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Article

Diversity Patterns of Alien Plant Species in Mountainous Areas: A Case Study from the Central Balkans

by
Vladan Djordjević
1,*,
Vera Stanković
2,
Eva Kabaš
1,
Predrag Lazarević
1,
Filip Verloove
3 and
Jasmina Šinžar-Sekulić
1
1
Institute of Botany and Botanical Garden “Jevremovac”, Faculty of Biology, University of Belgrade, Takovska 43, 11000 Belgrade, Serbia
2
Institute of Criminological and Sociological Research, Gračanička 18, 11000 Belgrade, Serbia
3
Meise Botanic Garden, Nieuwelaan 38, B-1860 Meise, Belgium
*
Author to whom correspondence should be addressed.
Diversity 2025, 17(11), 774; https://doi.org/10.3390/d17110774
Submission received: 18 September 2025 / Revised: 27 October 2025 / Accepted: 29 October 2025 / Published: 4 November 2025
(This article belongs to the Special Issue Functional and Taxonomic Plant Diversity: Applications for Ecological Monitoring and Management)
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Abstract

Due to global warming and intensified anthropogenic impacts, mountainous areas are increasingly being colonised by alien plant species. The diversity patterns of these species have not been sufficiently studied in the Central Balkans. The aims of this study were to determine the occurrence and richness of alien plant species in relation to habitat type and geological substrates, and to identify the factors with the greatest influence on the composition and abundance of these species on Zlatibor Mountain (Central Balkans). This area is known as an important tourist centre and a large mountainous massif in Serbia. Principal Component Analysis (PCA) and distance-based Redundancy Analysis (db-RDA) were employed to examine the influence of environmental factors on the abundance and composition of 18 alien plant taxa. Data on altitude, habitat type, bedrock type, bioclimatic variables, and indicator values (light regime, soil moisture, acidity, nitrogen and temperature) of dominant plant species within the habitats were used as explanatory variables. Erigeron annuus, Reynoutria × bohemica, Robinia pseudoacacia, and Erigeron canadensis were the most common alien taxa and had the highest abundances. Residential and tourist facilities and the peripheries of asphalt roads are the habitat types where most alien species occur, while the lowest number of species was found in natural and semi-natural herbaceous habitats. Most taxa were found on serpentine substrates, while the number of taxa was lower on siliceous and carbonate substrates. This study emphasises the predominant role of habitat type in the partitioning of ecological niches of alien plant species. Furthermore, habitat type has a much greater influence on species composition and abundance than climatic factors and bedrock type, suggesting that the diversity pattern of alien plant species is related to the type and intensity of anthropogenic influences. Our results provide a useful basis for developing effective strategies to protect native habitats from invasion by alien plants.

1. Introduction

Mountains are highly important for biodiversity due to the presence of diverse ecological communities, endemic and relict species, and because half of the world’s biodiversity hotspots are located in these areas [1,2]. In addition, mountains have significant historical, aesthetic, and economic value [3,4]. They cover 24% of the Earth’s land surface and provide various resources to humans, such as building materials, water, food, carbon storage, pastures and agricultural land [5]. Today, mountainous areas are threatened not only by climate change [6,7], but also by anthropogenic factors such as land use, intensive tourism development, and the increased occurrence of alien species [8,9,10].
Alien plant species are among the greatest threats to native ecosystems and have been the focus of numerous studies due to their detrimental effects on biodiversity and the environment in general [11,12,13,14,15,16]. Although alien plants are known to occur in areas with strong anthropogenic influence, such as urban areas, there is insufficient knowledge about their occurrence in mountainous areas. High mountain ecosystems are among the few in the world not yet heavily colonised by alien plants [10,17]. However, this is likely to change as species expand their range upwards to occupy their climatic niches and respond to ongoing anthropogenic disturbance [17,18,19]. Some authors attribute the lower number of recorded alien plant species in high-altitude regions to the reduced intensity of anthropogenic influence on these mountains [20,21], as well as to the tendency of alien species to initially colonise lowland areas [22]. It is assumed that alien plant species colonise mountains rapidly when habitat and climate change make conditions suitable for the growth and survival of lowland species [10,17,21]. The richness of alien species generally decreases with increasing altitude, so the number and abundance of these species is lowest in the highest mountain regions [21,22,23,24]. However, nearly 200 alien plant species have been recorded in alpine environments worldwide [25], and more than 100 invasive alien species require management and removal in different mountain regions [26]. The spread of alien plant species in mountainous areas is influenced by several factors, the most important being transport, land use and habitat disturbance [14,24]. Data on the spread of alien plants are very important and are often included in the MIREN network (The Mountain Invasion Research Network) to improve knowledge of plant invasions in mountainous areas [27].
Alien species that have colonised American mountainous regions are mainly of Eurasian origin and are historically linked to the European tradition of pastoralism and agriculture introduced by colonialists [24,26]. Most alien species first colonised the lowlands and then migrated spontaneously or through human activity along roads or other transport corridors [26]. In addition, most alien plant species in the mountains are of agricultural origin, while alien forest species and those used for ornamental purposes often pose the greatest threat [26]. The future risk of invasion is likely to increase significantly due to global warming and increasing human land use, including intensive tourism, population growth, and a general rise in human activities [10].
Among Balkan countries, Albania has 219 alien plant species occurring outside cultivation, while in Bosnia and Herzegovina the checklist of alien species includes 252 taxa [28]. In Bulgaria, 59 alien species have been documented, and in Croatia, 182 [28]. In Greece, 413 alien species have been recorded, and in Montenegro, 47 [28]. In North Macedonia, 44 alien plants have been identified, but there is no recent checklist [29]. So far, 186 alien plant species have been recorded in Serbia [28]. In addition, a recent study indicated that 60 invasive alien plant species have been found in Serbia [30]. Research on alien plant species and ruderal flora and vegetation in the Central Balkans has been conducted mainly in urban areas [31,32,33,34], in Ramsar sites [35,36], and in the riparian areas of Serbia [37], while there are few studies providing insight into these plants in mountainous areas [38,39,40]. The distribution and diversity patterns of alien plant species in the mountainous regions of the Central Balkans have not yet been sufficiently studied. Furthermore, little is known about the factors influencing the diversity patterns of these species in geologically heterogeneous mountainous areas. It is known that at the macro scale, factors such as macroclimate, historical factors, latitude and longitude influence species distribution, whereas at the fine scale, factors such as habitat type, bedrock type, microclimate, disturbance regime, light regime, soil moisture and biotic factors determine patterns of species distribution, abundance and composition [41,42]. However, the occurrence of alien plant species is mostly associated with anthropogenic factors [10], while the influence of other factors is less studied. Therefore, the joint effect of several factors was investigated in this study. We chose Zlatibor Mountain (Serbia, Central Balkans) as a model for the study of alien plant species because this mountain range is one of the largest tourist centres in Serbia and has a great diversity of geological substrates and habitat types.
The main aims of this study were: (a) to determine the presence of alien plant species on Zlatibor Mountain; (b) to determine the richness of alien plant taxa in relation to habitat type and bedrock type; (c) to verify whether certain factors have any noticeable influence on the distribution patterns, richness, abundance, and composition of these species on Zlatibor Mountain. The results of the study on the diversity patterns of alien plant species can contribute significantly to the improved design of strategies for the protection of natural habitats and the planning of measures to eradicate alien species. In this study, we tested the hypothetical positions that individual habitat types, specific geological substrates, and particular climatic factors are the primary drivers influencing the abundance, composition and distribution of alien plant species on Zlatibor Mountain. Additionally, we assumed that significantly fewer alien species occur on ultramafic substrates compared to carbonate substrates. This assumption is based on the extreme edaphic conditions typical of ultramafic habitats [43,44] and previous findings reporting lower alien species richness in ultramafic than in non-ultramafic substrates [45,46].

