The domestic use of firewood in rural communities of the Caatinga: How seasonality interferes with patterns of firewood collection

b i o m a s s a n d b i o e n e r g y 3 9 ( 2 0 1 2 ) 1 4 7 e1 5 8

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The domestic use of firewood in rural communities of the Caatinga: How seasonality interferes with patterns of firewood collection Marcelo Alves Ramos, Ulysses Paulino de Albuquerque* Federal Rural University of Pernambuco, Biology Department, Applied Ethnobotany Laboratory, Rua Dom Manoel de Medeiros s/n, Dois Irma˜os, 52171-900 Recife, Pernambuco, Brazil

article info

abstract

Article history:

One of the main methods of extracting vegetation from the Caatinga is the cutting of wood

Received 23 August 2011

for firewood. However, despite its social importance and its capacity for having environ-

Received in revised form

mental impacts, there are no studies that evaluate the dynamics of the collection of this

23 December 2011

resource in relation to temporal factors in the semi-arid regions of Brazil. Thus, the main

Accepted 4 January 2012

purpose of this study was to show that the seasonality of the savanna climate might

Available online 31 January 2012

influence local patterns of collecting firewood. Between December 2008 and February 2010, interviews and eleven in situ inventories were performed in the residences of two rural

Keywords:

communities in the municipality of Soledad in the state of Paraı´ba (Northeast Brazil).

Biomass

During the in situ inventories, all stocks were measured (m3), and species diversity was

Firewood harvesting

recorded. A total of 22 species were cataloged, but the pressure of collection was not

Semi-arid

distributed across all plants; there was a small group of species that were collected

In situ inventory

throughout the year, and these were found more frequently and with greater abundance in

Ethnobotany

the residences. Although species richness was not influenced by seasonality, the volume of

Dry forests

wood varied significantly between the dry and rainy seasons. More collections are performed in the dry season, and the local vegetation suffers greater extraction pressure from this use. The results obtained reinforce the need for studies that examine the potential for regrowth, plant productivity after selective cutting and the resting time necessary before performing a new cutting cycle, as this is the only way to better understand the implications regarding the use of firewood and its effects on local conservation. ª 2012 Elsevier Ltd. All rights reserved.

1.

Introduction

It is estimated that 54% of forest resources collected worldwide are to be used as firewood [1], indicating the importance of wood in the world energy balance and highlighting the significant and direct potential of this activity on forest loss [2,3]. Given this importance, studies have been conducted to contribute to the knowledge of the patterns of firewood use in

local and traditional communities [4e7]. However, information is still scarce, especially with regard to energy supply in the rural domestic sector, because energy planning prioritizes commercial energy, which is consumed in the industrial and agricultural sectors [1,8]. The literature on this subject has shown that rates of domestic firewood consumption are very inconstant and can vary due to family socioeconomic characteristics, such as size

* Corresponding author. Tel.: þ55 81 3320 6350; fax: þ55 81 3320 6360. E-mail address: [email protected] (U.P.de Albuquerque). 0961-9534/$ e see front matter ª 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2012.01.003

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and monthly household income, for example, and also as a function of geographical and climatic characteristics of the region, such as altitude, temperature, precipitation, season and others [8e10]. Understanding these factors and how they influence the consumption of firewood in Northeast Brazil is in its infancy because the number of studies is still small [6,7,11,12]. Moreover, previous studies have utilized punctual inventory methods, which did not follow the dynamics of input and output of material stocks. Thus, because one of the striking characteristics of studies on the use of firewood is the large variation in consumption rates [9,13], two rural communities located in the Brazilian semi-arid region, strongly influenced by seasonal characteristics [14], were selected for a study monitoring the stocks for domestic consumption. Given these conditions, the aim was to evaluate whether the patterns of collection and consumption of firewood change over the course of the year as a function of climate changes. These issues have already been discussed in some studies [9,13,15e17], but remain poorly understood. Several questions guided the development of this research; they are listed below, along with their expected responses. First, what is the relationship between the use of gas stoves and firewood consumption in the domestic sector of the Caatinga? It is expected that regardless of the presence of gas stoves in homes, firewood continues to be the primary fuel source in the region and that economic issues are the main motivation for the use of forested fuels. Second, is firewood collection pressure distributed equally among the many species used throughout the year? It is expected that the use of firewood is concentrated in a restricted group of species and does not vary as a function of time. It is assumed that collectors of firewood are selective and prioritize what they consider the species of superior quality. Third, do climatic seasons of the Caatinga alter patterns of firewood collection? It is believed that stocks are richer in species and volume during the dry season, and the population performs a greater number of trips to the forest to collect this resource during that time. This expectation was generated taking into account that timber resources are more accessible during the dry season because the lack of leaves facilitates trekking through the forest. Also, during this period, the wood is dry, making it easy to transport; wood is heavier and more difficult to ignite when wet [6,13].

2.

Materials and methods

2.1.

