Composition of Wild Plants Along an Urbanization Gradient in a Mediterranean City (Témara, Morocco)

Abstract

The accelerating pace of urbanization, both locally and regionally, is undoubtedly one of the main drivers impacting the structure and diversity of vegetation cover. However, the relationship between the diversity and distribution of plant communities and the degree of urbanization remains a topic requiring further research. This contribution aims to reveal the impact of the urbanization gradient on the structure and diversity of wild flora in the urban setting of a Mediterranean city (Témara, Morocco). The study area was subdivided into three sectors according to a decreasing urbanization gradient: the first sector delimits the city center (built-up area exceeding 75%), the second covers an area with a built-up area between 50 and 75%, and the third delimits the city’s peripheral area with a built-up area of less than 50%. Each sector was surveyed using four transects, and each transect was surveyed six times, resulting in 24 surveys covering 260.5 m² per sector. The comparative study of diversity between the three sectors was based on the calculation of alpha diversity (Shannon–Weaver index and Pielou’s evenness index) and beta diversity (Jaccard similarity index). The results showed modest specific similarity among the four transects (mean Jaccard index = 0.385) and greater floristic richness in the peripheral area than in the city center. However, no significant difference (F = 0.675, α = 0.05) was observed in specific diversity among the three sectors. In addition, the therophyte rate calculation revealed significant therophytization in the city center compared with the outskirts. Such findings may lead to a more complete understanding of the processes underlying the relationship between urbanization and plant diversity, which may have implications for the conservation of this diversity in urban settings.

1. Introduction

The urbanization gradient is an indirect and complex concept that depends on a range of environmental, social, and economic factors. It is defined as follows: “the spatial variation of environmental factors according to the intensity of urbanization, from natural landscapes to the highly urbanized areas” [1]. The urbanization gradient manifests itself physically by creating new land use patterns, altering the physical and chemical environment, creating new species combinations, and changing disturbance mechanisms [2]. The world’s population is increasingly drawn to urban centers, and it is predicted that by 2050, almost 68% of the population will live in urban areas [3]. For example, between 2012 and 2018, land use for urban expansion was 711 km²/year in Europe [4]. Rapid urban expansion has transformed large areas of natural land into impervious surfaces [5,6,7], resulting in instability of urban environments, habitat loss, and decreased biodiversity [5,6].

Spontaneous plants are characterized by their remarkable ability to adapt to urban conditions and serve as valuable habitats for other life forms [7]. Furthermore, these plants are known for their exceptional adaptability and growth in challenging habitats, such as cracks in walls and sidewalks, roadsides, and open spaces [8,9], and are therefore effective markers of urbanization patterns. Studies have found that the floristic composition of spontaneous plants in urban settings is influenced by a range of abiotic and biotic drivers [8,10]. Habitat-related drivers, including soil type and light intensity, can influence the distribution of spontaneous plant species diversity; however, at a larger scale, other drivers, such as climatic conditions, the degree of urbanization, and socio-economic status, explain most of the differences among plant communities [11]. The interaction between these different parameters can have consequences on the composition of wild plants in urban ecosystems. Therefore, the influence of urbanization on plant communities is becoming increasingly concerning and has become a hot topic in urban ecology [12,13]. Our comprehension of ecology and the factors shaping urban plant communities has thus evolved over the years. From examining how plants react to environmental pressures linked to urbanization to adopting theoretical models of landscape ecology, we now focus on the human and social factors that determine urban plant diversity. These changes are a reflection of ongoing efforts to apply new approaches toward a better understanding of these intricate dynamics [14,15,16].

In the Mediterranean region, previous studies on patterns of plant diversity along an urbanization gradient have mainly been focused on wooded areas (see, for example, [17,18,19]), the impact of buildings on plant communities in protected areas (e.g., [20,21]), ruderal vegetation and ecosystem services [22], the impact of chronic anthropogenic disturbances on peri-urban plant communities (e.g., [23,24,25]), and spatial patterns of land use (e.g., [10,26,27]). Studies conducted in Morocco are limited to examining changes in tree species diversity along an urban–rural gradient in a semi-natural forest [28], analyzing the diversity of spontaneous urban flora [29] and the ornamental flora in public green spaces [30]. Consequently, the impact of the urbanization gradient on natural plant communities in urban areas of Morocco needs to be investigated. This article is part of a broader study that aims to address two main objectives: the first is to analyze the diversity of spontaneous urban flora in Témara, and the second is to examine the impact of the urbanization gradient on its composition. The first objective was the subject of a previously published article [29]. The second is the subject of the present contribution, based on the flora inventoried in the first article, to address the following questions: (1) What is the relationship between the urbanization gradient and the richness of spontaneous plant species? (2) Does the floristic diversity of spontaneous flora vary according to the proportion of built-up areas?

2. Materials and Methods

2.1. Study Area

The study area (Témara, 33°55′13.177″ N, 6°55′38.629″ W) is a city located in northwestern Morocco (Figure 1). It is located 13 km southwest of the Bouregreg River, one of Morocco’s largest rivers (179 km), and 10 km northeast of the Yquem River. In terms of soil, the Témara area is characterized by red fersiallitic soils, locally known as Hamri (80%), and hydromorphic soils known as Hrach, which cover the remaining 20% [31]. It is characterized by rainfall that mainly occurs between October and April but remains exceptional from June to August (Figure 2). In terms of temperatures, this region has average annual temperatures ranging from 12 °C to 25 °C, with maximum temperatures recorded in August and minimum temperatures between November and March. The Témara station is part of the subhumid bioclimatic zone and is located on the edge of the semi-arid bioclimatic zone with a warm winter variant.

