Supplementary material 1 from: Ulsted TH, Westergaard KB, Dawson W, Speed JDM (2025) Horizon scanning of potential new alien vascular plant species and their climatic niche space across the Arctic. NeoBiota 104: 1-26. https://doi.org/10.3897/neobiota.104.165054

1 Supplementary materials Horizon scanning of potential new alien vascular plant species and their climatic niche space across the Arctic Tor Henrik Ulsted, Kristine Bakke Westergaard, Wayne Dawson, James D. M. Speed Table of Contents FIGURE S1: ................................................................................................................................................................... 2 FIGURE S2: ................................................................................................................................................................... 3 FIGURE S3 .................................................................................................................................................................... 4 FIGURE S4 .................................................................................................................................................................... 5 FIGURE S5: ................................................................................................................................................................... 6 TABLE S1: .................................................................................................................................................................... 7 TABLE S2: .................................................................................................................................................................... 8 TABLE S3: .................................................................................................................................................................... 9 TABLE S4 ................................................................................................................................................................... 15 TABLE S5 ................................................................................................................................................................... 16 REFERENCES ................................................................................................................................................................ 19 2 Figure S1: Restructuring of Arctic floristic provinces from the original Circumpolar Arctic Vegetation Map (CAVM; Walker et al. 2003) used in this study. Original provinces (grey boxes) were consolidated into broader regions (green boxes) to create more cohesive geographical units for analysis. Some original provinces were also split into separate units (e.g., North Iceland-Jan Mayen, Svalbard-Franz Joseph Land) to better reflect their distinct geographical separation. 3 Figure S2: Correlation matrix of Bioclimatic variables in the Arctic. Bio(n) refers to the corresponding Bioclimatic variable from WorldClim (Fick and Hijmans 2017). The red colors refer to a negative correlation, while blue refers to a positive correlation. Bioclimatic variables were chosen based on |rp|<0.5. The resulting analysis used bio_18 (Precipitation of Warmest Quarter), bio_10 (Mean Temperature of Warmest Quarter), bio_3 (Isothermality (BIO2/BIO7) (×100)), and bio_4 (Temperature Seasonality (standard deviation ×100)). 4 Figure S3: This figure outlines the workflow for processing climate data. The process begins by downloading and cropping WorldClim data to encompass the Circumpolar Arctic. Subsequently, the workflow extracts and scales bioclimatic variables. It then performs correlation analysis to identify and select variables with a correlation coefficient (|r p |) less than 0.5. Occurrences with fewer than 55 observations (log(nobs) ≤ 4) are excluded. The selected bioclimatic variables (18, 10, 3, 4) are extracted for both global and Arctic climates and saved for reuse, avoiding redundant subsetting for each taxon. Finally, the workflow intersects global climate data with occurrence records, producing the final climate dataset per taxon used in subsequent analyses. Saved data refers to data that has only been created once in the pipeline and reused later. 