Survival of Heterobasidion irregulare on red pine discs in cold temperatures

Disease foci of the conifer root and butt decay pathogen Heterobasidion irregulare are typically initiated following germination of spores deposited on freshly cut stumps, followed by expansion by tree to tree spread through root contacts and grafts. Although most abundant in autumn, inoculum of H. irregulare is also available during some cold winter periods in northern portions of the eastern United States. In both laboratory and field experiments, fresh stem discs of red pine (Pinus resinosa) were inoculated with H. irregulare conidia to test the null hypothesis that the pathogen would not survive prolonged exposure to cold temperatures experienced during winters in those regions. After exposure to cold for various periods of time, discs were incubated and then observed for presence of the Spiniger state of the pathogen. In each of two laboratory trials, the fungus survived on red pine discs incubated at ≤?20°C for 90 days. The field experiment was conducted during each of two winters at two infested red pine plantations. Inoculated discs were deployed periodically beginning in early winter and retrieved after various periods of time until spring. The Spiniger state of the pathogen was frequently observed on discs after laboratory incubation, even after field exposure of up to 6 months, during which temperatures ≤?25°C were sometimes recorded. Whether viable due to growth from inoculum initially placed on the discs, or natural inoculum deposited on discs exposed in the infested plantations, winter temperatures did not eliminate survival of the pathogen on this natural substrate. The potential for survival on stump surfaces during sub‐freezing temperatures during which application of stump protectants in water is impractical should be considered in evaluating the potential risk from H. irregulare to economically and environmentally valuable conifer forests of northcentral and northeastern North America.     

Changes to relative stand composition after almost 50 years of Heterobasidion root disease in California true fir and pine forests

The Agaricomycete Heterobasidion annosum sensu lato (s.l.), a species complex of fungal pathogens, causes root and butt rot on conifers throughout the northern hemisphere, thereby shaping structure, composition, and evolution of vast and diverse forest ecosystems. We analyze forest change 48–49 years following Heterobasidion root disease emergence in 63 permanent plots first established in 1970–1972 and measured at least once every decade through 2020. We use this dataset to infer the long-term consequences of Heterobasidion root disease in a set of common forest types that reflect some of the most important hosts for this set of diseases in western North America. We contrasted three host–pathogen systems located within the Sierra Nevada, southern Cascades Mountain Range and the Modoc Plateau: (1) H. irregulare in host communities dominated by several Pinus (pine) species and Calocedrus decurrens (incense cedar) in Yosemite Valley, on the Sierra Nevada Range western slope; (2) H. irregulare in a largely single species (Pinus jeffreyi) host disease system on the eastern slopes of the Sierra Nevada and southern Cascades as well as the Modoc Plateau; and (3) H. occidentale—also on the western slope of the Sierra Nevada—in stands with a mixture of susceptible Abies (true fir) and a diversity of non-hosts for this Heterobasidion species. Approximately 50 years after disease emergence, relative basal area and stem density were significantly reduced within disease centres in all three pathosystems, but changes to forest composition and relative species dominance were determined by pre-disease host and non-host diversity. In the western-slope H. occidentale system, the disease increased the dominance of non-susceptible species, Pinus species and C. decurrens. In the multi-genus Yosemite pathosystem, H. irregulare did not significantly shift species dominance, and as expected, species shifts did not occur in the largely single-genus eastern-slope forests. In these widespread California forest ecosystems, two factors appeared to determine forest conditions almost 50 years after Heterobasidion root disease monitoring: the size of the disease centre and the initial diversity of non-hosts. Along with pathogen species, these factors appear to affect the local severity of disease as well as the degree of species shifts relative to initial plot compositions, reaffirming host susceptibility classifications associated with these forest types.     

