Impact of wood logging on the phytomass and carbon sequestration in the guinea savanna of Ngaoundéré, Adamaoua Region, Cameroon - PDF

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Global Advanced Research Journal of Environmental Science and Toxicology (ISSN: ) Vol. 3(3) pp , August 2014 Available online Copyright 2014 Global Advanced

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Global Advanced Research Journal of Environmental Science and Toxicology (ISSN: ) Vol. 3(3) pp , August 2014 Available online Copyright 2014 Global Advanced Research Journals Full Length Research Paper Impact of wood logging on the phytomass and carbon sequestration in the guinea savanna of Ngaoundéré, Adamaoua Region, Cameroon Tchobsala 1 *, Mbolo, M 2 and Souare, K 3 1 Department of Biological Sciences, Faculty of Sciences, University of Ngaoundéré, P.O., Box 454 Ngaoundéré, Cameroon 2 Department of Plant Biology and Physiology, Faculty of Sciences, University of Yaoundé, P.O., Box 812 Yaoundé, Cameroon 3 Higher Institute of the Sahel, University of Maroua, P.O., Box 46 Maroua, Cameroon Abstract The present study estimated the impact of wood loggings on the phytomass production and carbon sequestration in the guinea savanna of Ngaoundéré, Adamaoua Region, Cameroon. The results showed that the phytomass of arborescent savanna is more important ( t.ha -1.year -1 ) than that of the shrubby savanna (49.18 t.ha -1. year -1 ). The sequestration of carbons correlated positively with phytomass (r= 0.98, P = 0.05). The very strong wood loggings (T3) are at the origin of the decline of phytomass production (36.53 tc.ha -1.year -1 ) and of the sequestration of carbons (17.17 tc.ha -1.year -1 ) in these savannas. These values are indicators of degradation of the outer-urban savannas in Ngaoundéré. The State government and the local population should jointly embark on the management for the protection of savannas in the Region. Keywords: Wood logging, phytomass, carbon, sequestration, guinea savannas, Adamaoua. INTRODUCTION The challenge of the climatic change requires efforts from the whole local and international communities. Cameroon, particularly conscious of the stakes of this phenomenon, is resolutely engaged to support the durable development. Within the framework of the negotiation of Copenhagen for the fight against the climatic change, the effort must be directed for the maintenance of the increase in the average temperature *Corresponding Author of the sphere in the side of 2 C compared to the preindustrial level by limiting to the maximum the level of carbon emission in the atmosphere. The only durable solution is to delimit deforestation and to encourage the reforestation and the durable management of the grounds. However in savannas, the deforestation of the wood loggings becomes extensively alarming these recent years. The deforestation of savannas due to the intensive wood loggings today is estimated at 154,000 km 2 /year (Aldhous, 1993). This leads to the emission of more than 0.32 Gt of carbon in the atmosphere (Kottosaméet al., 1997). Very few studies were carried out on Tchobsala et al. 039 the sequestration of the carbon in tropical Africa. Studies conducted by Kotto-Samé et al. (1997) are the most known. On the other hand, works were made in the United States on the carbon held in the agriculture (Krcmar, 2001) and in the natural environment (Jacinthe et al., 2002). Other authors were interested in the carbon held in the ground (Dolman et al., 2002; Vann den By gaart et al., 2002). Between 1850 and 1998, 270 Gt of carbon was emitted from the industries, with 176 Gt accumulated in the atmosphere and 120 Gt stored in the oceans (McCarty and Ritchie, 2002). During this period, the use of lands by man pulled a broadcast of about 136 Gt of carbon in the atmosphere. Forests are more important, because they hold carbon faster than the other ground circles. Krcmar (2001) showed that one m 3 of wood store approximately 200 kg of carbon. He also asserted that one ton of carbon held in the forest biomass corresponds