Urban vegetation of Almerı́a City—a contribution to urban ecology in Spain

Landscape and Urban Planning 59 (2002) 203±216

Urban vegetation of AlmerõÂa CityÐa contribution to urban ecology in Spain E.D. Dana*, S. Vivas, J.F. Mota Dpto. BiologõÂa Vegetal y EcologõÂa, Escuela PoliteÂcnica Superior, Universidad de AlmerõÂa, E-04120 AlmerõÂa, Spain Received 27 September 2000; received in revised form 2 January 2002; accepted 27 February 2002

Abstract In this paper, we analyzed the vegetation of the city of AlmerõÂa (southeast of Spain) using numerical methods. We distinguished 16 communities. Although most of them had an eminent ruderal character, some phytocoenoses were typical from non-disturbed environments. These communities can be distinguished not only by means of the dominant species, but also by the abundance of different biological forms. Thus, they can be grouped into six phytosociological classes. It was not found that diversity and coverage values were related to the features of the different habitats, but woody and herbaceous communities tended to occupy different types of biotopes. From the ecological point of view, the communities can be included into ®ve groups, the ¯oristic composition of which is related to the frequency of disturbance events as well as to the water availability of soils. According to the species composition and to the ecological signi®cance of the communities detected, the city can be subdivided into three zones. These areas match the three historical phases of the city development. Finally, the possible implications of the results obtained are discussed in the context of urban planning and development, taking into consideration the conservation of valuable rare species and plant communities. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Phytosociology; Ruderals; Urban ecology; Urban planning; Multivariate analysis

1. Introduction The increasing extension of urbanized landscapes is leading scientists to consider urban areas as a new ®eld for developing ecological studies in which the effect of humans upon the biocoenoses are analyzed (Rebele, 1994). Consequently, urban studies concerning very different topics have been developed in many European countries (Gilbert, 1995; Pysek, 1998). So far, however, this kind of research has hardly emerged in Spain, and thus, only very particular approaches *

Corresponding author. Tel.: ‡34-950-015003; fax: ‡34-950-015069. E-mail address: [email protected] (E.D. Dana). 0169-2046/02/$20.00 # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 2 0 4 6 ( 0 2 ) 0 0 0 3 9 - 7

have been made and for a very limited number of cities (e.g. BujaÂn et al., 1998). Therefore, many features of plant species and communities occurring in urban habitats remain unknown. With these precedents, the aims of this paper were: 1. to characterize and analyze the urban vegetation of a coastal city of South-eastern Spain: to our knowledge, no previous study has investigated the vegetation of Spanish cities; 2. to give an ecological interpretation, seeking for possible environmental factors, such as the type of habitat or the level and frequency of disturbance, which could play a major role in determining the attributes of the different types of communities;

204

E.D. Dana et al. / Landscape and Urban Planning 59 (2002) 203±216

3. to identify and discuss the implications of the results obtained for the design of the city and the planning of its further expansion. 2. Material and methods 2.1. Study site This study has been carried out within the city of AlmerõÂa, in the southeast of Spain (Fig. 1). It covers about 700 ha and has a population of 150 000 inhabitants. The altitude of the area is between 1 and 100 m. The annual mean rainfall is 250 mm and mean temperature is about 17 8C. Frosts are absent and rain occurs mainly from November to March. Nevertheless, since the meteorological data were recorded in the outer suburbs, temperatures were probably higher in urban sites. 2.2. Methods For this survey, we basically employed the methodology followed by Franceschi (1996) for the City of Rosario (Argentina). We visited different urban habitats such as gardens, vacant-lots, basins, walls, etc. In each of them, at least two vegetation samples were analyzed.

We repeated the process in order to obtain a complete representation of the types of vegetation present in the city. This was achieved with 106 samples, each of them consisting of a quadrate from which environmental information was recorded. Habitats were ®rst sampled in spring, marked and re-sampled in summer, in order to record the presence of the communities that segregate their phenological peak (see Dana et al., 2000). Thus, total coverage, presence of species, species coverage and the sort of biotope were recorded for each sample. In each releveÂ, and for each species, the coverage value was estimated using Braun-Blanquet (1964) scale. Nomenclature of the species is in accordance to that of Mateo and Crespo (1990). Several authors (Sukopp and Werner, 1983; Gilbert, 1995) have pointed out that the level and frequency of disturbance is different depending on the type of habitat. Therefore, the knowledge of the habitat features would allow, in an indirect way, to know the extent to which the communities are in¯uenced by disturbance. In order to achieve this target, we also recorded the type of habitat within each sample and in a qualitative way, we recorded some soil features (e.g. presence of salts, texture, presence of visible humidity/dryness of soil) when evident. Quadrate size varied slightly due to the different vegetation types present in the area. Thus, small

Fig. 1. Location of the AlmerõÂa City (southeast of Spain).

E.D. Dana et al. / Landscape and Urban Planning 59 (2002) 203±216

grassland-like communities (with species such as Chamaesyce spp. or Filago spp.), chamaephytic communities growing on ancient walls, and tall shrubs of nanophanerophytes were sampled on 3, 15 and 100 m2 releveÂs, respectively. For the rest of the physiognomic types of vegetation observed standard quadrates of 20 m2 were employed. This variability is a consequence of the high biotope diversity existing in an urban environment since urban habitats can be at very different succession states despite of their physical proximity (Rebele, 1994). The ®nal result is a highly patched landscape, which allows the close coexistence of very different vegetation types. Nevertheless, the quadrate size was always larger than the minimum areas suggested by Mueller-Dombois and Ellenberg (1974) for both herbaceous and woody communities. In order to classify and order the releveÂs, numerical classi®cations were employed, but prior to this, original cover-abundance data were transformed into the ordinal scale proposed by Van der Maarel (1979). To test the constancy of our results, we employed different classi®cation algorithms: single linkage, complete linkage and unweighted paired group method average (UPGMA) using the Euclidean distance, the squared Euclidean distance and 1-Pearson's R (Podani, 1994; McCune and Mefford, 1995). If despite of the differences between the classi®cation methods the results obtained were similar, we could be rather sure about the robust properties of our results. Nevertheless, as Loidi and FernaÂndez-GonzaÂlez (1994) suggest, numerical studies from vegetation samples may be improved with a rigorous inspection of original releveÂs. Hence, after recognizing the possible ¯oristic groups from the cluster analysis, we constructed a synthetic table (Mueller-Dombois and Ellenberg, 1974) in which the constancy and medium coverage value were recorded. The goal of this last procedure was to test whether the groups obtained through classi®cation correspond to communities in which there was a clear dominance and constancy of one or more species. Once the plant communities were recognized, we calculated for each of them the mean diversity and coverage values in order to characterize the structural features of each community. For the calculation of diversity values, we used the Shannon index (Hill, 1973; Peet, 1974; Pielou, 1975) since is the most widely used index of heterogeneity and is derived

