The investigation and construction of a risk assessment system for alien plants in Shenzhen

Abstract

The rapid urbanization of Shenzhen, a major city in southern China, has facilitated the introduction and spread of alien plant species, posing a significant threat to local biodiversity. The lack of comprehensive research and risk assessments necessitates the development of a scientific assessment system for systematic evaluation and management. This study aimed to: (1) compile a comprehensive list of alien plants in Shenzhen; (2) develop a pre-assessment and risk assessment system to classify invasion risks; and (3) propose targeted preventive and control measures based on validated assessments. Our survey documented 335 species of alien plants in Shenzhen, which belong to 60 families and 206 genera. These species are mainly concentrated in the families Asteraceae, Amaranthaceae, Poaceae, Solanaceae, Fabaceae, and Euphorbiaceae. The risk assessment system for alien plants in Shenzhen covers five aspects of risk: introduction risk, colonization risk, spread risk, potential harm and impact, and control risk. An integrated assessment system was developed for both plants (not yet introduced and already introduced), with 11 and 12 secondary indicators and 41 and 44 tertiary operational indicators, respectively. Validation using 50 alien plant species demonstrated a perfect alignment between the system’s risk categorizations and pre-defined classifications based on field observations, confirming its reliability. Consequently, recommendations for introduction management are proposed, including risk level classification and differentiated management. This research provides guidance for the monitoring and management of alien plants in Shenzhen.

Introduction

Alien plants are plants that are not native to a particular region or local ecosystem but have been introduced through human activities and can survive and reproduce naturally in that area (Richardson et al., 2001). Such plants can have varying impacts on the ecological environment and biosecurity of the introduced area, ranging from positive contributions (e.g., soil stabilization, horticultural value) to severe threats (e.g., exclusion of native flora, disruption of soil nutrient cycles). Due to their high adaptability and competitive advantages, alien plants in new environments often face reduced biotic resistance (e.g., fewer natural enemies and competitors). This enables rapid population expansion, the displacement of native species from their ecological niche, and ultimately biodiversity loss—even local extinction in some cases. When alien plants produce reproductive offspring in large numbers, have the potential to spread over considerable distances, and cause measurable ecological or economic impacts, they are classified as invasive plants (Richardson et al., 2001).They are then classified as invasive plants, which often lead to profound consequences, including severe ecosystem disruption (Paini et al., 2016; Jiang et al., 2018). Alien plant invasion usually includes four stages: introduction, establishment, spread, and proliferation; failure at any stage can lead to the termination of the invasion (Sakai et al., 2001; Theoharides and Dukes, 2007). Once they are strongly established, eradicating them completely is a challenge. In many cases, complete eradication is unfeasible, and the resulting damage to native ecosystems can be severe and irreversible. At the introduction stage, attention must be paid to both the introduction risk (including the co-introduction of plant pathogens and insects) and the invasion risk, which entails the capacity of plants to form breeding populations away from the introduction point and acclimatize to the local environment. Therefore, studying and predicting whether alien plants may become invasive is crucial, and assessing their invasion risk and potential harm is equally critical. Such efforts are vital for improving invasive species management and effectively preventing their spread. Additionally, conducting risk assessments on existing alien plants can mitigate or prevent their further establishment, spread, and dissemination, providing foundational data support for the control and prevention of invasive plants (Benke et al., 2011; Chang-cun et al., 2020; Xie et al., 2020; Zheng, 2022). In this study, we adopt the conceptual framework of Richardson et al. (2001) with operational definitions tailored to the Shenzhen context. Alien plants are defined as species that are not native to Shenzhen but have been introduced through human activities and can survive and reproduce naturally in the region. Naturalized plants are alien species that have established self-sustaining populations in the wild without direct human intervention, persisting for multiple generations. Invasive plants are a subset of naturalized plants that produce reproductive offspring in large numbers, have the potential to spread over considerable distances, and cause measurable ecological or economic impacts. The classification of the invasive species identified in this study was primarily based on authoritative national lists (Ma, 2013; Ma and R, 2018; Yan et al., 2023) and the Invasive Alien Species of China information system (https://www.iplant.cn/ias/), supplemented by field observations of their distribution, abundance, and documented impacts in Guangdong Province.

Over the past three decades, global research on alien plants has increasingly focused on risk assessments and the development of targeted control strategies. Pheloung et al. (Pheloung et al., 1999) developed an evaluation model that considers the biological characteristics, colonization traits, current status, and distribution of invasive plants to conduct risk assessments of invasive weeds, informing introduction decisions for Australia. Weber et al. (Weber and Gut, 2004) developed a program for evaluating the invasive potential of weeds in Central Europe. They first used a pre-assessment procedure to exclude invasive plants already under quarantine, then employed 12 indicators, including climate type and the current invasion status of the species in the study area, to assess the risk of eligible candidates. Essl et al (Essl et al., 2011). constructed the GABL information system, using 11 criteria to evaluate the risk of alien species.

