Materials and methods

Information available on agaves in AFS was systematized through the construction of the database “El género Agave en Sistemas Agroforestales de México” (The genus Agave in Agroforestry Systems of Mexico) which includes information about the species and the relevant characteristics of the systems that host them, considering: 1) a description of the systems that host agaves, product of our own research; 2) an archive of the literature that is part of the database “Sistemas Agroforestales de México” (http://red-sam.org/index.php/lista-de-publicaciones-sobre-sistemas-agroforestales/) and a typology of these systems developed by ^{Moreno-Calles et al. (2013}, ^2016b); and 3), an update of the searches of specialized studies on the subject in the Web of Science, Science Direct, Google Scholar databases, and ProQuest Dissertations & Theses, as well as TesiUNAM repositories. The keywords included in the search were: agave/maguey + agroforestería, agave/maguey + agroforestal, agave/maguey + sistemas agrícolas tradicionales, agroecosistemas + agave/maguey (agave/maguey + agroforestry, agave/maguey + agroforestal, agave/maguey + traditional agricultural systems, agroecosystems+ agave/maguey). These searches were also carried out with the terms in English. This update focused on a search from 2012 to the present. The review of 146 records included in 75 studies integrated information regarding the role that each species plays in the hosting system, considering the following fields: a) scientific name (taking as a reference http://www.theplantlist.org), b) common name, c) type of agroforestry system (sensu^{Moreno-Calles et al. 2013}), d) other systems where the species can be found with different management intensities, e) cultural group that manages the system, f) locality, state, g) agroforestry practice (sensu^{Moreno-Calles et al. 2011}), h) ecological aspects and interactions, i) uses, j) ecological status/management (sensu^{Blancas et al. 2010}), k) economic value, l) socio-cultural importance, m) density/intensity/dominance, n) evidence of domestication (sensu^{Colunga-GarcíaMarín et al. 2017}, ^{Figueredo-Urbina et al. 2017}, ^{Urbina et al. 2018}).

Results

Agave species present in agroforestry systems in Mexico. Based on the information from the current research and the studies reviewed (75), 31 species and 4 intraspecific variants of the genus Agave were registered in agroforestry systems; 29 records specified the presence of agaves identifying only the genus. The species with the highest number of records is Agave salmiana Otto ex Salm Dyck, which included references to the variety A. salmiana var. ferox (K.Kock) Gentry and the subspecies A. salmiana subsp. crassispina (Trel.) Gentry, with 22 records in total, followed by A. fourcroydes Lem., which was registered 14 times. Other species registered, in descending order of frequency are: A. angustifolia Haw., A. americana L., A. americana var. marginata Trel. in L.H.Bailey, A. tequilana F.A.C. Weber, A. marmorata Roezl., A. cupreata Trel. & A. Berger, A. sisalana Perrine, A. atrovirens Karw., A. mapisaga Trel. in L.H.Bailey, A. lechuguilla Torr., A. potatorum Zucc., A. scaposa Gentry, A. karwinskii Zucc., A. striata Zucc, A. striata subsp. falcata (Engelm.) Gentry, A. triangularis Jacobi, A. angustiarum Trel., A. asperrima Jacobi, A. rhodacantha Trel., A. promontorii Trel., A. peacockii Croucher, A. macroacantha Zucc., A. murpheyi F.Gibson, A. maximiliana Baker, A. inaequidens K.Koch, A. aff. weberi J.F. Cels ex J.Poiss., A. deserti Engelm, A. kerchovei Lem., A. cerulata Trel, A. celsii Hook. and A. aurea Brandegee (see Figure 1 and Appendix 1).

Figure 1 Species and number of studies that mention agave as part of an agroforestry system. *: Agave triangularis, A. angustiarum, A. asperrima, A. rhodacantha, A. promontori, A. peacockii, A. macroacantha, A. murpheyi, A. maximiliana, A. inaequidens, A. aff. weberi, A. deserti, A. kerchovei, A. cerulata, A. celsii, and A. aurea with only one report. 

Traditional agroforestry systems. Homegardens.- This is a type of agroforestry system generally found next to or very near the houses of the families that manage them. With an ancient history, which is crucial among the traditional production systems managed by household units in rural peasant zones. It is characterized by its high richness of native and exotic species diversity, and by its high complexity and structural variation (^{Ruenes-Morales & Montañez 2016}). Such abundance and heterogeneity determine the existence of microhabitats that allow the conservation and use of the genetic resources necessary for the self-sufficiency and incomes of the family’s members, mainly women (^{Moreno-Calles et al. 2016a})

