One Ecosystem :
Review Article
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Corresponding author: Aline Romero-Natale (aline_natale@hotmail.com)
Academic editor: Joachim Maes
Received: 12 Jul 2024 | Accepted: 06 Sep 2024 | Published: 13 Sep 2024
© 2024 Aline Romero-Natale, Otilio Acevedo-Sandoval, Arturo Sanchez-Porras
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Romero-Natale A, Acevedo-Sandoval O, Sanchez-Porras A (2024) Ecosystem Services in the Milpa System: A Systematic Review. One Ecosystem 9: e131969. https://doi.org/10.3897/oneeco.9.e131969
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The Milpa System is an ancient agroecosystem that has played a crucial role in Mesoamerican agriculture for over 9,000 years, particularly in Mexico and Central America. This system provides essential ecosystem services, such as food production, soil quality restoration, biodiversity conservation and the transmission of ecological knowledge. The objective of this systematic review is to inventory and analyse the potential ecosystem services provided by the Milpa System and similar maize-based intercropping systems. The review followed the PRISMA methodology, ensuring rigorous and reproducible research across studies published worldwide in English and Spanish between 2017 and 2023. The analysis included 47 studies that identified a total of 38 distinct ecosystem services. Amongst these, five provisioning services were identified, with 32 articles highlighting food provision. Twenty regulation and maintenance services were discussed, with biodiversity conservation being the most prominent, mentioned in 24 articles. However, cultural services were under-represented, appearing in only 12 articles. Despite the limited research on the Milpa System’s ecosystem services, particularly outside of Mexico, the findings underscore the system’s critical role in promoting agricultural resilience, ensuring food security and conserving biodiversity. This review emphasises the need for increased research to preserve and promote the Milpa System as a sustainable agricultural model that contributes to the well-being of both local communities and broader ecosystems.
agroecosystem, ecosystem services, Milpa System, native maize, sustainability, traditional cultivation
The Milpa System (MS) is an ancestral agroecosystem of Mesoamerican origin that plays a crucial role in agriculture. Its approach goes beyond food production by holistically integrating natural and cultural components with the environment (
One of the distinctive features of the MS is its biological diversity. The best-known and oldest MS in Mexico is the joint planting of maize with beans (Phaseolus spp.) and squash (Cucurbita spp.), known as the triada Mesoamericana (Mesoamerican triad). The planting of these three crops in the same field creates an agricultural synergy where each plant performs a specific ecological function: beans fix nitrogen in the soil, improving its fertility, while squash acts as ground cover, helping to retain soil moisture and control unwanted weeds (
Rooted in traditions and local knowledge, this system has withstood the test of time by playing a vital role in the food culture and nutritional security of indigenous and peasant communities (
The sustainable functioning of the MS largely depends on the ecosystem services (ES) that this agroecosystem continuously provides. ES are defined as the direct and indirect benefits that ecosystems provide to humans (
The systematic review positions itself as an essential tool to synthesise existing evidence, identify patterns and offer recommendations for future research, thus contributing to the understanding and sustainable promotion of this valuable agroecosystem. This methodological approach allows not only for a comprehensive analysis of the relationship between biodiversity and the ES provided by the MS, but also provides a solid foundation for the design of sustainable management strategies for agroecosystems which work under a similar principle.
Literature Search
This systematic review follows the principles established in the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement (
Selection Criteria
The article selection process began with the review of the abstracts of the 259 selected works. The software Abstrackr (
The application of these criteria resulted in a reduced list of articles that were subjected to a thorough review by two independent researchers. The specific objective of the extensive review was to identify the ES present in the studied agroecosystems. The process of the review is presented in Fig.
Flow diagram of the methodology and selection processes used for this systematic review. It follows the template of PRISMA (Preferred Reporting Items for Systematic Reviews).
This extensive review generated the formulation of additional exclusion criteria, this time focusing on the detailed description of ES:
Lack of specification of ES: Studies that identified and evaluated ES within the three main CICES categories were included. Those that did not clearly specify the ES in these categories were excluded.
Data Collection
A spreadsheet was created to compile essential information from the articles (i.e. title, journal, authors). In this sheet, each reviewer concisely summarised the content of the documents, including the filling out of the column included to list mentioned ES. Additionally, the number of incidences of each service was recorded. To achieve this, the services described in the various articles were standardised, based on the most recent Common International Classification of Ecosystem Services (CICES) (
The CICES classification was chosen because it is an international effort to present a common framework to measure, quantify and evaluate the provision of ES in different environments. According to this classification, there are three main classes of services: Provisioning, Regulation and Maintenance and Cultural. Provisioning services are material outputs from the ecosystem and the abiotic environment; Regulation and Maintenance services are ways in which living organisms can moderate or regulate the environment, thus affecting human health, safety and comfort; finally, Cultural services are intangible, non-consumable benefits that are not subject to competition, which affect people's mental and physical states (
Data Synthesis
With the information from the analysed articles, a detailed description of the final products obtained from each ES was prepared. The synthesis was focused on the services mentioned in more than four articles, considering how this value is the median frequency of the total of mentions in the analysed documents.
