ecologies
Review
Ecosystem Services Research Trends: A Bibliometric Analysis
from 2000–2020
Ruchira Gangahagedara 1 , Shyamantha Subasinghe 2, * , Madhushan Lankathilake 3 ,
Wasantha Athukorala 4 and Isurun Gamage 5
1
2
3
4
5
*
Postgraduate Institute of Humanities and Social Sciences, University of Peradeniya,
Peradeniya 20400, Sri Lanka; gangahagedara.ruchira@gmail.com
Department of Geography, University of Peradeniya, Peradeniya 20400, Sri Lanka
Library, University of Colombo, Colombo 00700, Sri Lanka; madhushan@lib.cmb.ac.lk
Department of Economics and Statistics, University of Peradeniya, Peradeniya 20400, Sri Lanka;
wathukorala@yahoo.com
Graduate School of Humanities and Social Sciences, University of Tsukuba, Tennodai 111,
Tsukuba 8571, Japan; isurun.upekshagamage@gmail.com
Correspondence: shyamgeo@pdn.ac.lk
Published: 4 December 2021
Abstract: The study of ecosystem services (ES) is becoming increasingly popular, as it plays an
important role in human wellbeing, economic growth, and livelihoods. The primary goal of this
research is to investigate the global trend in ES research using a rigorous systematic review of highly
cited articles. The articles for this study were extracted from Science Citation Index Expanded (SCI-E),
Emerging Sources Citation Index (ESCI), and Social Sciences Citation Index (SSCI) databases of Web
of Science Core Collection (WoSCC) covering the period from 2000 to 2020. This study was limited to
SCI-E, ESCI, and SSCI databases of the Web of Science. The term “ecosystem service/s” has been
used as a research term to filter the study sample and eliminate other databases from the analysis. A
citation level equal to or greater than 200 was used to further filtration of articles. This query could
restrict to 128 articles that are highly cited in the selected period. Bibliometric analysis results show
that, according to the author’s keywords, the “ecosystem service/s” keyword is highly connected
to the “biodiversity”, “valuation”, “marine spatial planning”, and “conservation planning”. The
U.S.A., Canada, China, France, and Australia are the leading countries in the cumulative number of
highly cited articles and networks of co-authors. The U.S.A. is a strong contributor to ES research
with China, Canada, and France. The most productive universities linked to the United States were
the University of Minnesota, the University of California-Santa Barbara (UC Santa Barbara), and the
Chinese Academy of Science. The most significant and compelling author is Halpern S Benjamin,
who represents UC Santa Barbara. He has earned international recognition for a model he developed
to analyze global data sets of anthropogenic drivers of ecological change in marine environments.
The most accessed and studied fields in the ES are terrestrial, urban, and marine environments.
Publisher’s Note: MDPI stays neutral
Keywords: research trend; bibliometric analysis; ecosystem services; highly cited papers
Citation: Gangahagedara, R.;
Subasinghe, S.; Lankathilake, M.;
Athukorala, W.; Gamage, I.
Ecosystem Services Research Trends:
A Bibliometric Analysis from
2000–2020. Ecologies 2021, 2, 366–379.
https://doi.org/10.3390/ecologies
2040021
Academic Editors: Valery E. Forbes
and José Ramón Arévalo Sierra
Received: 19 October 2021
Accepted: 1 December 2021
with regard to jurisdictional claims in
published maps and institutional affiliations.
1. Introduction
Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
The term ‘ecosystem service (ES)’ initially appeared in the 1980s [1]. Later, this
concept gained international attention through the global ecosystem initiative Millennium
Ecosystem Assessment [2]. In 2010, ES was included in the Aichi Targets framework of the
Convention on Biological Diversity [3]. The Intergovernmental Science–Policy Platform
on Biodiversity and Ecosystem Services (IPBES) eventually acknowledged this concept,
which is now incorporated in the Sustainable Development Goals (SDGs) [4–6]. ES has
become a key indicator of human wellbeing, as they support global economic prosperity
and wellbeing [7]. ES are mainly classified as provisioning, regulating, supporting, and
cultural services, which play a vital role in maintaining human wellbeing in many ways [2].
