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Review

Trends in Global Research on Seed Dispersal: A Bibliometric Analysis

by
Yuzhen Liu
1,2,†,
Caidi Li
1,2,†,
Wentin Liu
1,2,* and
Quanmin Dong
1,2,3,*
1
Academy of Animal Science and Veterinary Medicine, Qinghai University, Xining 810016, China
2
Qinghai Provincial Key Laboratory of Adaptive Management on Alpine Grassland, Xining 810016, China
3
State Key Laboratory of Plateau Ecology and Agriculture, Xining 810016, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Sustainability 2022, 14(24), 16577; https://doi.org/10.3390/su142416577
Submission received: 6 November 2022 / Revised: 30 November 2022 / Accepted: 8 December 2022 / Published: 10 December 2022
(This article belongs to the Section Sustainability, Biodiversity and Conservation)
Browse Figures
Versions Notes

Abstract

:
To understand the research trends and areas of focus of seed dispersal, a bibliometric study based on the Science Citation Index Expanded (SCI-E) and Social Science Citation Index (SSCI) databases of the Web of Science Core Collection (WoSCC) was performed. With the help of CiteSpace visualization software, a systematic analysis was carried out on 2911 publications from various countries in the field of seed dispersal. The activity index (AI) and attraction index (AAI) were used to evaluate the research effort and academic impact of different countries/territories in this field, and the global research progress and dynamic changes in research on seed dispersal were discussed. The number of publications on seed dispersal has increased rapidly since 1990, and research on seed dispersal is in the growth stage and has great potential. Ecology was the journal with the highest impact in this field, and ecology was the most popular subject category among the studies analyzed. The most productive authors in the field of seed dispersal are from Spain, and the most productive institution is in the USA. A keyword burst analysis showed that the new research frontiers were mainly concentrated on seed body size and the ecological network of seed dispersal. An in-depth analysis of seed dispersal research indicated that the increasing development of mathematical models related to seed dispersal creates an opportunity to study the processes of seed dispersal and their consequences.

1. Introduction

Seed dispersal, as an important part of the life history of seed plants, has often been the focus of research by biologists. Seed dispersal depends mainly on movement by wind, water and birds or mammals [1,2,3,4]. Since 1970, seed dispersal has become an important area of research in the field of ecology [5]. Seed dispersal is not only related to the coevolution of plants and animals but also closely associated with environmental issues such as biodiversity conservation, forest and grassland degradation, habitat fragmentation and the invasion of alien species [6,7]. In addition, seed dispersal also plays a very important role at the genetic and ecological level as the origin of species conservation [8,9].Therefore, monitoring international research progress and academic trends in the field of seed dispersal, tracking the influence of countries in related research fields and analyzing the characteristics of knowledge evolution in related fields are of great significance to future research in the field of seed dispersal. Moreover, understanding the state of research on seed dispersal can provide guidance for future research.
Regarding seed dispersal, only a few have focused on the following issues. (1) Which subject category is the most popular in the field of seed dispersal? (2) Which journal most represents research on seed dispersal? (3) Which country and institution are the most active contributors to seed dispersal research? What are the differences in research progress between countries? (4) Which author is most represented in seed dispersal research? (5) Which articles played a key role in the evolution of knowledge about seed dispersal? (6) What are the most important research areas in related fields? Addressing these questions is important for advancing research on seed dispersal; the answers will provide comprehensive insights into existing seed dispersal research and help scholars to discover important unsolved scientific problems and determine which problems they should focus on in the future. Although many scholars have published articles on seed dispersal, the scope of these articles is still somewhat limited, for example, by subject category or region [10,11,12]. Although many reviews have shown development trends in specific aspects of seed dispersal-related research fields, they have not provided a comprehensive quantitative analysis of the current status of seed dispersal-related research and emerging fields. Thus, a bibliometric analysis of seed dispersal research is needed.
Bibliometric analysis, an important quantitative analysis method, can effectively describe the overall trend of the development of a discipline or research field and has been widely used to measure the performance of various research fields [13,14]. Moreover, knowledge graphs can combine information visualization technology with traditional bibliometric analysis to generate different types of knowledge graphs through data mining, information processing, scientific measurement and graph drawing to provide researchers with intuitive data displays [15].
Therefore, we conducted a bibliometric analysis of the scientific literature on seed dispersal for the period 1985–2020. The main objectives of this research include (1) determining the basic characteristics of the literature, such as the number of articles and citations, categories of research topics and representative journals; (2) determining the research power in the field of seed dispersal, such as the countries, institutions and authors represented in the literature; (3) recognizing the knowledge base of the research field; (4) discovering the most productive research areas and trends over time; and (5) determining future research opportunities.