2.2. Sampling Methodology

In urban settings, traditional sampling methods are not suitable: the quadrat method, which uses sampling areas of fixed size (e.g., 1 m² for grasslands, 100 m² for forests [32]); the transect method, based on quadrats placed at regular intervals [33]; and the contact-point method, in which a rod is lowered at regular intervals and each contact with a plant is recorded [34]. The probability of selecting inaccessible areas or areas lacking vegetation is too high when using systematic sampling (taking surveys at regular intervals) or random sampling (selecting the location of stations to be surveyed at random) [35]. The study area was traversed by four transects labeled A, B, C, and D, starting from the city center. For each transect, sampling stations were selected based on three categories classified by size (Figure 3): (1) micro-habitats (0.5 m² survey plots) covering plants that grow spontaneously under trees, in cracks, at the base of walls, and on the edges of sidewalks; (2) meso-habitats (plots measuring 2 or 9 m²) that concern plants growing in medium-sized areas such as roadsides and public green spaces; and (3) macro-habitats (25 m² or 100 m² plots) that include relatively large sites such as wasteland and large non-built areas. Species were identified using the flora texts below: the Catalog of Plants of Morocco [36,37,38,39], and the Synonymic Index of the Flora of North Africa [40,41].

2.3. Urbanization Intensity Quantification

The study area was subdivided into three sectors according to a decreasing urbanization gradient: the first sector delimits the “city center” and is characterized by a built-up area exceeding 75%, the second covers a built-up area between 50 and 75%, and the third delimits the peripheral area of the city with a built-up area of less than 50% (Figure 4). Each sector was subjected to six floristic surveys per transect, totaling 24 surveys that covered a total area of 260.5 m² per sector (

Table 1. Distribution of survey plots by sector.

		Sector 1			Sector 2			Sector 3
T	Srv.	Area (m2)	Latitude	Longitude	Area (m2)	Latitude	Longitude	Area (m2)	Latitude	Longitude
A	1	9	33°55′20″ N	6°55′36″ W	2	33°55′52″ N	6°55′38″ W	9	33°56′10″ N	6°55′37″ W
	2	9	33°55′22″ N	6°55′36″ W	9	33°55′55″ N	6°55′38″ W	9	33°56′14″ N	6°55′37″ W
	3	9	33°55′26″ N	6°55′38″ W	2	33°55′57″ N	6°55′39″ W	25	33°56′20″ N	6°55′39″ W
	4	9	33°55′30″ N	6°55′38″ W	9	33°56′00″ N	6°55′39″ W	25	33°56′22″ N	6°55′40″ W
	5	0.5	33°55′33″ N	6°55′38″ W	9	33°56′02″ N	6°55′38″ W	25	33°56′27″ N	6°55′42″ W
	6	9	33°55′38″ N	6°55′39″ W	9	33°56′05″ N	6°55′38″ W	9	33°56′33″ N	6°55′44″ W
B	1	2	33°55′10″ N	6°55′35″ W	9	33°55′06″ N	6°56′10″ W	25	33°55′19″ N	6°57′12″ W
	2	9	33°55′12″ N	6°55′42″ W	25	33°55′06″ N	6°56′14″ W	25	33°55′28″ N	6°57′25″ W
	3	2	33°55′11″ N	6°55′47″ W	25	33°55′05″ N	6°56′20″ W	25	33°55′30″ N	6°57′28″ W
	4	25	33°55′09″ N	6°55′54″ W	25	33°55′12″ N	6°56′40″ W	9	33°55′33″ N	6°57′22″ W
	5	25	33°55′08″ N	6°55′59″ W	2	33°55′13″ N	6°56′48″ W	9	33°55′36″ N	6°57′38″ W
	6	25	33°55′07″ N	6°56′02″ W	25	33°55′11″ N	6°56′59″ W	9	33°55′35″ N	6°57′41″ W
C	1	9	33°55′06″ N	6°55′39″ W	0.5	33°54′21″ N	6°55′40″ W	0.5	33°53′45″ N	6°55′39″ W
	2	9	33°55′01″ N	6°55′39″ W	25	33°54′17″ N	6°55′40″ W	2	33°53′40″ N	6°55′38″ W
	3	0.5	33°54′56″ N	6°55′41″ W	25	33°54′15″ N	6°55′41″ W	2	33°53′35″ N	6°55′38″ W
	4	0.5	33°54′47″ N	6°55′40″ W	9	33°54′07″ N	6°55′40″ W	25	33°53′29″ N	6°55′39″ W
	5	25	33°54′42″ N	6°55′40″ W	0.5	33°53′59″ N	6°55′39″ W	9	33°53′27″ N	6°55′38″ W
	6	2	33°54′31″ N	6°55′40″ W	9	33°53′53″ N	6°55′38″ W	9	33°53′24″ N	6°55′38″ W
D	1	2	33°55′14″ N	6°55′39″ W	2	33°55′10″ N	6°54′48″ W	0.5	33°55′58″ N	6°53′31″ W
	2	2	33°55′14″ N	6°55′32″ W	9	33°55′07″ N	6°54′27″ W	0.5	33°55′04″ N	6°53′26″ W
	3	2	33°55′12″ N	6°55′24″ W	9	33°55′05″ N	6°54′16″ W	2	33°55′03″ N	6°53′19″ W
	4	25	33°55′11″ N	6°55′16″ W	9	33°55′05″ N	6°54′07″ W	2	33°55′04″ N	6°53′14″ W
	5	25	33°55′11″ N	6°55′11″ W	9	33°55′03″ N	6°54′01″ W	2	33°55′04″ N	6°53′05″ W
	6	25	33°55′10″ N	6°55′06″ W	2	33°55′03″ N	6°53′52″ W	2	33°55′05″ N	6°53′05″ W

T: transect, Srv.: survey.

