Fungal succession in sapwood of Norway spruce infested by the bark beetle Ips typographus

Fungal invasion of Norway spruce sapwood was investigated during a period of 130 weeks fol-lowing attack by the spruce bark beetle Ips typographus. Heavy beetle attack tended to overwhelm the trees quickly and no secondary resinosis was produced. Nonetheless, fungal penetration in the sapwood was initiated only slowly, although it accelerated during the fourth week after attack. Typically the leading edge of fungal penetration was a few millimeters in advance of the visible blue-stain during the sapwood colonization. Fungi invaded the sapwood in a successional pattern with the most pathogenic species Ophiostoma polonicum first, followed by other beetle-transmitted Ophiostoma and Graphium species. The later succession was probably influenced by sapwood moisture. Strong decaying white-rotters invaded near the base of the trees, where sapwood moisture remained favourable, while cf. Trichoderma viride dominated in the drier parts or the trees.     

Fungi associated with the spruce bark beetle Ips typographus in an endemic area in Norway

To investigate the fungal flora associated with the spruce bark beetle Ips typographus in an endemic area, beetles were collected during the flight period in six locations in Tr?ndelag, Norway. The beetles were inoculated into fresh Norway spruce logs, and the frequency of different species was monitored by fungal isolation from bark and wood. The most common species were Ophiostoma bicolor, O. penicillatum, O. polonicum and a previously undescribed Graphium species, the same species which were the most important associates of I. Typographus in an epidemic area in southeastern Norway. The frequency of the primary invader, O. polonicum, was, however, lower in Tr?ndelag, which may indicate that this species is less frequent in endemic areas than in epidemic areas.     

Interactions among Norway spruce,the bark beetle Ips typographus and its fungal symbionts in times of drought

Journal of Pest Science - Resilience and functionality of European Norway spruce forests are increasingly threatened by mass outbreaks of the bark beetle Ips typographus promoted by heat, wind...     

Types of bark beetle (Coleoptera: Scolytidae) infestation in spruce forest stands affected by air pollution, bark beetle outbreak and honey fungus (Armillaria mellea)

583 spruce stands in an area affected by air pollution and bark beetle outbreak in Eastern Slovakia were studied in 1996. According to bark beetle infestation of dominant and codominant trees, stands were classified into following types of spruce stand decline:Ips typographus-A,Ips typographus-B,Polygraphus poligraphus, I. typographus/P. poligraphus—A,I. typographus/P. poligraphus—B. The presence of attacked trees in forest edges, bark beetle spots and forest interior was the key important factor for the classification. Data from forest inventory and forest management evidence together with data on types of spruce stands decline were used in further analyses. Results shows that the distribution of forest stands classified into different types or uninfested stands is related mainly to host size and site quality. The percentage of spruce, exposition of stands and stand density showed significant effects. The mechanisms of spreading of studied bark beetle outbreak could be explained by direct effects of stress of trees caused by an abrupt increase of level of solar irradiation and by weakening of trees by the honey fungus.     

Persisting bark beetle outbreak indicates the unsustainability of secondary Norway spruce forests: case study from Central Europe

? Context

Secondary Norway spruce forests in the Western Beskids are among the most damaged forests in Europe. Although spruce bark beetle (Ips typographus) has been recently causing large-scale damage to these forests, our understanding of I. typographus dynamics in this environment is inadequate for evaluating forest sustainability.

? Aim

This study aims to evaluate the patterns of damage caused by I. typographus to spruce forests with compromised ecological stability.

? Methods

Forest infestation by I. typographus was inferred from sanitary felling data collected from 1998 to 2004. Stand and site data were obtained from forest management plans. Spatial-dependence analysis, ordinary kriging and neural network-based regression modelling were used to investigate the patterns of infestation and the casual relationships in the studied ecosystem.

? Results

I. typographus long-distance dispersal substantially decreased with outbreak culmination. The spread of infestation was only weakly related to stand and site parameters. Infestations spread isotropically at the stand and patch level but directionally at the regional scale.

? Conclusions

The large-scale spread of infestation can be explained by the uniform age and species composition of the investigated forests and by the ability of populations to overwhelm suboptimal trees. The observations presented here suggest that secondary spruce forests in Europe may be unsustainable due to unprecedented bark beetle outbreaks, which can be further amplified by changing climate.     

The nutrient status of Norway spruce in pure and in mixed-species stands

Atmospheric deposition of N and S appears to have caused nutrient imbalance in Norway spruce stands in southern Sweden. This calls for a change of forest management to procedures that promote nutrient balance. Studies have shown lower soil acidity in Norway spruce/deciduous mixed stands than in spruce monocultures, but the tree nutrient status in such mixtures has not been much investigated so far.

