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Review

Mapping Research Trends on Fire and Invasive Plant Species in Grassland Restoration: A Bibliometric Review

by
Sellina Ennie Nkosi
*,
Yingisani Chabalala
and
Mashudu Patience Mamathaba
Department of Environmental Sciences, University of South Africa, Florida Science Campus, Private Bag X6, Roodepoort 1710, South Africa
*
Author to whom correspondence should be addressed.
Conservation 2025, 5(4), 59; https://doi.org/10.3390/conservation5040059
Submission received: 5 July 2025 / Revised: 23 August 2025 / Accepted: 26 August 2025 / Published: 16 October 2025
(This article belongs to the Topic Conservation at the Crossroads: Forest Ecology, Wildlife Dynamics, and Emerging Challenges for Ecosystem Resilience)
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Abstract

Fire and invasive plant species interactions are critical drivers of biodiversity loss and ecological change in grassland ecosystems worldwide. However, research efforts on this topic are often fragmented, regionally based, and lack synthesis across disciplines. This study aims to map the intellectual structure, collaboration networks, thematic focus, and knowledge gaps in research on fire-invasive species interactions in grassland restoration. A systematic bibliometric analysis was conducted using the Web of Science Core Collection, focusing on peer-reviewed English-language articles published between 1990 and 2024. The search strategy targeted studies addressing fire regimes and invasive plant species in grassland ecosystems, using co-authorship, co-occurrence and thematic clustering analyses to reveal collaboration patterns and research trends. The results highlight a concentration of publications in key ecological journals, with a dominant contribution from institutions in the Global North, through growing representation from the Global South, particularly South Africa, is evident. Thematic clusters are centred on biological invasions, fire regimes, species traits and ecosystem resilience, while long-term post-fire recovery and studies from underrepresented regions remain critical knowledge gaps. This synthesis emphasises the need for interdisciplinary, regionally inclusive and policy-aligned research to inform effective grassland restoration strategies in the context of fire and invasive species challenges.