Species differences in total and vertical distribution of branch- and tree-level leaf area for the five primary conifer species in Maine, USA

Vertical distribution of leaf area largely governs both tree structure and function. Models of this important tree attribute have been constructed for several commercially important conifers. However, a limited number of studies have compared alternative modeling techniques and inherent species differences. This study used several existing datasets for the five primary conifer species in Maine, namely balsam fir [Abies balsamea (L.) Mill.], northern white-cedar [Thuja occidentalis (L.)], eastern hemlock [Tsuga canadensis (L.) Carr.], eastern white pine [Pinus strobus (L.)], and red spruce [Picea rubens (Sarg.)] to examine species variation in total and vertical distribution of projected leaf area at the individual branch- and tree-levels. In addition, multiple methods for modeling the vertical distribution of leaf area were examined across the species. For a given branch diameter and location within the crown, eastern hemlock branches held the greatest amount of leaf area, followed by balsam fir, northern white-cedar, white pine, and red spruce. At the tree-level, eastern white pine held the greatest amount of leaf area followed by eastern hemlock, balsam fir, red spruce, and northern white-cedar for a given tree size. Across species, the two-parameter, right-truncated Weibull distribution performed the best for predicting vertical distribution of leaf area when compared to the four-parameter beta and Johnson's S_B distributions (reduction of root mean square error of 1.7–21.1%). Northern white-cedar had a relative distribution of leaf area distinctly different than other species in this study with a mode shifted towards the upper crown. In contrast to red spruce and white pine, the mode of the relative distribution of leaf area for balsam fir and eastern hemlock occurred lower in the crown. Results of this study suggest that differences in total and vertical distribution of leaf area exist between species, but significant amounts of their variation are largely accounted for by bole and crown size.     

Growth of Phlebiopsis gigantea in wood of seven conifer species

Heterobasidion parviporum and Heterobasidion annosum are widely distributed root‐rot fungi that infect conifers throughout Europe. Infection of conifer stumps by spores of these pathogens can be controlled by treating fresh stumps with a competing non‐pathogenic fungus, Phlebiopsis gigantea. In this study, growth of three Latvian strains of P. gigantea and the biological control agent ‘Rotstop’ strain was evaluated in stem pieces of Norway spruce, Scots pine, lodgepole pine, Douglas‐fir, Weymouth pine, Siberian larch and Sitka spruce. The growth rates of one H. parviporum and one H. annosum isolate were also measured in the same stem pieces. The growth rate of P. gigantea varied greatly in wood of different conifer species. It was higher in the three pine species, lower in Norway spruce and lowest in Sitka spruce and Siberian larch, and in Douglas‐fir, this fungus did not grow. The largest area of wood occupied by P. gigantea was in lodgepole pine. Growth of Latvian isolates of P. gigantea in the wood of Pinus and Picea species was comparable to that of the Rotstop isolate. Consequently, stump treatment with local P. gigantea isolates should be recommended. However, our results suggest that Douglas‐fir stump treatment against Heterobasidion by P. gigantea may be ineffective and other stump treatment methods should be considered.     

Swiss stone pine trees and spruce stumps represent an important habitat for Heterobasidion spp. in subalpine forests

In the Western Italian Alps (WIA), the three European species of the forest pathogen Heterobasidion spp. can coexist in the same area. Heterobasidion parviporum Niemelä & Korhonen and Heterobasidion abietinum Niemelä & Korhonen are normally found in areas with a significant presence of their respective primary hosts, spruce (Picea spp.) and fir (Abies spp.). The host/niche occupied by Heterobasidion annosum (Fr.) Bref. in the region still remains unclear. Although Scots pine (Pinus sylvestris), a major host for this fungal species in other parts of Europe, is abundant in the region, little or no evidence of disease caused by H. annosum is visible in this tree species. Two different, but not mutually exclusive, hypotheses can explain the presence of H. annosum: (1) Scots pines are infected but largely asymptomatic and (2) H. annosum has adapted to different hosts. An analysis of Heterobasidion species was performed in two natural, mixed‐conifer forests using traditional isolation techniques and novel direct molecular diagnosis from wood. In a subalpine stand of mixed spruce (Picea abies), larch (Larix spp.), and Swiss stone pine (Pinus cembra), 18 naturally infected spruces and larches only yielded H. parviporum. A Swiss stone pine in the same stand was extensively colonized by both H. parviporum and H. annosum. In a second subalpine stand, an analysis of 18 spruce stumps and nine Swiss stone pine stumps yielded both H. parviporum and H. annosum isolates. Pine stumps had been mostly colonized by H. parviporum prior to tree felling, suggesting that this species may be secondarily infected by the locally predominant Heterobasidion species (i.e. H. parviporum). Results of our analysis also indicated that primary colonization of spruce stumps (e.g. through basidiospores) was caused by both H. parviporum and H. annosum, while secondary infection of such stumps was mostly because of H. parviporum.     