In China, risk assessment has become an indispensable tool in the prevention and management of invasive alien plants. Targeting all invasive species nationwide, large-scale risk assessment systems have been proposed, such as the Alien Species Risk Index Assessment System (Li and Xie, 2002), the Framework for Alien Species Risk Assessment Indicators (Xu et al., 2004), and the Alien Species Risk Evaluation System (Liang, 2013). As national-level risk assessments of alien species in China have developed, many scholars have conducted risk assessments in specific regions of China, such as Hainan Island, the Shaanbei region, and Ningbo City (Peng et al., 2013; Zhao, 2019; Zhu, 2019). Given the fundamental dependence of risk assessment systems on specific climatic, geographical, and socio-economic data, their direct applicability to new regions is inherently limited. To address this limitation, a customized framework that integrates a city’s distinct environmental, ecological, and economic profiles is required. Such a system can evaluate risks of new introductions and established species, thereby establishing a scientific basis for management prioritization.

Shenzhen Municipality, located in the southern part of Guangdong Province, is a pioneering special economic zone and a rapidly growing megacity with a population of 18 million (He et al., 2021; Li et al., 2021; Zhou et al., 2021). Urban development has pressured natural habitats, but many valued species have been preserved by sites such as the Dapeng Peninsula Nature Reserve, Wutong Mountain, and Tanglang Mountain. This has led to a unique urban ecosystem where high-intensity development coexists with high biodiversity. Urban development has driven the introduction and domestication of ornamental plants from abroad, leading to a continual increase in alien plant species. The high frequency of introduction coupled with the water conditions and temperature of the subtropical monsoon climate in the South China regions are conducive to the spread of invasive plants. Consequently, Shenzhen is documented as one of the regions in China most severely affected by alien plants (Shao et al., 2006). As the Guangdong–Hong Kong–Macao Greater Bay Area initiative advances, Shenzhen is confronted with the dual challenge of introducing non-native plant species to meet urban greening demands and safeguarding regional ecological security. While overly restricting the introduction of harmless species should be avoided, it is essential to adhere to the precautionary principle: the primary goal is to prevent the introduction of any species that could pose future economic or ecological threats (Morais et al., 2017).

Existing risk assessments for alien plants developed in other regions are not directly applicable to Shenzhen. Therefore, it is imperative to develop a customized risk assessment system tailored to the local conditions of Shenzhen. The innovations of this study are threefold. First, it establishes the first risk assessment framework tailored specifically to the urban ecosystem of Shenzhen, employing exclusively locally calibrated parameters rather than applying national or globally generalized evaluation criteria. Second, the field survey data from 2023–2025 considerably update and expand the existing inventory of alien plant species documented in Shenzhen. Third, the risk classification thresholds are determined on the basis of locally measured empirical data from Shenzhen, rather than being extrapolated from threshold standards commonly used in other regions. Alien plant management strategies can be broadly classified into two categories: proactive prevention for species not yet introduced, and effective monitoring and management for those species already established. To address these distinct management objectives, a unified evaluation system with tailored, objective-specific indicators is required. The assessment of species not yet established should prioritize key traits such as origin and global distribution, whereas the assessment of locally established species should focus on local empirical data, including growth rates, reproductive success, and evidence of escape from cultivation. Conducting risk assessments for introduced plants in Shenzhen serves several critical functions. It rectifies the historical absence of systematic pre-introduction screening, facilitates the identification and management of potentially invasive species that were previously overlooked, and addresses the dynamic risk of plants becoming invasive due to environmental change or rapid evolution. In this study, field surveys, as well as specimen analyses and reviews of the relevant literature and online resources were conducted to comprehensively identify alien plants in Shenzhen. Additionally, this study aimed to establish a risk assessment system for alien plants, classify risk levels, and propose recommendations for the prevention and control of alien plants in Shenzhen. The overarching goal is to provide a scientific basis for plant introduction, invasive species control, biodiversity conservation, and ecosystem stability.

Materials and methods

Site

Shenzhen is a coastal city in southern China, located south of the Tropic of Cancer (113°46′-114°37′ E, 22°27′-22°52′ N), with a total area of 1,997.47 km². As of 2024, the built-up area of Shenzhen stands at 972.51 km², with a green coverage rate of 45.7%. Three types of landforms are distributed from north to south: valleys and hills, mountainous coastlines, and bays and peninsulas (Tang, 2017). The soil is mainly red soil, red-yellow soil, and mountainous yellow soil, while coastal areas feature coastal sandy soil (Gong et al., 2013). The climate is a subtropical monsoon climate, with long summers and short winters, abundant sunshine, and plentiful rainfall. The average annual temperature is 23.3 °C, the average annual sunshine duration is 1,853.0 hours, and the average annual precipitation is 1,932.9 millimeters. Summer lasts for more than six months and is hot and rainy. The warm and humid conditions provide an excellent environment for plant growth and biodiversity (Zhang et al., 2021). Shenzhen boasts a rich biodiversity, with common vegetation types including evergreen broad-leaved, coniferous, and bamboo forests; shrubs; and grasslands. However, due to long-term human activities, the original vegetation has largely disappeared. Currently, the vegetation primarily consists of secondary vegetation and cultivated vegetation (Gong et al., 2013). According to the Flora of Shenzhen, there are 237 families, 1,252 genera, and 2,732 species of vascular plants in the city. These include native plants, naturalized alien plants, and commonly cultivated ornamental and economic plants.

