The Marceño Agroecosystem: Traditional Maize Production and Wetland Management in Tabasco, Mexico

: The marceño agroecosystem is based on traditional agriculture in the ﬂooded areas of the alluvial plains of Tabasco, Mexico. In the marceño system, the native maize, called “ mej é n ”, is cultivated during the dry season using residual soil moisture. At physiological maturity, mej é n is tolerant to ﬂooding. To estimate the potential area where marceño may be implemented, we characterized and deﬁned the areas where it is practiced, using geographic information systems (GIS), and determined the bioclimatic variables of the sites where 16 species of wild plants associated with the management of the marceño grow. We also analysed areas of agriculture and livestock in relation to the cyclical ﬂoods. This information was used to generate a probability model of marceño occurrence through MaxEnt, which was superimposed on an elevation model (LiDAR) geoprocessed with GIS. The marceño was observed in 203 localities across eight municipalities of Tabasco (~2% of the state area), at elevations of 1–7 m. The calculated area with potential for implementation of the marceño is about 18.4% of the state area. The implementation of this agroecosystem on a wider area might be an alternative for local agriculture development and a strategy for ecological conservation and restoration of wetlands.


Introduction
Currently, there is a primary need worldwide to develop strategies for agriculture and the adaptation of smallholders to global climate change (GCC), in order to reach the goal of increasing food production by 50% by 2030, as proposed by the Food and Agriculture Organization (FAO) [1]. The adverse effects of GCC will be more severe in regions where millions of people depend on subsistence agriculture and are more vulnerable to food insecurity [2]. The increased frequency of severe weather events will have drastic consequences for agricultural production [2,3]. Lowlands can be highly productive in several countries around the world but require particular attention in order to understand their dynamics and risks, and the ways to prevent and respond to these risks. In Tabasco, Mexico, nearly 62% of people are highly marginalised and 45% have limited access to food, with their The natural vegetation is associated with emerging hydrophytic plants, dominated by Thalia geniculata L. (locally called popal, which is 1-3 m in height) ( Figure 1). To promote the conservation of highly native varieties of maize, beans, and squash in the marceño agroecosystem, and to promote the maintenance of wetlands and their ecosystem services, the aims of this research were: (1) To characterize the marceño system environment, (2) to identify the localities where the system is practiced, and (3) to estimate flood-prone areas where this agroecosystem may potentially be implemented. To promote the conservation of highly native varieties of maize, beans, and squash in the marceño agroecosystem, and to promote the maintenance of wetlands and their ecosystem services, the aims of this research were: (1) To characterize the marceño system environment, (2) to identify the localities where the system is practiced, and (3) to estimate flood-prone areas where this agroecosystem may potentially be implemented.

Study Sites
This study covered eight municipalities of the alluvial plain of Tabasco, at elevations of −2 m to 15 m a.s.l. that are prone to cyclical flooding: Cárdenas, Huimanguillo, Comalcalco, Cunduacán, Jalpa de Méndez, Nacajuca, Centla, and Jonuta ( Figure 2). Tabasco is located in the basin of the Papaloapan, Grijalva-Mezcalapa, and Usumacinta Rivers, in the south of the Gulf of Mexico [26]. They form a complex net of deltaic channels interconnected with lakes, seasonal wetlands and marshes, which are interconnected from September to February. Moreover, 96% of the territory of Tabasco is on the coastal alluvial plains of the Gulf of Mexico [29]. The climate is warm-humid [30], with high precipitation during summer months, and an annual mean rainfall of 1500-2980 mm. Annual mean temperature during the dry season (March to June) is 25-30 • C. Before the middle of the 20th century, the area was about 50% covered by permanent and semi-permanent wetlands [26,28,29] and most of the remaining area was covered by tropical rainforests. Currently, only relics of these ecosystems exist because of anthropic disturbances, such as expansion of the agricultural and livestock frontier and the construction of dams [28,29]. Other relevant vegetation types are flooded rain forest, savanna and mangrove forest [29,31]. The soils in this area are vertisol, gleysol, cambisol, arcisol, luvisol, and fluvisol [32].

