Stockings for protection of containerized conifer seedlings against pine weevil (Hylobius abietis L.) damage

The effectiveness of a stocking, constructed of nylon and cotton netting, in protecting containerized conifer seedlings against pine weevil attack was evaluated in field tests on 37 clear‐cut reforestation areas in southern and central Sweden. The stockings significantly reduced pine weevil feeding on treated seedlings as well as seedling mortality. The protective effect of the stockings was similar to that of an insecticide (permethrin) treatment. In most experiments the survival of stocking‐enclosed seedlings was satisfactory from a practical point of view, whereas untreated control seedlings suffered heavy mortality.     

Damage by pine weevil Hylobius abietis to conifer seedlings after shelterwood removal

Abstract

Pine weevil (Hylobius abietis L.) damage to seedlings after overstorey removal was investigated in a survey study in six shelterwoods in the south–central part of Sweden. The shelterwoods predominantly consisted of Scots pine, except at one site where the shelter trees mainly consisted of Norway spruce. Before final cutting, 10 plots were laid out at each site and measurements of shelter trees and marked seedlings were taken. The seedlings were examined during the 2 years after final cutting. The study showed that removal of shelter trees increases the risk of severe damage by pine weevil and the variable that was most strongly correlated with the risk was the seedling root collar diameter. Both Scots pine and Norway spruce seedlings were severely damaged by pine weevil, and most of the feeding occurred during the first year after cutting. The amount of debarked area was significantly larger for Scots pine than for Norway spruce seedlings. Vitality (growth of the leading shoot before final cutting) of the seedlings also affected the probability of damage. Seedlings with high vitality were less damaged by pine weevil than seedlings with low vitality. For Scots pine the shelterwood density before final cutting was correlated to the intensity of pine weevil feeding after cutting. In conclusion, after the final cutting of a pine or spruce shelterwood, pine weevils will probably invade the area. To avoid serious damage, Norway spruce and Scots pine seedlings should have reached a diameter of at least 10–12 mm.     

Feeding barriers to reduce damage by pine weevil (Hylobius abietis)

The effectiveness of feeding barriers to protect seedlings against damage caused by pine weevil (Hylobius abietis) was evaluated in experiments established from 1995 to 1999 in southern Sweden. For this purpose the damage done to containerized seedlings protected by various types of barrier was evaluated, and compared with damage to untreated and insecticide (permethrin)-treated seedlings. Three types of feeding barrier that gave significant protection during the first 3 yrs were recognized: coating on the stem bark, shields with a collar at the top, and shields without a collar. The mean accumulated mortality caused by pine weevil for coatings (47%) and shields without a collar (59%) was significantly higher than the corresponding figure for permethrin treatment (13%), whereas shields with a collar (26%) did not differ significantly from the permethrin treatment in this respect. The highest mortality was found for untreated controls (87%).     

Effects of planting time on pine weevil (Hylobius abietis) damage to Norway spruce seedlings

Feeding by pine weevil (Hylobius abietis L.) causes severe damage to newly planted conifer seedlings in most parts of Scandinavia. We investigated the effect of planting time and insecticide treatment on pine weevil damage and seedling growth. The main objective was to study if planting in early autumn on fresh clear-cuts would promote seedling establishment and reduce the amount of damage caused by pine weevil the following season. The experiment was conducted in southern Sweden and in south-eastern Norway with an identical experimental design at three sites in each country. On each site, Norway spruce seedlings with or without insecticide treatment were planted at four different planting times: August, September, November and May the following year. In Sweden, the proportion of untreated seedlings that were killed by pine weevils was reduced when seedlings were planted at the earliest time (August/September) compared to late planting in November, or May the following year. This pattern was not found in Norway. The average length of leading shoot, diameter growth and biomass were clearly benefited by planting in August in both countries. Insecticide treatment decreased the number of seedlings killed or severely damaged in both Norway and Sweden.     

