Growth characteristics and reproductive output of dwarf mistletoe-infected Juniperus polycarpos in Iran

Dwarf mistletoes are parasitic flowering plants that infect conifers, resulting in substantial loss of growth and mortality. Recently, forest managers in Iran are contemplating whether infection of Juniperus polycarpos C. Koch forests by dwarf mistletoe, Arceuthobium oxycedri （DC.） M. Bieb, influences tree vigor and contributes to insuffieient natural regeneration. The present study aimed at assessing the severity of infection and its impact on growth and reproductive output of./., polycar- pos. Infected and uninfected trees （n =20 each） were selected for assess- ment of diameter, height, crown area, and crown volume as well as quantity and quality of cones and seeds. The severity of infection of trees was determined by Hawksworth＇s 6-class dwarf mistletoe rating （DMR） system. The DMR system revealed that 40% of the infected sample trees were lightly infected （DMR =1-2） and 60% were moderately infected （DMR =3--4）. Growth characteristics did not differ significantly （p 〉 0.05） between infected and uninfected trees. However, moderate infec- tion affected the reproductive output of./. polycarpos by significantly （p 〈0.05） reducing the mean number of cones per unit area of the crown, increasing the number of damaged seeds, and reducing seed size and seedgermination capacity. We conclude that reproductive output of J.. poly- carpos is more sensitive than growth characters to moderate infection by juniper dwarf mistletoe, and this might partly account for poor natural regeneration.     

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

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

Susceptibility of Coulter pine (Pinus coulteri) to western dwarf mistletoe (Arceuthobium campylopodum) in southern California

The susceptibility of Coulter pine (Pinus coulteri) to western dwarf mistletoe (Arceuthobium campylopodum) was evaluated in southern California. Eight stands infested with western dwarf mistletoe and dominated by Coulter and Jeffrey pines (Pinus jeffreyi) were sampled. Infection of Coulter pine was evaluated using circular plots established around large, severely infected Jeffrey pines and with rectangular transects. A total of 25 plots and 10 transects were sampled. In each plot and transect, live trees > 5 cm in diameter at breast height (1.4 m above the ground) were assigned a dwarf mistletoe rating (6‐class system). Nearly 600 Jeffrey pines and more than 400 Coulter pines were evaluated. Infection of Jeffrey and Coulter pines in the plots and transects averaged 96% and 97%, respectively. These data indicate that Coulter pine should be classified as a principal host of WDM and not as a secondary host as previously reported.     

Transformation of western hemlock (Tsuga heterophylla) tree crowns by dwarf mistletoe (Arceuthobium tsugense,Viscaceae)

Dwarf mistletoes (Arceuthobium species) are arboreal, hemiparasitic plants of conifers that can change the structure and function of the tree crown. Hemlock dwarf mistletoe (Arceuthobium tsugense subsp. tsugense) principally parasitizes western hemlock (Tsuga heterophylla) and effects 10.8% of all western hemlock trees in Oregon, USA. In this study, we climbed 16 western hemlock trees (age 97–321 years, height 33–54.7 m) across a gradient of infection (0%–100% of branches infected) and measured occurrence of all dwarf mistletoe infections, dwarf mistletoe caused deformities, foliage, branch and crown metrics, and sapwood area. We then modelled over 25 different response variables using linear and generalized linear models with three metrics of severity as explanatory variables: total infection incidence, proportion of all live branches infected, and proportion of all live, infected branches with 33 per cent or more foliage distal to infection. A strong effect of dwarf mistletoe intensification was the reduction of branch foliage and an increase in the proportional amount of foliage distal to infections, with severely infected trees having the majority of foliage distal to infections. Increasing severity led to an apparent crown compaction as crown volumes decreased and became increasingly comprised of deformities. Sapwood area was unrelated to infection severity. Branch length and diameters were unrelated to increasing infection severity despite severely infected branches supporting 1–70 infections. The most severely infected tree had 3,615 individual plants in the crown. Our results suggested that shifts in crown structure and branch deformation, foliage amount, and foliage distal to infection, reflected a likely reduction of capacity for tree growth that coincided with a hypothesized increase in resource demand by dwarf mistletoe plants as infection severity intensified.     

