OPCE-STR.vp Acta Bot. Croat. 69 (2), 215–227, 2010 CODEN: ABCRA 25 ISSN 0365–0588 Synanthropic vegetation: pattern of various disturbances on life history traits URBAN [ILC Institute of Biology, Scientific research centre of the Slovenian Academy of Sciences and Arts, Novi trg 2, 1000 Ljubljana, Slovenia Anthropogeneous vegetation was correlated to disturbance type. The large relevé dataset (2404 relevés) was divided according to different locations (arable land, semi-natural land, settlement) used as surrogates for disturbance types differing in areal extent, regular- ity, predictability and frequency. Using multivariate methods we detected main gradients in species composition and correlated them to plant traits. Plants in arable land are mainly annuals, therophytes and alien species. Species comprising ruderal habitats are richer in perennials and C strategists. The latter habitats were further divided into semi-natural sites and settlements. Phanerophytes and C strategists are more common in semi-natural vegetation and R strategists and archeophytes in settlements. Differences in village and town vegetation are observed in alien species that are more frequent in towns and on sites that are warmer and lighter. Keywords: Vegetation, ruderal, segetal, disturbance, Slovenia Introduction Anthropogeneous vegetation is by definition a product of human influence. Anthropo- genic pressure can be understood as a disturbance that differs according to areal extent, magnitude (intensity), frequency, predictability and turnover rate (SOUSA 1984). Distur- bance alters the site and recolonization and succession of open space will appear. Human activities are reflected in different vegetation types that thrive in man-made habitats. Synanthropic vegetation can be generally divided into two broad types: weed and ruderal vegetation (MUCINA et al. 1993, LOSOSOVÁ et al. 2006). Weed vegetation is found on arable land and ruderal vegetation is found in settlements, waste deposits, along transporta- tion routes, but also in semi-natural landscape (according to WESTHOFF 1983) comprising disturbed river shores and woodland fringes. Major differences in species composition are the product of different disturbance regimes and the life histories of plant species that oc- cupy these disturbed habitats. With greater disturbance (especially human activity) a land- scape becomes a mosaic of ecosystem patches with sharper boundaries (FORMAN and GODRON 1981) and sharper differences in ecological conditions and floristic composition. ACTA BOT. CROAT. 69 (2), 2010 215 * Corresponding author, e-mail: urban@zrc-sazu.si U:\ACTA BOTANICA\Acta-Botan 2-10\318 Urban.vp 11. listopad 2010 12:45:01 Color profile: Disabled Composite 150 lpi at 45 degrees Arable land is regularly disturbed at least once a year. Agrotechnical measures (plow- ing, tilling, harvesting) are highly predictable and of the intensive disturbance type (Fig. 1). The areal extent of disturbance is large and ecological conditions within large fields are uniform. Semi-natural habitats are small scale and the magnitude of human activity is rather low. They are less frequently disturbed (once in a few years) and predictability is low. Settlements are a synonym for human activity, although there are differences between village and town environments. The sites of these plant communities are generally small. Intensity of disturbance depends on the level of urbanization, where human density could be used as a surrogate. Usually it is higher in towns. Frequency of disturbance is high (again higher in urban settlements), but predictability is uncertain. These land use types that are the product of mostly human activities show differences in species composition since plant traits are filtered by different environmental conditions (ZOBEL 1997, KNAPP et al. 2008). The aim of our study was to analyze a large dataset of synanthropic vegetation and de- tect differences in