2. Materials and Methodology

2.1. Data Collection

Web of Science is an internationally recognized database that reflects the level of scientific research in a field. Among the resources included in Web of Science are the Science Citation Index Expanded (SCI-E), Social Science Citation Index (SSCI) and other citation index databases, such as Journal Citation Reports (JCR) and Essential Science Indicators (ESI), which are well-known in the global technology and education fields. In this study, we used the SCI-E and SSCI databases from the Web of Science core collection (WoSCC) as the object database (Web of Science at http://www.webofknowledge.com (accessed on 1 January 2022)) and set TI = ((dispersal AND wind) OR (dispersal AND water) OR (dispersal AND ballistic) OR (dispersal AND bird*) OR (dispersal AND mammal*) OR (dispersal AND ant*) OR (dispersal AND insect*) OR (“seed dispersal” OR “evolution of dispersal” OR “indirect seed dispersal” OR “secondary dispersal” OR “two-phase dispersal” OR “two-stage dispersal” OR “multiphase dispersal” OR “anemochory” OR “hydrochory” OR “zoochory” OR “autochory”)) as the retrieval condition, with a time span of 1990–2021, to search for related results about seed dispersal. We used the R package “litsearchr” to choose keywords and test their sensitivity [16]. The WoSCC is one of the main databases for bibliometric analysis [17]. A total of 3181 published articles were retrieved and 270 non-peer-reviewed articles, such as conference papers and books, were excluded to ensure that the results were representative. In the end, we selected 2911 articles for analysis. The retrieved records were downloaded and saved as a plain text file in the “Full Record and Cited References” format and used as a sample of the data analyzed in this study. The list of articles used for this study is provided as Supplementary Data S1.

2.2. Methodology

2.2.1. Bibliometric Analysis Methods

Bibliometrics is a form of mathematical statistics used to quantitatively analyze academic literature [18]. CiteSpace software is currently one of the analysis tools applied most often in the field of bibliometric analysis [19]. It is an application program for literature analysis and visualization and was developed by Chen [20]. The 5.7 R2 version of CiteSpace for 64-bit Windows with Java 8 was used. In this study, we focused on the assessment of three quantitative characteristics of the bibliometric data with (1) co-occurrence analysis, (2) collaboration networks and (3) co-citation analysis. Details of the analysis process in this study are shown in Figure S1 (Supporting Information).

2.2.2. Activity Index (AI) and Attraction Index (AAI)

On the basis of existing research [20,21,22], we employed two indicators in this study, the AI and AAI, to assess changes in the research effort and academic impact of different countries in the field of seed dispersal over time.
The AI can measure the degree of relative effort of a country in a research field, and it can be calculated with the following formula [23]:
A I i t = P i t / ∑ P T P t / ∑ T P
The AAI can evaluate the impact of a country on a research field through the number of citations of publications. This index can be calculated with the following formula [23]:
A A I i t = C i t / ∑ C T C t / ∑ T C
In the formulas, A I i t and A A I i t represent the AI and AAI of country i in year t, respectively; P i t and C i t represent the number of articles and citations of publications on seed dispersal from country i in year t; and ∑ P and ∑ C represent the total number of articles and the sum of citations to publications related to seed dispersal from country i during a period of time. Furthermore, T P t and T C t represent the global number of articles and citations of publications in year t; ∑ T P and ∑ T C represent the total number of articles and the sum of citations globally during the same period as that of ∑ P and ∑ C , respectively.
In these formulas, when A I i t = 1 and A A I i t = 1 , the research effort and academic impact, respectively, of country i in year t are equal to the global average. In addition, when A I i t > 1 or A I i t < 1 , the research effort of country i in year t is higher or lower than the global average, and when A A I i t > 1 or A A I i t < 1 , the number of citations of publications from country i in year t is more or less, respectively, than the global average level of citations.