Within- and between-stand distribution of attacks by pine weevil [Hylobius abietis (L.)]

The pine weevil (Hylobius abietis L.) is considered one of the most damaging pests in reforestation areas in Scandinavia. The purpose of this study was to ascertain the within- and between-stand distribution of pine weevil attacks. Between-stand distribution was examined by assessing the frequency of attacks in all newly planted coniferous stands in relation to stands clear-cut at two state forest districts in North Zealand, Denmark. Within-stand distribution was examined by investigating the position and damage to individual seedlings in relation to the position of breeding material. The stand-level attack frequency did not seem to be higher for stands in areas with more clear-cuts. The within-stand distribution of attacks was not influenced by the position of breeding material.     

Temporal patterns of seedling mortality by pine weevils (Hylobius abietis) after prescribed burning in northern Sweden

Damage by the large pine weevil, Hylobius abietis (L.), is a major threat to conifer plantations throughout Eurasia, but damage is usually less severe in northern areas. However, pine weevil damage seems to increase if the sites are burnt. The aim of this study was to determine the effects of variations in the time of planting (with respect to the total age of the clear-cut and the time since burning) on pine weevil damage to seedlings on burnt sites in northern Sweden. The study also explored whether there is an optimal time for planting at which damage levels are reduced to acceptable levels. Ten sites were selected in an inland area of northern Sweden where pine weevils are normally scarce. The sites were dry–mesic and represented a range of times since clear-cutting and since burning. The sites were planted in June 1998, 1999 and 2000 with 1-year-old container-grown seedlings of Norway spruce [Picea abies (L.) Karst.]. Pine weevil damage was reduced if planting was done no earlier than 3 years after clear-cutting and no earlier than 2 years after burning. Planting too soon after burning, irrespective of the age of the clear-cut, resulted in unacceptably high damage levels.     

Prediction of pine mistletoe infection using remote sensing imaging: A comparison of the artificial neural network model and logistic regression model

In this study, the prediction of pine mistletoe distribution in Scots pine ecosystems was explored using remote sensing variables to compare the multilayer perceptron (MLP) artificial neural network (ANN) and logistic regression (LR) model performances. For this purpose, 109 sample plots were distinguished in pure Scots pine forests (natural) in the Eastern Black Sea Region of Turkey. Distinguishing mistletoe-infected stands (69) and uninfected stands (40) was performed with field observations. The variables acquired from Landsat 8 (Level 1) images were used as independent variables for independent-sample t-test, MLP ANN and LR models. Remote sensing variables indicated that mistletoe-infected stands were in drier areas with a lower vegetation-leaf area index. Based on the performance results of both models, the sensitivity (SEN), specificity (SPE), positive predictive value (PPV), negative predictive value (NPV) and accuracy of the MLP ANN model were superior to those of the LR model. The prediction percentages (SEN, SPE, PPV and NPV) of mistletoe-infected stands were better than the prediction percentages of uninfected stands. The prediction accuracies of LR and MLP ANN models were 74.3% and 89.6%, respectively. However, all remote sensing variables were included in the prediction equation of the MLP ANN model, while the thermal infrared 1 (TIRS1) variable was included in the LR model. In the MLP ANN model, the TIRS1 variable also had the highest normalized importance (100%). The area under the curve (AUC) value for identifying the mistletoe-infected stands of Scots pine forests used by the MLP ANN model (0.892 ± 0.034) was higher than in the LR model (0.838 ± 0.039), explaining the more accurate predictions obtained from the MLP ANN model. The MLP ANN model showed much better performance than the LR model. The results of this study are expected to make important contributions to the identification of potential mistletoe-infected areas.     

Effect of site preparation intensity on the early growth of loblolly pine (Pinus taeda L.) and the incidence of pine tip moth (Rhyacionia spp.)