205

from a function used in the ®eld of information theory. The mean richness of each community was also obtained. Since the sampling area varied with the type of vegetation sampled, the formula Ri ˆ mean number of species in community i/log sampling area (cm2) was used. This correction allows comparing richness between different vegetation types with independence of the quadrates size (Magurran, 1989). In addition, we calculated the coverage of different biotypes. This gave us important information about the ecological features of the habitat and about the autoecological adaptation of the species and communities to the habitat within they live (Mueller-Dombois and Ellenberg, 1974; Cox, 1990). For the analysis of biological forms, we followed Raunkiaer (1934). Then we ordered the recognized communities using detrended correspondence analysis (DCA), an indirect ordination which extracts gradients present in the species composition data (Hill, 1979; Hill and Gauch, 1980). Thus, the axes derived correspond to gradients of species compositional changes. As Jonsson and Moen (1998) pointed out, normally these axes are then interpreted by correlating plot positions with values for explanatory variables recorded in the same plots, but it is also a good procedure for qualitative approximations. Therefore, this procedure can be used to distinguish either possible ¯oristic and environmental gradients. We used Sorensen distance, measured as percentage of dissimilarity. This is a proportion coef®cient measured in city-block space that works very well with quantitative data (McCune and Mefford, 1995). The distance between objects is, in shorthand, 1 2W=…A ‡ B†, where W is the sum of shared abundance and A and B are the sums of abundance in individual sample units. Roberts (1986) provided further details about the use of this distance. Due to the high amount and variety of information recorded, the results obtained will be showed in two different parts. First, we will consider the pure ¯oristic analysis, in which we will discuss the species composition of the recognized communities and the period of their main development. In a second point, and from an ecological view, we will analyze the structural parameters of the phytocoenoses such as the percentage of biological forms, mean coverage, mean richness, and mean diversity values. Although some of them may be considered as a consequence of the particular ¯oristic composition of each community

206

E.D. Dana et al. / Landscape and Urban Planning 59 (2002) 203±216

(e.g. representation of each biotype), there are strong relationships between these features and those derived from the type of habitat. 3. Results and discussion 3.1. Floristic analysis All the species found within the releveÂs are listed in Appendix A. The different clustering methods used in this paper showed similar groups. The most easily interpretable was the cluster obtained with the UPGMA algorithm and the 1-Pearson's R distance, but also clear clusters were extracted using other methods. After inspecting the resulting clusters and comparing the groups obtained to the ¯oristic composition of the releveÂs through the construction of a synthetic table, we concluded that most of them can be grouped into 16 communities (Fig. 2). Despite the differences in ¯oristic composition of communities 1 and 9, the corresponding quadrates were sampled on the same sort of habitat: trampled soils of gardens and basins. Nevertheless, community 1, in which Chamaesyce serpens and Chamaesyce chamaesyce are the dominant species, develops from late spring to early autumn, whereas community 9, characterized by the abundance of Poa annua and Coronopus didymus develops during winter time. On the other hand, Mesembryanthemum crystallinum and M. nodi¯orum (which bloom during late spring) dominated releveÂs of which we have considered as community 3. ReleveÂs corresponding to communities 2, 4 and 5 have as a common feature the abundance of therophytic species of Stellarietea mediae, and as it is shown in Table 3, Chenopodium murale, Malva parvi¯ora and Hordeum murinum, respectively dominated the correspondent quadrates. These ¯oristic groups develop during the rainy months (from autumn to mid-spring) and are replaced within the same habitats by alien-rich communities (10±12) during summer season. Communities 13, 15 and 16 are rich in woody taxa belonging to the Chenopodiaceae family such as Atriplex halimus, A. glauca, Salsola oppositifolia, Salsola genistoides and Suaeda vera. The alien species Zygophyllum fabago dominates releveÂs included

under community 14. All these communities bloom from summer to autumn. Antirrhinum mollissimum (a rupicolous species endemic to the southeast of Spain) dominates community 6, whereas the poorest releveÂs, dominated by Parietaria judaica, have been grouped as community 7. Community 8 is characterized by the dominance of the hemicryptophytic grass Piptatherum miliaceum. Therefore, after the analysis of the ¯oristic composition of the 16 communities overall we conclude that six phytosociological classes can be clearly distinguished in the case of AlmerõÂa City (Table 1). From these, Stellarietea mediae seems to be the best represented when the number of communities is considered. As we previously pointed out, there is a lack of studies concerning urban vegetation of Spanish cities, and hence, comparisons cannot be easily done. Nevertheless, it seems that although urban vegetation can largely vary from one city to another, some communities are widely spread and occur within cities under the same type of climate. The summer-alien communities (with Aster squamatus and/or Conyza spp.), the winter native communities (with Sisymbrium irio, Malva parivlora or Hordeum murinum), as well as the communities dominated by Piptatherum miliaceum or Parietaria judaica, are common in cities of the southeast of Spain such as Murcia, Alicante and Valencia (Dana, personal observation). In a parallel study (Dana and GarcõÂa-OcanÄa, unpublished data) some few communities (e.g. that of Malva parvi¯ora, Hordeum murinum, Parietaria judaica or Piptatherum miliaceum) have also been detected in the City of Granada (800 m a.s.l.). This city is located 180 km. far from AlmerõÂa City, near the National Park of Sierra Nevada, and is subjected to a continental climate with a great variation between winter and summer climatic conditions. The abundance of these communities contrasts with the dominance of Artemisietalia associations found in North and Central European cities (Sukopp and Werner, 1983). On the other hand, we must point out the abundance of communities in which alien species are dominant (most of them with an American origin such as Chamaesyce serpens, Aster squamatus, Conyza spp. or Coronopus didymus). This is not exclusive to the urban areas, since alien ¯ora is an important element in the ¯ora of the region, although only a low percentage is widely spread (Dana et al., 1999a).