Stem form variations in the natural stands of major commercial softwoods in eastern Canada

Stem form is often used as a sawlog assortment criterion and has an important effect on lumber recovery and mechanical properties. Based on 7018 stems collected from the natural stands in 3 regions in eastern Canada, this study quantified the variations in stem form (taper, sweep and eccentricity) for five major commercial softwood species, viz., jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana), white spruce (Picea glauca), red spruce (Picea rubens) and balsam fir (Abies balsamea). The majority of the stems had a diameter at breast height (DBH) ranging from 10 to 32 cm and total tree height from 10 to 20 m. Stem taper and butt taper increased steadily from 0.38 to 1.75 cm/m and from 0.74 to 4.23 cm/m, respectively, with DBH increasing from 8 to 48 cm. Stem sweep and basal sweep ranged from 0.12 to 7.28 cm/m and from 0.12 to 9.85 cm/m, respectively, with mean values of 0.87 and 0.95 cm/m. There were no significant differences in stem sweep and basal sweep between DBH classes and both sweeps distributed over a wide range within DBH classes, species and regions. About 0.77% of the stems and 1.2% of the butt logs had seriously curved shapes (sweep >3.0 cm/m). Eccentricity (ratio of smaller diameter to larger diameter) at the breast height (0.96) was very close to 1. Balsam fir and jack pine had the best and worst stem forms, respectively, while stem forms in black spruce were in-between. Butt logs were most seriously curved in red spruce and most tapered in white spruce. Region C (mainly eastern Quebec and the Atlantic Provinces) produced stems with smaller butt taper, basal sweep and stem sweep and larger eccentricity compared with other regions in eastern Canada. Overall stems in eastern Canada have a good stem form in terms of taper, sweep and eccentricity. The evaluation of stem form provides valuable timber quality information for the wood industry to optimize wood processing as well as for forest managers to define appropriate silvicultural regimes to improve stem form and economic value.     

Responses of conifer species of the Great Lakes region of North America to inoculation with the pitch canker pathogen Fusarium circinatum

Five conifer species grown in the Great Lakes region of North America were examined for their susceptibility to Fusarium circinatum, (syns. Fusarium subglutinans f. sp. pini and F. moniliforme var. subglutinans), the causal agent of pitch canker. Three‐year‐old (3‐0) seedlings of red (Pinus resinosa), jack (P. banksiana) eastern white (P. strobus), Scots (P. sylvestris) and Austrian (P. nigra) pine were planted in 4 l pots in a greenhouse at Auburn University in November 1998. In April and June 1999, seedlings were inoculated by removing a needle fascicle approximately 5 cm from the terminal bud and placing a drop containing F. circinatum conidia on the wound. Resin production, canker length and seedling mortality were recorded 12 weeks later. Jack, Scots and eastern white pine were the most susceptible with Austrian and red pine more resistant to the fungus. F. circinatum was re‐isolated from 37% to 96% of inoculated seedlings. The susceptibility of jack, Scots and eastern white pine indicates a potential risk to these important species of the region if F. circinatum were to be introduced into the area.     

Intersterilitätsgruppen und Klone von Heterobasidion annosum-Isolaten aus Koniferen- Wurzel- und -Stammfäulen

Intersterility groups and clones of Heterobasidion annosum isolates from root and butt rots of conifers 69 H. annousum heterokaryons from scots pine, Douglas fir, Norway spruce and larch belonged to the P group, three heterokaryons from Norway spruce to the S group. The results of a study with clones of H. annosum isolates from roots of Scotch pine trees in close neighbourhood suggest colonisation by H. annosum (partly) via root contacts.     

