Thinning Stumps Research Articles

Quantitative interactions between the biocontrol fungus Phlebiopsis gigantea, the forest pathogen Heterobasidion annosum and the fungal community inhabiting Norway spruce stumps

Protection against the root rot fungus Heterobasidion annosum s. l. is achieved by mechanically spraying stumps with spores of the antagonistic fungus Phlebiopsis gigantea, commercialized as Rotstop®. An extensive colonisation of the stump by P. gigantea is required for protection. Colonisation may depend on how the biocontrol agent interacts with the fungal community that is endophytically inhabiting the stump, as well as with other fungi establishing after the treatment is applied. In this research, we studied how the distribution and abundance of Heterobasidion and P. gigantea is modulated by the fungal community inhabiting Norway spruce (Picea abies) stumps. First thinning stumps were treated with Rotstop and/or artificially inoculated with H. parviporum under field conditions. After two months, P. gigantea or Heterobasidion distribution was measured by qPCR, and both pathogen and biocontrol abundance gradients were correlated with members of the fungal community determined by high throughput sequencing. Rotstop application decreased Heterobasidion biomass by almost 200 times, though the strongest biomass reductions were only achieved when stumps were well covered by P. gigantea. Poor Rotstop applications resulting in, for instance, a drop of 20% in terms of stump covered area by the biocontrol, were associated with a 2-fold biomass increase of the surviving Heterobasidion colonies. Unlike Heterobasidion, some fungi such as Peniophora sp. and F. pinicola did not change their relative abundance following the Rotstop treatment and were associated with areas of low P. gigantea presence. Yeast-like fungi of the genus Debaryomyces increased its relative abundance following Rotstop treatment, and were the only taxa associated with both a higher abundance of the biocontrol, and a lower abundance of the pathogen. Ours is the first study quantifying at microscale the interaction between H. parviporum and P. gigantea in stumps subjected to Rotstop treatment, showing how incomplete stump cover may result in large shifts in terms of biomass for either the pathogen or the biocontrol. Our results stress the importance of achieving a complete cover of the stump surface in practice. Debaryomyces sp. might facilitate P. gigantea colonisation of the stump and could be added as enhancers of Rotstop treatment, though the mechanism of interaction with the pathogen and the biocontrol should be further studied.

Armillaria novae‐zelandiae and other basidiomycete wood decay fungi in New Zealand Pinus radiata thinning stumps

SummaryTwo studies were undertaken in a young New Zealand Pinus radiata stand to find a biological control agent for armillaria root disease caused by Armillaria novae‐zelandiae. Fresh thinning stumps were inoculated with saprophytic basidiomycete species as wooden dowel cultures or as homogenized aqueous mycelial suspensions, while all stumps were also inoculated with dowel cultures of A. novae‐zelandiae. After a period of between one and two years, no differences were found among test fungi in the percentage of Armillaria species isolated from stumps. However, inoculation of Stereum sanguinolentum as homogenate, and of Phlebiopsis gigantea, Sistotrema brinkmannii, Hypholoma acutum and Rigidoporus concrescens as dowel cultures, significantly increased their isolation incidence in comparison with stumps not treated by these species. Phlebiopsis gigantea, Resinicium bicolor and R. concrescens were also isolated with greater frequency nearer to their dowel inoculation points. Results suggest that P. gigantea and S. sanguinolentum should be included in further testing. However, a future trial is likely to be more effective if evaluation is directed towards the portion of the stump below the soil surface, particularly the root system.

Control efficacy of stump treatment and influence of stump height on natural spore infection by Heterobasidion spp. of precommercial thinning stumps of Norway spruce and birch

An alternative precommercial thinning technique results in trees being cut higher up the stem compared to the normal method using a brush saw. The aims of this study were to investigate if primary infection of Heterobasidion spp. on precommercial thinning stumps of Norway spruce and birch is influenced by stump height and to test the control efficacy of stump treatment with Phlebiopsis gigantea on precommercial thinning stumps of Norway spruce. Small Norway spruce and birch trees were felled on five sites in southern Sweden and their stumps subjected to natural spore infection. For each species, two treatments of stump height were created: 15 and 100 cm. Half of the Norway spruce stumps were treated with P. gigantea. After two months, 896 stumps were sampled and infection by Heterobasidion spp. was quantified. The height of stumps did not significantly influence infection frequency or size of infection on either tree species. Untreated Norway spruce stumps had an infection frequency of 55% while 31% of the treated stumps were infected. The control efficacy of stump treatment in terms of reduced relative infected area was 61–65%. The area occupied by Heterobasidion spp. on birch stumps was generally small, on average 0.4 cm2 per infected stump, although 15% of the stumps were infected. The risk of primary infection in Norway spruce dominated stands should be considered when precommercial thinning is conducted but the control efficacy and economy of stump treatment warrants further investigation before practical recommendations can be made.