3. Results and Discussion

3.1. Basic Characteristics of the Literature

3.1.1. Quantity of Articles and Citations

From 1985 to 2020, the number of articles published in the field of seed dispersal worldwide increased, indicating that this field has received extensive attention from scholars and has strong developmental potential (Figure 1). From the perspective of the number of articles, there were two turning points in the publication of seed dispersal research. One turning point was in 1995, when the number of articles published exceeded 44 for the first time; prior to 1995, the number of articles published annually increased very slowly. The other turning point was in 2002, when the number of articles published exceeded 70 for the first time. Since 2002, the number of articles published has increased annually every year. From 2002 to 2021, an average of 120.75 articles were published each year, with an average annual growth rate of 6.04%. This result indicates that research on seed dispersal is in the growth stage and that this field has high research potential, such as how to accurately reveal spatially heterogeneous patterns of seed dispersal and secondary chemistry and the directed deterrence hypothesis [24,25]. There are still many unresolved questions about seed dispersal. From 1990 to 2021, the total number of citations was 97,962, and the number of citations per article was 33.65. The average number of citations per article was highest in 2000, reaching 79.43. Subsequently, the citations per article showed a downwards trend. There are two main reasons for the decline in citations: on the one hand, researchers generally prefer to cite high-impact articles, and on the other hand, there is a post-citation effect for newly published articles due to publication cycle constraints [9,26].

3.1.2. Analysis of Subject Categories

This study (Table 1) included ecology (1600 articles, accounting for 54.96% of the total), plant science (484 articles, 16.63%), evolutionary biology (316 articles, 10.86%), biodiversity conservation (226 articles, 7.76%), zoology (218 articles, 7.49%), forestry (206 articles, 7.08%), multidisciplinary sciences (165 articles, 5.67%), biology (147 articles, 5.05%), environmental sciences (166 articles, 5.70%) and genetic heredity (125 articles, 4.29%). The number of publications in each category reflects the trends of seed dispersal research in different domains.
The co-occurring subject category network shows that this network includes 126 nodes and 515 links (Figure S2). Through the subject category network, we found that seed dispersal research is a discipline that involves various subjects, such as ecology, plant science, evolutionary biology, biodiversity conservation and zoology. The co-occurring subject category network also shows that the three most frequent categories in seed dispersal research are ecology, plant science and evolutionary biology. Ecology has high centrality because it connects many subject categories, including environmental science, plant science, forestry and biodiversity conservation. Similar results have been found in other studies [27,28,29], all due to the wide range of ecological studies covered.

3.1.3. Journal Analysis

The 2911 articles on seed dispersal analyzed in this study appeared in 676 journals. Table 2 lists the 10 journals with the highest numbers of publications on seed dispersal. The number of articles published by these 10 journals in the field of seed dispersal encompassed 23.0% of all the analyzed publications. Biotropica was the most popular journal (91), followed by Ecology (79), Oecologia (77), Oikos (68), Journal of Ecology (66), Plos One (65), Journal of Tropical Ecology (62), Plant Ecology (60), Molecular Ecology (53) and Journal of Biogeography (47). The number of total citations of a journal (TC) and the average number of citations per paper of a journal (TC/P) reflect the impact of that journal. The impact factor (IF) and H-index can also measure journal impact. The top 10 productive journals showed that among the literature included in this study, Biotropica, Ecology, Oecologia, Oikos, Journal of Ecology and Plant Ecology each published more than 60 articles about seed dispersal. Ecology showed the highest impact in the field of seed dispersal, with the highest H-index (47), TC (5052) and TC/P (63.95). Biotropica is a highly valued source for original research on the ecology, conservation and management of all tropical ecosystems, as well as the evolution, behaviour and population biology of tropical organisms. It can also be shown that research on seed dispersal is mainly concentrated in tropical rainforests.

