Fungi associated with above-ground portions of declining oaks (Quercus robur) in Germany

Various disease symptoms on oak (Quercus robur L.) affected by oak decline in northern Germany were examined for fungal colonization. The isolated fungi are evaluated in respect to their possible pathogenic qualities and the results are compared with those of other authors and geographic regions.     

Incidence of Phytophthora species in oak forests in Austria and their possible involvement in oak decline

A survey on the occurrence of Phytophthora species in oak ecosystems in Austria was conducted from April to May 1999 and in June 2000. The investigations were carried out at 35 study sites distributed throughout the zone of oak forests in eastern Austria. Four oak species, including Quercus robur, Q. petraea, Q. cerris and Q. pubescens were considered in the survey. Rhizosphere soil samples were taken from sample trees, which consisted of healthy and declining trees as indicated by their crown transparency. Young oak leaflets were used as baits to recover Phytophthora species. The assemblage of Phytophthora spp. detected in Austrian oak forests consisted of five species, including Phytophthora quercina, P. citricola, P. gonapodyides, P. europaea and P. syringae. P. quercina and P. citricola were isolated from 11 and seven sites, respectively, and were thus the most common and most widely distributed species. The three other species were recovered only sporadically. P. citricola could be separated into two morphologically and genetically well‐characterized types (A and B). Phytophthora species, in particular the common P. quercina and P. citricola occurred on sites showing a wide variety of soil types, soil textures and moisture classes. There was mild evidence for connection between deteriorating crown status and the presence of Phytophthora spp. Furthermore, significant differences in contents of magnesium, as well as calcium, aluminium, nitrogen and carbon at different soil depths (0–10, 10–20 and 20–40 cm) were detected between Phytophthora‐infested and Phytophthora‐free sites. The results of the present study provide circumstantial evidence that Phytophthora species are involved in oak decline at certain sites in Austria.     

Bacillus pumilus and Stenotrophomonas maltophilia as two potentially causative agents involved in Persian oak decline in Zagros forests (Iran)

The oak decline is known as one of the most destructive complex diseases causing high economic losses around the world, especially in Iran. The main objective of the present study was to investigate the possible role of bacteria as causative agents of oak decline in the Zagros forests of Iran. To do this, stem, root and leaf samples were taken from symptomatic Persian oak trees (Quercus brantii) in different zones of Zagros forests (Ilam Province, Iran). From 150 bacterial isolates, 20 showed pathogenicity against Geranium seedlings. Among 20 hypersensitivity test positive strains, four strains showed pathogenicity against oak saplings. Based on morphological and 16S rRNA gene sequence analysis, three strains were identified as Bacillus pumilus and one strain as non‐sporulating Gram‐negative Stenotrophomonas maltophilia. Pathogenicity studies of different B. pumilus and S. maltophilia strains revealed that they have potential to cause the disease in oak saplings and symptoms of disorder in Persian oak trees. To our knowledge, there are no previous records of B. pumilus and S. maltophilia causing decline on Fagaceous trees like Q. brantii. More detailed field and molecular studies are required to confirm the absolute role of such bacteria in occurrence of oak decline in Zagros forests.     

Forest stand dynamics and sudden oak death: Mortality in mixed-evergreen forests dominated by coast live oak

Sudden oak death (SOD), caused by the recently discovered non-native invasive pathogen, Phytophthora ramorum, has already killed tens of thousands of native coast live oak and tanoak trees in California. Little is known of potential short and long term impacts of this novel plant–pathogen interaction on forest structure and composition. Coast live oak (Quercus agrifolia) and bay laurel (Umbellularia californica) form mixed-evergreen forests along the northern California coast. This study measured tree mortality over a gradient of disease in three time periods. Direct measurements of current mortality were taken during 2004, representing a point-in-time estimate of present and ongoing mortality. Past stand conditions, c. 1994, were estimated using a stand reconstruction technique. Future stand conditions, c. 2014, were calculated by assuming that, given a lack of host resistance, live trees showing signs of the disease in 2004 would die. Results indicate that coast live oaks died at a rate of 4.4–5.5% year⁻¹ between 1994 and 2004 in highly impacted sites, compared with a background rate of 0.49% year⁻¹, a ten-fold increase in mortality. From 2004 to 2014, mortality rates in the same sites were 0.8–2.6% year⁻¹. Over the entire period, in highly impacted sites, a 59–70% loss of coast live oak basal area was predicted, and coast live oak decreased from 60% to 40% of total stand basal area, while bay laurel increased from 22% to 37%. Future stand structures will likely have greater proportions of bay laurel relative to coast live oak.     