Study Sites
This study covered eight municipalities of the alluvial plain of Tabasco, at elevations of −2 m to 15 m a.s.l. that are prone to cyclical flooding: Cárdenas, Huimanguillo, Comalcalco, Cunduacán, Jalpa de Méndez, Nacajuca, Centla, and Jonuta ( Figure 2). Tabasco is located in the basin of the Papaloapan, Grijalva-Mezcalapa, and Usumacinta Rivers, in the south of the Gulf of Mexico [26]. They form a complex net of deltaic channels interconnected with lakes, seasonal wetlands and marshes, which are interconnected from September to February. Moreover, 96% of the territory of Tabasco is on the coastal alluvial plains of the Gulf of Mexico [29]. The climate is warm-humid [30], with high precipitation during summer months, and an annual mean rainfall of 1500-2980 mm. Annual mean temperature during the dry season (March to June) is 25-30 °C. Before the middle of the 20th century, the area was about 50% covered by permanent and semi-permanent wetlands [26,28,29] and most of the remaining area was covered by tropical rainforests. Currently, only relics of these ecosystems exist because of anthropic disturbances, such as expansion of the agricultural and livestock frontier and the construction of dams [28,29]. Other relevant vegetation types are flooded rain forest, savanna and mangrove forest [29,31]. The soils in this area are vertisol, gleysol, cambisol, arcisol, luvisol, and fluvisol [32].

Locating the Localities Where Marceño is Currently Practiced and the Potential Area for Its Implementation in Tabasco
We reviewed the literature about the marceño system [21,27,28,33,34], as well as the data from the census of the Department of Agricultural Development of the municipality of Comalcalco and all areas reported that use the marceño agroecosystem in the flood-prone areas of Tabasco ( Figure 2). To determine the localities that currently practice the marceño system, we undertook fieldtrips to identify the plots practising it and characterized the environment around the plots, including aquatic vegetation types, known locally as popales and tulares (vegetation dominated by Thalia geniculata L.

Locating the Localities Where Marceño is Currently Practiced and the Potential Area for Its Implementation in Tabasco
We reviewed the literature about the marceño system [21,27,28,33,34], as well as the data from the census of the Department of Agricultural Development of the municipality of Comalcalco and all areas reported that use the marceño agroecosystem in the flood-prone areas of Tabasco ( Figure 2). To determine the localities that currently practice the marceño system, we undertook fieldtrips to identify the plots practising it and characterized the environment around the plots, including aquatic vegetation types, known locally as popales and tulares (vegetation dominated by Thalia geniculata L. and Typha domingensis Pers, respectively) [21]. Additionally, we verified the practice of the marceño system in 80 plots within eight municipalities ( Figure 2). These plots were georeferenced with a Global Positioning System (GPS, Garmin e-trex 30, Kansas, USA). The presence of the marceño system was confirmed by the smallholders of the plots, who were also asked about the characteristics of the agroecosystem, particularly the flooding regime of the system.

Modelling the Potential Distribution of Plant Species Associated with the Agroecosystem Using MaxEnt
A model of the potential distribution of plant species associated with the marceño agroecosystem for the coastal plain of Tabasco was built as follows: (1) We included the plant communities associated with the agroecosystem located and georeferenced in the field and the historical occurrence of the 16 most frequent aquatic perennial herbs and tree species, both related to the agroecosystem and to the flood-prone areas of the alluvial plain of Tabasco [21] (Table 1); we also included the plant records for the Pacific and the Gulf coast of these species (a total of 3124 records, derived from the Global Biodiversity Information Facility website [35]). (2) We obtained 19 bio-environmental variables ( Table 2) from the Bioclimas Neotropicales website [36] updated for Mexico, which compiles monthly climatic layers for the interval 1910-2009 (Table 2). We elaborated the model using the MaxEnt (Maximum Entropy Species Distributions Modelling, Version 3.33k [37]) algorithm that uses the function of minimum entropy to calculate distribution probabilities [38][39][40]. In this study, we only included the probabilities calculated for the state of Tabasco.  Table 2. Climatic variables used in the modelling of the potential distribution of thirteen wild species related to the marceño agroecosystem based on Bioclimas Neotropicales [36].