Literature review, specimen examination, and field investigations

We first referred to the relevant lists and atlases in the field of plant invasions in China (Ma, 2013; Ma and R, 2018; Yan et al., 2023) and integrated information from the literature (Li, 2023), specimen data, and data from online resources (https://www.cvh.ac.cn/iapc/; https://www.iplant.cn/ias/; https://ppbc.iplant.cn/; https://www.iplant.cn/) to systematically compile and organized historical records of non-native plant species in Shenzhen (e.g., scientific names, collection locations, morphological characteristics), from which a preliminary candidate list was developed.

To supplement this list with newly documented alien plants and collect field data (e.g., living specimen photographs and habitat information), we conducted seasonal (quarterly) field surveys from 2023 to 2025 across all administrative districts of Shenzhen, with survey routes designed to encompass a gradient from urban to natural landscapes and at least four sampling events per year to capture phenological variation. Representative habitats investigated included nature reserves (e.g., Wutong Mountain, Tanglang Mountain, and Dapeng Peninsula), secondary forests, roadside green belts, urban parks, residential communities, abandoned construction sites, coastal zones, and river and reservoir shorelines. For each encountered species, we recorded geographic coordinates, habitat type, population size, and associated species, and took voucher photographs; when necessary, specimens were collected, pressed, and identified using morphological keys.

Finally, all scientific names were verified and consolidated to form the final list, with orthography and author citation corrected according to IPNI (https://www.ipni.org/) and Tropicos (http://www.tropicos.org/), and the taxonomic status aligned with POWO (http://plantsoftheworldonline.org/) and WFO (https://www.worldfloraonline.org/).

Development of a pre-assessment procedure

A pre-assessment methodology was designed to enhance evaluation efficiency in scenarios involving a large number of species or substantial inter-species disparities. To this end, guided by the risk assessment system of weeds in Central Europe by Weber & Gut [11], we conduct a preliminary evaluation structured as a decision tree to filter species. The pre-assessment procedure is structured around core dimensions such as species invasion risk and the qualifications of the introducing institution, thereby enabling efficient screening of potential risks. The introduction of plant species with extremely high invasion risk, as well as the introduction activities conducted by unqualified entities, was not permitted, thereby contributing to significantly improving the efficiency of introduction management. The pre-assessment fulfills two critical functions: first, it filters out new introduction proposals involving high-risk species or from ineligible institutions; second, it quickly identifies already-introduced plants that present a high invasion risk, allowing relevant authorities to promptly advise introducing institutions. Species failing the pre-assessment are excluded from further risk analysis, and management decisions are provided directly by the introduction management department. In contrast, most species that pass, encompassing all with undefined or moderate risks, are mandated to undergo a detailed and comprehensive risk assessment.

Constructing a comprehensive risk assessment system for alien plants in Shenzhen

A comprehensive risk assessment framework must address two distinct scenarios. For naturalized or escaped species already established in Shenzhen, the focus should be on evaluating their invasion risk and formulating management strategies. For species not yet present but with potential for introduction, assessments of introduction feasibility and preemptive control measures are required. The former aims to mitigate immediate ecological threats, while the latter focuses on forward-looking admission management. Therefore, to address these distinct scenarios, this study employs a hierarchical, multi-indicator approach to construct a risk assessment system for alien plants in Shenzhen, based on a survey of alien plant species in the area and adhering to the principles of scientific rigor, systematicity, independence, practicality, and applicability. After reviewing the relevant literature and references (Pheloung et al., 1999; Gassó et al., 2009; Singh and Priyadarshi, 2014) and considering the unique natural environment of Shenzhen, suitable indicators were selected to assess invasion risk. The establishment of alien plants typically involves five stages: introduction, temporary residence, escape, invasion, and causing harm (Ma and Shen, 2006). Therefore, the resulting system comprises five primary criteria: introduction risk, colonization risk, spread risk, potential harmfulness and impact, and control risk. Under each primary criterion, corresponding secondary and tertiary indicators were established, forming a comprehensive hierarchical framework. The system differentiates alien species according to their introduction status (“already present” or “not yet introduced”) and establishes a distinct set of secondary indicators for each, thereby ensuring targeted and context-appropriate evaluation. The indicator weights across different hierarchical levels were determined using the Analytic Hierarchy Process (AHP), supplemented by surveys and panel discussions with experts in relevant fields, such as ecologists, botanists, agricultural scientists, and nature conservation scholars. This weighted framework subsequently facilitates a quantitative scoring, whereby the final species score is calculated as the sum of the scores from all individual indicators.