). The comparative study of diversity between the three sectors was based on the measurement of alpha diversity (using the Shannon–Weaver diversity index and the Pielou equitability index) and beta diversity (using the Jaccard similarity index).

2.4. Data Analysis

2.4.1. Specific Similarity Measurement Between Transects

To estimate the degree of floristic similarity between the four transects, we used the Jaccard similarity index (J) [42], calculated using the following formula:

$${\displaystyle \frac{\mathrm{a}}{\mathrm{a}+\mathrm{b}+\mathrm{c}}}$$

where a is the number of species common to both transects, b is the number of species present in only one of the two transects, and c is the number of species present only in the other transect. This index ranges from 0, when there are no species common to both sites (0% similarity), to 1, when both sites share the same species (100% similarity).

2.4.2. Shannon–Weaver Diversity Index (H′)

The Shannon–Weaver index (H′), also known as the Shannon–Wiener index, expresses diversity by taking into account the number of plant species and the abundance of individuals within each of these species [43]. It is given by the following formula:

$${\mathrm{H}}^{\prime }=-{\displaystyle \sum _{\mathrm{i}=1}^{\mathrm{S}}}\mathrm{p}\mathrm{i}\ast \ln \mathrm{p}\mathrm{i}$$

where S is the total number of species in the sample (=species richness); pi represents the proportion of individuals of each species (i) relative to the total number of individuals, ni/N; (ni) is the number of individuals of the species (i); N is the total number of individuals of all species; and ln is the natural logarithm. Due to the difficulty in determining the number of individuals of each species in the study area, the Shannon–Weaver index was calculated using the van der Maarel (1979) method, which is based on converting abundance-dominance coefficients into percentage cover (Rij) according to

Table 2. Conversion of abundance–dominance coefficient to average coverage (%).

Braun Blanquet Abundance-Dominance Coefficient	Average Coverage (%)
+	0.1
1	5
2	17.5
3	37.5
4	62.5
5	87.5

[44]:

The specific diversity index (H′) is obtained as follows, adopting the approach of Vanpeene Bruhier (1998), using the following equation [45]:

$${\mathrm{H}}^{\prime }=-{\displaystyle \sum _{\mathrm{j}=1}^{\mathrm{n}\mathrm{i}}}\left[{\displaystyle \frac{\mathrm{R}\mathrm{i}\mathrm{j}}{{\displaystyle {\sum }_{\mathrm{j}=1}^{\mathrm{n}\mathrm{i}}}\mathrm{R}\mathrm{i}\mathrm{j}}}\times {\mathrm{l}\mathrm{o}\mathrm{g}}_2\left({\displaystyle \frac{\mathrm{R}\mathrm{i}\mathrm{j}}{{\displaystyle {\sum }_{\mathrm{j}=1}^{\mathrm{n}\mathrm{i}}}\mathrm{R}\mathrm{i}\mathrm{j}}}\right)\right]$$

where ni is the number of species present in survey (i), and Rij represents the relative coverage of the different species (j) in survey (i). The Shannon–Weaver index is expressed in bits and typically ranges from 1 to 5 bits. The higher the value of this index, the greater the diversity. When H′ exceeds 3.5 bits, this indicates high diversity within the plant community in question, meaning that environmental conditions are favorable for the establishment of a large number of species in almost equal proportions. On the other hand, if H′ is less than 2.6 bits, this indicates that environmental conditions are unfavorable and lead to a high degree of taxon specialization; the community is then dominated by a few species that largely share the coverage at the community level [46]. In addition, the H′ index makes it possible to quantify the heterogeneity of biodiversity in an environment and thus observe changes in a population over time. By expressing the number of species and their abundance, this index provides information on the response of vegetation to environmental disturbances caused by human activities [44,47]. To compare differences in alpha diversity composition among spontaneous plants, we first performed a Kolmogorov–Smirnov and a Shapiro–Wilk test to verify the normal distribution of the results and a Levene test to verify the homogeneity of variances. Then, a one-way analysis of variance (ANOVA) was performed (Tukey’s test) using IBM SPSS Statistics software (version 31.0.0.0, 2025) to compare Shannon–Weaver indices between surveys from different sectors.

2.4.3. Pielou’s Evenness Index (E)

Pielou’s evenness index (E) refers to the equal distribution of individuals within a species. In other words, it provides information on the relative abundance of different species and their regularity in the population [48]. Its value ranges from 0 (i.e., dominance of one species) to 1 (i.e., equal distribution of species). It is measured by the following expression:

$$\mathrm{E}={\displaystyle \frac{{\mathrm{H}}^{\prime }}{{\mathrm{H}}^{\prime }\mathrm{m}\mathrm{a}\mathrm{x}}}={\displaystyle \frac{{\mathrm{H}}^{\prime }}{\ln \left(\mathrm{S}\right)}}$$

where H′ is the Shannon–Weaver diversity index, S represents the total number of species in the sample, and H′max = ln(S) represents the maximum theoretical diversity.

