The Database of European Forest Insect and Disease Disturbances: DEFID2.

Insect and disease outbreaks in forests are biotic disturbances that can profoundly alter ecosystem dynamics. In many parts of the world, these disturbance regimes are intensifying as the climate changes and shifts the distribution of species and biomes. As a result, key forest ecosystem services, such as carbon sequestration, regulation of water flows, wood production, protection of soils, and the conservation of biodiversity, could be increasingly compromised. Despite the relevance of these detrimental effects, there are currently no spatially detailed databases that record insect and disease disturbances on forests at the pan-European scale. Here, we present the new Database of European Forest Insect and Disease Disturbances (DEFID2). It comprises over 650,000 harmonized georeferenced records, mapped as polygons or points, of insects and disease disturbances that occurred between 1963 and 2021 in European forests. The records currently span eight different countries and were acquired through diverse methods (e.g., ground surveys, remote sensing techniques). The records in DEFID2 are described by a set of qualitative attributes, including severity and patterns of damage symptoms, agents, host tree species, climate-driven trigger factors, silvicultural practices, and eventual sanitary interventions. They are further complemented with a satellite-based quantitative characterization of the affected forest areas based on Landsat Normalized Burn Ratio time series, and damage metrics derived from them using the LandTrendr spectral-temporal segmentation algorithm (including onset, duration, magnitude, and rate of the disturbance), and possible interactions with windthrow and wildfire events. The DEFID2 database is a novel resource for many large-scale applications dealing with biotic disturbances. It offers a unique contribution to design networks of experiments, improve our understanding of ecological processes underlying biotic forest disturbances, monitor their dynamics, and enhance their representation in land-climate models. Further data sharing is encouraged to extend and improve the DEFID2 database continuously. The database is freely available at https://jeodpp.jrc.ec.europa.eu/ftp/jrc-opendata/FOREST/DISTURBANCES/DEFID2/.

Balancing disturbance risk and ecosystem service provisioning in Swiss mountain forests: an increasing challenge under climate change.

Climate change severely affects mountain forests and their ecosystem services, e.g., by altering disturbance regimes. Increasing timber harvest (INC) via a close-to-nature forestry may offer a mitigation strategy to reduce disturbance predisposition. However, little is known about the efficiency of this strategy at the scale of forest enterprises and potential trade-offs with biodiversity and ecosystem services (BES). We applied a decision support system which accounts for disturbance predisposition and BES indicators to evaluate the effect of different harvest intensities and climate change scenarios on windthrow and bark beetle predisposition in a mountain forest enterprise in Switzerland. Simulations were carried out from 2010 to 2100 under historic climate and climate change scenarios (RCP4.5, RCP8.5). In terms of BES, biodiversity (structural and tree species diversity, deadwood amount) as well as timber production, recreation (visual attractiveness), carbon sequestration, and protection against gravitational hazards (rockfall, avalanche and landslides) were assessed. The INC strategy reduced disturbance predisposition to windthrow and bark beetles. However, the mitigation potential for bark beetle disturbance was relatively small (- 2.4%) compared to the opposite effect of climate change (+ 14% for RCP8.5). Besides, the INC strategy increased the share of broadleaved species and resulted in a synergy with recreation and timber production, and a trade-off with carbon sequestration and protection function. Our approach emphasized the disproportionally higher disturbance predisposition under the RCP8.5 climate change scenario, which may threaten currently unaffected mountain forests. Decision support systems accounting for climate change, disturbance predisposition, and BES can help coping with such complex planning situations. Supplementary Information: The online version contains supplementary material available at 10.1007/s10113-022-02015-w.

MAT--gene structure and mating behavior of Hymenoscyphus fraxineus and Hymenoscyphus albidus.