Ecologies 2021, 2, 366–379. https://doi.org/10.3390/ecologies2040021
https://www.mdpi.com/journal/ecologies
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However, many anthropogenic factors greatly influence the hinder of the service rendered
by the ES. According to Costanza et al., the worldwide value of ES fell from USD 4.3 trillion
to −20.2 trillion yearly due to changes in land use from 1997 to 2011 [8]; this analysis
also cautioned that around 60% of the ES utilized globally are unsustainable [2]. This
developing trend of ES degradation may significantly affect the global eco-security [2,9].
In such a context, numerous studies have been conducted to address the functioning,
assessment, and management of ES at regional and global levels [10,11]. Furthermore,
it has the potential to uncover a large number of studies related to the consequences of
climate change on ES [12,13].
Bibliometric analysis is an internationally recognized method for systematically and
qualitatively evaluating research trends and networks of researchers [14]. Furthermore,
this study provides a comprehensive direction and useful assistance to aspiring researchers
who want to begin formative research in a particular topic [15]. The analysis paves the
path for future studies, or else other reviews can combine with bibliometric research to
develop a systematic and conceptual–theoretical review of the studying discipline [16,17].
The primary output of the bibliometric analysis is to summarize the research trend and
scholarly network based on the keyword frequencies, trace the subject categories, and
research institutions, active authors, productive countries, publications, influential journals,
etc. [16,18]. We conducted the bibliometric analysis of this study based on highly cited
articles related to the ES.
Identifying the qualities of a highly cited article on a certain topic is one of the standard
components of previous bibliometric analysis [19,20]. With the presence of the worldwide
arena, highly cited papers are regarded the most significant and collaborative efforts.
The WoSCC database showcases more than 20,000 academic journals from 113 countries
throughout 254 scientific areas, according to the 2021 journal citation report (JCR). The JCR
report reveals that more than 14,000 journals published at the WoSCC database have at
least one gold open access publication, including 4600 journal articles published as open
access category. Therefore, we believe that selecting the WoSCC database is more suitable
for this analysis. When discussing the global trends of ES, there is a considerable gap in
the bibliometric analysis focused on scholarly networks. Consequently, the main objective
of this study is to examine the global trends and ES research through a bibliometric
analysis of highly cited articles from 2000 to 2020 found in the SCI-E, ESCI, and SSCI
databases (WoSCC).
2. Materials and Methods
2.1. Data Collection
We used the Web of Science Core Collection (WoSCC) database to aggregate publications from 2000 to 2020. Data were retrieved on 5 October 2021 at 1.30 p.m. of Coordinated
Universal (UTC) time (acceded from University of Tsukuba, Japan). We searched the
WoSCC for all articles pertaining to ES research (SCI-E, SSCI, and ESCI). Articles found
using the term “ecosystem service*” (asterisk symbol is used in WoSCC to broaden the
search term covering ecosystem service and ecosystem services). The “Title” field and
“articles” were filtered in the “document type” field to limit the search for articles only.
The articles were published in English during the specified period were considered. Total
citations equal to or greater than 200 were chosen to analyze the most cited articles in
the study [9,20,21]. Subsequently, author(s) name and affiliation, subject categories, name
of the journal (s), title(s), and published year were included in extracted articles for the
bibliometric analysis.
2.2. Bibliometric Analysis Methods
VOS viewer software was used to assess the data that had been retrieved (www.
vosviewer.com) (accessed on 5 October 2021). The researchers used a quantitative analysis
approach, knowledge mapping, and a network analysis tool. The study was based on the
author’s network strength, as well as the countries, keywords, and institutions. Through
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network analysis, the research clusters, scope, and structure of the discipline were discovered [22]. Modern research has shown that fractional counting is preferable over complete
counting [23]. The fractional counting method provides standardized field results [23]. We
used fractional counting as a part of our bibliometric analysis, which gave the following
results. The co-authorship network was analyzed to reveal the highly cited articles of top
countries, top institutions, and most productive authors. Meanwhile, we analyzed the
co-occurrence network to identify the most frequent author’s keywords.