Generating the Terrain Elevation Model
To generate the digital model of terrain elevation (−2.96 to 1146.25 m) for the state of Tabasco, we processed LiDAR images with ArcMap 10.2.1 Arc Gis Esri (1360 images in GRID format, E-15 region [41]). The horizontal resolution was 5 m. These models did not include infrastructure and vegetation in order to identify the localities that used the marceño agroecosystem. We used this model of terrain elevation to locate low elevation areas (0-7 m) in order to determine the areas subject to flooding and with potential to implement the marceño system.

Modelling the Potential Areas for the Marceño Agroecosystem
For this estimation, we included areas with both agriculture and pastures that naturally have floods and are therefore susceptible to productive reconversion to marceño.
We used the SIG ArcMap software to geoprocess the following information: (1) To determine the flood-prone areas with elevations from 0 to 7 m, we used LiDAR images of terrain elevation [41]; (2) to identify flood-prone areas with agricultural and cultivated grass pastures, and to discard preserved areas with aquatic vegetation (marshes, mangroves, flooded rain forest, and permanently flooded areas), rain forest areas, natural protected areas, urban areas, infrastructure, and drained areas with elevations of 18-1146 m, we used the layers of soil-gleysol and vertisol (silty-clay with poor drainage and high organic matter content)-and vegetation [32,42]; (3) we used the layer of highest probabilities of distribution of plant communities associated with the marceño system (as generated in Section 2.3); (4) we also added a layer with the location of the Maya Chontal population, with the data collected from [43]; (5) we superimposed all five layers to determine the areas with potential to use the marceño agroecosystem including the pasture areas with potential for reconversion to agriculture, the ethnic origin of the population and their influence area (biocultural region [25]).

Location of the Marceño Agroecosystem in the State of Tabasco
We located the presence of the marceño system in the field in 203 localities in the eight municipalities of Tabasco, particularly in Comalcalco, Nacajuca and Cunduacán (Table 3). According to the elevation model of the terrain (LiDAR), these localities are at elevations of 1−7 m with high precipitation (≥2980 mm). This high precipitation causes cyclic floods that maintain the seasonal swamps and other areas used for extensive cattle raising ( Figure 3, Table 3, Table 4, and Table A1).      Up to 61.6% (15081.9 km 2 ) of Tabasco is between 0 and 15 m a.s.l. Within this area, 16.6% is drained (2500 km 2 ) and 13.4% (3280.97 km 2 ) is permanently flooded (−2.96 to 0 m a.s.l.). We observed that the remaining aquatic vegetation covered 24% of the state (5902.48 km 2 ). However, most of this area is currently disturbed. We calculated that in Tabasco, 2365.13 km 2 are dominated by T. geniculata (popal) and 3537.36 km 2 by T. domingensis (cattail, tular) ( Figure 3). Data for each of the studied municipalities are presented in Table 5. Figure 4 shows the areas with high probability (0.807) for the distribution of plant communities associated with the marceño agroecosystem. This model, in conjunction with the terrain elevation model, provided us with information about the areas with potential for productive marceño agroecosystems. The area where the marceño agroecosystem is currently practiced had the greatest calculated potential (Figure 3, Figure 4b, and Table A1). Notes: (1) The areas originally covered by popal, were disturbed by clearance for agriculture, fires for turtle hunting, and cattle raising. Vegetation was substituted by aggressively introduced forages and weeds that cover vast areas with cyclic flooding. Additionally, the drainage of wetlands has dropped the phreatic level.  The geospatial analysis showed that approximately 1693.71 km 2 has a very high potential for marceño (0-2 m a.s.l.). Considering the predictable periodicity of seasonal flooding, only about 1259 km 2 has a high potential (2-4 m a.s.l.) because of its dependence on the severity of inundation. Moreover, approximately 1140.1 km 2 has a moderate potential and 471.3 km 2 has a low potential (4-6 and 6-7 m a.s.l., respectively) because this area is susceptible to flooding in years with atypically high rainfalls. The estimated potential of the marceño agroecosystem formed approximately 18.4% of Tabasco's area ( Figure 5, Table 6).  Table 6). The geospatial analysis showed that approximately 1693.71 km 2 has a very high potential for marceño (0-2 m a.s.l.). Considering the predictable periodicity of seasonal flooding, only about 1259 km 2 has a high potential (2-4 m a.s.l.) because of its dependence on the severity of inundation. Moreover, approximately 1140.1 km 2 has a moderate potential and 471.3 km 2 has a low potential (4-6 and 6-7 m a.s.l., respectively) because this area is susceptible to flooding in years with atypically high rainfalls. The estimated potential of the marceño agroecosystem formed approximately 18.4% of Tabasco's area ( Figure 5, Table 6). The geospatial analysis showed that approximately 1693.71 km 2 has a very high potential for marceño (0-2 m a.s.l.). Considering the predictable periodicity of seasonal flooding, only about 1259 km 2 has a high potential (2-4 m a.s.l.) because of its dependence on the severity of inundation. Moreover, approximately 1140.1 km 2 has a moderate potential and 471.3 km 2 has a low potential (4-6 and 6-7 m a.s.l., respectively) because this area is susceptible to flooding in years with atypically high rainfalls. The estimated potential of the marceño agroecosystem formed approximately 18.4% of Tabasco's area ( Figure 5, Table 6).  Table 6).  Table 6).