1. Introduction

Fire and invasive species are two of the most influential ecological drivers altering the structure and functioning of grassland ecosystems globally. Across a range of biogeographic contexts, fire plays a key role in maintaining grassland biodiversity, regulating plant functional traits, recycling nutrients and suppressing woody encroachment. In ecosystems such as the North American tallgrass prairie, Australian rangelands and South African savannas, periodic fire events are critical for sustaining herbaceous dominance, promoting seed germination of fire-adapted species and supporting nutrient cycling through biomass combustion [1,2,3]. The absence or alteration of fire regimes in these systems often leads to woody encroachment, reduced species diversity and shifts in ecosystem functioning [4,5]. Natural and anthropogenic fire regimes have historically shaped grassland vegetation composition and structure. These fire regimes remain central to restoration and conservation strategies today. However, shifts in fire regimes—caused by climate change, altered land-use patterns, and fire suppression policies—are increasingly creating conditions that facilitate the establishment and spread of invasive species [6]. These species, once established, can alter fire regimes themselves, often increasing fire frequency or intensity, leading to feedback loops that suppress native biodiversity and hinder ecosystem recovery [7].
Invasive alien plant species can dramatically reshape post-fire succession pathways, particularly in grasslands where rapid colonisation by aggressive invaders can outcompete recovering native flora [8]. Species such as Melinis minutiflora in South America, Imperata cylindrica in Southeast Asia, and Bromus tectorum in North America have been shown to alter fuel loads, fire frequency and intensity—ultimately impeding native species regeneration [6,9,10]. This altered feedback degrades biodiversity, ecosystem services, and complicates conservation and land management efforts, especially in fire-prone environments that are already under pressure from overgrazing, land conversion, and climate extremes [11].
The interaction between fire and alien invasive plant species is governed by a range of ecological mechanisms that influence both post-disturbance recovery and the likelihood of invasion. One such mechanism is the alteration of fuel properties by invasive species, which can increase fire frequency, intensity or spatial extent, thereby creating conditions that further disadvantage native species and favour fire-adapted invaders [6,7]. Additionally, fire may disrupt existing plant community structures and reduce competition, creating open niches that alien invasive species rapidly exploit. Some invasive plant species possess traits such as rapid resprouting, early seed production or heat-tolerant seedbank, enabling them to recover more quickly than native species after fire events [12,13]. These mechanisms often result in positive feedback loops, where fire promotes invasion and invasion, in turn, alters fire regimes, a cycle that undermines ecosystem resilience and complicates restoration efforts.
Globally, grassland restoration in invaded and frequently burned landscapes presents a significant ecological and management challenge. Restoration outcomes are often unpredictable due to the dual influence of fire and invasive species on vegetation recovery trajectories [14,15]. While fire can be a powerful tool in restoration—used strategically through prescribed burning to reduce invasive biomass or stimulate native growth—it can also exacerbate invasion when fuel loads are high or when post-fire conditions favour opportunistic non-native species [16]. As research in this domain expands, it becomes crucial to assess the evolution of scientific knowledge, identify emerging themes and knowledge gaps, and map key contributors and collaborations to offer insights into how scholarly attention has developed over time and where future research may be needed [17].
Despite a growing body of ecological research, our understanding of how invasive species and fire regimes co-drive vegetation dynamics in grasslands remains fragmented across ecosystems and geographical regions. While some studies report that prescribed fire can suppress invasive grasses by damaging their seed banks or altering competitive hierarchies [18]. Others have found that burning may unintentionally promote invasiveness by creating open niches or releasing nutrients that fast-growing non-native species can exploit [6,19]. Such contradictions point to a broader need for synthesis: patterns of post-fire invasion vary depending on timing, intensity, species traits, climatic conditions, and pre-fire community composition [20,21]. The cumulative effects of fire and invasion are also likely to be non-linear, context-dependent, and mediated by other disturbances such as grazing, drought, and land degradation [22].
The complexity of fire-invasive species interactions is compounded by a lack of integrated, cross-regional studies and systematic synthesis approaches that bridge ecological theory, land management and restoration practice. Research gaps persist in identifying when and where fire serves as a facilitator versus a barrier to restoration and how managers can tailor fire regimes to suppress invasive species while promoting native grassland resilience [23,24]. Furthermore, the proliferation of invasive species in fire-prone environments often forces trade-offs between short-term suppression strategies and long-term restoration goals. While herbicide application and reseeding efforts can be practical in post-fire restoration, their success is usually limited without coordinated fire and invasion management strategies [25]. This highlights the need to synthesise the growing but dispersed body of knowledge to support more coherent and evidence-informed grassland restoration strategies.
In response to this need, this bibliometric analysis was conducted to map the scientific landscape at the intersection of fire ecology, invasive plant species management and grassland restoration. In recent decades, several scientific publications on ecological restoration, fire ecology and biological invasions have increased substantially [26,27]. However, the literature on their intersection, specifically regarding fire-invasive interactions in grasslands, remains scattered across journals, disciplines and geographic regions. This dispersion poses a barrier to researchers, land managers and policymakers seeking evidence-based strategies to guide grassland restoration. Bibliometric analysis offers a robust and quantitative method to address this fragmentation by identifying research trends, co-authorship networks, leading contributors and emerging thematic priorities [28]. Researchers can identify emerging hotspots, gaps and opportunities for transdisciplinary collaboration and policy alignment by applying bibliometric methods to the fire-invasion-grassland relationship.
Another critical aspect of fire-invasive species interactions is their spatial heterogeneity and differential impacts across biogeographic regions. Ecosystems such as the North American prairies, South African savannas, Brazilian cerrado and Australian rangelands each pose unique fire histories, invasive species assemblages and post-disturbance successional pathways [29,30]. However, much of the global literature is disproportionately focused on temperate systems, particularly in North America and Australia, with an underrepresentation of research from African and South American grasslands [31]. This imbalance limits the generalizability of restoration models and obscures region-specific ecological dynamics. Additionally, many studies fail to integrate environmental, social and governance perspectives, often addressing either fire or invasion in disciplinary silos rather than as interlinked restoration challenges. Socio-economic drivers of fire regimes and invasive species introductions include agricultural expansion, grazing pressure and institutional fire governance [5,32].
To address the fragmentation in both geographic research coverage and disciplinary integration, where studies often focus on either fire or invasive species in isolation, interdisciplinary and cross-sectoral approaches are increasingly recognised as essential for managing fire-invasion dynamics in ways that support both ecological restoration and human well-being [33]. Community involvement, land tenure systems and the integration of traditional fire knowledge into formal management frameworks often mediate restoration success [34]. These socio-ecological dimensions are particularly relevant in regions where communal, or smallholder, land use intersects with conservation and restoration efforts. Furthermore, global environmental change, including shifts in rainfall patterns, increased drought frequency, and rising temperatures, adds another layer of complexity to fire-invasion interactions and their influence on grassland resilience [35]. These challenges call for a systematic and quantitative literature review to synthesise knowledge, highlight thematic gaps and guide future research and management priorities.
In response to these challenges, this study presents a global bibliometric review of research on fire-invasive plant species interactions in grassland restoration published between 1990 and 2024. The aim is to systematically map the scientific literature’s structure, growth and focus on the intersection of fire ecology, invasion biology and grassland recovery. Specifically, this study seeks to (1) examine temporal trends in publication output; (2) identify the most influential authors, institutions, journals and countries contributing to the field; (3) reveal dominant keywords and thematic clusters using co-occurrence and network analysis; and (4) assess the geographical and ecological distribution of research efforts, with an emphasis on underrepresented regions and restoration contexts. By applying established bibliometric tools such as VOSviewer (version 1.6.20), this review captures the evolution of scholarship in this emerging interdisciplinary field. The goal is to support evidence-informed decision-making and identify strategic research directions for restoring and sustaining the world’s fire-prone and invasion-impacted grasslands.