2. Materials and Methods

2.1. Study Area

The study area encompasses the entire territory of Zlatibor Mountain (western Serbia), situated in the Central Balkans and forming part of the eastern Dinaric Alps. This extensive mountain massif contains a significant proportion of serpentine substrate and is one of the most important tourist centres in Serbia (Figure 1). Mount Zlatibor extends in a northwest–southeast direction and covers an area of about 300 km2. The mountain is approximately 30 km long and up to 15 km wide. Within Zlatibor, there is a legally protected area—the Zlatibor Nature Park—which covers 41,923.26 ha. The average altitude of the central part of the mountain is around 1000 m, and the highest peaks are Tornik (1496 m), Brijač (1480 m), Ćuletina (1433 m), and Čigota (1422 m). The climate is a humid mountain climate of the alpine type. The average annual air temperature is 8.3 °C, annual precipitation is 1031.8 mm, and relative humidity is 75.4%. The average annual sunshine duration is 2043.6 h; there are 62.4 days with snowfall, 99.6 days with snow cover, and 139 days with fog (data from the Hydrometeorological Service of the Republic of Serbia). Geological substrates are characterised by a significant presence of ultramafics, as well as carbonate substrates and various types of siliceous rocks and ophiolitic mélanges [47,48]. The predominant zonal vegetation types are: oak forests (Quercion confertae and Quercion petraeo-cerridis), beech and hornbeam forests (Fagion sylvaticae and Carpinion betuli), and coniferous forests (Vaccinio-Piceetea). Notable forest types also include: pine forests on ultramafic substrates (Erico-Fraxinion orni), forests occurring mainly in limestone gorges (Fraxino orni-Ostryion), mixed beech-fir forests (Fagion sylvaticae), pure spruce forests, and mixed spruce-fir forests (Piceion excelsae). Herbaceous vegetation types include grasslands, meadows, tall-herb vegetation, swards (Festuco-Brometea, Molinio-Arrhenatheretea, Nardetea strictae, Juncetea trifidi, and Mulgedio-Aconitetea), marshland vegetation (Phragmito-Magnocaricetea), and fen vegetation (Scheuchzerio palustris-Caricetea fuscae). In 2023, Zlatibor Mountain recorded 348,922 tourist arrivals and 1,096,979 overnight stays [49].

2.2. Data Collection

During field investigations conducted between 2020 and 2023, data were recorded at 81 localities (plots), including the abundance of alien plant species, habitat type, geological substrate, geographic coordinates, and altitude. We used a strip transect survey method (10 m wide and 100 m long) to record plant occurrence. The abundance of each alien species and subspecies was determined by counting the total number of individuals within the sample area (c. 100 m2 at each locality). The minimal distance between two studied sites (plots) with the same ecological conditions (identical habitat and bedrock type) was c. 250 m, following the distance used by Djordjević et al. [50]. Abundance was expressed using the four-scale applied by Tsiftsis et al. [41] and Djordjević et al. [50]: (1) 1–5 individuals; (2) 6–20 individuals; (3) 21–50 individuals; (4) more than 50 individuals.
During fieldwork, habitat types are determined based on vegetation cover, human use, degree of human impact, and the presence of specific objects, such as buildings and roads. Habitat types were grouped into eight categories (Figure 2A–H): (A) Construction sites and material dumps. There is a strong anthropogenic influence here, reflected in the disturbance of the surface soil layers, covering of soil with construction waste, burning of materials, frequent presence of vehicles, and trampling. (B) Residential and tourist facilities. The presence of people is constant, and a strong influence is reflected in trampling, frequent movement of people on foot or by vehicle, introduction of cultivated plants and soil, burning, disturbance of soil layers, irrigation, and the presence of domestic animals. (C) Peripheries of asphalt roads. A strong anthropogenic impact is evident in the constant presence of vehicles, spreading of salt and other materials during winter, introduction of construction material, creation of empty spaces around roads, dumping of waste and small rubbish heaps, and burning of the area around the road. (D) Rows of vegetation and areas adjacent to village roads. The negative effect is reflected in the presence of people walking or using vehicles. (E) Vegetable gardens and orchards. Strong anthropogenic impact is reflected in the use of pesticides, fertilisers, irrigation, presence of people and vehicles, trampling, burning, ploughing, and disturbance of the surface soil layers. (F) Natural and semi-natural forest habitats and surroundings of forest roads. A relatively weak anthropogenic impact is reflected in trampling and the formation of small empty spaces next to the roads themselves. (G) Natural and semi-natural herbaceous habitats. A weak negative factor is the use of traditional agriculture with low intensity mowing and grazing. (H) Feeding grounds of wild animals. The negative impact is reflected in the supply of organic matter (food), primarily maize, as well as the less frequent presence of people and vehicles. Habitat types A, B, C, and E were under strong anthropogenic influence; habitat types D and H were under moderate influence, while habitat types F and G were under weak anthropogenic influence. In general, habitats A, B, C, D, E, and F are anthropogenic habitats, which according to the EUNIS habitat classification (https://eunis.eea.europa.eu/index.jsp, accessed on 20 August 2025) belong to vegetated man-made habitats (code V), while habitat F belongs to woodland, forest and other wooded land (code G), and habitat G to grassland and lands dominated by forbs, mosses or lichens (code E).
Bedrock types were determined using the geological map of the study area at a scale of 1:100,000 (https://geoliss.mre.gov.rs/prez/OGK/RasterSrbija/, accessed on 20 August 2025). The bedrock types were classified into four categories: limestones (Lime), ophiolitic mélanges (OphiM), schists–gneiss–phyllites (SchistsGPh), and serpentine (Serp).
Soil pH, soil available nitrogen, soil moisture, temperature, and the light regime of the habitat were determined using the ecological indicator values of dominant species within the habitats, as provided by Kojić et al. [51], who recalibrated the original values defined for Central Europe [52] for the territory of Serbia. If only one dominant plant species was present in the sample area where alien plant species were found, the indicator values of that species were used. However, if two or more dominant plant species were present in the sampling area, the cover values of the dominant species were considered. Combined cover-abundance values of Braun-Blanquet’s [53] alphanumeric scale were converted to the numeric scale of Westhoff and van der Maarel [54]. The average indicator value for each ecological factor (pH, soil available nitrogen, soil moisture, temperature, and light regime) in each sampling plot was calculated by multiplying each species’ indicator value by its abundance, summing these products, and dividing by the sum of all abundances. The climate variables were taken from the CHELSA dataset v2.1 [55].