The nutrient status of Norway spruce foliage and top mineral soil chemistry in monocultures and in stands mixed with beech, birch, or oak was investigated through paired comparisons on 30 sites in southern Sweden (27 sites) and eastern Denmark (three sites). In total, 45 mixed stands and 34 pure stands were included in the study.

Spruce needles from mixed stands had higher concentrations and ratios to N of K, P, and Zn than needles from pure spruce stands. Among the mixed stands, the K status appeared to be positively correlated with the percentage of deciduous tree basal area. Soil samples from mixed stands had a higher Mg concentration, base saturation, and BC/Al ratio than soil samples from pure stands. The spruce needle nutrient status was comparable in pure stands on fertile sites and in mixed stands on poor sites. We did not detect any differences in spruce tree growth between pure and mixed stands.

This paper discusses possible reasons for a positive effect on the tree nutrient status in mixed-species stands and the possibility of using mixed-species stands as a forest management procedure to avoid nutrient imbalance.     

Population levels and flight phenology of bark beetle predators in stands with and without previous infestations of the bark beetle Tomicus piniperda

Relative population levels and flight periods of Tomicus piniperda (L.) (Col.: Scolytidae) and two of its main predators, Thanasimus formicarius (L.) (Col.: Cleridae) and Rhizophagus depressus (F.) (Col.: Monotomidae) were monitored in 1995 in eight Scots pine stands in central Sweden using flight barrier traps (five per stand) baited with α-pinene and ethanol. In four of the stands (A-stands) T. piniperda and associated species had reproduced the previous year in stumps and slash remaining after thinnings conducted in the winter of 1993/1994. In the remaining four stands (B-stands) no bark beetle breeding material had been available during the five preceding years. In addition, the flight periods of the species were monitored in one stand in 1996. In 1995 the catches of T. piniperda and R. depressus were four to five times higher in the A-stands than in the B-stands, whereas there was no difference in the catch of T. formicarius between the two kinds of stands. The T. formicarius/T. piniperda ratio was ca. 50 times higher in the B-stands compared with the A-stands during the period of clerid predation on colonising bark beetle adults and six times higher during the period of clerid oviposition. The R. depressus/T. piniperda ratio was only slightly higher in the A-strands than in the B-stands as a result of the spatial distribution of T. piniperda. Three additional species of bark beetle predators were caught: Glischrochilus quadripunctatus (L.), Pityophagus ferrugineus (F.) (Col.: Nitidulidae) and Rhizophagus ferrugineus (Payk.) (Col.: Monotomidae). Based on their seasonal abundance the bark beetle predators can be divided into three temporal groups: the first species to occur in the spring is G. quadripunctatus, the second group consists of R. depressus and T. formicarius, and the last species to initiate flight are R. ferrugineus and P. ferrugineus.     

Impact of bark wounds on sapwood in Norway spruce and silver fir

Bark wounds by damage during harvesting are a serious problem in forestry due to fungi infection and wood deterioration. This paper presents results of an investigation about the influence of the wounds on the internal structure of such injured stems. In an experiment, bark wounds were artificially created at the stem base of Norway spruce [Picea abies (L.) Karst.] and silver fir (Abies alba Mill.). 2 years later, the injured stems along with undamaged controls were cut and the trunk portion below breast height subjected to computer tomographic (CT) analysis. Analysis of the CT-images revealed a substantial impact of wounding on sapwood properties in spruce: directly adjacent to the wound surface in all examined trees, a large disturbance zone was detected affecting on average 17% of the potential sapwood area. With increasing distance from the wound, the size of this disturbance zone diminished, but was still detectable in all trees at breast height ca. 1 m above the bark wound.     

Growth responses to climate in a multi-species tree-ring network in the Western Carpathian Tatra Mountains, Poland and Slovakia

We analyzed growth responses to climate of 24 tree-ring width and four maximum latewood density chronologies from the greater Tatra region in Poland and Slovakia. This network comprises 1183 ring-width and 153 density measurement series from four conifer species (Picea abies (L.) Karst., Larix decidua Mill., Abies alba (L.) Karst., and Pinus mugo (L.)) between 800 and 1550 m a.s.l. Individual spline detrending was used to retain annual to multi-decadal scale climate information in the data. Twentieth century temperature and precipitation data from 16 grid-boxes covering the 48-50 degrees N and 19-21 degrees E region were used for comparison. The network was analyzed to assess growth responses to climate as a function of species, elevation, parameter, frequency and site ecology. Twenty ring-width chronologies significantly correlated (P<0.05) with June-July temperatures, whereas the latewood density chronologies were correlated with the April-September temperatures. Climatic effects of the previous-year summer generally did not significantly influence ring formation, whereas site elevation and frequency of growth variations (i.e., inter-annual and decadal) were significant variables in explaining growth response to climate. Response to precipitation increased with decreasing elevation. Correlations between summer temperatures and annual growth rates were lower for Larix decidua than for Picea abies. Principal component analysis identified five dominant eigenvectors that express somewhat contrasting climatic signals. The first principal component contained highest loadings from 11 Picea abies ring-width chronologies and one Pinus mugo ring-width chronology and explained 42% of the network's variance. The mean of these 12 high-elevation chronologies was significantly correlated at 0.62 with June-July temperatures, whereas the mean of three latewood density chronologies, which loaded most strongly on the fourth principal component, significantly correlated at 0.69 with April-September temperatures (P<0.001 over the 1901-2002 period in both cases). These groupings allow for a robust estimation of June-July (1661-2004) and April-September (1709-2004) temperatures, respectively. Comparison with reconstructions from the Alps and Central Europe supports the general rule of the dominant influence of growing season temperature on high-elevation forest growth.     