species composition and plant traits of different types of vegetation of man-made habitats and to correlate these differences to different disturbance regimes. Materials We have collected a dataset of 2404 vegetation relevés of anthropogeneous vegetation from Slovenia stored in Slovenian phytosociological database ([ILC 2006). Relevés were selected according to the original author’s assignment to the synanthropic vegetation classes (Polygono-Poetea, Stellarietea medie, Artemisietea, Galio-Urticetea) (Fig. 2, Tab. 1). Using outlier analysis in the PC-ORD 5 software (MCCUNE and GRACE 2002) we have eliminated one plot deviating more than 3SD in floristic composition. To avoid over- sampling we divided the territory of Slovenia into grid squares (1.25 longitudinal and 0.75 latitudinal minutes) and performed stratified re-sampling. If more than one relevé of the same syntaxon and date were recorded in the same grid square we randomly selected only one. This procedure yielded a matrix of 1537 relevés x 461 species that was used in further analyses. 216 ACTA BOT. CROAT. 69 (2), 2010 [ILC U. Fig. 1. Schematic representation of dichotomous division of synanthropic vegetation according to disturbance type. U:\ACTA BOTANICA\Acta-Botan 2-10\318 Urban.vp 11. listopad 2010 12:45:02 Color profile: Disabled Composite 150 lpi at 45 degrees Explanatory variables For each vegetation plot a set of variables that are supposed to affect species composi- tion was compiled. Mean annual temperature, mean annual amount of precipitation, and al- titude were collected from plot locations and climatic maps (MEKINDA-MAJARON 1995, ZUPAN^I^ 1995) as layers in the Arc Gis 9.2 programme. Each plot was also categorized ac- cording to the location (given by the author) where the relevé was made: arable fields (two subsets – root crops and cereals), settlement (two subsets – town and village; 1000 inhabit- ants was the limit) and semi-natural. Location is a surrogate of disturbance type and further in the text we use the term disturbance type. Plant traits Plant traits from the Biolflor (KLOTZ et al. 2002) database were used to characterize spe- cies. Life span, life form, life strategy and residence time of alien species were used. To evaluate habitat characteristics ecological indicator values (ELLENBERG et al. 1992) were used. ACTA BOT. CROAT. 69 (2), 2010 217 SYNANTHROPIC VEGETATION Fig. 2. Distribution of relevés of synanthropic vegetation in Slovenia with indicated phytogeographical regions. Tab. 1. Classification of relevés used in the analysis into vegetation classes according to the location (disturbance) type and original author’s assignment. No. of relevés Settlement Arable land Semi-natural Polygono-Poetea 135 135 0 0 Stellarietea mediae 670 233 435 2 Artemisietea 306 268 16 22 Galio-Urticetea 426 321 0 105 U:\ACTA BOTANICA\Acta-Botan 2-10\318 Urban.vp 11. listopad 2010 12:45:06 Color profile: Disabled Composite 150 lpi at 45 degrees Subsets We have divided the dataset into three subsets according to the location where vegeta- tion plots were recorded and the type of disturbance that corresponds to that location. First analyses were made with the whole dataset. Then we divided the dataset into segetal and ruderal. Additionally, the ruderal subset was subdivided into semi-natural and settlement subsets. The latter was partitioned into town and village subsets. Subsets were analyzed with the same statistical procedure as described for the whole dataset. Methods The general pattern of variation in synanthropic vegetation was detected by using detrended correspondence analysis (DCA) in CANOCO 4.5 software package (TER BRAAK and [MILAUER 2002). As a long gradient (5.198 SD) was stated, we decided to use unimodal methods in further analyses (DCA, CCA) (LEP[ and [MILAUER 2003). To evaluate the im- portance of explanatory variables on species composition canonical correspondence analy- sis (CCA) was used with the Monte Carlo test with 999 permutations. DCA analysis was used to visualize the variation in samples and explanatory variables that are passively pro- jected. Partial detrended correspondence analysis (pDCA) was performed to present spe- cies variation and passively projected locations (presenting disturbance type) of vegetation plots. 