This document summarizes several presentations given at a seminar on forest and plant health held on November 14th, 2019 in Helsinki, Finland. The first presentation discussed fungal species associated with butt rot in mature pine and spruce trees in northern Finland, finding that Ascomycota fungi dominated. The second presentation compared characteristics of urban forests to rural forests, finding that urban forests provide diverse habitat but with less dead wood. The third presentation discussed screening Norway spruce clones for resistance to Heterobasidion fungus, finding variation in resistance and growth traits.

1. Seminar on Forest and Plant Health
November 14th, 2019
Natural Resources Institute Finland, Viikki, Helsinki
Photo: Urban forest in Vaskivuori, Vantaa (Southern Finland). Picture by Aku Korhonen

2. Seminar on Forest and Plant Health, November 14th
, 2019
Natural Resources Institute Finland, Viikki, Helsinki.
Fungal species associated with butt rot of mature Scots pine and Norway
spruce in Northern Ostrobothnia and Kainuu in Finland
Michael M. Müller1
, Juha Kaitera1
, Helena M. Henttonen2
,
1
Natural Resources Institute Finland (Luke), Natural Resources and Bioproduction, P.O. Box
413, FI-90014 University of Oulu, Finland
2
Natural Resources Institute Finland (Luke), Bioeconomy and Environment, P.O. Box 2, 00791
Helsinki
Email: micms.muller@gmail.com
Fungi were isolated from fresh stumps of Norway spruce and Scots pine in 101 regeneration
cutting sites. Soon after logging 6258 Scots pine and 5588 Norway spruce stumps were inspected
of which 50 Scots pine and 429 Norway spruce stumps showed signs of decay and were sampled
for fungal isolation. In total 510 isolates were obtained 209 of which were selected for
identification based on their ITS-DNA sequences. In Norway spruce 59 fungal species and in
Scots pine 6 species were detected based on ≥ 98 % similarity with sequences in GenBank and
additionally, in total from the two conifer species 62 fungal genera were found based on ≥ 95 %
similarity with sequences in GenBank
Only 18 % of the sequenced isolates were Basidiomycetes and 6 % were Zygomycetes while the
majority (74 %) were Ascomycetes. The most frequent Basidiomycetes were Stereum
sanguinolentum (7 isolates), Resinicium bicolor (4 isolates) and Armillaria borealis (3 isolates).
All the detected Basidiomycota species have been reported in earlier studies on Fennoscandian
forests except two yeast-like fungi identified. The low incidence of Heterobasidion parviporum
and absence of H. annosum may be due to low pH of the soil organic layer in the study area
because these species are known to be sensitive to soil acidity.
Among Ascomycetes the most frequent species were Ascocoryne cylichnium (35 isolates),
Cadophora sp. 1 (7 isolates) and Allantophomopsiella pseudotsugae (4 isolates). Only 22 out of
46 of ascomycetous and zygomycetous genera detected in this study have been identified in

3. earlier studies on Norway spruce stumps in Fennoscandia. Ascomycota dominated especially in
sites with high butt rot incidence. The investigation included six spruce stands with a high butt
rot incidence of over 20 % of stumps and samples from these sites were dominated by
Ascomycota compared to Basidiomycota in a ratio of 32:1 isolate while in the other spruce sites
a ratio of 3:1 was obtained. The decayed area was smaller in sample discs from which
Basidiomycota were isolated than in discs inhabited also by Ascomycota. Whether the organic
layer acidity in the study area (average pH 4.1 and range 3.5 – 4.9, causing probably an elevated
concentration of toxic metals in wood) restricts occurrence of other Basidiomycota allowing
Ascomycota to dominate remains open to speculation. The low number of Basidiomycete
isolates supports this hypothesis.
The results suggest that the mycoflora in decaying Norway spruce butt is a highly site- and/or
tree -specific.
This presentation is based on results published in the following three papers:
Müller, M. M., Kaitera, J. & Henttonen H. M. 2018. Butt rot incidence in the northernmost
distribution area of Heterobasidion in Finland. Forest Ecology and Management, 425: 154-
163.
Müller, M. M., Henttonen, H. M., Penttilä, R., Kulju, M., Helo, T. & Kaitera, J. 2018.
Distribution of Heterobasidion butt rot in northern Finland. Forest Ecology and
Management 425: 85-91.
Kaitera, J., Henttonen, H. M. & Müller, M. M. 2019. Fungal species associated with butt rot of
mature Scots pine and Norway spruce in northern boreal forests of Northern Ostrobothnia
and Kainuu in Finland. European Journal of Plant Pathology, 154 (3): 541-554.