2.3. Data Analysis

Alpha diversity was defined as the average number of taxa recorded per plot in each habitat/bedrock type. Gamma diversity was defined as the total number of taxa recorded in all plots belonging to a particular habitat/bedrock type. We calculated an index of beta diversity as: S/a − 1, where S is the total number of taxa, and a is the average number of taxa per plot. The calculation of alpha, gamma, and beta diversity was carried out using the vegan package of the R programming language.
To comprehensively represent the main ecological gradients that may affect the presence of plant species, the initial set of numerical environmental parameters was relatively large and included bioclimatic parameters (BIO1–BIO19), topography (altitude), climate indices (potential evapotranspiration, aridity index), and calculated average indicator values for environmental variables (pH, soil available nitrogen, soil moisture, temperature, and light regime) [51,55].
To determine the appropriate ordination method based on the gradient length in species composition, a Detrended Correspondence Analysis (DCA) was first performed. As the length of the gradient was relatively short (1.04 SD units), linear methods were appropriate. Principal Component Analysis (PCA) was then applied to the numerical environmental variables to examine the main environmental gradients and between-plot variation.
Prior to performing the distance-based redundancy analysis (db-RDA), a variance inflation factor (VIF) was calculated to identify and remove collinear numerical predictors. Only variables with VIF < 10 were retained for further analysis (BIO2—Mean Diurnal Range, BIO3—Isothermality, BIO11—Mean Temperature of Coldest Quarter, BIO14—Precipitation of Driest Month, BIO15—Precipitation Seasonality, PET—potential evapotranspiration, and calculated average indicator values for environmental variables). The bioenv function from the vegan R package, version 2.6-4 [56] was then applied to select the subset of environmental variables most strongly associated with variation in plant species composition, so only BIO2, BIO11, BIO14, BIO15, and PET were kept for further analysis [55].
Finally, a distance-based redundancy analysis (db-RDA) using Bray–Curtis dissimilarities was applied to quantify the extent to which environmental variables and habitat type explain variation in plant species composition among the studied plots. The significance of the influence of the variables used in db-RDA was tested by Monte Carlo permutations (999 permutations). All data analyses and visualisations were performed using the R statistical computing language, version 4.4.3 [57].

3. Results

3.1. Floristic Richness

A total of 18 alien plant taxa from 16 genera were recorded in 81 plots (localities) (Table 1). Erigeron annuus, Reynoutria × bohemica, Robinia pseudoacacia and Erigeron canadensis occurred most frequently and had the highest abundances (Table 1).
The majority of alien plant species originated from America (13 taxa in total), of which 10 species are native to North America, two species are native to both North and South America, and one species is native to both North America and East Asia (Table 1). Alien plant taxa from Asia are represented by five taxa (four taxa from eastern Asia and one from western Asia), while one species is native to southwestern Europe (Calendula officinalis from the western Mediterranean).
The distribution of plots (sites) with alien plant species on Mt. Zlatibor (Serbia) according to habitat type is shown in Figure 3, while their distribution according to specific bedrock type is shown in Figure 4. There are 26 plots in residential and tourist facilities, 22 plots on the peripheries of asphalt roads, nine plots in rows of vegetation and areas adjacent to village roads, seven plots on construction sites and material dumps, and seven plots in natural and semi-natural forest habitats and the surroundings of forest roads, which are widely distributed. In contrast, plots in other habitat types are narrowly distributed: five plots in vegetable gardens and orchards, three plots in natural and semi-natural herbaceous habitats and two plots in the feeding grounds of wild animals (Figure 3). Plots on serpentine substrate are widespread (59 plots), while plots on other bedrock types are narrowly distributed and confined to smaller areas: ophiolitic mélanges (11 plots), limestones (eight plots), and schists–gneiss–phyllites (three plots) (Figure 4).

3.2. Alpha, Beta and Gamma Diversity

The results of the analysis of alpha and gamma diversity of alien plant species in specific habitat types are presented in Figure 5. The results indicated significant differences in alpha and gamma diversity between the habitat types analysed. The lowest alpha diversity was found at construction sites and material dumps (A; 1 taxon), residential and tourist facilities (B; 1 taxon), peripheries of asphalt roads (C; 1 taxon), rows of vegetation and areas adjacent to village roads (D; 1 taxon), natural and semi-natural forest habitats and surroundings of forest roads (F; 1 taxon) and in the natural and semi-natural herbaceous habitats (G; 1 taxon) (Figure 5). The highest alpha diversity was recorded in the feeding grounds of wild animals (H; 3 taxa) and in vegetable gardens and orchards (E; 2 taxa). The lowest gamma diversity was found in natural and semi-natural herbaceous habitats (G; 2 taxa), in the rows of vegetation and areas adjacent to village roads (D; 3 taxa) and in the vegetable gardens and orchards (E; 3 taxa), whereas the highest values were found at residential and tourist facilities (B; 13 taxa) and in the peripheries of asphalt roads (C; 8 taxa) (Figure 5). The lowest beta diversity was recorded within vegetable gardens and orchards (E), and the highest in natural and semi-natural forest habitats and surroundings of forest roads (F) (Figure 6).
The results of the analysis of alpha and gamma diversity of alien plant species on particular bedrock types are presented in Figure 7, whereas the results of the analysis of beta diversity of alien plant species on specific bedrock types are shown in Figure 8.
The results indicated that there are no significant differences in alpha, gamma (Figure 7) and beta (Figure 8) diversity between the bedrock types analysed. However, the lowest gamma diversity was found on limestone (Lime; 4 taxa) and schists–gneiss–phyllites (SchistsGPh; 4 taxa), whereas the highest value was found on serpentine (Serp; 17 taxa) (Figure 7). The lowest beta diversity was recorded on serpentine (Serp) and schists–gneiss–phyllites (SchistsGPh), and the highest on ophiolitic mélanges (OphiM) (Figure 8).

3.3. Factors Affecting the Distribution, Abundance and Composition of Alien Species

The first two axes of the PCA, based on bioclimatic factors, altitude and indicator values of habitats, accounted for 73.49% of the total variation (45.71% for the first axis and 27.78% for the second) (Figure 9). Detailed PCA results are given in Table S1 (Supplementary Material).
The first principal component reflected a strong environmental gradient in temperature, with ALT (Altitude), BIO1 (Annual Mean Temperature), BIO9 (Mean Temperature of Driest Quarter), BIO5 (Maximum Temperature of Warmest Month) and BIO8 (Mean Temperature of Wettest Quarter) being the variables with the highest contributions to PC1. In particular, ALT was negatively related to the temperature variables on the first axis, suggesting that PC1 reflects a gradient from low-altitude, warm localities to high-altitude, cold ones. The second principal component represented a strong gradient with respect to precipitation, with BIO17 (Precipitation of Driest Quarter), BIO14 (Precipitation of Driest Month), BIO19 (Precipitation of Coldest Quarter), BIO12 (Annual Precipitation) and BIO15 (Precipitation Seasonality) being the variables with the highest contributions to PC2. Therefore, PC2 can be interpreted as separating sites along a moisture gradient, with higher PC2 values associated with wetter conditions and lower values associated with drier habitats.
To examine patterns of variation associated with both ecological and geological factors, PCA ordination diagrams were created with sites coloured by habitat type (Figure 9) and bedrock type (Figure 10). The ordination diagram obtained by PCA indicated overlap of plots belonging to different habitat types, suggesting a relatively homogeneous composition of alien species in individual habitats (Figure 9). Only plots on residential and tourist facilities (B) and semi-natural forest habitats and surroundings of forest roads (F) were partially separated from the others. The plots representing feeding grounds of wild animals (H) were the most distant from the other habitat types. The ordination diagram obtained by PCA showed that plots belonging to different bedrock types partially overlapped, especially those on serpentine and ophiolitic mélanges (Figure 10). Only plots on schists–gneiss–phyllites were separated from the others.
The results of distance-based Redundancy Analysis (db-RDA) are shown in Figure 11 and Figure 12 and Table S2 (Supplementary Material). The obtained model explained 26.5% of the total variation in alien species composition, with constrained inertia of 9.24 and overall inertia of 34.92. A permutation test confirmed that the obtained db-RDA model was statistically significant (F = 2.04, p = 0.001), suggesting that the analysed environmental variables together explain a substantial portion of the variation in species composition.
The first canonical axis explained 32.0% of the constrained variation, while the second one explained 27.9%. The results indicated that habitat type, which includes seven different types, and four bioclimatic factors (BIO2—Mean Diurnal Range (Mean of monthly (max temp–min temp), BIO11—Mean Temperature of Coldest Quarter, BIO14—Precipitation of Driest Month, BIO15—Precipitation Seasonality) and potential evapotranspiration (PET) significantly influence the composition and abundance of alien species on Mt. Zlatibor (Figure 11). The most important habitat types affecting the composition of alien species were the peripheries of asphalt roads (C) and rows of vegetation and areas adjacent to village roads (D), whereas the most important bioclimatic factors were BIO2 and BIO15 (Figure 11 and Figure 12).
Variation partitioning based on distance-based Redundancy Analysis (db-RDA) indicated that species composition was affected by habitat type, climatic factors, and bedrock type, with habitat type having the greatest influence (11.9%) compared to climatic variables (2%) and bedrock type (1.9%) (Figure 13; Table 2). Shared variance was also observed (Figure 13).