218 ACTA BOT. CROAT. 69 (2), 2010 [ILC U. Fig. 3. Detrended correspondence analysis (DCA) ordination of samples (dots) with passively projected explanatory variables. Triangles represent nominal variables. U:\ACTA BOTANICA\Acta-Botan 2-10\318 Urban.vp 11. listopad 2010 12:45:10 Color profile: Disabled Composite 150 lpi at 45 degrees Partial canonical correspondence analysis (pCCA) was used to obtain species scores according to the disturbance type, while the influence of other explanatory variables was partialled out. Location was used as an only explanatory variable, while other variables were used as covariables in the analysis. This procedure was used on the entire dataset (segetal vs. ruderal) and further on the subsets (semi-natural vs. settlement and town vs. village). A method combining the net effects of variables from pCCA and logistic regression (LOSOSOVÁ et al. 2004, 2006) was used to identify the correlation between plant traits and disturbance type of vegetation plot. Species scores on the first axis from pCCA of distur- bance type as a single explanatory variable, and plant traits were used in logistic regression. Species scores were the independent and plant traits (as presence/absence of a single trait) ACTA BOT. CROAT. 69 (2), 2010 219 SYNANTHROPIC VEGETATION -1 5 0 6 Malvneg Planmaj Poa ann6 Urtidio Chenalb Polyper Polyare Echicru Galipar Lamimac Rumeobt Dactglo Erigann Taraoff Loliper Dauccar Ranurep Setapum Achimil Aegopod Capsbur Convarv Stelmed Veroper Digisan Elytrep Lamipur Trifrep Calysep Poa tri Rubucae Artevul Galiapa Cirsarv Anthsyl Silelat Polyavi Violarv Arable Semi-natural Settlement Fig. 4. Partial detrended correspondence analysis (pDCA) of species and passively projected dis- turbance types. Other variables were used as covariables. Species abbreviations: Achi- mil-Achilea millefolium, Aegpod-Aegopodium podagraria, Anthsyl-Anthriscus sylvestris, Artevul-Artemisia vulgaris, Calysep-Calystegia sepium, Capsbur-Capsella bursa pastoris, Chenalb-Chenopodium album, Cirsarv-Cirsium arvensis, Dactglo-Dactylis glomerata, Dauccar-Daucus carota, Digisan-Digitaria sanguinalis, Echicru-Echinochloa crus-galli, Elytrep-Elytrigia repens, Erigann-Erigeron annuus, Galiapa-Galium aparine, Galipar-Ga- linsoga parviflora, Lamimac-Lamium maculatum, Lamipur-Lamium purpureum, Loliper- -Lolium perenne, Malneg-Malva neglecta, Polyper-Polygonum persicaria, Planmaj-Plantago major, Poaann-Poa annua, Polyare-Polygonum arenastrum, Polyavi-Polygonum aviculare, Ranurep-Ranunculus repens, Rubucae-Rubus caesius, Rumeobt-Rumex obtusifolius, Sile- lat-Silene latifolia, Stelmed-Stellaria media, Taraoff-Taraxacum officinale, Trifrep-Tri- folium perenne, Urtidio-Urtica dioica, Veroper-Veronica persica, Violarv-Viola arvensis. U:\ACTA BOTANICA\Acta-Botan 2-10\318 Urban.vp 11. listopad 2010 12:45:10 Color profile: Disabled Composite 150 lpi at 45 degrees dependent variable in analysis. For Ellenberg indicator values for particular species and their scores on the first pCCA axis we performed linear least-square regression. Regression analyses were performed by Statistica 8.0 (STATSOFT 2007). Results DCA analysis with passively projected explanatory variables shows their importance for species composition (Fig. 3). Disturbance type has less effect on species composition than climatic variables and year of sampling. Disturbance type correlates to the first axis. The eigenvalue of axis 1 is 0.607 and of axis 2 0.363, respectively. 220 ACTA BOT. CROAT. 