In addition to the systematic literature review, a bibliometric analysis was conducted to identify thematic trends in the research area. The bibliometric analysis was performed using the Science Mapping Process. For this study, the implementation for R of Bibliometrix (i.e. Biblioshiny) was used, which facilitated the execution of the science mapping process in the final steps of data analysis and visualisation (
Moreover, this review aimed to provide a comprehensive view of the challenges associated with the valuation of the ES offered by the MS. To this end, the cascade model developed by
The annual publication rate of research articles on the analysed topic showed relative stability. An average of seven articles per year were identified, with two notable exceptions: in 2017, only two were recorded, while in 2021, there was a significant increase, with a total of ten publications. It is noteworthy that more than one-fifth of the articles are published by corresponding authors affiliated with institutions in China (n = 10), closely followed by studies from the United States (n = 9). Corresponding authors from Mexico and Germany rank third in terms of contributions, with a total of four articles each. Furthermore, examining the geographical distribution of all authors involved in the reviewed articles reveals that Mexican authors constitute the largest group (n = 54), followed by American (n = 47) and Chinese (n = 43) authors (Fig.
a) Affiliation country of corresponding authors; SCP indicates Single Country Publications and MCP states Multiple Countries Publications; and b) Geographic distribution of all contributing authors of the reviewed literature.
The examined studies presented a wide range of ES, highlighting both their diversity and the scarce repetition of themes amongst them. Some articles moved away from the traditional focus solely on food production by exploring other types of services more deeply, ranging from cultural aspects to ecosystem regulation (Suppl. material
In 2017, two relevant studies were examined that mentioned cultural ES and pollination, a regulation service essential for biodiversity and ecosystems stability. In 2018, there was an increase in researcher interest with seven published articles mentioning the importance of maize agroecosystems for sustainable agriculture and how the implementation of polycultures increased yields compared to monocultures. For 2019, seven studies were reviewed, all of which mentioned biodiversity conservation as a significant benefit of polyculture agroecosystems, while three of them also mentioned cultural ES.
The articles published in 2020 mentioned the conservation of traditional agricultural practices as a tool to restore degraded ecosystems and recover the loss of ES, focusing on cultural and regulation services, with an emphasis on pest control. In 2021, there was a higher number of publications compared to the average of the other years analysed. Although these publications addressed a narrower range of ES, they revealed a broader distribution of services within the three considered categories. In 2022, most studies focused on how polycultures could contribute to food security and climate change mitigation. Finally, in 2023, seven studies were analysed that explored the relationship between polyculture agroecosystems, food security, increasing yields and biodiversity conservation as key for agricultural diversity and natural pest control.
Through the systematic review, 38 different ES were identified, revealing a characteristic pattern in the classification of ES linked to the MS. The results are presented in four sections, corresponding to the three CICES categories, followed by a summary of the review’s findings.
Provisioning Ecosystem Services
Research on polyculture systems has demonstrated how the implementation of such agroecosystems can significantly improve crop yields.
Many studies made the point of mentioning how even though food production is the main goal of these agroecosystems, they provided with a broad spectrum of additional ES. Some of the mentioned services include efficient water and soil nutrients use (
Regarding provisioning services, five were identified with 48 mentions, with the provision of plant-based food being the most recurrent. This finding was consistent, given that this study focused on an agroecosystem specialised in food production (Table
CICES Class |
CICES Code |
Identified Services |
Mentions |
Cultivated terrestrial plants (including fungi, algae) grown for nutritional purposes |
1.1.1.1 |
Food provision |
32 |
Fibres and other materials from cultivated plants, fungi, algae and bacteria for direct use or processing |
1.1.1.2 |
Biomass |
7 |
Cultivated plants (including fungi, algae) grown as a source of energy |
1.1.1.3 |
Fuel (Wood) |
4 |
Cultivated plants for health purposes |
1.1.1.X |
Medicinal Plants |
2 |
Surface water used as material (non drinking purposes) |
4.2.1.2 |
Water Supply |
3 |
Cultural Ecosystem Services
Cultural ES provided by polycultures are relevant for their capacity to strengthen cultural identity and the community sense. According to several studies there are objective and subjective values linked to the sense of identity for rural communities that participate in the development of traditional polycultures (
In the category of cultural services, a total of 13 services were recorded, with 51 mentions. The most notable include aesthetic beauty (mentioned in nine articles), education, cultural identity and recreation (Table