Fast and specific detection of the invasive forest pathogen Heterobasidion irregulare through a Loop‐mediated isothermal AMPlification (LAMP) assay

Heterobasidion irregulare is one of the most destructive fungal pathogens of pines in North America and was accidentally introduced into central Italy, where it has become invasive. The fungus is currently recommended for regulation by the European and Mediterranean Plant Protection Organisation (EPPO). In this work, an efficient diagnostic tool for the early detection of H. irregulare based on Loop‐mediated isothermal AMPlification (LAMP) coupled with two different DNA extraction methods was developed. The LAMP assay showed high specificity and good sensitivity, with a limit of detection of about 20 picograms of target DNA and time of detection of less than 40 min. The assay was successfully tested on a variety of different samples, including fungal fruiting bodies, infected plants and colonized wood. A survey on environmental samples collected in the field was also performed using the LAMP assay coupled with a rapid DNA extraction method. The possible applications of this molecular diagnostic tool encompass the monitoring of pine forests surrounding the current invasion area, laboratory or in‐field analyses of samples from suspected trees, and the surveillance in the ports of entry of wood imported from North America.     

Snag availability for cavity nesters across a chronosequence of post-harvest landscapes in western Newfoundland

We examined the availability and quality of standing dead trees (snags) for nesting habitat in a harvest chronosequence of boreal forests dominated by balsam fir (Abies balsamea) in western Newfoundland. Snag density declined substantially 10–15 years after harvest, then increased to reach its highest level in 81- to 100-year-old forests that had become senescent. Most (55%) of 1260 snags encountered were balsam fir, which contained 41% of the 81 cavities identified. Cavity presence was most strongly positively correlated to snag diameter at breast height (dbh), followed by decay class, time since harvest and height. Less than 40% of snags available throughout the chronosequence had large enough dbh for cavity nesters. Downy Woodpeckers (Picoides pubescens) were responsible for 47% of all cavities identified, excavating balsam fir 50% of the time. Two larger cavity nesters present, Northern Flickers (Colaptes auratus) and Three-toed Woodpeckers (Picoides tridactylus), were more likely to use large-diameter white birch (Betula papyrifera) snags. Northern Flickers excavated the largest cavities, potentially providing habitat for the greatest variety of secondary cavity nesters. Managing for snags with >30 cm dbh, which flickers target for excavation, has the greatest potential to enhance the broader snag cavity-based community in western Newfoundland.     

Stammfaulen in Douglasien-, Kiefern-, Fichten-Mischbestanden1

Butt rot in mixed conifer stands. 70 years old Pseudotsuga menziesii trees on sandy soil, grown together with Pinus syhestris, Picea abies, Fagus sylvatica were analysed for butt rot. 73 % resp. 70 % of the Douglas fir, 13% resp. 28% of the Scotch pine and 82% resp. 84% of the Norway spruce showed decay. The most frequent fungi in Pseudotsuga were Heterobasidion annosum, Calocera viscosa, Sparassis crispa, in Pinus Sparassis crispa and in Picea Heterobasidion annosum. In a neighbouring stand with 85 years old Pseudotsuga menziesii - more often thinned than the 70 years old stand - only 23 % of the trees were with decay.     

Modelling the incidence of Heterobasidion annosum butt rots and related economic losses in alpine mixed naturally regenerated forests of northern Italy

A total of 2257 recently felled stumps were sampled from 22 mixed naturally regenerated forest stands in the Aosta Valley, western Italian Alps, and examined for Heterobasidion annosum butt rots. Disease incidence ranged from 6% to 71% depending on sites, and H. annosum accounted for 92% of the total number of diseased stumps. H. annosum incidence was significantly higher (Chi‐squared multiple comparison tests, p < 0.05) on Norway spruce (44%) than on the other tree species (silver fir = 18%, larch = 12% and Scots pine = 6%). Based on the information on the airborne inoculum composition of the fungus, all the three European species of H. annosum were present, with a variable frequency, depending on site. A partial least squares regression analysis showed that the relative abundance of Norway spruce and four variables describing the size of trees were the best predictors for the incidence of H. annosum butt rots. A model having these variables as predictors was developed (r² = 0.75; p < 0.001) and successfully validated on five additional forest stands. An estimate of the losses in yield and value of timber associated with the disease, i.e. direct losses, was also carried out in the forests included in the survey. The percentage of direct financial losses was either comparable or lower than the average level of disease incidence.     