3.2. Research Power of Seed Dispersal

3.2.1. Analysis of Countries and Institutions

(1)
Quantity of articles and citations
The papers included in this study came from 113 countries around the world. The 10 most productive countries are listed in Table 3. The USA had the largest number of publications (934 articles) and total citations (27,291 citations). Spain had the second highest number of publications (312 articles), followed by Germany (267 articles), Brazil (232 articles), England (224 articles) and Australia (208 articles). The top 10 most productive countries showed that the distribution of countries/territories and the relationships of international cooperation with impact on seed dispersal research (Figure S3). The USA had the earliest publication on seed dispersal and was the most productive country during the study period. The USA had the highest degree of centrality (0.67), followed by Spain (0.23), Germany (0.20), Brazil (0.19) and China (0.16); these countries play an important role in collaboration networks. The analysis revealed that there was strong international cooperation between North America and Europe; however, China’s international cooperation was weak.
(2)
Collaboration network
The top 10 most productive countries in terms of relevant articles are shown in Table 4. Consejo Superior de Investigaciones Científicas (CSIC, Spain) was the most productive institution, followed by the Centre National de la Recherche Scientifique (CNRS, France), the University of California System (UC, USA), the Chinese Academy of Sciences (CAS, China) and the Estacion Biologica de Donana (EBD-CSIC, Spain). The network of academic collaboration on seed dispersal research between institutions is shown in Figure S4 (Supporting Information). The strongest collaborations were identified between the CSIC and INRA. The CSIC had the highest centrality (0.26). The Chinese Academy of Sciences (CAS, China) and the University of Tokyo (UT, Japan) international cooperation were weak.
(3)
The development of seed dispersal research in selected countries
To evaluate the changes in the academic impact of the 10 abovementioned countries in terms of seed dispersal research, the AI and AAI were used. It should be noted that because there is usually a lag between the publication time and the citation time of an article [31,32], the time range of the AAI was set 2 years behind that of the AI in this study.
The quadrant diagrams of the changes in the two indexes are shown in Figure 2, with quadrants I to IV representing four situations. The points in quadrant I represent the years in which the country’s AI and AAI indexes were both higher than the global average levels and those in quadrant II, the years in which the country’s AAI and AI indexes were higher and lower than the global average levels, respectively; the points in quadrant III represent the years in which the country’s AI and AAI indexes were both lower than the global average levels and those in quadrant IV, the years in which the country’s AI and AAI indexes were higher and lower than the global average levels, respectively.
In general, with the exception of England, Australia and Japan, the AI and AAI indexes of the 10 selected countries showed an upward trend during the study period. The research power and academic impact of Spain in most years were higher than the global average levels (Figure 2a–e). In contrast, although the USA had a relatively large number of published and cited articles, its academic impact was lower than the global average level in most years. The research power and academic impacts of Germany, Brazil and China were lower than the global average level in most years, but in recent years, their academic impact was higher than the global average level, indicating that the impact of these countries on seed dispersal research is continuously increasing. Spain has the highest academic impact, which may be due to the special geographical location of Spain, which makes its research biased towards seed dispersal. We have ranked the top 10 countries in terms of the World Bank’s GDP per capita in terms of the number of articles published, presented in clockwise order in Figure 1. We counted the number of studies in the first quadrant for each country, as this is representative of the country’s high level of research power. Our results show that the USA still has the highest research power and academic impact, but that its research power is not proportional to the country’s economic level (Figure 2f).