2.4.4. Disturbance Index

To assess the impact of human activities on the environment, a disturbance index (DI) was calculated. This index considers the proportion of therophytes and chamaephytes in relation to the total number of species recorded at a given site. The more a habitat is impacted by anthropization, the more therophytes and chamaephytes become prevalent there [49]. The main characteristic of therophytes lies in their ability to survive periods of disturbance in seed form, which gives them distinct advantages over other biological types. Indeed, in urban settings, where human activities disturb the soil and create bare patches, annual plants rapidly colonize these disturbed habitats thanks to their short life cycles [50], before a new disturbance occurs and before perennials become established. As for chamaephytes, these plants are characterized by their small size compared to other perennials and by their survival buds located close to the ground (less than 25 cm) [51]. This allows them to withstand physical disturbances (trampling or vehicle traffic). These plants, which are often creeping, cushion-like, or hugging the ground, protect their buds from direct mechanical damage. Furthermore, in Mediterranean climates, these plants can survive droughts thanks to the high level of heteromorphism in their transpiration organs [52]. The DI is obtained using the following expression:

$$\mathrm{D}\mathrm{I}={\displaystyle \frac{\mathrm{N}\mathrm{u}\mathrm{m}\mathrm{b}\mathrm{e}\mathrm{r} \mathrm{o}\mathrm{f} \mathrm{t}\mathrm{h}\mathrm{e}\mathrm{r}\mathrm{o}\mathrm{p}\mathrm{h}\mathrm{y}\mathrm{t}\mathrm{e}\mathrm{s}+\mathrm{N}\mathrm{u}\mathrm{m}\mathrm{b}\mathrm{e}\mathrm{r} \mathrm{o}\mathrm{f} \mathrm{c}\mathrm{h}\mathrm{a}\mathrm{m}\mathrm{a}\mathrm{e}\mathrm{p}\mathrm{h}\mathrm{y}\mathrm{t}\mathrm{e}\mathrm{s}}{\mathrm{T}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l} \mathrm{n}\mathrm{u}\mathrm{m}\mathrm{b}\mathrm{e}\mathrm{r} \mathrm{o}\mathrm{f} \mathrm{s}\mathrm{p}\mathrm{e}\mathrm{c}\mathrm{i}\mathrm{e}\mathrm{s}}}$$

3. Results and Discussion

3.1. Floristic Data

The 72 floristic surveys carried out enabled us to obtain the following results (

Table 3. Floristic composition by sector.

