**3. Results**

#### **3.1 Phytosociological characteristics, diversity and biomass estimation**

The phytosociological characteristics, diversity and biomass estimation of these protected forests were analysed in this study (**Table 1**). The table indicates that a total of 370 individual trees per hectare, disproportionately distributed between 53


#### **Table 1.**

*Growth characteristics, biodiversity indices and ecosystem services.*

*Phyto-Sociological Attributes, Ecosystem Services and Conservation Dynamics of Three… DOI: http://dx.doi.org/10.5772/intechopen.106433*

different species in 25 families, were encountered in Omo biosphere reserve while 381 stems in 63 species in 24 families and Okomu national park recorded 352 individual stems, 59 species and 25 families. There were significant differences in all the growth variables investigated in this study across the three protected forests (**Table 1**). The three protected forests had high tree species diversity index (Shannon-Wiener diversity index of 3.19 for Omo BR, 3.90 for Akure SNR and 3.45 for Okomu NP). The Simpson concentration index and species evenness are assessed for these protected forests as 0.954, 0.951 and 0.969 while 0.574, 0.571 and 0.707 for Omo BR, Akure SNR and Okomu NP, respectively. There were significant differences in all the biodiversity indices investigated in this study across the three protected forests (**Table 1**), indicating that diversity is dissimilar between the forests. The biological diversity indices of the protected forests compared favorably with other protected natural forests, sacred groves and other natural forest formations. The values for basal area (36.63, 72.39, and 32.47 m<sup>2</sup> ), volume (427.08, 929.05, and 366.71 m<sup>3</sup> ), above-ground biomass (153.20, 316.73, and 353.92 ton), below-ground biomass (30.64, 63.35, and 190.04 ton) and total carbon stock (70.78, 91.92, and 212.35 ton) for Omo BR, Akure SNR and Okomu NP, respectively. There were significant differences in all the biomass and carbon storage investigated in this study across the three protected forests (**Table 1**), indicating the carbon sequestration potentials of the forests.

#### **3.2 Diameter distribution and canopy structure of the protected forests**

The diameter distribution of trees in these protected forests followed inverted J distribution pattern common with tropical forest ecosystems (**Figure 1**). The figure reveals that the highest number of trees (205 stems/ha) was in the diameter class of less than 15 cm in Okomu NP followed by (168 and 108 stems/ha) Akure SNR and Omo BR Osogbo, respectively. The vertical structure of the selected protected forests is shown in **Figure 2**. The structures of these protected forests were determined by the canopy distribution of the forests, which was calculated based on the height distributions of the tree species. The figure reveals that the highest numbers of trees (111 stems/ha Akure SNR and 99 stems/ha Okomu NP) were in the middle canopy

**Figure 1.** *Diameter distribution class for the protected forests.*

**Figure 2.** *Canopy structure based on height distribution for the protected forests.*

structure of the forest followed by (108 stems/ha Omo BR) at the lower canopy structure of the forest.

## **4. Discussions**

In these protected forests, individual tree density and species were recorded 370 (53) Omo BR, 381 (63) Akure SNR and 352 (59) Okomu NP. Similar tree compositions were reported in different researches across the tropical ecosystems, Onyekwelu *et al.* [6] reported 55, 73 and 78 for Osun Osogbo, Idanre hill and Ogun Onire sacred groves, respectively, in Nigeria, Baul *et al.* [19] reported 52 tree species in farm forests in Nepal, Chowdhury *et al.* [20] reported 55 tree species in village common forests of Khagrachari while Roy *et al.* [21] reported 62 species in the home gardens of Bangladesh [22]. The assessment of plant species revealed that all the encountered trees in the three protected forests were indigenous tropical hardwood species that are of economic value to humans and their environment. This is an indication that the three protected forests are repositories of many indigenous tropical hardwood tree species that are of high ecological, social and economic values. Forest habitats play an important role in the effective functioning of the forest ecosystem, and protected forests serve as *in-situ* conservation for rare plants being disturbed by anthropogenic activities [23]. This is crucial to the sustainable management and preservation of tree diversity resources. The tree species diversity and abundance of these protected forests as determined by the biodiversity indices indicated that these protected forests fulfilled the mandate of a biodiversity conservation strategy [24].