Brenneria spp. and Rahnella victoriana associated with acute oak decline symptoms on oak and hornbeam in Iran

Decline diseases of forest trees are complex syndromes not attributable to single causal factors. In Iran, symptoms of decline disease have been observed in a number of native forest species including Quercus castaneifolia (chestnut‐leaved oak), Q. brantii (Persian oak) and Carpinus betulus (hornbeam). The symptoms are prevalent in the northern forests and the Zagros mountain forests. There are parallels between the disease in Iran and acute oak decline (AOD) reported in the UK, specifically the presence of weeping cankers, which have been attributed to a polybacterial complex wherein Brenneria goodwinii is considered a key necrogen. Based on the AOD symptomatology, and as a first step towards discovering potential causal agents of the stem weeping symptoms of affected trees in Iran, necrotic tissues were tested primarily for the presence of B. goodwinii. Symptomatic Q. castaneifolia and C. betulus from the Mazandaran Province and symptomatic Q. brantii from Kohgiluyeh and Boyerahmad Province were sampled. Isolation and culture on a selective medium yielded uniform bacterial colonies. Isolates were characterized using phenotypic and genotypic (DNA sequencing) tests. The isolates were phenotypically identical to members of Pectobacteriaceae and Yersiniaceae, specifically Brenneria and Rahnella spp. The nucleotide sequences of the 16S rRNA and housekeeping genes gyrB, infB and atpD (MLSA) amplified via PCR demonstrated that the isolates from the trees in Iran were indeed B. goodwinii, B. roseae subsp. roseae, Rahnella victoriana and an unknown species of Brenneria. Most bacteria isolated from non‐symptomatic trees were Gram‐positive, and Pseudomonas spp. were dominant, but bacterial species isolated from the diseased trees were not detected in healthy trees. Hypersensitivity response tests were positive, but inoculation on saplings was more variable with internal necrosis developing only once in the test period. Therefore, further testing is required. This is the first report of the incidence of B. goodwinii, B. roseae subsp. roseae, R. victoriana and Brenneria sp. associated with acute oak decline‐like symptoms on Q. castaneifolia, Q. brantii and C. betulus across the western forests of Iran and in the world.     

Tree-cavity occurrence, cavity occupation and reproductive performance of secondary cavity-nesting birds in oak forests: The role of traditional management practices

Secondary cavity-nesting birds (SCN), which cannot create their own breeding cavities, are expected to be influenced by habitat alteration caused by forest management practices, but the mechanisms underlying the distribution pattern of SCN subjected to different management systems are poorly known. To improve our knowledge on these mechanisms, we examine cavity abundance, cavity occupation and reproductive performance of SCN in Pyrenean oak (Quercus pyrenaica) forests subjected to two management systems: (i) dense “young forests”, maintained at such stage by clear-cuttings and burns, and (ii) “old forest”, subjected to extensive traditional grazing and scarce firewood extraction by selective cutting. Young forests had considerably lower density of cavities (1.29 ± 0.71 vs 15.09 ± 2.00 cavities ha⁻¹), SCN species (0.18 ± 0.11 vs 0.61 ± 0.07 species ha⁻¹) and nests (0.40 ± 0.27 vs 2.67 ± 0.25 nests of all SCN ha⁻¹) than old forests, indicating that a low availability of cavities may limit SCN assemblages in young oak forests. However, reproductive parameters of great (Parus major) and blue (Cyanistes caeruleus) tits associated with the availability of food (laying date, clutch size, nestling number and weight, adult weight) did not differ between both forest types, suggesting that food supply was not reduced in young forests, at least for tits during the breeding season. Large diameter (up to 170 cm dbh) decayed trees were the most likely to hold cavities, but birds preferred smaller living cavity-trees for nesting (90% of nests in 21-65 cm dbh trees). The preservation of cavity-trees within traditionally managed old oak forests is crucial in providing nesting opportunities to SCN. Besides, the protection of these traditionally managed forests would also benefit to other forest organisms that depend on old and open oak forests.     