2. Materials and Methods

2.1. Data Sources and Search Strategies

This bibliometric review was based on a systematic search of peer-reviewed journal articles indexed from the Web of Science (WoS) Core Collection, which serves as the sole data source for this study. The WoS Core Collection, particularly the Science Citation Index Expanded (SCI-E) and the Social Sciences Citation Index (SSCI), is widely recognised for its high-quality, curated coverage of scholarly literature across multiple disciplines, including ecology, environmental science, and restoration studies [36]. WoS was selected exclusively due to its consistent data structure, robust citation indexing and compatibility with leading bibliometric analysis tools such as VOSviewer (version 1.6.20) and Bibliometrix (version 5.0). Additionally, WoS allows detailed filtering by publication type, subject category and citation metrics, which is essential for ensuring a focused and high-quality dataset in bibliometric research [28,37]. The literature search was conducted on the 29th of April 2025 and limited to peer-reviewed journal articles published in English between 1990 and 2024, capturing about three decades of scholarly development on fire-invasive species interactions in grassland ecosystems. The following Boolean search string was used, targeting terms in the title, abstract, author keywords, and keywords plus (where available) as follows: (fire OR fire regime* OR burning OR wildfire* OR prescribed fire) AND (invasive plant species OR alien plant species OR non-native plant species OR exotic plant species) AND (grassland*) AND (restoration OR recovery OR regeneration OR resilience).
The search was tailored to WoS’s advanced query features to ensure precision and relevance. Following the search, all results were exported into Microsoft Excel and reviewed. Irrelevant records were removed.

2.2. Inclusion and Exclusion Criteria

A set of predefined inclusion and exclusion criteria was applied to ensure the relevance, consistency, and scientific quality of the literature analysed in this review (Table 1).
This rigorous screening ensured that the final dataset comprised only thematically aligned and methodologically robust studies suitable for analysing bibliometric patterns in the intersection of fire, invasive plant species, and grassland restoration. The articles from the refined data were uploaded onto Mendeley and later exported as a .ris file format for subsequent analysis in VOSviewer (version 1.6.20). This curated dataset formed the basis for bibliometric analysis and enabled the exploration of research output trends, collaboration networks, and citation dynamics within the field [28,38].

2.3. Article Retrieval, Screening and Selection

A representative sampling approach was adopted for this bibliometric analysis to ensure analytical feasibility while focusing on influential contributions within the field. From the 64,123 articles initially retrieved from WoS Core Collection using advanced filters (peer-reviewed, highly cited, English, published articles between 1990 and 2024, Environmental sciences categories, and only full-text availability), only the top 10% most cited articles (n = 6412) were retained. This step followed best practices in bibliometric research, which recommend narrowing to highly cited literature to improve analytical clarity and to better represent the intellectual core of the research field [28,37,39].
From the retrieval of 6412 top-cited records, a title screening was first performed to filter out studies that were clearly irrelevant to the scope of the review. This stage identified 919 articles that mentioned both fire-related and invasive species-related terms within the context of grassland ecosystems. To further refine the dataset, a manual screening process was performed in three distinct stages to ensure thoroughness and relevancy of the selected studies. Firstly, journal titles were reviewed for thematic relevance; secondly, keywords were assessed for alignment with the core focus of the study, and thirdly, the abstracts were examined in detail to confirm conceptual and methodological relevance. These processes resulted in the inclusion of 309 articles and the exclusion of 610 articles.
The refined set of 309 articles formed the basis of the bibliometric analysis. This number is scientifically justified within the context of bibliometric research, where quality and thematic coherence are prioritised over quantity to ensure analytical depth and interpretability. Bibliometric studies typically rely on representative, well-defined datasets rather than exhaustive collections, primarily when the research question is focused on a specific intersection, such as fire-invasive species interactions in grassland recovery [28,39]. The selection of 309 articles reflects a balanced trade-off between comprehensiveness and relevance, allowing for robust statistical analysis (co-authorship networks, keyword co-occurrence, citation mapping) while avoiding the inclusion of tangential or low-impact studies that could introduce noise or dilute thematic clarity. Similar bibliometric reviews with focused scope have used datasets ranging from 100 to 500 articles to effectively capture the intellectual structure and evolution of niche research fields [37].

3. Results

3.1. Publication Trends over Time

The number of published articles per year from 1990 to 2024 on fire and invasive plant species interactions was analysed. The publication count remained low throughout the 1990s, with a noticeable increase beginning around the early 2000s (Figure 1). This upward trend peaked between 2008 and 2016, where annual outputs frequently exceeded 15 articles. After 2016, a gradual decline in publication volume is observed, with a sharp drop after 2020. Article output becomes minimal by 2023 and 2024.

3.2. Temporal Distribution and Disciplinary Focus of Publications

A combined analysis of publication year (which is the year the articles were published) and WoS subject categories was conducted to understand the disciplinary focus and temporal distribution of the literature on fire-invasive plant species interactions (Table 2). Each article in the final dataset was classified based on the primary and secondary categories assigned in the WoS Core Collection to provide insight into the thematic orientation of research across time.
The analyses revealed that most articles were published in the 2010s, with a peak in 2010 (82 articles), indicating a surge in academic attention to this topic during that period. The most frequently represented categories include Ecology, Biodiversity Conservation, Environmental Sciences and Plant Sciences (Table 2), reflecting the multidisciplinary nature of the field.