Location of the study

This study was conducted in two rural communities (Cachoeira and Barrocas), located in the municipality of Soledad, in the state of Paraı´ba, Northeast Brazil. This municipality is characterized by a hot semi-arid climate (BShs, according to Ko¨ppen), with an altitude of 521 m above sea level and an annual rainfall of 300 mm. The dry season lasts roughly eight months, and the rains are concentrated between March and June. However, there may be years in which the drought extends for up to 11 months; thus, it is considered one of the driest regions of the Brazilian Northeast [18,19].

The municipality of Soledad has an area of 560,062 km2, with an estimated population of 13,623 inhabitants [20]. Approximately 70% of this population resides in urban areas, and 30% resides in rural areas. The soil is predominantly halomorphic with high salinity, which hinders projects utilizing groundwater [19]. Native vegetation, characterized as hyperxerophilous shrub-arboreal vegetation, covers an area of 24,981 ha. The following are examples of species that dominate the region, according to data from Brazilian Service to Support Micro and Small Enterprises [19]: Erythrina velutina Wildd. (mulungu), Schinopsis brasiliensis Engl. (barau´na), Chorisia glaziovii (O. Kuntze) E. Santos (barriguda), Aspidosperma pyrifolium Mart. (pereiro), Croton blanchetianus Baill. (marmeleiro) and many cacti that dominate the local landscape as a result of the felling of trees for use as fuel (firewood and charcoal) in homes in the region.

2.2.

Communities studied

The rural communities of Cachoeira and Barrocas were selected for the development of this study. The criterion for selection of these communities was the receptiveness of the residents to contribute with ethnobotanical work, taking into consideration that they had already participated in other studies of this type [11,21,22]. The two communities are neighbors and are distinguished by different regimes of access to forest resources: in Barrocas are private areas while in Cachoeira are common-use areas. The community of Barrocas possesses 12 inhabited residential units in the form of private farms (large rural properties), whose sizes range from 70 to 480 ha. In this region, farms are distant from each other, occupying a relatively large area to the extent that residents are divided in two parts: upper Barrocas and lower Barrocas [11,18]. There are no schools, health clinics or commercial centers in Barrocas, so residents who need to use these services must travel to the center of Soledad, which is approximately 12 km away, or more rarely, to the neighboring community called Bom Sucesso, about 3 km away. The areas of vegetation used to collect resources are within the farms, which makes access restricted to families who live on the property. In Cachoeira, there are 18 inhabited residences distributed along the edges of the rural highway that are organized as a village. There are no rural properties; instead, there are small houses built on land belonging to two families in the region. Most of the homes (14) were constructed on lots provided by one of the inhabitants, known locally as Dona Genuı´na [11,18]. In this community, there is a portion of forest that is for common use, i.e., all residents have access to the available resources without restriction. According to older residents, this contributed to the intense exploitation of the local vegetation, especially for the collection of wood for use as fuel (firewood and charcoal). The physiognomy of the vegetation in the two communities is characterized by the predominance of cacti and bromeliads and the presence of individual shrubs, while vegetation is more arboreal in areas bordering rivers and streams [21]. Due to the lack of rainfall in the region, government actions have implemented cisterns in all residences to capture rainwater so that residents of both communities have

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access to safe drinking water. However, in periods in which rain becomes very scarce, the cisterns are filled by the Brazilian Army [21].

Table 1 e Period of monitoring the firewood stocks in the communities of Barrocas and Cachoeira, Soledad, NE Brazil.

2.3.

In situ survey

Ethnobotanical inventory: interviews and free-list

Initially, all inhabited residences of the two communities were visited, with the main purpose of explaining the research objectives to the households. At this stage, each resident was informed that the work was a long-term analysis, and if he/ she agreed to contribute to the study, monthly visits would be made to their residences to measure the stocks of wood and to determine the plant species used as fuel. After the explanations, residents who agreed to participate signed a free and informed consent form according to the ethical standards required by the National Health Council through the Research Ethics Committee (Resolution 196/96). We obtained the participation of the heads of 25 households in the two communities (10 in Barrocas, 15 in Cachoeira), which accounted for 83.3% of inhabited households in the region. Residents of five houses (two in Barrocas, three in Cachoeira) refused to participate in the study, citing lack of time. In each home, we sought the collaboration of a responsible couple, but in some situations this was not possible, either for reasons related to the marital status of residents (some were widowed or single), or simply because one member of the couple declined to participate in the study. Thus, a total of 41 informants participated in all stages of data collection (16 in Barrocas, 9 men and 7 women; and 25 in Cachoeira, 11 men and 14 women). Initially, general interviews were held with all residents (41 informants), using semi-structured questionnaires [23]. At this point, the data collected included age, education, occupation, monthly income of all residents of the house, number of people living in the residence, types of fuels used in the home and the preferred species for firewood. The "preferred plants" in this study were the species perceived as a priority species for use, based on criteria adopted by each individual informant. Upon completion of this phase, it was possible to identify users of firewood in the region. Of the 25 households who had agreed to participate in the survey, three had abandoned the practice of using wood, while 22 homes participated in the following stages of the study. Users of firewood were subjected to new questions, which sought to identify the motive for continuing to use firewood and not other fuels, the best period for collection of this resource, the number of times that the wood stove was lit per day and per week, and those responsible for collection and transport of wood to the homes.