Species	Family	Biological Type	Sector 1	Sector 2	Sector 3
Achyranthes aspera L.	Amaranthaceae	Nph	1	1	0
Alternanthera caracasana Kunth	Amaranthaceae	Ge	1	0	0
Amaranthus blitum L.	Amaranthaceae	Th	1	0	0
Amaranthus deflexus L.	Amaranthaceae	Ge	1	0	1
Amaranthus retroflexus L.	Amaranthaceae	Th	0	1	1
Ammi majus L.	Apiaceae	Th	1	1	1
Anacyclus radiatus Loisel.	Asteraceae	Th	1	1	1
Anagallis foemina Mill.	Primulaceae	Th	0	0	1
Andryala integrifolia L. subsp ampelusia Maire	Asteraceae	Hem	1	1	0
Anisantha diandra (Roth) Tutin	Poaceae	Th	1	1	1
Arctotheca calendula (L.) Levyns	Asteraceae	Th	1	1	1
Arisarum vulgare O. Targ. Tozz.	Araceae	Ge	0	1	1
Arundo donax L.	Poaceae	Ge	0	1	0
Asparagus acutifolius L.	Asparagaceae	Ge	0	0	1
Astragalus hamosus L.	Fabaceae	Th	0	1	1
Atriplex patula L.	Amaranthaceae	Cham	1	1	1
Avena fatua L.	Poaceae	Th	1	1	0
Bromus hordeaceus L.	Poaceae	Th	0	1	0
Calendula arvensis (Vaill.) L.	Asteraceae	Th	1	1	0
Camphorosma monspeliaca L.	Amaranthaceae	Cham	0	0	1
Capsella bursa-pastoris (L.) Medik.	Brassicaceae	Th	1	1	1
Carduus pycnocephalus L.	Asteraceae	Th	1	0	1
Carduus tenuiflorus Curtis	Asteraceae	Hem	1	1	1
Centaurea calcitrapa L.	Asteraceae	Th	1	1	1
Centaurea sphaerocephala L.	Asteraceae	Hem	0	0	1
Cestrum parqui L’Hér.	Solanaceae	Nph	0	1	0
Chamaerops humilis L.	Arecaceae	Nph	0	0	1
Chenopodium ambrosioides L.	Amaranthaceae	Th	1	0	1
Chenopodium murale L.	Amaranthaceae	Th	1	1	1
Chenopodium vulvaria L.	Amaranthaceae	Th	0	0	1
Cichorium intybus L.	Asteraceae	Hem	0	1	1
Convolvulus althaeoides L.	Convolvulaceae	Hem	1	1	0
Crepis bursifolia L.	Asteraceae	Hem	1	1	1
Crepis foetida L.	Asteraceae	Th	1	1	1
Crepis sancta (L.) Bornm.	Asteraceae	Th	1	1	1
Cynodon dactylon (L.) Pers.	Poaceae	Hem	1	1	1
Cyperus rotundus L.	Cyperaceae	Ge	0	1	1
Dactylis glomerata L.	Poaceae	Hem	1	0	1
Datura stramonium L.	Solanaceae	Th	0	1	0
Dittrichia viscosa (L.) Greuter	Asteraceae	Cham	0	1	1
Echium plantagineum L.	Boraginaceae	Hem	1	1	1
Eleusine indica (L.) Gaertn.	Poaceae	Th	0	0	1
Elytrigia juncea (L.) Nevski	Poaceae	Ge	0	1	0
Elytrigia repens (L.) Desv. ex Nevski	Poaceae	Ge	1	0	0
Emex spinosa (L.) Campd.	Polygonaceae	Th	1	1	1
Eragrostis curvula (Schrad.) Nees	Poaceae	Hem	1	1	1
Erigeron bonariensis L.	Asteraceae	Th	1	1	1
Erigeron sumatrensis Retz.	Asteraceae	Th	1	0	1
Erodium ciconium (L.) L’Hér.	Geraniaceae	Th	1	1	1
Euphorbia terracina L.	Euphorbiaceae	Ge	1	1	1
Filago pyramidata L.	Asteraceae	Th	1	0	0
Frankenia hirsuta L.	Frankeniaceae	Cham	0	0	1
Galium tricornutum Dandy	Rubiaceae	Th	1	1	1
Glaucium flavum Crantz	Papaveraceae	Hem	1	0	0
Glebionis coronaria (L.) Spach	Asteraceae	Th	1	1	0
Heliotropium europaeum L.	Boraginaceae	Th	0	0	1
Hordeum murinum L.	Poaceae	Th	1	1	1
Lagurus ovatus L. subsp. nanus (Guss) Messeri	Poaceae	Th	1	0	1
Lamarckia aurea (L.) Moench	Poaceae	Th	1	0	0
Leontodon hispidus L.	Asteraceae	Hem	0	1	0
Lepidium didymum L.	Brassicaceae	Th	1	1	1
Limonium tuberculatum (Boiss.) Kuntze	Plumbaginaceae	Cham	0	0	1
Lolium multiflorum Lam.	Poaceae	Hem	1	1	1
Loncomelos narbonensis (L.) Raf.	Asparagaceae	Ge	0	0	1
Lotus creticus L.	Fabaceae	Hem	0	0	1
Lotus ornithopodioides L.	Fabaceae	Th	1	0	1
Lupinus micranthus Guss.	Fabaceae	Th	1	0	1
Lycium ferocissimum Miers	Solanaceae	Ph	1	1	1
Malva multiflora (Cav.) Soldano, Banfi & Galasso	Malvaceae	Hem	1	0	1
Malva parviflora L.	Malvaceae	Th	1	1	1
Marrubium vulgare L.	Lamiaceae	Cham	0	1	0
Medicago polymorpha L.	Fabaceae	Th	1	1	0
Melilotus indicus (L.) All.	Fabaceae	Th	0	1	0
Mercurialis annua L.	Euphorbiaceae	Th	1	1	1
Mirabilis jalapa L.	Nyctaginaceae	Hem	0	1	0
Myriolimon ferulaceum (L.) Lledo, Erben & M.B.Crespo	Plumbaginaceae	Cham	0	0	1
Nicotiana glauca Graham	Solanaceae	Nph	1	1	1
Notobasis syriaca (L.) Cass.	Asteraceae	Th	1	0	0
Ononis natrix L.	Fabaceae	Cham	0	1	0
Oxalis corniculata L.	Oxalidaceae	Th	1	0	1
Oxalis pes-caprae L.	Oxalidaceae	Ge	1	1	1
Panicum repens L.	Poaceae	Hem	1	0	0
Papaver dubium L.	Papaveraceae	Th	1	0	0
Parietaria judaica L.	Urticaceae	Hem	0	1	0
Paronychia argentea Lam.	Caryophyllaceae	Hem	0	1	0
Peganum harmala L.	Nitrariaceae	Cham	0	0	1
Persicaria decipiens (R. Br.) K. L. Wilson	Polygonaceae	Hem	1	1	1
Phleum pratense L.	Poaceae	Hem	0	1	1
Plantago macrorhiza Poir.	Plantaginaceae	Hem	0	0	1
Plantago major L.	Plantaginaceae	Hem	1	1	1
Poa trivialis L.	Poaceae	Hem	1	0	1
Polycarpon tetraphyllum (L.) L.	Caryophyllaceae	Th	0	1	1
Polygonum maritimum L.	Polygonaceae	Hem	1	0	1
Polypogon viridis (Gouan) Breistr.	Poaceae	Hem	1	1	0
Portulaca oleracea L.	Portulacaceae	Th	0	0	1
Raphanus raphanistrum L. subsp. landra (DC.) Bonnier & Layens	Brassicaceae	Th	1	1	1
Reichardia tingitana (L.) Roth	Asteraceae	Hem	1	0	1
Ricinus communis L.	Euphorbiaceae	Nph	1	0	1
Salpichroa origanifolia (Lam.) Baill.	Solanaceae	Cham	0	1	1
Salsola kali L.	Amaranthaceae	Th	0	0	1
Salvia aegyptiaca L.	Lamiaceae	Th	1	0	0
Salvia verbenaca L.	Lamiaceae	Hem	0	0	1
Scleranthus perennis L.	Caryophyllaceae	Hem	0	1	0
Scolymus hispanicus L.	Asteraceae	Hem	1	0	1
Setaria verticillata (L.) P. Beauv.	Poaceae	Th	0	0	1
Silene gallica L.	Caryophyllaceae	Th	0	1	0
Silybum marianum (L.) Gaertn.	Asteraceae	Hem	1	1	1
Sinapis arvensis L.	Brassicaceae	Th	1	1	1
Sinapis pubescens L.	Brassicaceae	Th	1	1	1
Sisymbrium irio L.	Brassicaceae	Th	1	0	0
Sisymbrium officinale (L.) Scop.	Brassicaceae	Th	0	1	0
Solanum linnaeanum Hepper & P.–M. L. Jaeger	Solanaceae	Cham	0	0	1
Solanum nigrum L.	Solanaceae	Th	1	0	0
Solanum villosum Mill.	Solanaceae	Th	0	1	0
Sonchus asper (L.) Hill	Asteraceae	Hem	0	1	1
Sonchus oleraceus L.	Asteraceae	Hem	1	1	1
Spergularia rubra (L.) J. Presl & C. Presl	Caryophyllaceae	Th	1	0	1
Squilla maritima (L.) Steinh.	Asparagaceae	Ge	0	0	1
Tamarix gallica L.	Tamaricaceae	Ph	0	0	1
Thapsia garganica L.	Apiaceae	Hem	0	0	1
Trifolium fragiferum L.	Fabaceae	Hem	0	0	1
Trisetaria panicea (Lam.) Paunero	Poaceae	Th	0	1	1
Urtica dioica L.	Urticaceae	Ge	1	1	0
Urospermum picroides (L.) Scop. ex F.W.Schmidt	Asteraceae	Th	0	1	1
Verbascum sinuatum L.	Scrophulariaceae	Hem	1	1	1
Verbesina encelioides (Cav.) Benth & Hooke.f. ex A.Gray	Asteraceae	Th	0	1	1
Visnaga daucoides Gaertn.	Apiaceae	Th	1	1	0
Volutaria tubuliflora (Murb.) Sennen	Asteraceae	Th	1	1	1
Total			75	76	90