CICES Class |
CICES Code |
Identified Services |
Mentions |
Characteristics of living systems that enable activities promoting health, recuperation or enjoyment through active or immersive interactions |
3.1.1.1 |
Tourism |
4 |
3.1.1.2 |
Physical and Mental Health |
3 |
|
Characteristics of living systems that enable scientific investigation or the creation of traditional ecological knowledge |
3.1.2.1 |
Stories |
1 |
Characteristics of living systems that enable education and training |
3.1.2.2 |
Spiritual and Intellectual Stimulation |
4 |
Education |
6 |
||
Characteristics of living systems that are resonant in terms of culture or heritage |
3.1.2.3 |
Social Cohesion |
3 |
Cultural Heritage |
4 |
||
Cultural Identity and Values |
6 |
||
Characteristics of living systems that enable aesthetic experiences |
3.1.2.4 |
Aesthetic |
9 |
Elements of living systems that have symbolic meaning |
3.2.1.1 |
Songs |
1 |
Cultural Inspiration |
1 |
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Elements of living systems that have sacred or religious meaning |
3.2.1.2 |
Religious |
3 |
Elements of living systems used for entertainment or representation |
3.2.1.3 |
Recreation |
6 |
Regulation and Maintenance Ecosystem Services
Several studies mentioned the effects that polyculture agroecosystems had on the regulation of mass flows and extreme events, such as underground water recharge and conservation (
As previously mentioned,
Most of the identified ES are predominantly grouped in the "Regulation and Maintenance" category, with a total of 20 services documented on 151 occasions. Amongst these, biodiversity conservation (mentioned in 24 articles) and soil fertility processes (cited in 23 articles) stood out as the most frequent (Table
CICES Class |
CICES Code |
Identified Services |
Mentions |
Control of erosion rates |
2.2.1.1 |
Soil Erosion Control |
8 |
Buffering and attenuation of mass movement |
2.2.1.2 |
Wind Reduction |
1 |
Hydrological cycle and water flow regulation (Including flood control) |
2.2.1.3 |
Drought Regulation |
1 |
Flood Regulation |
2 |
||
Pollination (or 'gamete' dispersal in a marine context) |
2.2.2.1 |
Pollination |
12 |
Seed dispersal |
2.2.2.2 |
Seed Dispersal |
1 |
Maintaining nursery populations and habitats (Including gene pool protection) |
2.2.2.3 |
Soil Biodiversity Conservation |
3 |
Biodiversity Conservation |
24 |
||
Pest control (including invasive species) |
2.2.3.1 |
Weed Control |
13 |
Disease control |
2.2.3.2 |
Pest and Disease Control |
17 |
Weathering processes and their effects on soil quality |
2.2.4.1 |
Soil Conservation |
7 |
Decomposition and fixation processes and their effects on soil quality |
2.2.4.2 |
Soil Fertility |
23 |
Nitrogen Fixation |
10 |
||
Decomposition and fixation processes and their effects on soil quality |
2.2.4.3 |
Carbon Sequestration |
14 |
Regulation of the chemical condition of freshwaters by living processes |
2.2.5.1 |
Water Quality |
3 |
Regulation of chemical composition of atmosphere |
2.2.6.1 |
Atmospheric Oxygen |
1 |
Regulation of temperature and humidity, including ventilation and transpiration |
2.2.6.2 |
Microclimate Regulation |
2 |
Other types of regulation and maintenance services provided by biotic processes |
2.3.x.x |
Climate Change Mitigation |
4 |
Maintenance and regulation by inorganic natural chemical and physical processes |
5.2.2.1 |
Well Recharge |
1 |
Water Conservation |
4 |
Number of mentions for each ES in the reviewed literature. The services with higher number of mentions in each category are highlighted.
Data synthesis
This study analysed the ES provided by maize-based intercropping agroecosystems, revealing its multifunctionality across the three ES categories. The most frequently mentioned ES was food provision, with 32 studies highlighting its significance. This aligns with the primary purpose of the MS as an agroecosystem designed for optimising food production. However, its contribution extends beyond mere food production. The next two most mentioned ES are biodiversity conservation and soil fertility, which fall within the "Regulation and Maintenance" category. Biodiversity conservation plays a crucial role in maintaining suitable conditions for plant and animal species, including those that act as natural pest predators. On the other hand, maintaining soil fertility is another critical service for the optimal functioning of the Milpa, particularly when managed as an organic system that avoids the use of agrochemical inputs.
Based on the analysis of the reviewed documents, it can be argued that the provisioning ES contributed by the MS mainly focus on plant production, including plants for food, wood and medicinal purposes. Conversely, the regulation and maintenance ES of the MS extend to various subsystems or compartments, encompassing soil (e.g. soil fertility and soil biodiversity conservation, as well as erosion control), water (such as water conservation and aquifer recharge), the biosphere (including biodiversity conservation, pest and weed control and seed dispersal), as well as the abiotic interface surrounding the system (emphasising carbon sequestration, microclimate regulation, flood mitigation and wind control). These ES demonstrate the multifunctionality and integral importance of the MS in providing and maintaining essential ES.