Twelve, 16-ha study sites were established in recently harvested (1980) stands of natural pine-mixed hardwoods located in the Piedmonts of South Carolina and Georgia. Treatments applied were check (no site preparation), herbicide-burn (3.4 kg ae Glyphosate/ha), chop-burn, shear-disc, shear-V blade-disc, shear-pile, and shear-pile-disc. Measurements collected after two growing seasons included pine height, diameter, and occurrence of pine tip moth (Rhyacionia spp.) infestation on the terminal shoot. After the second growing season, tree volume was 58% greater on mechanically-treated areas compared to the check and herbicide-burn areas. Average pine tip moth incidence was 15% for the check treatment and ranged from 24 to 36% for the other six treatments. Although the disced treatments had higher tip moth infestation (32 to 36%) compared to the check plots (15%), pine growth was significantly greater for treatments involving discing.     

MonitoringHylobius abietis (L.) (Col., curculionidae) by baited pitfall traps in relation to planting and treatment of seedlings in a re-forested area

The method of standardized baited pitfall, traps for monitoring population ofHylobius abietis (L.) was experimentally included into the routine planting and control schedule (model area) in the Czech Republic. It is recommended to determine characteristics of the area on the basis of long-term monitoring. A short-term prognosis per site must be drawn from monitoring done from the earliest beginning of the season. However, it seems advisable to treat all the individual seedlings immediately after theyhave been planted in the area where the over-all characteristics (ascertained by monitoring) indicate generally high population levels. To base a decision for treatment on the percentage of seedlings attacked (feeding scars) per site is considered unadvisable in comparison with data obtained bymonitoring using baited pitfall traps. Insecticides for the treatment of newly planted seedlings need to be applied to two-thirds of the trunk of a seedling (including the root collar), their action should be fast enough to paralyse (kill) the weevils before they reach xylem by feeding and, furthermore, the residues should be effective up to the end of the season.With one figure and 3 tables     

Scots pine (Pinus sylvestris L.) plantations contribute to the regeneration of holly (Ilex aquifolium L.) in mediterranean central Spain

The aim of this study is to evaluate the recruitment possibilities of holly (Ilex aquifolium L.) populations under Pinus sylvestris plantations in the mountains of Central Spain. Population recruitment of holly under P. sylvestris L. plantations was studied at two localities. We sampled holly seed rain, seed bank, and seedling emergence and survival (of both emerged and planted seedlings) in both localities. Seed germination was analysed by randomly sowing Ilex seeds and their subsequent recollection and analysis over the following 3 years (only in one locality). Seed rain, seed bank and emerged seedling densities did not differ between localities. Seed bank density was between 10 and 20 seeds m⁻², considerably higher than the observed seed rain (0.4–1.2 seeds m⁻²), and also higher than the emerged seedling density (0–4 seedlings m⁻²). But Ilex is not very efficient in germinating under pine forests (29.1% germination after 3 years). This may indicate a seed accumulation process of at least 5 years. Seedling survival for the first year differed among the studied sites (50–60 vs. 17%). Nevertheless these survival rates are higher than those found for the same seedling populations in different forest habitats (not Scots pine forests) from near locations. Differences in summer water stress between the study sites are proposed as the main cause of the observed differences in seedling survival. It is concluded that P. sylvestris forests may provide one of the best regeneration habitats for holly in the Mediterranean area, where this species is close to the Southern limit of its distribution.     

Modelling mortality of Scots pine (Pinus sylvestris L.) plantations in the northwest of Spain

Mortality is an important element of growth and yield models, especially if only low intensity silvicultural treatments are carried out. The objective of the present study was to develop a model for predicting tree number decline in planted even-aged stands of Scots pine (Pinus sylvestris L.) in Galicia (northwestern Spain). The model was constructed using data from two inventories of a trial network involving 68 permanent plots located in unthinned stands, or stands thinned lightly from below. Two alternatives were tested. In one alternative, a two-step modelling strategy was applied. First, a binary response function predicting the survival probability of all the trees in the stand was constructed, and an equation for reduction in tree number was developed, using only data where death had occurred over the period analyzed. Three different approaches were then used to compare the application of the above-mentioned functions together. In the other alternative, a mortality function for directly predicting the reduction in tree number was fitted, including all plots (with and without occurrence of mortality). Both alternatives provided similar results, showed logical behavior, and performed satisfactorily in evaluation tests. However, in choosing the best strategy for inclusion in a stand-level simulator, the use of the second alternative is recommended because it possesses the path invariance property required in a mortality model.     