This system was the most common among the studies reviewed. Agave species were identified in 57 studies (13 species), of which A. fourcroydes was the most common with ten records; A. angustifolia with seven: A. americana with six; A. tequilana and A. sisalana five; A. salmiana four; A. atrovirens and A. marmorata two, and A. angustiarum, A. lechuguilla, A. macroacantha, and A. striata with one record each. Eleven records only specified the genus level. The cultural groups mentioned in these studies as managers of agave in their homegardens were the Maya of the state of Yucatan, Campeche, and Quintana Roo (22 homegardens) (^{Herrera-Castro 1994}, ^{Poot-Pool 2008}, ^{Cahuich-Campos 2012}, ^{Mariaca-Méndez 2012}, ^{Poot-Pool et al. 2012}); Mestizo people from the states of Puebla, Chiapas, Nayarit, Tabasco, Mexico (13 homegardens) (^{Stienen 1990}, ^{Ruenes-Morales 1993}, ^{Tamayo-Ortega 1995}, ^{Gaytán-Ávila et al. 2001}, ^{Blanckaert et al. 2004}, ^{Pagaza-Calderón 2008}, ^{Rosales et al. 2008}, ^{Hernández-Soto 2009}, ^{Gómez-García 2011}, ^{Torres-Díaz 2011}); the Nahua of Puebla (nine); the Chontal of Tabasco (four); the Tzotzil/Tzeltal from Chiapas (three) (^{Gutiérrez-Miranda 2003}, ^{Guerrero-Peñuelas 2007}, ^{Pérezgrovas-Garza 2011}); the Mazahua of the State of Mexico (one); the Zapotec from Oaxaca (one) and the Totonac of Puebla (one).

A) Structural role of Agaves in homegardens.- Within these agroforestry systems agave density is mostly low, and may vary from one to dozens of individuals. The agaves within this system play different structural roles, such as that of blocking the passage of cattle or people, parting from agroforestry practices such as live fences or hedges, protecting the integrity of the homegarden and limiting the area that is considered as belonging to that family (^{Ffolliott 1998}). Agaves can be found along the borders or places where they do not represent an obstacle for moving around the homegarden, given that these often grow to a considerable size, sometimes occupying from 1 to 3 m² or more, while homegardens usually cover relatively small areas (between 100 and 500 m²), compared to other AFS in Mexico (1-4 ha). It is possible to find isolated individuals at the center of the homegarden (see Figure 2) or as part of vegetation islands.

Figure 2 Agave species and general management strategies in agroforestry systems. A) Metepantle in the municipality of Zacualtipán, Hidalgo (Photo: G. Álvarez), B) A. americana in a family homegarden in the municipality of Tlahuiltoltepec, Oaxaca (Photo: A.I. Moreno-Calles), C) A. triangularis and A. marmorata as part of a live fence in a AFS in a semiarid zone in Zapotitlán de las Salinas, Puebla. (Photo: I. Torres-García), D) Live fences and island of A. rhodacantha in an agrosilvopastoral system in Zapotitlán de Vadillo, Jalisco. (Photo: I. Torres-García). 

B) Ecological-functional role of Agaves in homegardens.- Agaves retain soil and humidity, promoting the infiltration of water into the ground. When they are allowed to flowering, they act as attractors of melliferous species (bees) and beneficial nectarivorous species (birds, bats, and other small mammals) both necessary to increase the productivity and fructification of other important species that compose the system, such as fruiting trees. Similarly, they are the habitat for animal species such as reptiles (mainly small lizards and snakes, see Figure 3), which control insect plagues and rodents inside the system.

Figure 3 Ecological interactions of agave in agroforestry systems. A) Anolis nebulosus in Agave cupreata, municipality of Tzitzio, Michoacán (Photo: I. Torres-García), B) Icterus wagleri feeding on an inflorescence of A. cupreata in the municipality of Tzitzio (Photo: C. Ojeda), C) Leptonycteris sp. Feeding on the inflorescences of A. cupreata in the Tzitzio municipality (Photo: I. Torres-García), D) Aegiale hesperiaris in A. scaposa in the municipality of Caltepec, Puebla (Photo: M. A. Negrellos-Balderas) and E) Sceloporus sp. in A. angustifolia in Zapotitlán de Vadillo (Photo: I. Torres-García). 

C) Utilitarian attributes of Agaves in homegardens.- In total 16 use categories were reported, eight have two or more records, being the most mentioned the ornamental, followed by medicinal, edible, and obtaining of fiber as the most important (see Figure 4 and Appendix 1). The majority of the Agave species registered have mainly an ornamental use with an aesthetic role in the system; there are other important uses as well, such as the medicinal and edible uses, given their immediate availability and accessibility as a constant element of homegardens. In Mayan homegardens flowering stalks and fibers are used as materials for constructing ka´anche, a sort of traditional seed-bed or elevated horticultural pots characteristic of this region, used for the production of vegetables. Some uses represent an economic incomen this category it is possible to include the commercialization of pulque, fiber extraction, processing and commercialization of crafts such as necklaces and rosaries, as well as articles of common use such as morrales (bags) and mecapales (a sort of rope implement made of agave fiber that is used to carry bulks on the back and which is borne on the forehead). In this system, it is possible to find the presence of species that have been cultivated and selected for a long time, and evident domestication syndromes are present, such as gigantism of the leaves, fibers and the whole individual, as well as a high concentration of carbohydrates. Species such as A. fourcroydes, A. angustifolia, and A. tequilana are part of a complex of species for which there is information about their domestication processes and the relationship with their wild relatives.

