Resultater fra overvåking av askeskuddsjuke – de unge faller fra, de gamle takler det bedre

Askeskuddsjuke, som forårsakes av en liten, innført begersopp, har i løpet av ca. 10 år spredt seg gjennom mesteparten av askas utbredelsesområde i Norge, fra Østlandet opp til Nordmøre. I 2016 var bare Trøndelag fortsatt fri for sjukdommen. Etter sju år med overvåking av askeskuddsjuke ser vi at skadeutviklingen på enkelttrær og i bestand skjer fort, også i områder hvor sjukdommen bare har vært til stede i noen få år. Skadeomfanget øker fra år til år, trær i alle aldersklasser angripes og dødeligheten er høy, særlig blant de yngste trærne. Fortsatt holder likevel noen trær seg friske, noe som kan gi håp om at det finnes motstandsdyktige individer som vil overleve epidemien. Som genressursbevaringstiltak har vi samlet inn frø fra de friske trærne i overvåkingsflatene, samt fra Hindrum i Nord-Trøndelag, et av Norges nordligste naturlige askebestand

Helsetilstanden i norske skoger. Resultater fra den landsrepresentative skogovervåkingen i 2010

Hos alle de overvåkete treslagene, gran, furu og bjørk, ble det i 2010 registrert en økning i kronetetthet i forhold til året før. Dette er tredje år på rad med en tydelig bedring for de tre overvåkete treslagene etter flere år med synkende kronetetthet. Derimot ble det observert økt misfarging hos alle treslagene, og særlig bjørk hadde en kraftig økning i andelen misfargete trær. Det ble registrert få biotiske og abiotiske skader på gran og furu i 2010, mens over 20 % av bjørketrærne var skadet, for det meste av målere eller bjørkerustsopp.publishedVersio

Progression of Ash Dieback in Norway Related to Tree Age, Disease History and Regional Aspects

Ash dieback, caused by the ascomycete Hymenoscyphus fraxineus, has been spreading throughout Europe since the early 1990s, threatening European ash at a continental scale. Little is known about the development of the disease in individual forest trees and in different age classes. In this study we monitored ash dieback on trees of different diameter classes in five permanent plots in ash stands in south-eastern Norway from 2009 to 2016, and from 2012 to 2016 in three plots in western Norway with a shorter disease history. Our results showed that more than 80% of the youngest and more than 40% of the intermediate future crop trees in the plots in south-eastern Norway were dead by 2016, while the disease development in large, dominant trees was slower. Although less damage has been observed in the plots in western Norway, the trend for the juvenile trees is the same as in south-eastern Norway with rapidly increasing damage and mortality. Most dead trees in south-eastern Norway were found at sites with high soil moisture and showed symptoms of root-rot caused by Armillaria species. Infected trees, both young and old ones, are weakened by the disease and appear to be more susceptible to other, secondary pathogens, especially under unfavourable site conditions.publishedVersio

European-wide forest monitoring substantiate the neccessity for a joint conservation strategy to rescue European ash species (Fraxinus spp.)

European ash (Fraxinus excelsior) and narrow-leafed ash (F. angustifolia) are keystone forest tree species with a broad ecological amplitude and significant economic importance. Besides global warming both species are currently under significant threat by an invasive fungal pathogen that has been spreading progressively throughout the continent for almost three decades. Ash dieback caused by the ascomycete Hymenoscyphus fraxineus is capable of damaging ash trees of all age classes and often ultimately leads to the death of a tree after years of progressively developing crown defoliation. While studies at national and regional level already suggested rapid decline of ash populations as a result of ash dieback, a comprehensive survey at European level with harmonized crown assessment data across countries could shed more light into the population decline from a pan-European perspective and could also pave the way for a new conservation strategy beyond national boarders. Here we present data from the ICP Forests Level I crown condition monitoring from 27 countries resulting in > 36,000 observations. We found a substantial increase in defoliation and mortality over time indicating that crown defoliation has almost doubled during the last three decades. Hotspots of mortality are currently situated in southern Scandinavia and north-eastern Europe. Overall survival probability after nearly 30 years of infection has already reached a critical value of 0.51, but with large differences among regions (0.20–0.86). Both a Cox proportional hazard model as well as an Aalen additive regression model strongly suggest that survival of ash is significantly lower in locations with excessive water regime and which experienced more extreme precipitation events during the last two decades. Our results underpin the necessity for fast governmental action and joint rescue efforts beyond national borders since overall mean defoliation will likely reach 50% as early as 2030 as suggested by time series forecasting.European-wide forest monitoring substantiate the neccessity for a joint conservation strategy to rescue European ash species (Fraxinus spp.)publishedVersio

