Ecosystem services are broadly defined as the benefits obtained directly or indirectly by humans from ecosystems that improve human well-being and provide fundamental life-support for human civilization [1
]. Assessments of ecosystem services are seen by many as a promising and effective communication tool for bridging the knowledge gap between science and policy-making, and supporting land management decisions, because they seek to highlight the multiple contributions of ecosystems to society and associated tradeoffs between different land use options [4
In a context of the increasing demand of human society for ecosystem services, there is often an ambition to maximize ecosystem services supply and to reduce its shortfalls through prudent land management [6
]. However, the key challenge of land management is determining how to manage multiple ecosystem services effectively to avoid unwanted tradeoffs [6
]. According to the results of Millennium Ecosystem Assessment and many others, increasing the supply of some ecosystem services, especially provisioning services such as food and timber, can cause a decline in other ecosystem services such as carbon sequestration, and unsustainable management may undermine the future provision of these services as well [1
]. Therefore, identifying ecosystem services tradeoffs and synergies is urgently needed in order to address this challenge [7
Tradeoffs and synergies are typical relationships between multiple ecosystem services [3
]. Tradeoffs describe a conflicting situation wherein the supply of one ecosystem service increases while another decreases. Synergies occur when the provision of two or more than two ecosystem services increase simultaneously [7
]. These relationships are driven by two non-exclusive mechanisms: (1) through common drivers (e.g., land use, climate change) that affect multiple ecosystem services at the same time, and (2) direct interactions among multiple ecosystem services (e.g., reliance on the same ecosystem processes and functions) [11
]. The purpose of tradeoffs and synergies analysis is to increase synergies and reduce or avoid unwanted tradeoffs, which is essential for net-gain decision-making [8
]. By confronting the increasing demand of the public and changes in the global environment, identifying the tradeoffs and synergies among ecosystem services is among the most pressing concerns in sustainable land management today [2
]. However, the identification of multiple ecosystem services tradeoffs and synergies is still limited [3
The results of tradeoffs and synergies analyses can be further used to inform ecosystem services bundles. A bundle is formed by a mix of synergistic ecosystem services, which repeatedly appear together across space or time [7
]. The analyses of multiple ecosystem services bundles would deepen the knowledge of ecosystem services tradeoffs and synergies and are useful tools for identifying the hotspots of multiple ecosystem services for optimizing management of multifunctional landscapes [7
A study by [22
] analyzed spatial interactions of ecosystem services in a global hotspot in the three parallel river regions in southern China. The study reveals complex relationships, spatial patterns, and distribution among ecosystem services in the mountainous areas. However, this study was limited by the “space-to-time” substitution method used due to temporal data scarcity. The study was also limited by the use of land use types to create ecosystem services, which could lead to some deviations. Hence, the authors recommend that a comprehensive database may be needed in future studies to effectively capture the spatial interaction among ecosystem services.
In another study on ecosystem services tradeoff, synergies, and drivers, [23
] focused on ecosystem services provided by slash pine (Pinus elliotii
) forests. The study examined interaction between carbon sequestration, timber production, and water yield, and how forest management practices affect these ecosystem services in northern Florida, U.S. Results showed tradeoffs between ecosystem services. One limitation of this study is the use of natural break algorithm to classify the dataset, as it does not reveal all the trends in continuous data. The study used 377 plots across the study area, which was relatively small. The authors, therefore, recommend that future studies using identical datasets should use them in their continuous form and a larger sample size will be ideal for such analysis.
Over the last 10 years, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) has conducted a number of studies and analyses on ecosystem services. These studies covered various topics with some specific ones that are relevant to our study. A study by [24
] assessed ecosystem services bundles based on socio-cultural preferences of individuals in Spain. The authors observed substantial differences in the social perception about the relative importance of different ecosystem service categories across three ecosystem service bundles. Broadly, results showed ecosystem service bundles can be identified from people’s systemic representations of interrelationships between ecosystem services, and tradeoffs can be identified from socio-cultural preferences as people’s willingness to tradeoff conservation of one ecosystem service against another.
Assessments of ecosystems and biodiversity have transitioned to include a wider range of values, valuation methods, and worldviews. The Natures Contribution to People (NCP) introduced by the IPBES initiative focuses on accounting for these wider values and valuation methods. Another study [25
] reviewed evidence from economic and socio-cultural valuation methods of instrumental and relational values of nature’s contributions to people (NCP) within the IPBES European and Central Asia region. Results showed that regulating NCP was more highly valued than material and non-material NCP. The authors observed substantial evidence of the instrumental values of NCP. The NCP concept was introduced by the IPBES as an improved concept to ecosystem services to shed more light on the contributions, both positive and negative, that people obtain from nature or affects people’s way of life. However, the introduction of NCP has not received total consensus as some researchers and the practice community believes NCP is not different from ecosystem services [26
In 2018, IPBES produced a regional assessment report on biodiversity and ecosystem services for the Americas [27
]. The report represents the state of knowledge on the Americas region and subregions. The report provides a critical assessment of the full range of issues facing decision-makers, including the importance, status, trends and threats to biodiversity, and nature’s contributions to people, as well as policy and management response options.