Figure 4 Main uses of agave in agroforestry and agroforest systems. A) Agave triangularis being used to delimit a plot (Photo: I. Torres-García), B) Condachos, Aegiale hesperiaris, roasting on a grill, municipality of Caltepec, Puebla (Photo: M.A. Negrellos-Balderas), C) Agave marmorata used as a live fence, municipality of Zapotitlán de las Salinas, Puebla, D) Walls of traditional housing made with inflorescences of A. scaposa, Municipality of Concepción Buenavista, Oaxaca, E) Goat barbacoa baked using leaves of A. salmiana var. ferox, municipality of Concepción Buenavista, Oaxaca, F) Distillation of mezcal made with A. cupreata in the municipality of Tzitzio, Michoacán (Photos: I. Torres-García). 

D) Management. Those individuals that are established and maintained in homegardens, in the case of domesticated species are mostly transplanted from adjacent homegardens or from shoots of individuals that have flowered. Due to their monocarpic reproduction, agaves die after flowering and are then reproduced through stoloniferous or bulbil shoots. In the case of wild species, individuals come from the adjacent ecosystems, and are cultivated primarily through transplanting the complete juvenile individuals that are of interest to people. The transplant location depends on the design of each homegarden and the function that transplanted agaves have as part of the system.

Agroforestry terraces.- This AFS is embankment-based structure located on the slopes of hills and mountains has contributed to its archeological identification in several zones of the country (^{Moreno-Calles et al. 2013}, ^2016b, and ^{Gonzáles-Jácome 2016}). The architecture of this system allows the conservation of soil and water trough of the roots of the useful trees and agaves, perennial bushes, and others, growing in board terraces allowing intensive annual and perennial management crops.

This system was mentioned in 21 of the studies reviewed in which five species are mentioned; among them, Agave salmiana was the most frequently referred to followed by A. americana A. atrovirens, A. salmiana var. ferox, and A. mapisaga. Seven studies identified the agaves only at the genus level, eight focused on the study of metepantles or terraces with agaves from the historic or prehistoric point of view, presenting palynological evidence, archeological evidence (as instruments to extract aguamiel), and archaeobotanical evidence (as remains of roasting pits with agave fibers associated with this type of agroforestry system in various parts of the country). Places such as the Teotihuacan Valley, Ixtapalapa, and Ixtacuixtla in Tlaxcala in central Mexico, but also in places in the north of Mexico, such as Parras de la Fuente, in Coahuila, La Quemada, in Zacatecas, and Cerro Juanaqueña in Chihuahua, are all places with a record of this agroforestry practice, all of them importantly including the presence of agaves. Through their roots, agaves confer stability to the terraces, which were usually established on slopes highly susceptible to erosion. This system was practiced in areas that were under high demographic pressure. Such was the case of the Aztec settlement in the Valley of Mexico, in which thousands of people lived before the arrival of the Spaniards. One of the explanations for how this human settlement survived highlights the intensive establishment of this system.

A) Structural role of agaves in agroforestry terraces.- Depending on their extension, terraces can host hundreds or thousands of individuals which are generally planted in lines following the level curves. Among the functions of agaves are, first of all, the limits created by the succulent and armed rosettes, which at the same time intercept and diminish the effect of rain on soil, allowing in this way the infiltration of water into the ground. Adding on to these effects, there is the strong hold of superficial roots (see Figure 2), which contribute to the effective prevention of erosion and to the conservation of the architecture of terraces.

B) Ecological-functional role of agaves in agroforestry terraces.- Some species of Agave in these systems are hosts to larvae of some lepidopteran species. These larvae have specialized to hatch, feed, grow, and find refuge on the tissues of agaves and depend completely on their existence to complete their life cycle. These larvae have been used as food by many cultures. In agaves other animals such as rodents, lagomorphs, and some reptiles also find shelter and when agaves bloom, they provide food to several insect, bat and bird species. The flowering stalks are perching and nesting sites for many bird species (see Figure 3). Some species defecate plant propagules that could be incorporated to the system.