3.2.2. Author Analysis

(1)
Author collaboration network
The 10 most productive authors according to the publications included in this study are shown in Table S1 (Supporting Information). As shown in Table S1, Traveset, A. had the highest numbers of publications. This author was followed by Jordano, P. (24 articles); Garcia, D. (23 articles); Nogales, M. (23 articles); Bohning-Gaese, K. (22 articles); Galetti, M (21 articles); Soons, M. B. (21 articles); Yi, X. F. (21 articles); Nathan, R. (21 articles); and Pizo, M. A. (18 articles). The 10 most productive authors all came from different research institutions; four of these authors were in Spain, and the remaining six were in different countries (Table S1).
The collaboration network map of the authors of seed dispersal research are shown in Figure 3. Five author groups were identified. (1) A team consisting of Schleuning, M., Traveset, A. and Bohning-Gaese, K. (circle A) focused their research on plant–animal interactions and long-distance seed dispersal [33,34,35]. (2) A group of authors led by Jordano, P. (circle B) focused on complex seed dispersal patterns [36]. (3) A group of authors led by Yi, X. F. (circle C) focused on animal–seed interactions [37,38]. (4) A group of authors led by Rogers, H. S. (circle D) studied tropical forest seed dispersal [39]. (5) Heleno, R. H. and Correia, M. formed a core team (circle E), and much of their research focused on seed dispersal on islands and Mycorrhizal plant seed dispersal [40,41].
(2)
Author co-citation network
The author collaboration analysis can reflect an author’s contributions to the field of seed dispersal and the cooperative relationship between authors, but it cannot reflect an author’s impact on seed dispersal research. Therefore, we used author co-citation analysis to provide further information. We selected the 10 most cited project themes from each topic to ensure that we targeted the most prominent authors.
On the basis of the author co-citation network analysis results, the authors with high citation frequency and their countries of origin were determined. As shown in Table S2 (Supporting Information), the author with the highest citation frequency is Nathan, R. (2302 citations, Israel), followed by Katul, G. G. (1364 citations, USA), Jordano, P. (1328 citations, Spain), Schupp, E. W. (1148 citations, USA), Soons, M. B. (1116 citations, The Netherlands), Levey, D. J. (1106 citations, USA), Garcia, D. (957 citations, Spain), Vander wall, S. B. (898 citations, USA), Wright, S. J. (857 citations, Panama), and Poschlod, P. (843 citations, Germany). Four of these authors are from the USA, two are from Spain, and the others are from Israel, the Netherlands, Panama and Germany.
By comparing Tables S1 and S2, we determined that there is a strong relationship between the 10 most cited authors and the 10 most productive authors. Nathan, R., Jordano, P. and Soons, M. B. appeared in both tables.

3.3. Intellectual Base

The number of citations of an article represents the degree of recognition it received in a particular research field or its academic impact [42,43]. The 10 most highly cited references are listed in Table 5. The most highly cited reference was published by Nathan, R., with a citation count of 1483. Through this review, the author shows that with the growing interest in spatial ecology, new methods for researching seed dispersal are emerging. Seed dispersal methods vary among plant species, populations and individuals; with distance from the parent plant; and by microsites and times. The development and improvement of mathematical models is expected to produce a deeper and more mechanical understanding of the seed dispersal process and its consequences. The articles with a high number of citations were published in the 21st century, mostly between 2000 and 2011. The content of these papers shows that the intellectual base focuses on long-distance seed dispersal and dispersal patterns in different habitat conditions. These findings provide a good foundation for future research.

3.4. Key Research Areas

3.4.1. Keyword Co-Occurrence

Keywords reflect an author’s intention and interests and summarize the main content of an article. People can obtain useful information, such as research goals, methods and important opinions, from the keywords of an article [44]. Therefore, keyword frequency analysis and period change analysis are essential to discussing key research areas and development changes within a research field [13].
We used keyword co-occurrence analysis in CiteSpace software to create a keyword co-occurrence network diagram of the seed dispersal research analyzed and identify the main research areas in this field (Figure S5, Supporting Information). Each node in the graph represents a keyword; larger nodes indicate keywords that appear more frequently. Similarly, the width of the links indicates the frequency of keywords appearing together; a thicker link indicates that the two connected keywords appear together more frequently. A total of 786 keywords were obtained, among which 11 appeared more than 200 times. There is no doubt that “seed dispersal”, the main keyword of this article, is the largest node in Figure S5; this keyword appears 535 times and is closely related to “pattern” (499 times), “plant” (293 times), “consequence” (282 times), “recruitment” (268 times), “evolution” (253 times) and “ecology” (249 times). Other keywords, such as “forest” (239 times), “population” (234 times), “germination” (208 times) and “tree” (207 times), also had high frequencies.