Biodiversity indices for these protected forests represent the diversity of floral compositions and their distribution in these forests. Tree species diversity and evenness indices found in this study are comparable to the study of Onyekwelu *et al.* [6], which reported that 3.19 (0.84), 3.25 (0.85) and 3.46 (0.86) for Osun Osogbo, Idanre hill and Ogun Onire sacred groves, respectively, in Nigeria. Lower Shannon-Wiener tree species diversity index of (1.80) was recorded in sacred grove of Igbo Olodumare, (1.23) was recorded for home gardens in Northern Bangladesh while (1.64) was recorded for protected forests of Bangladesh [25, 26], and (1.34) was recorded for collaborative forests in Nepal [27]. The Phytosociological attribute and floristic

*Phyto-Sociological Attributes, Ecosystem Services and Conservation Dynamics of Three… DOI: http://dx.doi.org/10.5772/intechopen.106433*

diversity of these selected protected forests were discovered to be comparable with other protected areas of tropical forest ecosystems of south-west, Nigeria [1]. The stand densities were also similar to those obtained for Garo hills, India [28], Borneo rainforest [29], Indonesian forest [30] and the Mexican tropical deciduous forest [31].

#### **4.1 Biomass and Carbon stock estimation**

Tropical forests are known to play an important role in regulating the global carbon cycle. The biomass of tropical forests plays a critical role in micro and macro absorption of carbon and carbon cycling of forest ecosystems [32]. However, tropical forest ecosystems particularly protected forests need to be adequately and regularly investigated for carbon stock accumulation. The total biomass of 183.83 kg ha<sup>1</sup> ; 380.08 kg ha<sup>1</sup> and 543.96 kg ha<sup>1</sup> was recorded for Omo BR, Akure SNR and Okomu NP, respectively, which is lower than 164.82 ton ha<sup>1</sup> recorded for India forest and 156.73 ton ha<sup>1</sup> for Nigerian forest, respectively [4, 33]. The result of biomass in these protected forests is comparable with the studies of Wittmann *et al.* [32], which estimated 259.45 kg ha<sup>1</sup> for Southern Pantanal, Brazil. Agbelade and Adeagbo [5] estimated 617.85 kg ha<sup>1</sup> and 209.26 kg ha<sup>1</sup> for Akure SNR and Osun Osogbo sacred grove, respectively. The disparity in the values maybe a result of the different methods and equations adopted, this study uses BEF while other researchers used allometric equations. Carbon storage of forest biomass is an important attribute of a stable forest ecosystem and a key link in global carbon cycle. The total carbon stock estimated for these protected forests is 70.78 kg ha<sup>1</sup> , 91.92 kg ha<sup>1</sup> and 212.35 kg ha<sup>1</sup> for Omo BR, Akure SNR and Okomu NP, respectively, which is lower than 617.86 kg ha1 recorded for Akure strict nature reserve and 209.27 kg ha<sup>1</sup> for Osun Osogbo sacred grove [5]. Adekunle *et al.* [4]; IPCC [16] recorded 82.41 ton ha<sup>1</sup> for Indian forest and 78.29 kg ha<sup>1</sup> for Eda SNR, which can be compared with the result of this study. Tabue *et al.* [34] estimated 354.73 Mg ha<sup>1</sup> for Dja wildlife reserve in Cameroon. Munishi and Shear [35] reported over 300 Mg ha<sup>1</sup> carbon stock in Tanzanian Eastern forests. The above results indicated that protected forests would contribute significantly to carbon sequestration and climate change mitigation as long as the forest is adequately protected from deforestation and degradation. Thus, besides being a reservoir of biodiversity, protected forests also act as sink of atmospheric CO2. The high biomass and carbon stock in this forest reserve is attributed to the effective conservation system that prevented the forest from degradation and deforestation as well as the federal government policy on National parks.

## **5. Conclusion**

The use of protected forests is important for biodiversity and climate change mitigation. The scientific information provided by this research would further promote accurate estimation of the tree species diversity, stand volume and carbon stock in the Okomu protected forest. The results of the study indicated that there are many indigenous tropical tree species that are rare and in danger of extinction. There is strong evidence of active regeneration status, which indicates a good future for the Okomu protected forest. The study shows that the biodiversity-protected forests act as sink of atmospheric CO2 because of their high carbon stock and high biomass. The research revealed the abundance of relative dominant trees as well as their contributions to the preservation of the environment. This reference can be used to compare

changes in carbon stocks over time. The current position of protected areas in terms of tree species abundance, evenness, carbon sequestration, productivity and structure shows the effectiveness of *in-situ* management. The forest has the potential to serve as a long-term carbon sink due to its good potential for carbon sequestration. To continue providing these ecosystem services and functions, the previous method that prevented the forest reserve from being degraded should be maintained and strengthened. According to the study, strict measures should be taken on identified protected areas so as to ensure their continuous impact on the environment.