5 Figure S4: The workflow begins with the Input of taxonomic and Arctic climate data from the climate handling process. The “Box Method,” implemented via the hypervolume function in the hypervolume R package, constructs the Arctic hypervolume (Blonder et al. 2025). Inclusion analysis then applies the hypervolume_inclusion_test function with “accurate” accuracy to exclude taxa that do not overlap with the Arctic hypervolume. The workflow proceeds to generate taxon hypervolumes and assess overlap again using the more precise “hypervolume_overlap_statistics” function on a hypervolume set that includes the Taxon and Arctic hypervolumes; Taxa with no overlap are excluded. Finally, the hypervolume_project function calculates taxon overlap projections using both the “Inclusion” (0, 1) and “probability” (gradient) methods, and outputs descriptive data. Saved Data refers to hypervolumes constructed once (e.g., the Arctic hypervolume) and reused across taxa to ensure consistency and reduce computational overhead. 6 Figure S5: Effect sizes (Cramér's V) for associations between species climatic niche overlap and Arctic floristic provinces, ranked by magnitude. Red bars indicate statistically significant associations after False Discovery Rate correction (p < 0.05), while blue bars show non-significant associations. Dashed lines represent conventional effect size thresholds: 0.1 (small), 0.3 (medium), and 0.5 (large). Franz Josef Land shows the only significant association with the largest effect size. 7 Table S1: Model comparison results showing AIC, BIC and their delta values for five zero-inflated beta regression models testing the relationship between absolute latitude and climate overlap. Models tested include: (1) a full model where absolute latitude was used as a predictor for the mean of non-zero climate overlap values, the dispersion parameter, and the probability of zero climate overlap; (2) a zero-only model where absolute latitude predicted the dispersion parameter and probability of zero climate overlap; (3) a magnitude-only model where absolute latitude predicted the mean climate overlap and dispersion parameter; (4) an intercept-only model where absolute latitude predicted only the dispersion parameter; and (5) a complete null model with intercept terms only. Lower AIC/BIC values indicate better model fit, with delta values showing the difference from the best-fitting (full) model. Model AIC Delta_AIC BIC Delta_BIC Full -6211.903 0.000 -6169.747 0.0000 Zero only -6188.609 23.294 -6153.479 16.2683 Magnitude only -1548.108 4663.795 -1512.978 4656.7693 Intercept only -1524.813 4687.090 -1496.710 4673.0377 Complete null -1522.251 4689.652 -1501.173 4668.5741 8 Table S2: Description of terms for the vascular plants used in this study. Term Definition Source Frequent Frequent, present more or less regularly in more than half of the area of the re g ion in question (Elven 2007) Scattered Scattered, either present more or less regularly but in less than half of the re g ion, or more scattered throu g hout. (Elven 2007) Rare Rare, present only in a small part of the region or very sparsely throu g hout the re g ion. (Elven 2007) Casual Alien plants that may flourish and even reproduce occasionally outside cultivation in an area, but that eventually die out because they do not form self-replacing populations, and rely on repeated introductions for their persistence. (Richardson et al. 2000, Pyšek et al. 2004) Borderline Arctic species that are present only in the southernmost part of Subzone E. (Daniëls et al. 2013 ) Unknown Present in the Arctic, but frequency unknown (Elven 2007) Uncertain