3.3. Leading Institutions Contributing to Research on Fire-Invasive Species Interactions

An institutional affiliation analysis was conducted based on the first author of each publication to identify key contributors to the body of literature on fire and invasive plant species interactions in grassland restoration (Table 3). This analysis provides insight into research leadership’s geographic and organisational distribution within the field. The results highlight the most prolific institutions in terms of article output, revealing a strong presence from research organisations in the United States. The University of California has produced the highest number of articles (13).

3.4. Geographic Distribution of First Author Institutions

An analysis was conducted based on the country affiliation of the first author’s institution for each article in the dataset to assess the geographic distribution of research leadership within fire-invasive species interactions (Figure 2). This metric is widely used in bibliometric studies to determine national research contributions and regional influence in scientific publishing. The United States dominates the field, contributing the highest number of publications (49), followed by notable representation from the United Kingdom (12) and Spain (10). The presence of European institutions such as those in the Czech Republic, Germany and Switzerland reflects vigorous research activity across diverse ecological and climatic contexts.

3.5. Most Productive Authors and Collaborative Networks

A co-authorship network analysis was conducted based on author collaborations in fire-invasive species interactions (Figure 3). Nodes represent individual authors, with larger nodes indicating more publications. The lines connecting nodes reflect co-authorship links, where thicker lines signify stronger collaboration relationships based on the frequency of shared publications. Distinct clusters of authors are evident, with groups connected by lines of varying thickness. The colour gradient represents each author’s average year of publications, with darker shades indicating earlier contributions and lighter shades indicating more recent activity. Authors such as Pyšek, Pergl, Vila, Hulme and van Kleunen are among the more central and prominent nodes in the network.

3.6. Core Journals and Citation Metrics

Figure 4 represents the distribution of the total citations across journals where the most cited articles on fire-invasive species interactions were published. The Journal of Ecology (7410), Journal of Applied Ecology (5483), and Diversity and Distributions (4946) emerge as the top three journals, each hosting highly cited articles that significantly contribute to the field. Other journals show smaller (<1000) but still meaningful citation totals, indicating the broad range of journals contributing to the field’s development.
The result of the cumulative citation counts of the most cited articles based on their assigned WoS categories is presented in Figure 5. The Biodiversity Conservation and Ecology categories have the highest citation totals, with Plant Sciences and Environmental Sciences following closely.
Results of the analyses on the distribution of articles across different academic journals revealed that the Journal of Applied Ecology has the highest number of articles (35), followed by Diversity and Distributions (29) and the Journal of Ecology (27) (Figure 6). Several other journals show moderate publication counts, while a range of additional journals contribute a smaller number of articles (fewer than 10 each).
A keyword co-occurrence network map was generated through the bibliometric analysis (Figure 7). Each node represents a keyword used in the analysed articles on fire-invasive species interactions. The size of the nodes indicates the frequency of keywords used, while the thickness of the lines between nodes reflects the strength of co-occurrence relationships. Keywords frequently appearing together are grouped into clusters, with different colours indicating distinct thematic groupings. Larger nodes such as “biological invasions”, “invasive species”, “fire” and “alien species” indicate core research themes in the field. More minor but notable keywords like “risk assessment”, “remote sensing”, functional traits” and “plant traits” are connected through co-occurrence relationships, suggesting subthemes and methodological approaches within the broader research landscape. The colour gradient shows the temporal evolution of research topics from 2008 to 2014.