C) Utilitarian attributes of agaves in agroforestry terraces.- These systems integrate the cultivation of diverse grains that are sown in the terrace structure under the shelter of agaves, therefore this structural component is at the same time a source of multiple resources. Regarding this issue the most important uses reported were aguamiel and fermented beverage (pulque), edible, fuel and provision of edible insects the most important ones (Figure 4) (^{Blanton 1972}, ^{Martínez-Saldaña et al. 1993}, ^{Hard et al. 1999}, ^{Martínez-Saldaña 2007}, ^{Borejsza et al. 2008}). In the past, large metepantle extensions were linked to great civilizations. The gathering of aguamiel in these systems represented a source of water in those relatively semiarid zones of the Mexican Plateau, as well as a source of food with high nutritional content. Moreover, the flowering stalks were elements for construction, while the thorns and teeth were employed to produce sharp instruments for sewing and performing rituals. The fibers were used to spin and sew textiles, the leaves for construction of roofs in the manner of tiles and when dry, these same leaves could be used as fuel for cooking food. Such was the versatility and importance of this resource that the plant was worshipped and even deified in the Aztec worldview. In contemporary times, the gathering of aguamiel and pulque for commercialization has radically diminished since the second half of the past century (^{Álvarez-Ríos 2015}). Nevertheless, currently these systems can be found in large extensions within the country in the states of Tlaxcala and Hidalgo, where resources such as aguamiel and pulque are collected, as well as edible insects for direct consumption by households and for commercialization. Another activity that characterizes this region is the use of agave leaves to prepare barbacoa de borrego (sheep barbecue), being sheep, a traditional animal managed in this area. The barbacoa is prepared in a pit oven in which the meat is covered with agave leaves, which serve as insulation from the direct heat of the ashes and give this regional dish a special taste.

D) Management.- The multiple individuals of agave that integrate this AFS have been obtained, selected and propagated asexually, through transplanting of stoloniferous shoots of the mother plants that were used and whose lifecycle has come to an end. This type of management is practiced in the case of domesticated species and their varieties: exchange of plants of other regions with similar management is performed by inhabitants with the intention of incorporating variants with different attributes. In the case of wild species, juvenile individuals may be transplanted from the surrounding ecosystems or may be tolerated at the moment of removing vegetation in order to cultivate other crops, and also transplanted in the same field to form the contention lines that form the terraces.

Agroforestry systems in semiarid zones: Melgas, apantles and coaxustles in the Tehuacán Valley, Puebla.- This type of AFS was recorded in 7 studies and included the presence of species like Agave salmiana var. ferox, A. scaposa, A. marmorata, and A. potatorum, with at least 9 use categories (see Appendix 1. It is in the semiarid zones of the Tehuacán-Cuicatlán Biosphere Reserve, which is inhabited by communities of Popolocan and Nahuatl ascent. All Agave species mentioned grow wild in the ecosystems within community territory. In these agroecosystems, a considerable number of individuals from species that form part of native forests are tolerated, promoted and/or protected due to the different benefits that can be obtained from them, agaves being the most precious elements.

Within these systems, agaves have the main function of limiting plots of land and constitute live fences to prevent the passage of cattle into the milpa (Figure 2). Agave potatorum (papalometl) and A. marmorata (pitzometl) are used in the community to produce alcoholic beverages like mezcal and pulque which have in recent years diminished due to extraction of individuals from populations of these species. Therefore, the authorities of the Biosphere Reserve have intervened to influence the communitarian authorities so as to establish a prohibition of extraction/felling of A. potatorum. Available literature reports that in some AFS of the Tehuacán Valley there exist the necessary conditions for this species to grow, given the species needs for nursing plants to germinate and establishment (^{Rangel-Landa et al. 2015}). It is within these systems where various species with different nursing qualities can be found, such as diverse bush species that are tolerated as part of agroforestry practices. These systems are also propitious spaces for seed dispersal by animals. The existence of proper conditions is very important for the conservation of these delicate interactions. Wild and cultivated agave extraction for mezcal production and sale has high cultural importance in this community, for it is not only consumed in patronal fests, but also as a remedy or stimulant for the hard labor in the fields. There is high demand for mezcal produced in this locality, and it has already a regional market, which means economic incomes for the families that produce it (^{Torres-García 2009}, ^{Moreno-Calles & Casas 2010}, ^{Torres-García et al. 2013}, ^{Delgado-Lemus et al. 2014a}, ^{Torres-García et al. 2015b}). Agave marmorata is employed to make cough syrup, pulque and mezcal, the flowering scapes are used in Easter to adorn churches, houses, and streets, as well as for making bird nests in houses; flowers are also consumed (the flower buds are called cacayas) and leaves are used as fuel (mezontete). Another singular species in these ASF is A. scaposa, a common species that is generally found as part of agroforestry practices like hedgerows and live fences, with the main purpose of retaining soil. This species has the highest abundance dominance in milpa-chichipera ASF. Also, its floral scapes are highly appreciated for house construction due to a scarcity of trees with straight trunks (Figure 4). In San Luis Atolotitlán, there exist rules that establish that in order to cut a flowering stalk, it needs to have blossomed and freed its seed, allowing for its natural regeneration, considering the biotic interactions as well that occur in the flower, which is visited by multiple nectarivorous species of insects, birds, and bats. It is also very important for the culinary culture of this community, since it is the habitat of a highly appreciated edible insect called condacho, of the species Aegiale hesperiaris Walker. These larvae can be found in the inner part of the succulent base of the leaves of this agave, and to extract them it is necessary to cut the leaves with much care so as not to harm the larvae. In this process agaves, which are in general those that have not blossomed, may be harmed, causing their death. Given these risks, rules were established by the community, allowing for the extraction of these larvae only one or two days in the year in the month of June (Figure 3 and 4) (^{Moreno-Calles & Casas 2010}, ^{Moreno-Calles et al. 2011}, ^{Moreno-Calles et al. 2016a}).