Discussion
During the fieldwork, we corroborated the presence of the marceño agroecosystem in Tabasco's rural communities, many of which have been inhabited by the Maya Chontal since pre-Hispanic times (Figures 3-5; Table 3). These localities are in the range of 1-14 m above sea level and are susceptible to seasonal flooding. Based on the reports of the Food Information Services of Tabasco [44], regarding the area of planted maize during the spring-summer cycle, it can be inferred from our model that, currently, the marceño system cover less than 463.52 km 2 , which represents approximately 10% of the potential area ( Figure 5, Table 3). The presence of marceño had been reported in 183 localities previously [33], whereas we found it in 203 localities. However, there might be many other locations in rural areas that use the marceño agroecosystem, as it is a current practice in rural areas used by both Maya Chontal and Mestizo people. It is also possible that a greater number of localities practice the marceño system in the lowlands and nearby towns of Tabasco, on the banks of the Usumacinta River in the state of Campeche (locality of Palizada), given the cultural similarities of the region.
The model of potential distribution of the plant communities associated with marceño allowed an estimation of the areas where the ecosystem is conducive to the implementation of the marceño agroecosystem as a rural development strategy in Tabasco. Marceño is cultivated predominantly to feed the Maya Chontal population. A total of 59% of this area is currently occupied by primary activities such as subsistence agriculture, mainly in the municipality of Nacajuca [43]. The management of the popal by the marceño agroecosystem is fundamental to the subsistence of this population. In Tabasco, there are 79694 Maya Chontal people (3.6% of the population) [43], 62% of which live within the "La Chontalpa" biocultural region [25]. This indigenous territory covers about 794.06 km 2 (3.2% of the area of the state), mainly in the municipalities of Nacajuca and Centla. In this study, we found that important areas of wetland vegetation were considered as popal. Our results showed that, in this area, 269.93 km 2 (11.4%) and 1521.2 km 2 (43%) are covered with popal and tular, respectively ( Figure 3, Table 4).
It is relevant that approximately 7% of the Mayan Chontal territory is located within the Natural Protected Area of the "Reserva de la Biosfera Pantanos de Centla" (3027.06 km 2 ) [45], one of the priority regions for the conservation of biodiversity and agrobiodiversity. This area has been protected by the Government of Mexico and the Ramsar Convention [46]. For that reason, we only used the areas actually used for cattle, and the marceño agroecosystem (using landraces, mainly mején), to calculate the potential areas for marceño. This conservation area protects against the construction of infrastructure for forced drainage that completely modifies the hydrology and the ecological cycles of wetlands [9,10]. In the marceño agroecosystem and other examples of extensive agricultural carried out in the wetlands, the combination of food production and ecosystem services in this area might contribute to the high resilience of both the wetlands and marceño system [21,24,27,28], which maintains other ecosystem services such as improving water quality, stopping floods, and maintaining biodiversity [7] and agrobiodiversity [9].