to 3.667t of carbons removed from the atmosphere. The carbon is a good indicator of the fertility of the soil and it is found, in the form of organic matter, it also increases the soil quality and improves the capacity of regulation of water and the atmosphere of the soil, by improving its structure, its capacity of water retention, its reserves in nourishing elements, its biodiversity as well as the depth of implanting of plants which grow therein (Lal et al., 2002). The vegetation generally and the forests in particular play an essential role in the global cycle of carbon by storing in the long term an important quantity of carbon in the biomass and in the soil. Forests cover approximately one third of the continents surface (Kramer, 1981) and they make approximately two thirds of the global photosynthesis (Watson et al., 1990). The forest ecosystems store generally times more carbon by unity of surface than farmlands (Ciesla, 1997). On the other hand, their soils, which contain about 40% of the total carbon, are of a major importance during the consideration of the management of forests. The destruction of forests and woody regions can have as consequence a big loss of carbon in the atmosphere (Wang et al., 2002), engendering, a degradation of the quality of soils, reduction of the phytomass which is the dry biomass and the sequestration of carbons. The phytomass is a key structure variable for research into ecosystem dynamics and it is defined as the net amount of energy fixed by plants (Terradas, 2001). In the outerurban zone of Ngaoundéré, the destruction of the vegetation by wood logging led to an increase of the cultivable surfaces from 120 ha in 1951 to 1,256 ha in 2001 with an increase rate of 22 ha/year (Tchotsoua, 2006). The direct consequence of the decline of plant production is felt on the heating of the earth, the change of the precipitation and the increase in temperature in the outer-urban zone of Ngaoundéré. In Ngaoundéré, studies on the stock of carbon in shrubby and arborescent savanna was conducted by Ibrahima and Habib (2008), but there is a dearth of data on carbon stock on the types of woods logging, the woody savannas, the seasons and some parameters of phytomass (production of useful wood, herbaceous phytomass, the litter and the residues of the litter). Thus, the study aimed at knowing the impact of wood loggings on the production of phytomass and sequestration of carbons in the guinea savanna of Ngaoundéré, Adamaoua Region, Cameroon. MATERIALS AND METHODS Study area The study was undertaken in ten (10) villages namely: Béka Hooseré, Onaref, Wakwa, Tizon, Beskewal, Ngaohora, Borongo, Dang, Darang and Mban-Mboum all located in the Ngaoundéré district of the Adamaoua Region, Cameroon (Figure 1). These villages are located at about 10 km for the shortest and 60 km for the farthest distance from Ngaoundéré the capital city of Adamaoua Region, Cameroon. Ngaoundéré is located at latitude 7 19' N and longitude 13 34' E. Its population was estimated at about inhabitants in 2001 (Tchotsoua, 2006) with an increase rate of 2.81 % per annum. The main ethnic groups are the Fulbés, Mbororos, Gbayas, Mboums, Dourous, Yemyems, Hausas, and the Koutinés. The economic activities of the local inhabitants are mainly animal husbandry and land farming. The soil of the area belongs to the geomorphological domain of the plateau of Adamaoua. They are characterized by sedimentary, volcanic, granitic and metamorphic rocks. The vegetation of the Adamaoua corresponds to a typical Sudano-guinea savanna constituted with shrubby, arborescent and woody savannas. The precipitations are maximal in August and practically null from November to February. The hygrometric is maximal in August with a monthly average humidity of %. Choice of the different wood logging zones in the guinea savannas of Adamaoua Region, Cameroon To choose the different wood logging, interviews were conducted with group of persons. The prospections with the population in the site were made. The types of wood logging in the savannas depended