4. Discussion

4.1. Floristic Richness and Diversity Indices

A total of 18 alien plant taxa recorded in the mountainous area of Zlatibor represents a relatively small proportion of the total number of alien species in Serbia (9.68% of the 186 taxa in Serbia) [28]. The lower number of alien plant species in the mountainous area of Zlatibor compared to urban areas [31] is consistent with previous studies showing that the number of alien species decreases with increasing altitude [23,24,58]. Additionally, the smaller number of alien species in this mountain may be explained by lower anthropogenic impact, reduced habitat disturbance and global warming effects, as well as the significant presence of ultramafic substrates, considering the stressful physico-chemical conditions of ultramafic soils and habitats [43,44]. In particular, Ailanthus altissima, one of the major invasive tree species worldwide [59], has low abundance and few occurrences on Zlatibor Mountain. This contrasts with the situation in almost all urban and rural areas of the Central Balkans, where this alien species is strongly represented and spreading. A recent study in Italy also showed that this species rarely inhabits ultramafic habitats [60]. Among the taxa with many occurrences in the study area, Erigeron annuus, Reynoutria × bohemica, Robinia pseudoacacia and Erigeron canadensis stand out. These plant taxa are highly adaptable and plastic, occurring in both non-ultramafic and ultramafic areas of the study area, and are among the most widespread alien species in Europe [61,62,63,64].
In contrast, some plant taxa have been recorded in only one or a few plots. An example is Cotoneaster bullatus, a recently recorded alien species not only in Serbia but also in the entire Balkan Peninsula [65]. This species threatens the semi-natural and natural pine forests of the study area. In addition, the occurrence of Calendula officinalis is among the rarest findings in Serbia [40]. Although ornamental plant taxa had fewer occurrences, recent studies show they pose a significant threat to natural ecosystems in mountainous areas [26].
In mountainous regions, alien species primarily colonise habitats modified by humans, such as ruderal sites, roadsides, settlements, pastures, and disturbed forests and plantations [10,24,66]. The results of our study are consistent with previous research showing that the abundance and richness of alien species are significantly higher at sites with tourism activity than at control sites [67,68]. The large number of alien plant taxa in residential and tourist facilities and their immediate surroundings can be explained by the constant influence of various anthropogenic factors that favour the spread and proliferation of alien species. Studies have shown that seeds of alien species can be transported on people’s clothing, and regulations have been introduced in some protected areas requiring clothing and footwear to be cleaned before entry [10,69]. In addition, these habitats are colonised by alien species through the creation of relatively bare areas devoid of vegetation cover. This is further exacerbated by disturbance factors such as trampling, burning, mowing, alteration of soil surface layers, access by domestic animals, and the establishment of gardens within these areas.
Among taxa frequently found on the peripheries of asphalt roads, Reynoutria × bohemica and Ambrosia artemisiifolia are notable. A large number of alien species in the vicinity of asphalt roads was expected, as these roads are important corridors for such species and facilitate their dispersal [10,23,70,71]. Moreover, it was found that alien species along roadsides invade habitats at high elevations more easily than at low elevations, and that the effects of roads and the introduction of alien species in lowlands cannot be extrapolated to mountain environments [72]. Vehicles are known to deposit between 2 and 78 seeds per kilometre, depending on vehicle type, climatic conditions, and road surface [10]. It has been shown that in dry conditions only 1–14% of seeds are lost over a distance of 256 km [73]. Additionally, the road environment is often affected by materials used during road construction or by salt applied to prevent freezing in winter. This has created microhabitats with a lower degree of competition between native plant species, as well as relatively bare areas that favour the growth of alien plant species.
A considerable number of alien species were found on construction sites and material dumps. These habitats have been significantly altered by anthropogenic factors due to construction works, including the movement of building materials, alteration of soil surface layers, and the use of transport structures and vehicles [74]. In the mountain area of Zlatibor, these habitats are numerous due to the intensive development of tourism and can be considered important hotspots for alien species.
Slightly fewer alien species were found at the feeding grounds of wild animals. These are partially modified sites that contain a certain amount of organic food (mainly maize), feeding structures, and involve vehicle circulation. A study in the predominantly forested landscape of the Western Carpathians (Slovakia) also found that wild animal feeders are inhabited by a considerable number of alien plant species [58]. The authors mention eight alien species in the vicinity of wild animal feeders, four of which are the same as those found in the Zlatibor Mountain area (Ambrosia artemisiifolia, Erigeron canadensis, Erigeron annuus, and Helianthus tuberosus).
The relatively low number of alien species in the natural and semi-natural forest habitats and near forest trails indicates the preservation of the forest ecosystems on this mountain. Ailanthus altissima has invaded the natural forest habitat at only one site. Tree rows, especially those with unsealed areas around the trees, often serve as habitats colonised by various plant species, including alien species [33]. However, on Zlatibor Mountain, they are mostly located in serpentine areas, which may explain the lower number of taxa. Among the species that grow extensively in the form of tree rows, Robinia pseudoacacia is notable. In contrast, species such as Galinsoga parviflora and Amaranthus retroflexus are abundant in vegetable gardens and orchards, mainly found in the calcareous areas of the mountain. Galinsoga parviflora, an annual species, is known to occur in disturbed habitats and agricultural land in many parts of the temperate and subtropical regions of the world and is considered a common weed in gardens, uncultivated land, and various crops such as wheat, maize, potatoes, beans, onions, cabbage, garlic, coffee, cotton, tobacco, sugar beet, tomatoes, pepper, citrus, bananas, and strawberries [75]. A recent study shows that irrigation methods in orchards determine the dominance of either alien species (flood irrigation) or native species (drip irrigation) [76]. In our study area, the vegetable gardens and orchards were irrigated by flood irrigation, which explains the occurrence of alien species in these habitats.
At first glance, the high number of alien species on serpentine plots appears unexpected, considering the extreme conditions of serpentine substrates for plant growth and development [77]. Serpentine plant communities are severely nitrogen-limited, which, combined with competition from resident species, promotes the resistance of these systems to invasions [46]. Moreover, a study in California’s North Coast Ranges showed that serpentine soils are considerably less invaded by alien species than non-serpentine soils [45]. The prevalence of alien plant species on serpentine substrates in our study area can be attributed to the extensive occurrence of this substrate in the region (up to three-fifths of the entire study area) and the fact that the centre of the tourist area is located on this geological substrate. In addition, the lower level of competition between plants in serpentine habitats [78] is one possible reason why many alien species have been able to successfully colonise these habitats. Furthermore, many serpentine habitats have been altered by human activities, especially through disturbance of the topsoil layer and the application of construction materials. At the same time, the deeper and wetter soils of the serpentine substrate have less-extreme features, primarily due to migration and removal of ions as well as the production of humus [79,80]. These factors minimise the differences between the ultramafic and non-ultramafic soils of the study area.
In the natural or semi-natural forest or herbaceous serpentine habitats of Zlatibor Mountain, most alien species are found at the habitat edges. This is consistent with results from California [45], where alien species were significantly more common in small serpentine patches (<5 ha) than in the interiors (>100 m from the edges) or in very large patches (>1 km2).
Significantly fewer alien plant taxa were found on non-serpentine bedrock types in the study areas. This can be explained by the lower presence and isolation of areas with these geological substrates in the study area, as well as by the absence of intensive tourism and general anthropogenic impacts in these areas.
The analysis of the composition of alien plant species in this study indicates a relatively homogeneous species composition per plot. This is not surprising considering that these species are important agents of biotic homogenisation in terrestrial ecosystems at different spatial scales [81]. Moreover, these species are usually able to adapt to a wide range of environmental conditions and can therefore invade different habitats and often become dominant there [82,83].