The Native Hymenoscyphus albidus and the Invasive Hymenoscyphus fraxineus Are Similar in Their Necrotrophic Growth Phase in Ash Leaves

The populations of European ash and its harmless fungal associate Hymenoscyphus albidus are in decline owing to ash dieback caused by the invasive Hymenoscyphus fraxineus, a fungus that in its native range in Asia is a harmless leaf endophyte of local ash species. To clarify the behavior of H. albidus and its spatial and temporal niche overlap with the invasive relative, we used light microscopy, fungal species-specific qPCR assays, and PacBio long-read amplicon sequencing of the ITS1-5.8S-ITS2 region to examine fungal growth and species composition in attached leaves of European ash. The plant material was collected from a healthy stand in central Norway, where ash saplings in late autumn showed leaflet vein necrosis like that commonly related to H. fraxineus. For reference, leaflet samples were analyzed from stands with epidemic level of ash dieback in southeastern Norway and Estonia. While H. albidus was predominant in the necrotic veins in the healthy stand, H. fraxineus was predominant in the diseased stands. Otherwise, endophytes with pathogenic potential in the genera Venturia (anamorph Fusicladium), Mycosphaerella (anamorph Ramularia), and Phoma, and basidiomycetous yeasts formed the core leaflet mycobiome both in the healthy and diseased stands. In necrotic leaf areas with high levels of either H. albidus or H. fraxineus DNA, one common feature was the high colonization of sclerenchyma and phloem, a region from which the ascomata of both species arise. Our data suggest that H. albidus can induce necrosis in ash leaves, but that owing to low infection pressure, this first takes place in tissues weakened by autumn senescence, 1–2 months later in the season than what is characteristic of H. fraxineus at an epidemic phase of ash dieback. The most striking difference between these fungi would appear to be the high fecundity of H. fraxineus. The adaptation to a host that is phylogenetically closely related to European ash, a tree species with high occurrence frequency in Europe, and the presence of environmental conditions favorable to H. fraxineus life cycle completion in most years may enable the build-up of high infection pressure and challenge of leaf defense prior to autumn senescence.The Native Hymenoscyphus albidus and the Invasive Hymenoscyphus fraxineus Are Similar in Their Necrotrophic Growth Phase in Ash LeavespublishedVersio

Norwegian monitoring programme for forest damage. Annual report 2007

I 2007 var hele 20 % av alle bjørketrær angrepet og skadet av insekter der fjellbjørkemåleren alene sto for 16 %. Hos furu var det færre insektangrep sammenlignet med fjoråret, men fortsatt var vel 2% av furutrærne angrepet av furubarveps. Antall nye toppbrekk, vindfall og andre snø- og vindrelaterte skader var omtrent på samme nivå som gjennomsnittet i overvåkingsperioden. Helsetilstanden til trær, registrert ved kronetetthet, misfarging og avdøing, påvirkes i stor grad direkte av klimatiske forhold som tørke, frost og vind, eller indirekte ved at klima påvirker omfanget av soppsykdommer og insektangrep. Langtransporterte luftforurensninger kan komme i tillegg til eller virke sammen med klimatiske forhold. Kronetettheten utviklet seg negativt på de landsrepresentative flatene for treslagene gran, furu og bjørk. Det var likevel store regionale forskjeller, og som kom tydeligst frem på de regionale flatene. Også i 2007 ble det registrert størst nedgang i kronetetthet for gran i Oppland, Hedmark og i Agderfylkene..

Propagule Pressure Build-Up by the Invasive Hymenoscyphus fraxineus Following Its Introduction to an Ash Forest Inhabited by the Native Hymenoscyphus albidus

Dieback of European ash, caused by the ascomycete Hymenoscyphus fraxineus originating from Asia, has rapidly spread across Europe, and is threatening this keystone tree at a continental scale. High propagule pressure is characteristic to invasive species. Consistently, the enormous production of windborne ascospores by H. fraxineus in an ash forest with epidemic level of disease obviously facilitates its invasiveness and long distance spread. To understand the rate of build-up of propagule pressure by this pathogen following its local introduction, during 2011–2017 we monitored its sporulation at a newly infested ash stand in south-western Norway characterized with mild winters and cool summers. We also monitored the propagule pressure by Hymenoscyphus albidus, a non-pathogenic native species that competes for the same sporulation niche with H. fraxineus. During the monitoring period, crown condition of ash trees had impaired, and 20% of the dominant trees were severely damaged in 2017. H. fraxineus showed an exponential increase in spore production between 2012 and 2015, followed by drastic decline in 2016 and 2017. During 2011–2013, the two Hymenoscyphus species showed similar sporulation level, but thereafter spores of H. albidus were no longer detected. The data suggest that following local introduction, the population of H. fraxineus reaches rapidly an exponential growth stage if the local weather conditions are favorable for ascomata maturation across years. In the North Atlantic climate, summer temperatures critically influence the pathogen infection pressure, warm summers allowing the population to grow according to its biotic potential, whereas cold summers can cause a drastic decline in propagule pressure