The scope of cultural ES encompasses a broad perspective, as it involves human interaction with the environment in two distinct contexts. First, it relates to the active or passive appreciation of the ecosystem's features, including elements, such as its aesthetic beauty, potential for tourism and recreation. Second, it connects to community creation through these experiences, encompassing aspects such as inspiration, the development of campesino identity and the influence of religious elements.
Following the ecosystem services cascade model proposed by
The primary limitation of this study is the scarcity of research specifically addressing the relationship between the MS and ES, particularly outside of Mexico. This lack of research restricts the generalization of our findings beyond Mexican borders, despite the evident benefits this agroecosystem offers to both farmers and consumers. To address this limitation, we expanded the scope of our review to include studies on ES in agroecosystems more broadly, with a particular focus on those involving maize production alongside other crops. While this broader approach deviates slightly from the original focus on the MS, it enabled us to explore a wider range of services that the MS can potentially provide by drawing comparisons with similar agroecosystems.
The loss of ES dependent on biodiversity could potentially limit access to basic necessities for a healthy life, highlighting inequality in the most vulnerable sectors, especially in areas with high levels of marginalisation and poverty.
Cultural ES are the least studied, with only 12 articles mentioning them. In general, other studies indicate that these services are the least researched due to the difficulty in quantifying them. Their study is greatly influenced by the subjectivity of each community and culture, complicating the creation of standardised quantification methods. Even when evaluation tools exist, they are subject to the subjective interpretation and valuation of each community and individual.
Another complication in the quantification of cultural ES lies on their economic valuation, which implies a challenge because these are intangible and often lack direct market value, making the use of economic evaluation tools difficult. However, their conservation is crucial as they contribute to human well-being by providing aesthetic, recreational and spiritual experiences and cultural identity through traditional practices, ceremonies and spiritual connections. They also promote sustainable tourism that benefits both the community and biodiversity. The inclusion of cultural perspectives in ecosystem management and conservation is essential to ensure a sustainable balance between human needs and environmental health.
Considering that the primary objective of the MS is to optimise production primarily for food provision, it is important to point it out as a final service. Thus, the ES refers to a connection of ecosystem events and functions, followed by the valuation of benefits such as the nutritional value of these foods and the economic resources that can derive from selling surplus production. This reflection shows how, in the context of ES, the line between the service and its utilisation can be blurred and cause confusion. However, it is important to consider the context in which we are working to more clearly identify the occurrence of the service.
This systematic review provides a comprehensive insight into the current state of knowledge on how diversity in the MS contributes to system health, agricultural productivity, human well-being, preservation of traditions and cultural aspects, as well as resilience to climate change. Through the systematic review of 47 articles collected from the Scopus database, 38 distinct ES were identified, according to the CICES classification.
Food provision stands out as the most mentioned ES, followed by biodiversity conservation and soil fertility. The reported services are predominantly grouped in the category of "Regulation and Maintenance", demonstrating the integral importance of the MS in the provision and maintenance of essential ES. Additionally, cultural ES play a crucial role, connecting aspects such as aesthetic beauty, education, cultural identity and recreation, highlighting the relevance of cultural aspects and the specific configuration of the MS in the provision of ES.
Despite the scarcity of studies conducted, both outside and within Mexico, that relate the MS and ES, this review provides a solid foundation for understanding the importance of diversity in the MS in the global context. Furthermore, it emphasises the need to promote sustainable agricultural practices, such as polycultures, to enhance agricultural system resilience and ensure food security and biodiversity preservation in a context of climate change.
The authors wish to acknowledge the support of CONAHCYT for the development of this research. The authors also extend their gratitude to Dr. Eduardo Torres for his valuable input which improved the quality of this manuscript.
Aline Romero-Natale: Conceptualisation, Methodology, Software, Writing - Original Draft, Editing; Otilio Arturo Acevedo-Sandoval: Conceptualisation, Validation, Writing - Review; Arturo Sanchez-Porras: Methodology, Software, Writing - Original Draft, Editing
This table summarises various ecosystem services (ES) identified in different sections, along with their respective mentions and references. Each entry is organised according to the Common International Classification of Ecosystem Services (CICES) class and code, focusing on specific characteristics of living and non-living systems that contribute to cultural, provisioning and regulatory ecosystem services. This table also includes the number of mentions each service has in literature, providing insight into the most studied or recognised services, such as food provision (32 mentions), biodiversity conservation (24 mentions) and soil fertility (23 mentions), with corresponding references for each service type. The table highlights the diversity of services ecosystems provided, classified into biotic (living) and abiotic (non-living) categories.