E.D. Dana et al. / Landscape and Urban Planning 59 (2002) 203±216

Fig. 2. Dendrogram showing the classi®cation of quadrates into 16 communities. 207

208

E.D. Dana et al. / Landscape and Urban Planning 59 (2002) 203±216

Table 1 Phytosociological classes found within the AlmerõÂa City. Nomenclature follows Alcaraz et al. (1991) Phytosociological class

Communities that belong to each class

Description

Pegano harmalae±Salsoletea vermiculatae

13, 14, 15, 16

Artemisietea vulgaris

8

Stellarietea mediae Polygono arenastri±Poetea annuae Saginetea maritimae Asplenietea trichomanis

2, 4, 5, 10, 11, 12 1, 9 3 6, 7

Nitrophilous srhubs in which chamaephytes and nanophanerophytes are dominant Nitrophilous vegetation dominated by perennial and herbaceous species Ruderal vegetation dominated by cosmopolitan annual species Reptant terophytes on trampled soils; cosmopolitan Terophytic vegetation settled on saline and nitrified soils Rupicolous vegetation of the Eurosiberian and Mediterranean territories

It has been noted a high proportion of alien taxa in other cities of the world (e.g. Franceschi, 1996; Kent et al., 1999; NiemelaÈ, 1999) although in some Mediterranean cities alien species are slightly less abundant (Chronopoulos and Christodoulakis, 1996; Celesti and Blasi, 1998; Celesti et al., 1999). Although the 106 species recorded in this study (Appendix A) represent only one-half of the total richness of the city (Dana et al., 1999a), the percentage of alien species that appeared in the releveÂs (17%) is rather similar to the alien richness of the Mediterranean cities. The reasons underlying these high proportions of alien species remain unclear. In the case of cities, it has been explained considering the abundance of warm and xeric habitats in urban areas (Davison, 1977; Kunick, 1980; Rebele, 1994). But Fox and Fox (1986) predicted that invasions do not succeed without previous or recurrent disturbance events, while Montenegro et al. (1991) noted that the success of invading species depends on the intensity and frequency of disturbance. In open areas, competition between native and alien species is reduced (Lepart and Debussche, 1991) and since these are common situations in urban areas, it could also explain the richness of exotic taxa in cities. In a recent study carried out on AlmerõÂa City (Dana et al., 2000), it was demonstrated that a temporal segregation of phenological development occurs. Mediterranean species tend to ¯ower and fruit during raining months whereas most of alien species do it during the dry summer time, and consequently, this phenological segregation could reduce the competence for resources and allow the alien plant to success. In order to explain the abundance of alien species other social features must also be considered. In our

case, the intense agricultural development of the surrounding areas, the coastal location of the city and the trading relationships with South America during last century have also been proposed as essential factors that can determine the importance of alien species in human-in¯uenced areas of the western Mediterranean coasts (Masalles et al., 1996). 3.2. Ecological analysis of communities Some of the structural parameters of the communities (e.g. coverage values and percentage of biological forms) varied greatly from one to each other (Table 3). Nevertheless, two clear groups could be distinguished by means of DCA: the short-live communities and the long-live perennials (Fig. 3). We did not ®nd a common pattern for diversity values since, as it can be seen in Table 3, high and low values were reached even in quadrates sampled on frequently disturbed habitats (e.g. compare communities 4 and 5 with number 13). On the one hand, some annual communities (4 and 5), dominated by Sisymbrium irio or Malva parvi¯ora and Hordeum murinum, were much more diverse than the rest of the phytocoenoses. On the other hand, some woody communities settled down on stressing areas such as walls (communities 6 and 7) or saline soils (community 13) reached low diversity values (Table 3). DCA also allowed us to detect ®ve ecological groups, the position of which in the scattergram seemed to be related to two main environmental complex variables. The corresponding bi-plot is shown in Fig. 3. The total variance explained by the two ®rst axes was not very high (Table 2). From these, axis 2 accounted for a higher percentage of variance (24.7%).

E.D. Dana et al. / Landscape and Urban Planning 59 (2002) 203±216

209

Fig. 3. Results of the DCA for the communities considered (C: community).

This could be caused by the multiplicity of factors that determine the composition of the urban ¯ora. The existence of complex gradients has been repeatedly noted (Rebele, 1994; NiemelaÈ, 1999). Nevertheless, and as a ®rst approximation, the graph of Fig. 3 shows a clear segregation among woody communities of groups I and II, (chamaephytes and nanophanerophytes) and the herbaceous phytocoenoses of groups III to V (therophytes and hemicryptophytes) (Table 3). ReleveÂs of the former groups were sampled on the most stable biotopes (abandoned crops and walls, respectively), while those of the latter came from repeatedly disturbed habitats. Since therophytes are the most favored by recurrent disturbance (Grime, 1979; Richards, 1986), axis 2 could be related to the frequency of disturbance events. The characteristic species of the communities of group I (e.g. Atriplex spp. or Salsola spp.) settle down Table 2 Percentage of variance explained by the axes as result of the application of detrended correspondence analysis to the releveÂs Axis