4. Seminar on Forest and Plant Health, November 14th
, 2019
Natural Resources Institute Finland, Viikki, Helsinki.
Stand characteristics and dead wood in urban forests: potential
biodiversity hotspots in managed boreal landscapes
Aku Korhonen1
, Juha Siitonen1
, D. Johan Kotze2
, Auli Immonen1
, Leena Hamberg1
1
Natural Resources Institute Finland, (Luke) PO Box 2 (Latokartanonkaari 9) FI-00791
Helsinki, Finland
2
Faculty of Biological and Environmental Sciences, Ecosystems and Environment Research
Programme, Niemenkatu 73, FI-15140, Lahti, University of Helsinki, Finland
Email: aku.korhonen@luke.fi
The potential of urban forests in biodiversity conservation has not been fully appreciated since
they are often perceived as low-quality habitats. However, urban forests are usually not
intensively managed and may provide suitable environments for many forest species whose
habitats are degraded by production forestry. Thus, urban forests have the potential of enhancing
biodiversity both within cities and at a larger landscape scale. The aim of this study was to
investigate stand structure of boreal urban forests, and to assess them in terms of naturalness and
biodiversity conservation potential. We sampled two types of urban stands: (1) random urban
stands as representatives of average urban forests, and (2) valuable urban stands that were known
to host high polypore species richness and thus assumed to represent urban biodiversity hotspots.
Urban forests were compared to rural forests of the same site type, including three categories
with different levels of naturalness: (3) from random managed production forests, (4) valuable
former production forests that have been recently protected and (5) protected semi-natural forests
with no recent history of management. Living and dead trees and cut stumps were measured
from all studied stands. Both urban forests categories have relatively diverse living tree
structures with abundant large-diameter trees. Median volume of dead wood in random urban
forests was almost four times as high as in random production forests but less than 20% of the
median volume in valuable production forests and less than 10% of the median volume in semi-
natural forests. On the other hand, valuable urban forests had higher median volume of dead
wood than valuable production forests. We conclude that the combination of diverse stand
composition and the presence of old-growth characteristics in boreal urban forests form a strong
baseline from which the biodiversity value of urban forests can be further developed, e.g. by
leaving more fallen or cut trees on the ground to form large-diameter dead wood substrates. We
propose that urban forests could become significant habitats for biodiversity conservation in the
future.

