Regional assessment of plant invasions across different habitat types Vilà, Montserrat1*; Pino, Joan

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I - Regularly or recently cultivated agricultural, horticultural and domestic habitats

I1 - Arable land and market gardens 18.15 <0.0001 0.08 397 -

date of relevés considered in this study ranged from 1926 to 2003 with 1993 as the mode. There was no correlation between date of publication and number of alien species (r²= 3.5 × 10^–4).

There was a large variation in plot size both between and within habitats; Plot size accounted for species com- position and diagnostic species, and were representative of differences in size and abundance of species (Fig.

2). There were signiﬁcant differences in mean plot size between ﬁrst order EUNIS habitat classes (F _7,₁₂₂₅₄=

^{680.59, p < 0.0001); inland surface water habitats (C)}

^{had the smallest and woodland habitats (G) the largest}

^{plots. However, mean plot sizes within habitats agreed}

^{with European standards (Chytrý & Otýpková 2003).}

Data analysis
We tested if the number of alien and native species was signiﬁcantly different between habitats by a General Linear/Non-linear Model (Anon. 1999) with a logarith- mic link function and a Poisson error distribution. Due to the large number of post-hoc multiple tests, pair-wise differences between habitats were corrected with the Bonferroni test (Cabin & Mitchell 2000).

Native and alien species richness relationships were investigated at two scales: among habitats and within habitats. In the analysis among habitats the sample units were the mean number of species per plot for each habitat. In contrast, in the analysis within habitats each plot was a sample unit.

Table 2. Correspondence of the EUNIS habitats with the syntaxonomic alliances originally identifying the relevés. Syntaxonomical nomenclature follows Bolòs & Vigo (1984) and Rivas-Martínez et al. (2001). See Table 1 for description of habitat types.

EUNIS	Alliance	EUNIS	Alliance	EUNIS	Alliance
^B1	Alkanno-Malcolmion parviﬂorae	^E4	Arabidion coeruleae	^F6	Gypsophilion hispanicae
	Ammophilion arundinaceae		Elymion medioeuropaeum		Lepidion subulati
	Crucianellion maritimae		Festucion eskiae		Rosmarino-Ericion
	Saginion maritimae		Festucion gautieri		Thymo longiﬂori-Siderition leucanthae
^B3	Crithmo-Limonion		Festucion scopariae		Thymo-Teucrion verticillati
	Medicagini-Lavaterion arboreae		Festucion supinae	^F7	Genistion lobelii
^C1	Isoetion		Laserpitio-Ranunculion thorae	^F9.1	Salicion pentandrae
	Lemnion minoris		Nardion strictae		Salicion triandro-fragilis
	Littorellion uniﬂorae		Primulion intricatae	^F9.3	Rubo ulmifolii-Nerion oleandri
	Potamion pectinatae		Salicion herbaceae		Tamaricion africanae
	Ruppion maritimae	^E5.2	Aegopodion podagrariae	^G1	Alno-Padion
^C2	Callitricho-Batrachion		Atropion belladonnae		Alno-Ulmion
	Cardamino-Montion		Bromo ramosi-Eupatorion cannabini		Fagion sylvaticae
	Cratoneurion commutati		Epilobion angustifolii		Fraxino-Carpinion
	Potamogetonion eurosibiricum		Geranion sanguinei		Populion albae
C3	Glycerio-Sparganion		Trifolion medii		Quercion pubescenti-petraeae
	Magnocaricion elatae	^E5.5	Adenostylion alliariae		Quercion robori-petraeae
	Phragmition australis		Arction lappae		Tilio-Acerion
^D1	Oxycocco-Ericion tetralicis	^E5.6	Bidention tripartitae	^G2	Quercion ilicis
^D2	Caricion nigrae		Bromo-Oryzopsion miliaceae	^G3	Abieti-Piceion
^D4	Caricion davallianae		Carrichtero-Amberboion		Deschampsio-Pinion
^D6	Juncion maritimi		Chenopodion muralis		Pino-Juniperion sabinae
^E1	Aegilopion		Convolvulion sepium	^H2	Androsacion alpinae
	Agropyro-Lygeion		Dauco-Melilotion		Andryalo-Glaucion
	Alysso-Sedion		Euphorbion peplis		Calamagrostion arundinaceae
	Aphyllanthion		Galio-Alliarion		Cystopteridion
	Brachypodion phoenicoidis		Glaucio-Cakilion		Galeopsion pyrenaicae
	Corynephorion canescentis		Hordeion leporini		Glaucion ﬂavi
	Helianthemion guttati		Onopordion acanthii		Iberidion spathulatae
	Mesobromion erecti		Onopordion arabici		Pimpinello-Gouffeion
	Ononidion striatae		Rumicion alpini		Scrophularion sciaphilae
	Phlomidio-Brachypodion retusi		Salsolo-Peganion		Senecion leucophylli
	Saturejo-Hyparrhenion hirtae		Silybo-Urticion		Stipion calamagrostis
	Sedo-Scleranthion		Sisymbrion ofﬁcinalis	^H3	Adiantion capilli-veneris
	Stipion capensis	^E6	Arthrocnemion fruticosi		Androsacion vandellii
	Taeniathero-Aegilopion geniculatae		Limoniastrion monopetali		Anomodontion europaeum
	Thero-Airion		Limonion galloprovincialis		Antirrhinion asarinae
	Thero-Brachypodion		Plantaginion crassifoliae		Asplenion petrarchae
	Tuberarion guttatae		Suaedion braun-blanquetii		Bartramio-Polypodion australis
	Xerobromion erecti		Suaedion brevifoliae		Homalothecio-Polypodion serrulati
^E2	Agrostion stoloniferae		Thero-Salicornion		Hypno-Polypodion vulgaris
	Arrhenatherion elatioris		Thero-Suaedion		Parietario-Centranthion rubri
	Cynosurion cristati	^F2	Juniperion nanae		Phagnalo-Cheilanthion fragrantis
	Deschampsion mediae		Loiseleurio-Vaccinion		Saxifragion mediae
	Violion cornutae		Rhododendro-Vaccinion	^H5.6	Agropyro-Rumicion crispi
^E3	Calthion palustris	F3	Berberidion vulgaris		Echio-Galactition
	Imperato-Erianthion		Genistion purgantis		Polygonion avicularis
	Isoetion		Pruno-Rubion ulmifolii		Trifolio-Cynodontion
	Juncion acutiﬂori		Rubion subatlanticum	^I1	Caucalidion platycarpae
	Lythrion tribracteati		Sambuco-Salicion capreae		Diplotaxion erucoidis
	Molinio-Holoschoenion vulgaris		Sarothamnion scoparii		Panico-Setarion
	Molinion coeruleae		Ulici-Ericion ciliaris		Polygono-Chenopodion polyspermi
	Nanocyperion ﬂavescentis	^F4	Calluno-Genistion		Scleranthion annui
	Paspalo-Polypogonion semiverticillati	^F5	Cistion laurifolii		Secalion mediterraneum
			Cistion mediomediterraneum
			Oleo-Ceratonion

