Ingrid Vesterdal Tjessem

• Tjessem, Ingrid Vesterdal; Brysting, Anne Krag; Reitan, Trond; Hjelle, Simen Salomonsen & Eidesen, Pernille Bronken (2026). A shift in species niche through autopolyploidy: From sexual to vegetative reproduction in Saxifraga oppositifolia. Annals of Botany. ISSN 0305-7364. doi: 10.1093/aob/mcag116. Full text in Research Archive Show summary

  Background and Aims Polyploidy has been essential in the evolution of angiosperms, facilitating novel adaptations, enhancing speciation and contributing to the establishment of larger evolutionary lineages. However, newly formed polyploids require sufficient niche differentiation to survive and coexist with the diploid ancestor. Polyploids are commonly reproductively challenged, which may lead to rapid development of asexual reproduction, which may, in turn, lead to reproductive barriers or ecological niche divergence. Through this study, we investigate whether autopolyploidization has induced a shift from sexual reproduction to vegetative propagation in the arctic–alpine Saxifraga oppositifolia (Saxifragaceae) and thus facilitated the establishment of polyploids in mixed-cytotype populations. Methods We sampled data on capsule and seed production, seed germination, rooting ability, and leaf production among cytotypes through a combination of growth chamber experiments and in situ observations in a field set-up across different habitats (ridges, slopes, riverbeds) in Svalbard including >700 georeferenced S. oppositifolia plants with known cytotype (diploid, triploid or tetraploid). Through hypothesis testing and an explorative model search for relevant covariates (e.g. growth form, habitat, soil type), we tested the effect of cytotype on sexual and vegetative reproductive outcomes. Key Results Polyploids had lower sexual reproductive investment (i.e. capsule production and seed production) and higher vegetative investment (i.e. leaf production and rooting ability), showing that polyploidy has significantly affected both sexual reproduction and vegetative propagation. Conclusions Our findings confirm a shift in reproductive strategy towards less sexual investment and enhanced vegetative investment in triploid and tetraploid individuals. This shift may enhance polyploid survival in habitats with shorter growing season and limited pollinator availability, and thus explains their higher frequency in such habitats. These results support autopolyploidy as an evolutionary mechanism that may allow Arctic species to adapt to ongoing, rapid changes.

• Naas, Adam Eindride; Simensen, Trond; Keetz, Lasse Torben; Tjessem, Ingrid Vesterdal; Bryn, Anders & Halvorsen, Rune [Show all 13 contributors for this article] (2026). Supporting spatial planning with high-spatial-resolution model-based ecosystem maps. Environmental impact assessment review. ISSN 0195-9255. 120. doi: 10.1016/j.eiar.2026.108433. Full text in Research Archive Show summary

  Field-based ecosystem maps are often used to support environmental impact assessments (EIAs) in later stages of spatial planning. During the early stages, however, information on geographical distributions of ecosystems is typically unavailable. This can result in uninformed decisions, with negative consequences for biodiversity and ecosystem services. Although model-based maps offer low-cost wall-to-wall coverage, they are rarely used for spatial planning. Using Norway as a study system, we aimed to: (1) quantify the coverage of field-based ecosystem maps in areas reserved for development; (2) use a model-based map to assess ecosystem extents in these areas; and (3) provide guidance on how model-based maps can support spatial planning. We first collated municipality-level land-use plans and intersected these with existing field-based ecosystem maps created for EIAs. Then, we constructed a model-based map for 17 ecosystem types with a 10 m × 10 m resolution that was intersected with the unsurveyed land-use plans. We estimated that 4.2 km2 of land is reserved for development in an average municipality, of which 0.3 km2 is covered by field-based maps. Our model-based map indicates, with moderate uncertainty, that 260 km2 covered by red-listed ecosystem types is at risk of being affected if unsurveyed land reserves are developed. However, improvements in model training and uncertainty quantification methodology should be considered to increase utility of the maps. We provide guidelines for using model-based ecosystem maps in spatial planning, especially in early planning stages, aiming to support decision-making while taking the limitations of model-based maps into account.

