Introduction

In Mexico, production in the backyard subsists mainly in rural areas, although with a tendency to disappear, due to the pressure from urbanization, as well as expanding the range of products produced by conventional farming systems (^{Murillo et al., 2010}). In the case of Mexico, there is a decline in the agricultural development of small farmers, mainly due to the reduction of state support in the maintenance of the agricultural research and extension, and the support credit and capital to invest on inputs and infrastructure necessary for the implementation of innovative technologies. This has caused farmers to leave their place of origin, migrate temporarily or permanently in search of paid employment, enabling them to earn an income for the support of the family and to finance their agricultural activity, trying to survive and face poverty (^{Chávez, 2007}).

Under these circumstances, the backyards are most likely suffering changes in uses and modes of production as well as changes on plant, and animal diversity, and the area devoted to it. Recent figures provided by the ^{CONEVAL (2012)} regarding poverty in Puebla. In 2008 it was recorded that 64.5% of the population lived in poverty and 18.2% live in extreme poverty. In 2012, the proportion of people in poverty is similar with 64.4% and 16.2% in extreme poverty. It is observed that poverty in the State of Puebla is higher than the national average. For both periods Puebla is located in the third place with the highest poverty and fourth in extreme poverty.

In the town of Huejotzingo, 61.3% are in poverty and 11.8% of these are located in extreme poverty, 25.6% is vulnerable for some social deprivation; From the indicators of social deprivation, 27.7% is about access to food and economic well-being 23.1% of the population below the minimum income line of well-being (^{CONEVAL, 2010}). Peasant households, have a strategy for survival, diversification of their activities, this multi-activity and production system grown perennial and annual species associated or overlapping (^{Álvarez, 2006}); and this diversification moves in spatial domain; on farms and in backyards of rural domestic units. The backyards are the last available space to survive, develop and exploit biodiversity (^{Dávila, 2010}).

The backyard is an agro-ecosystem that is traditionally located near the housing units in rural communities because of the large amount of labour required and the high diversity of species that are cultivated and preserved, both spatially, taking advantage of the small surface area of the horizontally and vertically; and from the temporal aspect, obtaining food through the year; not dependent on agrochemicals for maintenance and does not tend to standardize the habitat (^{Guerra, 2005}).

Traditionally it has been used by small population centres around the world and although mainly arises to meet the demands of family consumption, also surpluses are exchanged or traded locally which allows families to have extra income that guarantees to make it against some financial contingencies (^{Murillo et al., 2010}). The standard of living of rural communities are generally located at subsistence levels.

The use of agro-ecosystems taking place in backyards, provides options for conservation of plant biodiversity while ensuring food production (^{Cohen and Potter, 1991}). In these production systems, accounting and administrative management is scarce; this situation causes complicating calculation of production costs and profits, (^{FAO, 2004}; ^{Eslava and Coromoto, 2005}). Women have played an important role in the conservation and use of diversity of native, wild, domesticated or semi-domesticated species, actively contributing and participating in production of their communities (^{Vieyra et al., 2004}.) as well as in the transmission and preservation of traditional knowledge and farmers' knowledge among members of peasant households or interaction with neighbours and family. Biodiversity is increasingly dependent on human society as a survival strategy.

The specialization in production is a key issue, because it has a lower cost to produce a large amount of a single product, which few numbers with a larger number of products (^{Toledo, 1998}). ^{Escobar (2000)} states that diversity is the result of the interaction of the ecosystem and culture, creating rich agro-ecosystems adapted to local conditions.

Based on the foregoing, the objective of this research is to establish the relationship between perceived economic benefit from the sale of product generated in the backyard and destination of such income, the surfaces intended for backyard and index of plant diversity in the community of Santa María Nepopualco, Huejotzingo.

Materials and methods

Study area: the present study was conducted in the community of Santa María Nepopualco, assistant board of Huejotzingo, Puebla, located at the geographical coordinates 98° 29' west longitude and latitude 19° 06' 09' 14'', and of 2 540 m of elevation with a total population of 3 183 people, of which 1 540 are male and 1 643 female and has a total of 604 households (^{INEGI, 2010}).

Field work started on January 2011, defining the backyard as the unit of study, the primary sources of information were the members or heads of peasant households (UDC). For the study sample size was defined based on the total number of N= 604 families in the community and considering a confidence level of 95%; for this purpose we use the methodology described by this ^{Delelis (2005)}. The procedure for calculating the sample size was obtained by considering the following formula:

Where: d= 10% accuracy; Z= 1.96 (95%); S²n= maximum variance (0.25); N= 604 UDC; n= 83 assessment tools to apply.

Thus, by applying the formula proposed, a sample size of 83 UDC was obtained. In order to be more precise we decided to increase the size of the sample, making a total of 123 UDC in the questionnaires, integrating parameters and indicators for detailed information on each UDC applied. The assessment tool was designed to consider indicators and parameters of interest and included questions with open answers, multiple choice and Likert scale with distributed values on a scale of 1 to 5 (^{Cañadas and Sánchez 1998}).