Newly established agroforestry systems. Agrosilvopastoral systems and agaves in Jalisco.- On the foothills of the Nevado de Colima and the Volcán de Fuego in the Zapotitlán de Vadillo municipality in the community with the same name, it is possible to find some experiences of integrated management of mezcal agaves. This region continues a tradition of more than 300 years in the production of mezcal, tuxca or mezcal wine, spirits based on the fermentation of two species, one wild Agave angustifolia and the other with incipient domestication A. rhodacantha. In the beginning of the past century mezcal production in the zone was sustained by the extraction of wild agave populations in the tropical dry forest of the region, mainly A. angustifolia. It was during the 1990´s that these wild populations began to diminish. Considering this fact many families began to select plants with attributes desired for mezcal production and took them from wild habitats to cultivate them in their agricultural systems. A particular experience in Zapotitlán de Vadillo is that of one family that has developed an integral cultivation system that alternates around 14 wild varieties of A. angustifolia with corn, bean, squash, and other annual products, as well as with other forest elements that have been tolerated within parcels, such as pitayas (Stenocereus queretaroensis (F.A.C.Weber Buxb) which provide edible fruits, mezquites (Prosopis laevigata (Humb. & Bonpl. ex Willd.) M.C.Johnst., species whose sweet pods are used as forage or for human consumption, among other uses and huamúchiles (Pithecellobium dulce (Roxb.) Benth.), which are trees that provide shade to people and cattle (Figure 2). These areas are also used by goats that feed on the multiple weeds and forage that grows in this system. Of the two agave species present in this system, around 14 varieties of A. angustifolia, have been identified as having been obtained from the wild, and reproduced in this system through stoloniferous shoots, and transplanted in lines of only one variety (^{Vargas-Ponce et al. 2007}, ^{Vargas-Ponce et al. 2009}). There are two varieties of A. rhodacantha identified by people, who mention that they are only known as cultivated varieties, and these have evidence of domestication, mainly due to the size of individuals, the length of their leaves and the use that they had in past times for fiber provision. Their traditional names also evidence their use, because they are commonly known as ixtero verde (ixte or ixtle is another way of naming the fibers that come from Agave) and ixtero amarillo. Seven use categories have been registered for this species, the most important being mezcal production, followed by their use as live fences, food, condiment for barbacoa, medicinal, fiber and as a fermented drink (see Appendix 1). Currently, mezcal production in this region depends mainly in the production of agaves from agricultural lands that were established as a response to the shortage in the past. The production of mezcal wine or tuxca in this region is also a cultural activity of economic importance that has prevailed for many generations and in recent years, has reached commercialization channels at the local and national levels.

Agave agroforests in western Mexico.- This type of management has been observed and documented for species such as A. cupreata, A. inaequidens, and A. maximiliana. Although these are multipurpose species, they are currently used mainly for the preparing of spirits from mezcal and raicilla in Michoacán and Jalisco, respectively. This type of management has evolved in recent years. Spirit producers and managers of these species remark that mezcal in Michoacán and raicilla in Jalisco have been produced for at least 300 years. However, these species only started to be reproduced and cultivated in the past 15 to 20 years through sexual propagules, the only effective form of reproduction for species of the Crenatae group. The main reason why people started growing this crop was as a response to market pressure which caused the decrease in wild populations, as well as the growth in the number of producers in these zones.

In the case of Agave cupreata in the state of Michoacán, the cultivation of this species began approximately 20 years ago, mainly in the municipalities of Madero, Charo, Tzitzio, and Morelia. Cultivation of A. cupreata in this region was a reaction to pressure over the resource, which was used for making mezcal, and this activity determined a critical decrease of its wild populations. Experimentation with plant production in nurseries through seed sowing, started in the municipality of Madero. The tendency was to establish monocultures, similarly to A. tequilana; however, there are other cases in the region principally in Tzitzio and Charo, where A. cupreata is spread through agroforestry practices, through seeds in rustic nurseries. The main purpose of the plants grown in these nurseries is to reforest through plantations with a very high density of agaves, in places found on the transition between oak-pine forests and tropical dry forest, where relicts populations of these species can be found, and can be taken as a sign of the ideal habitat for production of this agave species. In these forest areas clearings of bushy species take place and some tree species have been tolerated, such as tepehuajes (Lysiloma spp.), papelillos and copales (Bursera spp.), anonas (Annona sp.), palo dulce (Eysenhardtia polystachya (Ortega) Sarg.), and palms (Brahea pimo Becc.) among others (Figure 5). Cattle are also allowed to feed in these systems, having the care of letting cattle feed where agaves already have a proper age, size, and configuration that allow it to resist being stepped-on by cattle. Although the predominant use in of A. cupreata in Michoacán in the present is the production and marketing of mezcal, nine other categories of use have been registered (see Appendix 1). In order of importance these are: as food, medicinal uses of the baked or grilled stem, the use of flowers as attractors for deer hunting, as live fences, ornamental, and ceremonial uses, and as a diversity of instruments and utensils (nests for little parrots, seats, thorns to take out splinters, caps for bottles). The bagasse that remains from mezcal production is used as a biofertilizer. Another highly demanded use is the commercialization of juvenile plants for the establishment of plantations to make mezcal, and the commercialization of seed, a product that can cost between US$210 and US$263 ($4000 and $5000 Mexican pesos) per kilo.