5. Seminar on Forest and Plant Health, November 14th
, 2019
Natural Resources Institute Finland, Viikki, Helsinki.
Resistance screening against Heterobasidion parviporum in Norway
spruce clones
Mengxia Liu1
, Matti Haapanen2
, Ha-Thanh Truong3
, Lise Rejasse3
and Fred O. Asiegbu1
1
Department of forest sciences, University of Helsinki, Helsinki, Finland.
2
Natural Resources Institute Finland (Luke), Helsinki, Finland.
3
École de Biologie Industrielle (EBI), Cergy, France.
Email: mengxia.liu@helsinki.fi
Root and stem rots of conifer trees caused by Heterobasidion annosum lead to huge economic
losses not only in Finland but also in other European countries. At present, numerous approaches
have been applied to control root rot diseases, such as silvicultural control by stump removal,
chemical control and biocontrol by stump treatment using urea suspension and ‘Rotstop’
Phlebiopsis gigantea isolates. Despite these efforts and methods, 100% control is not achieved.
Breeding or molecular genetic approach by exploiting inherent natural genetic might provide a
durable solution to the threats.
In our study, short-term screening was carried out by using the fungi Heterobasidion parviporum
to inoculate Norway spruce seedling clones. At the same time, the relationship between
resistance and growth traits was discussed. To explore the variation between resistant and
susceptible clones at the gene expression level, both RT-PCR and RNA sequencing were
conducted.
After screening, variation of growth traits and lesion size was detected among 70 clones.
According to the lesion size results, five resistant and five susceptible clones were selected.
Besides, there was negative correlation between lesion size and growth traits. In RT-PCR results,
three genes involved in cell wall reinforcement, signaling and phenylpropanoid pathway were
highly induced in resistant clones compared to the susceptible ones. Analysis based on RNA-seq
data is ongoing.

6. Seminar on Forest and Plant Health, November 14th
, 2019
Natural Resources Institute Finland, Viikki, Helsinki.
Optimizing crop rotation cycles that support natural
mycorrhization of vegetables
Sannakajsa Velmala, Aku Pakarinen, Hannu Fritze, Pirjo Kivijärvi, Terhi Suojala-Ahlfors, Taina
Pennanen, Minna Kavander, Juha-Matti Pitkänen, Tuija Hytönen
Natural Resources Institute Finland, Latokartanonkaari 7, 00790 Helsinki
Email: sannakajsa.velmala@luke.fi
Arbuscular mycorrhizal (AM) fungi are ubiquitous in soil ecosystems. Within agricultural fields,
they are particularly abundant under organic farming with low inorganic fertilization. Although
the host specificity of AM fungi is low, it seems that the best gain for growth and vitality is
achieved when the roots are colonised by a diverse population of AM fungi and when rotating
plants share their AM communities. We aim to optimize recommendations of the crop rotation
sequence to improve the yield of our most valuable vegetables onion (Allium cepa) and carrot
(Daucus carota). Thus we assessed the effects of the preceding green manure crops used in
rotation on the indigenous AM fungi and other root associated microbial communities. Green
manure crops are plants that are incorporated into the soil before sowing the cash crop. We grew
onion and carrot after mycotrophic (Vicia sativa, Trifolium incarnatum, Tagetes erecta) and
nonmycotrophic (Phacelia tanacetifolia, Lupinus albus, Sinapsis alba) green manure plants in
field and pot experiments. The trials were made in Finland on fine sandy soil under organic
farming practises. We identified the AM fungal species (18S) along with root associated
bacterial (16S) and fungal (ITS2) genera associated to roots of these green manure crops, onion
and carrot. In addition to high-throughput amplicon sequencing we applied neural lipid fatty acid
and microscopy techniques to quantify AM fungi. In the half-open pot systems the effect of the
host plants on the soil microbiome is strong. In the field the host impact is short termed as the
cash crop is rapidly colonized with AM regardless of the AM status of the green manure plants.
Based on our results we conclude that the host plant modifies soil microbial communities but
long-term effects in organic field systems are low as natural diversity is high and microbial
spores are persistent. However more research is needed concerning large field areas receiving
low spore dispersal.

