to plots without soil treatment.     

Mistletoe effects on Scots pine decline following drought events: insights from within-tree spatial patterns, growth and carbohydrates

Forest decline has been attributed to the interaction of several stressors including biotic factors such as mistletoes and climate-induced drought stress. However, few data exist on how mistletoes are spatially arranged within trees and how this spatial pattern is related to changes in radial growth, responses to drought stress and carbon use. We used dendrochronology to quantify how mistletoe (Viscum album L.) infestation and drought stress affected long-term growth patterns in Pinus sylvestris L. at different heights. Basal area increment (BAI) trends and comparisons between trees of three different infestation degrees (without mistletoe, ID1; moderately infested trees, ID2; and severely infested trees, ID3) were performed using linear mixed-effects models. To identify the main climatic drivers of tree growth tree-ring widths were converted into indexed chronologies and related to climate data using correlation functions. We performed spatial analyses of the 3D distribution of mistletoe individuals and their ages within the crowns of three severely infested pines to describe their patterns. Lastly, we quantified carbohydrate and nitrogen concentrations in needles and sapwood of branches from severely infested trees and from trees without mistletoe. Mistletoe individuals formed strongly clustered groups of similar age within tree crowns and their age increased towards the crown apex. Mistletoe infestation negatively impacted growth but this effect was stronger near the tree apex than in the rest of sampled heights, causing an average loss of 64% in BAI (loss of BAI was ～51% at 1.3 m or near the tree base). We found that BAI of severely infested trees and moderately or non-infested trees diverged since 2001 and such divergence was magnified by drought. Infested trees had lower concentrations of soluble sugars in their needles than non-infested ones. We conclude that mistletoe infestation causes growth decline and increases the sensitivity of trees to drought stress.     

Carbon budget for Scots pine trees: effects of size, competition and site fertility on growth allocation and production

Time series of carbon fluxes in individual Scots pine (Pinus sylvestris L.) trees were constructed based on biomass measurements and information about component-specific turnover and respiration rates. Foliage, branch, stem sapwood, heartwood and bark components of aboveground biomass were measured in 117 trees sampled from 17 stands varying in age, density and site fertility. A subsample of 32 trees was measured for belowground biomass excluding fine roots. Biomass of fine roots was estimated from the results of an earlier study. Statistical models were constructed to predict dry mass (DW) of components from tree height and basal area, and time derivatives of these models were used to estimate biomass increments from height growth and basal area growth. Biomass growth (G) was estimated by adding estimated biomass turnover rates to increments, and gross photosynthetic production (P) was estimated by adding estimated component respiration rates to growth. The method, which predicts the time course of G, P and biomass increment in individual trees as functions of height growth and basal area growth, was applied to eight example trees representing different dominance positions and site fertilities. Estimated G and P of the example trees varied with competition, site fertility and tree height, reaching maximum values of 22 and 43 kg(DW) year(-1), respectively. The site types did not show marked differences in productivity of trees of the same height, although height growth was greater on the fertile site. The G:P ratio decreased with tree height from 65 to 45%. Growth allocation to needles and branches increased with increasing dominance, whereas growth allocation to the stem decreased. Growth allocation to branches decreased and growth allocation to coarse roots increased with increasing tree size. Trees at the poor site allocated 49% more to fine roots than trees at the fertile site. The belowground parts accounted for 25 to 55% of annual G, increasing with tree size and decreasing with site fertility. Annual G and P per unit needle mass varied over the ranges 1.9-2.4 and 3.5-4.0 kg(DW) kg(-1), respectively. The relationship between P and needle mass in the example trees was linear and relatively independent of competition, site fertility and age.     

The effects of species mixture on the growth and yield of mid-rotation mixed stands of Scots pine and silver birch

The effect of tree species mixture on stand volume yield and on tree-species-specific diameter and height growth rates were analysed in managed mixed stands of Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Ehrn.).Data were obtained from 14 repeatedly measured stands located in Southern Finland on mineral soil sites with varying admixture of Scots pine and silver birch. Statistical analysis was carried out for studying the effect of species mixture on the development of stand characteristics. For the analysis, the plots were categorised into three groups (plot types) according to the species dominance. In order to analyse species-specific growth rates, individual-tree mixed linear growth models for tree diameter and height growth were developed for both tree species.The results clearly show that the yield of the managed mid-rotation, mixed stands was greater for stands dominated by Scots pine than for stands dominated by birch, and the stand volume increment decreased with an increasing proportion of silver birch. Analysis of diameter and height growth by tree species revealed that the main reason for this pattern is the negative impact of birch competition on the growth of pine trees. The increase in diameter of pine was clearly hampered if the proportion of birch was high. An abundance of birch also slightly decreased the growth in height of Scots pine, although the effect was less than on diameter growth. Species mixture did not affect the diameter growth of birch but did have a significant effect on height development. Height growth of birch was considerably greater in pine-dominated stands than in birch-dominated stands. In pine-dominated mixed stands, the height growth of birch was quite close to that of dominant pine trees, and birches can endure in competition with pines for light.The results apply for even-aged and single-storey managed stands, where stocking density and structure are controlled with pre-commercial and commercial thinnings. The results are not applicable to unmanaged mixed stands undergoing self-thinning. This study provides new information on mixed stands from a silvicultural perspective, which can be applied in decisions involving the management of mixed stands.     