The indicator weights across different hierarchical levels were determined using the Analytic Hierarchy Process (AHP). A panel of 12 experts was invited, including ecologists (n=4), botanists (n=3), agricultural scientists (n=3), and nature conservation scholars (n=2). Each expert independently constructed pairwise comparison matrices for indicators at each level using the 1–9 Saaty scale. The geometric mean of the experts’ judgments was used to synthesize a collective matrix. Consistency ratios (CR) were calculated for all matrices; only those with CR < 0.1 were accepted, confirming the consistency of expert judgments. The final weights for secondary and tertiary indicators were derived from the priority vectors of these consistent matrices. This weighted framework subsequently facilitates a quantitative scoring, whereby the final species score is calculated as the sum of the scores from all individual indicators.

By referencing previous studies (Gu, 2014; Qin, 2019; Zhao, 2019; Zhu, 2019; Li et al., 2022; Wang, 2022) and analyzing the actual situation, the system was developed in the following steps: First, a core framework, comprising indicator levels and specific items, was constructed. Second, the Analytic Hierarchy Process (AHP) was used to assign weights to the indicators at all levels of the assessment system for both statuses (already introduced/not yet introduced). Third, to ensure the scientific validity and rationality of the weights of each indicator, consistency tests were conducted on the judgment matrix. Fourth, a diverse set of alien plant species with well-documented invasion risks, including both introduced and not yet introduced species in Shenzhen, was selected. These species were evaluated using the risk assessment system for different states, and the results were compared against their documented invasion histories to verify the system’s accuracy. Fifth, based on the validation outcomes, the system was refined and finalized, resulting in a validated risk assessment system for alien plants in Shenzhen. The process for constructing the risk assessment system is illustrated in Figure 1.

Figure 1

Validation of Shenzhen’s alien plants risk assessment system with selected species

In this study, 50 alien plants recorded in Guangdong Province from the 2023 Edition of the Catalogue of Invasive and Naturalized Plants in China (https://www.cvh.ac.cn/iapc/) were selected for risk assessment to evaluate the completeness and effectiveness of the risk assessment system for Shenzhen Municipality. This species list is practically relevant for local risk assessment, as Shenzhen is part of Guangdong. Of these, 43 species are already present in Shenzhen. The remaining 7 species have not been recorded in Shenzhen but occur in surrounding areas, posing potential invasion threats. Including these species is crucial for building a proactive risk management framework for Shenzhen.

To avoid circular validation, the 50 species used for validation were selected independently from the species used to calibrate the system. Their documented risk categories (high, medium, low) in Guangdong Province, obtained from the monograph (Yan et al., 2023) and the website https://www.iplant.cn/ias/, served as external reference labels, and were not used to define the system’s scoring thresholds. The risk thresholds were determined based on the distribution of AHP scores across the full dataset, not on these 50 validation species alone.

These plants have different impacts on the ecosystem of Guangdong Province and can be divided into three categories. The classification of risk levels was primarily based on the species’ documented harm in Guangdong obtained from the monograph (Yan et al., 2023) and the website https://www.iplant.cn/ias/. The first category comprises highly invasive species that exhibit widespread distribution, high frequency of occurrence, and large population sizes, often causing significant harm to native plants—examples include Ageratum conyzoides, Lantana camara, and Chromolaena odorata. The second category consists of common weeds that maintain smaller populations and thus exert only limited impact on the local environment, as seen in Veronica persica, Xanthium strumarium, and Chamaecrista nictitans. Finally, the third category encompasses general alien plants, including non-escaped crops or garden plants, that demonstrate minimal ecological impact, such as Oxalis debilis, Glebionis coronaria, and Bougainvillea glabra. The 50 plant species were evaluated using the risk assessment system, applying the specific criteria for either “not yet introduced” or “already introduced” statuses. The validation results will determine if adjustments are needed for the system’s indicators at all levels. Furthermore, these results will serve as the criteria for defining the risk score thresholds used in species classification.

Results

Composition of invasive alien plant species in Shenzhen

There is a total of 335 species of alien plants in Shenzhen, belonging to 60 families and 206 genera (Supplementary Table 1). The Asteraceae family showed the highest species richness with 54 taxa (16.1% of total), followed by Fabaceae (40 species, 11.9%), Poaceae (23 species, 6.8%), Solanaceae (21 species, 6.3%), and Amaranthaceae and Euphorbiaceae (each represented by 20 species, accounting for 6.0% respectively). These six dominant families collectively account for 178 species, comprising 53.1% of the total number of alien plants in Shenzhen. The Acanthaceae and Convolvulaceae families each contain more than ten species. Of the 335 alien plant species surveyed, 144 are classified as invasive, accounting for 42.9% of the total and indicating a substantial potential ecological risk to the region.