7. Seminar on Forest and Plant Health, November 14th
, 2019
Natural Resources Institute Finland, Viikki, Helsinki.
Microbial activity and community in long-term organic and
conventional farming systems
Krista Peltoniemi, Sannakajsa Velmala, Hannu Fritze and Taina Pennanen
Natural Resources Institute Finland (Luke), Helsinki, Finland
Email: krista.peltoniemi@luke.fi
Several studies have shown enhanced soil fertility and higher microbial biodiversity in
organically grown plots compared to conventionally grown. Organic systems have been reported
to have 32% to 84% greater microbial biomass, carbon and nitrogen content, total phospholipid
fatty acids and enzyme activities than conventional systems. Higher microbial diversity in
organically farmed fields is expected to impact positively, e.g. to carbon sequestration, GHG
mitigation, nutrient and water uptake and pathogen control. Our aim was to detect changes in the
activity, carbon and nitrogen in biomass, abundance and community composition of microbiota
between organic and conventionally farmed systems in boreal region. Two samplings were
conducted from the long-term experimental site for cereal and dairy crops under organic and
conventional farming from the first 10 cm soil layer in May before sowing and after the harvest
in August in 2018. Microbial activity, microbial biomass derived carbon and nitrogen contents as
well as gene copy amounts were determined. Microbial community composition for all fungi
(ITS), arbuscular mycorrhizal fungi (18S rRNA) and bacteria (16S rRNA) were investigated
from sequenced data obtained with Illumina amplicon sequencing. There was significantly
higher microbial activity, microbial biomass derived carbon and nitrogen content and fungal ITS
copies in the field of organic cereal crop production compared to the corresponding conventional
farming systems. Results indicate that organic farming especially for cereals may promote more
diverse fungal community which might be responsible for higher microbial activity and carbon
sequestration into microbial biomass especially in autumn. In addition, also cropping type and
season have impacts on overall fungal and bacterial community composition.

8. Seminar on Forest and Plant Health, November 14th
, 2019
Natural Resources Institute Finland, Viikki, Helsinki.
Bark beetle-fungus interactions and their threats to forest health
Riikka Linnakoski
Natural Resources Institute Finland, Latokartanonkaari 9, 00790 Helsinki, Finland
Email: riikka.linnakoski@luke.fi
Most bark beetles (Coleoptera: Scolytinae) live in already dead, dying or weakened trees. Some
are regarded as forest pests that can develop large populations that are capable invading and
killing also healthy trees. Bark beetles live in close association with fungi; most notable are their
associations with so-called ophiostomatoid or blue stain fungi (Ascomycota). Majority of these
fungi cause discoloration in timber, but this artificial group of morphologically similar fungi
adapted to insect dispersal contains also serious tree pathogens. Also yeasts are abundant
organisms found in the bark beetle galleries, but their diversity and roles in this niche remain
unexplored. Some of the most devastating forest health problems involve associations between
forest insects as fungi, such as the Dutch elm disease. The beetle-fungus interactions can be
particularly harmful in their introduced range. However, in many parts of the world, only little is
known regarding the baseline fungal diversity and dynamics of the beetle-fungus interactions.
Rich fungal diversity is typically associated with bark beetles, and it is has been shown that some
fungi have the potential to amplify the negative effects of the bark beetles. Most insect and
fungal species are not recognized as harmful in their native ranges, and have therefore received
little research attention. Such fundamental research is further complicated by the need for
accurate identification of fungi; the vast majority of the species remain undescribed. Novel
associations between insects and fungi have been recognized as an increasing threat to tree health
globally. Their effects to tree health are typically unexpected and unpredictable. A clear example
of novel associations is our recent study that detected new insect vectors and host trees harboring
the Dutch elm disease fungi, suggesting that the pathogen host and vector range in forest
ecosystems in Europe is much broader than previously thought.