4. Discussion

4.1. Findings Within a Broader Context

The temporal distribution of publications on fire and invasive plant species interactions in restoration from 1990 to 2024 reveals three broad phases: an initial emergence, a period of growth and a recent decline. In the early 1990s, the field was still emerging, marked by limited scholarly attention, likely reflecting a lack of integration between fire ecology and invasion biology within restoration discourse. However, from the early 2000s, a steady increase in research activity became evident. This surge corresponded with the global expansion of invasive species databases, the rising adoption of ecosystem-based approaches to restoration, and increasing recognition of fire as both a threat and a management tool in ecosystem recovery efforts [7,40].
A particularly significant research burst occurred between 2008 and 2016 (Figure 2), with annual publications often exceeding 15 articles. This period aligns with the growing global policy attention following the United Nations’ 2009 declaration of the Decade on Biodiversity (2011–2020), along with intensified efforts to address climate change and land degradation [41,42]. In South Africa, national programmes such as Working for Water, which explicitly integrates fire and invasive plant management strategies, began to draw academic interest in 1995 [43]. Simultaneously, catastrophic fire events such as the 2009 Black Saturday bushfires in Australia and the escalating wildfire frequency in the western United States contributed to increased scientific scrutiny on the role of invasive grasses in altering fire regimes and affecting restoration outcomes [6,44]. After 2016 (Figure 1), publication output began to decline, with a sharp decrease observed after 2020. One likely explanation is the disruption of fieldwork and academic publishing caused by the COVID-19 pandemic, which broadly affected environmental science research timelines [45].
A shift in scholarly focus towards broader themes such as climate resilience, socio-ecological systems, and land-use transitions may have diluted narrowly focused outputs on fire and invasion interactions. Furthermore, the possible saturation of foundational research during the earlier peak years may have led to a stabilisation in output, with newer contributions perhaps appearing under broader interdisciplinary categories not fully captured by standard search terms. These patterns emphasise the dynamic nature of academic interest in this area and reinforce the importance of bibliometric analyses to track and interpret such shifts over time.
The disciplinary spread of publications indicates that research on fire and invasive plant species interactions in restoration is deeply interdisciplinary. While the field is primarily rooted in ecology, biodiversity conservation and environmental sciences, it also encompasses plant sciences, geosciences and remote sensing (Table 2). The inclusion of areas such as forestry, evolutionary biology, environmental engineering and sustainability science highlights the increasing diversification of tools and perspectives applied to understanding these interactions [7,44]. Interestingly, niche fields like ethics and philosophy of science appeared in earlier years, perhaps reflecting initial theoretical engagement with the concepts of disturbance and restoration, which were later expanded upon with empirical and applied studies. A notable structural pattern emerges in the concentration of research output within a relatively small number of institutions, predominantly from the United States, the United Kingdom and Australia, often produced through inter-institutional collaborations among author collectives (Table 3). These institutions benefit from well-established research infrastructure, robust science funding mechanisms and access to high-impact journals and international networks [46]. Such advantages enhance the productivity and global visibility of their research outputs. These institutions dominate the volume of publications, often acting as key coordinators of research activity within international author collectives. They shape the framing of restoration priorities and methodologies and export these approaches to international contexts. Encouragingly, the rising contribution of South African institutions, especially Stellenbosch University, points to emerging research leadership from historically underrepresented regions and demonstrates growing investment in ecological sciences in the Global South [47,48].
Despite notable progress, geographic disparities in research contributions persist, as reflected in the limited or absent representation of institutions from Latin America, Southeast Asia and much of sub-Saharan Africa in the bibliometric results. Although these regions are facing severe ecological pressures from both fire and biological [49]. This underrepresentation is linked to systemic barriers such as limited funding, language challenges in English-dominated publishing, and the centralisation of editorial boards in the Global North [50]. These disparities emphasise the need for more equitable global collaborations, capacity-building initiatives and inclusive leadership models in restoration science. Frameworks like the United Nations Decade on Ecosystem Restoration present an opportune moment to embed these equity principles into both research design and implementation [14].
The global research landscape on fire and invasive plant species interactions remains uneven, as illustrated by the geographic distribution of first-author institutions (Figure 2). High-income countries such as the United States, United Kingdom, Australia, Germany and Switzerland continue to dominate output, benefitting from long-standing academic traditions, access to international networks and substantial research funding [28,51]. South Africa’s emergence as a visible contributor reflects the strength of its ecological research community and policy-driven initiatives like Working for Water, which integrate fire management with invasive species control [52]. However, Latin America and Southeast Asia remain underrepresented despite their ecosystems facing similar challenges. These gaps in visibility and capacity highlight the urgent need for regional research hubs and inclusive global partnerships to ensure that restoration science reflects the full spectrum of ecological and socio-political contexts [53].
The co-authorship network analysis reveals a tightly connected core of researchers such as Pyšek, Pergl, Vila, Hulme and van Kleunen, who have been central to shaping the field (Figure 3). Their collaborations span multiple institutions and continents, particularly in Europe, where EU-funded multi-institutional projects have supported sustained research on invasion biology and ecosystem management [38,54,55]. This dense network indicates strong continuity and leadership, but the relatively sparse participation from peripheral authors suggests that access to funding, collaborative opportunities, and data infrastructure continues to restrict broader engagement in the field [56]. Such concentration may inadvertently steer research agendas and methodologies, reinforce dominant paradigms while marginalising alternative knowledge systems or region-specific concerns.
Journal citation patterns reinforce the centrality of applied ecological research in this domain. Journals like Journal of Ecology and Journal of Applied Ecology consistently receive high citation counts for articles on fire-invasive species dynamics (Figure 4), due to their thematic alignment with disturbance ecology, biodiversity and species management [57,58]. The unexpected prominence of Atmospheric Chemistry and Physics, and Global Change Biology suggests an expanding interest in the links between fire, invasive species and climate feedback [59]. While plant science remains foundational, the presence of fields like geosciences and atmospheric sciences indicates that the study of fire-invasion interactions is broadening into new interdisciplinary spaces, linking ecological processes with global change phenomena [60,61,62,63,64,65]. The Journal of Applied Ecology, Diversity and Distributions, and Journal of Ecology (Figure 6) emerge as leading outlets, suggesting researchers prefer journals that blend theoretical and applied perspectives on ecological processes, species distributions and biodiversity management. This trend reflects the thematic fit of these journals for studies at the interface of disturbance ecology and ecosystem recovery, where issues such as invasive plant dynamics and fire regimes are central. Similar patterns have been observed in other specialised fields of ecological research, where publication output tends to cluster in journals that explicitly prioritise applied ecological frameworks and practical conservation strategies [66]. The visibility of more targeted journals such as Biological Invasions, Global Ecology and Biogeography, and Rangeland Ecology & Management highlights the continued relevance of disciplinary niches that cater to distinct research communities focused on invasion biology, biogeography and land-use management. Journals like Ecology Letters and Biogeosciences, despite their prestige and broad readership, typically prioritise theoretical advances, novel methodologies or biogeochemical processes, which may explain their lower representation in this dataset [67,68]. This finding emphasises how the fit between journal scope and study topic continues to guide publication decisions, especially in interdisciplinary research areas like fire ecology and invasion biology.
An unexpected pattern is the relatively low publication count in specific high-impact journals that do cover relevant ecological topics. For instance, Ecology (a foundational journal in the field) published only eight (8) articles in this dataset (Figure 6), despite its reputation for hosting a broad range of ecological research. This may reflect editorial preferences or author submission strategies, where researchers opt for journals with a stronger applied focus or those that regularly feature themed issues on disturbance ecology and restoration [69]. Another unexpected result is the relatively strong representation of Atmospheric Chemistry and Physics, which suggests that some research on fire and invasive species interactions is published within journals typically associated with atmospheric sciences. This could reflect an emerging interest in the feedback between fire events, invasive species dynamics and atmospheric processes such as emissions and climate interactions [64,70,71,72,73,74]. This crossover highlights the inherently multidisciplinary nature of fire-invasive species research, indicating that while applied ecology journals dominate, there are opportunities for broader integration with fields such as Earth system science, environmental modelling and climate policy. Such findings suggest that the boundaries of this research field are porous and evolving, warranting attention to how efforts may shift over time and across publication settings.
Keyword co-occurrence analysis emphasises the field’s intellectual structure, with consistent emphasis on “invasive species”, “fire” and “biological invasions” (Figure 7). The emergence of terms such as “functional traits”, “remote sensing”, and “risk assessment” in more recent years reflects a shift toward predictive and management-oriented frameworks [24,71]. Additionally, the presence of concepts like “community assembly” and “climate change” indicates increasing theoretical sophistication and integration with global ecological concerns [75,76]. The interconnectedness of keyword patterns is consistent with previous bibliometric analyses in ecology and conservation, which show that research on complex ecological problems tends to be networked around a few core concepts while also diversifying into related methodological and thematic clusters [28,61]. The network also suggests that while some topics are well integrated into the core of the field, others, such as sagebrush or invasibility, may represent more specialised areas of study. Despite the field’s maturation, significant knowledge gaps remain, especially concerning long-term post-fire dynamics and the underrepresentation of ecologically vulnerable regions such as Africa and Latin America [12,77,78,79]. This geographic bias limits the generalisability of findings and emphasises the need for more inclusive, regionally diverse research efforts.
Emerging trends in the field point to an evolving understanding of fire as both a threat and a tool in grassland restoration. There is a discernible shift from traditional fire suppression policies towards greater exploration of prescribed burning, recognising its potential to manage invasive species and promote native biodiversity under controlled conditions [16,80]. Additionally, a growing focus on ecosystem services and resilience reflects a broader integration of ecological, socio-economic and policy considerations into fire-invasive species research [81]. There is also increasing interest in policy-relevant studies, which examine how fire management practices, invasive species regulations, and restoration guidelines can be aligned for effective outcomes, highlighting the field’s gradual move towards applied, decision-support research [82].