2.4.

Ethnobotanical inventory: in situ survey

Between December 2008 and February 2010, eleven visits were made to the homes of the region (Table 1) to monitor the inventory of wood through the dry and rainy seasons. A minimum interval of 30 days was maintained between consecutive visits. However, there were some months when visits were not made: February, June, September and October of 2009. These intervals were used to minimize the effects of the constant presence of the researcher in the informant’s home. This decision was considered to be correct because it

Is1 Is2 Is3 Is4 Is5 Is6 Is7 Is8 Is9 Is10 Is11

Month/Year

Season classification

No of residences with stock

December/2008 January/2009 March/2009 April/2009 May/2009 July/2009 August/2009 November/2009 December/2009 January/2010 February/2010

Dry Dry Rainy Rainy Rainy Rainy Rainy Dry Dry Dry Dry

19 17 19 17 16 19 17 21 19 20 20

ensured the completion of the experiments without creating uncomfortable situations for the informants and researchers. In each of the visits, the monthly frequency of firewood collection was assessed, along with the day of the last collection and the day that they intended to perform a new wood collection. Shortly thereafter, the in situ inventory technique was applied [24], which consisted of going together with the local informants to the property where the firewood was stored. The stocks were then analyzed for each material present, and we asked that the respondents report the name of the plant and its origin. On some occasions, the collector did not recognize the woody material present in the stock, which required the aid of a key informant (Mr. Germano de Almeida Ramos), who was present when performing most of the inventories. If there were still doubts or difficulties in recognizing the species, it was not counted. During the inventory-monitoring period, the months were classified as "dry" or "rainy" (Table 1). The criteria adopted for this classification were a) the opinion of the informants with respect to distribution of rainfall in the months studied and b) rainfall data obtained from the Executive Agency for Water Management of the State of Paraı´ba (AESA). After recording the diversity of all species present in the stocks, the volume of stacked wood (cubic meters) was measured in each household [24,25]. This volume was calculated using the following formula: R Stacked volume ¼ L x x h, where L is the length of the pile, R is the width of the pile and h is the average of different heights of the pile. All the plants recorded in the inventories throughout the monitoring period were collected with the help of an informant, identified and submitted to the Vasconcelos Sobrinho Herbarium (PEUFR) of the Rural Federal University of Pernambuco. The species were classified according to the proposal of the “Angiosperm Phylogeny Group” [26].

2.5.

Data analysis

The nonparametric Kruskal-Wallis test was used to verify whether or not the average volumes of wood present in the home inventories of Barrocas and Cachoeira varied among themselves and to determine whether there were differences in the frequencies of firewood collections between the dry and

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rainy seasons. The same test was used to compare the frequency of collection in households that used different methods of transporting firewood. The Spearman correlation test was used to identify the species most common in inventories in situ that were present in most homes. The chi-square test was used to verify whether there were differences between the total volumes of wood logged in Barrocas and Cachoeira and whether there were variations in species richness and volume of fuel stored between the dry and rainy months in the region. All the tests were performed using BioEstat 5.0 software [27]. To determine whether or not there were grouping trends for species in relation to their frequency of use in homes, a cluster analysis was performed to characterize the groups of plants suffering greatest pressure of use. A principal components analysis (PCA) was performed to verify whether the different in situ inventories were grouped according to species composition and/or size of the volumes of wood in homes studied. Analyses were performed using MVSP 3.1 software [28]. The Jaccard similarity coefficient [29] was used to verify the similarity in species composition among the eleven in situ inventories conducted during the monitoring of stocks. The frequency of occurrence of species in inventories (FqI) was calculated from the number of times a species was recorded among different inventories divided by the total number of inventories in the region (11) and multiplied by 100. The frequency of occurrence of species in residences (FqR) was calculated from the number of households where a species was recorded divided by the total number of households using firewood in the region (22), multiplied by 100.

3.

Results

3.1.