Quantifying the effect of pine mistletoe on the growth of Scots pine

Mistletoe infection results in substantial growth losses in mistletoe‐infected forests. This study reports and evaluates the results of retrospective analyses of radial growth of Scots pine (Pinus sylvestris) in relation to the level of infection of pine mistletoe (Viscum album ssp. austriacum). A total of 43 Scots pine trees were destructively sampled from different sites. Of these trees, 14 were uninfected and 29 were infected. Infection classes were determined using six‐class dwarf mistletoe rating system (DMRS). All needle and mistletoe biomass were removed completely and weighed for each sampled tree. Subsamples from needles and all mistletoe biomass were taken to the laboratory for oven‐dried weight determinations. Five‐cm‐thick wood discs were cut from the stem at the breast height (1.3 m) to determine annual basal area increment for the last 25 years. In addition to DMRS, new infection classes were created using mistletoe‐to‐needle biomass (MB/NB) ratio. The results showed that the radial growth losses could be as much as 41% to 64% at different infection levels. The rate of growth loss in relation to DMRS and MB/NB ratio was similar, but with a larger variability in DMRS values. The results showed that both DMRS rating and MB/NB ratio seem to be important for quantifying growth loss on Scots pine trees infected with mistletoe. The results of this study can also be invaluable in modelling the effects of mistletoe on the growth of Scots pine trees.     

Susceptibility of red fir and white fir to fir dwarf mistletoe (Arceuthobium abietinum) in California

Fir dwarf mistletoe (Arceuthobium abietinum, Viscaceae) is a damaging parasite of true firs (Abies spp.) in California. In the Sierra Nevada Mountains, fir dwarf mistletoe consists of two special forms (formae speciales, f. sp.) which are morphologically similar, but exhibit a high degree of host specificity: A. abietinum f. sp. concoloris whose principal host is Sierra white fir (Abies lowiana) and A. abietinum f. sp. magnificae which only parasitizes red fir (Abies magnifica). Although field observations and cross‐inoculation studies have consistently supported the extreme host specialization demonstrated by these special forms of fir dwarf mistletoe, little quantitative data from mixed red fir/white fir stands infested with fir dwarf mistletoe have been available. Therefore, I sampled 20 mixed conifer stands dominated by red and white fir and infested with f. sp. concoloris (8 stands) or f. sp. magnificae (12 stands) from near Mount Shasta to the southern Sierra Nevada Mountains near Sherman Pass. Infection of red and white fir was evaluated using temporary circular plots (0.012 ha) established around large, severely infected trees and with rectangular transects placed within fir dwarf mistletoe‐infested stands. In each plot and transect, live trees >5 cm in diameter at breast height were assigned a dwarf mistletoe rating (6‐class system). A total of 55 plots and 51 transects were established in the 20 stands, and over 1,900 red firs and 1,700 white firs were sampled. Ninety‐nine per cent of the red firs and 98% of the white firs were infected in stands infested with f. sp. magnificae or f. sp. concoloris, respectively. In contrast, no infection of red fir was observed in stands infested with f. sp. concoloris and no infected white firs were observed in stands infested with f. sp. magnificae. These data provide further support that the special forms of fir dwarf mistletoe are extremely host specific in California.     

Mortality and growth of dwarf mistletoe‐infected red and white fir and the efficacy of thinning for reducing associated losses

In managed forests dominated by true fir (Abies) species, stands are often restocked using understory trees retained during timber harvest, making the effects of dwarf mistletoe (Arceuthobium spp.) infestation on small true fir a concern. This study examined the response of small red (A. magnifica) and white (A. concolor) fir and their dwarf mistletoes (A. abietinum f.sp. magnificae and A. abietinum f.sp. concoloris, respectively) to precommercial thinning treatments in fir‐dominated stands in the Sierra Nevada Mountains of California. Tree diameters and dwarf mistletoe ratings were monitored from 1981 to 2001, and mortality was observed from 1981 to 2006. Red and white fir survival and radial growth decreased significantly with greater mistletoe ratings and increased with larger diameters and live crown ratios. Thinning significantly increased survival and growth of white, but not red fir. Over the course of the study, mistletoe ratings for both fir species did not change significantly in unthinned stands, but increased in thinned stands. However, while statistically significant, increases in mistletoe ratings in thinned stands were gradual and mistletoe ratings did not statistically differ between treatments 20 years post‐thinning. Additionally, thinning did not significantly influence mistletoe spread to uninfected trees, indicating that precommercial thinning in lightly infested red and white fir stands will not likely result in substantial increases in dwarf mistletoe abundance over typical harvesting intervals. Overall, while severe dwarf mistletoe infection ratings reduced tree survival and growth, because ratings remained low, actual losses resulting from mistletoes during this study were minor and will not likely result in substantial economic losses over normal harvesting intervals. This finding indicates that precommercial thinning treatments designed specifically to compensate for mistletoe‐associated losses may not be necessary when managing red and white fir for timber production.     