4.2. Consideration for Research and Practice

The implications of these findings for restoration science are profound. The study highlights the need for interdisciplinary research that combines ecological theory, management practices and social science perspectives to tackle the complex feedback between fire regimes and invasive species dynamics. It also reinforces the value of community-based and co-produced research approaches, especially in regions where fire and invasion pressures intersect with traditional land use and local livelihoods. Effective restoration in fire-prone grasslands will increasingly require partnerships across academia, practitioners, policymakers and local communities to ensure that interventions are ecologically sound, context-specific and socially equitable [34].
This study has several limitations that warrant consideration. First, the analysis relied exclusively on English-language articles indexed in the WoS Core Collection, which may have excluded relevant studies published in other languages, regional journals or other databases, thereby underrepresenting research efforts from non-English-speaking countries. Additionally, while bibliometric analysis offers valuable insight into research patterns and trends, it does not assess the methodological rigour, study quality or ecological validity of individual articles. This means that while citation counts reflect influence and visibility, they do not necessarily equate to scientific reliability or impact on practice [37]. Another limitation stems from the research strategy itself, which focused on studies conducted specifically within grassland ecosystems. This limitation was a deliberate choice to maintain a focused scope aligned with the study’s objectives: to map knowledge specifically on fire-invasive species interactions in grassland restoration. Including studies from a broader range of ecosystems would have diluted the specificity of the analysis and potentially obscured trends unique to grasslands, which differ significantly in fire regimes, species composition and restoration strategies compared to other biomes [83]. Thus, while this focus limits cross-ecosystem generalisability, it strengthens the relevance and applicability of findings to grassland-specific restoration sciences.
Looking ahead, future research should prioritise long-term monitoring of fire-invasive species interactions, particularly in underrepresented regions such as Africa, Latin America and Southeast Asia. There is also a need for more integrative studies that combine remote sensing, field experiments and socio-ecological analyses to better understand system-wide dynamics. In addition, future research should explore the mechanistic pathways and thresholds through which fire suppresses or facilitates plant invasion in ecosystems. Key factors such as fire frequency, intensity, seasonality and species-specific traits can significantly influence post-fire competitive dynamics and ecosystem recovery. Understanding how these variables interact to shape shifts in species composition, functional traits, and soil conditions will offer valuable insights into ecosystem resilience and critical tipping points. Such research is vital for developing adaptive fire management strategies that are context-specific and ecologically grounded. Studies highlight how species’ regeneration traits and fire regimes co-evolve, influencing invasion outcomes in fire-prone systems [21]. Finally, fostering interdisciplinary collaboration and engaging local communities as active partners in research will be essential for developing practical, scalable solutions that enhance the resilience of grassland ecosystems in the face of fire, invasion and climate change.