Figure 5 Agave agroforests. A, B) Agave cupreata agroforests in the municipality of Tzitzio and Charo, Michoacán, C) Agroforests of A. maximiliana in the municipality of Mascota, Jalisco, D) Agroforests of A. inaequidens in the municipality of Queréndaro, Michoacán (Photos: I. Torres-García). 

Agave inaequidens has a similar history. In the municipalities of Indaparapeo and Queréndaro -with around 40 maguey managers and mezcal producers- around 20 years ago producers began to establish monocultures of agave as a response to the shortage of wild agave due to a faster extraction-to-regeneration rate, following the production tendency of tequila maguey. Nevertheless, there exist wild populations managed in situ which are reforested with individuals produced in rustic nurseries. Several management practices contribute to the conservation of this species. Among these practices it is possible to find the tolerance of agaves when clearing the underbrush in forest patches of pine-oak and pine-fir, the protection or promotion of specific individuals when transplanting to sites with better conditions for growth, and the dispersion of seeds by scattering on favorable sites for germination -in total 10 types of in situ management practices (Figure 5). A total of 16 use categories and 34 specific uses have been registered for this species of which the most important by order of mention is the making of mezcal, which has had a boom in the past 10 years (see Appendix 1). However, to a lesser extent it also has edible and medicinal uses, it is used as insulation and as condiment for making barbacoa, as veterinary medicine, for the extraction of aguamiel and pulque, as live fences, forage, construction material, fiber extraction, sale of juvenile agave, erosion control, as bait to attract deer for hunting, for ornamental uses, and as utensils (^{Torres-García et al. 2015a}).

In the case of Agave maximiliana in the region of Mascota, Jalisco, registries mention that 15 years ago the rates of extraction of wild populations of this species determined its critical decrease, promoting the establishment of commercial monocultures in deforested areas and abandoned agricultural lands. Some managers have established agroforests with agaves such as the ones mentioned above; these sites result from the clearing of forests and the planting of juvenile agave that have been grown in rustic nurseries in pine-oak forest zones (Figure 5). Inhabitants recognize the incidence of frost in the zone, a fact that affects species found in open areas with no canopy cover. It is in these areas that inhabitants have established this crop, trying to reproduce the natural conditions of the populations that grow under tree canopy in order to keep them from frost. For this species, 11 use categories have been registered, of which the most important is the making and marketing of raicilla, (a spirit that is going through a market boom) followed by uses as medicine, fuel, forage, marketing, and bartering, as fertilizer, as ornament, as insulation and condiment, as a fermented drink, to retain soil and as bait for deer hunting (^{Huerta-Galván 2018}).

Agave agroforest management in Guerrero. In the Mountain region of Chilapa, Guerrero, there exists a management experience that has been developing for many years. This experience has been the fruit of the interaction between the community of Nahuatl mezcal producers of Acateyahualco, Guerrero and the non-governmental organization GEA A.C. (Grupo de Estudios Ambientales y Sociales). GEA has nearly 20 years carrying out arduous participatory action research that has had a positive impact in the community´s management of their territory and its natural resources. This community has developed an important management strategy, based on ecological information generated through demographic studies of the local wild Agave cupreata populations, which integrates the biological and reproductive dimension of this species in the design and application of annual systematic monitoring schemes. Indicators regarding the structure of wild agave populations are analyzed in community assemblies. In this way, the community decides how many mature agaves can be extracted based on the harvest thresholds established in the demographic models; that is harvesting that does not alter the recruitment rates in order to allow for population equilibrium. This monitoring scheme allows maguey to be harvested in a period of one year, and it specifies that it can only be processed by the community of Acateyahualco to satisfy its demand of mezcal. At the same time, the community practices a rotation system of the extraction sites, by establishing different stands within natural vegetation, where they carry extraction and monitoring. This extraction model implies that the sites where extraction happens must be shifted over time in order to assure that natural regeneration of the species happens in its natural habitat, allowing individuals to naturally blossom and disperse their seeds. They also have a systematized management of the cattle that grazes on this territory. The management of cattle assures seed production, dispersion, and establishment of new agave generations, at the same time that pollination processes are promoted. On one hand, the restriction of cattle to enter plots where mezcal seeds are germinating protects these seeds from being eaten. On the other hand, this restriction allows tender inflorescences to blossom in order to let pollination processes occur. When seeds germinate and there are seedlings on the fields, cattle may step over these seedlings, so the entrance of cattle into these stands during these susceptible stages is restricted. This species is mainly pollinized by bats of the genus Leptonycteris and given that this agave does not produce stoloniferous shoots, seeds are the only way it can reproduce. This is an example of community management of a collective resource through a very interesting collaboration between Academia, NGOs and rural communities to sustainably manage natural resources, ecosystems and territories (^{Illsley et al. 2007}, ^{Martin et al. 2011}, ^{Illsley et al. 2018}). Forest areas next to this community are being conserved for being the natural habitat of Agave cupreata. This action contributes significantly to the conservation of diversity of accompanying species and ecosystem benefits that are determinant to the quality of life of the community. Mezcal is a very important part of local and regional culture: it is consumed in patronal fests and is one of the few cultural activities that determine a tangible economic income for the inhabitants of this community.