69 (2), 2010 [ILC U. Tab. 2. Relationships between life history plant traits and Ellenberg indicator values and different habitat types. The negative sign is correlated with the first variable. *p < 0.01, ** p < 0.05. Segetal vs. ruderal Seminatural vs. settlement Town vs. village Estimate P Estimate P Estimate P Life span Annuals –1.283 ** 0.702 ** –0.767 ** Biannuals 0.152 0.524 * 0.220 Perennials 1.124 ** –0.562 ** 0.608 ** Alien status Neophytes –0.360 * –0.210 –0.892 ** Archaeophytes –0.855 ** 1.542 ** –0.527 * Life form T –0.080 ** 0.637 ** –0.748 ** G 0.056 –0.282 0.595 * H 0.232 * 0.322 * 0.439 ** C 1.585 ** –0.382 –0.326 ** P 2.336 ** –0.610 * 0.147 Strategy c 0.957 ** –0.331 * 0.399 ** cr –0.554 ** 0.563 ** –0.418 * cs 1.094 ** –0.664 ** 0.444 csr 0.337 * 0.444 * 0.298 r –0.828 ** 0.906 ** –0.748 ** sr –0.551 * 1.080 –1.692 s not enough variables –1.138 –0.197 Ellenberg indicator values Light 0.009 –0.128 * 0.196 * Temperature 0.268 ** –0.084 0.313 ** Continentality –0.016 0.021 0.143 Moisture –0.178 ** 0.355 ** –0.301 ** Reaction –0.264 ** 0.076 0.082 Nutrients –0.091 –0.056 0.050 U:\ACTA BOTANICA\Acta-Botan 2-10\318 Urban.vp 11. listopad 2010 12:45:10 Color profile: Disabled Composite 150 lpi at 45 degrees The results of pCCA revealed that the most important factor in the whole dataset is the location of the vegetation plot, i.e. the disturbance type. The importance of other variables is lower, they follow in the following order: precipitation, temperature, year of sampling and altitude. All variables are significant at p<0.001. The influence of disturbance type (segetal vs. ruderal) after partialling out the effects of other explanatory variables is shown on the pDCA graph (Fig. 4). Plant life history traits show significant differences between segetal and ruderal vegeta- tion (Tab. 2). Weed vegetation is composed of annuals, therophytes and R-strategists (and correlated CR and SR strategy). Notably, segetal vegetation is richer in archeophytes and neophytes. Species are thermophilous. In ruderal vegetation perennial species are more common, mostly phanerophytes, chamephytes and hemicriptophytes. They have C-strat- egy and related CS and CSR strategy. They tend to thrive on moist sites and are basiphilous. Species characteristic of segetal and ruderal habitats are presented in table 3. There is an evident disproportion in favor of species typical of arable land and especially cereal fields. Fifty species were determined with highest fit and species scores on the first axis of pCCA with disturbance type of the vegetation plot as the only explanatory variable (Tab. 3). Differences between semi-natural and settlement vegetation in life history traits show that in settlements there are annuals and biennials, archeophytes, therophytes and hemi- cryptophytes. Their strategy is ruderal (R-strategy and also CR and CSR). Plants in settle- ments are heliophilous. On the other hand, perennials and phanerophytes are more com- mon in semi-natural vegetation and have a C-strategy. Habitats in semi-natural land are more humid. If we compare village and town, vegetation in towns is composed of annual species; therophytes and chamephytes are more common. Alien species (archeophytes and neo- phytes) are more frequent, and the strategy is ruderal (R and CR). Species of vegetation in towns are more heliophilous and thermophilous whereas village vegetation has more perennials, hemicryptophytes and geophytes, which are C-strategists. The habitat is wetter. Discussion Our aim was to detect differences in species composition and life history traits in anthropogenous vegetation related to disturbance. According to our previous knowledge we made a hypothesis that the primary division is between arable and ruderal habitats. The latter have different disturbance regimes and can be further divided into semi-natural land and habitats in settlements. According to the number of inhabitants and related urbaniza- tion we can further divide this type of vegetation into village and town habitats. Differentiation of weed and ruderal vegetation in the narrower sense is obvious. Distur- bance in segetal vegetation is regular and uniform in large areas (LOSOSOVÁ et al. 2006), while in ruderal habitats it varies in all characteristics mentioned above (SOUSA 1984) thus resulting in patchy vegetation. The mosaic of vegetation types is composed of temporally and spatially differentiated patches. ACTA BOT. CROAT. 