Increment

Cumulative

1 2 3

18.0 24.7 2.1

18.0 42.7 44.8

on saline soils (Castroviejo et al., 1990). The dependence of some of these communities upon soils with a certain content of salts has been previously reported. Thus, Alcaraz et al. (1991) noted that the soils on which these communities settle have high levels of clay and compactness as common features. In some cases, such as in the community with Salsola genistoides, these soils are characterized by high levels of clay, cations (mainly Na‡, Mg2‡), as well as by a low water reserve in a similar way to other communities growing on marine sediments (Cabello, 1997). According to numerous authors (e.g. MaranÄeÂs et al., 1998) saline and sub-saline soils conform a stressing substrate for plant development, which can arise in reductions of vegetative growing of non-adapted taxa by reducing water availability. Recently, it has been proposed that a clear relationship between edaphic salinity, seed bank and above-ground vegetation exists for some Chenopodiaceae communities (Egan and Ungar, 2000). In addition, therophytic communities of group IV which colonize slightly wet grounds (Dana et al., 1999b) are pulled to the right part of the axis 1. Therefore, axis 1 could be related to the water content of soil and/or to the moist regime. The highest percentage of phanerophytes was found in communities of group 1 (brushwoods of Chenopodiaceae), which showed also the lowest proportion of therophytes and hemicryptophytes. This fact could be

Table 3 Structural parameters of each community Community

Maximum development

Dominant species and their mean coverage

1

Summer

2 3

Winter Late Spring

4

Winter-Early Spring Winter-Early Spring

5

6 7

All year All year

8 9

Spring Winter

10

Summer

11

Summer

12

Summer

13 14 15

All year Summer All year

16

All year

Mean H' Mean Species coverage density

Percentage of coverage of biological forms

Chamaesyce chamaesyce (7.5) ‡ Chamaesyce serpens (38.8) ‡ Lollium rigidum (7.5) Chenopodium murale (50.0) Mesembryanthemum crystallinum (16) ‡ M. nodiflorum (11) ‡ Frankenia pulverulenta (7.0) Malva parviflora (17.1) ‡ Sisymbrium irio (5.3)

0.883

55.05

0.66

47.55

7.50

0

0

0

0.516 1.734

55.73 47.20

0.86 0.97

55.52 47.20

0.65 0

0 0

0 0

0 0

2.108

44.96

1.65

41.44

0.23

1.70

0

1.60

Hordeum murinum (16.5) ‡ Echium creticum (11.5) ‡ Beta vulgaris (7.5) ‡ Plantago lagopus (7.5) ‡ Spergularia bocconnei (6.0) Antirrhinum mollissimum (24.0) Parietaria judaica (70.8) ‡ Piptatherum miliaceum (8.1) Piptatherum miliaceum (75.0) Coronopus didymus (22.5) ‡ Poa annua (10.0) ‡ Aster squamatus (10.0) Aster squamatus (43.3) ‡ Piptatherum miliaceum (10.5) Conyza sumatrensis (28.3) ‡ Aster squamatus (10.0) ‡ Conyza bonariensis (9.2) ‡ Amaranthus muricatus (5.1) Conyza bonariensis (70.8) ‡ Piptatherum miliaceum (5.8) ‡ Amaranthus viridis (5.1) Atriplex halimus (75.0) Zygophyllum fabago (47.5) Salsola oppossitifoliae (46.0) ‡ Salsola vermiculata (13.5) ‡ Suaeda vera (11.0) Salsola genistoides (30.0)

2.017

57.18

1.82

57.14

0

0.02

0

0.02

0.770 0.554

30.12 82.58

0.63 0.65

0.55 10.38

3.28 75.00

26.29 1.92

0 0.63

0 0.03

0.76 1.263

87.8 45.2

1.70 1.42

78.40 44.40

6.98 0

1.92 0.83

0.63 0

0.03 0

1.55

70.5

1.27

51.39

10.78

4.30

0.50

3.53

1.738

100.9

1.32

54.63

8.75

0.43

0

0.704

85.9

0.91

79.20

5.43

0

0.83

0.198 1.157 1.064

77.8 65.8 73.2

0.92 0.89 0.76

1.45 5.90 0.17

0 1.70 0

1.039

40.2

1.17

1.73

0

Therophytes

Hemicryptophytes Chamaephytes Phanerophytes Geophytes

37.50 0

0.10 50.0 1.94

75.05 7.60 70.52

1.30 0.56 0

3.43

33.30

0

The term ``development'' is referred to the moment of the year in which maximum growth can be observed, whereas ``all year'' is reserved for perennial communities (mainly chamaephytes and nano-phanerophytes) in which no clear period of maximum development was detected. H' is measured as the Shannon diversity index using natural logarithms. Species density has been calculated as mean number of species/log sampling area (cm2); asterisk in superscript indicates those species that appeared in at least, 75% of the releveÂs. Only species with mean coverage values over 5% are presented in the table.

E.D. Dana et al. / Landscape and Urban Planning 59 (2002) 203±216

explained by the major competitive advantages of phanerophytes in stable environments (Grime, 1979) such as abandoned crops and old vacant-lots where they settle down. Group II, which contains the communities of ancient walls, is still pulled up to the upper part of the scattergram, at the left side of axis 1. Some authors have noted the stressing features of such types of habitats, mainly due to restrictions of water availability (Woodell, 1979; Woodell and Rossiter, 1959). This fact, together with the low disturbance that this type of biotope undergoes in the city, could explain their position in the scattergram. As a supporting prove of this assumption, we must note the presence of hairy leaves in Antirrhinum mollissimum or the succulence of Sarcocapnos enneaphylla, characteristics that have also been found in rupicolous vegetation of other cities (Gilbert, 1981; Prieto et al., 1973). In addition, the closenessÐbut at lower positionÐof community 7, with Parietaria judaica could be explained by the accumulation of nutrients and water at the base of the walls (Woodell, 1979; Gilbert, 1995). Group III is at an intermediate position of axis 1, but its `gravity center' is rather near that of group V, the releveÂs of which were sampled on watered gardens and basins. Hence, phytocoenoses of group III seem to show a slight preference by wet soils, preference that is clearer for communities 10 and 11. The position of these phytocoenoses together with that of number 12 in relation to axis 1, re¯ects the same water need found by Carretero (1994) for these three communities in rural environments. Finally, their position regarding axis 2 seems to support our ®eld observations: community 11 settles down on vacant-lots with fewer disturbance evidences than communities 8, 10 and 12. Position of the releveÂs of group IV in the scattergram is in agreement with our observations, since they are at the bottom of the graph. These quadrates were sampled on areas that undergo frequent and drastic disturbance events (complete destruction of vegetation can occur several times in a year). Although the communities belong to different classes (Table 1) they colonize very similar habitats: dumps, vacant-lots and basins. The biological adaptation of the implied species is evidenced by the great proportion of short-live species (Table 3) as indicated earlier. The communities of group V came from humid and disturbed soils: quadrates of community 1 came from