on the degree of accessibility to the site (absence or proximity to easy access road), the distance to the village (0-0.5 km, km, 1-2 km, 2-4 km, 4-6 km, 6km) and the percentage of the wood cut. At the end of prospection, four types of wood logging were selected: Pilot or witness logging (T 0 ): made up with natural formation where the estimated percentage of wood logging is less or equal to 10 %. They are generally 040 Glo. Adv. Res. J. Environ. Sci. Toxicol. N Figure 1. Map of study area protected areas by the inhabitants; Weak logging (T 1 ): vegetation where the percentage of wood logging is between 11 and 25%; Average logging (T 2 ): vegetation where the percentage or wood logging is between 26 and 50%; Complete or total logging (T 3 ): vegetation where more than 50% of woods are cuts. Experimental Design The study was a split-plot design with 3 factors (shrubby savanna, arborescent savanna and woody savannas) (Table 1). The pieces were numbered from 1 to 12, delimitated by numbered cement terminals or wood stakes. One hundred and twenty sites (3 types of savannas 4 types of cuts 10 villages) were selected with 30 sites for each treatment. Measure of the vegetation phytomass The measure of the vegetation phytomass was obtained by determination of the biomass of the different plant formations. The measures of the biomasses were made at the height of the rainy season (June to September), the beginning of dry season (October to December) and at the height of the dry season (January to March) during three years in the quadrats of 10 x 10 m. The measure of the biomass of shrubs (size lower than 2 m) was realized according the method of Kotto-Samé et al. (1997) and Mbolo (2005). The quandrants and right angles of the plots of land were measured using a decameter and a set square respectively. In every site, five quadrants (10m x 10m) were retained to know the biomass of the ligneous flora affected by man inorder to estimate the risk which this degradation can cause on the vegetation, in the survival of the man and the animal. In all 120 sites, 600 Tchobsala et al. 041 Table 1. Experimental design. Villages S/No DAN BEK ONA BOR WAK TIZ NGA BES DAR MBA 1 SbT2 SaT3 SbT0 SaT3 ScT1 SaT0 SaT0 SaT2 ScT1 SbT2 2 SbT3 SaT0 SbT1 SaT2 SbT0 ScT2 ScT0 ScT2 SbT0 SbT1 3 ScT3 SbT3 SaT2 ScT0 SaT0 ScT0 ScT3 ScT3 SbT2 SaT1 4 ScT1 ScT2 ScT1 ScT0 ScT3 SbT2 ScT3 SaT3 SbT2 ScT3 5 SaT2 ScT1 SaT3 ScT1 SaT1 SaT3 ScT2 SbT0 SbT1 SbT3 6 ScT3 SbT1 SaT0 SaT0 SaT1 ScT0 SaT0 ScT2 SbT0 SbT3 7 SaT1 SbT3 SaT1 SaT3 ScT2 SaT2 SbT1 ScT1 SbT1 SbT3 8 SbT1 SbT0 SbT1 SbT3 ScT1 SbT1 SbT3 ScT0 ScT3 SaT2 9 SaT2 SaT3 SaT1 SaT2 ScT0 ScT0 ScT2 ScT3 ScT2 ScT0 10 SbT2 ScT0 SaT1 ScT3 SbT1 SaT1 SbT0 SbT3 SaT0 ScT2 11 ScT2 SaT0 SbT3 SbT0 SbT2 SaT0 SaT2 SaT1 SbT0 SbT2 12 SaT2 SbT0 SbT1 SbT3 SaT0 SbT2 SaT1 SaT3 SaT3 ScT1 Keyword: BES: Beskewal; BEK: Beka; ONA: ONAREF; BOR: Borongo; WAK: Wakwa; TIZ: Tizon; NGA: Ngaouhoura; DAR: Darang; DAN: Dang; MBA: Mbang-Mboum; Sa: shrubby savannas; Sb: raised savannas; Sc: wooded savannas. samples of 100 m 2 each were retained. The scientific names of all the species, their diameter to15 cm above the ground and their heights, their area surfaces and the numbers of the individuals by species were registered. To determine the biomasses of shrubs, we proceeded to the systematic cutting of these shrubs between 0 to 5 cm from the ground by means of machetes and they were separated species by species. A fraction of 10 kg of these samples was taken to the steam room of the University of Ngaoundéré for the drying and the determination of the Total Dry Mass (TDM). The Total Dry Mass (TDM) was calculated according to the following formula: TDM = 100 x TDT/ (100+Y), where TDT is the Total Dampness Mass and Y the moisture content. Y = (DM- DM)/DS) x 100, where DM is the Dampness Mass and DS the dry mass of the sample. The coefficient of the relationship between the dry weights over the weight of samples was calculated and used to estimate the phytomass of shrubs in the various plant formations according to the types of wood loggings. This