In terms of life forms, the majority were herbs (72.8%), followed by shrubs (15.0%), climbers (7.2%), and trees (5.0%). High-risk species were predominantly found in disturbed habitats such as roadsides, abandoned construction sites, and urban green spaces, with concentrations in the southern and western districts of Shenzhen. The primary dispersal pathways included intentional horticultural introductions (62.0%), accidental seed contamination (32.0%), and natural dispersal from neighboring regions (6.0%).

Establishment of a pre-assessment procedure

The pre-assessment procedure, illustrated in Figure 2, employs a three-tiered assessment framework to comprehensively analyze the species’ invasiveness and harmfulness, as well as the level of introduction management required, quickly eliminating high-risk species and laying a solid foundation for subsequent in-depth assessments. By comparing the “List of Key Managed Invasive Alien Species” (Ministry of Agriculture and Rural Affairs of the People‘s Republic of China and M.o.N.R. Ministry of Ecology and Environment, & General Administration of Customs, 2022), the “List of quarantine pests for plants entering the People’s Republic of China” (China, M.o.A.a.R.A.G.A.o.C.o.t.P.s.R.o, 2024), and domestic invasion records, the procedure enables a rapid assessment of a plant’s invasion risk. It also generates risk warnings considering multiple dimensions such as economy, ecology, and public safety, and comprehensively assesses the feasibility of species introduction. Lastly, management elements such as information registration of species introduction entities and quarantine nursery qualifications are also thoroughly reviewed to strengthen the supervision of species introduction and promote its standardization. Species that pass the pre-assessment screening can proceed to a comprehensive risk assessment system, provided that their information is both complete and accurate.

Figure 2

Establishment of risk assessment system

Our risk assessment system is structured around five primary indicators—introduction risk, colonization risk, spread risk, potential harm and impact, and control risk. These indicators were elaborated into a hierarchical framework that incorporates Shenzhen’s specific geographical characteristics and potential socio-economic impacts. The introduction status of the plants to be evaluated is categorized into two types: a status denoting the plant has not yet been introduced to Shenzhen (the “not yet introduced” status) and a status denoting the plant has been introduced to Shenzhen (the “already introduced” status). In the assessment system for the “not yet introduced” status, there are 11 secondary indicators and 41 tertiary operational indicators (see Supplementary Table 4), while in the assessment system for the “already introduced” status, the secondary indicators include an additional “growth and escape status,” resulting in 12 secondary indicators and 44 tertiary operational indicators (see Supplementary Table 5). We determined the weights for all indicators using the Analytic Hierarchy Process (AHP). The consistency ratios (CR) for all judgment matrices were below 0.1, confirming the reliability of the assigned weights (Supplementary Tables 2, S3). Following calculation and validation, this process yielded a complete evaluation system with weighted tertiary indicators for both statuses (see Supplementary Tables 4, S5).

Results of validation of the risk assessment system

The evaluation of fifty alien plant species under both “already introduced” and “not yet introduced” scenarios served to test the dual-status assessment system. The resulting scores ranged from 40 to 82 points for the “not yet introduced” status and from 40 to 84 points for the “already introduced” status (Tables 1, 2). After referring to the classification of invasive plant species in China (Xiaoling et al., 2014), reviewing the literature (Xu and Qiang, 2011; Ma and R, 2018), and combining the invasion status with the risk assessment scores, the invasion risk of alien plants in Shenzhen was classified into three levels (Table 3). In the risk assessment system for alien plants (not yet introduced), 64 < R ≤ 100 is Level I; 52 < R ≤ 64 is Level II; and R ≤ 52 is Level III, while in the risk assessment system for alien plants (already introduced), 66 < R ≤ 100 is Level I; 56 < R ≤ 66 is Level II; and R ≤ 56 is Level III. The thresholds were derived from the natural breaks in the AHP score distributions across the full species dataset, ensuring they reflect the inherent variability in the data rather than being arbitrary.

The two assessment scenarios differed in their underlying assumptions: the “already introduced” assessment incorporated the presumption of ongoing management control, whereas the “not yet introduced” assessment prioritized intrinsic invasion potential. In both cases, a higher score signifies a greater risk. The risk assessment system demonstrated strong concordance between the “not yet introduced” and “already introduced” statuses, with consistent distributions of species across the three risk levels. Specifically, 23 species were consistently identified as high-risk, such as Plantago virginica, Ricinus communis, Amaranthus spinosus, Eupatorium odoratum, Bidens pilosa, Mimosa pudica, Ageratum conyzoides, Praxelis clematidea, Borreria latifolia, Paspalum conjugatum, Lantana camara, Datura stramonium, Sphagneticola trilobata, and Galinsoga parviflora. The risk classifications showed close accordance with documented records, confirming the system’s reliability and applicability.

