SIZE AREA, PATCh hETEROGENEITy AND PLANT SPECIES ...

Vie et milieu - Life and environment, 2012, 62 (4): 165-171

Size area, patch heterogeneity and plant species richness across archaeological sites of Rome: different patterns for different guilds S. Ceschin 1*, L. Cancellieri 1, G. Caneva 1, C. Battisti 2 University of Roma Tre, Dep. of Environmental Biology, Viale G. Marconi 446, 00146 Rome, Italy Environmental Service (“protected areas – regional parks”), Province of Rome, Via Tiburtina, 691, 00159 Rome, Italy * Corresponding author: [email protected] 1

2

Heterogeneity Species-area curves Plant assemblage Species guild

Archaeological sites Rome

ABSTRACT. – In this study we analyzed species-area relationships in vascular plant assemblages occurring in a set of archaeological sites in Rome. The relationship was investigated both for total species richness and for richness of habitat-related guilds, also controlling the role of habitat heterogeneity at site scale. By floristic sampling, we obtained 585 plant species, about 50 % of the spontaneous flora of Rome. The power equation between total site area and total species number showed a weak relationship (R2 = 0.36) but when considering the relationship between total site area and species number of each habitat guild, the regression value increased as human disturbance decreased (woods and uncultivated lands vs synanthropic and cultivated lands). When controlling for patch heterogeneity, we observed significant correlations between species number of three guilds linked to woods, shrubs and uncultivated lands and their site areas. The investigated archaeological sites, despite their spatial arrangement dispersed in an urban matrix, do not respond to classical rules of insular biogeography theory, at least when we consider all species. Species-area relationships were significant only in semi-natural habitat guilds, especially when we control for habitat heterogeneity. The patterns observed in both total species richness and more synanthropic habitat guilds are probably affected less by biogeographic processes when compared to stochastic processes at patch scale (e.g., site-specific anthropic management) that locally may drive within-patch habitat heterogeneity.

INTRODUCTION Species-area relationship (MacArthur & Wilson 1967) is a wide topic with many implications in animal ecology, biogeography and biodiversity conservation, especially in its application to terrestrial landscapes (see review in Spellerberg & Sawyer 1999, Watling & Donnelly 2006). Although, in mainland landscapes, a large number of studies on species-area curves have been carried out on taxa-related assemblages of vertebrates (mainly birds), less research on plant assemblages is available, at least in the Mediterranean area (e.g., Rey Benayas et al. 1999, Kallimanis et al. 2008, Venegas et al. 2008). Indeed, most of these studies on species-area relationship for plants have been carried out in Northern and Central Europe (e.g., Møller & Rordam 1985, Dzwonko & Loster 1989, Klotz 1990, Zacharias & Brandes 1990, Köchy 1991, Köchy & Rydin 1997, Panitsa et al.2006, Brose 2001, Oertli et al. 2002, Petit et al. 2004). In species-area curves, it has been suggested that the z coefficient and the variance in point dispersion (calculated by the coefficient of determination, R2) may be affected by a large set of intrinsic or extrinsic ecological and taxa-related factors which are strictly linked to peculiar features of single geographic or ecological islands (Diamond 1975, Diamond & May 1976,Watling & Donnelly 2006). Among these factors, habitat heterogeneity is a driving force that

affects species assemblages and may explain the patterns of species richness observed in species-area relationships (MacArthur & Wilson 1967, Tews et al. 2004). The role of heterogeneity has been highlighted mainly in mainland archipelagos, i.e., ‘archipelagos’ of natural or semi-natural habitat fragments in human-transformed landscapes (Diamond & May 1976, Tews et al. 2004). Many archaeological sites are placed within urban areas and may be considered habitat fragments embedded in anthropized landscapes (mainly heavily urbanized). They are very common in Mediterranean areas. Especially in cities like Rome, such sites, in addition to their undoubted historical and archaeological value, are important from a naturalistic point of view. Indeed, several plant studies underline the relevance of these sites as ecological green islands, which preserve very high species richness and maintain some plant species that in other areas of the city lose their habitat (Celesti Grapow et al. 1994, 2001, Celesti Grapow & Blasi 2003, Ceschin et al. 2006). In some works the role of area, management activities and habitat heterogeneity were analyzed in conditioning plant diversity in archaeological sites (e.g., Caneva et al. 2003, Ceschin et al. 2005, Celka 2011), but these investigations have used only a qualitative approach. Therefore, this paper, through a more analytical and quantitative method, aims to: i) identify the species-area relationships in plant assemblages and in sets of species guilds occurring in