Impact of armillaria root disease and the effect of thinning in a late‐rotation Pinus radiata plantation

SummaryIn a search for alternative methods for managing armillaria root disease in Pinus radiata plantations in New Zealand, a thinning trial was established in a 1985 planted stand infested by Armillaria novae‐zelandiae. The incidence of chronic (non‐lethal) infection rose significantly following a first thinning at age 7 years that provided additional inoculum in the form of colonized stumps. However, this effect diminished before age 19 years when the small stumps had decomposed and, contrary to expectations, a further increase in infection did not follow a second thinning at age 13.5 years, despite a high incidence of larger colonized second thinning stumps. Apparently the increased vigour and associated resistance in the released older trees was sufficient to counter any increase in inoculum potential following treatment. It therefore now appears that thinning may not be detrimental to the final crop volume in contemporary diseased second‐rotation plantations. However, this treatment furnishes no disease control benefit, and should still be deployed judiciously in heavily infested stands. There was a small, but significant reduction in volume growth on the more severely infected trees during the first 13 years in this trial, but on the larger trees later in the rotation at age 19 years there was no difference in stem volume between infection severity categories. A previous assessment based only on the earlier data therefore overestimates the impact of Armillaria in present and future pine plantations in New Zealand. Nevertheless, its widespread distribution and its demonstrated pathogenicity indicate that forest owners should be conscious of the presence of Armillaria during plantation management.

The effect of winter thinning on the spread of Heterobasidion parviporum in Norway spruce stands

Genets of Heterobasidion were identified in eight 43- to 56-year-old Norway spruce ( Picea abies (L.) Karst.) stands in southern Finland. Four of the stands had been thinned in winter ca. 10 years prior to the study, and four had been left unthinned. It was hypothesized that the felling of decayed trees promotes the vegetative spread of the fungus from thinning stumps into the adjacent trees, and hence the Heterobasidion genets should be larger in thinned stands. Although the number of infected stumps per areal unit was lower and the genets were slightly smaller in the previous tree generation of thinned plots, the genets, particularly the old ones, in the present tree generation were larger on thinned plots. The genets originating from the previous rotation included, on average, 12.2 trees on thinned plots and 6.7 trees on unthinned plots. The mean number of trees infected by new genets (not found in previous generation) was also slightly higher (p < 0.05) on thinned than on unthinned plots, 1.8 and 1.2 trees, respectively. The results indicate that the rapid expansion of old Heterobasidion infections after a thinning operation may significantly contribute to the occurrence of root rot in the residual stand.

Spatial distribution and persistence of Heterobasidion parviporum genets on a Norway spruce site

SummarySpatial distribution of Heterobasidion genets over a period of ca 50 years in two successive generations of Norway spruce (Picea abies) was unravelled. The genets were first identified in 1993 in a naturally regenerated 43‐year‐old spruce stand that had been thinned the previous winter. Heterobasidion parviporum was found in 17.5% of the old stumps of the previous spruce generation. Nine genets were identified on the study plot; seven of them were present in old stumps of the previous tree generation and two only in the new spruce generation. Eighteen spruce trees of the new generation were infected, 15 of them by vegetative growth of genets originating from the old stumps. The study plot was investigated again in 2005. No new genets had been established after thinning, and three old genets had died out. The remaining genets had infected five new trees, most likely from the thinning stumps of diseased trees. At the age of 56 years, 16.1% of the residual spruces were infected by Heterobasidion. The results of this study suggest that if spore infection to stumps of spruce can be prevented, the decay frequency caused by H. parviporum will not necessarily increase in successive generations.