Butt-rot of Scots pine in Thetford Forest caused by Heterobasidion annosum: a local phenomenon

Heterobasidion annosum was found to be the main cause of decay in 50–60-year-old Scots pine in Thetford Forest in East England. On some sites, up to 15% of the trees could be suffering from H. annosum rot, with decay occasionally extending 2 m or more up the stem. Prior to this study, Scots pine had been considered as resistant to H. annosum butt-rot in Britain, except in overmature trees.     

Susceptibility of Sitka spruce and grand fir trees to decay by Heterobasidion annosum

The susceptibility of Sitka spruce (Picea sitchensis) and grand fir (Abies grandis) to decay by Heterobasidion annosum was compared on a site with a previous history of serious disease. The incidence of decay 15–16 years after planting was 1.5% in grand fir, compared with 34.8% in Sitka spruce. These results are broadly similar to those reported from other trials. More information is required for older trees in Britain but the evidence so far available suggests that grand fir is more resistant to H. annosum than Sitka spruce. Planting grand fir on severely infested sites may therefore significantly reduce the serious losses that could be expected with Sitka spruce. In 14 out of 271 decayed Sitka spruce H. annosum was absent from the middle or base of the decay column but present at the top. Approximately 3% of infected spruce showed features suggesting some degree of resistance. Resin bleeding was observed at the base of 23.2% of the infected spruce, and the mean height of the decay column in these trees was significantly greater (0.96 m) than in those without this feature (0.66 m). The inoculum for infection was provided by stumps of the previous crop, and the genets of H. annosum that were present in some infected trees were also identified in stumps. The majority of infected trees contained only a single genet but three trees contained two genets. In this young crop individual genets were smaller than those found elsewhere; the largest extended to include six trees.     

Glucanohydrolase enzyme activity in embryos of Scots,Corsican and lodgepole pines infected in vitro with Heterobasidion annosum

Embryos of Scots pine (Pinus sylvestris), Corsican pine (P. nigra var. maritima) and Lodgepole pine (P. contorta) were infected in vitro with Heterobasidion annosum and the activities of 1,3-β-glucanase, chitinase and β-glucosidase were monitored. Both the infected and control embryos of the three pine species showed the presence of the enzymes. Statistical analysis showed no significant increase (P > 0.05) in the levels of 1,3-β-glucanase in infected embryos for all the three pine species. However, there was a significant increase in levels of chitinase in infected embryos of P. contorta and P. nigra var. maritima and also in levels of β-glucosidase in infected embryos of all three of the pine species. The study has therefore revealed that constitutive levels of glucanohydrolase enzymes exist in the embryos of the three pine species and that the induction of chitinase and β-glucosidase was a factor in the response of the embryos to stimulation by H. annosum infection.     

Identification of wood‐decay fungi and assessment of damage in log depots of Western Black Sea Region (Turkey)

The aim of this study was to determine and quantify the wood‐decay fungi found on logs of forest tree species (beech, oak, hornbeam, Scots pine and fir) stored in log depots located in six different provinces in the Western Black Sea Region of Turkey. Additionally, it was aimed to determine the natural durability of some important wood species against the most commonly detected wood‐decay fungi. Eighteen families, 31 genera and 45 species belonging to the division Basidiomycota were detected; Antrodia crassa was identified for the first time in Turkey. The abundance of Panus neostrigosus, Polyporus meridionalis, Trametes hirsuta, T. versicolor and Stereum hirsutumincreased significantly with the holding time of the logs (r = 0.99, 0.87, 0.53, 0.57 and 0.78, respectively, p < 0.05). The majority of the fungal species were detected on logs stored in depots for 4–6 years (66%). The percentage of fungal species found on the logs with a holding time of three years or less was 29%, whereas the percentage for those detected on logs stored for seven or more years was 31%. Among the wood species, the greatest number of fungal species (29) and highest amount of fungi (2,539) occurred on beech wood. Natural durability tests showed that T. versicolor caused the greatest loss of wood mass, with an average of 23%. Field studies and natural durability tests performed in the laboratory showed that beech wood lost the most mass among the timber species studied.     