The effects of Arceuthobium sichuanense infection on needles and current‐year shoots of mature and young Qinghai spruce (Picea crassifolia) trees

Arceuthobium sichuanense is a hemiparasitic angiosperm that infects Qinghai spruce (Picea crassifolia Kom.) in Qinghai province, China, and causes severe damage to spruce forests in Qinghai‐Tibet Plateau. In this study, the impact of A. sichuanense infection on mature and young trees of Qinghai spruce was evaluated by examining needle and current‐year shoot morphology, needle water and nitrogen‐use efficiency (NUE) and needle nitrogen concentration. The most apparent effect of A. sichuanense infection was a significant reduction in both needle size distal to infection and current‐year shoot length in the infected branches (p < 0.001). Per cent reductions in needle and current‐year shoot length were similar between mature and young trees (58.9 vs. 56.3%; 59.7 vs. 62.9%). There was a high degree of correlation in foliar δ¹⁵N values between the dwarf mistletoe and its host trees (R² = 0.9017, p < 0.001), while the foliar δ¹³C values of A. sichuanense were similar to those of infected mature and young spruce trees. The dwarf mistletoe infection also resulted in a significant decrease in host needle N concentration and δ¹³C values (p < 0.001). The per cent reduction in needle N concentration in young trees was nearly twice as much as that in mature trees (20.49 vs. 11.54%), while the per cent reduction in needle δ¹³C values was similar between young and mature trees (?0.98 vs.?1.1‰). The NUE in mature trees was not affected by A. sichuanense infection, but the NUE in young trees was increased by the infection.     

Thinning and prescribed fire effects on dwarf mistletoe severity in an eastern Cascade Range dry forest,Washington

Forest thinning and prescribed fire practices are widely used, either separately or in combination, to address tree stocking, species composition, and wildland fire concerns in western US mixed conifer forests. We examined the effects of these fuel treatments alone and combined on dwarf mistletoe infection severity immediately after treatment and for the following 100 years. Thinning, burning, thin + burn, and control treatments were applied to 10 ha units; each treatment was replicated three times. Dwarf mistletoe was found in ponderosa pine and/or Douglas-fir in all units prior to treatment. Stand infection severity was low to moderate, and severely infected trees were the largest in the overstory. Thinning produced the greatest reductions in tree stocking and mistletoe severity. Burning reduced stocking somewhat less because spring burns were relatively cool with spotty fuel consumption and mortality. Burning effects on vegetation were enhanced when combined with thinning; thin + burn treatments also reduced mistletoe severity in all size classes. Stand growth simulations using the Forest Vegetation Simulator (FVS) showed a trend of reduced mistletoe spread and intensification over time for all active treatments. When thinned and unthinned treatments were compared, thinning reduced infected basal area and treatment effects were obvious, beginning in the second decade. The same was true with burned and unburned treatments. Treatment effects on infected tree density were similar to infected basal area; however, treatment effects diminished after 20 years, suggesting a re-treatment interval for dwarf mistletoe.     

Factors influencing the dispersion of Arceuthobium oxycedri in Central Spain: evaluation with a new null model for marked point patterns

The dwarf mistletoe, Arceuthobium oxycedri, is found on populations of Juniperus oxycedrus, in central Spain. This species can have negative effects on the physiology of its host, including mortality. Understanding the mechanisms that control its distribution and dispersal is critical to assessing its potential for spread. We assessed dwarf mistletoe distribution within a population of J. oxycedrus, including infected and uninfected host individuals. A new null model of parasitic dispersion was built using two dispersal kernel forms that were simulated with lower and upper envelopes for second‐order functions to summarize a point pattern, such as Ripley's K, nearest‐neighbour distribution and pair correlation functions. Nine dispersal scenarios were constructed with half‐bandwidth kernels (10, 20, 30 m) and initial population of infected trees (P₀ = 05, 10 and 20). These scenarios were compared with the observed pattern and evaluated using the goodness‐of‐fit test. Significant differences at short distance (r < 10 m) were found between the observed pattern and simulated patterns, corresponding to the range of seed dispersal of the dwarf mistletoe. Interactions between infected and uninfected hosts patterns at all scales were identified, suggesting that A. oxycedri uses other mechanisms in addition to ballistic seed shooting as secondary dispersal agents to spread to distances greater than 20 m. Given that the seed characteristics facilitate dispersal by adhesion, we infer that spread between host individuals is amplified by seed transport by birds or small mammals.     