蒙古栎林在温带落叶阔叶林群落分级中的地位

为清楚阐明蒙古栎林的群落分级及其在温带落叶阔叶林群落分级中的地位，我们收集了东北亚201个蒙古栎林和日本的153个栎林的资料．将其综合于一个简表中．并应用Braun—Blanquet方法对这些森林植被进行了比较。结果表明：在温带落叶阔叶林的群落分级系统中。蒙古栎林与水青冈纲占据着同等重要的地位，它们共同构成温带落叶阔叶林纲群(Class-group)。不同生境下的蒙古栎的20个群集或群落被归纳成为2个目、3个群团和3个亚群团。     

Understory succession in post-agricultural oak forests: Habitat fragmentation affects forest specialists and generalists differently

The herbaceous understory forms the richest stratum in temperate broadleaved forests in terms of plant diversity. Understanding the process of understory succession is thus of critical importance for the development of management guidelines for biodiversity restoration in post-agricultural plantation forests.We studied effects of stand age, forest fragmentation, and soil and canopy conditions on species richness and abundance of four species groups in the understory of post-arable oak plantations in southern Sweden: herbaceous forest specialists, habitat generalists and open-land species, and woody species.The group of forest specialists may approach the richness of continuously forested sites after 60-80 years in non-fragmented plantations, but many forest species were sensitive to habitat fragmentation. Open-land species richness decreased during succession, while the richness of woody species and of generalists remained stable, and was not affected by fragmentation. Abundance of generalists gradually decreased in non-fragmented plantations, probably due to competition from colonizing forest specialists. Soil pH in post-arable stands remained consistently higher than in continuously forested stands, which maintained differences in species composition. The development of a shrub layer seemed to imply a competitive advantage for forest specialists compared to generalist species.For successful recovery of a rich understory, we suggest that post-arable plantations should be established on loamy soils of intermediate to high pH proximate to older forest with source populations, and that a continuous overstory canopy cover of 70-80% is maintained by regular light thinnings and promotion of a shrub layer.     

Seed dispersal by small rodents favors oak over pine regeneration in the pine-oak forests of the Qinling mountains,China

Abstract

Natural regeneration differences between oak and pine are common in the Qinling Mountains of central China. Thus, we examined whether this difference could be explained by seed dispersal. We investigated the seed dispersal of Quercus aliena var. acuteserrata Maxim. and Pinus tabulaeformis Carr. and the regeneration characteristics of both species were investigated in the pine-oak forest belt (oak stands, pine-oak stands, and pine stands) of Huoditang Forest in the Qinling Mountains in central China. We found that Q. aliena var. acuteserrata acorns were usually scatterhoarded, while seeds of P. tabulaeformis were generally consumed immediately. We found that 55% of the released acorns were transferred to the P. tabulaeformis stands. Moreover, Q. aliena var. acuteserrata regenerated successfully and was recruited in the three forest stands. However, the natural regeneration of P. tabulaeformis was very low in all stands because of high predation by small rodents. We propose, therefore, that the seed dispersal advantage of Q. aliena var. acuteserrata compared with P. tabulaeformis contributed greatly to the regeneration difference between these two species in the pine-oak forest belt of the Qinling Mountains in China.     