Profile of the communities in relation to firewood use

The majority of those interviewed used firewood in their homes (88%). Of these, 18.2% relied on this resource as the only energy source for cooking food, while 81.8% used firewood and liquefied petroleum gas (LPG). The residents identified this combination of two fuel sources as a strategy to reduce household spending, and the type of fuel selected depended mainly on the type of meal being prepared. For example, to the preparation of meat and beans, informants reported that prioritize the use of firewood, keeping in mind that the cooking time of these foods is long. Despite the presence of gas stoves in the residence, their use appeared to be limited, which was clear when the informants were asked about the number of times they used their wood stoves. The majority (97%) of the informants reported that they were in the habit of lighting their stove every day, with some lighting it twice a day (68.5%) and others only once (28.5%), but they continued to add wood for the rest of the day until all their meals were cooked. Only one person reported that he did not light the wood stove on a daily basis but only lit it to prepare foods that required longer cooking times, such as meat and beans; this occurred at an average frequency of three times a week. In Soledad, the reasons for the residents’ continued use of wood were related to economic issues (according to 88.24% of

respondents), followed by maintaining local tradition (8.82%) or simply as a matter of preference (2.94%). This last group consisted of a single user, who indicated that the use of wood in cooking resulted in tastier foods. Thus, the most common justification identified by respondents for maintaining the use of firewood in the community was socioeconomic factors. The arguments used to reinforce that justification were the high costs related to acquisition/exchange of gas canisters and the facility of obtaining firewood without having to pay for it.

3.2.

Composition and richness of firewood stocks

Throughout the study period, a total of 22 species were identified in the wood stocks from the two communities, and these species were distributed among 10 botanical families, especially Mimosaceae (5 spp.), Anacardiaceae (4 spp.) and Euphorbiaceae (4 spp.); combined, these families accounted for 60% of the species used (Table 2). However, an average use of only 8.5 (2.5) species per household was recorded, and the plants most often present in the houses were Poincianella pyramidalis (Tul.) L. P. Queiroz (100.0%), A. pyrifolium Mart. (95.5%), C. blanchetianus Baill. (86.4%), Mimosa tenuiflora (Willd.) Poir. (81.8%), Myracrodruon urundeuva Allema˜o (77.3%), Commiphora leptophloeos (Mart.) J. B. Gillett (72.7%) and Prosopis juliflora (Sw.) D.C. (72.7%) (Table 2). While these plants were present at the highest frequencies, roughly 32% of the plants inventoried were rare, occurring in only one residence. Through the Jaccard coefficient, an average similarity of 0.752 (0.081) was observed in relation to species present in the firewood stocks, considering all in situ inventories. This result confirms that a particular species richness was found constantly in stocks, independent of the season. In particular, P. pyramidalis, C. blanchetianus, M. tenuiflora, M. urundeuva, P. juliflora and Spondias tuberosa Arruda species were encountered in all in situ inventories (Table 2). There was a high correlation between the frequencies of species in residences and their frequencies among different in situ inventories (rs ¼ 0.86, p < 0.0001), demonstrating that plants were continuously collected during the year and were also used by most people; species that occurred occasionally in inventories were collected in only one or a few survey months and were used by few people. However, some species did not follow this pattern: umbuzeiro (S. tuberosa Arruda), mulungu (E. velutina Willd.), jurema-branca (Piptadenia stipulaceae (Benth.) Ducke) and angico (Anadenanthera colubrina (Vell.) Brenan). These species were encountered in few residential firewood stocks, despite being recorded in most in situ inventories. Five groups of species were identified by a cluster analysis, taking into account their frequencies of occurrence in different stocks and in situ inventories. The first group (AG1) was characterized by the presence of species that were subject to greater extraction for firewood in the region: catingueira (P. pyramidalis), marmeleiro (C. blanchetianus) and pereiro (A. pyrifolium) (Fig. 1). The second group (AG2) was also composed of species with a high degree of exploitation, though the degree of exploitation was often smaller than that of the species of the previous group: jurema-preta (M. tenuiflora),

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Table 2 e Species recorded in the firewood stocks during the eleven in situ inventories performed in the communities of Barrocas and Cachoeira, Soledad, NE Brazil. Family Anacardiaceae

Apocynaceae Burseraceae Cactaceae Caesalpinaceae Combretaceae Euphorbiaceae

Fabaceae Mimosaceae

Sapotaceae

Scientific name Anacardium occidentale L. Myracrodruon urundeuva Alla Schinopsis brasiliensis Engla Spondias tuberosa Arr. Aspidosperma pyrifolium Mart. Commiphora leptophloeos (Mart.) J. B. Gillett Pilosocereus pachycladus F.Ritter. Bauhinia cheilantha (Bong.) Steud. Poincianella pyramidalis (Tul.) L. P. Queiroza Combretum glaucocarpum Mart. Croton blanchetianus Bailla Croton heliotropiifolius Kunth Jatropha mollissima (Pohl) Baill. Manihot dichotoma Ule Amburana cearensis (Allema˜o) A.C.Sm. Erythrina velutina Willd. Anadenanthera colubrina (Vell.) Brenan Mimosa ophthalmocentra Mart. ex Benth. Mimosa tenuiflora (Willd.) Poira Piptadenia stipulaceae (Benth.) Ducke Prosopis juliflora (Sw.)D.Ca Sideroxylon obtusifolium (Roem. & Schult.) T.D.Penn.