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

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

Effect of dothistroma needle blight on needle and shoot lengths

The needles of pine trees are indicative of the overall health of the tree, and their length is affected by many factors. This study describes the effect of high levels of pathogen infection on lengths of both needles and shoots. Dothistroma septosporum is an important foliar pathogen of pines causing necrosis and premature defoliation with successive years of high infection leading to growth reduction and in extreme cases tree death. Corsican pine trees with all foliage infected by D. septosporum had needles of primary, secondary and tertiary shoots reduced by 31.8%, 44.0% and 64.2%, respectively, compared to non‐infected trees. Needle lengths were reduced both in the upper and lower portions of the canopy, with a greater reduction lower in the canopy. Trees with high levels of infection had shorter shoots in the upper canopy with fewer, shorter needles on these shoots compared to trees with low levels of infection. The results demonstrate the substantial negative effect on needle and shoot lengths of trees with high levels of D. septosporum infection, comparable to factors such as water and nutrient availability known to have a strong influence on these parameters. The reductions in length reduce the photosynthetic capacity of the tree and compound the immediate reductions caused by necrosis and premature defoliation. These effects on needle and shoot lengths contribute to the reductions in volume growth of affected trees and, moreover, are longer lasting than the immediate effects of necrosis and premature defoliation.     

Pine mistletoe (Viscum album ssp. austriacum) contributes to Scots pine (Pinus sylvestris) mortality in the Rhone valley of Switzerland

In recent years unusual high mortality of Scots pine (Pinus sylvestris) has been observed in the Swiss Rhone Valley. The exact causes, however, are not known. At a 2‐ha monitoring plot, tree mortality and crown condition have been monitored since 1996. Between 1996 and 2004, 59% of the Scots pines died, most of them following the drought periods 1996–1998 and 2003–2004, while only 15% of the deciduous trees died. Crown transparency, needle discolouration, dead branch percentage, mistletoe (Viscum album ssp. austriacum) rating, Tomicus sp. shoot feeding, male flowering effect, tree stem diameter, crown shading and social tree class assessed in 1998 were used in a logistic regression model to predict tree mortality. Crown transparency, mistletoe rating and percentage of dead branches were found significant in the model and the probability of tree mortality increased with increasing rankings of these parameters. Needle discolouration could be used to substitute ‘dead branch percentage’ as predictor. While crown transparency increased with mistletoe rating, for trees in the same transparency class, trees with medium and heavy mistletoe infection were two to four times more likely to die than trees with no or only low mistletoe infection. For the surviving trees we found that trees with mistletoes showed a significantly higher increase in transparency in the year following a drought than trees without, while in a drought year the opposite was true. At the beginning of the observations no significant differences in transparency had been found between the trees with and without mistletoe. However, by the end of the observation period trees with mistletoe had significantly higher crown transparency. We conclude that mistletoe infection can be considered as both a predisposing factor for tree death, by increasing needle loss following drought and a contributing factor by increasing water stress during drought.     

The impact of Sirococcus shoot blight on radial and height growth of Norway spruce (Picea abies) in young plantations

The impact of Sirococcus shoot blight on the radial and height growth of Norway spruce in a young plantation (approximately 20 years old) was investigated by examining the increment losses for four infection intensities (classes). The average diameter at breast height of trees in the lightly damaged class was 72% when compared with the average diameter of the healthy trees, whereas moderately and severely damaged tree classes were 67 and 57%, respectively. Using tree ring analysis, the development of radial growth over time due to intensity of infection was studied. Height growth of affected trees was also significantly reduced (up to 43%) compared with the healthy trees, thus indicating a dramatic impact of Sirococcus conigenus on the growth of young Norway spruce.     

Evidence of resistance to hemlock dwarf mistletoe (Arceuthobium tsugense) in western hemlock (Tsuga heterophylla) clones

Records from western hemlock (Tsuga heterophylla) trees naturally exposed to infection by hemlock dwarf mistletoe (Arceuthobium tsugense) and controlled inoculations of grafted branch scions from a selection of these trees indicated a repeatability of the levels of resistance to the disease in the clonal material. Evidence pointed to a resistance mechanism operating within, rather than outside, the host branch.     