3.4.2. Keyword Burst Analysis

Keyword burst analysis identifies keywords with a sharp increase in frequency. Burst detection is a useful analytical method for finding keywords that are of particular interest to the relevant scientific community over a given period of time [45]. Therefore, bursting keywords can be used as indicators of research frontiers and to forecast research trends. Figure 4 shows the 20 keywords with the strongest citation bursts from 1990 to 2021. In this figure, the strength of the burst represents the intensity of focus on a given topic. In the field of seed dispersal research, tropical rainforests have been an important research area since 1900, with the focus subsequently diversifying to include “dynamics” (strength: 11.21) and “migration” (strength: 11.19). We found that in the last 10 years (2012–2021), studies related to “pollination”, “frugivore”, “body size” and “ecological network” are emerging active topics (Figure 4).

3.4.3. Keywords in Different Countries

Due to differences in climate, geographical features, and historical and economic conditions, the development of research in a certain field in different countries or regions may not be balanced. Figure 5 shows the high-frequency keywords, main research types and regional distribution of relevant research in the 10 countries with the highest numbers of publications. In the field of seed dispersal, the differences between countries or territories are not very large, and the study of “seed dispersal pattern” has received the most attention. For example, from 1990 to 2021, the most frequently used keywords in the USA were “seed dispersal” (186 times) and “pattern” (143 times); the most frequently used keywords in Spain during this period were “pattern” (74 times) and “seed dispersal” (51 times).

4. Conclusions and Limitations

In this study, the SCI-E and SSCI databases of the WoSCC were used as sample data, and CiteSpace software was applied to visualize information about seed dispersal research. Based on the bibliometric analysis method, we systematically analyzed the basic characteristics, main research institutions and research areas of the literature in the field of seed dispersal. Furthermore, we used the AI and AAI to assess the research efficiency and academic impact of major countries. The following conclusions were drawn from the results:
(1)
The number of publications on seed dispersal research globally increased significantly over time. The number of citations per publication peaked in 2000. The 10 most productive journals accounted for 22.95% of all publications in the field of seed dispersal, and Ecology had the highest impact in this field. Researchers in the field of seed dispersal are mostly from the USA and European countries, and a collaboration network centered on the USA, Spain, Germany, Australia, Britain and France gradually formed.
(2)
On the basis of the AI and AAI, we determined that different countries/territories have different research abilities in the field of seed dispersal. The research effort and academic impact of Spain were higher than the global average level in most years. Although the research effort and academic impact of Germany, Brazil, China and Japan were lower than the global average level in most years, their academic impact has continuously increased in recent years. We also found that seed dispersal research was performed by five author groups with outstanding research records.
(3)
The burst analysis showed that myrmecochorous is a very important field of seed dispersal research, and new research areas or frontiers have mainly concentrated on seed body size and the ecological network of seed dispersal.
(4)
Currently, many studies are limited to only the number of seeds and distance of seed dispersal and do not systematically investigate every process of the seed renewal stage (seed production, seed dispersal, seed germination, seedling settlement, seedling establishment, etc.). As the monitoring of seed germination and seedling growth in the later stages of seed dispersal is time-consuming and labor-intensive, relevant research is still lacking. In addition, too much attention has been given to the negative impacts of human interference on the spread of seeds by animals, and the beneficial aspects of human interference in the process of seed dispersal have been ignored [46]. Finally, the development of mathematical models related to seed dispersal has created an opportunity to study the processes of seed dispersal and its potential consequences.
Although our research provides guidance for future research directions in related fields, it still has some limitations. First, we strictly limited the scope of publications in the literature search to avoid obtaining search results that were inconsistent with the research goals. Second, although we identified the main research areas and future directions, a deeper analysis of the research areas, such as the methods applied to identify them and the theoretical background, is still needed. Finally, CiteSpace software itself has certain limitations, although much research has been conducted using this software. For example, in the process of this research, we found that the software cannot distinguish the first author of a paper from the corresponding author, and the distinction between some areas is not very accurate. Nevertheless, the conclusions of our study are based on objective data, which are accurate and reliable.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/su142416577/s1, Figure S1: Outline of research design; Figure S2: A visualization of the co-occurring subject categories’ network; Figure S3: The collaboration network of countries; Figure S4: The collaboration network of institutions; Figure S5: Keyword co-occurrence network from 1990 to 2021; Table S1: Top 10 most productive authors based on publications; Table S2: Top 10 most productive authors based on total citations.

