Aboveground Biomass and Carbon Content of a Cocoa – Gliricida Sepium Agroforestry System in Ghana
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https://dx.doi.org/10.4314/gjas.v53i1.4 45 Aboveground Biomass and Carbon content of a cocoa – Gliricida sepium agroforestry system in Ghana S. OWUSU, L. C. N. ANGLAAERE & S. ABUGRE* (S. O. & L. C. N. A.: CSIR-Forestry Research Institute of Ghana (CSIR-FORIG), Kumasi, Ghana.; S. A.: School of Natural Resources, University of Energy and Natural Resources, Sunyani, Ghana.) *Corresponding author’s email: [email protected] ABSTRACT To help overcome the challenge faced in re-establishing cocoa in degraded lands, some agroforestry trials were established with exotic leguminous tree species to determine their suitability for cocoa cultivation. However, our understanding of biomass accumulation and carbon sequestration in such specific agroforestry practices is still limited. In this study the above-ground biomass and carbon storage and partitioning in a gliricidia-cocoa agroforestry system was investigated. Above-ground biomass accumulation and carbon stock varied significantly between the components of the system, with the gliricidia shade trees having the highest values and the cocoa trees having the lowest. The inclusion of the gliricidia shade trees in the system increased above-ground biomass and carbon cap- ture of the system by some 60%, a greater proportion of which was contained in the branches of the shade trees. This pattern of dry matter distribution makes the species appropriate for use as a biomass producing species in agroforestry systems and demonstrates the potential of cocoa agroforestry sys- tems for capturing and storing more atmospheric carbon than sole cocoa systems. Original scientific paper. Received 2 Mar 2015; revised 19 Apr 2016 Introduction planted on newly cleared forest land (Dixon Cocoa (Theobroma cacao L.) agroforests are a et al., 2001). In Ghana, for instance, it is es- common farming system in the humid zone of timated that 80 % of the forest area has dis- West and Central Africa, in which forest trees appeared since cocoa trees were introduced provide shade and other environmental services (Cleaver, 1992). Presently, the traditional co- as well as marketable products (Oke & Odebiyi, coa-growing areas in many places are degrad- 2007). Traditionally, small holder cocoa farm- ed and have been abandoned. Re-establishing ers establish their farms by removing the forest cocoa in these areas has proven difficult due to under-storey and thinning the forest canopy so low soil fertility, bush fires, diseases and pest, that cocoa seedlings can grow into productive and inappropriate vegetation cover to provide trees (Duguma et al., 2001). shade for young cocoa (Adams, 1962; Ayan- However, in Africa cocoa cultivation is jala, 1983). Depletion of soil carbon has been generally considered to be a major cause of documented to result in decreased productivi- deforestation since the cocoa trees are often ty, poor soil physical and chemical properties, Ghana Jnl Agric. Sci. 53, 45 - 60 GJAS is an Open Access Journal and distributed under the terms of the Creative Commons (CC) License [CC BY 4.0] 46 S. Owusu et. al (2018) Ghana Jnl. Agric. Sci. 53, 45 - 60 and negative secondary environmental impacts instance, Tandon et al., (1991), estimated bole (Jose & Bardhan, 2012). To help overcome biomass and aboveground biomass of Populus the challenge faced in re-establishing cocoa in deltoides trees planted in agroforestry with a these degraded lands, some agroforestry trials spacing of 5 m × 5 m (400 trees/ha). Bole bi- were established with exotic leguminous tree omass was 17.42, 37.47 and 47.80 Mg ha–1 at species, including Gliricidia sepium (Jacq.) the age of 3, 5 and 7 years respectively. The Walp, to determine their suitability for cocoa total aboveground biomass (boles, branches cultivation in Ghana. These species are sup- and foliage) was estimated to be 26.91, 52.43 posed to replenish the soils through nitrogen and 65.76 Mg ha–1for 3, 5 and 7-yr-old plan- fixation and nutrient cycling, while providing tations respectively. Negi & Tandon, (1997), some other benefits such as fuel wood and fod- studied the biomass production of P. deltoides der, among others, for the farmers. It has been plantations having 917, 500, 489 and 783 trees well established that conversion of degraded ha–1for 3, 5, 7 and 9-yr-old tree respectively. agricultural soils into agroforestry systems can The standing bole biomass was in the order regenerate soil productivity (Jose & Bardhan, of 7.1, 15.3, 44.4 and 83.2 Mg ha–1respective- 2012). ly. According to Lodhiyal et al., (1992), total It has been pointed out that agroforestry aboveground biomass of P. deltoides varied systems have the potential to combine agricul- from 67.6 to 149.3 t ha–1, of which bole bio- tural production, the supply of woody biomass mass range was 41.3–101.8 Mg ha–1for 5– 9-yr- and the provision of numerous