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S. CESCHIN, L. CANCELLIERI, G. CANEVA, C. BATTISTI

archaeological sites in Rome; ii) analyze the role of area as a factor influencing plant species richness in these patchy ecosystems; iii) evaluate the role of patch heterogeneity as a factor affecting species-area relationships. MATERIALS AND METHODS Study area. The study area corresponds to the main Roman archaeological sites within Rome which belong to the central archaeological area (Imperial and Trajan Fori, Palatine, Colosseum, Baths of Caracalla, Mount Testaccio) and Regional Park of the Appia Antica, located in a suburban sector of the city (Park of the Caffarella, Maxentius’s villa and Quintili’s Villa) (Fig. 1). These areas constitute part of one of the main biological corridors of Rome, which runs from the south-eastern sector of the city through the Via Appia Antica and links suburban and central green areas (Di Giovine 1999, 2001, Ricotta et al. 2001). All investigated archaeological sites are homogeneous cli-

matically and lithologically, at least at local scale. From a climatic point of view, they fall within the transitional Mediterranean region, like most of the territory of the Roman urban landscape. It is a climate with hot and dry summers, mild winter temperatures and rainfalls that are concentrated in autumn and winter (Blasi 2001). As far as the lithology, the soil base is volcanic, particularly dark leucitic lava, with an accumulation of calcareous heterogeneous materials, primarily tuff (Funiciello et al. 1995). The archaeological sites differ in age of excavation, management policy and type of human disturbance. Human disturbance, which mainly occurs in the central archaeological sites, is expressed in various forms and regimes (chemical weed control, mowing, trampling, compaction and rearrangement of soil for excavation activities), giving rise to different micro-environmental conditions (Ceschin et al. 2005). The suburban archaeological sites still maintain wide green areas, where human disturbance is limited to sporadic trampling by tourists, mechanical mowing and marginal pastoral activities.

Fig. 1. – Investigated archaeological sites within the city of Rome. 1: Trajan Fori, 2: Imperial Fori, 3: Palatine, 4: Colosseum, 5: Baths of Caracalla, 6: Mt. Testaccio, 7: Park of the Caffarella, 8: Maxentius’s Villa, 9: Quintili’s Villa.

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AREA, HETEROGENEITY, PLANTS IN ARCHAEOLOGICAL SITES

Floristic sampling. For the aims of this study we used data of both wild and ornamental vascular plants that were collected by the authors in previous studies, relating to the sites listed above (Ceschin & Caneva 2001, Ceschin et al. 2006). In order to make the analysis more complete, we also considered other important historic-archaeological sites in Rome, whose floristic data were taken from literature. These sites include the Park of Caffarella (Buccomino & Stanisci 2000), the Baths of Caracalla (Celesti Grapow & Blasi 2003), the Colosseum (Celesti Grapow et al. 2001) and Mount Testaccio (Pavesi & Leporatti 1998). Each floristic study was carried out using an analogous sampling methodology and in a comparable time span (about 4 years), therefore we assume that the research effort in each site is similar. For taxonomical determination of the plants, we used the analytical keys in Pignatti (1982), while for nomenclatural update, we followed Conti et al. (2005). In this paper we used the term “species assemblage” to indicate the total set of plant species occurring in the same area during the study period. Therefore, we identified nine species assemblages, one in each of the nine archaeological sites considered in this study. We used the term “species guild” to indicate a set of species that share similar habitat type in a study area (Verner 1984, Magurran 2004). This approach is useful when differences due to ecological constraints may show specific patterns (e.g., in species-area curves). We recognized seven main “species guilds”, by analysis of species-habitat co-occurrence. In particular, we assigned to each plant species the relative more suitable habitat type. Species guilds are related to the following habitat types: woods, shrubs, uncultivated lands, wetlands (as semi-natural habitats), and synanthropic habitats, cultivated lands (as anthropic habitats). We refered the term ‘synanthropic’ to species and habitat types that are strictly ecologically-related to human-dominated ecosystems (e.g., walls, rubble, trampled areas). The first group of habitat types was considered as seminatural habitats and not natural ones because they anyway are subject to a human disturbance in the studied areas. Each species guild should be further subdivided into more precise species patterns, but for our aims and for the analysis of species-area relationships through mapping procedures, this level of analysis can be considered adequate. Mapping procedures. The boundaries of the archaeological sites were digitized on aerial photographs, and area and perimeter were determined for each site in a GIS software environment. Different types of habitats occurring in each site were mapped at an approximate scale of 1:1000 with a cell size of 0.264 m (data from PCN.minambiente.it: orthophoto 2008), using ArcGis 9.0 (ESRI inc. Redland, CA). We digitized the recognized seven habitat types (see “floristic sampling”). When compared to overall size area of each studied site, the vertical surfaces (e.g., walls and buildings) may be considered not relevant when compared to the larger horizontal surfaces. Therefore, in the mapping procedure, we have considered the object projection on the horizontal surface (in particular for walls and buildings), without considering the vertical surfaces. In addition, to make the