Efficacy of different concentrations of Rotstop® and Rotstop®S and imperfect coverage of Rotstop®S against Heterobasidion spp. spore infections on Norway spruce stumps

SummaryTwo Rotstop® preparations, one containing a Phlebiopsis gigantea strain from Finland (Rotstop F) and the other one from Sweden (Rotstop S), were used in different concentrations to treat thinning stumps of Picea abies against spore infections by Heterobasidion spp. in southern Sweden. Trees were cut on three sites during the summer of 2004, and 285 stumps were treated manually ensuring 100% coverage. Spore concentrations in the treatment suspensions were ca 5 × 106 and 10 × 106 spores/l, and approximately 10 ml of suspension was applied per 100 cm2 of stump surface. An additional 31 stumps on one of the sites were treated mechanically with Rotstop S; in this treatment the spore concentration was high, about 20 × 106 spores/l, but the coverage was incomplete. Three months later there was a significant reduction in frequency and relative areas of Heterobasidion spp. infections on stumps with manual treatment compared with the untreated stumps. However, there was no significant difference between the preparations or the concentration of active ingredient in terms of their reduction of Heterobasidion infection. Mechanical treatment with incomplete coverage failed to control infection. Therefore, in conditions of moderate Heterobasidion spore load in the environment there seems to be no reason to use higher concentrations of P. gigantea in the treatment of spruce stumps.

Fomes root rot in Thetford Forest, East Anglia: past, present and future

Fomes root rot caused by the pathogenic wood-rotting basidiomycete, Heterobasidion annosum, has caused much mortality in the pine plantations of Thetford Forest, East Anglia, which were first established in the period between the two World Wars. This paper presents an evaluation of over 50 years of research into the disease, and includes much previously unpublished data. Special emphasis is given to the position of Corsican pine, Pinus nigra ssp. laricio, as this is now the principal tree used in the plantations. Freshly cut stumps of both Corsican and Scots pine (P. sylvestris) are equally susceptible to colonization by air-borne basidiospores of H. annosum and, in both species, this colonization can be effectively prevented by treatment with spores of Phlebiopsis gigantea. It is well known that on first-rotation sites, a high soil pH favours the development of disease from thinning stumps. Data from one experiment show that on a site with a pH of 7.5-8.0, 1095 trees per hectare had been killed by the time the crop of Scots pine was 36 years old; representing 25 per cent of the original planting. Losses tend to fall as the crop reaches the end of the rotation. There are some data to show that pure Corsican pine is less vulnerable than Scots pine to disease developing after thinning. When a new crop of pine is planted on a site carrying H. annosum-colonized stumps, losses averaging 30 per cent can occur during the first 10 years on soils with a pH >6.0. Even on soils with a pH <6.0, losses average nearly 20 per cent. At this early age, Corsican pine is as susceptible to the disease as Scots pine. A series of experiments has shown that it is only through stump removal that adequate control can be achieved, and for 30 years, this process has been standard practice as the first-rotation crops have been progressively felled. Experiments with a wide range of trees on different soil types have shown that very few species are resistant both to killing and to buttrot caused by H. annosum. Those that have performed best - most notably Picea omorika, Abies grandis and Fagus sylvatica - have major limitations for use in the forest. Nevertheless it is concluded that, while the justification for using Corsican pine as the principal species is well founded, there are reasons for making some continued use of other species, most notably Scots pine, on certain sites. A continued commitment to good quality stump treatment is required in order to minimize H. annosum problems in future rotations.

Natural infection of Sitka spruce thinning stumps in Britain by spores of Heterobasidion annosum and long-term survival of the fungus

Summary On 48 sites throughout Scotland and north England freshly cut stumps were either inoculated with basidiospores of H. annosum or allowed to become infected naturally. Sites were in first rotation plantations growing in high rainfall or low rainfall areas on either peat or mineral soils. After 2 years, infection varied greatly between sites. It was generally much higher following inoculation, but otherwise little of the variation can be explained. Overall, only 10.5 per cent of stumps became infected naturally; colonies were generally small and almost half the stumps contained only homokaryons. Colonization took place principally in the heartwood but stumps sampled 8 years after inoculation showed that in contrast to previous findings this did not prejudice long-term survival. The cross-sectional area of each stump occupied by H. annosum at two years was also not a good predictor of survival. There was a marked decline in survival of H. annosum in stumps sampled after 8 years, which implied a corresponding decline in the overall level of incidence to only 2.8 per cent across all sites. Even in those stumps in which the fungus survived, it failed to colonize two-thirds of the available roots. These results reinforce the conclusions of earlier work that there is a low risk of serious disease on peat soils in the uplands. It is suggested that for Sitka spruce stumps on wet sites, the risk of successful colonization is so low, particularly on peaty soils, that H. annosum may not become permanently established in stands on these site types, even if ambient spore loads increase. By contrast, on mineral soils in low rainfall areas, the risk of a build-up of inoculum in unprotected thinning stumps and the transfer of infection to residual trees in the stand is much higher.