211

highly trampled soils in which water remains on the surface for a long time. In these communities, water may come from rainfall, e.g. in the case of releveÂs of community 9Ðduring the most humid months as well as from summer watering (community 1). If we consider the characteristics of the urban phytocoenoses in the studied site, the city of AlmerõÂa could be divided into several zones (see Fig. 4). Fig. 4 shows a synthetic view of the distribution patterns of the communities identi®ed in the present study, as well as the possible in¯uence of propagule donor sites. The zone designed as Z1 corresponds to the inner center built up to 1850, whereas Z2 matches the area covered by the city up to the 1960s±1970s. From the physiognomic viewpoint, the only difference is that ancient walls and ruins are present in Z1 whereas they are practically absent in Z2. Z3 can be considered as a complex matrix on saline soils in which both heavily and slightly disturbed habitats occur. This is the area more recently urbanized and harbors fragments of communities present in the outer rural lands together with typical urban communities (e.g. those of Stellarietea mediae). The presence of the endemic community of Antirrhinum mollissimum in the ancient walls of the urban area is related to its occurrence on the natural rocky cliffs that surround the western border of the city (FernaÂndez-Casas, 1971). The penetration of some rare non-ruderal species such as Ballota hirsuta, Satureja obovata or the endemisms Sarcocapnos enneaphylla and Antirrhinum mollissimum supports this hypothesis. Similarly, the salt-loving communities dominated by Chenopodiaceae species, broadly represented in the outer northern and eastern lands, could play a similar role in Z3 and its surroundings since there are still large proportions of saline and nonurbanized grounds in this zone. 3.3. Implications for urban planning The results obtained in this survey can be interpreted at two levels from the planning point of view. At the community level, the associations dominated by Antirrhinum mollissimum and by Salsola genistoides should be protected according to the European Habitats Directive (Anon, 1992). Their narrow distribution, especially in the former community, the speci®city of the habitat required and the legal necessity of adapting the protection strategies to the European criteria, justi®es the

212

E.D. Dana et al. / Landscape and Urban Planning 59 (2002) 203±216

Fig. 4. City-zones map of the urban area of AlmerõÂa. For abbreviations see text.

consideration of these communities for conservation strategies in the general. It should be noted that in the outer areas that are progressively being occupied, some communities are being intensively destroyed (e.g. Dana et al., 1998) in detriment of the maintenance of avian diversity (Manrique, 1993). At the species level, some of the taxa recorded within the releveÂs such as Antirrhinum mollissimum, Hammada articulata, Salsola genistoides, and Teucrium intricatum (see Appendix A), are listed at national and regional level in some red lists of threatened ¯ora (Barreno et al., 1984; Mota et al., 1998; DomõÂnguez-Lozano, 2000). Clearly, the occurrence of these species in the city of AlmerõÂa indicates the existence of suitable biotopes, even though their extent has been reduced and their connectivity fragmented (Fig. 4). Therefore, it would be necessary to allow the permanence of these habitats along with the develop-

ment of urbanization plans. How this could be achieved has been largely discussed for other cities (e.g. Haila and Levins, 1992; Gilbert, 1995) and speci®c methods for habitat selection have been developed (Wittig and Schreiber, 1983). It probably needs of integrating theoretical and practical basis from social and environmental sciences (Sukopp and Wittig, 1993; Pickett et al., 1997a,b). In the particular case of southeastern Spain, it has been proposed to keep large patches of selected communities as `natural' public parks. These urban parks might be connected by `green corridors' to stands located far from the city in¯uence (Mota et al., 1996). This would avoid the isolation of the preserved patches, which is one of the most important shortcomings for the maintenance of target species and communities in urban areas (Celesti and Fanelli, 1993; JokimaÈki, 1999; NiemelaÈ, 1999).

E.D. Dana et al. / Landscape and Urban Planning 59 (2002) 203±216

On the other hand, vegetation management in selected areas should emulate to some extent the natural disturbance conditions in those most valuable zones for conservation. For instance, in inner city areas, vegetation of ancient walls should be cleaned-up only in those buildings with a greater architectonic value and studies devoted to evaluate the possible damage caused by wall-dwelling taxa on other constructions should be conducted since systematic clearance of wall-dwelling species would cause a decrease in urban biodiversity. The occupation of those grounds covered by scrublands (e.g. those of Pegano salsoletea) should not be extensive, and patches of intact populations should be kept as they provide refuge to fauna and prevent soil against erosion. The lands cultivated by traditional means and nowadays abandoned represent a habitatsmatrix within the urban and suburban area of AlmerõÂa and should not be completely replaced by modern urbanization. Instead, local and regional authorities should promote re-occupation by farmers of some of the traditionally cultivated suburban areas and the use of not-intensive agriculture and grazing, activities generally compatible with the maintenance of a great number of species in the Mediterranean Basin (Groves and di Castri, 1991). 4. Conclusions For the ®rst time, urban vegetation has been studied in the Iberian Peninsula. In the case of the city of AlmerõÂa, 16 different plant communities have been found. Therophytes are the best represented due to their greater tolerance to disturbance. Nevertheless, we also found woody perennial species in biotopes such as ancient walls and old vacant-lots, where disturbance operates to a lesser extent. Despite the ¯oristic differences, these 16 communities can be resumed within ®ve ecological groups that seem to depend on two major parameters: disturbanceÐfrequency and intensityÐ and water availability for plant communities. According to the ¯oristic composition and to the ecological signi®cance of the communities detected, the city can be subdivided into three zones, which match the three historical phases of the city development. The presence of rare species and plant communities, some of them protected or quite frequently