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mapping and the floristic data comparison, we included species linked to walls in the broader category synanthropic type. Data analysis. Species-area relationships. The power mathematical model (Arrhenius 1921), S = cAz, usually presented as the log10 transformation of both variables (Preston 1962, MacArthur & Wilson 1967), log10S = c + zlog10A, was used to describe the effect of size area on species richness of the study areas. In the equation, S is number of species, A is area, and c and z are the constants which vary in accordance with organisms and geographical system examined. The power equation was tested on different data sets. Firstly, we considered the relationship between total area of each archaeological site and total species number in the plant assemblage collected within it (A1: Atot vs Stot). Secondly, we analysed the relationship between total area of each site and total species number of the guild linked to each habitat type occurring in each site (after, habitat guilds; A2: Atot vs Stot hab.type). Finally, we compared the nine sites considering the total area of each habitat type and the total number of species belonging to the guild linked to each habitat type occurring in each site (A3: Atot hab. type vs Stot hab.type). For A2 and A3 analyses, we grouped the plant species in relation to their preferential habitats according to our field observations (see “floristic sampling”). The regression analysis was performed using the statistical package R 2.14.0. The critical level for statistical significance was set at p < 0.05 Species-habitat heterogeneity relationship. In order to assess if the species richness of a site is a function of the spatial heterogeneity, we calculated for each archaeological site landscape metrics, such as Shannon’s Diversity Index (SDI) (McGarigal & Marks 1995). The formula of SDI is:

where pi corresponds to the ratio CA/TLA, CA = Class Area (sum of areas of all patches belonging to a habitat type) and TLA = Total Landscape Area (sum of areas of all patches in the landscape). The calculation was carried out at landscape level on the vector map regarding each site, using Patch Analyst extension for Arc Map version 4.2 (Rempel et al. 2008). In order to have always positive values of log10 in the regression analysis, the values of SDI have been transformed into SDI +1.

RESULTS Floristic data The obtained data concern 585 plant species, about 50 % of the spontaneous flora known for Rome (Celesti Grapow 1995).The total species assemblage collected in each archaeological site was reported in Table I. Maxentius’s Villa, Palatine and Quintili’s Villa show the highest values of floristic richness, while Colosseum and Mount of Testaccio the lowest ones. Table I shows also the per

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Table I. – Area (ha), SDI values, species assemblage and percent values of habitat guilds for each archaeological site are shown. Archaeological site

Area (ha)

SDI

Species assemblages

Woods (%)

Shrubs (%)

Uncultivated Wetlands lands (%) (%)

Synanthropic Cultivated habitats lands (%) (%)