69 (2), 2010 221 SYNANTHROPIC VEGETATION U:\ACTA BOTANICA\Acta-Botan 2-10\318 Urban.vp 11. listopad 2010 12:45:10 Color profile: Disabled Composite 150 lpi at 45 degrees 222 A C T A B O T .C R O A T .69 (2),2010 [ IL C U . Tab. 3. Fifty species with highest fit and species scores on the first axis of pCCA with disturbance type of the vegetation plot as the only explanatory variable. Segetal vs. Ruderal Ax1 score Fit Semi-natural vs. Settlement Ax1 score Fit Town vs. Village Ax1 score Fit Valerianella locusta 2.67 0.071 Carex acutiformis 2.66 0.021 Viola odorata 2.14 0.011 Buglossoides arvensis 2.40 0.043 Populus alba 2.64 0.016 Veronica cymbalaria 1.94 0.008 Sherardia arvensis 2.09 0.058 Galega officinalis 2.53 0.023 Euphorbia peplus 1.81 0.010 Legousia speculum-veneris 2.03 0.130 Iberis amara 2.52 0.018 Catapodium rigidum 1.78 0.009 Ranunculus arvensis 2.01 0.056 Populus nigra 2.44 0.027 Eragrostis minor 1.73 0.020 Centaurea cyanus 1.93 0.076 Antirrhinum majus 2.42 0.033 Trifolium hybridum 1.72 0.008 Anthemis arvensis 1.86 0.135 Impatiens glandulifera 2.17 0.125 Euphorbia lathyris 1.69 0.011 Aphanes arvensis 1.83 0.195 Verbascum austriacum 2.12 0.055 Euphorbia maculata 1.61 0.007 Vicia angustifolia 1.82 0.078 Rudbeckia laciniata 2.01 0.081 Verbena officinalis 1.55 0.018 Vicia hirsuta 1.75 0.076 Echinops exaltatus 1.93 0.097 Chenopodium hybridum 1.53 0.010 Apera spica-venti 1.68 0.078 Salix purpurea 1.91 0.055 Solidago canadensis 1.53 0.022 Veronica hederifolia 1.65 0.053 Cerastium sylvaticum 1.85 0.030 Conyza bonariensis 1.31 0.007 Myosotis scorpioides 1.65 0.217 Erucastrum gallicum 1.91 0.025 Carduus acanthoides 1.31 0.018 Raphanus raphanistrum 1.64 0.069 Euphorbia stricta 1.77 0.016 Hordeum leporinum 1.24 0.008 Papaver rhoeas 1.64 0.180 Helianthus tuberosus 1.83 0.057 Galinsoga ciliata 1.26 0.015 Viola arvensis 1.54 0.251 Barbarea vulgaris 1.64 0.038 Portulaca oleracea 1.23 0.009 Mentha arvensis 1.43 0.107 Galeopsis speciosa 1.52 0.072 Panicum capillare 1.20 0.009 Euphorbia helioscopia 1.41 0.111 Epilobium hirsutum 1.38 0.031 Raphanus raphanistrum 1.18 0.009 Arenaria serpyllifolia 1.41 0.071 Scrophularia canina 1.45 0.031 Verbascum nigrum 1.18 0.011 Polygonum lapathifolium 1.35 0.097 Peucedanum verticillare 1.37 0.020 Mercurialis annua 1.15 0.010 Lamium purpureum 1.26 0.135 Phalaris arundinacea 1.36 0.048 Oenothera biennis 1.08 0.012 Stachys palustris 1.24 0.064 Senecio ovatus 1.32 0.019 Tripleurospermum inodorum 0.92 0.014 Amaranthus hybridus agg. 1.23 0.044 Saponaria officinalis 1.21 0.050 Microrrhinum minus 0.79 0.012 Chenopodium polyspermum 1.23 0.106 Myosoton aquaticum 1.25 0.135 Saponaria officinalis 0.84 0.010 Matricaria chamomilla 1.22 0.072 Solidago gigantea 1.17 0.054 Hedera helix 0.76 0.009 U : \ A C T A B O T A N I C A \ A c t a - B o t a n 2 - 1 0 \ 3 1 8 U r b a n . v p 1 1 . l i s t o p a d 2 0 1 0 1 2 : 4 5 : 1 0 C o l o r p r o f i l e : D i s a b l e d C o m p o s i t e 1 5 0 l p i a t 4 5 d e g r e e s A C T A B O T .C R O A T .69 (2),2010 223 S Y N A N T H R O P IC V E G E T A T IO N Tab. 3. – continued Segetal vs. Ruderal Ax1 score Fit Semi-natural vs. Settlement Ax1 score Fit Town vs. Village Ax1 score Fit Veronica arvensis 1.21 0.081 Fallopia dumetorum 1.16 0.032 Polygonum lapathifolium 0.71 0.010 Echinochloa crus-galli 1.19 0.101 Poa palustris 1.07 0.028 Galeopsis tetrahit 0.68 0.008 Amaranthus retroflexus 1.17 0.081 Petasites hybridus 1.00 0.054 Diplotaxis tenuifolia 0.59 0.016 Cerastium glomeratum 1.16 0.097 Humulus lupulus 0.99 0.054 Setaria viridis 0.57 0.010 Oxalis fontana 