Distribution of Armillaria species in upland Ozark Mountain forests with respect to site,overstory species composition and oak decline

Armillaria root disease is a contributing factor to oak decline in the Ozark Mountains of central USA. We have identified Armillaria gallica, Armillaria mellea, and Armillaria tabescens in Quercus‐Carya‐Pinus forests of the region. Presence/absence patterns of each Armillaria species as well as all possible Armillaria species combinations were analysed by contingency tables and/or stepwise logistic multiple regressions with principal characteristics of the studied sites and forest stands, both quantitative and qualitative: geographic land‐type association, bedrock type, landform position, slope direction (aspect), soil type and soil surface stone cover, down woody debris, abundance and basal area of woody vegetation and decline mortality by species. Most decline mortality consisted of two red oak species (section Erythrobalanus, Quercus coccinea and Quercus velutina), which also were most sensitive to Armillaria infection. Site characteristics related to the distributions of Armillaria species and decline mortality were also related to the preponderance of Q. coccinea and Q. velutina, regional vegetation history (i.e. conversion of Pinus echinata stands to hardwoods), and the different strategies of territory acquisition and spread of the Armillaria species involved. The presence of A. gallica may reduce the activity of more virulent Armillaria species.     

Gliocladium virens in an alginate prill ineffective as a biological control of Fusarium root disease in container-grown Douglas-fir

An alginate prill formulation of Gliocladium virens (GL-21) was added as a top-dressings (54 g per m²) or incorporated into medium (1.2 kg per m³) used to grow Douglas-fir seedlings in styrofoam containers. Seedlings in the top-dress treatment were similar to control seedlings; infection and colonization by naturally-occurring Fusarium was unaffected by treatment. Incorporated G. virens reduced seedling growth and increased occurrence and colonization intensity of Fusarium. In a laboratory experiment, inoculating Douglas-fir seedlings with G. virens (10% w/w) prior to inoculation with Fusarium increased survival time when compared to concurrent inoculations of fungi.University of Idaho, Idaho Forest, Wildlife and Range Experiment Station Contribution No. 742.     

Behaviour of an Armillaria in some Eucalyptus obliqua – Eucalyptus regnans forests in Tasmania and its role in their decline

An undescribed but native species of Armillaria is a secondary pathogen in declining stands of Eucalyptus obliqua and Eucalyptus regnans in southern Tasmania. The fungus is almost ubiquitous in healthy and diseased forest and occurred epiphytically or parasitically in local lesions on the roots of 74 % of eucalypts partially excavated in 15 forest stands, 25–75 years of age. The fungus infected 85 % of logging stumps and 64 % of fire killed trees. Although the fungus only infected the sapwood of the eucalypts, it survived in infected stumps for at least 70 years. Rhizomorphs initiated most infections but did not grow freely through the soil. Pathogenicity tests confirmed that the Armillaria is a weak pathogen.     

Litter flammability in oak woodlands and shrublands of southeastern France

Characterizing the flammability of litter fuels is of major importance for assessing wildland fire ignition hazard. Here we compared the flammability of litter within a mosaic of Quercus suber (cork oak) woodlands and shrublands in a Mediterranean fire-prone area (Maures massif, southeastern France) to test whether the characteristics and the flammability of litter vary with the vegetation types. We tested experimentally the ignitability, the sustainability, the combustibility and the consumability of undisturbed (=non-reconstructed) litter samples with a point-source mode of ignition. Although the frequency of ignition was similar between all the vegetation types, we distinguished four groups having litter of specific composition and flammability: low and sparse shrublands dominated by Cistus species, medium shrublands with cork oak, high Erica shrublands with sparse cork oak woodlands, and mixed mature oak woodlands with Q. suber, Q. ilex and Q. pubescens. As these vegetation types corresponded to a specific range of past fire recurrence, we also tested the effect of the number of fires and the time since the last fire on litter flammability. Litters of plots recurrently burned had low ability to propagate flames and low flame sustainability. We discuss how the recent fire history can modify vegetation and litter flammability, and thus the fire ignition hazard.     