Modeling the effects of growth rate on the intra-tree variation in basic density in hinoki cypress (Chamaecyparis obtusa)

The purpose of this study is to evaluate the effect of growth rate on intra-tree variation in basic density of hinoki cypress (Chamaecyparis obtusa) quantitatively using the statistical modeling technique. Nineteen sample trees were harvested from 50-year-old hinoki stand which consists of two different growth rate plots. Disks were cut from sample trees at height positions of 2, 4 m, and then 4 m intervals until 16 m position. Radial strips were cut from the disks, and ring widths and basic density were measured at 5-ring intervals. The basic density decreased with age at any height positions. The linear mixed model was fitted to the age trend data having two nested grouping levels, i.e., tree and position within tree. Models having various mean and covariance structures were tested in devising an appropriate wood density model. The model, consisting of the mean structure with quadratic function of cambial age was able to describe the intra-tree variation in basic density. The model containing the random effects which consist of effect of the tree level and vertical stem position level explained the density variation adequately. The growth rate did not show the significant effect on the basic density variation within the stem.     

Delayed soil thawing affects root and shoot functioning and growth in Scots pine

In boreal regions, soil can remain frozen after the start of the growing season. We compared relationships between root characteristics and water relations in Scots pine (Pinus sylvestris L.) saplings subjected to soil frost treatments before and during the first week of the growing period in a controlled environment experiment. Delayed soil thawing delayed the onset of sap flow or totally blocked it if soil thawing lagged the start of the growing period by 7 days. This effect was reflected in the electrical impedance of needles and trunks and in the relative electrolyte leakage of needles. Prolonged soil frost reduced or completely inhibited root growth. In unfrozen soil, limited trunk sap flow was observed despite unfavorable aboveground growing conditions (low temperature, low irradiance, short photoperiod). Following the earliest soil thaw, sap flow varied during the growing season, depending on light and temperature conditions, phenological stage of the plant and the amount of live needles in the canopy. The results suggest that delayed soil thawing can reduce tree growth, and if prolonged, it can be lethal.     

Effect of heavy metal pollution of forest soil on radial growth of Scots pine

A field experiment with artificial soil contamination by the heavy metals copper and nickel was established in Kola Peninsula, northern Russia. To study the effect of soil contamination by heavy metals without SO₂ air pollution on the Scots pine trees growth the experiment was located outside the range of forest damage due to emissions from a copper–nickel smelter. Retardation in tree diameter growth over 15 years after contamination with 20 kg of metallurgical dust per 100 m² plot was 54%, 10 kg 27%, 5 kg 16% and 2.5 kg 7%, respectively, compared with growth in control plots. Thus, decreasing Scots pine growth due to heavy metal pollution was demonstrated.     

Elevated temperature and CO(2) concentration effects on xylem anatomy of Scots pine

We studied the effects of elevated temperature and carbon dioxide concentration ([CO(2)]) alone and together on wood anatomy of 20-year-old Scots pine (Pinus sylvestris L.) trees. The study was conducted in 16 closed chambers, providing a factorial combination of two temperature regimes and two CO(2) concentrations (ambient and elevated), with four trees in each treatment. The climate scenario included a doubling of [CO(2)] and a corresponding increase of 2-6 degrees C in temperature at the site depending on the season. Anatomical characteristics analyzed were annual earlywood, latewood and ring widths, intra-ring wood densities (earlywood, latewood and mean wood density), tracheid width, length, wall thickness, lumen diameter, wall thickness:lumen diameter ratio and mass per unit length (coarseness), and numbers of rays, resin canals and tracheids per xylem cross-sectional area. Elevated [CO(2)] increased ring width in four of six treatment years; earlywood width increased in the first two years and latewood width in the third year. Tracheid walls in both the earlywood and latewood tended to become thicker over the 6-year treatment period when temperature or [CO(2)] was elevated alone, whereas in the combined treatment they tended to become thinner relative to the tracheids of trees grown under ambient conditions. Latewood tracheid lumen diameters were larger in all the treatments relative to ambient conditions over the 6-year period, whereas lumen diameters in earlywood increased only in response to elevated [CO(2)] and were 3-6% smaller in the treatments with elevated temperature than in ambient conditions. Tracheid width, length and coarseness were greater in trees grown in elevated than in ambient temperature. The number of resin canals per mm(2) decreased in the elevated [CO(2)] treatment and increased in the elevated temperature treatments relative to ambient conditions. The treatments decreased the number of rays and tracheids per mm(2) of cross-sectional area, the greatest decrease occurring in the elevated [CO(2)] treatment. It seemed that xylem anatomy was affected more by elevated temperature than by elevated [CO(2)] and that the effects of temperature were confined to the earlywood.     

