1. Introduction
The emergence of seed plants was a major breakthrough in the evolution of plant life history (Rutishauser 1993). Seed dispersal, as an important part of the life history of seed plants, has often been the focus of attention from and research by biologists. Seed dispersal depends mainly on movement by wind, water and birds or mammals (Proctor and V. 1968, Howe 1986, Tackenberg et al. 2003, Kowarik and Sumel 2008). There are approximately 260,000 kinds of seed plants in the world, and they all have unique morphological structures to ensure their successful dispersal. Since 1970, seed dispersal has become one of the research hotspots in the field of ecology (Butler et al. 2010). Seed dispersal is not only related to the co-evolution of plants and animals but also associated closely with environmental issues such as biodiversity conservation, forest and grassland degradation, habitat fragmentation, and the invasion of alien species (Byrne and Levey 1993, Campos-Arceiz and Blake 2011). Therefore, monitoring the international research progress and academic trends in the field of seed dispersal, tracking the influence of countries in related research fields and analysing 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 scientific guidance for related research.
Although there are many related studies on seed dispersal, there are still few studies 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 research hotspots in related fields, and how have they developed and evolved? Addressing these questions is important for advancing research on seed dispersal; the answers will provide comprehensive insight into existing seed dispersal research and help scholars discover important unsolved scientific problems and determine which problems they should focus their research on. Although many scholars have published empirical and qualitative articles in the field of seed dispersal, these scope of these articles is still somewhat limited, for example, by subject category or region (Fuzessya et al. 2018, Camargo et al. 2019, Li et al. 2021). 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, 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 (Wang et al. 2018, Liu et al. 2019). 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 more intuitive data displays (Boyack 2004).
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 research hotspots and trends of research hotspots over time; and (5) determining future research opportunities.