Societies in the world have practiced the cultivation of arboreal species in agricultural spaces in close relation to the main purpose of food production (Steppler & Nair 1987, Nair 2011). In tropical America, farmers have traditionally simulated forest conditions in their crop fields, mimicking the structure of forests by planting species with different growth habits (Steppler & Nair 1987). Agroforestry systems "combine agricultural crops, tree crops, and forest plants and / or animals simultaneously or sequentially, and applies management practices that are compatible with the cultural patterns of the local population" (Bene et al. 1977). These systems are distinguished by integrating agricultural, forestry and cultural diversity (Moreno-Calles et al. 2016) and have been maintained over time to produce food, fiber, and fuel, among other essentials (Power 2010, Boafo et al. 2016), which is why they are considered the best option for food security and biodiversity conservation (Segnon et al. 2015).
Multi-strata agroforestry systems have shown that they can contribute to the conservation of tropical biodiversity when forests are maintained within the agricultural landscape (Harvey & González-Villalobos 2007). Among the main agroforestry systems are agroforests, home gardens, terraces, and shifting cultivation or slash-and-burn agricultural systems (Moreno-Calles et al. 2016); in addition, they are characterized for their plant diversity in form of polycultures and agroforestry patterns (Rosset & Altieri 2018).
In Mexico, agroforestry systems are part of a biocultural heritage (Moreno-Calles et al. 2013) where woody species in agricultural spaces are used as fruit trees, firewood, shade, ornaments, respect for nature and other environmental benefits (Vallejo et al. 2014). This cultivation system is used in the milpa in Yucatán, where the farmer selects some suitable woody species for construction, trees, fruit trees and shade (López-Forment 1998). In studies carried out in Mayan family gardens, a mosaic of stages is observed as in natural vegetation, and fulfills the function of protecting the resources of forest vegetation and the processes of the natural ecosystem of the area (De Clerck & Negreros-Castillo 2000).
Another important agroforestry system in Mexico is the traditional shaded coffee plantations produced mainly by small producers of indigenous communities and located in areas of biogeographic and ecological importance (Moguel & Toledo 1999). In the coffee plantations of the Sierra Norte de Puebla it was found that 80 % of native plants that are mainly used as medicinal and edible (Martínez et al. 2007). In the Sierra Sur of Mexico, the set of heterogeneous plantations of coffee plantations has proven valuable for the conservation of plant diversity (Bandeira et al. 2005)
At present, the conservation of areas with biodiversity is necessary, but also the satisfaction of human needs with the development of sustainable ways to use the resources that local ecosystems provide (Sarukhán et al. 2009). Traditional agroforestry systems can help maintain a higher level of biodiversity compared to practices that require greater transformation of ecosystems (Schroth et al. 2004, Bhagwat et al. 2008).
In this context, the importance of plant resources has been evaluated quantitatively through ethnobotanical indices, with use value (UV) being the most widely used indicator (Phillips & Gentry 1993 a,b, Ribeiro et al. 2014, Shaheen et al. 2015, Kunwar et al. 2016, Lopes et al. 2017). The use of plant resources is influenced by socioeconomic factors, with age, gender, schooling, language and economic activity being the most influential (Saynes-Vásquez et al. 2013, Andriamparany et al. 2014, Laleye et al. 2015, Segnon et al. 2015, Kunwar et al. 2018). In this study we define primary economic activities as those involve natural resource extraction and management, whereas tertiary activities are the providing of services.
In this study, the use value index was used to determine the importance of useful plants in three agroforestry system (home gardens, milpa and coffee plantations) in the town of Las Delicias, municipality of San Juan Juquila Vijanos, Sierra Norte. This region has great biological and cultural diversity, which is why it is recognized as part of a priority Terrestrial Region (number 130, Arriaga-Cabrera 2009) and Biocultural Region (number 17, Boege 2008), classifications that consider centers of origin, species diversification, and the presence of agroecosystems with domesticated native agrobiodiversity. Therefore, it is important to know the plant diversity in these agricultural spaces, the importance they have and how people manage them. Thus, this study aims to answer the following questions: 1) What plants of the three agroforestry systems are used in this Zapotec community, and what is the UV of these species? 2) What agroforestry system contains plants with the greatest UV? 3) What floristic similarity exists between agroforestry systems? 4) What sociodemographic factors influence the distribution of knowledge of plants in the community of Las Delicias?
Materials and methods
Study area. The locality Las Delicias is located in the communal lands of the municipality of San Juan Juquila Vijanos, Sierra Norte (Figure 1). Groups of people of Zapotec culture (INEGI 2005) settled there; therefore, the inhabitants have deep traditional knowledge about use and management of natural resources (González 2001). It occupies 62.02 km2; 77.80 % of the vegetation corresponds to forest, 20.20 % to agriculture and 2.0 % to human settlements (INEGI 2005). Because land ownership is communal (González 2001), the inhabitants can own land in any part of the municipality.
Location of Las Delicias, in San Juan Juquila Vijanos, Sierra Norte, Oaxaca, Mexico.
The climate is semiwarm humid and temperate wet (INEGI 2005). Precipitation ranges from 1,200 to 2,000 mm (INEGI 2005), is common throughout the year but reaches maximum levels in summer (Pérez-García & Del Castillo 2016). Middle temperature ranges from 16 to 22 °C. The altitude ranges from 900 to 2,400 meters above sea level, The landscape is composed of riparian vegetation, pine forest, pine-oak forest, cloud montane forest, secondary vegetation and cultivated areas like milpa and coffee fields, (Del Castillo & Blanco-Macías 2007, Pérez-García & Del Castillo 2016).
Of the above, shade-grown coffee represents the majority of economic income for the local farmers (Nader 1964). The mosaic of natural vegetation with interspersed cultivated areas (Figure 2) is due to slash-and-burn systems (Pérez-García & Del Castillo 2016).