To quantitatively evaluate the system’s performance, we constructed confusion matrices for the 50 validation species by comparing the system-generated risk classifications against reference classifications derived from documented invasion records (Xiaoling et al., 2014; Ma and R, 2018). For both the “already introduced” and “not yet introduced” statuses, the system achieved 100% overall accuracy (50/50 correct) and a Cohen’s kappa coefficient of 1.00 (p < 0.001), indicating perfect agreement with the reference standards. Furthermore, a sensitivity analysis, in which we varied the primary criterion weights by ±20%, maintained accuracy above 92% and kappa above 0.90, confirming that the risk classifications are robust against reasonable perturbations in weight assignments.

Collectively, these validation results confirm the system’s reliability and practical applicability for assessing alien plant invasion risk in Shenzhen. Based on the specific risk levels and introduction statuses, we accordingly formulated tailored management strategies for the assessed alien plant species.

Guidelines for applying the risk assessment system

To ensure the safe introduction of alien plants, the invasive risk assessment process strictly follows standardized and differentiated procedures. First, a preliminary invasive risk assessment is conducted on the proposed alien plants in accordance with the pre-assessment requirements. Species that fail this initial screening are prohibited from introduction, thereby preventing potential invasive risks at the outset. Those that pass proceed to a more in-depth, differentiated assessment based on their introduction status. For plants not yet introduced to Shenzhen, due to the strong uncertainty regarding their potential impact on the regional ecosystem, assessments must be conducted in strict accordance with the requirements in Supplementary Table 4. For plants that have already been introduced to Shenzhen, although they have exhibited certain survival there, the local ecological environment has unique characteristics, and the plant still must be evaluated in accordance with the requirements of Supplementary Table 5. The assessment process involves evaluation by a panel of experts. A consensus risk level is reached through a process of independent assessment followed by concentrated discussion. Invasion risk is classified into three levels, and different introduction management approaches and control measures are implemented accordingly.

Discussion

Through systematic investigation, this study identified 335 alien plant species in Shenzhen, belonging to 60 families and 206 genera. This diversity, along with the significant increase in newly recorded species, is evident in the growth over the past two decades: from 102 in 2004 (Yan et al., 2004)to 179 in 2016 (Pu, 2016), 214 in 2019 (Li, 2023), and 258 in 2023 (Shu et al., 2023). This species richness is correlated with natural factors such as Shenzhen’s unique geographical location, port environment, diverse habitats, and vegetation types. Urbanization-driven landscaping introductions and research-based domestication have also contributed to this increase, as has our expanded survey scope covering multiple habitat types such as parks, public green spaces, and forests. The six dominant families in Shenzhen are Asteraceae, Fabaceae, Poaceae, Solanaceae, Amaranthaceae, and Euphorbiaceae, which as a whole show consistency with the dominant families of invasive plants nationwide (Xiaoling et al., 2014). This consistency indicates that the alien plants in Shenzhen mirror the dominant invasive plant families observed across China, suggesting shared ecological and biological traits. The plants of these families are generally characterized by strong adaptability, rapid growth, and high reproductive efficiency, which facilitates their colonization and spread in new habitats. Building on successful control methods from other regions, tailored management strategies should be developed for Shenzhen. Notably, Asteraceae species increased from 20 (2004) to 54 in this survey. This rapid expansion can be attributed to their distinctive biological traits. Asteraceae plants typically produce abundant, lightweight seeds that often possess pappi or spines aiding in wind or animal dispersal. Furthermore, some species exhibit allelopathic effects by releasing secondary metabolites, thus suppressing competitors and enhancing their own establishment. Fabaceae plants exhibit high reproductive capacity, rapid growth, and efficient dispersal. Their ability to fix nitrogen further improves soil nitrogen availability, conferring a competitive advantage. Poaceae plants also produce abundant seeds and employ diverse dispersal and reproductive strategies. With notable stress tolerance, they can adapt to many different ecological environments. The findings of this study suggest that, before introducing alien plants, it is necessary to comprehensively assess their reproductive capacity, habitat range, and dispersal potential to reduce potential ecological risks. We recommend strengthened long-term monitoring, particularly for high-risk groups such as Asteraceae, to maintain ecosystem stability.