In order to understand and describe the existing plant diversity in the community backyards, we proceeded to the following:

The silhouette of the backyard was drawn indicating linear meters of the strokes. Within this draw was included the vegetal content and other plant components in the yard space, in order to make a stroke of spatial arrangement in which the operation of the system works. Each UDC randomly selected, performed the count of the number of plant species per yard or indices of species richness (S). With this value, and in order to quantify plant diversity, we proceeded to use Weber and ^{Shannon indices (H') (1949)}; and based on the counting of plant species index we obtained the vegetal diversity index as well the specific use of vegetal species.

For this case, it was considered as sampling units the UDC and as units of diversity and varieties within crops that were recorded in every home.

For which the following formula ^{Shannon-Weber (H') (1949)} was used:

Where: S= n umber of species (species richness); p_i= proportion of individuals of the species i with respect to all the individuals (i. e. relative species abundance of i):niN n_i= number of individuals of the species i; N= n umber of all individuals of all species.

Thus, the index takes the number of species in the study area (species richness) and the relative number of individuals of each of these species (abundance).

For knowing the diversity distributed vertically in the backyards, we proceeded to divide species in the herbaceous, shrub and tree strata. Thus, we divided the species into three categories located by size (^{Marín, 1997}) as: type I (RG-I): 10 cm to 1 m in height, type II (RG-II): 1.01 to 3 m height, type III (RG-III): larger than 3.01 m in height.

For the results of horizontal distribution of the plant species we listed and divided in 9 categories or types: ornamental, fruit, medicinal, spices, vegetables, cacti and agavaceas, trees and shrubs, fodder and seeds. We used the Weber and ^{Shannon (H') (1949)} formula for obtaining the resulting plant diversity index of the division of the nine categories or types equally. On the other hand, the number of spices in each UDC and total transfers was recorded with the help of Ecosim700 program, a diversity index (H ') was obtained for the community.

Results and discussion

Based on the study, the UDC of the community Santa María Nepopualco, we observed that are integrated with an average of 4.4 people, with the at least one person and a maximum of 8 members per family. 45.5% of respondents are male and 55.5% female, elementary school is the most representative with 66.9%.

Backyard features

The average backyard area is 29.5 m². 47.52% of the respondents indicated that there have not been any changes in the area, 2.9% had increased their area and, 49.5% decreased the area used for the backyard, making the main reason for this reduction, the expanding of homes or new construction. Economic, human, social and infrastructure factors differentiate the biodiversity in the backyards (^{Cruz, 2011}).

Regarding the perception of respondent on the importance and economic contribution of the backyard to the UDC, the present study found that, backyard activities contribute 19% with "very little" to the family income, 6.5% of the UDC reported "half" of income and 2.4% of families considered the backyard brings to the family economy "more than half" of the family income. It is noteworthy that 71.5% of respondents indicated having nothing or "almost nothing" of income of backyard activities to the family unit. It is observed that this practice is not oriented as an economic element that deprives the sale of products rather is subsistence-oriented; meeting the food needs with harmless and nutritional characteristics (FAO, 2006). But in the end implies a strong support to the family budget, not disburse financial resources to purchase these supplies.

Backyard activities are among the agricultural activities in the community. This activity allows the UDC for having an economy savings, since the sale of fruit and other products help to have extra income when surpluses are traded, getting families to meet immediate needs in a time of crisis; allowing them meet their social and religious commitments. Thus, by helping the economy of rural families, the activities and backyard products obtained are highly relevant when inserted within the local and regional markets (^{Schumann, 2006}), and help to the subsistence and reproduction of the production units.

The classification and related variables obtained with the CHAID technique are shown in Figure 1. The variable “saving” was best classified by the people that said backyards contribute to the family income. 6.5% of the people use their backyard occasionally. The income is used for saving, classified by some products selling. Regarding the variable selling some products, it was classified into two groups, for those who sell products of the backyard the variable that best classify was the surface of the backyard and for the node that did not sell any product at all, the best classified variable is the variable income that can be generated is the backyard for family support. He income generated in the backyard is regularly used as savings. Establishing a relationship of the income into savings by selling some of the products generated in the backyard and related to the surface they have, which corresponds to 20 to 40 m².

Figure 1 Relationship of perceived benefit of income from the backyard, bound income, backyard area and sale of any product. 

Plant diversity in the backyard

In the community study we found that alpha diversity (specified diversity index) is 130 species, with an index of diversity (H') of 3.45 bits. In similar studies made by ^{García (2000)} in backyards of Yucatán, recorded 156 species and an average H' Shannon value of 3.77 bits. In this study, the diversity indices were higher than those reported in studies performed other countries, like Thailand in the range of 1.9 to 2.7 bits (^{Gajaseni and Gajaseny, 1999}) or Indonesia with values of​ 2.79 and 3.71 bits (^{Christanty, 1990}), indicating the existence, prevalence and importance of a basic subsistence strategy underlying the design and use of the backyard of the UDC community study.