Th: Therophyte, Hem: Hemicryptophyte, Ge: Geophyte, Cham: Chamaephyte, Nph: Nanophanerophyte, Ph: Phanerophyte.

): Sector 1 recorded 75 species and 66 genera belonging to 21 botanical families, among which Asteraceae and Poaceae predominate with 20 species (26.66%) and 13 species (17.33%), respectively. Sector 2 showed 76 species and 72 genera distributed across 23 families, with Asteraceae (19 species and 16 genera, 25%) and Poaceae (13 species and 13 genera, 17.1%) also dominating. Sector 3 yielded 90 species and 76 genera belonging to 28 families, with Asteraceae and Poaceae being the most represented (21 species, or 23.33%, and 12 species, or 13.33%, respectively).

3.2. Biological Types by Sector

The classification of plant species based on their life forms has been widely used as an indicator of the adaptive strategies employed by these species, thereby enabling the testing of hypotheses regarding the relationship between the environment and the functional traits of plants [53,54,55]. Analysis of the biological spectrum of the three sectors (S1, S2, and S3) revealed a specific adaptive response of the spontaneous flora to the urbanization gradient (Figure 5). Indeed, the results show close values in terms of the number of therophytes (S1 = 42; S2 = 38; S3 = 42), hemicryptophytes (S1 = 22; S2 = 21; S3 = 26), geophytes (S1 = 6; S2 = 8; S3 = 8), nanophanerophytes (S1 = 3; S2 = 3; S3 = 3), and phanerophytes (S1 = 1; S2 = 1; S3 = 2). Furthermore, a predominance of therophytes and hemicryptophytes was observed in all three sectors. This finding is consistent with the results observed in other Mediterranean cities, such as Bologna (Italy) [56], Rome [57] and in seven cities in the Po Valley, (northern Italy) [58]. This can be explained by the rapid life cycle of these plants. Indeed, Grime (2006), in his work on species adaptation strategies, noted that unstable environments favor fast-growing life forms [59]. Furthermore, Fanelli et al. (2006) used the therophyte-to-hemicryptophyte (T/H) ratio to assess the impact of anthropogenic disturbance on urban flora [60]. The authors found that this ratio correlates with the CR (competitive, ruderal) and CSR (competitive, stress-tolerant, ruderal) adaptive strategies proposed by Grime. The T/H ratio values for the three sectors are close (S1 = 1.9; S2 = 1.81; and S3 = 1.61). Geophytes are the third most common life form in the study area. The buds of these plants are carried by underground storage organs (rhizomes, tubers, bulbs or corms) that serve as food reserves, enabling geophytes to reproduce vegetatively more rapidly than many other life forms once the unfavorable season ends [61]. This life strategy may give it an advantage against human disturbances and the harsh climatic conditions prevalent in the Mediterranean basin. Nanophanerophytes and phanerophytes are the least common in all three sectors. These plant types generally prefer stable and less disturbed habitats [53], conditions that are, in most cases, unavailable in urban settings. Furthermore, soil impermeability represents a significant constraint on deep root development required by these woody plants. Moreover, the frequent and systematic management of the urban environment (mowing, pruning, cleaning) eliminates these plants at early stages of their development.

3.3. Specific Similarity Between Transects

Calculating the Jaccard index (J) allowed us to assess the specific similarity between the four transects (

Table 4. Assessment of similarity between transects. (a): number of species common to both transects, (b): number of species exclusively present in one of the two transects, (c): number of species exclusively present in the other transect.

Compared Transects	a	b	c	Jaccard Similarity Index (J)
Transect A vs. Transect B	39	30	52	0.322
Transect A vs. Transect C	38	31	26	0.40
Transect A vs. Transect D	35	34	34	0.339
Transect B vs. Transect C	47	44	17	0.435
Transect B vs. Transect D	47	44	22	0.415
Transect C vs. Transect D	38	26	31	0.40

). The results revealed a greater similarity between transects B and C (J = 0.435), followed by that between transects B and D (J = 0.415). In addition, the similarities between A and B and between A and D were very close (J = 0.322 and J = 0.339, respectively), while the transects A vs. C and C vs. D had the same value (J = 0.40), meaning that they share the same species. Generally, the similarity between the four transects in the study area is considered modest (average J index = 0.385). This can be explained by the nature of the urban environment. Indeed, this ecosystem, which is fragmented and subject to human action, is a mosaic of microhabitats with different and even contrasting characteristics. In other words, each transect may pass through sampling points that are largely distinct from the other transects in terms of floristic composition. Consequently, very few species will be shared by these transects.

