Introduction

The dendroenergy (wood energy) is all the energy obtained from solid biofuels, liquid or gaseous primary or secondary derived from forests, forest plantations, urban woodlands and trees in general. It represents the energy produced after combustion of wood fuel, such as firewood, charcoal, pallets, briquettes, etc., and corresponds to the net calorific value of the fuel (^{Guyat, 2004}).

The extraction and use of firewood negatively impact forest resources, either for self-consumption or sale (Ortiz, 2009). Most users of firewood in Mexico is concentrated in the states of Chiapas, Guanajuato, Guerrero, Hidalgo, Michoacán, Morelos, Oaxaca, Puebla, Quintana Roo, Tabasco, Veracruz and Yucatán (^{Díaz, 2000}), with an annual consumption of 38 million cubic meters (^{CONAFOR, 2007}).

Firewood extraction is a very present activity in the communities of Morelos. There are 45 species used for this purpose, corresponding to 7.5% of the useful plants, but the species most in demand are: tepemezquite or tlahuitol (Lysiloma divaricata), brazilwood (Haematoxylum brasiletto), licorice (Eysenhardtia polystachya) and tecolhuixtle (Mimosa benthamii) (^{Atender, 2008}).

The community Los Sauces, municipality of Tepalcingo, is located in the buffer zone of the Biósfera de la Sierra de Huautla (Rebiosh). It is located in the state of Morelos, between latitudes N 18° 33' 08" and 18° 37' 00" and lengths W 98° 58' and 98° 55', at an altitude of 1 216 m. The type of vegetation is tropical dry forest (Figure 1).

Figure 1 Macrolocation the common Los Sauces, Tepalcingo, Morelos. 

Some species representative of the community are Guazuma ulmifolia (cuahulote) and other amates and cuajiotes. There are also several secondary associations formed mainly by thorny bushes of the family Fabaceae. The climate is warm humid with rains in summer, with an annual rainfall of between 800 and 1 000 mm and an average annual temperature of 22 °C (^{INEGI, 2011}).

The main economic activities in the common of Los Sauces are agriculture, livestock, collecting resins, picking fruit, mezcal production, collection of medicinal plants and firewood extraction; the latter is used mainly for cooking food and for sale between neighboring or nearby villages in order to achieve extraordinary income in the low water season when tasks decreases in other activities. Firewood, as one of the resources used as fuel for most people, is in high demand it represents pressure on plant resources and causes decrease in the availability of tree species with this use, a situation that intensifies with increase of the population.

Materials and methods

Local knowledge is understood as the body of knowledge, beliefs, customs and perceptions unique to a culture or a given society (^{Monu, 1997}; ^{Grenier, 1998}). Generally, in the case of that knowledge linked to natural resources, derived from everyday observations and experimentation with ways of life, production systems and natural ecosystems (^{Mora, 2007}).

Based on a series of interviews conducted previously by students of the 2010-2011 generation of expertise in agroforestry, for a more detailed local knowledge about the species most commonly used as firewood (dendroenergetic) questionnaire applied to 25 he was prepared % of families living in the community of Los Sauces. There are two types of interviews, one for woodcutters and one for housewives, because these groups do not have the same vision for firewood.

Once you know the list of species most commonly of wood energy use, through interviews, we proceeded to the collection of seed and logs of wood to make determinations protocol germination, heat of combustion, ash, density and moisture, taking these samples from trees with the best features.

According to the method of ^{Kollman (1959)}, for obtaining density a piece of wood species was collected and three cubes of approximately 2 x 2 cm were removed, which were dried in the open for 24 hours, then spent a desiccator for 24 h to remove the air in the timber and allow the entry of water were then weighed using an electronic balance; to obtain the volume, the cubes were immersed in a glass of water with the aid of a dissecting needle and weighed to obtain the volume difference.

After this, the cubes were immersed in water for seven days, once after that time, they were weighed and put in an oven at 103 °C for four days to remove water contained in them, from the fourth day began weighing daily until no weight change these, then calculate the volume by the method of glass with water. Once taken data volume and dry weight basic density and moisture content were obtained.

The heat of combustion was determined by the method described by ^{Soto and Núñez (2008)} which consisted of grinding a piece of stem of each species until a gram of sample. 0.5 g of each species of wood sample was weighed, with two repeats (Figure 2).

Figure 2 Ground sample of the species studied and weighing them. 

The sample was placed in heavy cover support of the combustion chamber, placing 10 cm wire to initiate combustion (Figure 3).

Figure 3 Placing the wire and mounting the sample in the holder. 

This support was set at the oxygen pump, which was inserted by sealing oxygen (25 to 30 atmospheres).

Parallel to this process, two liters of water were heated to a temperature of 30 °C which were added into the cuvette of isoperibolic calorimeter, with hot water; the bomb was placed inside the calorimeter and sample data were introduced to computer software for reading the result.

