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EFFECTS OF ANTHROPOGENIC DISTURBANCES ON BIOMASS AND POTENTIAL CARBON STORAGE IN LAF FOREST RESERVE (CAMEROON)

1. University of Maroua, Faculty of Science, Department of Biological Sciences, P.O. Box: 814 Maroua. 2. University of Maroua, Higher Teacher’s Training College, Department of Life and Earth Sciences, P.O. Box: 56 Maroua. 3. University of Ngaoundéré, Faculty of Science, Department of Biological Sciences, P.O. Box: 454 Ngaoundéré. . Manuscript Info Abstract . . Manuscript History Received: 05 May 2020 Final Accepted: 10 June 2020 Published: July 2020

Forested zones represent habitats where the greatest quantity of biomass and carbon are concentrated. The survey assessed the spatiotemporal dynamics of the landscapes of Laf forest reserve and the effect of human activities on its biomass and carbon storage. We used diachronic analysis of two Landsat satellite images LCOS_LITP of 1999 and 2019, which were processed using ArcGIS software. Three collection units (CU) were considered: i) CU 1 at the periphery; ii) CU 2 installed at 200 m from CU 1 , and iii) CU 3 at the middle of the reserve in order to estimate biomass and carbon storage in relation to anthropogenic disturbances. In each CU, transects of 1000 m x 20 m were installed, and within each transect, all trees with a diameter at breast height (dbh) ≥ 10 cm were recorded and characterized by the following attributes: species name, dbh at 1.30 m above ground level and height. Individuals which branch before 1.30 m were measured at 10 cm from the soil. The results indicate that the extension of the agricultural land passed from 630.42 ha in 1999 to 3094.17 ha in 2019. A total of 6866 trees was recorded, representing 55 species, 37 Genera and 21 Families. Basal areas were: CU 1 (BA = 6.11 m 2 /ha); CU 2 (BA = 18.00 m 2 /ha) and CU 3 (BA = 16.81 m 2 /ha). All the collection units were characterized by low Shannon diversity index (ISH < 3.5 bits). The woody biomass and carbon storage were: CU 1 (TB= 6.33 t/ha; CS= 2.98 tC/ha); CU 2 (TB= 16.12 t/ha; CS= 7.6 tC/ha); CU 3 (TB= 12.46 t/ha; CS= 5.86 tC/ha). The equivalent carbons were as follows: CU 1 (CO 2 eq= 10.93 t/ha); CU 2 (CO 2 eq= 27.89 t/ha) and CU 3 (CO 2 eq= 21.5 t/ha). There was a significant difference between CU 1 and the two other collection units (p < 0.001). The Laf Forest Reserve appears to be heavily disturbed particularly near villages. CU 2 performs the most important quantity of carbon storage due to enrichment plantations. Management efforts are required for the recovery of the reserve's ecosystems.

ISSN: 2320-5407
Int. J. Adv. Res. 8(07), 01-11 2 Introduction:-Global surface temperatures have increased by 0.8°C since the late nineteenth century, and 11 out of the 12 warmest years on record have occurred since 1995 (IPCC, 2007). Earth's mean temperature is projected to increase by 1. .8°C during the twenty-first century. The rate of increase in global temperature has been 0.15°C per decade since 1975 (IPCC, 2001). The observed climate changes are reportedly caused by emission of greenhouse gases (GHGs) through anthropogenic activities including land-use change, deforestation, biomass burning, draining of wetlands, soil cultivation and fossil fuel combustion. There's a strong interest in stabilizing the atmospheric abundance of CO 2 and other GHGs in order to mitigate the risks of global warming (Kluger, 2007;Walsh, 2007). Understanding the patterns of storage and production of organic matter in forests in relation to the disturbances is critical for management purposes and an essential aspect of studies of carbon cycle (Keller et al., 2001;Cairns et al., 2003). This can also be used to understand changes in forest structure resulting from succession or to differentiate between forest types (Cairns et al., 2003).
In the last few years, there has been increasing interest in the quantification of the biomass of forest ecosystems and its potential carbon fixation (Jhariya et al., 2014;Ibrahima et al., 2019). Living tree biomass pool is an important source of uncertainty in carbon balance from the tropical regions in part due to scarcity of reliable estimates of tree biomass and its variation across landscapes and forest types (Alves et al., 2010). In developing countries, protected areas are facing high anthropogenic disturbances due to fire, grazing, logging, felling, fuel wood extraction and collection of non-timber forest products (NTFPs) for livelihood of forest dwelling populations (Souare et al., 2012;Froumsia et al., 2012;Jhariya et al., 2014). Various anthropogenic activities are developed around and inside the Laf forest reserve since its creation in 1948, namely overgrazing, logging, biomass burning and agricultural activities. Fotsing et al. (2003) observed that between 1987 and 1999, the spaces occupied by muskuwari fields passed from 13.5% to 35%. This situation has not been improved despite the green sahel project set up by the government in the sudano-sahelian zone of Cameroon in 2008. There is severe ongoing anthropogenic pressure on the Laf forest reserve which needs to be raised in order to integrate and protect local and global forest values. The need for a local assessment of land cover, particularly in developing countries has been highlighted by several studies (Lambin et al., 2003;Vadrevu et al., 2015). The study was carried out specifically to: -assess the spatio-temporal extension of the land use/ land cover of the Laf forest reserve in 1999 and 2019; -inventory the woody species of the reserve; -estimate the biomass and carbon storage of the reserve.