Control of heather (Calluna vulgaris (L.) Hull) by steam treatment: Effects on establishment and early growth of Scots pine

Following boreal forest ecosystem disturbance,such as fire and clear-cutting, the ericaceousspecies Calluna vulgaris often becomescompletely dominant and may convert forestlandinto heathland. Calluna is known toeffectively exclude other vegetation and causes``growth check' or stagnation of coniferseedlings to result in poor tree regeneration.In this study we investigated the use of steamtreatment as an alternative method forvegetation control of Calluna vulgaris.Scots pine (Pinus sylvestris L.)establishment and growth were recorded in botha planting and a seeding experiment. Steamtreatment was compared with mechanical soilscarification and intact vegetation in theplanting experiment and with intact vegetationin the seeding experiment. The results showthat the vegetation is still strongly reducedfive years after the treatment. The steamtreatment strongly favoured the establishmentand growth of both seeded and planted Scotspine. The planted seedlings grown in the steamtreated plots had a dry weight more than twiceas high when compared to scarified plots.Seedling height and basal diameter were alsohighest for seedlings grown in steamed plots.Seedlings planted in scarified plots did notgrow as well during the first years possiblydue to injuries caused by frost heaving. Theseeding experiment showed an increasedestablishment and growth of Scots pineseedlings in steam treated plots compared to inintact vegetation.     

Predicting probability of A-quality lumber of Scots pine (Pinus sylvestris L.) prior to or concurrently with logging operation

Knot properties have a profound influence on the suitability of wood for many wood products leading to significant value differences between different quality grades. It would therefore be rather advantageous to maximise the volume of good quality timber attained from the logs. The objective of this study was to assess how well A-quality lumber of Scots pine derived from log tomography features can be predicted with characteristics measured prior to or concurrently with the logging operation. The study is based on field experiments and X-ray scanning of 204 stems from southern Finland in 2014. We employed mixed logistic regression techniques to model the relationship between the main stem characteristics and probability of A-quality lumber. From the tree characteristics that can be measured or detected from standing trees, the height from the ground level to the lowest dead branch was found to be the best predictor of A-quality lumber. From the characteristics that could, at least in theory, be detected and measured at the moment of harvest, early growth rate and size of tree were found to be the best combination for predicting the probability of A-class quality.     

Photosynthetic acclimation of shade-grown red pine (Pinus resinosa Ait.) seedlings to a high light environment

Photosynthetic light acclimation in red pine (Pinus resinosa Ait.) seedlings was examined in a greenhouse study to better understand the physiological response of this species to increased light intensity following release from competition. Seedlings grown in a high (HL), medium (ML) or low (LL) light environment for 12 weeks were transferred to high light. Gas exchange and chlorophyll fluorescence of ML and LL seedlings were measured prior to and following transfer and compared with the HL control treatment. Photosynthetic characteristics were related to initial light treatment and time after transfer. Acclimation of gas exchange features to high light in shade formed ML and LL foliage was relatively rapid, with similar values among light treatments within 57 days of transfer. Acclimation of net photosynthetic rate was similar in ML and LL seedlings, and was associated primarily with increased mesophyll conductance to CO₂. The ratio of variable to maximal chlorophyll fluorescence (F_v/F_m) decreased initially after transfer, especially in LL seedlings, but recovered to normal values after 57 days. Red pine seedlings appear to be well adapted for photosynthetic acclimation to high light intensity, consistent with that reported for other early successional tree species.     