Discussion

In total, our study identified 31 species of Agave (of the 210 described, according to ^{García-Mendoza et al. 2019}), within traditional AFS and newly established AFS in Mexico; that is, 11 percent of total Agave richness. However, these are preliminary and surely underestimated data, for the research efforts have to the present focused on specific regions and ethnic groups, leaving out others that also have an important history of AFS and agave management. Moreover, adding to this bias in the regions and ethnic groups studied, the lack of studies regarding AFS and agaves is also because studies that concentrate on these topics are only very recently gaining importance and being performed (^{Moreno-Calles et al. 2016b}). Other problems also limit the analysis efforts of this study, such as the lack of studies that identify agaves to the species level. An explanation for this can be that Agave species are hardly collected to be put in a herbarium, or that the sampling does not always coincide with the presence of floral structures, and above all, that the preparation of herbarium samples requires dedication and specialized techniques, or that species under agroforestry management are not of interest to wider groups of researchers. The lack of herbarium material makes it difficult to identify species, moreover when these are domesticated cultivars.

Agave are indisputably one of the most important groups of resources for the survival and development of Aridoamerican and Mesoamerican cultures. Just as ^{Gentry (1982)} reported in his works dedicated to this group of plants, focusing on the symbiosis Agave-human, the present study also reports this symbiosis, which is reflected in the multiple utilitarian, cultural, evolutionary and socioeconomic expressions studied. Magueyes, agaves, mezcales, lechuguillas, among others (Agave spp.), have an elevated number of uses (22) at the local level compared to other plant species. Agaves are a crucial part of the lives of the communities, providing nutrition, energy production, construction, making of medicinal remedies, as well as an important base for the generation of economic resources needed in a rural context. It is of interest that in Figure 6 these species have a greater number of uses in agroforestry milpas, family homegardens and terraces in comparison to agroforests destined to produce mezcal. This tendency is worrisome because it not only represents the loss of ecological and biocultural richness, it also represents the loss of the multiple functions of these species as they are integrated into global emerging markets, as is the case for mezcal, edible insects or the so-called superfoods markets, as in the case of agave syrup. This situation poses a dilemma about the production models where the satisfaction of local rural necessities (food, health, housing, fuel, preservation of soil and water) competes with the global urban “necessities” like recreation with alcoholic beverages or alternative nutrition through so-called “superfoods”. Many species show clear signs of domestication and the archaeobotanical, paleontological, historic, and contemporary and actual evidences suggest a long history of their importance within agricultural, forest and agroforestry systems. According to our work, 12 of the 64 existing cultural groups present in the territory (^{Boege 2008}) have incorporated and maintained agaves in ethnoagroforestry systems and various mestizo groups also use these elements as part of their management systems. It is possible that due to the wide distribution of this genus of plants in Mexico many more cultures use them in their agri-food systems.

Figure 6 Comparison of the percentages of mentions of the registered use categories in this study for agave present in various agroforestry systems. For comparison purposes they were separated into: a) use categories with the highest number of mentions, b) use categories with the least number of mentions. 

Homegardens represent one of the oldest, and most intimate agroforestry management systems, given that in general they are adjacent to houses and they play many roles, from aesthetics, ornamental and utilitarian purposes, such as serving as food and medicine. ^{González-Jácome (2009)}, determined that homegardens are living laboratories where selection processes and hybridization processes may have taken place, for it is in these places where species with disjunctive distributions found and coincided with each other. These AFS are generally vast in diversity and surely, processes like the ones mentioned above took place in these places. In this context, one of the species most documented for the Mexican Southeast is Agave fourcroydes, species that is recognized as the product of the domestication of A. angustifola (^{Colunga-GarcíaMarín & May-Pat 1997}, ^{Colunga-GarcíaMarín & Zizumbo-Villarreal 2004}).