Fungal succession in decomposing ash leaves colonized by the ash dieback pathogen Hymenoscyphus fraxineus or its harmless relative Hymenoscyphus albidus

Introduction: The ascomycete Hymenoscyphus fraxineus, originating from Asia, is currently threatening common ash (Fraxinus excelsior) in Europe, massive ascospore production from the saprotrophic phase being a key determinant of its invasiveness. Methods: To consider whether fungal diversity and succession in decomposing leaf litter are affected by this invader, we used ITS-1 metabarcoding to profile changes in fungal community composition during overwintering. The subjected ash leaf petioles, collected from a diseased forest and a healthy ash stand hosting the harmless ash endophyte Hymenoscyphus albidus, were incubated in the forest floor of the diseased stand between October 2017 and June 2018 and harvested at 2–3-month intervals. Results: Total fungal DNA level showed a 3-fold increase during overwintering as estimated by FungiQuant qPCR. Petioles from the healthy site showed pronounced changes during overwintering; ascomycetes of the class Dothideomycetes were predominant after leaf shed, but the basidiomycete genus Mycena (class Agaricomycetes) became predominant by April, whereas H. albidus showed low prevalence. Petioles from the diseased site showed little change during overwintering; H. fraxineus was predominant, while Mycena spp. showed increased read proportion by June. Discussion: The low species richness and evenness in petioles from the diseased site in comparison to petioles from the healthy site were obviously related to tremendous infection pressure of H. fraxineus in diseased forests. Changes in leaf litter quality, owing to accumulation of host defense phenolics in the pathogen challenged leaves, and strong saprophytic competence of H. fraxineus are other factors that probably influence fungal succession. For additional comparison, we examined fungal community structure in petioles collected in the healthy stand in August 2013 and showing H. albidus ascomata. This species was similarly predominant in these petioles as H. fraxineus was in petioles from the diseased site, suggesting that both fungi have similar suppressive effects on fungal richness in petiole/rachis segments they have secured for completion of their life cycle. However, the ability of H. fraxineus to secure the entire leaf nerve system in diseased forests, in opposite to H. albidus, impacts the general diversity and successional trajectory of fungi in decomposing ash petioles.publishedVersio

The state of health of Norwegian forests. Results from the national forest damage monitoring 2017

Source at http://hdl.handle.net/11250/2559230Skogens helsetilstand påvirkes i stor grad av klima og værforhold, enten direkte ved tørke, frost og vind, eller indirekte ved at klimaet påvirker omfanget av soppsykdommer og insektangrep. Klimaendringene og den forventede økningen i klimarelaterte skogskader gir store utfordringer for forvaltningen av framtidas skogressurser. Det samme gjør invaderende skadegjørere, både allerede etablerte arter og nye som kan komme til Norge i nær framtid. Denne rapporten presenterer resultater fra skogskadeovervåkingen i Norge i 2017 og trender over tid for følgende temaer...Forest health is to a large extent affected by climate and weather conditions, either directly by e.g. drought, frost and wind, or indirectly when climatic conditions influence the occurrence and abundance of pests and diseases. Climate change and the expected increase in abiotic damage are a challenge to the management of future forest resources. The same is true for invasive damage agents, both species which are already established and species which can possibly migrate to Norway in the future. This report presents results from the Norwegian forest damage monitoring in 2017 and trends over time for..

Skogens helsetilstand i Norge. Resultater fra skogskadeovervåkingen i 2016

Skogens helsetilstand påvirkes i stor grad av klima og værforhold, enten direkte ved tørke, frost og vind, eller indirekte ved at klimaet påvirker omfanget av soppsykdommer og insektangrep. Klimaendringene og den forventede økningen i klimarelaterte skogskader gir store utfordringer for forvaltningen av framtidas skogressurser. Det samme gjør invaderende skadegjørere, både allerede etablerte arter og nye som kan komme til Norge som følge av økt handel og import. Eksempler på begge er omtalt i denne rapporten som presenterer resultater fra skogskadeovervåkingen i Norge i 2016........publishedVersio