phytomass was then expressed in ton per hectare per year (t.ha - 1.year -1 ). The biomass of the big trees (size upper to 2 m) was estimated indirectly on the same plots of land by using an allometric model taking into account the parameters of the tree such as the DHP and the height. The equation of Anderson and Ingram (1993) was used to estimate the biomass because it was developed in the climatic conditions where the annual average rainfall varied between 1500 and 4000 mm thereby including that of Adamaoua which is between mm. The equation is as follows: B (kg) = exp. ( Ln (D 2 H)), where B is the biomass of trees in kg, D the diameter DHP and H the height of the tree. The height of the big trees was estimated by clinometers.this was used to measure the vertical angles and estimate the heights of these big trees. With the help of clinometers, the contact point of the tree with the ground aimed at obtaining the angle ß 1. The angle ß 2 is obtained by aiming at the summit of the tree s base. The distance d is determined by measuring the gap which separates the observer from the tree. The height was determined by the Tangent (ß) = h/d, where h is the opposite side, d the adjacent side and ß the considered angle. The total height is defined by the sum of the heights: H t = h 1 +h 2. The biomass of trees was then expressed in ton per hectare per year (t.ha -1 year -1 ). The coefficient of the ratio dry weight overdamp weight within the framework of the phytomass of shrubs was applied to the biomass of trees to determine the exact value of the phytomass of trees. Measure of the subterranean phytomass The subterranean biomass was estimated in the same plots. Blocks of grounds of m 3 (0.25 m x 0.25 m x 0.10 m) and m 3 (0.25 m x 0.25 m x 0.15 m) were extracted at two deep levels: cm and cm. These weighed blocks, were sieved with a sieve having1mm stitch, then roots were manually sorted out and separated in two classes according to their diameters (Vogt et al., 1991). The fine roots ( 2 mm) and small roots (included between 2 and 5 mm) were separated. These two groups were then weighed. Before the sieving, one sub-samples of ground was taken and weighed to calculate its moisture content and its apparent density. These sub-samples were returned to the laboratory to be 042 Glo. Adv. Res. J. Environ. Sci. Toxicol. dried at 60 C in the autoclave for 48 hours until a constant dry mass was obtained. The moisture content was calculated as previously. From the total dry mass of the samples of the ground, the visible density of the ground (D) was calculated as follows: D = STD/(L 2 x h), where L is the side of the block of the ground (25 cm) and h is the height of the block of the ground or the depth of the hole (10 or 15 cm). It was expressed in kilogram per cubic meter (Kg. m -3 ) then transformed to t. ha -1.year -1. Measure of the production of useful wood We call useful wood any cut and available wood on the ground in the savanna by man, animals, derooting or by other climatic factors and ready to be used for firewood orusage. This was realized by a team of three persons collecting systematically died trees on a surface of 50 x 50 m. These stored woods were classified by category of diameter and weighed on the spot by means of a portable weighing balance. The production of useful wood has been evaluated in the 120 parcels under the 4 conditions (T 0, T 1, T 2 and T 3 ). A team of three persons collected woods cut down by animals, people, wind and water. These woods were classified as function of the diameter and weighed. A fraction of 10 kg of each category was dried and the weight of the whole sample evaluated. Estimation of wood logging in savannas We took into account origins of wood logging. The diameter and the height of every cut stalk were measured from the ground. This allowed us to estimate the volume of cut stumps for the whole vegetation. We considered 90 % of these volumes as the part used by the local population for fire wood and usage. Quantification and loss of the herbaceous phytomass in the different