213

listed in red catalogues, highlights the existence of suitable habitats for their survival within the urban matrix. These ®ndings suggest that it is possible to develop a more rational planning of urban development in southeastern Spain, in which cities would play a certain role in conservation policies. However, this would require not only the development of speci®c studies, but also the change of builders, managers and planners mentality and the integration of ecological and social sciences in the design of cities. In short, besides a restrictive policy dealing with urban planning, progressive ideas for improved vegetation management should be related to decision makers. Acknowledgements This work was partially supported by the Provincial Council of AlmerõÂa. Sincere thanks are due to Dr. J. PenÄas and Dr. J. Cabello (University of AlmerõÂa) for their help in the design of the study. We want to thank the valuable comments of Professor J.-J. Maillet about invasive plants during the 7th Symposium of the Sociedad EspanÄola de MalherbologõÂa. Ultimately, we are grateful to Dr. Anne Vivas (City Liberal Studies, University of Shef®eld) for her help with English. Appendix A Species recorded in the quadrates Adiantum capillus-veneris Amaranthus muricatus Amaranthus viridis Anagallis arvensis Anacyclus clavatus Antirrhinum mollissimum Arundo donax Asparagus horridus Asphodelus tenuifolium Asteriscus aquaticus Aster squamatus Atriplex glauca Atriplex halimus Atriplex semibaccata Avena barbata Ballota hirsuta

Hyoscyamus albus Lactuca serriola Lamarckia aurea Lavandula multifida Linum ussitatissimum Lolium rigidum Malva parviflora Malva sylvestris Matricaria chamomilla Melilotus indicus Mercurialis annua Mesembryanthemum crystallinum Mesembryanthemum nodiflorum Nicotiana glauca Oxalis pes-caprae Parapholis incurva

214

E.D. Dana et al. / Landscape and Urban Planning 59 (2002) 203±216

Appendix A (Continued )

References

Bassia hyssopifolia Beta vulgaris Bromus diandrus Bromus rigidus Calendula arvensis Capsella bursa-pastoris Carrichtera annua Cardaria draba

Alcaraz, F., SaÂnchez-GoÂmez, P., de la Torre, A., RõÂos, S., Rogel, J.A., 1991. Datos sobre la vegetacioÂn de Murcia (EspanÄa). Ediciones DM, Murcia. Anon, 1992. Directive 92/43 of the Council of the European Community on the Conservation of Habitats and Wild Fauna and Flora. European Community, Brussels. Barreno, E., Bramwell, D., Cabezudo, B., Cardona, M.A., Costa, M., FernaÂndez-Casas, J., FernaÂndez-Galiano, E., FernaÂndezPrieto, J.A., GoÂmez-Campo, C., HernaÂndez-Bermejo, E., Heywood, V.H., Izco, J., Llorens, L., Molero, J., Montserrat, P., Rivas-MartõÂnez, S., SaÂenz, C., Santos, A., ValdeÂs, B., Wilpret, W., 1984. Listado de plantas endeÂmicas, raras o amenazadas de EspanÄa. InformacioÂn Ambiental, 3, I-XXIV, MOPU, Madrid. Braun-Blanquet, J., 1964. P¯anzensoziologie. GruÈnduze der Vegetationskunde, 3rd Edition. Springer, Vienna (in German). BujaÂn, M., DõÂaz-VizcaõÂno, E., Cascudo, A., Iglesias, A., Rigueiro, A., 1998. Competition ¯oristique et abondance des mauvises herbes des anciens remparts de Lugo (Galice, Espagne). In: Proceedings 6eÁme Symposium Mediterraneen EWRS. Montpellier, pp. 221±223. Cabello, J., 1997. Factores ambientales, estructura y diversidad en comunidades de matorral de ambiente mediterraÂneo semiaÂrido (Tabernas-Sierra Alhamilla-NõÂjar, SE IbeÂrico), Tesis doctoral ineÂdita. Universidad de AlmerõÂa. Carretero, J.L., 1994. Las comunidades vegetales de Conyza bonariensis, Conyza canadensis, Conyza sumatrensis y Aster squamatus en EspanÄa. EcologõÂa 8, 193±202. Castroviejo, S., LaõÂnz, M., LoÂpez-GonzaÂlez, G., Monserrat, P., MunÄoz-Garmendia, F., Paiva, J., Villar, L. (Eds.), 1990. Flora IbeÂrica. Plantas vasculares de la PenõÂnsula IbeÂrica e Islas Baleares, Vol. II. Platanaceae-Plumbaginaceae. Real JardõÂn BotaÂnico de Madrid, CSIC, Madrid. Celesti, L., Fanelli, G., 1993. The vanishing landscape of the Campagna Romana. Landsc. Urban Plann. 24, 69±76. Celesti, G.L., Blasi, C., 1998. A comparison of the urban ¯ora of different phytoclimatic regions in Italy. Global Ecol. Biogeogr. Lett. 7, 367±378. Celesti, G.L., di Marzio, P., Blasi, C., 1999. The importance of alien and native species in the urban ¯ora of Italy. In: Proceedings of the 5th International Conference on the Ecology of Invasive Plants. Sardinia, p. 35. Chronopoulos, G., Christodoulakis, D., 1996. Contribution to the urban ecology of Greece: the ¯ora of the city of Patras and the surrounding area. Botanica Helvetica 106, 159±176. Cox, G.W., 1990. Laboratory Manual of General Ecology. Wm. C. Brown Publishers, Dubuque. Dana, E., Cabello, J., Mota, J.F., PenÄas, J., 1998. Acerca de tres especies nitro®las en la provincia de AlmerõÂa. Acta Botanica Malacitana 23, 252±256. Dana, E., Mota, J.F., Sanz-Elorza, M., Sobrino, E., 1999a. The alien ¯ora of south-eastern Spain. An advance for the exotic plants databaseÐa national research project. In: Proceedings of the 5th International Conference on the Ecology of Invasive Plants. Sardinia, p. 49.