Herbivory by the pine weevil (Hylobius abietis L.) and short-snouted weevils (Strophosoma melanogrammum Forst. and Otiorhynchus scaber L.) during the conversion of a wind-thrown Norway spruce forest into a mixed-species plantation

The influence of above-ground insect herbivory and other agents of damage to seedlings was studied in a field experiment. Nine different tree species were planted in each of five randomised blocks. The species were: Alnus glutinosa (L.) Gaertner, Betula pendula Roth., Fagus sylvatica L., Fraxinus excelsior L., Larix eurolepis Henry, Picea abies (L.) Karst., Prunus avium L., Quercus robur L. and Tilia cordata Mill. The seedlings were monitored through the 2000–2002 growing seasons. Pine weevils (Hylobius abietis L.) fed significantly more on Norway spruce seedlings than on all other tree species. The following rough preference order was obtained: Norway sprucelarch>birch, beech, oak>cherry>alder, ash, lime. Thus, during the conversion of single-species coniferous plantations to mixed-species broadleaved stands, the use of costly insecticides against pine weevil is not required. Short-snouted weevils (e.g. Strophosoma melanogrammum Forst. and Otiorhynchus scaber L.) and other insects caused leaf and needle area loss primarily during the first growing season.     

Influence of a high Mn supply on Norway spruce (Picea abies (L.) Karst.) seedlings in relation to the nitrogen source

Effects of 3, 25, 100, 200 and 800 microM Mn on biomass and pigment, starch and nitrate concentrations were studied in Norway spruce (Picea abies (L.) Karst.) seedlings grown with either NO(3) (-) or NH(4) (+) as the sole nitrogen source. After 77 days of exposure to 800 microM Mn, shoot growth had ceased in about 50% of the seedlings independently of the N source. Despite high Mn concentrations in roots and shoots of the Mn-treated seedlings, no visible symptoms of Mn toxicity were evident. The rate of root elongation was decreased by treatment with >/= 200 microM Mn when N was supplied as NO(3) (-), but not when it was supplied as NH(4) (+). This difference could be attributed to the higher Mn concentrations in root tips of the NO(3) (-)-grown seedlings compared with the NH(4) (+)-grown seedlings. In Mn-treated seedlings, the concentration of Mg, and to a lesser extent that of Ca, decreased. Depletion of these elements might account for the observed growth depression. Potassium concentrations were similar in the control and Mn-treated seedlings. Treatment of seedlings with 800 microM Mn for 50 days led to several physiological changes: starch accumulated, the concentrations of nitrate and phenolic compounds increased, pigment concentrations decreased, and in vivo nitrate reductase activity in roots was reduced.     

Annual variation in predation and dispersal of Arolla pine (Pinus cembra L.) seeds by Eurasian red squirrels and other seed-eaters

Seed predation and dispersal are key processes in the survival and distribution of plant species. Many animals cache seeds for later consumption, and, failing to recover some of these seeds, act as seed dispersers, influencing post-dispersal seed and seedling survival. Both animal and plant benefit from scatterhoarding and natural selection of seed characteristics and adaptations of seed predators (and dispersers) is one of the most important examples of co-evolution and mutualism. We studied the producer–consumer Arolla pine (Pinus cembra)–red squirrel (Sciurus vulgaris) system in a subalpine forest in the Italian Alps. Arolla pine produced large seed-crops (masting) at irregular intervals, followed by years with poor or moderate seed production. Squirrel density fluctuated in synchrony with the food resource, eliminating the time-lag normally present when resources are produced in pulses. In all years except 2009 (a mast-crop year), all Arolla pine cones were harvested (their seeds consumed and/or cached) by September to late October by different species. Both squirrels and nutcrackers (Nucifraga caryocatactes) fed on seeds, and their relative pre-dispersal predation rates (on cones in the canopy) differed between years. Overall, nutcrackers consumed more seeds between July and October than squirrels, but in 1 year squirrels took the largest number of seeds. Pre-dispersal seed predation by squirrels tended to be lower in years with large seed-crop size and there was a positive correlation, over the entire study period, between density of recovered hoards and Arolla pine seed density of the previous year. We conclude that (i) squirrels and nutcrackers are important pre-dispersal seed predators and seeds dispersers; (ii) squirrels are also post-dispersal seed predators, and (iii) the proportion of cached seeds consumed by squirrels increased with the size of the Arolla pine seed-crop, suggesting that red squirrel is a conditional mutualistic scatterhoarder of Arolla pine seeds.     