3. Results and Discussion
After filtering, we found 4949 articles. Accordingly, we were able to retrieve 128 highly
cited articles. The selected number of articles represents 2.6% of the total articles. Figure 1
shows the distribution of the number of citations of 4949 articles published over the last
two decades. From 2000 to 2005, the number of publications and citations related to ES
remained minimal, counted as less than 5000, and the publication counted as less than
100. Between 2006 and 2015, the number of total citations and publications related to ES
increased gradually. At the end of 2015, the number of total citations counted as more
than 15,000, and the publications counted as 400. From 2015 to 2020, the total number of
citations counted as more than 30,000, and the publication counted as more than 700. The
year 2005 marked the milestone of the global attention to the ES, notably publishing the
Millennium Ecosystem Assessment (MEA) report in 2005 and The Economics of Ecosystems
and Biodiversity (TEEB) in 2010; these might be the reason for this historical paradigm
shift [24]. This emerging trend popularized ES-related studies globally [25,26].
Figure 1. Number publications and citations related to ecosystem services research in Web of Science Core Collection
(WoSCC) database from 2000 to 2020.
Table 1 shows bibliometric details of the top 10 out of 4949 articles published in
ES research during the last two decades. The publication of Worm et al. [27] at Science
journal leads the list with 2564 citations. Rey Benayas et al. [28], whose publication bears
887 citations at the same journal, placed seventh on the list. Ecological Economics journal
is also on the list with two publications; that of Fisher et al. [29] placed fourth and carries
1497 citations, and that of Boyd and Banzhaf [30] placed seventh and carries 1049 citations.
Ecological Economics, Science, and Proceedings of the National Academy of Science of the United
States of America (PNAS), displayed the highest impact factor in the list; according to
Zhang et al. [31] ES-related publications immensely help gain the highest impact factor
of these journals. There are eight journals listed in the top 10 rankings of highly cited
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articles extracted. When analyzed, these top-ranking journals, along with 128 highly cited
articles (selected according to the ≥200 thresholds), Ecological Economics journal accounts
for 22 highly cited articles (i.e., 17.2% of the total), carrying the impact factor of 5.389
in 2020.
Table 1. Top 10 highly cited articles (≥200, citation) in ecosystem services research in Web of Science Core Collection
(WoSCC) database from 2000 to 2020.
Author(s)
Publication Year
Journal
NC
IF (2019)
Worm et al. [27]
2006
2564
47.728
Costanza et al. [32]
2014
2120
10.466
de Groot et al. [33]
Fisher et al. [29]
Carpenter et al. [34]
Boyd and Banzhaf [30]
Rey Benayas et al. [28]
Mace et al. [35]
Isbell et al. [36]
Kremen [37]
2010
2009
2009
2007
2009
2012
2011
2005
Science
Global Environmental Change-Human and
Policy Dimensions
Ecological Complexity
Ecological Economics
PNAS
Ecological Economics
Science
Trends in Ecology and Evolution (Opinion)
Nature
Ecology Letters
1691
1497
1212
1049
887
822
799
792
1.882
5.389
11.205
5.389
47.728
14.764
42.779
8.665
Note: Number of Citations (NC); Impact Factor (IF) the details were extracted from the journal website.
When analyzing the objectives of the top 10 articles in Table 1, Worm et al. [27]
placed first of the list focused on marine ecosystem service. It examined how biodiversity loss affects the maritime ecosystem service across the temporal and spatial scale.
Costanza et al. [32] focused on the environmental valuation on a global scale. At the same
time, de Groot et al. [33] focused on the challenges involved in applying ecosystem service
assessment and valuation. The study’s primary objective of Fisher et al. [29] is to provide a
consistent definition for ecosystem service. Following such, Carpenter et al. [34] discussed
the potential challenges faced in implementing Millennium Ecosystem Assessment.
Boyd and Banzhaf [30] examined the necessity of applying standardizing units for the
accounting and procurement of ecosystem services as a nonmarket commodity. Further, this
study focused on reasons for such “standardizing units” showing slow development. Rey
Benayas et al. [28] studies focused on providing insights for ecological restoration through
meta-analysis. The main objective of Mace et al.’s [35] study was to find out the relationship
between ecosystem service and biodiversity. Isbell et al. [36] study focused on maintaining
the ecosystem service to protect the plant diversity. Finally, the Kremen [37] study concentrated on the research plan, which includes Adaptive management, community structure,
conservation planning, diversity–function, ecological economics, and ecosystem function
to develop environmental policy and natural resource management plans.
When examining the literature of the top 10 articles listed in Table 1, more attention
is gained by valuing ecosystem service globally. Next, the classifying and understanding
or defining the ecosystem service earned more focused among them the studying of the
marine ecosystem service across the temporal and spatial scale gain significant attention.