3.4. Diversity and Disturbance Indices

According to the results presented in

Table 5. Floristic diversity, regularity, therophytization, and disturbance in the three sectors studied (S: Species richness, N (Th): Number of therophytes, N (Cham): Number of chamaephytes, DI: Disturbance index).

Sector	S	H′	E	N (Th)	N (Cham)	Therophytization (%)	DI (%)
1	75	1.90 bits	0.44	42	1	56.00	57.33
2	76	1.84 bits	0.42	38	5	49.33	56.57
3	90	1.60 bits	0.35	42	9	46.66	56.66

, sector 3 (built-up area < 50%) shows the highest species richness (90 species), but with the lowest Pielou index. This indicates that this area is the richest in species but has a less equitable and less regular distribution among its taxa than the other two sectors. Sector 1 (built-up area > 75%) and sector 2 (built-up area between 50 and 75%) showed almost similar species richness (75 species for sector 1 and 76 species for sector 2) and evenness (E_{Sector 1} = 0.44 and E_{Sector 2} = 0.42). Regarding the Shannon–Weaver index (H′), the results showed a non-significant difference (F = 0.675, α = 0.05) between the specific diversities of the three sectors (H′_{Sector 1} = 1.90 bits, H′_{Sector 2} = 1.84 bits, H′_{Sector 3} = 1.60 bits) (Figure 6). Consequently, we confirm that the percentage of urbanized areas (explanatory variable) has no significant impact on the specific diversity of spontaneous plant communities (explained variable) in the study area. These results are consistent with the study by Blouin et al. (2019), which recorded no effect of the local level of intensity of urbanization on spontaneous plant communities in vacant lots, whether in a more urbanized landscape (Montreal) or another less urbanized one (Quebec) [62]. Thus, Chen et al. (2025) found that there is no significant correlation between spontaneous plant diversity and the degree of urbanization in different habitats (park green space, road green space, and wilderness habitat) in the city of Jinan (China) [63]. In addition, Qian and his team (2020) showed that urban growth and natural landscape characteristics (type and quality of habitats and topography) impact the composition of urban spontaneous vegetation [64]. This suggests that the effect of urbanization is not always consistent and can be shaped by a city’s natural landscape. Figure 7 shows three Quantile-Quantile plots comparing the distribution of the Shannon–Weaver Index to a theoretical normal distribution for the three sectors. We note that the majority of values follow a straight line, with slight dispersion, particularly at the extremes, for the three graphs. This indicates that the distribution of Shannon index values in the three sectors follows a normal distribution. In other words, most of the plots surveyed show moderate plant diversity with few extreme points (very poor or very diverse areas), with some minor differences in terms of diversity between the three sectors. Sector 2 showed slightly higher Shannon index values (reaching approximately 4) compared to sectors 2 and 3, which stopped at around 3 or 3.5. Therefore, sector 1 can be considered more diverse overall. In terms of homogeneity, sector 2 showed slightly more variation in terms of dispersion and deviation from the straight line compared to the other two sectors, which may reflect greater heterogeneity within this sector.

Urbanization acts as an environmental filter that promotes functional traits related to resilience and biotic homogenization, where perennial species are displaced by therophytes [65,66]. Analysis of the proportion of therophytes in the three surveyed areas revealed that it follows the urbanization gradient. Indeed, the city center (sector 1), where anthropogenic pressure is generally highest, recorded the highest proportion (56%), followed by the adjacent area (sector 2) with 49.33% and then the peripheral area (sector 3; 46.66%), where human impact is less intense. At the local scale (Mediterranean region), Baldi et al. (2025) confirmed that the abundance of therophytes is highest in open and trampled spaces, while it decreases under tree canopies where hemicryptophytes become dominant [67]. This suggests that the intensity of urbanization can explain the marked therophytization of the urban settings. On a global scale, Palma et al. (2017) analyzed the flora of 11 cities across four continents and found that colonizing life forms in urban environments are more often annual plants than locally extinct species [65]. While we know that urbanization impacts the distribution of plant diversity [68,69], the pattern of this distribution varies considerably across studies. For example, Chen and Wang (2025) showed that species richness and the Shannon–Weaver index of spontaneous plants in the urban area of Guiyang (China) decreased with increasing urbanization gradient and that there was no clear urban–rural gradient in their distribution [11]. Furthermore, Ran and colleagues (2024) revealed that maintenance levels, the urbanization gradient, and the proportion of green spaces are the key factors influencing the structure and distribution of spontaneous plant communities in urban settings [70]. However, a study conducted by Wang et al. (2020), in which the authors sampled 134 sites along two transects crossing the urban center of Shanghai (China), showed that the richness of native plant species showed no significant relationship with the degree of urbanization, while the richness of annual herbs and Shannon–Weaver diversity all showed a negative relationship with the level of urbanization [71]. In addition, some studies have shown that plant richness, including trees, shrubs, and grasses, is highest in areas with moderate urbanization [72,73,74]. Wang and his colleagues [75] found that the total number of species, native species, and exotic species was lowest in areas with a medium degree of urbanization, while the total number of plants and native plants was highest in areas with the lowest level of urbanization, and the richness of exotic plants was highest in areas with a high degree of urbanization. Other studies have shown that total species richness and native species richness were highest in heavily urbanized areas [76,77]. McDonnell and Hahs examined existing studies on gradient patterns and found at least six distinct models of species distribution along the urbanization gradient [1]: no response, negative response, punctuated response, intermediate response, positive response, and bimodal response (Figure 8). These observations indicate that the spatial distribution scheme of plant species is not uniform along the urban–rural gradient. In our study, the assessment of the impact of built-up area percentage on the composition of spontaneous flora revealed that this proxy indicator of the urbanization gradient does not exert a significant effect on these plant communities. This indicates that these communities conform to the “no response” model among the strategies proposed by McDonnell and Hahs. However, it should be noted that only a single variable (built-up area percentage) was tested here, and it is necessary to address the effect of other variables associated with the urbanization gradient in future research (see Section 4 ‘Study Limitations’).