桉树枯萎病菌的生物学特性及对杀菌剂的敏感性试验

对桉树枯萎病菌的生物学研究结果显示,病菌的最适生长温度为25℃,最适pH值为5.5,光照对生长影响不大。菌丝致死温度为65℃。糖源对分生孢子萌发无明显作用。杀菌剂毒力测定显示根腐灵、宝宁对菌丝生长抑制较强,克露和宝宁对孢子发芽有较强的抑制作用。     

Effects and etiology of sudden aspen decline in southwestern Colorado,USA

Sudden aspen decline (SAD), affecting Populus tremuloides, was first observed in Colorado in 2004. By 2008 it affected at least 220,000 ha, an estimated 17% of the aspen cover type in the state. In southwestern Colorado, we examined site and stand features in paired healthy and damaged plots to assess the effects of SAD on aspen and to identify factors associated with decline. Root mortality increased significantly with recent crown loss. Consequently, density of regeneration did not increase as the overstory deteriorated, and regeneration that originated since 2002 decreased significantly in stands with moderate to severe SAD. However, mortality of regeneration did not increase with that of the overstory. Remeasurement of a subset of plots after 1–2 yrs showed significant increases in severity. Contrary to expectations, overstory age and diameter were not related to SAD severity as measured by recent crown loss or mortality. Severity of SAD was inversely, but weakly, related to basal area, stem slenderness, and site index, and positively related to upper slope positions. This is consistent with moisture stress as an underlying factor. To test the role of climate as an inciting factor for SAD, a landscape-scale climate model was used to compare moisture status of declining and healthy aspen at the height of the warm drought in water year 2002. Polygons identified as damaged aspen in the 2008 aerial survey had greater moisture deficits than healthy aspen in the 2002 water year. SAD has led to loss of aspen cover in some stands, and is occurring in areas where early loss of aspen due to climate change has been predicted. Further warm, dry growing seasons will likely lead to recurrence of SAD.     

The role of isolated old oak trees in maintaining beetle diversity within larch plantations in the central mountainous region of Japan

Old oak trees (Quercus crispula Blume) that are remnants of former old-growth forests have been isolated singly or as small patches within a matrix of conifer plantations in the central mountainous region of Japan. Fifty-six aerial Malaise traps were deployed around seven isolated oak trees within larch [Larix kaempferi (Lamb.) Carrière] plantations and at seven larch plots within larch plantations. The species richness and composition of beetles (Cerambycidae, Curculionidae, Elateridae, Chrysomelidae, and Lycidae) around the oak trees were compared to those in the larch plantations. Species richness was higher around the oak trees than in the larch plantations, and the species composition differed. A number of saproxylic beetles were characteristic of isolated old oak trees. These results emphasize the importance of isolated old oak trees for maintaining beetle diversity in larch plantations and raise the possibility that further losses of these isolated oak trees could eliminate many individuals and reduce beetle diversity in larch plantations.     

Leaf litterfall concentrations and fluxes of elements in deciduous tree species

The influence of tree species and soil properties on leaf litterfall concentrations and fluxes of elements were studied in three mixed deciduous forest stands. Leaf litterfall fluxes of sixteen elements were measured during autumn defoliation in 100 to 150 yr old individuals of Fagus sylvatica L., Quercus robur L., Carpinus betulus L., Tilia cordata Mill, and Acer platanoides L. Compared to throughfall and precipitation, leaf litterfall dominated the flux of P, Ca, Mn, N and Mg (in decreasing order) to the soil below the tree canopies. For K and especially S and Na, however, the importance of leaf litterfall input to the total fluxes was small. Fluxes and especially concentrations of Ca, Mg, K, P and partly N were positively related to base saturation of the soil, while Mn was negatively related due to a higher mobilization rate and plant uptake of this element on acid soils. Litterfall fluxes for C. betulus were strongly positively influenced by base saturation and fluxes were usually higher than for F. sylvatica and Q. robur at the richest site. Quercus robur had often the lowest fluxes, especially of Ca and Mg. Tilia cordata had the highest leaf litter concentrations in twelve of the sixteen elements, and the highest fluxes particularly of N and K. Acer platanoides had the highest or among the highest concentrations and fluxes of Ca, Zn and Mn. The concentration of Al in C. betulus leaf litterfall, was about five times higher than in all other tree species at all sites.     