The topics such as “restoration” and the “effects on biodiversity due to environmental
degradation” were comparatively less focused at the top 10 ES publications. However,
the impacts of climate change on ES, especially on the marine ecosystems and combined
studies of valuing and restoring the marine ecosystem on a global scale are missing from
the literature discussed in the top 10 articles.
Figure 2 shows the most productive journals which contain the highest number of
total citations. Ecological Economics (established in 1989) is the most effective journal on the
list. This journal focuses on transdisciplinary research within the purview of ecology and
economics. Costanza et al. [32] are dominant in this journal. In contrast, from 2002 to 2014,
this team contributes most of the highly cited articles to the journal, indicating the ES’s
developing importance in this journal.
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Figure 2. Number citations related to ecosystem services research in Web of Science Core Collection (WoSCC) database
obtained by the highly cited journals from 2000 to 2020.
The next leading journal is PNAS, accounting for 14 articles (i.e., 10.9% of the total)
and bearing an impact factor of 11.2 in 2020. Science and Global Environmental Change-Human
and Policy Dimensions journals contributed four articles (i.e., 4% of the total each), however
those journals bear 47.7 and 10.47 of impact factor, respectively. Ecosystem Services journal,
established in 2012, dedicated to promoting publications related to the ES, accounts for
six articles, including the article ‘Mapping ecosystem services for policy support and
decision making in the European Union’ which bears 511 citations but is not listed in
the top 10 list. According to McDonough K. et al. [26] this journal further expands its
scope in ES as the journal is relatively new. Ecological Economics, Science, and PNAS
journals are transdisciplinary journals that publish various research articles covering
different disciplines. Therefore, unarguably justifies the reason for these journals to be
ranked in the top ten list. On the other hand, these journals can absorb multidisciplinary
research, including ES and conceptual development. Inevitably this trend proves that,
more or less, ES in its nature is a multidisciplinary concept and is rapidly emerging in the
transdisciplinary platform.
Commonly used author keywords or the top author keywords indicated scientists’
and researchers’ research priorities and directions in any given discipline, which can be generalized to the ES. According to Figure 3, 156 keywords are distributed among 22 clusters,
where the most significant cluster shown in the middle in ash color consists of 22 keywords
represents the period of 2000–2020. ES is the keyword has the highest number of occurrence
(25 times) followed by biodiversity (6 times) and four other keywords (cultural ecosystem
services, ecosystem service, marine spatial planning, and multifunctionality) with the occurrence of three times. Fourteen keywords have an occurrence of twice, whereas the other
keywords have a unique occurrence. ES had the most potent link strength among all author
keywords and was highly connected to biodiversity. The strength of the network displayed
in Figure 3 shows the relationship between the clusters following such ES and biodiversity
in Figure 3 indicates a close relationship between these two concepts. Additionally, many
researchers regarding this link paid high interest to this linkage [38–41].
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Figure 3. Co-occurrence network (author keywords) related to ecosystem services research in Web of Science Core Collection
(WoSCC) database obtained by the highly cited journals from 2000 to 2020. Note: The threshold value = 1, applied for highly
cited articles of 128, resulting in 156 keywords distributed among 22 clusters. The bubble size shows the total number of
highly cited articles, the line thickness shows the linkage’s strength, and the color shows the cluster.
Climate change impact also shows a direct link to the ES. Compared to other links,
it displayed a relatively more minor link strength, where a considerable gap is shown;
therefore, it needs to expand the scope of ES research involving climate change impacts.
In this analysis, keywords such as “landscape” did not appear in the author keywords
network (Figure 3). The term “landscape” is associated with natural or cultural landscape
in the ES research fraternity. Again, a considerable gap developed between ES research
involving “landscape” is associated with natural and cultural domains. However, the
keywords such as “land use”, “agriculture”, and “urban ecology”, also related to natural
landscapes, agriculture, and agricultural biodiversity, may have a link to the ES of urban
ecology which is missing, thus displayed a gap in research interest.
On the other hand, only a few keywords are presented and associated with cultural
landscapes in the network. Emerging concepts such as “trade-off” and “synergy” are less
focused on ecosystem research. Many empirical studies emphasized the importance of
these concepts to be incorporated into ecosystem research [42–45]. The frequent appearance
of the keyword “Sustainability” may shed a light that these emerging concepts are widely
discussed in future studies.