1.08 0.083 Filipendula ulmaria 0.92 0.024 Hordeum murinum 0.56 0.008 Anagallis arvensis 1.06 0.067 Deschampsia cespitosa 0.85 0.019 Lactuca serriola 0.50 0.016 Veronica persica 1.06 0.131 Lysimachia nummularia 0.88 0.017 Oxalis fontana 0.52 0.008 Setaria pumila 1.00 0.075 Chaerophyllum hirsutum 0.79 0.018 Conyza canadensis 0.46 0.018 Galinsoga parviflora 0.99 0.060 Cuscuta europaea 0.75 0.028 Sonchus oleraceus 0.41 0.012 Stellaria media 0.99 0.127 Angelica sylvestris 0.76 0.040 Picris hieracioides 0.41 0.016 Fallopia convolvulus 0.94 0.077 Symphytum officinale 0.71 0.032 Artemisia vulgaris 0.28 0.020 Chenopodium album agg. 0.81 0.118 Cirsium oleraceum 0.58 0.032 Medicago lupulina 0.25 0.010 Convolvulus arvensis 0.81 0.113 Eupatorium cannabinum 0.68 0.045 Erigeron annuus 0.27 0.019 Polygonum persicaria 0.80 0.066 Polygala comosa 0.55 0.016 Dactylis glomerata agg. –0.12 0.009 Cirsium arvense 0.69 0.086 Vicia cracca 0.46 0.031 Poa trivialis –0.14 0.008 Capsella bursa-pastoris 0.63 0.082 Rubus caesius 0.33 0.021 Urtica dioica –0.14 0.012 Urtica dioica –0.68 0.092 Calystegia sepium 0.32 0.029 Galium aparine –0.20 0.008 Arrhenatherum elatius –0.69 0.042 Taraxacum officinale agg. –0.22 0.030 Lamium maculatum –0.21 0.014 Dactylis glomerata agg. –0.71 0.117 Plantago major –0.30 0.019 Veronica chamaedrys –0.21 0.010 Heracleum sphondylium –0.73 0.054 Lolium perenne –0.31 0.019 Galium album –0.22 0.012 Veronica chamaedrys –0.74 0.045 Cichorium intybus –0.32 0.019 Stachys sylvatica –0.34 0.009 Artemisia vulgaris –0.76 0.067 Trifolium repens –0.33 0.020 Scrophularia nodosa –0.36 0.010 Lamium maculatum –0.77 0.074 Capsella bursa-pastoris –0.34 0.024 Pimpinella major –0.45 0.010 Rubus caesius –0.79 0.047 Convolvulus arvensis –0.35 0.016 Sorghum halepense –0.98 0.007 Galium album –0.82 0.059 Poa annua –0.36 0.021 Petasites paradoxus –1.71 0.009 U : \ A C T A B O T A N I C A \ A c t a - B o t a n 2 - 1 0 \ 3 1 8 U r b a n . v p 1 1 . l i s t o p a d 2 0 1 0 1 2 : 4 5 : 1 0 C o l o r p r o f i l e : D i s a b l e d C o m p o s i t e 1 5 0 l p i a t 4 5 d e g r e e s Life span Vegetation of arable fields harbors mainly annual species (SUTHERLAND 2004), as they are best adapted to regular disturbance (plowing, harvesting). Other ruderal types have a higher proportion of perennials, as there are habitats that are less frequently disturbed and are succesionally more developed. This is particularly evident for semi-natural vegetation and vegetation of villages. The occurrence of more annuals in towns could be explained by intensive and irregular disturbances (KNAPP et al. 2008) but also by ecological conditions. Drought in sealed urbanized soils could be as severe as disturbance is for plant species (HILL et al. 2002). Life form Therophytes are most common in arable land as they take advantage of disturbance, i.e. disturbance of the soil (MCINTYRE and LAVOREL 1995). Chamaephytes and phanerophytes are less adapted to regular disturbance because they cannot complete their life cycle. In semi-natural land and settlement this division is not so clear except for therophytes, as in urban areas disturbance is more intense. Phanerophytes are more common in semi-natural vegetation as they thrive in fringe vegetation and on shores of water bodies with less fre- quent disturbance. Therefore successionally more developed communities are able to evolve. Anthropogeneous communities in semi-natural landscape are usually in contact with natural communities that are a source of perennials. More therophytes in towns than villages have already been reported (SUKOPP and WERNER 1983, PY[EK and PY[EK 1990). The high proportion of chamaephytes (for example, Sagina procumbens, Silene vulgaris, Chenopodium ambrosioides) in towns is rather sur- prising, but they can also be found in trampled communities with low soil disturbance. Invasion status The high proportion of alien species (archaeophytes and neophytes) in disturbed habi- tats