Author Contributions

Q.D., Y.L. and C.L. designed the research; Y.L. and C.L. collected data used in the analysis and performed the analysis; Q.D., Y.L., C.L. and W.L. wrote the paper. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Platform of the Adaptive Management of the Alpine Grassland-livestock System (2021-ZJ-901), the Joint Funds of the National Natural Science Foundation of China (U20A2007), the National Key R&D Program of China (2021YFD1300500) and the National Natural Science Foundation of China (32160340).

Data Availability Statement

Upon a reasonable request, the authors will provide the data that supported the findings of this study. This article, along with any supplementary files, includes the entire dataset supporting the findings of this study.

Acknowledgments

Our thanks goes to the anonymous reviewers who offered insightful comments.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that may affect the work described herein.

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Figure 1. Trends in the quantity of articles and average number of citations identified by Web of Science (WOS) that are related to seed dispersal from 1990 to 2021.
Figure 1. Trends in the quantity of articles and average number of citations identified by Web of Science (WOS) that are related to seed dispersal from 1990 to 2021.
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Figure 2. Relational chart of AI and AAI for 10 countries: (a) USA and Spain; (b) Germany and Brazil; (c) England and Australia; (d) France and China; (e) Canada and Japan; (f) Number of points in quadrant I The reference line x = y represents a balance AI and AAI of seed dispersal research in a given country.
Figure 2. Relational chart of AI and AAI for 10 countries: (a) USA and Spain; (b) Germany and Brazil; (c) England and Australia; (d) France and China; (e) Canada and Japan; (f) Number of points in quadrant I The reference line x = y represents a balance AI and AAI of seed dispersal research in a given country.
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Figure 3. Collaboration network of authors. Nodes represent authors. The size of node is proportional to amount of papers published by the author. The color of the rings and links corresponds to the year. The purple rings indicate high centrality.
Figure 3. Collaboration network of authors. Nodes represent authors. The size of node is proportional to amount of papers published by the author. The color of the rings and links corresponds to the year. The purple rings indicate high centrality.
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Figure 4. Top 20 keywords with the strongest citation bursts from 1990 to 2021. The blue line represents the period during which the keyword appeared, and the red line indicates the period during which the keyword received wide attention.
Figure 4. Top 20 keywords with the strongest citation bursts from 1990 to 2021. The blue line represents the period during which the keyword appeared, and the red line indicates the period during which the keyword received wide attention.
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Figure 5. The most frequently used keywords in the 10 most influential countries.
Figure 5. The most frequently used keywords in the 10 most influential countries.
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Table
Table 1. The article output of the top 10 subject categories of seed dispersal research.
Table 1. The article output of the top 10 subject categories of seed dispersal research.
Subject Category1990–2021%Subject Category1990–2021%
Ecology160054.96Forestry2067.08
Plant Sciences48416.63Multidisciplinary Sciences1655.67
Evolutionary Biology31610.86Biology1475.05
Biodiversity Conservation2267.76Environmental Sciences1665.7
Zoology2187.49Genetics Heredity1254.29
Table
Table 2. Top 10 productive journals in terms of related studies.
Table 2. Top 10 productive journals in terms of related studies.
JournalsPs%TC aTC/P bH-Index cIF dInitial Year
Biotropica913.13251127.59 322.5081991
Ecology792.71505263.95 475.4991990
Oecologia772.65347445.12 393.2251992
Oikos682.34205330.19 293.9031991