4.2. Factors Affecting the Abundance and Composition of Alien Plant Species

Habitat heterogeneity is recognised as one of the most important factors influencing the diversity patterns of plant taxa [84]. Our study highlights the significance of different habitat types as key factors affecting the abundance and composition of alien species in the mountainous area of Zlatibor. The results are consistent with previous studies on the urban flora of Serbia [33] and Central Europe [85]. The habitats in the study area varied in the type and intensity of anthropogenic factors, i.e., land use. Our study demonstrated that the importance of habitat type in determining the diversity pattern of alien species is greater than the influence of the climatic factor, which is also in line with previously published studies [11,33,85,86,87,88]. All this underscores that habitat type is the most significant predictor of plant invasion intensity [11,86,87,88], surpassing the role of climate [86]. Contrary to the initial assumption that bedrock type significantly influences the abundance and composition of alien species, the role of geological substrates was found to be much less significant than that of habitat type.
The lesser importance of the climatic factor can be attributed to the relatively small size of the study area, which experiences only limited climatic fluctuations. However, the results indicate that species inhabiting rows of vegetation and areas adjacent to village roads are positively and significantly correlated with the bioclimatic factor BIO2—mean diurnal range (mean value of monthly (max temp–min temp)). This means that Robinia pseudoacacia, Ailanthus altissima and Oenothera biennis are best able to tolerate large differences in monthly temperatures. Recent studies have shown that Robinia pseudoacacia can tolerate prolonged warm conditions and drought by reducing water loss through both reduced leaf size and transpiration [89]. However, this species cannot be considered a water-saving tree because it does not regulate its transpiration under well-watered conditions [89]. Furthermore, it is known that the resistance of Ailanthus altissima to high temperature and drought is an important factor enabling the wide expansion of this species in Europe and North America [90,91]. A study indicated that seedlings of A. altissima are able to survive drought by utilising a highly effective water-saving mechanism involving reduced water loss through the leaves and reduced hydraulic conductivity of the roots [90].
In addition, the alien species inhabiting most habitats (B, E, F, G and H) are positively and significantly correlated with the bioclimatic factor BIO14 (precipitation of driest month) and negatively and significantly correlated with potential evapotranspiration. This means that their survival largely depends on precipitation during the driest summer period, with lower levels of evapotranspiration. A recent study has shown that precipitation during the warmest quarter has a major impact on modelling the potential distribution of Reynoutria species and the hybrid Reynoutria × bohemica in southeastern Europe [63]. Additionally, modelling of potential distribution highlighted R. × bohemica’s high temperature tolerance across seasons and strong drought resistance, requiring up to 60 mm less annual precipitation than its parental species [63]. Furthermore, the alien species occurring near asphalt roads are negatively and significantly correlated with the bioclimatic factor BIO11 (mean temperature of coldest quarter), suggesting that these species best tolerate cold temperature conditions during winter. Moreover, the results indicate that species growing on limestones and schists–gneiss–phyllites are positively and significantly correlated with precipitation seasonality (coefficient of variation). This indicates that these species correspond to a higher amount of precipitation during the year.
Altitude is one of the most important factors influencing patterns of alien species diversity in mountains [26,72,92,93]. Several hypotheses explain the decline in abundance of alien species with increasing altitude: low-altitude filter effects, low propagule pressure, and genetic swamping of peripheral populations at higher altitudes [92]. The proximal lowland alien flora has been identified as the main determinant of a mountain’s alien flora composition [26]. However, in our study, the influence of altitude was not as significant. This is because the study area is primarily a mountain plateau, despite some variation in altitude (from 599 to 1450 m).

4.3. Implications for Management Strategies

In general, management strategies for alien species fall into the following categories: prevention, which is the most cost-effective and environmentally desirable approach; early detection and rapid response to eradicate new invasions of alien species; and control and containment of established populations [10,17,94,95]. Based on the results of our study, we propose the following suggestions for the management of alien species:
(a) Control the introduction and cultivation of alien species in the gardens of residential and tourist facilities. A study of alien species in mountain areas indicated that ornamental and woody plants pose the greatest threat [26]. Therefore, residents of Zlatibor Mountain and tourists should be educated about the dangers posed, especially by alien species widely cultivated on this mountain. Instead of planting alien taxa such as Alcea rosea, Calendula officinalis, Cosmos bipinnatus and Reynoutria × bohemica, the cultivation of native plants should be promoted. As the tourist settlement is partially located in a protected nature area, it is necessary to regulate the import of soil from other areas.
(b) Nature protection services should restrict the entry of private vehicles and tourists into special nature reserves. Both official and private vehicles should undergo seed cleaning before entering protected natural areas, as is also recommended in other mountains and protected areas [10,69]. Tourists’ footwear should also be regularly cleaned of alien plant propagules.
(c) Construction sites and construction material dumps should be marked, monitored, and adequately fenced off from the protected natural areas of the mountain.
(d) For alien species present in a limited number of locations, it is necessary to immediately use the most effective permitted methods: mechanical methods, targeted chemical application, biological control or cultural practices such as prescribed burning and habitat manipulation. This primarily concerns Ailanthus altissima, Ambrosia artemisiifolia, Cotoneaster bullatus, Calendula officinalis, Cosmos bipinnatus, Oxalis stricta and Xanthium orientale. In most cases, an integrated control approach should be applied, as recommended in other regions [96,97,98]. For example, management of A. altissima is known to require a combination of mechanical and chemical methods [59,99]. Cooperation with local authorities and protected area managers is necessary to implement chemical or biological control programmes.
(e) A combination of mechanical removal and herbicide use should be considered to eliminate alien species along roadsides. The optimal approach is to remove plants before they produce seeds, clean all equipment, and properly dispose of plant material by bagging and burning. A recent study indicated that optimal management of Ambrosia artemisiifolia along roadsides must be adjusted to its phenological development [100]. Specifically, the most effective mowing method involves a first cut shortly before male flowering to limit the quantity of released pollen, followed by subsequent cuts before new flowers appear on the resprouting lateral shoots [100].
(f) In vegetable gardens and orchards, it is important to use drip irrigation instead of flood irrigation, as drip irrigation favours the survival of native species [76].
(g) For rows of vegetation and areas adjacent to village roads, prioritise the planting of native species such as Pinus nigra J. F. Arnold, Pinus sylvestris L., Sorbus aucuparia L., Quercus spp., Fagus sylvatica L. and Carpinus betulus L. instead of the alien species Robinia pseudoacacia.
(h) The edges of protected forest areas and herbaceous vegetation types should be included in monitoring programmes. These areas are most vulnerable to the spread of alien species, as shown in other mountain regions, especially on serpentine substrates [45]. In many locations, it should be considered that natural trees and shrubs need to be reinforced and additionally planted.
(i) For the feeding grounds of wild animals, ensure that food is cleaned and disinfected before entry and that food remains are removed from the feeding area. Food should be delivered in vehicles that have undergone seed cleaning to reduce the risk of introducing alien species.
(j) It is necessary to strengthen citizen science and the collection of data on alien species using widely used applications and data entry platforms, such as iNaturalist and similar tools. This has also been suggested in other studies on alien species in mountain regions [93,101,102].
(k) Using modern forecasting tools, including geographic information systems and species distribution modelling, it is necessary to predict future occurrences of alien plant species on Zlatibor Mountain. Scientists in the Australian Alps developed a method to identify priority locations for alien species control across a landscape [103]. They indicated that visiting sites where the species are most likely to occur and applying a moderate amount of effort at these sites is the most efficient strategy.
In the ultramafic area, which mainly covers the mountain plateau and higher altitudes and contains most tourist facilities, management priorities for alien species are the surroundings of residential and tourist facilities, construction sites and material dumps, and the peripheries of asphalt roads. Here, disturbance of the surface soil layers, introduction of construction materials and debris, and the creation of relatively empty spaces play a key role in the establishment and spread of alien species. In this area, monitoring of Reynoutria × bohemica, Ailanthus altissima, Ambrosia artemisiifolia, Cotoneaster bullatus, and Robinia pseudoacacia should be prioritised. In contrast, in the carbonate area of the mountain, located at lower altitudes, the main management priorities are areas affected by soil fertilisation, such as vegetable gardens, orchards, rows of vegetation and areas adjacent to village roads. In the carbonate areas of the mountain, it is a priority to monitor populations of Amaranthus retroflexus, Galinsoga parviflora, and Erigeron annuus. In the siliceous area of the mountain, efforts should focus on managing forest stands invaded by alien species.

