**3. Result and discussion**

#### **3.1 Carbon stock in tree species**

During biophysical survey total of 37 tree species from 16 families were found in the study area. There were equal species distribution in all villages. Carbon stock per individual tree were computed to identify the tree species which contribute more to the carbon stock in all the agroforestry technology. Over all the Tree species found during the field survey the *Mangifera indica* species were found to have

high carbon stock 189.88 Mg C ha−1 followed by *Cocos nucifera* 98.44 Mg C ha−1. *Theobroma cacao* and *Vertex doniana* had 0.0013 MgCha−1 and 0.0008 MgCha−1 respectively which is lesser in the list of all species studied **Table 1**.


#### **Table 1.**

*Biomass accumulated and carbon sequestered in different tree species.*


**Table 2.**

*Average estimated biomass and carbon stock under different agroforestry system.*

#### **3.2 Carbon stock in different agroforestry technologies**

Also, biomass and carbon stock were computed and presented based on agroforestry technology. Based on agroforestry technology Total biomass average were 46.43 ± 7.85 for Boundary, 813.09 ± 352.32 for Home garden, 41.84 ± 10.67 for mixed intercropping and 57.92 ± 14.75 for Parkland. Carbon stock for agroforestry technologies were also computed and the results shows that Boundary had 23.22 ± 3.92, Home garden 406.55 ± 176.16, Mixed intercropping 20.92 ± 5.34 and Parkland were 28.96 ± 7.38 (**Table 2**)

## **4. Discussion**

#### **4.1 Carbon stock in tree species**

From the results all the 37 species obtained during biophysical survey *Mangifera indica* had the highest amount of carbon stock on its biomass 189.88 MgCha−1 followed by *Cocos nucifera* with 98.44MgCha−1. High amount of carbon in this species may be due to its dominance as a result of high demand of mango tree product as well as palm tree products (fruits and coconut juice) both domestic and local market demand [23]. This cannot be explained only by the total number of appearances of *Mangifera indica* which is 178 because there were other species which appeared mostly than *Mangifera indica* but by the superiority of the Dbh than the other species. Study conducted in Philippines on carbon sequestration revealed that *Mangifera indica* can sequester 100.71 MgCha−1. This is lower than the amount obtained in this study. In fact, Brown [24] and Gibbs, [25] reported that Dbh is 95% of the total biomass, and in this study *Mangifera indica* present huge biomass and carbon stock which can be due to its high average diameter and height. Other species like *Theobroma cacao* and *Vertex doniana* had lesser carbon stock due to smaller average diameter and height. Age of the tree and number of occurrences of a tree in the plots also can be used to justify the amount of carbon stored in a particular species [26]. Usually, older tree undergone photosynthetic activities with much longer time compare to younger tree and consequently are absorbing and storing more carbon [26]. The top most tree with highest biomass were tree species used for food (*Cocos nucifera*), fruits (*Mangifera indica and Persea americana*), timber production, (*Tectona grandis*) and one mostly used for shade (*Ficus stuhlmannii*). Variety of species documented and observed during the field display the potential for agroforestry to enhance the resilience for farmer for present and future climate risk. For example, farmer in both villages maintain varieties of trees for timber, fruits, animal fodder to support livestock during drought. Similar study conducted in Kenya shows that majority of small holder farmers maintain trees

*Carbon Sequestration in Agroforestry Technologies as a Strategy for Climate Change Mitigation DOI: http://dx.doi.org/10.5772/intechopen.100036*

not only for food support but also for the soil and water conservation [27, 28]. There was variable distribution of tree species on different land uses. High tree species diversity was found in home garden where multipurpose trees for various purpose such as shade, timber, and food are grown. For example, the tree with high frequency in home garden were *Mangifera indica*, *Cocos nucifera, Persea americana, Tectona grandis and Ficus stuhlmannii*. Moreover, Kindt *et al*., [29] pointed out that usually high economic values trees are widely spread in a farm land.

## **4.2 Carbon stock in agroforestry technologies**

A number of studies have shown that agroforestry in tropics have high Carbon stock than any crop field or pasture [5, 30]. From the result home garden leads in the carbon sequestration with 19 514.2 Mg C ha−1. This result is highly influenced by the mixture of component of agroforestry such as cattle's, high occurrence of trees and agricultural crops. In other way home garden have been observed as the potential technology for carbon sequestration due to the fact that it sequesters carbon in biomass as well as in soil, reduce fossils fuel burning by encouraging fuelwood production and reduce pressure on natural forest. More ever in home garden there is no complete removal of biomass [31, 32]. Similar study conducted in India shows that home garden of 12-17 years accumulate 55.8-162MgCha−1[33]. Agroforestry technology study conducted in by Kumar [34] showed that based on species composition, soil and climate generally agroforestry can sequester carbon of 68–228 Mg C ha−1. High amount of carbon stock in home garden maybe the progress of carbon sequestration which was estimated to be 391 000MgCha−1 by 2010 and 586 000MgCha−1 by 2040 [35]. Mixed intercropping which involves wood perennial and herbaceous crop were observed to store 648.44 Mg C ha−1. High carbon within the mixed intercropping is higher than those of from the sole cropping system due to addition carbon pool in tree and increased carbon soil carbon pool as a result of carbon input from litter fall and fine root turn over [36] mixed intercropping can store 121–125 Mg C ha−1 and this was explained by the higher growth and assimilation rates [37]. Parkland technology was observed to store 144 MgCha−1. Parkland technology unlike

mixed intercropping the trees are not arranged in accordance with crops but some little trees are left on the crop land. Study conducted in Guinea shows parkland carbon stock may also range from 22.22–70.8 Mg C ha−1 [38]. Parkland agroforestry are very stable (long standing) and high carbon storage [39]. On boundary agroforestry the tree is planted purposely for indicating the boundary or fencing. In this study boundary agroforestry technology stored 139.29

Mg C ha−1. Study show that Boundary planting have positive effect on both soil character tics, crop production and carbon sequestration [30]. Hooda *et al*., [40] indicate that tree boundary and herbaceous crop can have carbon storage ranging from 18.53–116.29 Mg C ha−1. Other study indicates that greater potential of carbon sequestration was found in the boundary plantation of *Populus deltoides* and Eucalyptus hybrid [41]. In this study the carbon stock was found to be higher compared to other studies conducted in various areas. The difference in the carbon stock can be explained by factors such as allometric equation which could be a limitation resulting in large variation in such estimate [42]. Low cutting of trees in the field could also be the source of high mount of carbon. In the study many trees observed were for various purposes such as food, fruits, shade, wind break and for boundary hence maintained for long time hence sequestering high amount of carbon.