Vernacular name

FqI (%)

FqR (%)

Cajueiro Aroeira Barau´na Umbuzeiro Pereiro Imburana Facheiro Mororo´ Catingueira Joa˜o-mole Marmeleiro Quebra-faca Pinha˜o Manic¸oba Cumaru Mulungu Angico Jurema-de-imbira Jurema-preta Jurema-branca Algaroba Quixabeira

27.3% 100.0% 81.8% 100.0% 90.9% 90.9% 90.9% 18.2% 100.0% 27.3% 100.0% 18.2% 18.2% 9.1% 18.2% 81.8% 72.7% 81.8% 100.0% 72.7% 100.0% 9.1%

4.5% 77.3% 40.9% 22.7% 95.5% 72.7% 31.8% 4.5% 100.0% 4.5% 86.4% 4.5% 13.6% 4.5% 4.5% 18.2% 22.7% 50.0% 81.8% 36.4% 72.7% 4.5%

FqI ¼ Frequency of occurrence of species in inventories; FqR ¼ Frequency of occurrence of species in residences. a Species cited as preferred for firewood in the interviews.

aroeira (M. urundeuva), algaroba (P. juliflora) and imburana (C. leptophloeos). It should be noted that among the plants that made up these two groups, only two species were not mentioned as preferred by the local population (A. pyrifolium and C. leptophloeos). The last group (AG5) (Fig. 1) was the richest and was characterized by the presence of species that occurred only occasionally in inventories; therefore, these plants did not face strong pressure for use as firewood.

3.3. Total volume of firewood stocked in the communities of Barrocas and Cachoeira A total of 738.9 m3 was recorded in the 11 inventories performed in the two communities (Barrocas and Cachoeira). Of this total, 407.48 m3 was derived from stocks from only one residence, located in the Community of Barrocas. This region was excluded from analysis involving volume, because it was

Fig. 1 e Dendrogram showing groupings (AG) of the species used as firewood in the communities of Barrocas and Cachoeira, Soledad, NE Brazil. *Indicates species listed as preferred in the interviews.

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different from the general scenario presented by the other residences. Thus, in the community of Barrocas, a total of 124.16 m3 was recorded throughout the study period, averaging 11.29 m3 (9.06) of firewood in each in situ inventory and 1.48 m3 (2.9) of firewood per household. In Cachoeira, a total of 207.21 m3 was recorded, with averages of 18.84 m3 (7.27) in each inventory and 1.90 m3 (2.96) per residence. The total volumes of wood collected were statistically different between the two communities (c2 ¼ 20.81; p < 0.0001). This difference must be related to the larger numbers of stocks measured in Cachoeira, which is a community with more homes. When comparing the volumes of wood in the individual residences, there were no statistical differences (H ¼ 2.41, p ¼ 0.12), indicating that all collectors tended to maintain a similar volume, independent of the community in which they lived.

they show variations in the amount of wood stored as a function of the method of transportation utilized. One of the explanations to the questions posed above is the frequency of collection; in homes where wood was transported on the head, the average interval between two consecutive samples was lower (12.2  6.29 days) than in homes where transport was performed with animal-drawn wagons (27.63  22 days) (H ¼ 3.87, p ¼ 0.04) or by the collector (23.82  1.1 days) (H ¼ 5.04, p ¼ 0.02). Thus, it is important to consider that the use of a more efficient method with greater firewood transportation capacity is not always indicative of greater collection pressure. Throughout the study period, the stocks were always greater for houses whose collectors used the most traditional forms of transportation (loading on the head) compared to the average presented by other homes.

3.4.

3.6. Influence of season on richness of species used as firewood

Frequency of wood collection

In the residences studied, collectors of firewood were quite heterogeneous regarding the frequency with which they gathered wood. This is because the collectors had to divide their time between carrying out different tasks on their properties, including agriculture, acquiring water, feeding animals, household chores, child care, etc. When comparing the frequency of firewood collection in the dry months and in the rainy months, it was found that collection underwent significant changes throughout the year (H ¼ 4.03, p ¼ 0.04). During the dry season, the average interval between two collections was smaller (16.27  1.85 days) than during the rainy season (21.45  5.76 days), i.e., collectors increased the numbers of firewood collection excursions during the dry season. This corroborated the information reported in interviews, in which informants said that they prefer to collect in the dry season, due to ease of travel within the “bare” vegetation.

3.5.