The U.S.A., Australia, England, Canada, and France were among the top-ranked
countries related to highly cited articles published in the ES research field from 2000–2020
(Figure 4). Only one Asian country (China) and one African country (South Africa) are
visible representing the Asian and African continent. The U.S.A. and England bear a total
link strength of 10, which means these countries may have a strong link, and connects with
the other countries that dominate ecosystem research. China also plays a leading role in the
Asian region and strongly associates with the U.S.A. Further, the U.S.A., Canada, England,
and Australia connect with the strong linkage of the ecosystem research field. The U.S.A.
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holds 21 highly cited articles and accounts for 4147 total citations; this indicates the U.S.A.
is leading in ES research.
Figure 4. Co-authorship network of the top countries related to ecosystem services research in Web of Science Core
Collection (WoSCC) database obtained by the highly cited journals from 2000 to 2020. Note: The threshold value = 1, applied
for highly cited articles of 128, resulting in 12 countries. The bubble size shows the total number of highly cited articles, the
line thickness shows the linkage’s strength, and the color shows the cluster.
The co-authorship network presented in Figure 4 reflects the state of collaboration between the most productive countries and highly connected the U.S.A. to Canada, England,
China, France, and Australia. It reflects a substantial portion of the U.S.A. network that is
involved with these five countries. The results forecast the identification of three clusters,
as follows: The countries surrounding the U.S.A. (green cluster); countries surrounding
England (red cluster); and countries surrounding Australia (blue cluster). Notably, China
is included in the U.S.A. cluster.
According to Figure 5, four organizations have a total link strength of 3; the Council of
Scientific and Industrial Research (CSIR) in India, Stanford University, UC Santa Barbara,
and the University of Minnesota. When considering the citations of highly cited articles, the
University of Minnesota has the highest number of citations (814), followed by the Chinese
Academy of Science (812) and Stanford University (810). Recently, Stanford University has
developed the InVEST model (a subset of the Natural Capital Project), gaining popularity
among researchers. On the other hand, according to Figure 5, CSIR is leading in the list. The
Indian government founded the CSIR in 2013. CSIR consisted of more than 38 laboratories,
and nearly 4800 scientists were working at this institution. However, the results indicate
that the CSIR incorporated a minimal number of ES-related studies in the Asian region.
There are three identical clusters in Figure 4 represented by 12 countries from 2000–2020.
Compared with the link strength and the bubble size, the U.S.A. cluster is more potent than
the other clusters. However, the U.S.A. cluster connects with many countries, including
the Asian region countries such as China. Therefore, it is legitimate to conclude that the
U.S.A.-based green cluster is dominant in ecosystem service research.
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Figure 5. Co-authorship network of the top universities and institutions related to ecosystem services research in Web of
Science Core Collection (WoSCC) database obtained by the highly cited journals from 2000 to 2020. Note: The threshold
value = 2, applied for highly cited articles of 128, resulting in 23 institutions. The bubble size shows the total number of
highly cited articles, the line thickness shows the linkage’s strength, and the color shows the cluster.
Further, the results indicate that the red cluster represents the most productive institutions in the ES. There are seven institutions included in this cluster. Chinese Academy
of Science (CAS) is included in this cluster, which indicated that the research conduct
relates to the ES in China has a solid link to the U.S.A. universities. As the U.S.A.’s most
productive institution, Sanford University had the highest link strength with the University
of Minnesota among all other institutions in the country. The U.S.A. is carrying out many
actions related to environmental protection, including the National Ecosystem Services
Partnership, the Natural Capital Project, and the development of USEPA’s Enviro Atlas
tool [26]. The University of British Colombia and CSIR in India connect to the U.S.A. and
Australia. Additionally, the University of East Anglia and the University of Stockholm also
represent the east European partnership to the ES research. Among them, the University of
Stockholm shows the highest total link strength (Figure 5).
There are two main clusters displayed in (Figure 6). The red color cluster consists of
21 items, whereas the green color consists of six clusters. Halpern S. Benjamin is dominant
in the green color cluster with 26 links and the highest link strength in both clusters.