Frost damage on the terminal shoot as a risk factor of fork incidence on common beech (Fagus sylvatica L.)

Forking is a frequent flaw in beech which can adversely affect the formation of high quality logs. Even though the hypothesis that late frosts increase forking is widely accepted by forest managers, it remains to be proved and quantified experimentally. Damage caused by a late frost on 15 May 1995 to young beech trees in an experimental site at Lyons-La-Forêt (France) and the consequences on the development of forking were analysed. The beech trees were 17 years old with heights between 1.5 and 9 m. Of all the plantation densities tested only the lowest density (625/ha) showed various and severe frost damage. Three levels of immediate damage to the growing terminal shoot were observed, with increasing intensity from: (1) no trace of frost damage, (2) reddened leaves and (3) frost-nipped shoots. The intensity of visible damage to the terminal shoot appeared to be very dependent on the height of the plant which justified our original experimental approach, based on an evaluation of the damage for each individual. Almost all of the beech trees less than 4 m high suffered frost damage and all those taller than 7 m were unaffected. Three-year-old forks due to frost which occured in May 1995 were recorded at the end of 1997 using an objective definition based on dendrometric and age criteria. The worst frost damage resulted in a significant increase in the risk of fork emergence (71.7% of the plants were forked). With a risk related to forking in the presence of frost-nipped shoots equal to 2.15 and a fraction of the attributed risk of 0.36 it was concluded that the late frost observed played a significant role in the degradation of the shape of the beech affected by frost and the overall quality of the stand.     

Modelling the distribution of wood properties along the stems of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) as affected by silvicultural management

In this work, empirical ring-based models were developed to predict the distribution of early wood percentage, wood density and fibre length along the stems of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) as affected by silvicultural management. The performance of the ring-based models was also compared for Scots pine and Norway spruce with corresponding disc-based (cross-sectional) models. Moreover, both models were integrated with example simulations by a process-based growth and yield model to analyze how management, such as thinning, affects the growth and wood properties of Scots pine trees over a rotation as an average for the tree stem, but also along the stem.The ring-based models built for annual early wood percentage (explained by ring width), air dry wood density (explained by early wood percentage and cambial age) and fibre length (explained by radial growth percentage and cambial age) predicted reasonably well the wood properties both at an intra-ring level, but also at a cross-sectional level. These predictions were also reasonably well in line with corresponding cross-sectional predictions by the disc-based models (which predicted the properties based on the number of annual rings and diameter at breast height and/or the cross-section being considered and temperature sum). The example simulations also demonstrated that both models predicted slightly lower wood density for dominant trees compared to dominated ones grown in thinned and unthinned Scots pine stands over a rotation. Unlike the disc-based model, the ring-based model predicted, on average, higher early wood percentage in dominant trees than in dominated ones. However, fibre length was not significantly affected when the averages of the whole stems were predicted, and this held true for both ring- and disc-based models.In summary, the incorporation of empirical ring-based wood property models into a process-based growth and yield model, offers a means to study in detail how environmental conditions, forest structure and management affect the quantity and properties of stem wood produced over a rotation. The disc-based wood property models used in this work are based on data with large geographical and genetic variation, and therefore may turn out to be more applicable for predicting future wood and fibre resources at a regional and national level. This kind of integrated use of wood property models with a process-based growth and yield model could help us to evaluate the forest resources under current and changing climate.