Agroforestry systems of the lowland alluvial valleys of the Tehuacán-Cuicatlán Biosphere Reserve: an evaluation of their biocultural capacity

The TCV is located at the southeast of the state of Puebla and the northwest of the state of Oaxaca [47], covering an area of 10,000 km² with a high environmental heterogeneity including 36 vegetation types [45, 48]. Most of the regional territory is semiarid with annual mean precipitation of 300–500 mm [49]. This zone is recognized for its high biodiversity, with more than 3,000 plant species, nearly 400 of them being endemic to the region [38]. It is also culturally diverse, with eight indigenous ethnic groups inhabiting the area [39]. These entire elements make the TCV one of the most important biocultural regions of Mexico (Figure 1).

Our study was conducted in forests and AFS of the lowlands of the region, which is an extent alluvial valley formed by the Salado and Grade rivers, both of them tributaries of the Papaloapan River, one of the greatest rivers of Mexico. The original vegetation in this zone is formed by a combination of thorn-scrub forest, tropical dry forest, and riparian vegetation dominated by the mezquite Prosopis laevigata, reason why Valiente-Banuet et al. [50] describe them using the term mezquitales. We conducted the study in three areas following the main rivers. One of them is part of the territory of the community of Santiago Quiotepec, Oaxaca, which is inhabited by Mestizo and Cuicatec people. The second area is part of the community of San José Axusco, Puebla, inhabited by Nahua people. The third area is part of the community of Zapotitlán de las Salinas, Puebla, inhabited by Mestizo, Mixtec and Popoloca peoples (Figure 1). In Quiotepec, people are predominantly dedicated to agriculture, cultivating the multi-crop maize system called milpa, complemented by commercialization of lemon and mango; it is located at an elevation of 545 m, where vegetation is tropical dry forest. In Axusco people complement resources from milpa with monetary incomes from intensive cultivation of sugar cane; it is located at elevation of 900 m, where vegetation are thorn and tropical dry forests dominated by mezquite. In Zapotitlán the milpa system is complemented with incomes from the extraction of mineral salt and mining and handicrafts manufactured with onyx; it is located at elevations of 1400 m, with patches of thorn forest and columnar cacti forests dominated by mezquite.

In all communities, we studied the milpa system that combines management of maize, beans, squashes, and in some cases chili peppers. In general, the milpa is a small system of nearly one-hectare extent, whose production is for direct consumption by households. We sampled five plots of AFS in each site, in total 15 AFS units. We carried out characterizations at both regional and local levels per community, considering human cultural, technological, and economic aspects related to the management of each AFS plot, as well as ecological and biodiversity conservation issues. For characterizing AFS we mapped each plot, identifying and measuring the area covered by each type of agroforestry practices. Based on these maps we calculated the percentage of vegetation cover of each plot and we censed all species of shrubs and trees occurring in the vegetation patches. We conducted semi-structured interviews to people managing each plot analysed, all of them being the owners of the plot. Interviews focused on five main topics: (1) Physical aspects of the terrain, plot size, use period, land tenure. (2) Agricultural practices, crops managed, fallow periods, patterns of crop rotation, use of fire, instruments, tools and /or machines used, use of agrochemical inputs, irrigation, labour hand invested. (3) Techniques of vegetation management associated to each type of agroforestry practices, reasons why people maintain or remove wild plants, caring actions, and the most valued plant species. (4) Governmental and non-governmental programs enhancing or not AFS, and communitarian rules regulating use and management of forest. (5) Pastoralist practices, how people manage livestock associated to AFS.

The authors state that the study was conducted after the correspondent permit and consent from the authorities of the Biosphere Reserve Tehuacán-Cuicatlán, the local authorities and communitarian meetings in the communities of Quiotpec, Axusco and Zapotitlán de las Salinas, as well as the persons collaborating in the research.

AFS studied have a spatial arrangement according to the specific type of terrain, which are organized in ground terraces or ‘bancales’, which is a pre-Columbian technique practiced in terrains over soft slopes, slightly modifying the surface. This is generally a system directed to retain and protect soils through hedgerows of bushes and ground borders along edges [59, 60]. In this region the technique has the Náhuatl name of ‘metepantle’, meaning “space between agaves” [61], although some variations of the technique use other specific names; for instance, they can be called ‘apantle’ when agaves are absent or ‘melgas’ (term that makes reference to the space destined to cultivation) and ‘estacadas or cabezales’, properly to the ground border. It is just on the ground borders where people maintain wild plant species, sometimes combining with cultivated shrubs and trees (Figure 2). This AFS is so important at the regional level that significantly model the landscape and makes conspicuous the spatial arrangement of terrains in alluvial valleys (Figure 3).