Methods used for transport of firewood

Three different methods for transporting wood were recorded. In the first method, the load is carried on the head (used in 45.5% of households). This method, carrying the bundles containing 20e30 kg of wood on the head, had the peculiarity of being practiced exclusively by women. In the second method, the load is carried by an animal-drawn wagon (horse/donkey) (41% of households). This method is practiced only by men and was characterized by carrying a large amount of firewood, which according to the collectors, may vary from 150 to 200 kg. In the third method, loads are transported by human-powered carts (13.5% of households). This method is practiced by both men and women, and each wagon load carried an average of 50 kg of firewood. In the homes where wood was transported in bundles carried on the head, stocks showed a greater average volume (2.05 m3  2.97) than stocks of homes whose collectors used animal-drawn wagons (1.50 m3  1.83) or human-powered carts (0.42 m3  0.28) for this function. Although these data were not significantly different, they are interesting because

Although the average number of species used as firewood in the dry months was higher (15.17  1.32) than in the rainy months (14.2  1.32), there were no statistical differences between these values (c2 ¼ 0.032; p ¼ 0.86), indicating that species richness in these stocks was constant throughout the year. This is curious because when evaluating the interviews of the informants regarding the best times of collection, with the exception of two, all informants were emphatic in stating their preference for collecting in the dry season, explaining that the vegetation was more “open” in this period, facilitating the movement of people inside the forest, and the wood was not wet. Therefore, we expected to find greater species richness in the dry months. Via principal components analysis (PCA) and considering the species composition among the different inventories, it was observed that there was a tendency for grouping between inventories in the rainy season (Fig. 2), separated from inventories performed during the dry season. This signifies that although there was variation in the total richness of plants as a function of time, when evaluating the composition of the stocks, it was observed that there was a set of species present between these two seasons that were subjected to variations due to seasonality. Analyzing the temporal availability of the species in Fig. 3, it was observed that the differences noted above might be due to the fluctuating group of species that inventoried the firewood stocks between the different seasons. In the summer, for example, there were four exclusive species (Anacardium occidentale L., Croton heliotropiifolius Kunth, Manihot cf. dichotoma Ule and Sideroxylon obtusifolium (Roem. & Schult.) T.D.Penn.) and a greater frequency of use of A. colubrina (Vell.) Brenan and Combretum glaucocarpum Mart. In the rainy season, there were only two exclusive species (Amburana cearensis (Allema˜o) A.C.Sm. and Bauhinia cheilantha (Bong.) Steud.). We suggest that the oscillation in the stocks of these species is related to the fact that these species also offer other products at specific times of year, such as leaves and fruits; therefore, residents take advantage of the period in which these products are available and also collect wood from these species.

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Fig. 2 e Principal components analysis of the composition of the species present in the firewood stocks based on in situ inventories performed in the dry and rainy seasons in the communities of Barrocas and Cachoeira, Soledad, NE Brazil.

3.7. Influence of season on the volumes of wood stocked in the residences

Fig. 3 e Registration of plants used as firewood in eleven inventories in situ carried out in domestic stocks of rural communities of Barrocas and Cachoeira, Soledad, NE Brazil. Legend: Dark grey [ dry months, Soft grey [ rainy months.

There was an average of 39.29 m3 (10.58) of firewood stored in the communities of Barrocas and Cachoeira in the dry months, and 19.13 m3 (9.93) was stored in the rainy months (Table 3). These values were significantly different (c2 ¼ 6.96; p ¼ 0.008), indicating that the seasonality of the Caatinga has a strong influence on patterns of firewood collection in the region. The principal components analysis of the sizes of the volumes of wood in the residences confirmed the scenario described above. There was a tendency for grouping among the inventories performed in the dry season and those performed in the rainy season (Fig. 4), demonstrating that the stocks with smaller quantities were encountered in inventories performed during the rainy months. The decrease in stocks during the rainy season does not occur because people fail to collect this resource or because they have abandoned its use. During this time of the year, wood consumption decreases because residents tend to increase the intervals between two consecutive collections. With a smaller volume in stock, it is necessary to economize the wood available, thus reducing the number of times the wood stove is lit during the week and increasing the frequency of gas stove use. However, not all homes can be adjusted this way because there are houses whose residents use only

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Fig. 4 e Principal components analysis of the volume of firewood stocks from inventories conducted in situ in the dry and rainy seasons, in the communities of Barrocas and Cachoeira, Soledad, NE Brazil.

firewood as an energy source; therefore, the only strategy adopted by these residents is to reduce the number of times they light the wood stove during the week. A possible solution the problem of diminishing supplies of firewood in the winter would be to collect and store wood throughout the summer so that it is available for consumption during the rainy season. Such actions would have strong conservationist implications. The residents of Barrocas and

Cachoeira do not have this habit because the storage sites (stocks) are the backyards of their homes, and these sites are unprotected from the rain. The accumulation of large volumes of wood would not solve the problem because during the rainy period, the wood would be wet and unsuitable for burning. Therefore, residents adapted to this temporary condition by collecting a smaller amount of firewood and storing it inside their homes or in shelters.