5. Conclusions

This bibliometric review has mapped the intellectual and collaborative landscape of research on fire and invasive plant species interactions in grassland restoration, revealing a dynamic, evolving field shaped by global environmental challenges, growing interdisciplinary engagement and regional research priorities. While the volume of publications has fluctuated over the years, the temporal clustering of research activity emphasises how scientific attention has often been reactive, driven by global events, ecological crises and shifting policy priorities. The recent decline in publication rates does not signal a diminishing importance of this field; rather, it shows a turning point where fire-invasion research is transitioning toward more integrated, cross-cutting approaches that link biodiversity conservation, ecosystem services and socio-ecological resilience.
The analysis highlights that while a broad range of journals, authors and institutions contribute to the field, a small core of influential journals and a tight network of leading scholars dominate knowledge production. This concentration—predominantly in the Global North—raises important questions about equity, access and the representation of diverse ecological contexts, particularly from underrepresented regions. Yet, the growing visibility of South African institutions and the emergence of interdisciplinary collaborations suggest a positive shift towards a more inclusive and globally relevant research agenda. Keywords co-occurrence patterns and thematic clusters reveal that fire-invasive species research has matured around key concepts such as biological invasions, fire regimes and species traits, while also embracing new areas, including risk assessment, ecosystem services and climate change resilience. While these patterns suggest a shift towards more integrated and policy-relevant research, it is important to note that such interpretations are drawn in context and not directly evidenced by the keyword co-occurrence analysis. The clustering of terms such as climate change, risk assessment and ecosystem services points to evolving research interests, but does not in itself confirm causality related to policy or institutional change. These broader dynamics are inferred in relation to global environmental discourse and the emergence of interdisciplinary framing in the literature.
Importantly, this review affirms that addressing the complex interactions between fire and invasive species in grassland restoration demands an interdisciplinary, systems-based approach. Future research must prioritise long-term monitoring, particularly in underrepresented regions, while fostering equitable partnerships, community engagement and the co-production of knowledge. Such efforts are critical to advancing restoration science in a way that is not only scientifically rigorous but also socially just and globally inclusive. In closing, this study emphasises the importance of ongoing synthesis efforts to track knowledge development, identify gaps and guide future research and practice. By mapping the contours of this field, we hope to support more informed, collaborative and context-sensitive approaches to restoring the world’s grasslands in the face of escalating fire events and invasion challenges.

Author Contributions

S.E.N., Y.C. and M.P.M. jointly conceived and designed the study. S.E.N. retrieved and curated the bibliometric data from the Web of Science Core Collection and performed the analysis. S.E.N. drafted the manuscript, and all authors contributed to critical revisions. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The raw data supporting this article will be made available by the authors on request.

Acknowledgments

During the preparation of this manuscript, the authors used OpenAI in a limited capacity to support language refinement and to clarify bibliometric terminology. All data analysis, interpretation, and core scientific content were developed independently by the authors. AI was not used for data generation, literature screening or drawing scientific conclusions. The authors take full responsibility for the integrity and originality of the work. The authors also acknowledge the use of Web of Science Core Collection as the primary source of bibliographic data for the bibliometric analysis. The authors further used VOSviewer (version 1.6.20) to facilitate data visualisation and thematic mapping in this study.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
EUEuropean Union
UKUnited Kingdom
UNUnited Nations
USUnited States
WoSWeb of Science