Colosseum

2.1

0.557

215

1.6

2.0

41.5

5.1

44.6

5.2

Mt. Testaccio

3.0

1.063

172

7.0

7.6

54.7

0.6

26.7

3.4

Trajan Fori

3.2

0.785

226

1.9

0.4

42.6

7.2

45.6

2.3

Maxentius’s Villa

10.1

1.186

377

5.2

3.3

51.5

4.8

31.4

3.8

Imperial Fori

11.1

0.983

329

2.9

2.1

44.8

6.1

39.3

4.8

Baths of Caracalla

12.2

1.142

308

4.3

3.4

46.6

4.3

38.0

3.4

Quintili’s Villa

21.7

0.802

340

2.6

2.8

51.6

7.0

34.1

1.9

Palatine

24.2

1.408

343

5.1

4.6

46.5

5.1

34.6

4.1

Caffarella

260.0

1.542

302

5.9

3.8

52.8

7.1

27.8

2.6

cent values of the species guilds belonging to different habitat types for each archaeological site. Generally, species linked to uncultivated lands, as well as synanthropic habitats, are dominant, although those associated with woods, shrubs and wetlands, which are rarer in Rome, are not negligible. The cultivated species are relatively few.

Table II. – R2, z and log10c values of the power equation at different analysis level. * = p < 0.05. Analysis level

Relation

log10C

z

R2

p value

A1

Atot ~ Stot

2 335

0.109

0.359

0.088

A2

Atot ~ Swoods

0.763

0.280

0.456

0.046*

Species-area relationships

Atot ~ Sshrubs

0.613

0.297

0.242

0.179

Atot ~ Suncult. lands

2 030

0.143

0.474

0.040*

Using the first dataset (A1: Atot vs Stot), the power equation highlights a weak relationship between the two variables (low variance of regression: R2 = 0.36; not significant p value). Considering the relationship between total size area of each site and species assemblage of each habitat type (A2: Atot vs Stot hab.type), we obtain a regression with

Atot ~ Swetlands

0.800

0.329

0.223

0.199

Atot ~ Ssyn. habitats

1 479

0.127

0.268

0.153

Atot ~ Scult. lands

0.985

0.037

0.015

0.754

Awood ~ Swoods

0.443

0.191

0.749

0.012*

Ashrub ~ Sshrubs

0.865

0.056

0.170

0.036*

Auncult.land ~ Suncult. lands 1 548

0.135

0.564

0.020*

Awetland ~ Swetlands

1 113

0.063

0.472

0.200

Asyn.hab. ~ Ssyn. habitats

1 480

0.127

0.268

0.153

Acult.land ~ Scult. lands

0.706

0.081

0.157

0.330

Atot ~ SDI+1

0.224

0.078

0.551

0.023*

A3

B

Fig. 2. – Log10-transformed area-species relationships in nine archaeological sites. Relationship between total area of each site and total species number of habitat guilds (woods, uncultivated lands).

a higher R2 value for the guilds linked to two habitat types: woods (0.46) and uncultivated lands (0.47) (Fig. 2), both of them with a species number significantly correlated to total size area (Table II). Comparing the nine archaeological sites and considering the third dataset (A3: Atot hab. type vs Stot hab. type), the correlation between variables is significant for three guilds linked to the following habitat types: woods, shrubs and uncultivated lands (Fig. 3). Among them, two guilds (woods and uncultivated lands) have higher R2 values, when compared to A2 species-area relationship. In other cases R 2 values are low, often below 0.3. It should be noted that if we compare the z value between A2 analysis and A3, it decreases for hygrophilous and shrub communities.

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Fig. 4. – Log10-transformed area-SDI+1 relationship in nine archaeological sites. Relationship between total area and habitat heterogeneity (SDI index) of each site.

Fig. 3. – Log10-transformed area-species relationships in nine archaeological sites. Relationship between total area of each habitat type and total number of habitat guilds (woods, shrubs, uncultivated lands).

Species-habitat heterogeneity relationship The habitat heterogeneity (SDI index) of the sites ranged from 0.557 (Colosseum) to 1.542 (Park of the Caffarella) (Table I). The linear regression analysis showed a significant relationship between site area and habitat heterogeneity (R2 = 0.551, p < 0.05) (Fig. 4). DISCUSSION A high floristic richness characterizes the Roman archaeological sites, especially when compared to the total flora surveyed throughout the Rome urban area (Celesti Grapow 1995, Ricotta et al. 2001). These data point out how these sites are semi-natural habitat patches included in heavily urbanized areas and hosting a rich floristic diversity, also of conservation concern (Celesti Grapow et al. 1994, Ceschin et al. 2006, 2009).