Parietaria judaica Phalaris minor Piptatherum miliaceum Plantago coronopus Plantago lagopus Poa annua Polygonum aviculare Polypogon monspeliensis Chenopodium album Polycarpon tetraphyllum Chenopodium murale Portulaca oleracea Chondrilla juncea Reichardia tingitana Chrysanthemum coronarium Salsola genistoides Conyza albida Salsola oppositifolia Conyza bonariensis Salsola vermiculata Coronopus didymus Sarcocapnos enneaphylla Convolvulus arvensis Satureja obovata Coyncia tournefortii Schismus barbatus Cymbalaria muralis Sedum sediforme Cynodon dactylon Senecio vulgaris Cyperus rotundus Setaria verticillata Dittrichia viscosa Silene rubella Echium creticum Sisymbrium erysimoides Emex spinosa Sisymbrium irio Erodium chium Solanum nigrum Eruca vesicaria Sonchus asper Chamaesyce chamaesyce Sonchus oleraceus Chamaesyce serpens Sonchus tenerrimus Fagonia cretica Spergularia bocconnii Filago spp. Spergularia diandra Foeniculum vulgare Suaeda vera Frankenia pulverulenta Teucrium intricatum Halogeton sativus Urospermum picroides Hammada articulata Urtica urens Heliotropium curassavicum Volutaria lippii Hordeum murinum Zygophyllum fabago Hymenolobus procumbens Single asterisk indicates non-native species according to Mateo and Crespo (1990). Total alien species: 18. Double asterisks indicate those valuable species from the conservation viewpoint according to Barreno et al. (1984), Mota et al. (1998), Anon (1992) and DomÂõnguez-Lozano (2000). Number of species listed in red lists of vascular ¯ora: 5.

E.D. Dana et al. / Landscape and Urban Planning 59 (2002) 203±216 Dana, E., Cabello, J., Mota, J.F., Cueto, M., PenÄas, J., 1999b. Flora urbanõÂcola de la ciudad de Almeria: estudio ¯orõÂstico, ®tocenoloÂgico y autoecoloÂgico. MonografõÂas de Flora y VegetacioÂn BeÂticas 11, 133±149. Dana, E., Cabello, J., Mota, J.F., Cueto, M., PenÄas, J., 2000. FenologõÂa de la Flora Urbana en el Sureste IbeÂrico: AlmerõÂa (EspanÄa). Collectanea Botanica 25 (2), 207±216. Davison, A.W., 1977. The ecology of Hordeum murinum L. Part 3. Some effects of adverse climate. J. Ecol. 65, 523±530. DomõÂnguez-Lozano, F. (Ed.), 2000. Lista Roja de la Flora Vascular EspanÄola (Red List of Spanish Vascular Flora). ConservacioÂn Vegetal, no. 6. Universidad AutoÂnoma de Madrid, Madrid. Egan, T.P., Ungar, I.A., 2000. Similarity between seed banks and above-ground vegetation along a salinity gradient. J. Veg. Sci. 11, 189±194. FernaÂndez-Casas, J., 1971. ContribucioÂn al estudio de la vegetacioÂn almeriense. BoletõÂn Instituto BiologõÂa Aplicada 50, 49± 57. Fox, M.D., Fox, B.J., 1986. The susceptibility of natural communities to invasion. In: Groves, R.H., Burdon, J.J. (Eds.), Ecology of Biological Invasions: An Australian Perspective. Australian Academy of Science, Canberra, pp. 57±66. Franceschi, E.A., 1996. The ruderal vegetation of Rosario City, Argentina. Landsc. Urban Plann. 34, 11±18. Gilbert, O.L., 1981. Plant communities in urban environments. Landsc. Res. 6, 5±7. Gilbert, O.L., 1995. The Ecology of Urban Habitats. Chapman & Hall, Cambridge. Grime, J.P., 1979. Plant Strategies and Vegetation Processes. Wiley, Chichester. Groves, R.H., di Castri, F., 1991. Biogeography of Mediterranean Invasions. Cambridge University Press, Cambridge. Haila, Y., Levins, R., 1992. Humanity and Nature. Pluto Press, London. Hill, M.O., 1973. Diversity and evenness: a unifying notation and its consequences. Ecology 54, 427±432. Hill, M.O., 1979. DECORANAÐA FORTRAN Program for Detrended Correspondence Analysis and Reciprocal Averaging. Cornell University Press, Ithaca, NY. Hill, M.O., Gauch, H.G., 1980. Detrended correspondence analysis: an improved ordination technique. Vegetatio 42, 47± 58. JokimaÈki, J., 1999. Occurrence of breeding bird species in urban parks: effects of park structure and broad-scale variables. Urban Ecosyst. 3, 21±34. Jonsson, B.G., Moen, J., 1998. Patterns in species associations in plant communities: the importance of scale. J. Veg. Sci. 9 (3), 327±332. Kent, M., Stevens, R.A., Zhang, L., 1999. Urban plant ecology patterns and processes: a case study of the ¯ora of the City of Plymouth, Devon, UK. J. Biogeogr. 26, 1281±1298. Kunick, W., 1980. Comparison of the ¯ora of some cities of the central European lowlands. In: Bornkamm, R., Lee, J.A., Seaward, M.R.D. (Eds.), Urban Ecology. Proceedings of the 2nd European Ecology Symposium, BerlõÂn. Blackwell, Oxford, pp. 13±22.