Table 3 e Volume of wood stacked and species richness in each inventory performed in situ in the communities of Barrocas and Cachoeira, Soledad, NE Brazil. In situ survey (season)

Is1 (dry) Is2 (dry) Is3 (rainy) Is4 (rainy) Is5 (rainy) Is6 (rainy) Is7 (rainy) Is8 (dry) Is9 (dry) Is10 (dry) Is11 (dry)

Volume of wood stacked (m3)

Species richness Total

Barrocas

Cachoeira

Total

Barrocas

Cachoeira

13 14 14 13 13 16 15 16 16 17 16

12 10 13 11 9 12 10 14 12 15 8

12 12 10 9 12 13 14 14 15 11 16

27.87 35.63 35.54 20.80 12.31 10.96 16.03 31.72 40.54 41.94 58.02

8.35 8.32 10.53 3.51 4.17 3.10 3.03 9.22 24.00 22.04 27.89

19.52 27.31 25.01 17.30 8.14 7.86 13.00 22.50 16.54 19.90 30.13

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4.

Discussion

4.1. Profiles of the communities relative to the use of firewood The use of different fuel sources, as observed in this study, is a common practice among different populations in rural areas [30e32]. These data may suggest a possible decrease in consumption of forest biomass, but according to Heltberg [33], the addition of a new fuel does not always indicate the abandonment of the more traditional source. Studies conducted in Mexico [31,32] and South Africa [30] have confirmed that the presence of gas stoves in residences did not replace or diminish the importance of solid fuels (charcoal and firewood). These remained actively employed, while gas was consumed only at certain times. In Cachoeira and Barrocas, the same scenario was observed, confirming the results of this study. In Maputo, the capital of Mozambique, Brouwer and Falca˜o [3] also stressed that the most commonly used domestic fuels were firewood and fossil fuels, with few residences using only biomass. In the Caatinga, one of the reasons that people to rely on wood as a primary source of fuel is the high retail price of cooking gas (LPG). To purchase this fuel, it is necessary to have an amount of money inconsistent with the economic profile of much of the population living in the Brazilian semi-arid region [34]. However, economic factors are not the only factors that justify the current use of firewood. Although there was no emphasis on other factors in Soledad, some studies have demonstrated the contribution of cultural elements to the continuation of this practice, especially when the respondents indicate a preference for food cooked on wood stoves [30,32].

4.2.

Richness of wood stocks

Through continuous monitoring of stocks, it was possible to obtain a list of species used as firewood in the region (22 spp.). Sa´ and Silva et al. [11] reported a much lower diversity when evaluating the use of firewood by punctual inventory methodologies in the same communities: seven species were reported in interviews, and 14 species were reported by analysis of the stocks. Thus, the differences reported here emphasize the importance of long-term studies, especially when making inferences regarding the impacts of logging. In Sa´ and Silva et al. [11], the interviews revealed only species that occurred more frequently in the stocks than those reported in this study. This shows that studies on the consumption of firewood that use data obtained exclusively from interviews may produce inaccurate results because they cannot capture the dynamics of people’s use of different species. The application of punctual inventory generates a more reliable list of species than data collected in interviews; however are still limiting because they do not capture the temporal variations in the consumption of firewood. But it is necessary to note that in studies of rapid diagnosis, the technique of interviews and punctual inventory are important because they can redeem the preferred species richness with less cost and in less time. It was possible to show that the pressure of collection was not evenly distributed among all plants recorded in the stocks;

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there was a group of plants that was more frequently targeted during the collection activities, independent of the season. The intensive use of some species should be closely associated with the local perception of their qualitative attributes in the combustion, because some of the most exploited species such as P. pyramidalis, C. blanchetianus, M. tenuiflora, M. urundeuva and Prosopis. Juliflora were studied for their physical properties by Ramos et al. [7], and showed high Fuel Value Index (FVI)The impacts of this activity are still poorly understood because there is a lack of basic information on the capacity of regeneration and the productivity recovery of the species subject to harvest in the Caatinga [34,35] highlighted four species that were widely used as fuel in the region (P. pyramidalis, Croton sonderiaus, M. tenuiflora and Mimosa ophthalmocentra) and revealed high sprouting capacities for these plants, indicating that some species of the Caatinga can regenerate after human interventions; however, some authors point out that the restoration of ecological processes is not always guaranteed [35e37]. Regarding the question raised above, the influence of management type used by wood collectors should be emphasized. Each species responds to different cutting treatments; thus, human actions have a direct role in the regeneration capacity of the plants and can alter the characteristics of a plant community, including the distribution of diametric classes of species and the increased mortality of the trunks [38e40].