Study site:
The study was carried out in the Laf Forest Reserve (LFR) in the sudano-sahelian zone of Cameroon. The Reserve, at its creation in 1948, covered an area of 5 000 ha and lies between 10°14'24'' to 10°19'12'' N and 14°15'0'' to 14°21' 0'' E ( Figure 1). The average altitude is about 450 m and the vertisols (karal) are the most represented soils where muskuwari (dry season sorghum) is cultivated, and ferruginous soils or planosols where rainy season crops are grown (maize, groundnuts, millet). Laf is situated in the domain of thorny steppe, but the general physiognomy is that of the savannah. The most represented species are: Acacia hockii, Albizia chevaleri, Balanites aegyptiaca, Bauhinia rufescens, Combretum aculeatum, Dichrostachys cinerea, Ziziphus mauritiana, Piliostigma reticulatum, Strychnos spinosa and Ximenia americana (Letouzey, 1985). More than 18 915 people (Bucrep, 2005) live at the periphery of the reserve and rely on agriculture, livestock, and forest resources such as non-timber forest products to meet their basic needs.
3 Figure 1:-Map of location of the study site.

Data collection: Estimation of land use/land cover change:
The approach is based on a diachronic analysis of satellite images, and direct observations on the field. The remote sensing data consists of Landsat images LCOS_LITB and data base SOGEFI 1999 and 2019 showing land cover taken in 1999 and 2019, respectively. The images contain location information provided by the National Geospatial Agency and the US Geological Survey which are freely downloadable. Geocover images have the advantage of being orthorectified Landsat images, so they can be easily integrated into a geographic information system (GIS). The images were acquired at the same period, on January in dry season. Images captured in dry season have the advantage of low cloud cover.

Woody species inventory:
The transect method developed by Lejoly (1993) and Guedje (2002) was used for the inventory of the woody species. Three collection units (CU) constituting the treatments were established at the periphery (CU 1 ), CU 2 at 200 m from CU 1 and CU 3 at the middle of the reserve. Four transects (1000 m x 10 m) constituting the replications were installed in each collection unit, following the four points of the compass, with a total of twelve 1-ha. Along each transect, all woody individuals with a diameter at breast height (dbh) ≥ 10 cm were measured. Individuals that plug in before 1.30 m in height were measured at 10 cm from the ground (Jiagho et al., 2016).

Estimation of biomass and carbon storage of the woody species:
The total biomass of standing woody plants is constituted of the Above Ground Biomass (AGB) and Below Ground Biomass (BGB). We used the non-destructive method to evaluate the biomass, and as such the AGB was estimated with the allometric model developed by Djomo et al. (2010) for dry forest of tropical Africa and the BGB with the method developed by the IPCC (2006). We used the method developed by IPCC (2006) to estimate the carbon stock. The method consists in multiplying the estimated total biomass by 0.47.