Occurrence of Heterobasidion basidiocarps on cull pieces of Norway spruce left on cutting areas and in mature spruce stands

Fruiting of Heterobasidion on cull pieces and stumps of Norway spruce was investigated in cutting areas and mature spruce stands located in southern Finland. Cull pieces of variable size and showing butt rot were left on three clear‐cut areas and in one thinned stand. Additionally, a part of the cull pieces was transported to mature forest sites with closed canopy. During the succeeding 3–4 years the cull pieces were investigated annually for sporocarps of Heterobasidion, and the area of actively sporulating pore layer of each sporocarp was measured. Root bases of spruce stumps in the logging areas were excavated and sporocarps found on the stumps also measured. At the onset of the experiment, Heterobasidion spp. were isolated from 76% of the cull pieces showing butt rot; 85% of the isolates were identified as H. parviporum and 15% as H. annosum s.s. During the following 3–4 years sporocarps were found on 20% of the 1938 cull pieces where Heterobasidion butt rot was initially detected visually. Sporocarp formation was promoted by advancement of butt rot, increasing cull piece diameter and end‐to‐end ground contact, but restricted by the colonization of the cull piece by Stereum sanguinolentum. Between‐site differences were significant but could not be explained by differences in tree cover. At the end of the investigation period the average sporulating area of Heterobasidion sporocarp per metre of cull piece was higher than the average sporulating area per stump at three of four logging sites. Hence, leaving cull pieces containing Heterobasidion butt rot at logging areas in southern Finland can considerably increase local production of Heterobasidion spores.     

A comparison of litterfall and element fluxes in even aged Norway spruce,sitka spruce and beech stands in Denmark

Litterfall was investigated in three even-aged Norway spruce (Picea abies), sitka spruce (Picea sitchensis) and beech (Fagus sylvatica) stands on a nutrient poor-soil in Southern Denmark. Dry weights and N, P, K, S, Mg, Ca, Na, Al, and Fe concentrations and fluxes were examined in litterfall fractions. Foliage litter amounted to 90% of total litterfall. The tree stands showed a similar mean annual litterfall. In the spruce stands, annual litterfall was correlated negatively with the current year increment and positively with the previous year increment. Annual litterfall in beech was constant during the 6 study years whereas Norway spruce and sitka spruce showed large fluctuations between years caused by drought, spruce aphid infestations and probably sea salt stress. Norway spruce responded with a long lasting elevated needle loss. Sitka spruce responded to infestations with premature needle loss during short periods. The presence of a large syrphid (Coccinellidae) population was important in regulating aphid (Elatobium abietinum) population density. The between-year variation in element concentrations of litterfall was small whereas variations during the year were large. Interspecific levels were recognized: Norway spruce>beech>sitka spruce. High concentrations in Norway spruce were ascribed to a combination of drought, sea salt stress and elevated transpiration. In sitka spruce, aphid infestations reduced the litterfall N content. Sitka spruce showed the smallest amount of base cation fluxes with litterfall. In contrast, spruce and beech exhibited even litterfall element fluxes. Litterfall studies revealed reduced vitality in the non-native spruce stands and underlined the perception of a healthy stand of native beech.     

Relationship between seedbed properties and the emergence of spruce germinants in recently cut Norway spruce selection stands in Southern Finland

The purpose of this study was to examine the effects of type and amount of ground vegetation and substrate on the germination and early survival of Norway spruce (Picea abies (L.) Karst) seedlings in uneven-aged stands on mineral soils in Southern Finland. The study was conducted on two permanent plots representing average site quality for spruce stands in the area. A gradient in selection cut intensity and residual stand density was imposed across each of the two permanent plots. Regeneration and vegetation surveys were repeated annually on a grid of unmanipulated microplots and on a set of soil treatment microplots. The results indicated that the number of spruce germinants per unit area was positively correlated with herb cover but negatively correlated with total plant cover. Germinant density was also related to vegetation-free seedbed conditions, high overstory competition index and presence of larger spruce seedlings. Regeneration microsites dominated by moss or with plants with a relatively high light demand were associated with low germinant numbers. Bare humus layer and decayed stumps seemed to promote germinant emergence. Exposure of mineral soil resulted in germination rates that were 4.3–6.9 times higher than in undisturbed conditions during the first growing season.     