5. Conclusions

A total of 18 alien plant taxa were recorded on Zlatibor Mountain (Central Balkans). Significant differences were found among the habitat types analysed, both in taxa richness and composition. Residential and tourist facilities, as well as the peripheries of asphalt roads, exhibited the highest occurrences of alien species, indicating a strong correlation between alien plant species richness and the type and intensity of anthropogenic impacts. Furthermore, serpentine geological substrates hosted the highest number of alien species, a pattern attributable to the dominance of this substrate and its association with the tourism centre in the mountain region. In contrast, carbonate and siliceous geological substrates were less colonised by alien plant species, likely due to their isolation, limited extent, and lower levels of anthropogenic disturbance. This study underscores that habitat type exerts a much greater influence on species composition and abundance than climatic factors or bedrock type. Thus, the findings emphasise the critical role of habitat heterogeneity, disturbance intensity, tourism pressures, and land-use diversity in shaping patterns of alien plant species diversity. Moreover, the results indicate that anthropogenic drivers mitigate and mask the impact of natural environmental factors, such as climate, bedrock type, and habitat type, and significantly control species dispersal and distribution. Therefore, future studies should focus on precise measurement of the intensity of anthropogenic factors, including trampling, burning, vehicle frequency, use of fertilisers, cultivation of ornamental plants, changes in the physical and chemical characteristics of soil, as well as general land use history and its patterns. This study provides a solid foundation for developing effective strategies to protect natural habitats from the invasion of alien plant taxa.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/d17110774/s1, Table S1: Detailed results for PCA; Table S2: Detailed results of distance-based Redundancy Analysis (db-RDA).

Author Contributions

Conceptualization, V.D., E.K. and J.Š.-S.; methodology, V.D. and J.Š.-S.; software, J.Š.-S.; validation, V.D., E.K., V.S. and J.Š.-S.; formal analysis, J.Š.-S. and V.D.; investigation, V.D., E.K., V.S. and P.L.; resources, V.D., E.K., P.L., V.S. and J.Š.-S.; data curation, V.D., E.K., P.L. and V.S.; writing—original draft preparation, V.D.; writing—review and editing, V.D., F.V., V.S., E.K., P.L. and J.Š.-S.; visualization, V.D., P.L. and J.Š.-S.; funding acquisition, V.D., E.K., P.L. and J.Š.-S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the Science Fund of the Republic of Serbia, grant number 7750112—Balkan biodiversity across spatial and temporal scales—patterns and mechanisms driving vascular plant diversity (BalkBioDrivers), by the Ministry of Science, Technological Development and Innovation of the Republic of Serbia (451-03-136/2025-03/200178; 451-03-137/2025-03/200178; 451-03-136/2025-03/200039), and the State Enterprise for Management Forest “Srbijašume”, Forest Estate “Užice”—Protected Plants Monitoring Project.

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The data presented in this study are available upon request from the corresponding author.