Serpula himantioides,Heterobasidion annosum and Calocera viscosa as butt rot fungi in a Danish Douglas‐fir stand

A scattered wind fall of 50 trees in a 46‐year‐old stand of Douglas‐fir (Pseudotsuga menziesii) revealed Serpula himantioides, Heterobasidion annosum and Calocera viscosa as decay causing fungi. Sixty‐four percent of the stumps had visible rot on the stump surface. Mainly, a central brown rot was seen, caused by either S. himantioides or C. viscosa combined with eccentrically placed spots of incipient H. annosum rot. Subsequently, the appearance of fruitbodies disclosed that in total 76% of the wind thrown trees were associated with one or more of the three decay fungi. S. himantioides was present in a surprisingly large number of trees (54%), and the rot column extended up to 2 m into the stem. This investigation represents the first known incidence of S. himantioides and C. viscosa causing root and butt rot in living conifers in Denmark.     

Comparison of model forms for estimating stem taper and volume in the primary conifer species of the North American Acadian Region

? The performance of ten commonly used taper equations for predicting both stem form and volume in balsam fir [Abies balsamea (L.) Mill], red spruce[Picea rubens (Sarg.)], and white pine[Pinus strobus (L.)] in the Acadian Region of North America was investigated.

? Results show that the Kozak (2004) and Bi (2000) equations were superior to the other equations in predicting diameter inside bark for red spruce and white pine, while the Valentine and Gregoire (2001) equation performed slightly better for balsam fir.

? For stem volume, the Clark et al. (1991) equation provided the best predictions across all species when upper stem diameter measurements were available, while the Kozak (2004) and compatible taper equation of Fang et al. (2000) performed well when those measurements were unavailable.

? The incorporation of crown variables substantially improved stem volume predictions (mean absolute bias reduction of 7–15%; root mean square error reduction of 10–15%) for all three species, but had little impact on stem form predictions.

? The best taper equation reduced the predicted root mean square error by 16, 39, and 45% compared to estimates from the widely used Honer (1965) regional stem volume equations for balsam fir, red spruce, and white pine, respectively.

? When multiple taper equations exist for a certain species, the use of the geometric mean of all predictions is an attractive alternative to selecting the “best” equation.

     

Modelling primary branch frequency and size for five conifer species in Maine,USA

Quantitative models of crown structure have been developed for several conifer species, but these studies have rarely simultaneously fit the models across multiple species. This study used extensive crown structure data for the five primary conifer species in Maine to test for species differences in maximum branch diameter profile, branch density, and relative branch diameter distribution. The species included balsam fir [Abies balsamea (L.) Mill], northern white-cedar [Thuja occidentalis (L.)], eastern hemlock [Tsuga canadensis (L.) Carr.], eastern white pine [Pinus strobus (L.)], and red spruce [Picea rubens (Sarg.)]. After accounting for key covariates, significant species differences were found in all crown structural attributes examined in this study. Profiles for the mean tree indicated that northern white-cedar had the smallest maximum branch diameters throughout the crown and white pine had the largest, except near the base of the crown where the species switched in rank. The density of live branches in a crown had the widest range of variation of the examined crown structural attributes. Red spruce had a significantly higher density of primary branches than the other conifers, particularly in the upper crown. The relative branch diameter distribution indicated that balsam fir had a distribution more skewed towards larger relative branch sizes, while eastern hemlock and red spruce had distributions shifted towards smaller relative branches. This study highlights the range of variability in key crown structural attributes due to inherent species differences, but indicates that models fit across multiple species can perform quite well as the amount of explained variation was relatively high.