Presence in the Arctic uncertain (Elven 2007) Excluded The following species and races have been reported from the Arctic or at near arctic localities but we exclude them from the Checklist. The five main reasons for exclusion are: (1) the records are from areas outside the Arctic as circumscribed for the Checklist (i.e., not even "borderline"); (2) the records are based on misidentifications (when it concerns single or a few specimens); (3) we understand or circumscribe the taxon differently from many previous authors; (4) the taxon has been misunderstood and its name has been misapplied (when it concerns whole parts of ranges); or (5) we do not accept a taxon. (Elven 2007) Naturalized (established) Alien plants that sustain self-replacing populations for at least 10 years without direct intervention by people (or in spite of human intervention) by recruitment from seed or ramets (tillers, tubers, bulbs, fra g ments, etc. ) capable of independent g rowth. (Richardson et al. 2000, Pyšek et al. 2004) Invasive Invasive plants are a subset of naturalized plants that produce reproductive offspring, often in very large numbers, at considerable distances from the parent plants, and thus have the potential to spread over a lar g e area. (Richardson et al. 2000, Pyšek et al. 2004) Native Taxa that have originated in a given area without human involvement or that have arrived there without intentional or unintentional intervention of humans from an area in which they are native. (Pyšek et al. 2004) Alien Plant taxa in a given area whose presence there is due to intentional oraccidental introduction as a result of human activity (synonyms: exotic plants, non-native plants; nonindi g enous plants ) (Richardson et al. 2000, Pyšek et al. 2004 ) Invasive Transformer A subset of invasive plants which change the character, condition, form or nature of ecosystems over a substantial area relative to the extent of that ecos y stem. (Richardson et al. 2000) 9 Table S3: This table documents verbatim names from the original datasets that required manual intervention to align with accepted scientific nomenclature. The datasets included the Arctic Inventory Plant List (APIL), Arctic Alien Plant List (AAPL), and the Global Naturalized Alien Flora list (GloNAF). Each entry includes the original name (verbatimName), its standardized counterpart (Accepted Scientific Name), the taxonomic authority consulted, and a justification for manual handling. The Original Source column indicates the list from which the name was derived; suffixes denote the taxon's status in that source: _p for ‘present’ and _a for ‘absent’. Authorities consulted are as abbreviations and describe: World Flora Online (WFO), Expert Decision (ED), Global Biodiversity Information Facility (GBIF), Norwegian Biodiversity Information Centre (NBIC), Global Naturalized Alien Flora (GloNAF), European and Mediterranean Plant Protection Organization (EPPO), and the Pan-Arctic Flora (PAF). Resolutions primarily address synonymy, subspecies standardization, and hybrid name clarification to ensure consistency across datasets. Verbatim Name Origin al Sourc e Accepted Scientific Name Authority Justification for Manual Handling 040105a E. arvense ssp. arvense APIL_ p Equisetum arvense L. WFO Synonym; subspecies resolved to species level. 130201a P. abies ssp. abies APIL_ p Picea abies (L.) H.Karst. ED Nominate subspecies resolved to species level for standardization. 270402a L. cordata var. cordata APIL_ p Neottia cordata (L.) Rich. GBIF/ED Synonym and Nominate subspecies resolved to species level for standardization. 320112 J. bulbosus (ssp. bulbosus) APIL_ p Juncus bulbosus L. ED Nominate subspecies resolved to species level for standardization. 330506 E. x sorenseni APIL_ p Eriophorum × rousseauianum Ra y mond GBIF Synonym; 'E. × sorenseni' is an unaccepted name for this hybrid. 330507a E. scheuchzeri ssp. scheuchzeri APIL_ p Eriophorum scheuchzeri Hoppe ED Nominate subspecies resolved to species level for standardization. 