• Tjessem, Ingrid Vesterdal; Horvath, Peter; Volden, Inger Kristine Følling; Naas, Adam Eindride; Torma, Michal & Bryn, Anders (2025). A century of treeline and forest line data for Betula pubescens subsp. czerepanovii across high elevations in Norway. Biodiversity Data Journal. ISSN 1314-2836. 13. doi: 10.3897/bdj.13.e160358. Full text in Research Archive Show summary

  Background The global climate is warming, especially in northern regions due to high-latitude amplification. This high-latitude warming leads to range expansion with advancing tree- and forest-lines (TFLs) in the Northern Hemisphere. However, empirical studies can rarely provide a well-documented elevational expansion rate, especially for timescales longer than 40–50 years. This study provides a unique long-term dataset on TFL dynamics of Betula pubescens subsp. czerepanovii in Norway, based on a combination of resampled historical data (n = 319) and new field registrations (n = 447). Our dataset includes a total of 766 registrations from five counties in Norway. In total, the dataset contains 439 treelines and 327 forest lines, most likely representing the highest recorded TFLs for the region at the given time. For all data, both resampled and new, locality, coordinates, elevation, aspect and spatial uncertainty and the resampling/sampling methods and definitions are provided. The entire material is stored and available for download through the Global Biodiversity Information Facility (GBIF) portal. New information This dataset includes newly-resampled TFLs, based on 57–127-year-old registrations. The entries provide elevational changes, georeferenced localities and potential sites for monitoring climate change effects. The entries enable regional analyses of TFL dynamics on intermediate timescales, including the effect of time lags. The material is available for modelling TFL range shifts along the boreal-alpine ecotone. This dataset most likely provides the highest registered Betula pubescens subsp. czerepanovii locations within their specific regions, thus representing the contemporary ecophysiological range limits for the life-form tree. Additional high-elevation TFL sites and localities have been added to make the material suitable for future remapping and monitoring of climatic TFL dynamics.

• Høiland, Klaus; Danielsen, Jørgen Skyrud; Gulden, Gro Sissel; Marthinsen, Gunnhild & Tjessem, Ingrid Vesterdal (2025). Web caps Cortinarius and Phlegmacium (Agaricales, Cortinariaceae) in Svalbard and on Bear Island. AGARICA. ISSN 0800-1820. 45, p. 1–71. doi: 10.5617/agarica.12688. Full text in Research Archive Show summary

  We identified 33 species of the old genus Cortinarius s. lat. (web caps) from Svalbard and Bear Island based on collections from the fungaria in Oslo (O) and Tromsø (TROM) and recently collected material (afterwards kept in O). Morphological and molecular methods, i.e., ITS barcoding, were employed. Two of the ten recently defined genera formerly included in Cortinarius s. lat. are represented: Cortinarius (Pers.) Gray and Phlegmacium (Fr.) Wünsche. The following species of genus Cortinarius were identified: Subgenus Dermocybe: Cortinarius cinnamomeoluteus, C. polaris. Subgenus Myxacium: C. alpinus. Subgenus Telamonia: C. ammophiloides,C. casimiri coll., C. castaneus, C. decipiens, C. desertorum, C. gossypinus*, C. heterodepressus*, C. mallaensis*, C. murinascens*, C. neofallax*, C. parvannulatus, C. pseudofallax, C. pseudofusisporus*, C. pulchripes, C. rusticellus*, C. saniosus, C. saturninus, C. scotoides, C. subtilior. Subgenus Camphorati: C. anomalus, C. delibutus, C. tabularis. Subgenus Iodolentes: C. obtusus. More uncertain is the identity of these: Telamonia: C. cf. inops, C. cf. levipileus*, C. cf. sagarum. Camphorati: C. cf. caninus. Not yet assigned subgenus: C. cf. balaustinus, C. cf. subfloccopus. The genus Phlegmacium has only one member, P. badiolatum var. chamaesalicis, in the area. An asterisk * indicates species not previously published from Norway including Svalbard and Bear Island. Locality and MUSIT number are given for every collection in O and TROM. GenBank accessions are reported for all sequenced collections. Ecology and distribution for the studied species in Svalbard are reported and discussed. A high number of micro niches are assumed, explaining the relatively high diversity of web caps in some of the investigated sites.