The floristic richness that was recorded is not strictly linked to the area of the sites. Indeed, the application of the power equation shows how here the classic relationship between species assemblages and total area of sites is very weak. Considering the second level of analysis (i.e., the relationship between number of species of single habitat guilds and total area of patchy archaeological sites), we observed a significant correlation and a direct relationship only for the guilds linked to woods and uncultivated lands. On the contrary, the explained variance values (here expressed by the coefficient of determination) are lower in the cases of the relationships between site area and species number for guilds linked to shrub, wet, ruderal and synanthropic habitats. On the basis of the third level of analysis (i.e., the relationship between species number of single habitat guilds and sub-areas of relative habitat types in the archipelago of archaeological sites), we observed a strong significant correlation (and a high coefficient of determination in the relationship) when we related the size of semi-natural sub-areas to the species number of semi-natural habitat guilds (e.g., for uncultivated lands and woods), while we did not observe significant correlations when we considered guilds belonging to cultivated and synanthropic habitats. First, it is not the total area of the archaeological site to affect the floristic richness, but the sub-areas of each habitat types within the sites. Species-area relationship is strong only for semi-natural guilds where probably the classic immigration and extinction process (MacArthur & Wilson 1967) acts in this peculiar archipelago structured by semi-natural habitats surrounded by a heavily anthropized matrix (synanthropic habitats inside and outside the archaeological sites). Differently, local anthropogenic determinants and chance may drive the occurrence of cultivated and synanthropic species guilds for which the relationships between area and number of species are very weak (with non-significant correlations between variables). In particular, in the third level of analysis we have controlled for the habitat heterogeneity, stratifying

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the single habitat sub-areas. When controlling for this spatial variable, we observed an increase of explained variance (here expressed by the coefficient of determination), also increasing the coefficient of correlation. These data would seem to support the hypothesis that the Roman archaeological sites at Rome, despite their spatial arrangement is like an archipelago of islands surrounded by urban landscape, do not respond to classical rules of insular biogeography theory. In these sites and for the species guilds considered there is a weak species-area relationship, with the exception of the semi-natural habitats. Indeed, the semi-natural habitats are few subjected to human activities and are isolated in a synanthropic matrix, and so the true mechanism of colonization/extinction of species of the insular biogeography theory are respected. Conversely, the pattern of species richness related to anthropic habitats is probably affected both by a continuous colonization by some ruderal plants coming from surrounding urban landscape matrix, causing an absence of true isolation of the single habitats. Moreover local drivers and processes as environmental heterogeneity caused by different and not deterministic (stochastic) anthropic management may act in each site. In some of the investigated archaeological sites, such as Colosseum, Imperial Fori and Palatine, the presence within the same area of different management activities strongly affects the floristic diversity, and especially the number of species related to anthropic habitats (Caneva et al. 2003, Ceschin et al. 2005). Indeed, these areas are heavily managed for cultural purposes by municipal agencies and the associated disturbances (as mowing, trampling, introduction or diffusion of synanthropic and alien species) may locally alter the general species-area pattern at landscape scale, independently by immigration-extinction processes, traditionally considered the causes of the species-area patterns (Watling & Donnelly 2006). Probably, the anthropogenic disturbances locally develop a within-patch pattern of different habitat types, so increasing the habitat heterogeneity at this scale. A strong direct relationship between area and habitat heterogeneity is widely known (e.g., Tews et al. 2004) and the increase of heterogeneity at patch scale has been suggested as one of the main factors that explain the power function (MacArthur &Wilson 1967, Watling & Donnelly 2006). Our results underline a direct relationship between site area and environmental heterogeneity, so confirming a general pattern, here applied to peculiar anthropogenic patches (i.e., archaeological sites) where rarely this relationship was tested. In conclusion, our results may suggest some implications for management of archaeological sites following a plant diversity vision. Indeed, an Agency managing these sites may develop different strategies aimed to increase local plant species richness. In sites where the main habitat types are semi-natural, they should work to increase their area so allowing that natural processes of coloniza-

tion may increase the species richness. Differently, in sites where the main habitat types are synanthropic, an increase of their area does not imply a corresponding increase of species richness. In these sites, managers should actively act to restoring semi-natural habitats. A cknowledgements . - The authors wish to thank the Archaeological Superintendence of Rome and the Superintendence Cultural Heritage of Municipality of Rome to have given the opportunity to access areas closed to the public and to provide data and information relating to the studied areas.