After taking the data, the calorimeter was uncovered by removing the pump with pliers then open to the weather as it contains oxygen pressure; once opened wire unburned removed, the interior of the pump, the holder and cover with distilled water rinsed by pouring this solution into an Erlenmeyer f lask and then titrate with sodium carbonate, this in order to know whether there presence of acid. To obtain these two variables laboratory procedures proposed by ^{Sosa (1979)} were used. Statistical analysis was performed using the GLM procedure of SAS (2002). The tests compared with 0.05 mean statistical significance were performed using the Tukey test (^{Steel et al., 1997})

The methodology for the development of treatments germination was taken of the work that used the INE (²⁰⁰⁷) for tree seeds deciduous forest. Once the pregerminative treatment applied to seeds in trays were seeded styrofoam cavities 200, using as substrate peat moss to subsequently obtain the germination percentage and days of seedling emergence. To structure the design and agroforestry technologies proposed diagnostic methodology and design described by ^{Raintree (1987)} was used, which basically consists of five stages: pre-diagnosis, diagnosis, design and evaluation, planning and implementation.

Results

According to the results of the interviews conducted in the community of Los Sauces, there is a process of replacement of fuel wood for home, LP is the substitute fuel, which still fails to be established. Interests and vision around the wood of housewives is different from the lumberjacks, since the latter prefer the easy species to cut, linear chappy and quick drying, while women are inclined species smokeless and, depending on the needs, sometimes they require species that are slow and steady fire, as in the case of cooked beans; or, firewood rapid fire, "caught", which is required to make “tortillas”.

Household fuels are a necessity both in urban and rural communities, which are used for food preparation, but also to temper the water used for personal hygiene. Firewood is a proper fuel in rural communities to be replaced by fossil fuels to the extent that people have access to the latter and the necessary equipment and facilities for use.

The firewood in communities is a resource that is handled appropriately by rural dwellers, cut and processed for use, devices for use are very basic and are reduced to simple instrumental that the producers themselves made while the use of fossil fuels requires equipment and facilities to be acquired in the cities and are usually expensive and rarely available to the budget of marginalized farmers.

In addition, the value of fuel requires payment in cash, limiting situation for these people, so in the town of Los Sauces 40% of households use only firewood, do not have equipment for fossil fuel called "gas LP" which It corresponds to butane, sold in 20 kg cylinders at a cost of 235 pesos, while 60% of households combined firewood and "gas", which means a transition in relation to fuels. Despite this, the use of "gas" is sporadic, but possession of stoves, water heaters and grills, plus an enclosed space for kitchen and bathrooms, are part of the social prestige in the village, it represents to the family community economic capacity, many times associated with the migration of children abroad.

However,the culture of use of fire wood is rooted in the "taste" of housewives by the "best taste" of food or by obtaining simmered or "taken" necessary for cooking certain dishes therefore 90% of them prefer the wood. There are opinions on the matter: "no [would not stop cooking with firewood] because that makes it one tortillas and taste better, and beans also cook with firewood nicer" (Verónica, 49 years).

It also identifies with the culture of the older generations and even pejoratively calls the new: "for there [would not stop cooking with firewood] because i am old, and now girls [young women] are loose, too lazy turn the stove" (Gregoria, 60 years).

They establish the conditions in which the change is justified "gas stove itself is necessary for when you get sick at night, a quick tea on the stove, because in one of wood [stove] just do not burn the fire, and as not, and that's more a stove" (Victoria, 38 years). "The gas we use when, in the rainy season, the wood is wet but I like to use firewood because the food is cooked better" (Janet, 30 years).

The amount of fire wood used depends on the number of family members, small use only one to two loads per month, while in big can reach six. Highlights the fact that 90% of respondents are in the first case. Efficiency in the use of firewood is a concern of government programs, whose implementation has resulted in about 50% of families have saving stoves.

The dendroenergetic species possess characteristics associated with their use as firewood. Housewives have preferences according to the type of fire they get from each of them, as shown in Table 1.

Table 1 Species dendroenergetic, fuel characteristics, frequency of use and drying time. 

Fuente: elaboración con información de campo.

In contrast, wood burning is preferred to prepare fast foods that do not require to be long on the stove, like tortillas, in this case white cubata is the one with that feature. It highlights the preference of species that do not produce smoke or minimum. Also to reduce smoke emission drying of wood to be used in the stove is heading, you can burn with humidity however smoke emission is very evident.

For them, the species most in demand are the tlahuitol, brazilwood and tepehuaje, and because the size allows obtaining greater amount of wood per tree compared to any other species. On the other hand has white cubata, which has branches and stems rights. This, says Margarito lumberjack, 60 years old, "is very easy to cut with an ax and you cut a branch, not to cut brazilwood is very hard and the wood [stringy bark] entangles". The ease of cutting and acceptance of buyers led to the decline of this species to a near disappearance situation, which should be considered strategies rational use of white cubata.