Incidence of Heterobasidion annosum in precommercial thinning stumps in coastal British Columbia

SummaryConiferous stumps in 83 stands in coastal British Columbia were sampled 3‐5 years after precommercial thinning. The percentage of stumps and surface area colonized by Heterobasidion annosum were determined for 25 stumps of each species in each 5‐cm diameter class present in each stand. There were significant differences among species in the percentages of stumps and surface area colonized, with Douglas‐fir (Pseudotsuga menziesii) having the lowest values, amabilis fir (Abies amabilis) and Sitka spruce (Picea sitchensis) the highest and western hemlock (Tsuga heterophylla) being intermediate. For stumps of each species 5–20 cm in diameter, both the percentage of stumps and surface area colonized increased with increasing diameter. In stumps that were grafted to an adjacent tree, there was decreased incidence of H. annosum for Douglas‐fir and Sitka spruce and increased incidence for western hemlock and amabilis fir. There were trends in the percentage of stumps and area colonized for season of thinning and biogeoclimatic subzones with the values for most species decreasing as the amount of precipitation increased. Colonization of precommercial thinning stumps by H. annosum occurs throughout the coastal region of British Columbia, and this will increase the amount of inoculum and will likely increase the incidence of butt rot. The results of this study suggest that the increase in inoculum can be minimized by thinning before age 15, by cutting only trees less than 10 cm in diameter and by thinning during low risk seasons.

Incidence of Armillaria species in precommercial thinning stumps and spread of Armillaria ostoyae to adjacent Douglas-fir trees

Les auteurs ont etudie la frequence des differentes especes du complexe Armillaria presentes dans les souches des arbres abattus lors d'eclaircies precommerciales ainsi que l'interaction au point de contact des racines entre les Douglas taxifolies (Pseudotsuga menziesii (Mirb.) Franco) du peuplement final et les souches colonisees par Armillaria ostoyae (Romagn.) Herink. Les sites choisis pour l'etude etaient disperses dans quatre zones biogeoclimatiques le long d'un transect allant de la zone cotiere a la zone continentale dans le sud de la Colombie-Britannique. La frequence des souches colonisees par A. ostoyae et Armillaria sinapina Berube & Dessureault variait selon la position sur la pente le long du transect. Dans les sites cotiers, A. sinapina dominait les hygrotopes frais tandis que A. ostoyae dominait les hygrotopes legerement secs mais aucun des deux champignons n'etait frequent dans les hygrotopes humides. Dans les sites continentaux, A. ostoyae etait present dans tous les hygrotopes mais a une frequence plus faible dans les sites les plus sec. La distribution des deux especes du complexe Armillaria dans les sites est apparemment determinee par l'anoxie associee a la saturation periodique des sols, au dessechement des sols et par la reaction de l'hote qui limite la progression des especes pathogenes. Au point de contact entre les racines des souches colonisees et les racines des arbres du peuplement final, la transmission et l'infection par A. ostoyae survenaient plus frequemment dans les zones biogeoclimatiques humides que dans les zones seches. La dimension des lesions sur les racines des arbres du peuplement final etait reliee au volume d'inoculum dans certains sites et au diametre des racines des souches dans d'autres sites. Le pourcentage de lesions aux racines pour lesquelles les arbres du peuplement final formaient un callus etait associe au volume du fut. Les resultats indiquent qu'il y aura de la mortalite parmi les arbres du peuplement final apres une eclaircie precommerciale, particulierement ou le niveau d'inoculum est eleve dans les zones biogeoclimatiques continentales caracterisees par la presence de cedre et de pruche ou de Douglas taxifolie.