However, Halpern S. Benjamin linked both clusters, and he represents the UC Santa
Barbara. Halpern S. Benjamin et al. [44] article obtained 5948 citations for ‘a global map of
human impact on marine ecosystems’ publication. This article developed an ‘ecosystemspecific, multiscale spatial model’ to evaluate global data sets of anthropogenic drivers of
ecological change for marine ecosystems. They found almost every marine ecosystem is
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subjected to human impact other than the ecosystems close to the polar regions. The green
color cluster mainly followed similar marine ecosystem-based research.
Figure 6. Co-authorship network of the most productive authors related to ecosystem services research in Web of Science
Core Collection (WoSCC) database obtained by the highly cited journals from 2000 to 2020. Note: The threshold value =
3, applied for highly cited articles of 128, resulting in 27 authors. The bubble size shows the total number of highly cited
articles, the line thickness shows the linkage’s strength, and the color shows the cluster.
Our paper focuses on the 2000–2020 period and finding new research trends in ES
research so that Costanza et al.’s publications in early 1994 are not included. The ‘Economic
value of ES at the global scale’ by Costanza et al. made a tremendous contribution to the ES
research field [8]. The unit value-based approach began from the study of Costanza et al. [8],
which has been cited approximately 6000 times until 2017. This study established the first
framework for estimating the economic value of 17 ES for 16 biomes. Additionally, Costanza
and Kubiszewski [46] discussed the importance of valuing ES stressed the importance of
introducing new common asset institutions to take the ES value better into account other
than defining them in the conventional markets. The red color cluster more prominence
given to climate change, valuation, ecological economics, modeling, etc.
The results also revealed that the authors such as Halpern S. Benjamin and Robert
Costanza contributed immensely to developing ES-related research studies globally. Further, Robert Costanza’s research interests include ecological economics, landscape ecology,
and ES. Meanwhile, in January 2011, Robert Costanza was recognized as the most productive author in the WoSCC [46].
Figure 7 displayed the data regarding ‘types of ecosystems’, ‘ecosystem services’,
‘research focus’, and ‘study cites’ of 128 highly cited articles across the continents related to
their origin. North America and Europe are the dominant continents in ES related studies,
concerning the highly cited articles and the number of ecosystem studies conducted
from 2000 to 2020 (Figure 7). Moreover, these top two continents (North America and
Europe) were highlighted in the other studies. In contrast, there was a minimal number
of studies conducted in South America and Oceania. The most accessed ecosystems
were terrestrial urban and ocean Figure 7a. The terrestrial ecosystem was the dominant
type of ecosystem accessed in Europe, while the ocean ecosystem received particular
consideration in North America. In contrast, this analysis found very few assessments
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involving grassland, freshwater, and wetland ecosystems among the highly cited articles.
However, the studies conducted by Wen L. et al. [47] and Zheng X. et al. [48], focused on
the degradation of grassland, which shows high trending rates in citations; therefore, these
ES studies may see a high preference in the future.
Figure 7. Highly cited articles: (a) Ecosystem Type, (b) Services of Ecosystem, (c) Research interest, and (d) Geographical
locations of the study area.
Figure 7b displayed the data of ES regulating services were the most dominant, consistent with the previous finding [31]. The highly cited articles with the four continents,
i.e., Europe, North America, Asia, and Africa, gave more attention to the regulating and
provisioning services. The complexity that occurred while evaluating the cultural and
supporting services might be the reason for the declining number of citations in this category [49,50]. In Oceania, there were no highly cited articles focusing on cultural services.
The results of the research focus are given in Figure 7c. Quantitative assessment is
top in the research list, focusing on studies on ES, followed by qualitative assessment,
policy evaluation, monetary valuation, and literature review. Quantitative assessments
comprised all kinds of empirical studies of ES. In comparison, these studies used various
statistical or computational techniques [51]. The tools used to evaluate the ecosystem
services in quantitatively (1) ’Integrated Valuation of Ecosystem Services and trade-offs
(InVEST)’ and (2) ‘Social Values for Ecosystem Services (SolVES)’ [52]. In addition, some
studies incorporated ES and biodiversity as additional components to fit and visualize the
consequences of land use on multiple ES and their trade-off [53,54].