Acknowledgments

We thank the State Enterprise for Forest Management “Srbijašume”, Forest Estate “Užice”, for their logistical field support. The authors dedicate this research to Slobodan Jovanović, who was our greatest teacher of urban flora and alien plant species. We are grateful to Snežana Vukojičić (University of Belgrade) for her help during the fieldwork. We thank two anonymous reviewers for their valuable suggestions and comments on a previous version of the manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Map of the study area: (A)—position of the study area in the world and the Balkan Peninsula and Serbia (the boundaries of the study area are marked by the frame of the circle); (B)—the distribution of plots (sites) with alien plant species on Mt. Zlatibor (Serbia).
Figure 1. Map of the study area: (A)—position of the study area in the world and the Balkan Peninsula and Serbia (the boundaries of the study area are marked by the frame of the circle); (B)—the distribution of plots (sites) with alien plant species on Mt. Zlatibor (Serbia).
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Figure 2. Investigated habitat types in the study area (Mt. Zlatibor, Serbia): (A)—construction sites and material dumps, (B)—residential and tourist facilities, (C)—peripheries of asphalt roads, (D)—rows of vegetation and areas adjacent to village roads, (E)—vegetable gardens and orchards, (F)—natural and semi-natural forest habitats and surroundings of forest roads, (G)—natural and semi-natural herbaceous habitats, (H)—feeding grounds of wild animals (photos: V. Djordjević).
Figure 2. Investigated habitat types in the study area (Mt. Zlatibor, Serbia): (A)—construction sites and material dumps, (B)—residential and tourist facilities, (C)—peripheries of asphalt roads, (D)—rows of vegetation and areas adjacent to village roads, (E)—vegetable gardens and orchards, (F)—natural and semi-natural forest habitats and surroundings of forest roads, (G)—natural and semi-natural herbaceous habitats, (H)—feeding grounds of wild animals (photos: V. Djordjević).
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Figure 3. Distribution of plots (sites) with alien plant species on Mt. Zlatibor (Serbia) according to habitat type. Abbreviations: A—construction sites and material dumps, B—residential and tourist facilities, C—peripheries of asphalt roads, D—rows of vegetation and areas adjacent to village roads, E—vegetable gardens and orchards, F—natural and semi-natural forest habitats and surroundings of forest roads, G—natural and semi-natural herbaceous habitats, H—feeding grounds of wild animals.
Figure 3. Distribution of plots (sites) with alien plant species on Mt. Zlatibor (Serbia) according to habitat type. Abbreviations: A—construction sites and material dumps, B—residential and tourist facilities, C—peripheries of asphalt roads, D—rows of vegetation and areas adjacent to village roads, E—vegetable gardens and orchards, F—natural and semi-natural forest habitats and surroundings of forest roads, G—natural and semi-natural herbaceous habitats, H—feeding grounds of wild animals.
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Figure 4. Distribution of plots (sites) with alien plant species on Mt. Zlatibor (Serbia) according to bedrock type. Abbreviations: Lime—limestones, OphiM—ophiolitic mélanges, SchistsGPh—schists–gneiss–phyllites, Serp—serpentine.
Figure 4. Distribution of plots (sites) with alien plant species on Mt. Zlatibor (Serbia) according to bedrock type. Abbreviations: Lime—limestones, OphiM—ophiolitic mélanges, SchistsGPh—schists–gneiss–phyllites, Serp—serpentine.
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Figure 5. Alpha diversity (box plots) and gamma diversity (numbers above) of alien plant taxa in specific habitat types. X-axis abbreviations: A—construction sites and material dumps, B—residential and tourist facilities, C—peripheries of asphalt roads, D—rows of vegetation and areas adjacent to village roads, E—vegetable gardens and orchards, F—natural and semi-natural forest habitats and surroundings of forest roads, G—natural and semi-natural herbaceous habitats, H—feeding grounds of wild animals. Habitat types sharing the same lowercase letter do not differ significantly (p < 0.05).
Figure 5. Alpha diversity (box plots) and gamma diversity (numbers above) of alien plant taxa in specific habitat types. X-axis abbreviations: A—construction sites and material dumps, B—residential and tourist facilities, C—peripheries of asphalt roads, D—rows of vegetation and areas adjacent to village roads, E—vegetable gardens and orchards, F—natural and semi-natural forest habitats and surroundings of forest roads, G—natural and semi-natural herbaceous habitats, H—feeding grounds of wild animals. Habitat types sharing the same lowercase letter do not differ significantly (p < 0.05).
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Figure 6. Beta diversity of alien plant taxa within habitat types. X-axis abbreviations: A—construction sites and material dumps, B—residential and tourist facilities, C—peripheries of asphalt roads, D—rows of vegetation and areas adjacent to village roads, E—vegetable gardens and orchards, F—natural and semi-natural forest habitats and surroundings of forest roads, G—natural and semi-natural herbaceous habitats, H—feeding grounds of wild animals. Habitat types sharing the same lowercase letter do not differ significantly (p < 0.05).
Figure 6. Beta diversity of alien plant taxa within habitat types. X-axis abbreviations: A—construction sites and material dumps, B—residential and tourist facilities, C—peripheries of asphalt roads, D—rows of vegetation and areas adjacent to village roads, E—vegetable gardens and orchards, F—natural and semi-natural forest habitats and surroundings of forest roads, G—natural and semi-natural herbaceous habitats, H—feeding grounds of wild animals. Habitat types sharing the same lowercase letter do not differ significantly (p < 0.05).
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Figure 7. Alpha diversity (box plots) and gamma diversity (numbers above) of alien plant taxa on specific bedrock types. X-axis abbreviations: Lime—limestones, OphiM—ophiolitic mélanges, Schists—schists–gneiss–phyllites, Serp—serpentine. Bedrock types sharing the same lowercase letter do not differ significantly (p < 0.05).
Figure 7. Alpha diversity (box plots) and gamma diversity (numbers above) of alien plant taxa on specific bedrock types. X-axis abbreviations: Lime—limestones, OphiM—ophiolitic mélanges, Schists—schists–gneiss–phyllites, Serp—serpentine. Bedrock types sharing the same lowercase letter do not differ significantly (p < 0.05).
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Figure 8. Beta diversity of alien plant taxa within habitat types. X-axis abbreviations: Lime—limestones, OphiM—ophiolitic mélanges, Schists—schists–gneiss–phyllites, Serp—serpentine. Bedrock types sharing the same lowercase letter do not differ significantly (p < 0.05).
Figure 8. Beta diversity of alien plant taxa within habitat types. X-axis abbreviations: Lime—limestones, OphiM—ophiolitic mélanges, Schists—schists–gneiss–phyllites, Serp—serpentine. Bedrock types sharing the same lowercase letter do not differ significantly (p < 0.05).
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Figure 9. PCA ordination of plots based on environmental variables. Only variables with cos2 ≥ 0.75 and loadings ≥ 0.7 on at least one of the principal component axes are displayed. Site symbols are coloured according to habitat type. Abbreviations: BIO—bioclimatic factors: BIO1—Annual Mean Temperature, BIO5—Maximum Temperature of Warmest Month; BIO8—Mean Temperature of Wettest Quarter, BIO9—Mean Temperature of Driest Quarter; BIO10—Mean Temperature of Warmest Quarter; BIO11—Mean Temperature of Coldest Quarter, BIO12—Annual Precipitation; BIO14—Precipitation of Driest Month, BIO15—Precipitation Seasonality (Coefficient of Variation), BIO17—Precipitation of Driest Quarter; BIO19—Precipitation of Coldest Quarter, PET—potential evapotranspiration, ALT—altitude. Colour abbreviations for habitat types are explained in Figure 3. The direction of the arrow indicates correlations between variables, whereas its length represents the relative importance of each variable in the analysis.
Figure 9. PCA ordination of plots based on environmental variables. Only variables with cos2 ≥ 0.75 and loadings ≥ 0.7 on at least one of the principal component axes are displayed. Site symbols are coloured according to habitat type. Abbreviations: BIO—bioclimatic factors: BIO1—Annual Mean Temperature, BIO5—Maximum Temperature of Warmest Month; BIO8—Mean Temperature of Wettest Quarter, BIO9—Mean Temperature of Driest Quarter; BIO10—Mean Temperature of Warmest Quarter; BIO11—Mean Temperature of Coldest Quarter, BIO12—Annual Precipitation; BIO14—Precipitation of Driest Month, BIO15—Precipitation Seasonality (Coefficient of Variation), BIO17—Precipitation of Driest Quarter; BIO19—Precipitation of Coldest Quarter, PET—potential evapotranspiration, ALT—altitude. Colour abbreviations for habitat types are explained in Figure 3. The direction of the arrow indicates correlations between variables, whereas its length represents the relative importance of each variable in the analysis.