type s ofsavannas The production of the herbaceous phytomass was measured during three years. To estimate this phytomass, 5 small places of 1 x 1 m on an area of 10 x 10 m were measured by means of a ribbon meter. The measures were systematically realized in the intersection of two diagonals of each plot of land of 10 x 10 m. Twenty (25) small places by hectare were held as replication that is a total of 1,600 small places of 1x1 m². The fresh biomass was collected and in continuation dried in the autoclave at the University of Ngaoundéré and then weighed. The loss of herbaceous phytomasswas estimated at 10 %. Quantification of the litter and residues of the litter The litters of shrubs and big trees were collected on 10 feet chosen at random on elementary surfaces of 1x1m 2 in the plots of land of 50 x 50 m. Samples, collected during the period of maximal production of the litter (October to February) were sorted out to free diverse fragments (representing 10 % of the litter). In all 1,200 samples were collected, dried in the steam room and weighed with a precision weighing balance. Evaluation of the total phytomass of savannas The total phytomass was established by the air and subterranean phytomass of shrubs and trees, useful wood and cuts, herbaceous phytomass and by the litter. Carbon sequestration in the savannas Sequestration of epigeic carbon For the shrubs, carbon sequestration was estimated as follows: QCv = (TDM x C)/100, where, QC is the quantity of sequestrated carbon (t/ha/year); C = concentration in carbon. The value of carbon concentration (45 %) was used (Kotto-Samé et al., 1997). For big trees, the allometric equation of Brownet al. (1989) and Gauquelin et al. (1995) were adopted: Y = x D x D 2, where Y = biomass (t. C ha -1 ), D = DPH; R 2 = 0.78 was adopted. Sequestration of hypogeic carbon For shrubs with small roots, the carbon was estimated as follows: QCs = (D x C x d)/100; where QCs is the quantity of soil carbon, d the depth of the soil, D the apparent density of soil, C the concentration of the soil. For big trees with big roots, the weights are calculated according to the following formula: Wr = (D 2 H) 0.775, Wr (kg), where D is the diameter (cm) and H the height (m). Data Analysis Data were analysed using statigraphics and excel. The Duncan Multiple Test was used for the separation of means on the quantification of phytomass and useful woods of the savanna. XL stat used to analyse of the principal component. Tchobsala et al. 043 Quantity phytomass and Carbon sequastration (t/ha/year) Sb 1 Sb 2 Sb 3 Ar 1 Ar 2 Ar 3 Wo 1 Wo 2 Wo 3 Type of different plant formation related to seasons T0Ph T0Se T1Ph T1Se T2Ph T2Se T3Ph T3Se Figure 2. Phytomass and carbon sequestration of trees in relation to different types of wood loggings and season in the guinea savanna of Ngaoundéré, Adamaoua, Region, Cameroon Keysword: numerals on the X-axis means:1=full rainy season (June - October); 2= beginning of dry season (November - December); 3= full dry season (January - March); Sb= shruubysavanna; Ar=arborescent savanna; Wo=woody savanna T0P: control; T1Ph: weak wood looging; T2Ph: average wood logging; T3P : high wood logging, Ph= Phytomass; Se= carbon sequestration. RESULTS Phytomass and carbon sequestration of trees in relation to different types of wood loggings and seasons The phytomass of the three savannas (shrubby, arborescent and woody) in relation to the different types of wood loggings and seasons was presented in Figure 2. The phytomass of the ligneous decreased drastically from tha -1 year -1 at the peak of the rainy season (June to October) to t. ha -1 year -1 at the peak of the dry season (January to February) in shrubby savanna. In arborescent savanna these values varied from 30.03t.ha - 1 year -1 at the peak of the rainy season to t ha -1 years- 1 at the peak of the dry season. Likewise, the phytomass decreased drastically from 35 t.ha -1 year -1 to t.ha -1 year -1 respectively in the rainy season to the dry season in woody s
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