The species used for firewood also have uses as fodder, timber,medicine,hedgerows and shade. This work confirms what ^{Maldonado (1997)} mentions about the species used as firewood in the the Biósfera de la Sierra de Huautla (Rebiosh), which are the tlahuitol, tepehuaje, tecolhuixtle, brazilwood and sweet stick with characteristic to produce a minimum amount of smoke.

Discussion

^{Sosa (1979)} states that higher ash less amount of organic matter and higher heat of combustion (^{Bravo, 1989}), the organics responsible for the amount of combustion heat. Using the correlation between the data obtained from combustion heat and ash, tepehuaje and tlahuitol meet the rule, although the second produces a little ash.

Statistically analyzing the results obtain at least one treatment is different, using the Tukey test (p≤ 0.05) have four groups that exist where tlahuitol and tepehuaje produce the least amount of ashes (1.86 and 2.31% respectively), counterparty have the highest amount of organic matter (88.14 and 87.69% respectively). Here are other features that are corroborated based on the information obtained through interviews (local knowledge), since the ashes produce smoke and this has more than 200 chemical compounds, most of them toxic inhalants with a smaller diameter to 10 microns, causing breathing problems (^{Junemann and Legarreta, 2007}).

^{Restrepo et al. (1983)} mention "that the analysis of the composition of wood smoke has shown that it is a suspension of small particles in hot air and other gases resulting from incomplete combustion. The gases are variable but always contains carbon monoxide and carbon dioxide; if sulfur, whether in small quantities, sulfur dioxide, tar vapors and/ or unsaturated hydrocarbons occurs. The carbon particles are coated with combustible materials such as organic acids and aldehydes ".

The statistically analyzing the results we obtain that at least one treatment is different, using the Tukey test (p≤ 0.05) note that there are five groups where tepehuaje and tlahuitol have the lowest moisture content (6.36 and 6.96% respectively). Comparing the qualitative data (local knowledge) with laboratory, we get that wood energy species that they mention with more moisture are the same, this could be because when species were collected, they already had a week have been cut.

The dendroenergetic density species is the weight of the unit volume of wood and depends largely moisture (^{Bruzos, 2009}); ^{Otero et al. (2004)} mention that greater density greater combustion heat; correlating data density heat of combustion and the rule is not met at all since the brazilwood and sweet stick rank first with respect to heat and combustion are in the second group. Statistically analyzing the data reveals that at least one treatment is different, using the Tukey test (p≤ 0.05) we have that there are four groups and the brazilwood and licorice are those with the highest density (0.81 and 0.78% respectively). ^{Zhang (1997)} mentions that the density has more to do with the quality of the wood which is corroborated by the information provided by the people in the community, which ensures that the hardest to cut trees are brazilwood, tlahuitol, sweet stick, tecolhuixtle, tepehuaje and white cubata.

The species that were collected seed licorice, white cubata and tepehuaje, using two treatments according to the recommendation of the INE (2007); which he was used to immerse licorice seeds for one minute in hot water at 50 °C obtaining a germination rate of 80%; they began to emerge seedlings six days after planting. The INE (2007) scored 60% seed germination, this is because the storage time decreases seed viability thereof (^{Arriaga et al., 1994}); which he was used two years in those conditions, in the case of this work seeds having three months of storage were used.

For white cubata and tepehuaje treatment and sanding until change color, thinner seed coat was applied; 55% germination in the first case and 60% in the second were obtained; time of seedling emergence was 7 and 4 days respectively; comparing the results with the INE (2007), 90% of seed germination and seedling emergence five days was obtained; This is possibly because tepehuaje seeds and cubata sanded more damaging the embryo.

Conclusions

The species most used as firewood in the community Los Sauces are: tlahuitol (Lysiloma divaricata), white cubata (Acacia pennatula), tepehuaje (Lysiloma acapulcense), brazilwood (Haematoxylum brasiletto), licorice (Eysenhardtia polystachya) and tecolhuixtle (Mimosa benthamii).

In Los Sauces there is a process of replacing fuelwood by fossil fuels, however, despite the widespread, these are used sporadically and are perceived as a feature of "social prestige". There are also differences in species preference among housewives and lumberjacks.

Based on the analysis results, the species, in order of importance for their quality, are: tepehuaje (Lysiloma acapulcense), tlahuitol (Lysiloma divaricata), tecolhuixtle (Mimosa benthamii), brazilwood (Haematoxylum brasiletto), licorice (Eysenhardtia polystachya) and white cubata (Acacia pennatula).

The agroforestry technologies proposed for the common Los Sauces, municipality of Tepalcingo, Morelos, are scattered trees in pastures and hedgerows, as land use is associated with livestock and fuelwood needs they can be covered with trees arranged in these fields.