Ecological Archives E096-072-A3

Petr Pyšek, Ameur M. Manceur, Christina Alba, Kirsty F. McGregor, Jan Pergl, Kateřina Štajerová, Milan Chytrý, Jiří Danihelka, John Kartesz, Jitka Klimešová, Magdalena Lučanová,10 Lenka Moravcová, Misako Nishino, Jiří Sádlo, Jan Suda, Lubomír Tichý, and Ingolf Kühn. 2015. Naturalization of central European plants in North America: species traits, habitats, propagule pressure, residence time. Ecology 96:762–774.

Appendix C. Detailed description of explanatory variables.

Unless specified otherwise, information on species biological traits was derived from CzechFlor, a working database of the Czech flora held at the Institute of Botany, Průhonice (see Pyšek et al. 2012 for details), and the database of biological and ecological traits of the flora of Germany, BiolFlor (Klotz et al. 2002). Biological traits used include: (1) life history: annual, monocarpic perennial herb, polycarpic perennial herb, shrub, tree; data available for 466 species; (2) life strategy, using the scheme of Grime, and distinguishing the three basic categories (competitive, ruderal and stress tolerant; Grime et al. 1988, Grime 2001); species with combined strategies were assigned to each of the respective categories (n = 456); (3) plant height, calculated as the mean from minimum and maximum height reported in the national flora (range 0.1–40 m; n = 465); (4) clonality, expressed as clonal index, a semiquantitative measure of how many offspring an individual produces per year and how far they spread laterally (Johansson et al. 2011); it is only relevant for clonal plants where it reaches values on a scale of 2–7, and the information does not exist for woody plants. We coded annual plants as 0 (= no vegetative propagation) and non-clonal perennials as 1. This information was taken from the CLOPLA database (see Klimešová and Klimeš 2006, 2008 for definition of categories; n = 416); (5) ploidy level refers to the number of complete chromosome sets; three categories were distinguished: diploid, polyploid, and diploidized polyploid (n = 466); (6) nuclear genome size (DNA amount), measured by two terms, holoploid genome size (1C = 0.16–76 × 10-12 g) and monoploid genome size (1Cx = 0.05–76 × 10-12 g; n = 296); (7) length of the flowering period, defined as the number of months over which the plant flowers in the native range (1–12; n = 466); (8) type of reproduction, reflecting the relative importance of seed reproduction on a semiquantitative scale (from 4, exclusively by seed, to 1, largely vegetatively; n = 466); (9) sex type, a combined measure based on self-compatibility (defined as the ability to produce viable zygotes after selfing) and dioecy/monoecy, resulting in whether one or two plants are needed for sexual reproduction; it only reflects generative reproduction, not vegetative propagation (n = 462); (10) pollen vector: insects, wind, selfing (n = 461); (11) number of pollen vectors, obtained by summing up the above-mentioned pollen vectors of one species (1–3); (12) propagule size is the length of the dispersal unit (seed or fruit; 0.2–45 mm; n = 446); (13) seed bank persistence, expressed as a seed longevity index (Bekker et al. 1998) and referring to the persistence of the soil seed bank; the reported records are coded as 0 for transient, 0.5 for short-term, and 1 for long-term persistent, and we used the range of these values, obtained from the LEDA database (Kleyer et al. 2008; n = 348); (14) dispersal vector describes the mode by which the generative propagules (seeds or fruits) are dispersed: ants, other animals (epizoochory, endozoochory), wind, water, and self, which considered together result in (15) the number of dispersal vectors (1–4; n = 461). Humans as a dispersal vector were excluded because this vector is assumed to be involved in all introductions of alien species by definition. Two physiological measures adopted, taken from LEDA (Kleyer et al. 2008) include (16) specific leaf area (SLA, 4.3–102.3 cm2g–1; n = 387), and (17) leaf dry matter content (LDMC, 63.0–438.8 mg2g–1; n = 357).

Geographic characteristics refer to the distribution in the native range and include: (1) Regional frequency in central Europe, expressed as the number of grid cells from which the species is reported in the Czech Republic and Germany (7–3652, n = 466), together covering a large part of central Europe. This system uses a grid of 10' (arc-minutes longitude) × 6' (latitude), which at 50°N is approximately 12.0 × 11.1 km or 133.2 km² (Schönfelder 1999). The data for the Czech Republic were taken from the Database of the Flora of the Czech Republic (, accessed in June 2012), with permission of the original data providers (Institute of Botany AS CR, Masaryk University and Czech Botanical Society). The data from Germany was taken from FLORKART (, as of 2003), the database of the Flora of Germany, maintained by the Federal Agency for Nature Conservation on behalf of the German Network for Phytodiversity (NetPhyD). As shown previously, species frequencies in the Czech Republic are closely correlated with those in temperate Europe (Pyšek et al. 2009a). (2) Number of habitats in which the species occurs in the Czech Republic out of 88 habitats recognized (Sádlo et al. 2007; 1–41, n = 466). Here, as well, species growing in many habitats and across a broad altitudinal range in the Czech Republic do so in the whole of central Europe (Pyšek et al. 2014). (3) Number of global floristic zones (1–9, n = 463) in which the species occurs in the whole of its native range are characteristic sequences of plant assemblages reflecting the climate zones from the poles to the equator; this variable represents a proxy for climatic versatility (taken from Klotz et al. 2002). (4) Altitudinal range (85–1485 m a.s.l.), derived from the range of altitudinal belts over which the species occurs in the Czech Republic (n = 465), is another proxy for climatic versatility. Altitudinal range for Germany was calculated by subtracting the mean altitude of the lowest grid cell from the mean altitude of the highest grid cell in which a species is reported. The altitudinal ranges, despite being derived using different procedures, are well correlated between the Czech Republic and Germany (r = 0.57, p < 0.001). (5) Cultivation in the native range reflects the intensity of planting in the Czech Republic using a semiquantitative scale from 0 to 3 (0, not planted; 1, planted for horticultural purposes in gardens, parks etc.; 2, planted in the wild outside gardens; 3, subject to breeding processes to enhance their performance, and planted in the wild (n = 466).

Finally, we collated information on drivers that may mediate the effect of the above mentioned variables on naturalization success in the invaded range: (1) year of introduction to North America, which made it possible to derive minimum residence time (with the term 'minimum' referring to it being inferred from the earliest known record; Rejmánek 2000) on this continent (by subtracting from 2010; 0–410 yrs, n = 444). Information on the year of the first record in the wild was extracted from primary botanical literature and other sources, including early floras and on-line herbaria (e.g., Gronovius 1743, John Clayton Herbarium), that were inspected for species' descriptions to confirm or correct, where possible, the identity of individual species alien to North America. Plant species names were validated and synonymized using relevant on-line databases (see Appendix D for information sources). (2) Cultivation in the invaded range, as a proxy for propagule pressure, based on BONAP data (Kartesz 2010) classifying species by whether they are (i) used in horticulture, (ii) economically important, or (iii) used by humans for other purposes; from this information a scale (0–3) was derived (n = 466).


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