Predicting moisture content and density distribution of Scots pine by microwave scanning of sawn timber

This study was carried out to investigate the possibility of calibrating a prediction model for the moisture content and density distribution of Scots pine (Pinus sylvestris) using microwave sensors. The material was initially of green moisture content and was thereafter dried in several steps to zero moisture content. At each step, all the pieces were weighed, scanned with a microwave sensor (Satimo 9,4GHz), and computed tomography (CT)-scanned with a medical CT scanner (Siemens Somatom AR.T.). The output variables from the microwave sensor were used as predictors, and CT images that correlated with known moisture content were used as response variables. Multivariate models to predict average moisture content and density were calibrated using the partial least squares (PLS) regression. The models for average moisture content and density were applied at the pixel level, and the distribution was visualized. The results show that it is possible to predict both moisture content distribution and density distribution with high accuracy using microwave sensors.     

The influence of pine twist rust (Melampsora pinitorqua) on growth and development of Scots pine (Pinus sylvestris)

The influence of pine twist must (Alelampsora pinitorqsat) on growth and development of Scots pine was studied during three consecutive years. The experimental material included three provenances from natural stands and one open pollinated seed orchrd progeny. Trees severely affected by pine twist must reached an average of 38% lower height than did not-affected trees. while mildly affected trees grew somewhat better, on the average, than did non-affected trees. Pine twist must caused tha greatest loss of height increment in the seed orchard progeny.     

Large-scale genetic structure and drought-induced effects on European Scots pine (Pinus sylvestris L.) seedlings

Seedlings of ten provenances of Scots pine (Pinus sylvestris L.) from the southwestern to the central part of the species distribution range were investigated in a greenhouse experiment under dry conditions compared to a well-watered control. We conducted an isozyme study and recorded phenology as well as growth traits during the first year of growth. Genetic variability and genetic diversity increased from the westernmost provenances to those central to the distribution. Provenances from the Apennines and Spain revealed the strongest genetic differentiation compared to all others, whereas populations from Germany, Poland and Bulgaria were found to belong to the same gene pool. Seedling development and bud set were faster in northern populations. Shoot length was highest for Polish and German provenances within both regimes, populations from France and Spain had the longest roots. Reduced soil moisture slowed later development stages and delayed bud set for all provenances by about 5 days. Shoot growth decreased considerably under the dry regime for all provenances. German provenances were the most sensitive to drought, whereas Spanish provenances showed adaptation to drought conditions indicated by the lowest reduction in shoot growth relative to optimum conditions. The results of this pilot study show that under more pronounced drought conditions with repeated drought events, the so far established superiority of northeastern provenances compared to southwestern ones could diminish in the future.     

Effects of nickel and copper on growth and mycorrhiza of Scots pine seedlings inoculated with Gremmeniella abietina

Scots pine (Pinus sylvestris) seedlings were planted in soil originating from two localities with different background levels of nickel and copper. In addition, some of the seedlings were exposed to additional nickel (20.5 mg Ni/l of soil) or copper (63.5 mg Cu/l of soil), or a combination of both Ni and Cu, via soil without direct shoot exposure during their second growing period. The seedlings were either irrigated with spring water (pH 6) or got only natural rain during the whole field experiment. All seedlings were inoculated with conidia of a shoot‐pathogen Gremmeniella abietina during their third growing season, and harvested the following spring. Lengths of shoots of different year‐classes were used as growth estimates. In roots, the proportion of fungal (assumedly mycorrhizal) biomass was estimated by measuring ergosterol concentration. Guajacol peroxidase activity was measured. Short roots were classified into two groups according to their condition and the composition of the mycorrhizal community was expressed as a proportion of morphotypes in the roots. The seedlings exposed to additional Ni had higher shoot growth than the seedlings in the other treatments. The mean Ni concentration in the roots of seedlings exposed to additional Ni was 79 p.p.m. and in other seedlings 16 p.p.m. Additional Ni also decreased the frequency of clearly senescent short roots and the proportion of the mycorrhizal morphotype with the thinnest mantle. These results indicate that the Ni exposure levels used in this experiment had some positive effects on the seedlings. The relative fungal biomass was about 6% lower (p = 0.0981) in the fine roots of seedlings treated with additional Cu. The mean Cu concentration in the roots of seedlings exposed to additional Cu was 256 p.p.m. and in other seedlings 29 p.p.m. Peroxidase activity, which was used as a general stress indicator in this study, was not affected by any of the treatments. The shoot growth and the relative biomass of fungi in the fine roots were positively correlated in all seedlings, and this correlation was stronger in seedlings exposed to additional Ni that were not irrigated compared with seedlings not exposed to additional Ni that were irrigated. The frequency of asymptomatic infections of G. abietina was positively correlated with the proportion of senescent short roots in the irrigated seedlings but not in not‐irrigated seedlings. The general condition of seedlings may be an important factor for infection by G. abietina when moisture is high enough for the fungi to infect seedlings by conidia.