According to the interviews, the establishment of ground terraces helps to manage water from rainfall (retaining it and controlling the run-off causing erosion) as well as from the irrigation system (directing its flow and favouring infiltration). In addition, terraces helps to prevents soil erosion; in both roles, vegetation maintained on the borders plays a central role (Table 3). But maintaining vegetation has more reasons; people mentioned a total of 20 reasons, including utilitarian explanations mainly provision of fruits (7%) and other edible resources (7%), fuel wood (5%), medicines (2%) and fodder for livestock (5%). People also made reference to functions (ecosystem services) such as preventing soil erosion (2%), (make the terrain planner (2%), protection against strong wind (7%), retention of water (7%), provision of shade (14%), barrier of access to domestic animals (2%), as well as attractors of wild animals that may affect the crops (2%). For instance, they mentioned birds, which in wild vegetation find food that otherwise is looked for in the crops. People in addition mentioned reasons related to provision of habitat to other desirable specie (9%); for instance, the edible caterpillar called ‘cuchamá’ the larvae of the butterfly Paradirphia fumosa, which are food highly appreciated in the region and has considerable economic value. The larvae ‘cuchamá’ grow associated to the tree ‘manteco’ Parkinsonia praecox, which for this and other reasons is particularly appreciated and maintained by people in AFS. Another animal protected in AFS are the edible insects (Hemiptera), ‘cocopache’. Also important is the ‘pitahaya’ Hylocereus undatus, associated to mezquite (Prosopis laevigata), which produces edible fruits. We also recorded aesthetic reasons (14%) (beauty) for maintaining trees and shrubs, in some areas people call these beautiful plants “wild luxury”, these are the cases of ‘sotolín’ (Beaucarnea gracilis), the ‘viejito’ (Cephalocereus columna-trajani) and other succulent plants. In addition, people gave ethic and spiritual reasons (“if there is no reason to remove them, why to do it”; the ‘pirul’ Schinus molle provides protection against ‘bad spirits’) (2%). Not all reasons are equally important, the most frequently mentioned were those of beauty and shade provision (14%), followed by provision of fruit, protection against strong wind and water retention (7% each) (Table 3).

In each community studied, the reasons for maintaining shrubs and trees in AFS were variable, but two reasons were mentioned in all sites: protection against strong wind and beauty of the plot. Each person mentioned from one to five reasons. In Zapotitlán, people mentioned 11 of the 20 reasons referred to in the whole region, each person mentioned on average four reasons, the most important being beauty of crop field (25% of mentions). In Axusco people mentioned on average 2.6 reasons, the most important being provision of food and ethic motives (15% each). In Quiotepec people mentioned on average 2.2 reasons, the most important being obtaining of fruit (27%, Table 3). However, when asking the question about the most interesting attribute of shrubs and trees maintained, people mentioned specific uses (65%) followed by their size, they prefer big trees (35%).

Trees and shrubs more valued by people interviewed were mezquites (Prosopis laevigata), ‘guajes’ (Leucaena esculenta), lemon (Citrus limon), ‘manteco’ (Parkinsonia praecox) and ‘nopales’ (Opuntia spp.) (Table 4). Prosopis laevigata had the highest record of preference and the highest number of uses. It is valued as protection barrier against strong wind, levelling the terrain, its pods and leaves are good fodder, its wood is very good fuel wood and material for construction and handicrafts. It is particularly good support for growing ‘pitahaya’ (Hylocereus undatus), the edible insects ‘cocopaches’ live on this tree, and it provides shade and beauty to the plot.

The number of trees and shrubs and vegetation cover maintained in AFS is highly variable. On average, vegetation cover is 12% of agricultural plots. In Zapotitlán the cover was on average 18% while in Axusco it was 5% and in Quiotepec 10%. Reasons mentioned to remove vegetation cover were: “…plants cause obstruction to the pass of tractor and plough”, and “…it is necessary to remove plants growing fast and difficult to control which affect crop growing”. People also mentioned to remove those plants with spines that hurt persons, those that compete with crops, and those determining excessive shade that affects maize growth and that do not provide any other important function to the system.

People prevent problems associated to maintain trees and shrubs through agroforestry practices that allow them getting benefits and reducing negative effects. In general people maintain vegetation in ground borders (75%), and they function as windbreaker barriers, whereas those in limits of the plot function as live fences. Put in these ways vegetation maintained allow free passing to tractors and plough in the cultivated areas. Trees and shrubs should be pruned to control shade, and the resulting material provide fuel wood. In 80% of the plots studied, people extract fuel wood for direct consumption by the households. The species more valued for this purpose are Prosopis laevigata and Parkinsonia praecox. These important trees are tolerated as isolated trees within the cultivation areas. Other species are usually transplanted from the centre of the plot to the terraces or borders, but not all of them establish successfully after transplantation. The most successful to this action are agaves and cacti. The agroforestry practices mentioned were recorded in all sites studied, the main difference among sites is the total vegetation cover and the reasons to maintain shrubs and trees.