Abstracts, The Canadian Phytopathological Society, Annual Meeting, Toronto, Ontario, 25-28 June 1995

Abstracts, The Canadian Phytopathological Society, Annual Meeting, Toronto, Ontario, 25-28 June 1995

Population Dynamics of the Root Rot Fungus Heterobasidion annosum Following Thinning of Picea abies

Populations of Heterobasidion annosum were studied in two equally aged stands of Norway spruce Picea abies at the same site. The stands were 2 and 7 ha large and had been thinned one and seven years, respectively, before the investigation. The 7-yearold thinning was more thoroughly investigated since spread of the disease could be followed. One third of thinning stumps were free of H. annosum, and 36% hosted one genet; the rest were colonised by between 2 and 13 genets each. In contrast, only a single genet was found in each of the decayed trees. Groups of decayed trees infected by the same genet were found. Sixty-three percent of the trees had started to decay within 7 years of thinning. Of 262 genets examined, 158 were restricted to thinning stumps, 18 infected both stumps and trees and 86 were restricted to trees. Based on mating tests, 95% of the isolated strains were assigned to the S intersterility group and 2% to the P group; the other 3% could not be classified. Some stumps contained genets of both intersterility groups, but trees were not infected by the P group. The number of genets per stump was correlated better with the stump diameter than with stump surface area. The percentage of decayed trees increased with stem diameter. Similarities in the population densities between the two stands despite the 6-year difference in the time since thinning indicate that disturbance is essential for fungal establishment. It was concluded that trees were infected by mycelial spread from stumps rather than by spore infection of wounds.

Inoculation of Eucalyptus diversicolor thinning stumps with wood decay fungi for control of Armillaria luteobubalina

Eucalyptus diversicolor thinning stumps were simultaneously inoculated with the pathogen Armillaria luteobubalina and one of Coriolus versicolor, Stereum hirsutum and Xylaria hypoxylon to determine if these saprotrophic wood decay fungi could prevent or limit colonization of stumps by A. luteobubalina . The extent of fungal colonization 2 yr after inoculation was assessed at three positions in the stumps (10 cm above ground level, at ground level and 15 cm below ground level). The three fungi equally significantly reduced colonization of stumps by A. luteobubalina , at each of the positions. C. versicolor decayed the upper portions of stumps most and X. hypoxylon least. Fruit-body production by the test fungi was significantly correlated to the relative wood density of the above ground portions of stumps. Some stumps were also colonized below ground by a naturally occurring cord-forming Hypholoma sp., resulting in complete or partial exclusion of A. luteobubalina and the test fungi from lower portions of those stumps. This fungus may prove more useful than the test fungi for control of A. luteobubalina .

Heterobasidion annosum: Development of Butt Rot following Thinning in two young First Rotation Stands of Norway Spruce

Severe butt rot caused by Heterobasidion annosum (Fomes annosus) developed in two stands of first rotation Norway spruce on old agricultural land within 11 years of first thinning. At Site I (Devon), 11 per cent of thinning stumps and 23 per cent of clear felled stumps were found to be decayed when examined soon after the crop was felled at age 37 years. It is estimated that between 4.4 per cent and 6.6 per cent of potential volume was lost on clear felling. Significant butt rot had also developed in a 33-year-old stand of Norway spruce in Site II (Aberdeenshire) 11 years after a Scots pine nurse crop was removed. Here, the disease was found to be widespread on an area of 2 ha, and 73 per cent of trees had butt rot. Decay extended 3 m up the stems, and occupied significant areas of the butt. In both cases, the presence of butt rot in the crops led to premature clear felling, which resulted in additional loss of potential revenue. It seems most likely that the disease became established following infection of thinning stumps by airborne spores of the fungus: at Site I, the thinning stumps were not protected whilst at Site II it would appear that a chemical or biological treatment applied to the pine stumps failed. The subsequent rapid development of the disease was due, in part, to a variety of environmental and edaphic factors.

Infection Foci of Armillaria mellea in First-rotation Hardwoods

Infection foci of ArmiUaria mellea , often 10-20 m in diameter, were discovered in first-rotation plantings of oak and beech on former arable or heathland sites - they were commonly associated with thinning stumps containing the fungus. Since the foci were scattered and contained different mycelial types of A. mellea it seemed probable that they had arisen as a result of stump infection by basidiospores. There was evidence that many years had elapsed between stump infection and the production of rhizomorphs, and that subsequent growth of these depended upon the presence of suitable living roots. Larger oaks seemed little affected whereas many small and medium-sized trees had been killed.