Because in general it has been observed and modelled that the association between native and alien species richness is scale-dependent with negative relationships in small plots and positive relationships in large plots (Shea & Chesson 2002; Fridley et al. 2004; Sax & Gaines

2003) the correlation between alien and native species was tested once the effect of area has been accounted for

by a multiple regression analysis of the form: number of alien species = area + number of native species. In the analysis among habitats we also compared if the habitats with positive, negative or non-signiﬁcant relationships differed in plot size by a Kruskall-Wallis test (Herben et al. 2004).

Results
The number of alien species per relevé was 0.29 ±

^{0.006 (mean ± SE) ranging from 0 to 12 species per plot}

^{and representing 1.95 ± 0.05 % of the total number of}

^{species per relevé. The occurrence of alien species (i.e.}

^{percentage of plots with aliens) within a certain habitat}

^{type was also low (16.79 ± 3.24 %). Among all invaded}

^{habitats, there was a positive relationship between the}

^{degree of occurrence in a habitat and mean alien rich-}

^{ness in this habitat (number of alien species = 0.02×,}

^{occurrence –0.089,}^r²⁼^0.869)^but^not^with^mean^native

^{species richness (Number of native species = – 0.72×,}

^occurrence^+19.31,^r²⁼^0.035).

^{Of the inventoried habitats, the following never had}

^{aliens: surface running waters (C2), raised and blanket}

^{bogs (D1), valley mires, poor fens and transition mires}

^{(D2), base-rich fens (D4), alpine and sub-alpine grasslands}

^{(E4), sub-alpine moist or wet tall-herb and fern habitats}

^{(E5.5), alpine and sub-alpine scrub habitats (F2) and spiny}

^{Mediterranean heaths (F7) (Fig. 3). We are conﬁdent that}

^{this lack of aliens was not related to the sampling effort}

^{because the number of relevés in habitats without aliens}

^{was not under-represented compared to habitats with}

^{aliens (mean ± SE, 314 ± 151.08 and 547.62 ± 116.07,}

^{respectively, t-test = 1.06, p = 0.297).}

^{Of the 24 EUNIS habitat types that were invaded}

^{there were signiﬁcant differences in alien species richness}

^among^habitats⁽^χ²⁼^8959.09,^p^<^0.0001).^The^habitats

^{with the highest alien richness were arable land and gar-}

^{dens (I1) followed by anthropogenic forb-rich habitats}

^{(E5.6), riverine and lakeshore scrubs (F9.1), southern}

^{riparian galleries and thickets (F9.3) and trampled areas}

^{(H5.6) (Fig. 3). Differences among habitats in the per-}

^{centage of alien species followed the same pattern (Fig.}

^4).

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