Environmental and plant-based controls of water use in a Mediterranean oak stand

In this work, new information is reported on water relations of the Mediterranean oak species Quercus pyrenaica based on environmental and physiological measurements carried out during the growing seasons of 2006 and 2007. The interest in this species has increased due to its use in reforestation programs and its impacts on the water resources due to the extensive spontaneous afforestation after the abandonment of forest (firewood, charcoal, livestock, etc.) and agricultural activities, in general in some areas in the Mediterranean region and in particular, in the studied area (Sistema Central range, Spain). The objectives were to evaluate the long-term water use of this stand and its limit and to analyse the specific traits to cope with summer drought, especially the use of stem water storage and deep soil water reserves. Tree water stress associated with depletion of soil water reserves was not observed since the oak trees appeared to avoid a marked water stress using water reserves from deeper soil layers as summer drought progresses. The contribution of mean daily stem water storage to transpiration was low (4%), although it could be greater under dryer conditions. Only at the end of summer of 2006, the transpiration and canopy conductance were reduced due to soil drought. Despite the absence of marked water stress an upper limit was found in transpiration (slightly higher than 3 mm day⁻¹). The heavy use of soil water resources by this species (75% of available soil water in this study) should be considered when evaluating the impact of spontaneous afforestation and reforestation programs on water resources.     

Germination characteristics and diversity of soil seed banks and above-ground vegetation in disturbed and undisturbed oak forests

The destruction of natural ecosystems is an important issue in many parts of the world. In the west of Iran, a vast area of the Zagros Mountain range is covered by typical vegetation including several rare plant species, of which many are currently considered endangered by anthropogenic activities. Despite the important role of soil seed banks to help conserve these degraded plant communities, the floristic studies in the Zagros forests have only focused on above- ground vegetation. In this study, the characteristics of soil seed banks and above-ground vegetation were examined at two forest sites： an undisturbed control （Un） and a disturbed （D） site. The objectives of this study were 1） to investigate the diversity of above-ground vegetation and soil seed banks in disturbed and undisturbed forests, 2） to examine the soil properties and the germination characteristics of the soil seed bank in disturbed and undisturbed oak forests and 3） to estimate the potential of soil seed banks in the restoration of disturbed sites. The results show that soil properties between Un and D sites were significantly different with higher values of pH, NH4-N, N~o,, CEC, OC, clay and canopy percentage in the Un site than in the D site. The Simpson diversity, Margalef richness and evenness indices differed significantly between sites, either for the soil seed banks or the above-ground vegetation. After a period of 26 weeks, the germination speed and the mean daily number of germinants were significantly different between Un and D sites. Without other conservation measures, soil seed banks alone cannot result in a full recovery after severe disturbances in the oak forests of Zagros.     

香荚兰镰刀菌根腐病药剂毒力测定及幼根接种防治试验

在ＰＤＡ含毒介质上的试验表明,苯莱特（５０％ＷＰ）、多菌灵（５０％ＷＰ）、甲基托布津（７０％ＷＰ）抑菌效果最好,稀释３０万倍的药液对尖孢镰刀菌抑菌率分别为１００％、９１．９％、６７．９％,而粉锈灵（１５％ＷＰ）３０００倍液,抑菌率仅为７０．１％;苯莱特、粉锈灵１５００倍液对腐皮镰刀菌抑菌率仅为９４．４％和１４．０％。苯莱特和粉锈灵对尖孢镰刀菌的抑菌效果明显高于腐皮镰刀菌。抑菌圈法试验,多菌灵、苯莱特５００～１０００倍液对腐皮菌的防效又优于尖孢镰刀菌,而粉锈灵对２种镰刀菌均不产生抑菌圈。香荚兰幼根接种药效试验,粉锈灵对尖孢镰刀菌防效最好（５６．６％）,多菌灵、甲基托布津次之（５１．６％、５０．９％）,而苯莱特较差（４０．４％）。粉锈灵１０００倍液浸泡１ｈ和盆栽施药,均对香荚兰幼根产生药害。