215

Loidi, J., FernaÂndez-GonzaÂlez, F., 1994. The gypsophilous scrub communities of the Ebro Valley (Spain). Phytocoenologia 24, 383±399. Lepart, J., Debussche, M., 1991. Invasion processes as related to succession and disturbance. In: Groves, H.R., di Castri, F. (Eds.), Biogeography of Mediterranean Invasions. Cambridge University Press, Cambridge, pp. 159±177. McCune, B., Mefford, M.J., 1995. PC-ORD: Multivariate Analysis of Ecological Data, Version 2.0. MjM Software Design. Gleneden Beach, OR. Magurran, A., 1989. Diversidad ecoloÂgica y su medicioÂn. VedraÂ, Barcelona. Manrique, J., 1993. Las Aves de AlmerõÂa. Temas de AlmerõÂa, no. 3. Instituto de Estudios Almerienses, DiputacioÂn Provincial de AlmerõÂa, AlmerõÂa. MaranÄeÂs, A., SaÂnchez-Garrido, J.A., de Haro, S., SaÂnchez-LoÂpez, S.T., del Moral, F., 1998. AnaÂlisis de suelos: metodologõÂa e interpretacioÂn. Universidad de AlmerõÂa, Servicio de Publicaciones, AlmerõÂa. Masalles, R.M., Sans, F.X., Pino, J., 1996. Flora aloÂctona de origen americano en los cultivos de CatalunÄa. Anales del JardõÂn BotaÂnico de Madrid 54, 436±442. Mateo, G., Crespo, M.B., 1990. Claves para la Flora Valenciana. Del Cenia al Segura, Valencia. Montenegro, G., Teillier, S., Arce, P., Poblete, V., 1991. Introduction of plants into the Mediterranean-type climate area of Chile. In: Groves, H.R., di Castri, F. (Eds.), Biogeography of Mediterranean Invasions. Cambridge University Press, Cambridge, pp. 103±114. Mota, J.F., PenÄas, J., Castro, H., Guirado, J.S., Cabello, J., 1996. Agricultural, biodiversity development vs. biodiversity conservation: the Mediterranean semiarid vegetation in El Ejido (AlmerõÂa, southeastern Spain). Biodivers. Conserv. 5 (12), 1597±1617. Mota, J., PenÄas, J., PeÂrez-GarcõÂa, F.J., Cabello, J., Cueto, M., Merlo, E., 1998. Listado preliminar de la endemo¯ora de la provincia de AlmerõÂa y evaluacioÂn de su grado de amenaza. InvestigacioÂn y GestioÂn 3, 79±90. Mueller-Dombois, D., Ellenberg, H., 1974. Aims and Methods of Vegetation Ecology. Wiley, New York. NiemelaÈ, J., 1999. Ecology and urban planning. Biodivers. Conserv. 8, 119±131. Peet, R.K., 1974. The measurement of species diversity. Annu. Rev. Ecol. Systemat. 5, 285±307. Pickett, S.T.A., Burch Jr., W.R., Dalton, S.E., 1997a. Integrated urban ecosystem research. Urban Ecosyst. 1, 183±184. Pickett, S.T.A., Burch Jr., W.R., Dalton, S.E., Foresman, T.W., Grove, J.M., Rowntree, R., 1997b. A conceptual framework for the study of human ecosystems in urban areas. Urban Ecosyst. 1, 185±199. Pielou, E.C., 1975. Ecological Diversity. Wiley, New York. Podani, J., 1994. Multivariate Data Analysis in Ecology and Systematics: A Methodological Guide to the SYN-TAX 5.0 Package. SPB Academic Publishing, The Hague, The Netherlands. Prieto, P., Espinosa, P., FernaÂndez-FaÂbregas, S., 1973. EcologõÂa y ¯ora de los tejados de Granada, Vol. 2-2. Trabajos del

216

E.D. Dana et al. / Landscape and Urban Planning 59 (2002) 203±216

Departamento de BotaÂnica de la Universidad de Granada, pp. 97±102. Pysek, P., 1998. Alien and native species in Central European urban ¯oras: a quantitative comparison. J. Biogeogr. 25, 155±163. Raunkiaer, C., 1934. The Life Forms of Plants and Statistical Geography. Clarendon Press, Oxford. Rebele, F., 1994. Urban ecology and special features of urban ecosystems. Global Ecol. Biogeogr. Lett. 4, 173±187. Richards, A.J., 1986. Plant Breeding Systems. George Allen & Unwin, London. Roberts, D.W., 1986. Ordination on the basis of fuzzy set theory. Vegetatio 66, 123±131. Sukopp, H., Werner, P., 1983. Urban environment and vegetation. In: Holner, N., Werger, M.J.A., Ikusima, I. (Eds.), Man's Impact on Vegetation. Dr. W. Junk Publisher, The Hague, The Netherlands, pp. 247±260. È kologische Stadtplanung. In: Sukopp, H., Wittig, R., 1993. O Sukopp, H., Wittig, R. (Eds.), StadtoÈkologie. Gustav Fischer, Stuttgart, pp. 348±373. Van der Maarel, E., 1979. Transformation of cover-abundance data values in phytosociology and its effects on community similarity. Vegetatio 39, 97±114. Wittig, R., Schreiber, K.-F., 1983. A quick method for assessing the importance of open spaces in towns for urban nature conservation. Biol. Conserv. 26, 57±64. Woodell, S., 1979. The ¯ora of walls and pavings. In: Laurie, I.C. (Ed.), Nature in Cities. Wiley, Chichester, pp. 135±157. Woodell, S., Rossiter, J., 1959. The ¯ora of Durham's walls. In: Proceedings of the Botanical Society of the British Islands, Vol. 3, pp. 257±273. ElõÂas D. Dana is an Associate Professor of Weed Science and Botany at the Department of Plant Biology and Ecology of the

University of AlmerõÂa (Spain) and is author or co-author of over 30 national and international publications in the field of plant ecology. His actual main research field concentrates around urban ecology, weed ecology, plant invasions and plant succession. He is one of the co-ordinators of the National Work Group for the Study of Urban and Alien Plants of the Spanish Society for Weed Science (visit the website of the group http:// www.ual.es/personal/edana/alienplants for more information)  ridas'' and member of the research group ``EcologõÂa en Zonas A (code RNM-174). Soledad Vivas is in receipt of a PhD Grant at the University of AlmerõÂa. Her research activity is actually focused on the biological evaluation of the rivers of the southeast of Spain, their ecological functioning and the modelling of rivers response to human influence. She is also interested in the study of the influence of biological invasions upon native ecosystems. Juan Francisco Mota is Professor at the Department of Plant Biology and Ecology of the University of AlmerõÂa (Spain). He has been the Director of the Department from 1987 to 1997 and nowadays is the Director of the research group ``EcologõÂa en Zonas  ridas'' (RNM-174). His current research concentrates on plant A demography, plant succession and biodiversity evaluation. He has directed several PhD and is the author of over 50 publications on flora, vegetation, and plant ecology, some of them in international journals such as Plant Ecology (formerly Vegetatio), Biodiversity and Conservation and Journal of Vegetation Science. He is also the author of several books dealing with vegetation and flora of south Spain and the director of several Granted Research Projects.  ridas'' is Further information about the group ``EcologõÂa en Zonas A available at the website http://www.ual.es or can be directly requested from the team-leader.