In México land tenure may be private, ejidal and communal, and all of these types are represented in the sites studied. However, in Zapotitlán all AFS studied are in communal land, whereas in Axusco in ejidal land and in Quiotepec in private areas. Cutting trees, even those in sites of the production area is under regulation, requiring permit from local authorities. In Zapotitlán the regulations are particularly strict, the study zone is part of a protected area and sanctions are supervised by the Mexican Ministry of Environment as well as by local authorities. In Axusco the Ejidal authority or Comisariado is the one in charge of authorizing or not the vegetation removal, whereas in Quiotepec it is the Communal authority (Comisariado), but people may remove trees without permit in their private land. Sanctions are generally economic but in Zapotitlán people that disobey may be jailed.

On average, we recorded 13 species of trees and shrubs per plot of AFS. However, variation is very high, ranging from 3 to 33 species per plot. In Zapotitán we recorded the highest number of woody species (17.5 ± 5) per plot, whereas in Quiotepec and Axusco we recorded 11.6 ± 3 and 9.2 ± 1.15 woody species per plot, respectively.

AFS in the sites studied are mainly dedicated to cultivation of milpa (maize, beans, squashes, chilli pepper), together with some fruit-producing trees (mainly lemon, sapodilla and mango) and other horticultural crops such as watermelon and melon in irrigated plots. The milpa products are directly consumed by households whereas fruits are commercialized. Corn (varieties ‘criollo’, ‘rojo’, ‘azul’, and ‘híbrido’), beans (Phaseolus vulgaris varieties ‘enredador’, ‘flor de mayo’, ‘mosquito’, ‘blanco’, ‘delgado’, ‘mazateco’, ‘negro’, and ‘rojo’) and squashes (Cucurbita pepo or ‘calabaza de castilla’, C. argyrosperma or ‘calabaza acamotada’ and C. moschata or ‘calabaza deapenita’) are grown. We found on average three crop species per plot, but some of them have six crop species (in Zapotitlán 2.5, in Axusco 3, and in Quiotepec 3). No significant differences were identified in this aspect among sites.

We found that nearly 80% of the agricultural plots sampled had irrigation; all agriculturalists make use of tractor for tilling the earth, some of them alternating with plough. The agricultural cycle is from three to four months, in Quiotepec people practicing two cycles of cultivation per year, leaving land in fallow only two months, whereas in Zapotitlán and Axusco people practice one single cultivation cycle per year leaving land in fallow 7 to 8 months. To maintain the soil fertility, people make use of organic inputs, mainly goat dung and leaves; in nearly 60% of the plots sampled people make use of chemical fertilizers. For controlling pests of animals, nearly 60% of people interviewed said to add chemical insecticides whereas the rest said not to make use of any type of pest control. In Axusco all people interviewed said to make use of chemicals for controlling larvae affecting maize. Control of weeds is mainly conducted manually, only 14% people interviewed (all of them from Axusco) said to make use of herbicides.

Calculations of Intensification Value (Figure 8) indicated that the community of Axusco had the highest values. In this community people make use of machinery more frequently, the higher use of agrochemical inputs was recorded there and agricultural practices are in general more intensive than in the other sites studied (e. g. longer use of land in relation to the fallow period, more frequent use of fire). Axusco is followed by Zapotitlán where people make use of tractor combined with plough, but agrochemicals are practically non-used, and the agricultural practices are intense; they have used the land in consecutive cycles for long time. Quiotepec had the lowest values of intensification since use of machinery is less frequent than in the other sites, and although people make use of chemicals this is much less frequent and in lower amounts than in Axusco. In Quiotepec people practice two agricultural cycles per year but they started this use pattern until recently, after land was long time in fallow. Production was generally similar in all sites studied. In Axusco people harvest on average 720 ± 49 kg of maize per ha, whereas in Quiotepec 640 ± 25 kg/ha and in Zapotitlán 588 ± 23 kg / ha.

Livestock raising was markedly different among sites. In Zapotitlán people do not raise domestic animals in the plots of AFS, whereas in Quiotepec 80% of the plots are used for feeding animals during the dry season (mainly maize straw and remaining weeds) and in Axusco 60% of the plots have a similar situation. However, in general few animals are maintained in AFS plots (on average two oxen, one donkey and one horse), in Quiotepec the owner of one plot maintain in his AFS plot 30 goats.