Vertical analysis of plant diversity, the layers present in the backyards of the study community; the most representative stratus was type I or herbaceous. In this layer 62% with 81 plant species, followed by the type II or shrub with 20% and 27 different species, and finally the tree type III with 11% represented by 22 (Figure 2). The fact that the herbaceous layer recorded the highest proportion may be associated with the characteristics of the study site, in order to have a humid temperate climate with rains in summer and by the time the fieldwork was conducted. In this regard, ^{Allison (1983)} reports for orchards or backyards non-tropical in Tlaxcala, 59.8% of the herbaceous layer, 26.8% of the trees, and 13.4% of the shrub layer, while for tropical gardens this author found in these strata, Tabasco represented 35, 43 and 22% respectively.

Figure 2 Vertical plant diversity in species Nepopualco Santa María. n= 123. 

For making the horizontal analysis of the plant diversity in the backyards of Santa María Nepopualco, the species were divided into 9 different uses, which are presented below by ranking higher diversity.

Within the ornamental 57 species were found with a diversity rate of 4.4 bits, highlighting the Rosaceae, Araceae, Lilaceae, Onagraceae and Astaraceae family, which represents 44% of the species found to be the highest proportion in backyards of the UDC.

With regard to fruit, 25 species of which a diversity index for fruit UDC studied was found at 3.8 bits, some families with the largest proportion are Lauraceae, Juglandaceae, Rosaceae and Malpighiaceae.

In the medicinal plants 15 species were recorded with an index of 3.6 bits, most notably the families Compositae, Asteraceae, Chenopodiaceae, Rutaceae, Labiatae and Myrtaceae. In this regard, a study made by ^{Martínez et al. (2006)} in 4 markets in the State of Puebla, of the species observed, 12 species are recorded from those found in this work.

Medicinal plants in the UDC studied, occupy the third category in abundance. According to the results of a significant proportion are identified as "healing" which shows that traditional medicine continues to be used by the population l (^{Guerrero, 2007}).

For cacti and agavaceas, 3 species were registred, which contribute in the backyard with diversity index of 3.3 bits.

Trees and shrubs that were found in the backyards were represented by 10 species with a diversity index of 2.8 bits, the most representative families were Pinaceae, Oleaceae, Cupresaseae and Palmaceae.

Vegetables grown in the backyards were 11 species with a diversity index of 2.5 bits, the prominent families for this use are Liliaceae, Cucurbitaceae and Solanaceae.

In plants commonly used as condiments for the villagers, they found 5 species with a diversity index of 2.4 bits, represented by families such as Lauraceae, Umbelliferae, Labiatae and Piperaceae (Table 1).

Table 1 Plant species for use and diversity index in backyards of Santa María Nepopualco. 

Usos	Especies	(%)	Índice de diversidad H’ Shannon (bits)
Ornamentales	57	44	4.4
Frutales	25	19	3.8
Medicinal	15	11.3	3.6
Cactáceas	3	1	3.3
Árboles y arbustos	10	8	2.8
Hortalizas	11	7	2.5
Condimentos	5	5	2.4
Semillas	3	4	1.5
Forrajero	1	0.7	0.6
Total	130	100	2.76

Fuente: encuesta en la comunidad de Santa María Nepopualco, Huejotzingo, Puebla, 2011. n= 123.

Of the plants used due to their seeds, in the backyard 3 different species were found, which provide an index of diversity of 1.5 bits. These include maize (Zea mays) family of grasses, beans (Phaseolus vulgaris) of the family Fabaceae and to a lesser extent like the broad bean (Vicia faba).

Within the backyard, we can only to find alfalfa (Medicago sativa) for forage purposes, which belongs to the family Fabaceae with a diversity index of 0.6.

Edible species are represented with 35%, with a value that is not specified by ^{Guerrero (2007)}, where the edible species predominated with 42% in the community La Purísima Concepción de Mayorazgo in the State of Mexico.

Conclusions

Economic activities identified in the community are based on agriculture, generating a collective work for all the members, taking care of their food security with the production of plants, this activity allows families to respond to social commitments and also generate an income by selling products.

The backyards of the community of Santa María Nepopualco are mainly characterized by the rich biodiversity in relatively small units, and the use of mechanisms for the handling of highly specialized and successful plants. The number of plant species in the UDC of the community under study relates to the activities of the head of the family and the income that accessed by the conditioned area for construction and backyard. The diversity of plant species in the community has remained constant over the past two decades, 50% maintained their backyards dimensions.

Plant species are represented by a horizontal ornamental and herbaceous in a vertical direction. The importance of the crop in the community considers different aspects, for this reason, researches should aim to reassess these systems holistically. The backyards are a tool of economic and nutritional support at home because they spread could be important for food security.