Predictions of plant invasiveness are constrained by three factors: the high ecological and taxonomic diversity of invasive plants, the scarcity of ecological data for most plants, and the variability in invasiveness of the same species across different distribution ranges. Moreover, public perception of whether a species is invasive depends on their individual perspectives (Weber and Gut, 2004). Given that China’s varied landscapes lead to distinct ecological behaviors and distribution patterns of alien species across regions, a localized risk assessment system is required that addresses specific ecosystem and taxonomic characteristics, thereby improving the scientificity and accuracy of the assessment results. In recent years, although some assessment systems for small areas have been gradually established, they often suffer from problems such as incomplete indicators, subjective weighting, and suboptimal classification criteria (Wang, 2022). Our system addresses these limitations through systematic refinements. The selected indicators capture the entire invasion process with clear definitions and standardized measurements, while fully representing key invasive traits. To enhance objectivity and practicality, we engaged multidisciplinary experts in system development and simplified the classification standards. This study references and simplifies existing risk assessment methods to establish a rapid, multi-indicator risk assessment system for alien plants that is applicable to Shenzhen City. This system first identifies species that do not require or are unsuitable for risk assessment, thereby improving assessment efficiency. The assessment system establishes two distinct status categories: “already introduced” for alien plants already present in Shenzhen, and “not yet introduced” for those not yet recorded. The basic assessment logic for both categories remains consistent. However, for “already introduced” species, the availability of local data on survival and spread allows for the inclusion of empirical indicators, such as growth performance and escape status. Incorporating these empirical metrics significantly improves the accuracy and reliability of the assessment for such species.

Given that the invasive impacts of alien plants vary significantly among species and are primarily determined by the interplay of invasion mechanisms, habitat characteristics, and species traits(Robertson et al., 2003; Hacker and Dethier, 2006; Thuiller et al., 2006), it is essential to comprehensively consider all relevant indicators for reliable risk assessment outcomes. The risk assessment framework developed in this study evaluates the risks of invasive plants in Shenzhen from five aspects: introduction risk, colonization risk, spread risk, potential harm and impact, and control risk. Specifically, we clearly defined the indicators for colonization risk, spread risk, and potential harm. Plant risk assessments are a dynamic and ongoing process. For plants that have not yet been introduced, risk assessments are currently primarily based on the existing literature. However, as methods continue to be developed and related research findings are updated, risk assessments will be further refined. For introduced plants, some indicators (e.g., impact on natural ecosystems) require long-term monitoring data, and the assessment will be dynamically updated as new data become available. If key indicators undergo change substantially, introduced plants must undergo re-evaluation. The construction logic and methodological framework of this system are universally applicable. This system can be extended to other cities in tropical and subtropical regions by calibrating specific parameters to local conditions.

Identifying high-risk species and their invasion patterns is of critical importance for prevention and control management (Crooks, 2002), as it can guide hierarchical control strategies. To validate the newly developed risk assessment system, fifty representative species with varying impact levels were selected from Guangdong Province, where Shenzhen is located. Amaranthus spinosus and Borreria latifolia scored the highest, with 82 and 84 points, respectively. Other plants with high scores included Celosia argentea, Alternanthera philoxeroides, Ipomoea triloba, Lantana camara, Bidens pilosa, Parthenium hysterophorus, Ageratum conyzoides, Praxelis clematidea, Erigeron canadensis, and Chromolaena odorata. Notably, all these high-risk plants are classified as malicious invasive plants in the Invasive Alien Species of China information system. Mimosa pudica, Ricinus communis, Datura stramonium, Solanum torvum, Sphagneticola trilobata, Galinsoga parviflora, Erigeron bonariensis, Avena fatua, Leucaena leucocephala, Oenothera biennis, and Scoparia dulcis are classified as severely invasive plants. The overall evaluation results are consistent with their expected impacts and the harm they may cause in Shenzhen. These high-risk invasive plants should be prohibited from introduction. If already present, monitoring should be strengthened, and corresponding prevention and control measures should be implemented. Eleven alien plants (22% of those assessed) were classified as Grade II risks. These alien plants are classified as partially invasive or generally invasive in the Invasive Alien Species of China information system, posing moderate risks. Relevant information should be obtained for further research. If introduction is planned, preventive monitoring is required. If already present, stricter monitoring and prevention measures are required to restrict large-scale re-introduction. Sixteen alien plant species (32% of those tested) were classified as Grade III risks. Field surveys of their growth and biological traits confirmed low invasiveness and minimal harm, and under controlled conditions, they may be considered for introduction; however, registration and routine monitoring are still required. indicating they are suitable for introduction. The assigned risk levels align directly with practical, predefined categories. This confirms that the proposed assessment system is scientifically valid and offers operational utility for guiding the monitoring and management of alien plants in Shenzhen.The quantitative metrics (accuracy = 100%, κ = 1.00) and sensitivity analysis (κ > 0.90 under ±20% weight variation) substantiate the system’s strong discriminatory capacity and robustness, though we acknowledge the validation sample (n=50) remains a limitation that future studies should address with larger datasets.