340107a E. fibrosus ssp. fibrosus APIL_ p Elymus fibrosus (Schrenk) Tzvelev WFO Nominate subspecies resolved to species level for standardization. 342801 xA. scleroclada APIL_ p Arctodupontia × scleroclada (Rupr.) Tzvelev WFO Corrected formatting of hybrid name. 343106 P. banksiana APIL_ p Puccinellia banksiensis Consaul WFO Corrected typographical error in specific epithet. 343301 xP. vacillans APIL_ p Pucciphippsia × vacillans (Th.Fr.) Tzvelev WFO Corrected formatting of hybrid name. 343302 xP. czukczorum APIL_ p Pucciphippsia × czukczorum Tzvelev WFO Corrected formatting of hybrid name. 360602a T. sparsiflorum ssp. sparsiflorum APIL_ p Thalictrum sparsiflorum Turcz. ex Fisch. & C.A.Mey. ED Nominate subspecies resolved to species level for standardization. 360706a D. elatum ssp. elatum APIL_ p Delphinium elatum L. ED Nominate subspecies resolved to species level for standardization. 360801a A. lycoctonum ssp. septentrionale APIL_ p Aconitum lycoctonum L. WFO Subspecies resolved to species level; WFO lists it as a synonym. 361315 R. eschscholtzii APIL_ p Ranunculus eschscholtzii Schltdl. WFO Nominate subspecies resolved to species level for standardization. 16 Table S5: This table shows the total number of unique taxon names associated with each origin country, sorted in descending order. “Total Connections” (TC) represents the count of distinct taxa that have each country listed as their origin. For example, 1 787 unique taxa includes occurrence data from Germany. The table is formatted in three column pairs to display all origin countries efficiently. Origin Country TC Origin Country TC Origin Country TC Germany 1787 Turkey-in-Europe 376 Cuba 51 France 1707 Florida 375 Trinidad-Tobago 49 Sweden 1658 Mexico Southwest 375 Brazil North 47 Austria 1618 Queensland 365 Mozambique 46 Great Britain 1540 Chile Central 363 New Caledonia 46 Belgium 1528 Algeria 361 Labrador 46 Czechoslovakia 1485 Mexico Gulf 355 Nansei-shoto 46 Italy 1473 Kriti 350 New Guinea 45 Switzerland 1397 Krasnoyarsk 349 Jamaica 44 Norway 1387 China Southeast 344 Tibet 44 Spain 1379 Primorye 342 Mauritius 42 Denmark 1357 North Dakota 340 Inner Mongolia 42 Netherlands 1333 Louisiana 337 Nigeria 42 Yugoslavia 1328 Western Australia 334 Mexican Pacific Is. 41 Ukraine 1293 Prince Edward I. 332 Cameroon 40 Poland 1222 Azores 331 Togo 39 Central European Russia 1196 Madeira 331 Chatham Is. 38 Hungary 1171 Iran 330 Malawi 38 Finland 1110 Buryatiya 317 Kuwait 38 Portugal 1105 Korea 316 Belize 37 Ontario 1072 Palestine 312 Bahamas 35 Colorado 1043 Colombia 309 Bangladesh 35 New York 1030 Northern Provinces 303 Zaïre 34 California 1021 Ecuador 296 Myanmar 34 Pennsylvania 996 Mexico Southeast 294 Oman 34 Belarus 996 Taiwan 291 Zambia 33 Oregon 985 China North-Central 286 Benin 33 North Caucasus 983 Cyprus 265 French Guiana 31 Romania 982 Uruguay 262 Cook Is. 31 Washington 980 Alaska 261 Sumatera 30 Baltic States 971 Newfoundland 260 St.Helena 29 British Columbia 949 Kirgizistan 258 Lesotho 28 Greece 927 India 256 Aleutian Is. 27 Michigan 922 West Himalaya 247 Seychelles 27 Ireland 913 KwaZulu-Natal 243 Caprivi Strip 26 Bulgaria 878 Uzbekistan 238 Libya 26 Illinois 870 Peru 232 Angola 25 Turkey 861 Mongolia 224 Laos 25 Transcaucasus 859 Argentina South 222 Qinghai 25 Massachusetts 835 Lebanon-Syria 212 Ghana 24 17 Krym 827 Argentina Northwest 212 Sulawesi 23 Ohio 806 Brazil South 207 Easter Is. 23 Québec 805 Bolivia 205 Borneo 21 East European Russia 800 Pakistan 189 Senegal 21 Corse 794 Iraq 187 Cambodia 20 Wisconsin 785 China South-Central 185 Greenland 20 North Carolina 782 Chile South 179 Sinai 20 Virginia 782 Kamchatka 172 Afghanistan 19 Maryland 779 Brazil Southeast 172 Marianas 18 New Jersey 772 Sakhalin 171 Christmas I. 16 West Siberia 771 Hawaii 169 Netherlands Antilles 15 Connecticut 758 Khabarovsk 157 Cayman Is. 15 South European Russia 752 Réunion 153 Burkina 14 Idaho 748 Guatemala 143 Burundi 