REFERENCES Arrhenius O 1921. Species and area. J Ecol 9: 95-99. Blasi C 2001. Carta del fitoclima dell’area romana (1:100.000). Inf Bot Ital 33(1): 240-243. Brose U 2001. Relative importance of isolation, area and habitat heterogeneity for vascular plant species richness of temporary wetlands in east-German farmland. Ecography 24: 722730. Buccomino G, Stanisci A 2000. Contributo alla conoscenza floristica della Valle della Caffarella (Roma). Inf Bot Ital 32(13): 3-15. Caneva G, Pacini A, Celesti Grapow L, Ceschin S, 2003. The Colosseum’s use and state of abandonment as analysed through its flora. Int Biodet Biodegr, 51: 211-219. Celesti Grapow L, Pignatti S, Pignatti E, 1994. Analisi della flora dei siti archeologici di Roma. Allionia 32: 113-118. Celesti Grapow L, Blasi C 2003. I siti archeologici nella conservazione della biodiversità in ambito urbano: la flora vascolare spontanea delle Terme di Caracalla a Roma. Webbia 58(1): 77-102. Celesti Grapow L 1995. Atlante della Flora di Roma. La distribuzione delle piante spontanee come indicatore ambientale. Argos Ed., Roma. Quad. Ambiente 3: 1-222. Celesti Grapow L, Caneva G, Pacini A 2001. La Flora del Colosseo (Roma). Webbia 56(2): 321-242. Celka Z 2011. Relics of cultivation in the vascular flora of medieval West Slavic settlements and castles. Biodiv. Res. Conserv. 22: 1-110. Ceschin S, Caneva G 2001. Contributo alla conoscenza della flora dell’area archeologica del Palatino (Roma). Inf Bot Ital 33(2): 391-406. Ceschin S, Caneva G, Kumbaric A 2005. Analisi ecologica della flora nell’area archeologica centrale di Roma in relazione all’uso antropico del sito. Atti dei Convegni Lincei “Ecosistema Roma” 218: 421-431. Ceschin S, Caneva G, Kumbaric A 2006. Biodiversità ed emergenze floristiche nelle aree archeologiche romane. Webbia 61(1): 133-144. Ceschin S, Salerno G, Caneva G 2009. Multitemporal floristic analysis of a humid area in Rome’s archaeological site as indicator for environmental change. Environ Monitor Assess 149: 29-42. Conti F, Abbate G, Alessandrini A, Blasi C (Eds.) 2005. An Annotated Checklist of Italian Flora. Palombi & Partner, Roma.

Vie Milieu, 2012, 62 (4)