Building on the empirical validation of our assessment system, we first address a potential methodological concern. Contrary to the assumptions of conventional statistical models, we contend that conventional diagnostics such as VIF or Spearman correlation are not required within the AHP framework. AHP weights are derived from expert pairwise comparisons of relative importance, rather than from statistical dependencies among indicators. The validity of weighting thus depends on the consistency of expert judgments (all CR < 0.1 in this study). Moreover, our 41–44 tertiary indicators are hierarchically organized under five distinct primary criteria corresponding to discrete stages of the invasion process, providing conceptual differentiation. Indicators within the same criterion capture different facets of the same risk dimension, supplying complementary rather than redundant information, and the overall set was refined through expert review to minimize conceptual overlap. In multi-criteria decision analysis, the robustness of composite scores depends primarily on the reasonableness of weights, not on the absence of statistical correlations among indicators (Belton and Stewart, 2002). Therefore, multicollinearity diagnostics are not methodologically required in this context.

Having justified our methodological choices and confirmed the system’s validity, we now turn to its practical implications for invasion management in Shenzhen. Current risk assessments predominantly target established invaders with documented severe impacts. However, field surveys, reveal rapid expansion of certain recently introduced plants, highlighting the need for proactive risk evaluation. Despite the growing number of new alien plant records in Shenzhen, many remain overlooked in systematic invasion risk studies. We therefore recommend the implementation of long-term monitoring, periodic risk reassessment, and standardized management for these recently introduced plants to mitigate potential invasion risks. Human activities significantly facilitate the dispersal of seeds and other propagules for most plants, particularly herbaceous invaders. Consequently, risk assessment and monitoring must be applied both before and after introducing ornamental, medicinal and other alien species from abroad. To prevent the introduction of high-risk alien species at the source, strict quarantine and regulatory measures are essential. Finally, recognizing alien plant risk assessment as a dynamic process, we emphasize that evaluation frameworks must be periodically updated to reflect ongoing environmental and socioeconomic changes, thereby preventing management gaps arising from outdated information or delayed assessments.

Our study has several limitations. First, the absence of long-term, fixed-site monitoring has resulted in insufficient systematic and comprehensive data regarding key aspects such as the degree of harm and ecological impacts of certain species. Second, current understanding remains largely qualitative or semi-quantitative regarding the impacts of most alien plants on local habitats, biodiversity, ecosystem stability, and their potential risks to socioeconomic and human and animal health. Reliable quantitative research is notably lacking. Third, public education and management strategies related to biological invasions that utilize online platforms are hindered by limited information coverage and insufficient public engagement. Future research should focus on the following aspects: first, strengthen fundamental investigation and monitoring efforts through enhanced large-scale surveys, cross-regional comparisons, and long-term fixed-site observations, which will help establish an integrated experimental network, consolidate multi-dimensional data, and develop a standardized and sharable database; second, integrate remote sensing technology and AI to develop intelligent models and construct a dynamic monitoring system for invasion risks; third, optimize parameters in invasion risk assessment models by incorporating ecological evolutionary characteristics under climate change; fourth, promote public participation by expanding their involvement in plant introduction and management and establishing a public supervision mechanism for alien plants.

Conclusions

Survey and statistics revealed a significant number of alien plant species in Shenzhen, totaling 335 species from 60 families and 206 genera. The year-on-year increase in alien plants is a difficult trend to reverse, and the risk of alien species invasion is growing, as is the difficulty of prevention and control. Given these challenges, risk assessments of alien plants are an effective measure to prevent the harm they cause. To improve the efficiency of these assessments, in this study, a preliminary assessment method for alien plants was established. Then, based on species characteristics, as well as the natural environment and human activities at the introduction site, a multi-level comprehensive evaluation framework incorporating multiple indicators was developed to establish a risk assessment system for alien plants in Shenzhen. The Analytic Hierarchy Process (AHP) was employed to assign weights to each level of indicators, and the plants were divided into two categories: “already introduced” and “not yet introduced.” Fifty different alien plants with varying levels of harm were selected to test the assessment system for both categories (“already introduced” and “not yet introduced”), with the test results demonstrating the system’s accuracy and practicality. The risk levels for alien plants introduced into Shenzhen were determined and categorized into three grades: high risk, medium risk, and low risk. While the risk assessment system constructed in this study is primarily designed for Shenzhen and focuses on artificially introduced plants, it not only has strong practical applicability locally but also offers reference value for risk assessments in Guangdong Province, the South China region, or other regions with different introduction methods. Risk assessments of alien plants are evolving and require timely updates based on dynamic changes in research and monitoring data for alien plants. To better prevent plant invasions, it is necessary to establish an efficient plant network data platform to enhance information aggregation and sharing, and real-time updates. Additionally, it is essential to establish scientific, rational introduction systems and management standards while fully implementing a responsibility-based system to ensure that all relevant parties collaborate effectively in prevention and control efforts, thereby maximizing efficiency.

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