Terraces like homegardens, are systems with an ancient history in several regions and cultures in our country. There is palynological and archaeological evidence of this extensive practice related to the development of some highly populated Mesoamerican cultures (^{Blanton 1972}, ^{Evans 1990}, ^{Trombold & Israde-Alcantara 2005}, ^{Borejsza et al. 2008}). Nevertheless, the extension and use of this type of system has diminished at a significant and accelerated rate since the last half of the 20^th century. The main reason for this is the decay in the consumption of pulque in a number of places in Mexico, but mainly in Mexico City (^{Álvarez-Ríos 2015}). The theft of the cuticle of the maguey pulquero leaves for the making of mixiotes also discourages managers of this species (^{Moreno-Calles et al. 2016b}).

The existence of a gradient of management applied to different species of Agave registered in agroforestry systems is evident. This gradient can be observed from in situ to ex situ management (^{Casas et al. 2007}, ^{Blancas et al. 2010}), which also expresses a complexity gradient. In situ management; in the case of community forest management, no reforestation nor complex manipulation actions are performed; the work is already strategic, since it incorporates ecological techniques appropriated by inhabitants, and a decision-making process through the community assembly, to decide the extraction rates based on models. Under this management regime, the forest is not radically impacted, only when mature individuals are harvested, and while transporting them to the places where mezcal is produced. In agroforests, there is an impact directed mainly at the understory vegetation in order to establish agave produced in nurseries, which implies greater effort and planning, besides harvesting. Ex situ management: it is in homegardens and terraces where managers apply a greater complexity of management practices, since these are environments with a high presence of domesticated and cultivated species. These places also count with several tolerated wild species, as well as wild elements that have been either transplanted, tolerated or promoted, from adjacent natural systems into these agroforestry systems. The presence of these tolerated or promoted wild species in homegardens and terraces also implies the accompanying development of agricultural labors and the maintenance of lines or borders of agave within these systems.

Challenges and perspectives in the management of Agave in AFS in Mexico. The loss of Agave species and the abandonment of these agroforestry systems is a phenomenon related to multiple factors, some of them associated to migration and transculturation. The collective TEK of communities has suffered losses, and above all the loss of the practice of this knowledge. Another determining factor for the abandonment in the use of agave, mainly the fibers, a very important use in the past centuries, has been caused by the production of cordage by the hydrocarbon industry, polyethylene, etc. This industry came to displace the making of cordage made with agave in practically the entire Mexican territory and determined the fall of a very important economic activity for the Yucatán peninsula in the past century. However, the preservation of Agave fourcroydes in family homegardens is an example of how cultures treasure resources, those same resources that may have been displaced by market tendencies and which are maintained and managed in these environments due to utilitarian and aesthetic reasons, although at a smaller scale, but fulfilling biocultural and ecological functions in the present.

The crisis of distilled spirits in Mexico, the market tendencies and the boom in mezcal demand are determining the establishment of monocultures, which are systems that in the long term become dependent on agrotoxics, and determine many biological, environmental and sociocultural losses. The establishment of new agroforestry and forest management forms described in this study are alternatives to produce raw material for this industry. They also promote the conservation of part or the whole of biodiversity of the ecosystems where they are found. At the same time, all this biodiversity represents an opportunity for designing future strategies for management and conservation of such valuable genetic resources. The market tendencies could recognize -through labeling and publicity- those spirits that come from these types of management.

The recognition, valuation and promotion of this important group of resources within these management systems, beyond the production of spirits, is very important in the effort to guarantee the availability of the different types of foods and raw materials for productive activities. As well as considering the sub-products that are disposed of in the production of spirits, such as leaves, bagasses, and vinasses. The leaves are left in the fields were harvesting of the agave heads occur, bagasses are the fibers that are disposed after distillation (^{Martínez-Gutiérrez et al. 2015}) and vinasses are acidic liquids that are also disposed, mainly to water bodies, after distillation (^{Robles-González et al. 2012}). These sub-products which represent a development potential in agriculture, food, and pharmaceuticals and an alternative to complement the economy of producers (^{López-Romero et al. 2018}). Likewise, it is important to guarantee the preservation of important elements of the identity of the communities and cultural groups that host this diversity.

Agroforestry systems are spaces where wild and agricultural diversity coexist (^{Casas et al. 1997a}, ^{Moreno-Calles et al. 2013}), and in Mexico, agaves are very important components of these systems. Commonly, Mesoamerican agaves constitute complexes of wild and domesticated taxa whose identity also represents a constant scientific challenge. In this way, including agaves in the agricultural or forest component is frequently very difficult. Domesticated agaves are part of the agricultural component, while wild agave is part of the forest component. This definition, the lack of research and the difficulty in identifying agave and their wild or domesticated status make it difficult to arrive at conclusions. This first approach allows to identify: (1) the structural, functional and cultural importance of Agave in agroforestry systems, (2) the importance of such spaces for the conservation of these species (wild and domesticated) and agave varieties, ergo, their role in in situ conservation of these genetic resources, (3) the need to do in-depth research about the composition of these systems and the related links to agave management, (4) the importance of going in-depth into the management techniques for agave in these systems as a basis to take advantage of the techniques developed traditionally in conservation programs in forests and agroforestry systems, (5) the value of studying these systems as referents of their value in the conservation of biodiversity and of biocultural heritage.