9. Seminar on Forest and Plant Health, November 14th
, 2019
Natural Resources Institute Finland, Viikki, Helsinki.
Health of elms and Dutch Elm disease in Estonia
Liina Jürisoo, Rein Drenkhan
Institute of Forestry and Rural Engineering, Estonian University of Life Sciences, Fr.R.
Kreutzwaldi, 5, 51 014 Tartu, Estonia.
E-mail: liina.jyrisoo@emu.ee
Dutch elm disease (DED) is a vascular wilt disease caused by Ophiostoma spp., which has been
known as a destroyer of millions of elm trees (Ulmus spp.). DED was registered first in Estonia
in 1930s, known as Ophiostoma ulmi (Buisman) Nannf. New agent O. novo-ulmi was detected in
2006.
Our survey of DED in Estonia lasted for three years (2014–2016). There were assessed 1,225
elm trees at 4 different sampling sites and 2 sub-sites in Estonia. Ophiostoma novo-ulmi subsp.
americana was identified only in Tallinn, and Ophiostoma novo-ulmi subsp. novo-ulmi was
spread all over southwestern sampling sites. Simultaneous occurrence of both subspecies and
their hybrids was not detected.
Repetitively surveyed Ulmus glabra’s health appeared worse in Tallinn than at other sampling
site: O. novo-ulmi subsp. americana demonstrated higher aggressiveness. DED signs were noted
on 39% of all 1,225 surveyed trees. Among the assessed elm species, U. laevis showed higher
resistance than U. glabra: 82% and 66% of trees, respectively, showed high vitality. In addition,
no U. laevis trees were found dead, compared to 18% of the U. glabra.
Keywords: DED, Ophiostoma novo-ulmi subsp. americana, O. novo-ulmi subsp. novo-ulmi,
Ulmus spp, vitality class.

10. Seminar on Forest and Plant Health, November 14th
, 2019
Natural Resources Institute Finland, Viikki, Helsinki.
From a rare inhabitant into a potential pest – Status of the nun
moth (Lymantria monacha) population in Finland based on
pheromone trapping
Melin M.1
, Viiri H.1,2
, Tikkanen O.-P.3
, Elfving R.1,4
Neuvonen S.5
1
Natural Resources Institute Finland, Yliopistokatu 6b, FI-80100 Joensuu
2
Current address: UPM-Kymmene Oyj, UPM Forest, Åkerlundinkatu 11 B, FI-33100 Tampere
3
University of Eastern Finland, School of Forest Sciences, Yliopistokatu 6, FI-80100 Joensuu
4
Current address: University of Oulu, Department of Biology, Pentti Kaiteran katu 1, FI-90014
Oulu
5
University of Turku, Biodiversity Unit, Kevo Subarctic Research Institute, FI-20014 Turku
E-mail: markus.melin@luke.fi
Forests are being hit by climate change in various ways. This includes abiotic factors such as
droughts, but also an increased risk of damage caused by biotic agents such as insects. There are
numerous examples from cases where a pest insect has benefitted from endured growing season
or from warmer summers. Similarly, new pest insects have been able to expand their range due
to climatic conditions that have changed from hostile to tolerable.
Such seems to be the case with the nun moth (Lymantria monacha), Europe’s most
significant defoliator of coniferous trees. For centuries, the species has had massive outbreaks
across Central-Europe while it has been only a rare inhabitant in Northern Europe. Recently, the
nun moth population in Finland has not only expanded in range, but also grown more abundant.
In this presentation, I will discuss the results from the first survey years (2018-2019) of a
monitoring program that is being conducted with pheromone traps across central and southern
Finland.
So far, the northernmost individuals were trapped near the 64 N degrees. However, there
were more southern where no moths were trapped. The species was present in every trapping site
below the latitude of 62 N degrees. More importantly, at some sites the abundance of the nun
moth suggested that local forest damage may not be a distant scenario. Given the current climatic
scenarios for Fennoscandia, it is likely that the nun moth populations will continue to grow,
which is why systematic surveys on their abundance and range expansions are vital.
Keywords: forest damage; forest health; climate change; range expansion; insect; forestry

11. Seminar on Forest and Plant Health, November 14th
, 2019
Natural Resources Institute Finland, Viikki, Helsinki.
JIAYAO WU from the Department of forest sciences, University of Helsinki (Helsinki, Finland)
is acknowledged for her presentation: “A comparative Genomics platform for the analysis of
fungal laccases". Email: jiayao.wu@helsinki.fi