Journal of Ecology662.27334850.73 386.2561993
Plos One652.23124719.18 193.242008
Journal of Tropical Ecology622.13164726.56 271.3941990
Plant Ecology602.06122920.48 231.8541997
Molecular Ecology531.82249347.04 306.1851996
Journal of Biogeography471.61171236.43 244.3241991
TC a: the total citations for a journal. TC/P b: average number of citations per paper for a journal. H-index c: according to Hirsch in 2005 [30], a scientist has index H if H of his/her Np papers have at least H citations each, and the other Np-H papers have no more than H citations each, in which Np is the number of articles published during n years. A high H-index indicates greater academic impact. IF d: impact factor; impact factors data are from the 2021 edition of Journal Citation Reports in Web of Science.
Table
Table 3. Top 10 most productive countries in terms of relevant articles.
Table 3. Top 10 most productive countries in terms of relevant articles.
CountryPsTC aTC/P bH-Index
USA93427,29129.22 99
Spain312775024.84 58
Germany267770928.87 54
Brazil232453019.53 41
England224980243.76 55
Australia208555626.71 45
France186573630.84 45
China172199711.61 25
Canada149435029.19 36
Japan149201913.5526
TC a: the total citations for a country. TC/P b: average number of citations per paper for a country. The H-index mentioned in the table refers to the overall H-index of universities in each country.
Table
Table 4. Top 10 most productive institutions in terms of relevant articles.
Table 4. Top 10 most productive institutions in terms of relevant articles.
InstitutionCountryPsTC aTC/P bH-Index
Consejo Superior de Investigaciones CientíficasSpain175474927.14 45
Centre National de la Recherche ScientifiqueFrance125391731.34 37
University of California SystemUSA86427949.76 36
Chinese Academy of SciencesChina7985710.85 17
CSIC Estacion Biologica de Donana EBDSpain78245431.46 32
State University System of FloridaUSA68322847.47 34
Smithsonian InstitutionUSA56366865.50 27
Institut de Recherche pour le DeveloppementFrance54204837.93 25
Universidade de Sao PauloBrazil53110220.79 20
Universidade Estadual PaulistaBrazil53104119.6420
TC a: the total citations for an institution. TC/P b: average number of citations per paper for an institution.
Table
Table 5. Top 10 highly cited references.
Table 5. Top 10 highly cited references.
AuthorJournal/BookTitleYearTC
Nathan, R.Trends in Ecology & EvolutionSpatial patterns of seed dispersal, their determinants and consequences for recruitment20001483
Cain, M. L.American Journal of BotanyLong-distance seed dispersal in plant populations2000790
Schupp, E. W.VegetatioQuantity, quality and the effectiveness of seed dispersal by animals1993671
Clark, J. S.EcologySeed dispersal near and far patterns across temperate and tropical forests1999638
Liljegren, S. J.NatureSHATTERPROOF MADS-box genes control seed dispersal in Arabidopsis2000613
Johnson, M.L.Annual Review of Ecology Evolution & SystematicsEvolution of Dispersal: Theoretical Models and Empirical Tests Using Birds and Mammals1990688
Schupp, E. W.The New phytologistSeed dispersal effectiveness revisited: a conceptual review2010648
Mcpeek, M. A.The American NaturalistThe evolution of dispersal in spatially and temporally varying environments1992586
Paradis, E.Journal of Animal EcologyPatterns of natal and breeding dispersal in birds2000570
Bakker, J. P.Acta Botanica NeerlandicaSeed banks and seed dispersal: important topics in restoration ecology1996492
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Liu, Y.; Li, C.; Liu, W.; Dong, Q. Trends in Global Research on Seed Dispersal: A Bibliometric Analysis. Sustainability 2022, 14, 16577. https://doi.org/10.3390/su142416577

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Liu Y, Li C, Liu W, Dong Q. Trends in Global Research on Seed Dispersal: A Bibliometric Analysis. Sustainability. 2022; 14(24):16577. https://doi.org/10.3390/su142416577

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Liu, Yuzhen, Caidi Li, Wentin Liu, and Quanmin Dong. 2022. "Trends in Global Research on Seed Dispersal: A Bibliometric Analysis" Sustainability 14, no. 24: 16577. https://doi.org/10.3390/su142416577

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