4.3. Total volume of firewood reported, frequency of collection and methods used for transport of firewood The total volume of firewood in stocks at residences was lower than the results obtained by Sa´ and Silva et al. [11] in the same region. One explanation for this variation may be related to the different methods used in these studies. Sa´ and Silva et al. [11] used a punctual inventory methodology; their data should be viewed with care because they does not consider the dynamics of domestic firewood consumption rates, which are very inconsistent. In Nigeria, a comparative study on the consumption of firewood in five different areas also showed variations in the consumption rates of this resource, although these differences were not significant [41]. The explanation used by those authors to clarify the differences in consumption was related to the total number of collectors in each region studied. As observed in the results of this study, there were also significant differences in the total volumes of fuel stored between the communities of Cachoeira and Barrocas; the number of collectors is a plausible explanation of the observed results. Different tools for the transportation of firewood are mentioned in the literature, including carts pulled by oxen or donkeys, bicycles and cars [5,16,41e43]. However, the most traditional and most widely used means of transport was carrying the wood on the head. Regarding this type of transportation, Abbot and Homewood [42] reported some peculiar features, such as the fact that women were mainly responsible for this practice and that they prioritized the collection of twigs with small diameters because a collection consisting of large logs makes the load very heavy and impairs the transport of different species. The use of different transport methods, as was observed in Cachoeira and Barrocas, is also common in some other

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regions of the world, but few studies have evaluated the impacts of collection caused by the use of different transportation modalities [5,41,42,44]. In the communities of Barrocas and Cachoeira, it was found that the use of more efficient tools with the capacity to carry a greater amount of wood was not associated with a greater impact because the residences that used these techniques performed collections less frequently and always had stocks with smaller volumes of wood compared to the stocks of households whose collectors transported firewood on their heads.

4.4. The influence of season on the richness of species and the volume of wood stored In the communities of Barrocas and Cachoeira, the patterns of collection were strongly influenced by regional seasonal factors. Although richness of species did not vary as a function of time of year, the stock volumes were higher in the dry season, and species compositions were also different. Confirming the results of this study, other studies have considered seasonality as an important element in shaping the relationships of inhabitants with the biological resources available [13,16,42,45,46]. In studies on the use of firewood, the influence of seasonal factors has generated different responses; these differences are mainly related to the needs of each population involved. For example, contrary to what was found in Cachoeira and Barrocas, Shankar et al. [16] recorded a greater consumption of firewood during the rainy season in India because the low temperatures during this period increased the frequency of consumption of hot beverages like coffee and tea. In agreement with this finding, during the rainy period, inhabitants stopped working in open areas and spent more time inside the houses and therefore used wood more frequently. Marufu et al. [15] indicated that during the winter, people are more likely to use firewood because there is increased need for heating. However, these habits are not common in the regions studied in the present work. In Zimbabwe, Campbell et al. [47] reported an interesting scenario regarding the influence of seasonality on the distribution of household chores; the scenario may be used to explain the differences between frequencies of collection of forest resources throughout the year. After the construction of a seasonal calendar, the authors found that residents were relatively free from agricultural work in the dry season; thus, local workers focused on the extraction of forest products. This circumstance applies to the results found in the communities of Barrocas and Cachoeira as well; in these locations, there was also a marked difference in the distribution of tasks depending on the season. In the rainy season, for example, residents needed to dedicate more time to activities related to agriculture, and other tasks had a lower priority.

5.

Final considerations

The use of firewood in the communities studied was not affected by the presence of gas stoves in the homes. Forest fuels were used throughout the year, but collection was

concentrated in the dry periods. During the rainy season, the difficulty of obtaining these resources and the need to prioritize other subsistence activities, such as agriculture, caused residents to collect firewood less often; thus, rates of firewood use decreased. During this time, the residences that do not depend exclusively on firewood used fuels derived from petroleum more frequently. Despite the richness of species present in the stocks, the extraction of wood in Cachoeira and Barrocas was selective: there was a small group of species that were collected by nearly all residents throughout the year. These include P. pyramidalis (Tul.) L. P. Queiroz, A. pyrifolium Mart., C. blanchetianus Baill., M. tenuiflora (Willd.) Poir., M. urundeuva Allema˜o, P. juliflora (Sw.) D.C. and C. leptophloeos (Mart.) J. B. Gillett. Because these species represent the group of plants suffering greatest local pressure for fuel, it is imperative that studies address the regeneration capacity of these plants after cutting so that information is provided on the proper management of these species and so that these data are made accessible to the local population.

Acknowledgments The authors thank to the residents of the communities of Barrocas and Cachoeira for their hospitality, patience and assistance. We also thank A. T. Nunes and V. T. do Nascimento for their assistance in the field work. This paper is the contribution P010 of the Rede de Investigac¸a˜o em Biodiversidade e Saberes Locais (REBISA-Network of Research in Biodiversity and Local Knowledge), with financial support from: FACEPE (Foundation for Support of Science and Technology) to the project Nu`cleo de Pesquisa em Ecologia, conservac¸a˜o e Potencial de Uso de Recursos Biolo´gicos no Semia´rido do Nordeste do Brasil (Center for Research in Ecology, Conservation and Potential Use of Biological Resources in the Semi-Arid Region of Northeastern Brazil-APQ-1264-2.05/10), and PNPDCAPES (National Program of Post-doctoral e Capes Foundation, Ministry of Education of Brazil) to the project: Ecology, conservation and potential of use of biological resources in semiarid northeastern Brazil.

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