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Figure 10. PCA ordination of plots based on environmental variables. Only variables with cos2 ≥ 0.75 and loadings ≥ 0.7 on at least one of the principal component axes are shown. Site symbols are coloured according to bedrock type. Abbreviations: BIO—bioclimatic factors: BIO1 = Annual Mean Temperature, BIO5—Maximum Temperature of Warmest Month; BIO8—Mean Temperature of Wettest Quarter, BIO9—Mean Temperature of Driest Quarter; BIO10—Mean Temperature of Warmest Quarter; BIO11—Mean Temperature of Coldest Quarter, BIO12—Annual Precipitation; BIO14—Precipitation of Driest Month, BIO15—Precipitation Seasonality (Coefficient of Variation), BIO17—Precipitation of Driest Quarter; BIO19—Precipitation of Coldest Quarter, PET—potential evapotranspiration, ALT—altitude. Colour abbreviations for bedrock types are explained in Figure 4. The direction of the arrow indicates correlations between variables, whereas its length represents the relative importance of each variable in the analysis.
Figure 10. PCA ordination of plots based on environmental variables. Only variables with cos2 ≥ 0.75 and loadings ≥ 0.7 on at least one of the principal component axes are shown. Site symbols are coloured according to bedrock type. Abbreviations: BIO—bioclimatic factors: BIO1 = Annual Mean Temperature, BIO5—Maximum Temperature of Warmest Month; BIO8—Mean Temperature of Wettest Quarter, BIO9—Mean Temperature of Driest Quarter; BIO10—Mean Temperature of Warmest Quarter; BIO11—Mean Temperature of Coldest Quarter, BIO12—Annual Precipitation; BIO14—Precipitation of Driest Month, BIO15—Precipitation Seasonality (Coefficient of Variation), BIO17—Precipitation of Driest Quarter; BIO19—Precipitation of Coldest Quarter, PET—potential evapotranspiration, ALT—altitude. Colour abbreviations for bedrock types are explained in Figure 4. The direction of the arrow indicates correlations between variables, whereas its length represents the relative importance of each variable in the analysis.
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Figure 11. Distance-based Redundancy Analysis (db-RDA) of species composition based on environmental variables, with site symbols coloured according to habitat type. The direction of each arrow indicates correlations between variables, whereas its length describes the relative importance of each variable in the analysis. Abbreviations: BIO—bioclimatic factors: BIO2—Mean Diurnal Range (Mean of monthly (max temp–min temp)), BIO11—Mean Temperature of Coldest Quarter, BIO14—Precipitation of Driest Month, BIO15—Precipitation Seasonality (Coefficient of Variation), PET—potential evapotranspiration. Habitat and colour abbreviations for habitat types are explained in Figure 3.
Figure 11. Distance-based Redundancy Analysis (db-RDA) of species composition based on environmental variables, with site symbols coloured according to habitat type. The direction of each arrow indicates correlations between variables, whereas its length describes the relative importance of each variable in the analysis. Abbreviations: BIO—bioclimatic factors: BIO2—Mean Diurnal Range (Mean of monthly (max temp–min temp)), BIO11—Mean Temperature of Coldest Quarter, BIO14—Precipitation of Driest Month, BIO15—Precipitation Seasonality (Coefficient of Variation), PET—potential evapotranspiration. Habitat and colour abbreviations for habitat types are explained in Figure 3.
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Figure 12. Distance-based Redundancy Analysis (db-RDA) of species composition based on environmental variables, with site symbols coloured according to bedrock type. The direction of the arrow indicates correlations between variables, whereas its length describes the relative importance of each variable in the analysis. Abbreviations: BIO—bioclimatic factors: BIO2—Mean Diurnal Range (Mean of monthly (max temp–min temp)), BIO11—Mean Temperature of Coldest Quarter, BIO14—Precipitation of Driest Month, BIO15—Precipitation Seasonality (Coefficient of Variation), PET—potential evapotranspiration. Habitat abbreviations are explained in Figure 3; colour abbreviations of bedrock types are explained in Figure 4.
Figure 12. Distance-based Redundancy Analysis (db-RDA) of species composition based on environmental variables, with site symbols coloured according to bedrock type. The direction of the arrow indicates correlations between variables, whereas its length describes the relative importance of each variable in the analysis. Abbreviations: BIO—bioclimatic factors: BIO2—Mean Diurnal Range (Mean of monthly (max temp–min temp)), BIO11—Mean Temperature of Coldest Quarter, BIO14—Precipitation of Driest Month, BIO15—Precipitation Seasonality (Coefficient of Variation), PET—potential evapotranspiration. Habitat abbreviations are explained in Figure 3; colour abbreviations of bedrock types are explained in Figure 4.
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Figure 13. Variance partitioning based on distance-based redundancy analysis (db-RDA) of the influence of habitat types, climatic variables and bedrock types, as well as their shared effect on plant species composition in the analysed plots.
Figure 13. Variance partitioning based on distance-based redundancy analysis (db-RDA) of the influence of habitat types, climatic variables and bedrock types, as well as their shared effect on plant species composition in the analysed plots.
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Table 1. Overview of alien plant taxa per habitat and bedrock type on Mt. Zlatibor (Serbia) with information on their origin and occurrence.
Table 1. Overview of alien plant taxa per habitat and bedrock type on Mt. Zlatibor (Serbia) with information on their origin and occurrence.
TaxonOriginOcc.ABCDEFGHLimeOphiMSchistsGPhSerp
Ailanthus altissima (Mill.) SwingleE-As3000201000003
Alcea rosea L.W-As2110000000002
Amaranthus retroflexus L.N-Am6011040004101
Ambrosia artemisiifolia L.N-Am3002000010102
Calendula officinalis L.SW-Eur1010000000001
Cosmos bipinnatus Cav.N-Am2101000000002
Cotoneaster bullatus BoisE-As1000001000001
Erigeron annuus (L.) Desf.N-Am2921260232243121
Erigeron canadensis L.N-Am10042002111306
Galinsoga parviflora Cav.N+S-Am5010040004100
Helianthus tuberosus L.N-Am3020000010201
Oenothera biennis L.N-Am3020100000003
Oenothera glazioviana MicheliN-Am3030000000012
Oxalis stricta L.E-As, N-Am1010000000001
Reynoutria × bohemica Chrtek & ChrtkováE-As1935110000000118
Robinia pseudoacacia L.N-Am14044600000518
Solidago gigantea AitonN-Am4121000000004
Xanthium orientale L.N+S-Am2100000010101
Abbreviations: Origin—origin of taxon; Am—America, As—Asia, Eur—Europe, N—North, S—South, E—East, W—West, SW—Southwest; Occ.—total number of occurrences; numbers 1–29—number of occurrences of the taxon recorded in the specific habitat/bedrock type; 0—taxon not recorded in the specific habitat/bedrock type; A—construction sites and material dumps, B—residential and tourist facilities, C—peripheries of asphalt roads, D—rows of vegetation and areas adjacent to village roads, E—vegetable gardens and orchards, F—natural and semi-natural forest habitats and surroundings of forest roads, G—natural and semi-natural herbaceous habitats, H—feeding grounds of wild animals; Lime—limestones, OphiM—ophiolitic mélanges, SchistsGPh—schists–gneiss–phyllites, Serp—serpentine.
Table 2. Total explained variation, and the influence of habitat type, potential evapotranspiration and climatic variables on plant species composition in the analysed plots. HAB—habitat types; PET—potential evapotranspiration; BIO—bioclimatic variables: BIO2—Mean Diurnal Range (Mean of monthly (max temp–min temp)), BIO11—Mean Temperature of Coldest Quarter, BIO14—Precipitation of Driest Month, BIO15—Precipitation Seasonality (Coefficient of Variation); NA—not applicable.
Table 2. Total explained variation, and the influence of habitat type, potential evapotranspiration and climatic variables on plant species composition in the analysed plots. HAB—habitat types; PET—potential evapotranspiration; BIO—bioclimatic variables: BIO2—Mean Diurnal Range (Mean of monthly (max temp–min temp)), BIO11—Mean Temperature of Coldest Quarter, BIO14—Precipitation of Driest Month, BIO15—Precipitation Seasonality (Coefficient of Variation); NA—not applicable.
DfVarianceFPr (>F)
HAB71.6259153.3305580.001
PET10.0726041.0410720.367
BIO210.0855821.227150.262
BIO1110.0733871.0522870.366
BIO1410.099361.4247140.193
BIO1510.0749091.074120.357
Residual684.742329NANA
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Djordjević, V.; Stanković, V.; Kabaš, E.; Lazarević, P.; Verloove, F.; Šinžar-Sekulić, J. Diversity Patterns of Alien Plant Species in Mountainous Areas: A Case Study from the Central Balkans. Diversity 2025, 17, 774. https://doi.org/10.3390/d17110774

AMA Style

Djordjević V, Stanković V, Kabaš E, Lazarević P, Verloove F, Šinžar-Sekulić J. Diversity Patterns of Alien Plant Species in Mountainous Areas: A Case Study from the Central Balkans. Diversity. 2025; 17(11):774. https://doi.org/10.3390/d17110774

Chicago/Turabian Style

Djordjević, Vladan, Vera Stanković, Eva Kabaš, Predrag Lazarević, Filip Verloove, and Jasmina Šinžar-Sekulić. 2025. "Diversity Patterns of Alien Plant Species in Mountainous Areas: A Case Study from the Central Balkans" Diversity 17, no. 11: 774. https://doi.org/10.3390/d17110774

APA Style

Djordjević, V., Stanković, V., Kabaš, E., Lazarević, P., Verloove, F., & Šinžar-Sekulić, J. (2025). Diversity Patterns of Alien Plant Species in Mountainous Areas: A Case Study from the Central Balkans. Diversity, 17(11), 774. https://doi.org/10.3390/d17110774

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