14 Minnesota 729 Iceland 140 Society Is. 14 New Zealand North 726 Chita 137 Aruba 14 New Zealand South 723 Free State 135 Falkland Is. 14 New South Wales 685 Amur 133 Somalia 14 Texas 685 Yukon 132 Kermadec Is. 13 Utah 681 Tuva 130 Fiji 12 Northwest European Russia 671 Costa Rica 129 Gambia, The 12 Tennessee 656 Tunisia 128 Guyana 12 Indiana 651 Nepal 128 Vanuatu 12 Vermont 635 Norfolk Is. 128 Ivory Coast 12 Victoria 618 Xinjiang 118 Western Sahara 12 Kazakhstan 609 Manchuria 118 Yemen 12 Missouri 600 East Himalaya 114 Gulf of Guinea Is. 11 Alberta 595 Panama 113 Svalbard 11 Maine 591 Northern Territory 110 Comoros 11 New Hampshire 589 El Salvador 104 Nunavut 10 Nova Scotia 581 Honduras 103 Chad 10 Kansas 573 Malaya 103 Mauritania 10 Montana 571 Kenya 102 Turkmenistan 10 Arizona 568 Thailand 101 Samoa 9 New Mexico 566 Brazil West-Central 101 Hainan 8 Georgia 558 Yakutskiya 100 Ogasawara-shoto 8 Arkansas 557 Northwest Territories 97 Niger 7 West Virginia 545 Puerto Rico 96 Mali 7 Altay 544 Jawa 95 Socotra 7 Iowa 539 Dominican Republic 94 Sudan 7 Nebraska 533 Zimbabwe 93 Maluku 6 Mexico Northeast 527 Sri Lanka 84 Antipodean Is. 6 Kentucky 526 Kuril Is. 82 Gabon 6 Alabama 515 Ethiopia 82 Caroline Is. 6 18 New Brunswick 514 Madagascar 79 Solomon Is. 6 Sicilia 509 Lesser Sunda Is. 79 Surinam 6 Nevada 508 Egypt 79 Chagos Archipelago 6 Rhode I. 502 Brazil Northeast 77 Guinea 5 Albania 485 Vietnam 76 Congo 5 Cape Provinces 476 Bermuda 76 Tonga 5 North European Russia 475 Philippines 75 Liberia 4 South Dakota 467 Assam 72 Guinea-Bissau 4 South Carolina 464 Galápagos 70 Southwest Caribbean 4 Mexico Central 457 Nicaragua 70 Rodrigues 4 Tasmania 456 Tadzhikistan 69 Turks-Caicos Is. 4 Morocco 456 Gulf States 68 Sierra Leone 4 Baleares 454 Haiti 67 Andaman Is. 3 South Australia 451 Leeward Is. AB Ant 65 South Georgia 3 Manitoba 448 Venezuela 62 Niue 3 Oklahoma 447 Tanzania 61 Venezuelan Antilles 3 Sardegna 443 Føroyar 60 Tuamotu 2 District of Columbia 442 Botswana 59 Nauru 1 Delaware 434 Swaziland 58 Bismarck Archipelago 1 Irkutsk 433 Rwanda 57 Antarctica 1 Wyoming 424 Uganda 57 Eritrea 1 Mexico Northwest 420 Namibia 56 Maldives 1 East Aegean Is. 420 Windward Is. 55 Macquarie Is. 1 Japan 416 Cape Verde 55 Cocos (Keeling) I. 1 Saskatchewan 415 Saudi Arabia 55 Tokelau-Manihiki 1 Mississippi 413 Magadan 54 Ascension 1 Argentina Northeast 395 Paraguay 54 Wallis-Futuna Is. 1 Canary Is. 387 Chile North 54 19 References Blonder B, Morrow CB, Brown S, Butruille G, Chen D, Laini A, Harris DJ, Violet C (2025) hypervolume: High Dimensional Geometry, Set Operations, Projection, and Inference Using Kernel Density Estimation, Support Vector Machines, and Convex Hulls. Available from: https://CRAN.Rproject.org/package=hypervolume. Daniëls FJA, Gillespie LJ, Poulin M (Eds) (2013) appendix 9.1. In: Arctic Biodiversity Assessment: status and trends in Arcitc biodiversity. The Conservation of Arctic Flora and Fauna, Akureyri, Iceland, 35. Elven R (2007) Checklist of the Panarctic Flora (PAF) Vascular Plants. National Centre of Biosystematics, Natural History Museum, University of Oslo, Oslo, Norway. Fick SE, Hijmans RJ (2017) WorldClim 2: new 1-km spatial resolution climate surfaces for global land areas. International Journal of Climatology 37: 4302–4315. https://doi.org/10.1002/joc.5086 Pyšek P, Richardson DM, Rejmánek M, Webster GL, Williamson M, Kirschner J (2004) Alien plants in checklists and floras: towards better communication between taxonomists and ecologists. TAXON 53: 131–143. https://doi.org/10.2307/4135498 Richardson DM, Pyšek P, Rejmánek M, Barbour MG, Panetta FD, West CJ (2000) Naturalization and invasion of alien plants: concepts and definitions. Diversity and Distributions 6: 93–107. https://doi.org/10.1046/j.1472-4642.2000.00083.x Walker DA, Raynolds MK, Maier HA, Trahan NG (2003) Circumpolar Arctic vegetation. U.S. Fish and Wildlife Service ; Geophysical Institute Map Office [distributor], Anchorage, Alaska, Fairbanks.