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Figure 1. Annual distribution of peer-reviewed articles (1990–2024) on fire and invasive plant species interactions.
Figure 1. Annual distribution of peer-reviewed articles (1990–2024) on fire and invasive plant species interactions.
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Figure 2. Country-level distribution of first-author institutions.
Figure 2. Country-level distribution of first-author institutions.
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Figure 3. Co-authorship network of authors contributing to research on fire-invasive species interactions.
Figure 3. Co-authorship network of authors contributing to research on fire-invasive species interactions.
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Figure 4. Most cited journals based on the total citations of articles published within each journal.
Figure 4. Most cited journals based on the total citations of articles published within each journal.
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Figure 5. Total citations of the most cited articles on fire-invasive species interactions within the WoS subject categories.
Figure 5. Total citations of the most cited articles on fire-invasive species interactions within the WoS subject categories.
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Figure 6. Distribution of articles on fire-invasive species interactions across academic journals.
Figure 6. Distribution of articles on fire-invasive species interactions across academic journals.
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Figure 7. Keyword co-occurrence network map of research on fire-invasive species interactions.
Figure 7. Keyword co-occurrence network map of research on fire-invasive species interactions.
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Table 1. Summary of article inclusion and exclusion criteria.
Table 1. Summary of article inclusion and exclusion criteria.
CriteriaIncludedExcluded
TopicFire-invasive species interactions
in grasslands		Studies on forests, aquatic, marine, desert or urban systems
FocusEcological processes: recovery,
restoration, regeneration, resilience		Fire or invasive species studies in isolation
Study TypeOriginal peer-reviewed researchReviews, book chapters, theses, grey literature, editorials, conference proceedings
LanguageEnglishNon-English articles
Year1990–2024Before 1990 or after 2024
DatabaseIndexed in WoS Core CollectionNot indexed in WoS
RelevanceLinked to ecology or vegetation
restoration		Focus on health, pollution, detection, and fauna/microbes unrelated to grassland recovery
AccessFull-text availableNo full-text access
Table 2. Distribution of articles by year of publication and associated WoS subject categories.
Table 2. Distribution of articles by year of publication and associated WoS subject categories.
Year of PublicationNo. of ArticlesWoS Categories
201082Biodiversity Conservation; Ecology
201336Ecology
199830Plant Sciences; Ecology
200326Environmental Sciences; Meteorology & Atmospheric Sciences
201118Ecology; Environmental Sciences
201416Biodiversity Conservation; Ecology; Environmental Sciences
201113Ecology; Geography, Physical
20139Biology; Ecology; Evolutionary Biology
20158Ecology; Evolutionary Biology
20207Ecology; Forestry
20076Plant Sciences; Ecology; Forestry
19965Agriculture, Dairy & Animal Science; Ecology
20145Ecology; Geosciences, Multidisciplinary
20205Engineering, Environmental; Environmental Sciences
20075Environmental Sciences; Geography, Physical
20135Environmental Sciences; Geosciences, Multidisciplinary; Remote Sensing; Imaging Science & Photographic Technology
20144Environmental Sciences; Geosciences, Multidisciplinary
20054Environmental Sciences; Geosciences, Multidisciplinary; Meteorology &
Atmospheric Sciences
20053Agriculture, Multidisciplinary; Ethics; Environmental Sciences; History &
Philosophy of Science
20163Environmental Sciences; Remote Sensing; Imaging Science & Photographic
Technology
20102Ecology; Environmental Studies
20162Ecology; Environmental Studies; Geography; Geography, Physical; Regional &
Urban Planning; Urban Studies
20082Ecology; Evolutionary Biology; Genetics & Heredity
20202Environmental Sciences
20162Environmental Sciences; Environmental Studies; Geography
20161Biochemistry & Molecular Biology; Ecology; Evolutionary Biology
20171Biodiversity Conservation
20171Biodiversity Conservation; Environmental Sciences
20151Chemistry, Multidisciplinary; Energy & Fuels; Engineering, Chemical;
Environmental Sciences
20131Ecology; Microbiology
20061Ecology; Zoology
20221Environmental Sciences; Environmental Studies; Meteorology & Atmospheric
Sciences
20161Environmental Sciences; Limnology; Water Resources
20191Green & Sustainable Science & Technology; Environmental Sciences;
Environmental Studies
Table 3. Top institutions based on the number of articles contributed by first authors.
Table 3. Top institutions based on the number of articles contributed by first authors.
No. of ArticlesInstitution of First Author
13University of California System
7Consejo Superior de Investigaciones Cientificas (CSIC)
7Stellenbosch University
7UK Centre for Ecology & Hydrology (UKCEH)
7United States Department of the Interior
7University of Melbourne
6Czech Academy of Sciences
6University of Konstanz
5United States Department of Agriculture (USDA)
5University of Bern
5University of London
4Colorado State University System
4Lincoln University, New Zealand
4Stanford University
4State University System of Florida
4University of Idaho
4University of Montana System
4University System of Maryland
3Autonomous University of Barcelona
3Martin Luther University Halle-Wittenberg
3Masaryk University Brno
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MDPI and ACS Style

Nkosi, S.E.; Chabalala, Y.; Mamathaba, M.P. Mapping Research Trends on Fire and Invasive Plant Species in Grassland Restoration: A Bibliometric Review. Conservation 2025, 5, 59. https://doi.org/10.3390/conservation5040059

AMA Style

Nkosi SE, Chabalala Y, Mamathaba MP. Mapping Research Trends on Fire and Invasive Plant Species in Grassland Restoration: A Bibliometric Review. Conservation. 2025; 5(4):59. https://doi.org/10.3390/conservation5040059

Chicago/Turabian Style

Nkosi, Sellina Ennie, Yingisani Chabalala, and Mashudu Patience Mamathaba. 2025. "Mapping Research Trends on Fire and Invasive Plant Species in Grassland Restoration: A Bibliometric Review" Conservation 5, no. 4: 59. https://doi.org/10.3390/conservation5040059

APA Style

Nkosi, S. E., Chabalala, Y., & Mamathaba, M. P. (2025). Mapping Research Trends on Fire and Invasive Plant Species in Grassland Restoration: A Bibliometric Review. Conservation, 5(4), 59. https://doi.org/10.3390/conservation5040059

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