Infection patterns and hosts of Arceuthobium oxycedri (DC.) M. Bieb. in Slovenia

Eleven mixed populations of Juniperus oxycedrus L. and Juniperus communis L. were inventoried for the presence of parasitic woody species Arceuthobium oxycedri (DC.) M. Bieb. infections. Both J. oxycedrus and A. oxycedri are rare and distributed in marginal populations in Slovenia. To our knowledge, this is the first detailed research on the host species as well as on the infection and spreading patterns of A. oxycedri in Europe. Assessment of the infection rate was based on the Hawksworth six‐class dwarf mistletoe rating system (DMR). The dimensions of A. oxycedri specimens were surprisingly large and often exceeded 25 cm in diameter, the largest even measuring up to 40 cm. Six juniper populations of 11 were infected, and the proportion of infected host individuals in these ranged between 29.17 and 82.93%. The proportion of infected J. oxycedrus specimens in infected populations was 76.56%, while this percentage for J. communis was 54.90%, which is surprisingly high for this species. A different pattern of infection was observed for the two hosts. A typical infection on J. communis was more localized. Usually, only a single infection was present and was most common on the trunk in the middle third of the crown and much less common on the branches. In J. oxycedrus, infections were also most common in the middle third, but also frequent in other areas of the trunk as well as on the branches. Mostly, we observed a dotted pattern of infection with uninfected areas in between. We assume that A. oxycedri will continue to slowly spread in Slovenia, primarily in areas where it is already present. However, its control is probably not yet necessary.     

An in vitro method for screening Colletotrichum gloeosporioides as a biological control agent for western hemlock dwarf mistletoe

An in vitro system using detached western hemlock branches infected with dwarf mistletoe was developed to screen the virulence of five isolates of Colletotrichum gloeosporioides, a hyperparasite of dwarf mistletoe shoots and berries. Detached branches infected with dwarf mistletoe were placed in nutrient‐saturated rock‐wool blocks and mistletoe shoots were inoculated with a conidial suspension of C. gloeosporioides. One month after inoculation, lesions on mistletoe stems and berries were well developed. Infection levels for individual isolates varied from 40% to 60% of shoots and 60% to 80% of berries. Significant differences were found between the isolates and control (p = 0.02 and 0.001, respectively) while no differences were noted between the isolates for both the shoots and berries. Parallel inoculation of mistletoe shoots detached from hemlock branches on moist filter paper and in rock‐wool blocks failed because these shoots deteriorated rapidly, fragmenting into segments within a week. This in vitro test may provide an alternative method for rapid screening of potentially virulent C. gloeosporioides isolates.     

The ability of the pine-top weevil to carry spores and infect Scots pine with Endocronartium pini

The pine-top weevil Pissodes piniphilus is known to be often associated with trees infected with resin-top disease. In this paper, the ability of the weevil to carry Endocronartium pini spores in laboratory conditions and its ability to infect pines in the field were studied. The weevil may carry spores and cause infection in healthy pines.     

Individual vulnerability factors of Silver fir (Abies alba Mill.) to parasitism by two contrasting biotic agents: mistletoe (Viscum album L. ssp. abietis) and bark beetles (Coleoptera: Curculionidae: Scolytinae) during a decline process

? Context

In recent decades, there have been increasing reports of forest decline, especially in Mediterranean forest ecosystems. Decline in tree vitality is usually due to complex interactions between abiotic factors and biotic agents that attack weakened trees.

? Aims and methods

Estimating dendrometrical characteristics [basal area increment (BAI), age at DBH from tree ring counting, social status, height, and diameter], tree health status, and a competition index, we investigated the individual vulnerability of a French declining silver fir forest to both mistletoe (Viscum album L. ssp. abietis) and bark beetles (Pityophthorus pityographus Ratz., Pityokteines vorontzovi Jac., and Pityokteines spinidens Reitt.).

? Results

BAI was negatively correlated with both mistletoe infection (via mistletoe biomass) and bark beetle attack (number of insects per square meter), but there was evidence of divergence in tree choice between two groups of parasites. Mistletoe preferentially infected isolated and dominant trees that showed higher past growth rates than non-infected ones. Conversely, bark beetles mainly attacked defoliated and preferably declining trees with diameter (DBH) lower than 44.5 cm and slower past growth.

? Conclusion

While successive severe drought periods are thought to greatly weaken southern silver fir populations, mistletoe and bark beetles may contribute actively to their decline processes as inciting and contributing factors, respectively.     

Incidence and severity of annosus root rot in Loblolly pine plantations in Virginia

Fourteen plots of 25 loblolly pines each were excavated by bulldozers in order to determine incidence and severity of Heterobasidion annosus in asymptomatic loblolly pine in Virginia. Of the 350 trees sampled, 85% were infected with H. annosus. Basidiocarps were found on 9% of the sampled trees. The average frequency of roots infected per tree with H. annosus, for all measured trees (trees with > 1% infection evident), was 30% of the primary roots and 31% of the secondary roots. The average root length infected for all the measured trees was 14% for primary roots and 15% for secondary roots.