• Eidesen, Pernille Bronken; Brysting, Anne Krag; Hagen, Kathleen Rani; Hjelle, Simen Salomonsen; Revéret, Aloïs Nicolas & Tjessem, Ingrid Vesterdal [Show all 26 contributors for this article] (2025). Ecological and evolutionary consequences of ploidy-driven trait variation: insights from Saxifraga oppositifolia L. Arctic Science. ISSN 2368-7460. 11, p. 1–26. doi: 10.1139/as-2024-0020. Full text in Research Archive Show summary

  The ecological and evolutionary consequences of ploidy-driven trait variation, particularly for autopolyploids, remain poorly understood. <i>Saxifraga oppositifolia</i> L. (purple saxifrage), is a highly successful arctic-alpine plant species with significant genetic and phenotypic variation potentially related to autopolyploidy. Over the past decade, we have accumulated knowledge of <i>S. oppositifolia</i> through student projects at the University Centre in Svalbard. Building on this knowledge, we initiated the long-term “SO-field study” in 2018 including 768 permanently tagged plants screened for ploidy level, trait variation and environmental associations. Here we summarize main findings from unpublished student projects, consolidating and extending these findings with the available data from the ongoing SO-field study, containing 63% diploids, 16% triploids, and 21% tetraploids. Our results support that Svalbard is a mixed-ploidy contact zone, where ploidy is strongly associated with certain traits, including growth form, leaf mass area, flower investment, seed production and habitat. Autopolyploidy has significantly influenced both ecology and evolution of <i>S. oppositifolia </i>and needs to be accounted for when autopolyploids are used as a study species or evaluated for management purposes. Our findings suggest considerable re-interpretation of former research and pave the way for new inquiries and hypotheses to be tested within this framework.

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• Tjessem, Ingrid Vesterdal (2026). Naturregnskap med biologiske briller. Full text in Research Archive
• Bryn, Anders; Brynildsrud, Katrine Marie; Folland, Amanda A.; Hemsing, Lars Østby; Horvath, Peter & Høitomt, Torbjørn [Show all 14 contributors for this article] (2025). Feltbaserte kart over arter og naturtyper: likheter, forskjeller og kart vi mangler. Biolog. ISSN 0801-0722. 3, p. 4–11. doi: https:/bio.no/images/Feltbaserte%20_kart.pdf. Full text in Research Archive Show summary

  I debatten om naturmangfold og naturforvaltning i Norge, er en tilbakevendende utfordring forståelsen av ulike feltbaserte temakart. I dette essayet beskrives grunnleggende likheter og forskjeller mellom to sentrale feltbaserte temakart over naturmangfold: artskart og naturtypekart. Disse kartene representerer ulike nivåer i hierarkiet over naturmangfold og har supplerende funksjoner i forvaltningen.

• Tjessem, Ingrid Vesterdal; Bryn, Anders; Horvath, Peter; Naas, Adam Eindride; Halvorsen, Rune & Berntsen, Terje Koren [Show all 10 contributors for this article] (2025). Tales from the past: remapping rising tree- and forest lines in response to changing climate and land use regimes. Full text in Research Archive
• Naas, Adam Eindride; Simensen, Trond; Keetz, Lasse Torben; Tjessem, Ingrid Vesterdal; Bryn, Anders & Halvorsen, Rune [Show all 13 contributors for this article] (2025). Ecosystem distribution models to support area management – a case study from Norway. Full text in Research Archive
• Bryn, Anders; Halvorsen, Rune; Horvath, Peter; Keetz, Lasse Torben; Mienna, Ida Marielle & Simensen, Trond [Show all 12 contributors for this article] (2025). Ecosystem distribution models to support area management - a case study from Norway. Full text in Research Archive
• Bryn, Anders; Berntsen, Terje Koren; Horvath, Peter; Isaksen, Ketil; Liahjell, Gunnar Thorsen & Naas, Adam Eindride [Show all 10 contributors for this article] (2024). På vei mot nye høyder: tre- og skoggrensene stiger. Arr - Idéhistorisk tidsskrift. ISSN 0802-7005. p. 87–100. Full text in Research Archive
• Tjessem, Ingrid Vesterdal (2024). Hva er NiN og hva brukes det til? Full text in Research Archive
• Bryn, Anders; Horvath, Peter; Volden, Inger Kristine; Stordal, Frode; Torma, Michal & Tjessem, Ingrid Vesterdal [Show all 7 contributors for this article] (2023). Citizen science for treeline mapping. Full text in Research Archive
• Tjessem, Ingrid Vesterdal; Bryn, Anders; Horvath, Peter & Naas, Adam Eindride (2023). Changing treeline: A 150-year perspective​. Full text in Research Archive
• Bryn, Anders; Horvath, Peter; Naas, Adam Eindride & Tjessem, Ingrid Vesterdal (2023). Kartlegging av naturtyper etter Natur i Norge (NiN). Biolog. ISSN 0801-0722. p. 16–23. Full text in Research Archive

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