Currently, there are examples of reactivation of pre-Hispanic agricultural systems in wetlands, such as the waru waru or suka kollus system in Lake Titicaca [47] and the implementation of the "chinampas chontales" in Nacajuca, Tabasco, which are similar to the chinampas system in the Valley of Mexico [48]. Similarly, the calculated potential areas for the marceño agroecosystem represent a viable alternative to produce food for ecological restoration programs of the lowlands of Tabasco and other tropical regions where the traditional cultivation of corn is the basis of the smallholders' diet. Additionally, the marceño agroecosystem is recognized by the smallholders for its high soil fertility and good yield of corn crops in flooded areas (actually ∼4.3 ton ha −1 of grain, including native maize varieties such as mején).
The characteristic abundance of popal in the hydrophilic vegetation of the landscape and culture of the Tabasco lowlands has been altered by a lack of interest and understanding of its cultural and ecological relevance, as well as a lack of knowledge about its management and productive potential. The marceño agroecosystem is part of the local biocultural identity and its maintenance and enhancement may also contribute to the conservation of the Tabasco wetlands and biocultural heritage. Abandoning the marceño agroecosystem would represent the loss of a unique agrobiodiversity and a biocultural landscape that represents the important identity of the Tabasco lowlands. On the other hand, the marceño might contribute to the tropical subsistence agriculture. This is relevant because the FAO reports that, in Central America, household traditional agriculture farmers produce about 50% of the agricultural production of the region and more than 70% of the foods.
The findings of this study have an important implication for other wetland areas in Mexico and elsewhere in the world, such as the Rhine [49], Danube, and Mississippi [50] River basins. It could also be adopted as a model in agricultural development plans in other tropical regions with cyclical floods and food poverty. This would also allow in situ conservation of agrobiodiversity of varieties of crops that have adapted to high humidity conditions, such as maize mején, which represents a genetic reservoir for research on new varieties that are tolerant to waterlogging. Marceño represents an opportunity for agroecological studies that allows communities settled in areas susceptible to cyclical floods (61.6% of the state of Tabasco) to develop. This might allow sustainable development, which could be accompanied by ecological restoration programs and the conservation of the biocultural landscape of the Tabasco wetlands.

Conclusions
Marceño is relevant for smallholders who produce food for self-consumption in one of the poorest and most vulnerable regions of Mexico. The adoption of practices of sustainable management of natural resources and the retention of traditional agricultural systems by smallholders has been proposed by the FAO as part of a strategy to adapt to climate change, eradicate global poverty and end hunger. The Intergovernmental Panel on Climate Change estimates that agronomic adaptation could improve yields by 15 to 18% [49]. This demonstrates the significance of household agriculture, such as marceño, for the food sovereignty of the smallholder communities [50,51]. In Tabasco, the maize crop occurs in the rainy season, but the marceño system occurs in the dry season, allowing an additional staggered agricultural cycle during the recession of the flood. This study improves the understanding of the current context of the marceño agroecosystem in the lowlands of Tabasco.

Conflicts of Interest:
The authors declare no conflict of interest.
Appendix A Table A1. Localities indicated in the Figure 3.

Municipality
Id Number and Locality Showed in Figure 3 Cárdenas