The disturbance index (DI) calculation showed very similar disturbance rates between the three sectors (Sector 1 = 57.33%, Sector 2 = 56.57%, and Sector 3 = 56.66%). The low variation among the three sectors could, on the one hand, explain the similarity in species diversity among them. On the other hand, this suggests that the city of Témara is experiencing a homogenization of anthropogenic pressures. This phenomenon indicates that peripheral areas, often perceived as refuge areas for biodiversity, are in fact already highly fragmented or subject to intense anthropogenic pressures (construction sites and urban pastures). In fact, urbanization is often associated with biotic homogenization, that is, an increase in the similarity of species, traits, or genetic composition across spatial scales [78,79,80,81]. This pattern is often accompanied by the simultaneous disappearance of specialized native species and the introduction of non-native or ruderal species [82,83,84]. Additionally, in recent decades, Morocco has experienced significant urbanization and has faced challenges linked to urban sprawl and the loss of fertile land [85,86,87]. Rapid, unplanned urban sprawl can create a uniform pattern of disturbance across different areas of the city. As a result, the outskirts of Témara do not function as a buffer zone, but rather as an active transition zone that is already saturated and may therefore exhibit characteristics similar to those of the city center.

4. Limitations of the Study

Despite the importance of the topic and the findings of this study, it is necessary to clarify some of the theoretical and methodological limitations of this work. Perhaps the most significant limitation is the adoption of a simplified and reductive operational definition of the concept of “urbanization gradient,” as the analysis was limited to a single variable (the proportion of built-up area) as a proxy indicator. While urbanization is considered a complex and multidimensional socio-ecological phenomenon, it encompasses other equally important variables such as land use, population density, the urban cohesion index, pollution levels, and the practices adopted in the management of urban green spaces. The reliance on the built-up area ratio index stems from the fact that it was a methodological choice dictated by the nature of the extensive fieldwork and the need for a quantitative measure that is easy to replicate and statistically comparable across a large number of sampling points. Additionally, it is available as consistent cartographic data for the study area. Therefore, we recommend that future studies incorporate the other quantitative and qualitative variables mentioned earlier, enabling a more comprehensive understanding of the patterns of spontaneous plant diversity response to the pressures of urban expansion.

5. Conclusions and Recommendations

This study, which examined the effect of the proportion of built-up area on spontaneous plant diversity in the city of Temara, yielded a set of findings that may contribute to understanding the dynamics of spontaneous flora within the Moroccan urban ecosystem. Statistical results showed no significant differences in plant diversity between the city center, the city outskirts, and the intermediate zone (F = 0.675, α = 0.05). This result indicates that the percentage of built-up area, as a proxy for the degree of urbanization, did not result in a significant difference in the composition of spontaneous vegetation across the compared habitats. Additionally, this homogeneity may reflect the fact that these plant species have reached a state of relative stability in the face of environmental pressures across different areas of the city. Furthermore, analysis of the disturbance index reinforced these findings, showing very similar values across the three sectors, which explains the homogeneity of plant diversity levels in these latter. This reflects the equivalence of the pressures exerted on spontaneous plant communities throughout the entire city’s territory. However, an analysis of the life forms of these species revealed a slight prevalence of therophytes in the city center compared to the outskirts, reflecting the adaptive strategy of annual plants being better suited to the frequent disturbances characteristic of the city center than to the relatively stable conditions of the outskirts. These results may offer useful guidelines for the development of programs to promote and preserve plant biodiversity in the urban setting of Témara. However, the factors driving the relationship between urbanization and plant diversity require further investigation. Accordingly, we recommend the following:

Conducting similar studies but on a broader spatial and temporal scale, encompassing various Mediterranean cities, to determine whether the lack of an effect of urbanization on plant diversity is a general pattern in the region or specific to the study area. In addition, incorporate additional environmental and physical variables into these studies, such as soil moisture content, soil pH values, heavy metal concentrations in soil, proportion of green spaces, economic status, and the rate of urban expansion in the studied area.

Addressing the functional aspects of plant species (such as adaptation and reproduction mechanisms, growth cycle duration, and changes in the size and shape of leaves and flowers), rather than focusing solely on taxonomic diversity. It is possible that the urbanization gradient does not affect species numbers but favors species with specific functional traits, such as resistance to harsh climatic conditions, efficiency in seed dispersal, or tolerance to trampling.

It is important to draw urban planners’ attention to the ecological value of spontaneous vegetation in the urban area under study. The fact that it is largely unaffected by the urbanization gradient may reflect the importance of these plants as a basis for urban biodiversity, which calls for their conservation and enhancement rather than their eradication.

Cities are generally considered hotspots for the proliferation of invasive species [88]. We therefore recommend that future studies focus on the impact of urbanization on the patterns and mechanisms of introduction and spread of non-native and invasive species, which are better adapted to the pressures of the urban environment, at the expense of native species.