environmental old plantations having a density of 400 trees/ services, such as carbon storage, conservation ha. Lodhiyal et al., (1995) again studied the of biodiversity and soil protection (Jose, 2009). dry-matter production in poplar and found that Aboveground woody biomass plays a decisive in an agrisilviculture system, the estimated car- role considering the economic value of the bon stock in stem wood and aboveground bio- agroforestry systems as well as the carbon stor- mass was 42.36 and 65.62 Mg ha–1respectively, age. Production systems like agroforestry have for 8 – year old plantations. Total carbon stock to meet ecological and socio-economic sustain- as tree biomass in agrisilviculture systems was ability as a condition for acceptance and im- estimated to be 83.07 Mg ha–1 at a rotation pe- plementation by producers and society (Abra- riod of 7 years. hamson et al., 1998). As has been highlighted, Utilization of trees and shrubs has long aboveground woody biomass of agroforestry been recognized to be one of the most effective systems plays a decisive role for the assess- means of improving both the supply and the ments of the economic viability and several quality of forage in tropical smallholder live- ecosystems studies on carbon sequestration, stock systems, especially during the dry season energy and nutrients flows, forest and green- (Gutteridge & Shelton, 1994; Robinson, 1985). house gas inventories (Afas et al., 2008). Bio- Green fodder from nitrogen-fixing leguminous mass studies in agroforestry systems in Ghana trees, in particular, contains much higher lev- are still quite limited. However, a number of els of protein than the poor quality basal feeds biomass studies have been carried out for var- (grasses and crop residues such as stover) ious tree-crop combinations elsewhere that available during the dry season, and persists demonstrate and highlight the importance of for longer owing to the trees’ deep roots (Rizvi, these studies for ecosystem management. For 2011). Aboveground Biomass and Carbon content of a Cocoa–Gliricida sepium... 47 As pointed out by Dhyani et al., (2009), wood alone and 96.23 Mg ha–1 in total biomass agroforestry is an ideal option to increase pro- of trees. Fang et al., (2007), comparing carbon ductivity of wastelands, increase tree cover storage in P. deltoides plantations with differ- outside the forest and reduce human pressure ent stocking densities, found that total carbon on forests under different agro-ecological re- storage in the poplar plantation of 1,111 stems gions, and is then a viable option to prevent and ha–1 was the highest and about 72.0 Mg ha–1, mitigate climate-change effects. Cocoa based which was 5.4%, 11.9% and 24.8% higher than agroforestry systems are credited for stocking that in plantations of 833, 625 and 500 stems significant amounts of carbon and hence have ha–1 respectively, clearly indicating the influ- the potential to mitigate climate change. Global ence of tree stocking density on C stock. In a climate change and energy security are two key study by Rizvi et al., (2011) they recorded a issues that are at the forefront of environmen- standing/total carbon stock of 3.78–11.62 Mg tal discussions the world over. Although they C ha-1 under poplar-based agroforestry in the bring up unique challenges, global warming upper Gangetic region, where 70 million pop- and energy security are inextricably interlinked lar trees are standing with agricultural crops. (Jose & Bardhan, 2012). Studies have revealed Woody biomass constitutes the major that deforestation and conversion of forest to source of energy in the developing countries agricultural lands contribute 17.4% of global of the world. In Ghana, fuelwood shortage has greenhouse gas emissions (IPCC, 2007). Many been identified as a pressing domestic problem observers see agroforestry systems as present- affecting many households (Otsyina, 1989). ing a promising alternative to common-prac- The need to establish energy plantations has tice agriculture in the tropics because they can been recognized. Several multipurpose tree serve as carbon sinks and biodiversity pools species, including G. sepium, have been recom- and may play a significant role in mitigating mended in Ghana for use in different land use or adapting to climate change (Tscharntke et systems to reduce or solve the pressing fuel- al., 2011; Soto-Pinto et al., 2010; Nair et al., wood problems which face many households 2009). A number of studies have estimated in the country (Quashie-Sam et al., 1990), as C stocks of different agroforestry systems in well as mitigate soil fertility problems and pro- other settings outside Ghana. Carbon stocks vide valuable fodder for livestock. One of the in shaded agroforestry systems with perennial commodities agroforestry is well suited to pro- crops, such as coffee (Coffea arabica L.), rub- ducing is biomass for bio power and biofuels ber (Hevea brasiliensis Muell.-Arg.), and co- (Jose et al., 2012).