Resin pocket occurrence in Norway spruce depending on tree and climate variables

Resin or pitch pockets cause a significant reduction in timber quality of Norway spruce (Picea abies (L.) Karst). Their occurrence is very variable within the stem and between trees and stands. Researchers have suggested several causes of resin pocket formation with a majority arguing in favour of storms as the main causing factor.     

Vertical distribution of the ectomycorrhizal community in the top soil of Norway spruce stands

The vertical distribution of the ectomycorrhizal (ECM) community was studied in four old high-mountain Norway spruce (Picea abies [L.] Karst.) stands in northern Italy. The aim was to verify if the variability in the community structure could be explained by characteristics of the organic and mineral soil horizons. The community structure was evaluated in terms of both fungal species and their ability to explore soil (exploration types). From the 128 humus profiles sampled over the two study periods, 31 ECM species were recorded. The study demonstrated that the number of both non-vital tips and vital non-mycorrhized tips decreases with soil depth, from organic to mineral horizons, while the number of ectomycorrhizal tips mainly increases with soil depth. A preference was found of some ECM species and exploration types for specific organic or mineral soil layers and their features, especially moisture and available nitrogen. These results can help in understanding how the functional role of the single consortia and the ecological features determining this “adaptive diversity” in ectomycorrhizal communities could be of major importance to assess the resilience in forest soil ecosystems.     

Facultative and obligate diapause phenotypes in populations of the European spruce bark beetle Ips typographus

The bark beetle Ips typographus is the most destructive insect pest in Norway spruce-dominated forests. Its potential to establish multiple generations per year (multivoltinism) is one major trait that makes this beetle a severe pest. Ips typographus enters diapause to adjust its life cycle to seasonally changing environments. Diapause is characterized by developmental and reproductive arrest; it prolongs generation time and thus affects voltinism. In I. typographus a facultative, photoperiod-regulated diapause in the adult stage has been described. In addition, the presence of an obligate, photoperiod-independent, diapause has been hypothesized. The diapause phenotype has important implications for I. typographus voltinism, as populations with obligate diapausing individuals would be univoltine. To test for the presence of different I. typographus diapause phenotypes, we exposed Central and Northern European individuals to a set of photoperiodic treatments. We used two ovarian traits (egg number and vitellarium size) that are associated with gonad development, to infer reproductive arrest and thus diapause. We found a distinct effect of photoperiod on ovarian development, with variable responses in Central and Northern European beetles. We observed obligate diapausing (independent of photoperiod) individuals in Northern Europe, and both facultative (photoperiod-regulated) as well as obligate diapausing individuals in Central Europe. Our results show within-species variation for diapause induction, an adaptation to match life cycles with seasonally fluctuating environmental conditions. As the diapause phenotype affects the potential number of generations per season, our data are the basis for assessing the risk of outbreaks of this destructive bark beetle.

     

Permanence of resilience and protection efficiency in mountain Norway spruce forest stands: A simulation study

An objective of mountain forest management is to increase the ability of forest stands to protect human activities against natural hazards such as rock-falls and snow avalanches in a sustainable way. The challenge is to find a compromise between efficient instantaneous protection, favoured by dense stands, and continuous renewal, minimizing time periods of low protection efficiency. We used a Norway spruce stand dynamics model to compare the respective advantages of individual tree and gap selection silviculture in this context. We simulated stand dynamics over 800 years with either individual tree or gap thinning every 20 years with several thinning intensities. At each time step, we evaluated stand resilience, protection efficiency against rock-falls, protection efficiency against avalanches, and structural complexity with four indicators based on stand structure. Every scenario produced short time periods with low stand resilience and protection efficiency. Such periods can be tolerated if they are sufficiently rare compared to the local disturbance regime. We characterized the permanence of resilience and protection of a forest stand as its ability to remain within boundary values of the different indicators, without going out of them during continuous time periods longer than fixed maximum durations. Permanence of resilience and permanence of protection decreased with thinning intensity. Efficient protection against rock-falls was obtained with gap thinning of intermediate intensity while protection against avalanches was obtained only for very low thinning intensities. For our ecological context, the best compromise between resilience and protection was obtained with three 10 m radius gaps per hectare every 20 years (9.5% of the area of a stand). This strategy led to uneven-aged stand structures with a high diversity of diameters classes. Our results suggest that small gap silviculture may be a good way to combine forest renewal and protection efficiency in mountain regions.