is consistent with several papers (KOWARIK 1995, HILL et al. 2002, LOSOSOVÁ et al 2006). But in other studies the pattern is different: more archaeophytes in arable land and more neophytes in settlements (LOSOSOVÁ et al 2006). In our case we found a higher pro- portion of both types of alien species in the arable land. Our dataset consists of all types of ruderal vegetation (annual and perennial) and this could be the reason for differences with the reported results. Representation of archaeophytes and neophytes may vary considerably between different habitats (LOSOSOVÁ et al. 2006), and the mosaic structure of some land- scapes shows varying human impact with differently disturbed areas (KOWARIK 1995). Comparing semi-natural vegetation and settlements, archaeophytes are more common in the latter, while proportions of alien species are higher in towns. Strategy Ruderal strategy is most common in arable land, while other ruderal communities in this dichotomous division are richer in competitors. Disturbance is frequent and regular and resources are abundant in arable fields. Ruderal vegetation is less intensively or infre- quently disturbed and is invaded by species from natural vegetation. These species are mostly perennial herbs that exhibit CSR strategy with the widest range of strategies (GRIME 2002). 224 ACTA BOT. CROAT. 69 (2), 2010 [ILC U. U:\ACTA BOTANICA\Acta-Botan 2-10\318 Urban.vp 11. listopad 2010 12:45:10 Color profile: Disabled Composite 150 lpi at 45 degrees The strategy of plants in a semi-natural habitat (C and CS) shows that the habitat is rela- tively undisturbed (compared to other anthropogeneous habitats) and it is mainly competi- tion that influences species composition. The vegetation of settlements is composed of ruderal strategists, indicating that disturbance is the main gradient. Intensity and frequency of human disturbance decrease along this coenocline from trampled habitats towards ruderals in the narrower sense (MUCINA 1989). Differences in disturbance between town and village flora again favor ruderal strategists in towns. Ecological conditions and perma- nent disturbances in urban landscapes are factors to which R strategists are best adapted (SUKOPP and WERNER 1983, BENVENUTI 2004, LOSOSOVÁ et. al. 2006). Habitat preferences and species Ruderal habitats are more shaded and humid than arable land, but only when we com- pare the whole ruderal dataset. Generally, moist habitats are found in semi-natural land- scapes, while urban habitats are drier and warmer (LOSOSOVÁ et al. 2006). In this study, dif- ferences between cereals and root crops were not tested, as this has been done in previous studies ([ILC 2008, [ILC et al. 2009). But segetal species with the highest fit (Table 2) are mostly from cereal fields indicating that weeds of root crops are less specialized and are found also in other ruderal habitats. This could be explained by similar disturbance types in root crops and in settlements. Other reasons for floristic similarity could be differences in seasonal aspect (PINKE et al. 2009) as ruderal communities and root crops are generally best developed in summer and autumn. Species in towns are more light- and warmth-demanding, while in villages they thrive in more humid habitats. We found more C4 plants in towns (e.g. Eragrostis minor, Euphorbia maculata) that are indicators of an environment more suitable to thermophilous species (HÜGIN 1999). We confirmed the heat island effect in urban settlements (SUKOPP and WERNER 1983), although it was not found in a similar study by LOSOSOVÁ et al. (2006). However, their dataset consisted only of annual anthropogeneous vegetation. Acknowledgements I would like to thank A. ^arni for comments in previous versions of the manuscript. The English was revised by A. McConnell-Duff. This work was supported by a grant from the Slovenian Research Agency ARRS P1-0236. 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