Data processing and analysis:
For the image processing, the first phase of the treatment consisted of the combination of different spectral bands and allowed to obtain the images of two dates: 1999 and 2019. The images were all geo-rectified with UTM WGS 84 with radiometric corrections. Coloured compositions were created after adjusting the images, and then the study 4 area was extracted from the scene to determine the land cover types by classifying images. The images were segmented into sub-classes, namely wooded savannah, shrub savannah, fields and naked soils. These sub-classes allowed appreciating the land cover in 1999 and 2019. The ArcQGIS software was used to perform the images.
We assessed diversity of plant species with Shannon-Weaver diversity index (H') (Magurran, 2004) and Shannon's Evenness index (EQ). Diversity index takes into account not only the number of species but also whether species are more or less equally abundant, or whether in contrast one or a few species dominate. H' = -ΣNi/N log 2 Ni/N, where H' = index of species diversity (bits), Ni = number of individuals of a given species i, N = total number of individuals, log 2 = logarithm in basis 2. EQ = H'/log 2 N, this index varies from 0 to 1.
To describe the ecological importance of species and families within each transect as well as for the total flora, the species importance value index (IVI) and family importance value index (FIV) (Mori et al., 1983), were also calculated: Relative abundance = (number of trees of the species or family/total number of trees) × 100 Relative frequency = (frequency of a species/sum of all frequencies) × 100 Family relative diversity = (number of species in a family/total number of species) × 100 IVI = relative density + relative frequency + relative dominance FIV = family relative diversity + relative density + relative dominance

Diversity and species richness within the collection units (CU):
A total of 6 866 individual trees with dbh ≥ 10 cm was recorded within the three collection units (CU), representing 55 species, 37 genera and 21 families. All the trees were identified at the level of the species, and the number of species varied from 22 to 47 species per CU. The number of species was lower in CU 1 at the periphery of the reserve (22 species), moderate in CU 2 (38 species) and higher in CU 3 (47 species) ( and Shannon's evenness index value (Pearson, r = 0.99) (Figure 3). There was a significant difference between CU 1 and the two other collection units (ANOVA, p < 0.001).    Biomass and potential carbon storage of woody species : Total biomass (TB) in the different collection units varied from 6.33 t/ha to 16.12 t/ha and the total biomass in the three collection units of 12 ha inventoried were 34.91 t/ha. CU 2 recorded the most important biomass and carbon storage (TB = 16.12 t/ha; CS = 7.6 tC/ha), and the lower values were recorded in CU 1 (TB = 6.33 t/ha; CS = 2.98 tC/ha). The total carbon storage for the three collection units was 16.44 tC/ha. The carbon equivalent was also higher in CU 2 and less in CU 1 (CO 2 eq = 27.89 t/ha; 10.93 t/ha respectively) ( Table 5).   Mimosaceae and Combretaceae in the study site is due to the fact that drought in the Sahel has allowed natural selection of the most robust species like these families. They are resistant to the lack and insufficient rains but also to high temperatures. These families are the most common and highly represented in tropical countries, particularly in African savannahs and more typical in sudano-sahelian zones. Similar results were found by Bognounou et al.

Biomass and carbon storage:
In Laf forest reserve, characteristics of woody biomass and carbon storage varied from a collection unit to another. These characteristics constituted a good tool of appreciation of the anthropogenic activities in the sector. They turned out to be weak in CU 1 at the periphery but moderate in CU 2 and CU 3 (  ., 2016). The quantities of biomass and carbon stock are low in savannahs because of their grassy character, therefore less rich in tree species. In the Laf forest reserve, this situation is exaggerated by the anthropogenic activities, namely logging, overgrazing and agricultural activities. However, our results are much lower than those of the Sudano-Guinean savannahs of Ngaoundere in Cameroon, between 81.48 tC/ha and 118.36 tC/ha (Ibrahima and Fanta, 2008). In fact, the Sudano-guinean zone of Cameroon is situated between the tropical rain forests of the South and the dry savannahs of the North which present similar climatic characteristics of wet savannahs. Now, the carbon storage capacity is higher in wet savannahs compared to those of dry savannahs (Ciesla, 1997).

Conclusion:-
Anthropogenic activities in tropical areas threaten biodiversity and protected area integrity and then affect global ecosystem function and services. The survey aimed at assessing the effect of anthropogenic disturbances on biomass and carbon storage within Laf forest reserve in 1999 and 2019. The results showed that anthropogenic activities have negative impact on the stability of the reserve. The appropriation of land for the installation of fields has evolved over time, from the neighboring villages to the center of the reserve, given the increasing of the populations around and the growing needs for arable land. We observed a decline of shrub savannah, from 4161. 30  ) performed a good woody biomass (TB = 16.12 t/ha) and carbon storage (CS = 7.6 tC/ha) because the reforestation actions established in the unit. There was a significant difference between CU 1 and the two other collection units (ANOVA, P = 0.001). The Laf Forest Reserve appears to be heavily disturbed particularly near villages. Therefore, forestry agents of the Laf Forest Reserve can benefit from this study by planting local species in order to enrich the Reserve.