Recently, different reproductive modes were proposed between the emerging forest pathogen Hymenoscyphus fraxineus and its closely related avirulent sister species, Hymenoscyphus albidus. In the present study, inter- and intraspecific crosses were performed to experimentally assess the reproduction barriers between the two species and to verify H. albidus' putative haploid-selfing reproductive mode. By means of H. fraxineus-specific microsatellite markers, no hybridization was observed in 29 apothecia that emerged from inter-specific crosses, suggesting reproduction barriers are well-established. In a similar experimental setup, we used two newly developed polymorphic H. albidus-specific microsatellites to show that haploid-selfing is H. albidus' only reproductive mode (N=17 apothecia). Further to this, the reproductive modes of both species were investigated under natural conditions. Microsatellite allele-segregation studies of H. fraxineus' single-spore progeny of apothecia (N=31) from field samples suggest that often more than two paternal nuclei are involved in mating. In contrast, analysis of single-spore progeny of field-collected H. albidus apothecia (N=21) confirmed the solely haploid-selfing reproductive mode detected in vitro. Furthermore, we present the complete mating type 1-1 locus of H. fraxineus and report the finding of three additional genes within this region; the as yet unobserved typical mating type gene MAT1-1-1, a DNA polymerase zeta catalytic subunit-like gene and a pre-mRNA-splicing factor SLU7-like gene. The same genes were also detected in the homothallic mating type locus of H. albidus. Further analysis confirmed the expression of all typical mating type genes (MAT1-2-1, MAT1-1-3, MAT1-1-1) in both species. Interestingly, the MAT1-1-3 gene of homothallic H. albidus is expressed despite three stop codons interrupting the coding sequence. Overall, our findings highlight vital differences in the reproduction systems of the two species and suggest that interspecific hybridization is not possible.

Investigating Host Preference of Root Endophytes of Three European Tree Species, with a Focus on Members of the Phialocephala fortinii-Acephala applanata Species Complex (PAC).

Host preference of root endophytes of the three European tree species of Norway spruce (Picea abies), common ash (Fraxinus excelsior), and sycamore maple (Acer pseudoplatanus) were investigated in two forest stands near Zurich, Switzerland. The focus was placed on members of the Phialocephala fortinii s.l. (sensu lato)-Acephala applanata species complex (PAC), as well as other dark septate endopyhtes (DSE). PAC species were identified based on 13 microsatellite loci. Eleven PAC species were found, with Phialocephala helvetica, P. europaea being the most frequent. All but cryptic species 12 (CSP12) preferred Norway spruce as a host. Though very rare in general, CSP12 was most frequently isolated from maple roots. Regarding the abundant PAC species, P. helvetica and P. europaea, the preference of spruce as a host was least pronounced in P. europaea, as it was also often isolated from ash and maple. It is the first record of PAC found on common ash (Fraxinus excelsior). Cadophora orchidicola, a close relative of PAC, has frequently been isolated from ash. Various species of the Nectriaceae (Cylindrocarpon spp.) have often been isolated, particularly from maple roots. By comparison, Pezicula spp. (Cryptosporiopsis spp.) was found to be abundant on all three hosts. Phomopsis phaseoli exhibits a clear preference for spruce.

Biotic threats for 23 major non-native tree species in Europe.

For non-native tree species with an origin outside of Europe a detailed compilation of enemy species including the severity of their attack is lacking up to now. We collected information on native and non-native species attacking non-native trees, i.e. type, extent and time of first observation of damage for 23 important non-native trees in 27 European countries. Our database includes about 2300 synthesised attack records (synthesised per biotic threat, tree and country) from over 800 species. Insects (49%) and fungi (45%) are the main observed biotic threats, but also arachnids, bacteria including phytoplasmas, mammals, nematodes, plants and viruses have been recorded. This information will be valuable to identify patterns and drivers of attacks, and trees with a lower current health risk to be considered for planting. In addition, our database will provide a baseline to which future impacts on non-native tree species could be compared with and thus will allow to analyse temporal trends of impacts.

Competitiveness of endophytic Phialocephala fortinii s.l. - Acephala applanata strains in Norway spruce roots.

Dark septate endophytes of the Phialocephala fortinii s.l. - Acephala applanata species complex (PAC) are presumed to be the most abundant root colonizing endophytes of conifers across the Northern hemisphere. To test the competitiveness of different PAC strains, PAC-free Picea abies saplings were inoculated with five different PAC strains by planting them in pre-colonized substrates. Saplings were left to grow for six weeks and then transplanted crosswise into a substrate colonized by one of the other four strains for a further two weeks. PAC were isolated and genotyped using microsatellite markers. The power of colonization, i.e. the ability of colonizing roots already colonized by another PAC strain, and the power of retention, i.e. the ability of a resident strain of not being suppressed by an invading PAC strain, were calculated for each strain in every combination. The experiment was run twice under two different climatic conditions. Our results show that PAC strains differ (1) in their ability to colonize PAC-free, non-sterile roots, (2) in resistance against being suppressed by another PAC strain and (3) in their ability to invade roots already colonized by another PAC strain. In addition, both the PAC-PAC and the PAC-host interactions depend on the climatic conditions.