The assessment concludes that the Americas are endowed with much greater capacity for nature to contribute to people’s quality of life than the global average, and that the economic value of the terrestrial contributions of nature to people is estimated to be at least $24.3 trillion per year, equivalent to the region’s gross domestic product. The assessment also concludes that the majority of the countries in the Americas are using nature at a rate that exceeds nature’s ability to renew the contributions it makes to the quality of life. The assessment also found that biodiversity and ecosystem conditions in the Americas are declining, resulting in a reduction of the contributions of nature to the quality of life of people. The dominant direct drivers of this are habitat conversion, fragmentation, and overexploitation or overharvesting. Climate change is recognized as becoming increasingly important, amplifying the other direct drivers.
The report concludes that there are options and initiatives, some ongoing, that can slow down and reverse ecosystem degradation, and enhance the provision of nature’s contributions to people, including ecological restoration and sustainable land management outside protected areas. These require implementation of effective governance processes and evidence-based policy instruments. Kentucky State has a horizontally-distinct distribution of physiography and land use land cover (LULC), which is typical in many parts of the world, with mountainous landscape in the east, pasture landscape in the central, and cultivated landscape in the west. Such a distinctive heterogeneity of LULC at regional scales makes it an ideal system to examine the bundles and hotspots of multiple ecosystem services. This study combined geographic data and spatially-explicit models to identify multiple ecosystem services bundles and hotspots for state-level optimized conservation policy-making in Kentucky, U.S. The objectives of this study are to: (1) map spatial patterns of multiple ecosystem services at the state scale; (2) identify the interactions between each paired ecosystem services; (3) assess multiple ecosystem services bundles and their main characteristics; and (4) determine the hotspots of multiple ecosystem services.
Mapping ecosystem services biophysical values and analyzing their interactions are considered as important and cost-effective measures for ecosystem management and decision making [4
]. The interactions in ecosystem services in this study were consistent with many other studies in that tradeoffs often occur between provisioning and regulating services, while synergies are more likely to happen within/between regulating and cultural services [2
]. In this study, the tradeoffs’ interactions existed between one provisioning service (i.e., water provision) and a regulating service (i.e., soil retention and carbon sequestration). The tradeoffs between water provision and nitrogen retention were much higher, followed by the interactions between water provision and phosphorus retention. However, another provision service (i.e., timber production) presented tradeoff interactions with water provision and water retention, and synergy interactions with soil retention and carbon sequestration. However, most of the paired regulating services presented synergistic interactions with each other [2
], except water retention and soil retention, which showed a tradeoff interaction. These results showed that provisioning services are not always in tradeoff relationships with regulating services, which is also evidenced in another case study in which there were synergies between timber production and regulating services [20
]. In most cases, increasing some of the regulating services would be at the expense of losing some provisioning services. In other cases, some provisioning and regulating services could be enhanced simultaneously, like timber production and carbon sequestration.
Beyond tradeoffs and synergies, the analysis of ecosystem services bundles can also be used to manifest the relationships between ecosystem services [20
]. The ecosystem services bundles can help policy makers decide on better management strategies by taking ecosystem services tradeoffs and synergies into consideration towards sustainable land management [40
]. From the ecosystem services bundles revealed in this study, land managers can enhance their understanding of the characteristics of each ecosystem service and their interactions. Such evidence-based information would be vital in making targeted policy decisions for a more sustainable social and economic development, as well as maintaining the effective functioning of natural and anthropogenic land systems [2
]. Forest is the dominant land system in Kentucky, occupying approximately 50% of the state’s total area. However, forest area decreased more than 5000 sq. km2
from 1992 to 2011, resulting in a significant degradation of water-related ecosystem services at the state level [42
]. Much of the forest loss was attributed to coal mining and the subsequent reclamation to the grassland in eastern Kentucky [43
]. Restoration of abandoned coal mines to forest in the Appalachian region has been advocated by a coalition of citizens, government officials, and coal industry representatives for quite some time [44
], yet its adoption is very limited, partly due to the lack of appreciation of ecosystem services provided by forest by the local residents and stakeholders. Our tradeoff and synergy study shows that timber production has a strong synergy with carbon sequestration, soil retention, and nutrients retention, which may help reverse the public opinion and increase the use of forestry-based restoration on the previously mined lands in Kentucky.
In this study, we found three bundles, which represented the interactions among ecosystem services in Kentucky. Each bundle clustered the spatial areas with similar major ecosystem services together, which dominated in one or several ecosystem services. Consistent with other studies [7
], we found mountainous area bundle had high regulating ecosystem services, such as soil retention and nitrogen retention, as well as a provisioning service (i.e., timber production). The agricultural area bundle had high water provision services. The pasture area bundle had high water retention services. According to the characteristic of those three bundles, Kentucky can be divided into provisioning areas and regulating areas. The provisioning areas were mainly composed of cultivated land, while the regulating areas were mainly composed of forest, pasture and grassland. A similar composite pattern of ecosystems and services in a bundle, which share common environmental conditions and challenges, would be suitable for similar management strategies [20
]. Additionally, the overlap characteristics of ecosystem services hotspots can provide identification of prioritization sites for comprehensive, compact, and cost-effective management [46
On a final note, there are a few challenges that we encountered in this research that we leave for further research. One important challenge for ecosystem services interactions and bundles research is the choice of indicators. Capacity indicators or flow indicators, middle service indicators or final service indicators, question the results and interpretations of the ecosystem services interactions and bundles [19
]. Another important challenge is the choice of scale. The scale effect on ecosystem services is worth further exploring. The interactions and bundles of ecosystem services may vary at different scales. Finally, understanding the drivers of ecosystem services interactions and bundles is useful and important to inform decision making and for policy implementation. The drivers, such as the biophysical variables and human activities factors [2
], can result in the complexity and integrity of spatial patterns of ecosystems.