Qualitative research on ES is mainly confined to surveys, experiments, or questionnaires. Some of the studies have addressed the relationship between ecosystem and
biodiversity [55]. In addition, the Payment for Ecosystem Services (PES) has a developing
trend on a global scale [56]. Costa Rica pioneered implementing PES for environmental
conservation in 1997. China is also moving ahead with effective PES policy implementation,
such as the Natural Forest Conservation Program (NFCP) and the Grain to Green Program
(GTGP), notably the most prominent environmental conservation programs worldwide [57].
Through programs such as National Forest Commission (CONAFOR), Mexico also im-
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plemented PES and became one of the world-leading advocates in PES. [58]. Wetland
mitigation banking is another Neoliberal environmental policy implemented by the U.S.A.,
which paves the path to creating a stable ES market [59]. The monetary valuation approach
is another widely used method for valuing ES; unit value transfer, contingent valuation,
and market and nonmarket valuation methods come under this category [60].
Figure 7d displayed the ES study cites around the world. According to the results,
case study citations were not equally distributed across the continents. They are mainly
confined to the U.S.A. and Europe. The top five countries in case study sites were the
U.S.A., China, Sweden, Germany, and the U.K. Interestingly, China is an Asian country
that immensely contributed to ES-related research, but did not contribute to other Asian
countries towards ES-related research compared to China.
4. Limitation of This Study
This bibliometric analysis is solely based on the Web of Science’s SCI-E, ESCI, and
SSCI databases. The term ‘ecosystem service/s’ is used in research to broaden the scope of
the investigation. The analysis excludes any other databases. We note that results may vary
depending on the database used, such as Scopus and Google Scholar, and, in the interim,
the addition of other search phrases such ecosystem valuation. Author keywords were
missing from certain highly cited publications published in journals such as PLoS ONE and
PNAS. Therefore, our study depends on the author’s keywords and includes such articles
only for the presentation of the network of keywords. The baseline (≥200) is the most cited
article in this bibliometric analysis. Therefore, according to the limitations above, we must
interpret any conclusions present in this study.
5. Conclusions
This paper presents the global ES research trend and a scholarly network covering the
period of 2000 to 2020. Our bibliometric analysis includes publication outputs, journals,
author keywords, countries, institutions, and authors, and is based on 128 highly cited
research articles retrieved from the SCI-E, ESCI, and SSCI databases of the Web of Science.
The types of ecosystem and ES were evaluated, including the studies’ research focus and
the geographical location of the case study.
A comparative increase in the highly cited articles in ES research indicates the global
attention it is acquired. The most frequently used author keywords were “ecosystem
services”, “biodiversity”, “valuation”, “marine spatial planning”, and “conservation planning”. Based on the author’s keywords network, “ecosystem services” are strongly linked
to biodiversity and climate change impacts with relatively ‘old’ keywords such as “sustainability” and new keywords such as “payment for ecosystem service”. The concepts behind
these keywords are equally relevant in the author keywords network.
Ecological Economics is placed on first in the total citation ranking, followed by PNAS
journal that obtained the second place and third place received by the Science journal.
Concerning the impact factor, the Science journal gained the highest impact factor according
to the 2020 JCR reports. The U.S.A., Canada, China, France, and Australia are considered
to be the most influential countries related to the cumulative number of highly cited
articles and co-authorship networks. Distinctly, the U.S.A. is highly connected with China,
Canada, and France. The University of Minnesota, UC Santa Barbara, and the Chinese
Academy of Science were noted as the most productive universities connected to the U.S.A.
However, Halpern S. Benjamin represents the UC Santa Barbara and is considered the
most influential and compelling author. Halpern S. Benjamin developed an ‘ecosystemspecific, multiscale spatial model’ to evaluate global data sets of anthropogenic drivers of
ecological change for marine ecosystems, which gained international attention. Terrestrial,
urban, and marine ecosystems are considered the most accessed and studied fields in the
ecosystem service. Quantitative and qualitative evaluations methods were highly focused
on ecosystem service studies. Most studies were conducted in the U.S.A. and China.
Ecologies 2021, 2
377
Author Contributions: Conceptualization, R.G., S.S., M.L. and W.A.; methodology, R.G. and S.S.;
formal analysis, R.G., S.S., W.A. and I.G.; writing—original draft preparation, R.G., S.S., M.L. and
I.G.; review and editing, R.G., S.S. and I.G.; visualization, S.S. and M.L. All authors have read and
agreed to the published version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of interest.
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