Di Giovine M 1999. I corridoi biologici nell’area di Roma, la via Appia, corridoio per l’ingresso di elementi naturali nel centro urbano. Atti del Workshop, “Paesaggi rurali di domani”. ANPA-ARPA Piemonte: 83-89. Di Giovine M 2001. La rete ecologica: un approccio integrato di pianificazione e gestione sviluppato dal Dipartimento Ambiente del Comune di Roma. Inf Bot Ital 33(1): 7-10. Diamond JM 1975. The island dilemma: lessons of modern biogeographic studies for the design of natural reserves. Biol Conserv 7: 129-145. Diamond JM, May RM 1976. Island biogeography and the design of natural reserves. In May RM, Saunders Co eds, Theoretical Ecology Principles and Applications. Philadelphia, Penn: 163-186. Dzwonko Z, Loster S 1989. Distribution of vascular plant species in small woodlands on the Western Carpathian foothills. Oikos 56: 77-86. ESRI 2002. ArcView GIS, version 3.3. Environmental Systems Research Institute, Redlands, CA, USA. Funiciello R, Marra F, Rosa C 1995. I caratteri geologici-stratigrafici. In Cignini B, Massari G, Pignatti S eds, L’Ecosistema Roma, ambiente e territorio. Fratelli Palombi Ed, Roma: 29-39. Kallimanis AS, Mazaris AD, Tzanopoulos J, Halley JM, Pantis JD, Sgardelis SP 2008. How does habitat diversity affect the species–area relationship? Global Ecol Biogeogr 17(4): 532538. Klotz S 1990. Species/area and species/inhabitants relations in European cities. In Sukopp H, Hejny S, Kowarik I eds, Urban Ecology: Plants and Plant Communities in Urban Environments. SPB Academic Publishing, The Hague: 99-103. Köchy M 1991. Species-area relationships of vascular plants on field islands. Medd Växtbiol Inst Uppsala 1: 1-41. Köchy M, Rydin H 1997. Biogeography of vascular plants on habitat islands, peninsulas and mainlands in an east-central Swedish agricultural landscape. Nordic J Bot 17(2): 215223. MacArthur RH, Wilson EO 1967.The theory of island biogeography. Princeton Univ Press, Princeton, New Jersey. McGarigal K, Marks BJ 1995. FRAGSTAT - Spatial pattern analysis program for quantifying landscape structure. General Technical Report PNW-GTR-351, USDA Forest Service, Pacific Northwest Research Station, Portland, OR. Magurran AE2004. Measuring biological diversity. Blackwell Publishing, Australia. Møller TR, Rordam CP 1985. Species numbers of vascular plants in relation to area, isolation and age of ponds in Denmark. Oikos 45: 8-16.

171

Oertli B, Auderset Joye D, Castella E, Juge R, Cambin D, Lachavanne J-B 2002. Does size matter? The relationship between pond area and biodiversity. Biol Conserv 104: 59-70. Panitsa M, Tzanoudakis D, Triantis KA, Sfenthourakis S 2006. Patterns of species richness on very small islands: the plants of the Aegean archipelago. J. Biogeography 33: 1223-1234. Pavesi A, Leporatti ML 1998. La flora vascolare del monte Testaccio in Roma (Lazio). Inf Bot Ital 30(1-3): 25-36. Pignatti S 1982. Flora d’Italia. 3 vol Edagricole, Bologna. Petit S, Griffiths L, Smart SS, Smith GM, Stuart RC, Wright SM 2004.Effects of area and isolation of woodland patches on herbaceous plant species richness across Great Britain. Landsci Ecol 19: 463-471. Preston FW 1962. The canonical distribution of commonness and rarity. Ecology 43: 185-215; 410-432. Rempel RS, Carr AP, Kaukinen D 2008. Patch Analyst extension for ArcMap: Version 4.2. Ontario Ministry of Natural Resources. http://flash.lakeheadu.ca/~rrempel/patch. Rey Benayas JM, Colomer MGS, Levassor C 1999. Effects of area, environmental status and environmental variation on species richness per unit area in Mediterranean wetlands. J Veg Science 10: 275-280. Ricotta C, Celesti Grapow L, Avena G, Blasi C 2001. Topological analysis of the spatial distribution of plant species richness across the city of Rome (Italy) with the echelon approach. Landsci Urban Plann 57: 69-76. Spellerberg IF, Sawyer JW 1999. An introduction to applied biogeography. Cambridge University Press, Cambridge. Tews J, Brose U, Grimm V, Tielbörger K, Wichmann MC, Schwager M, Jeltsch F 2004. Animal species diversity driven by habitat heterogeneity/diversity: the importance of keystone structures. J Biogeogr 31: 79-92. Venegas FM, Fanlo R, Toboso A, Patón D 2008. Plant speciesarea relationships in grasslands and woodlands of the Mediterranean Basin: Consequences for the size of reserves. Opt Médit Ser A 79: 7-10. Verner J 1984. The guild concept applied to management of bird population. Environ Manage 8:1-14. Watling JI, Donnelly MA 2006. Fragments as islands: a synthesis of faunal responses to habitat patchiness. Conserv Biol 20: 1016-1025. Zacharias D, Brandes D 1990. Species area-relationships and frequency - Floristical data analysis of 44 isolated woods in North-Western Germany. Vegetatio 88: 21-29. Received June 4, 2012 Accepted October 4, 2012 Associate Editor : E Magnanou

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