Diversity and biovolume of tree species in natural forest ecosystem in the bitumen-producing area of ondo state, Nigeria: a baseline study

Abstract

Tree species diversity, biovolume and forest stand structure were investigated in natural forest ecosystem located around some selected communities in the bitumenproducing area of Ondo state, Nigeria. Two forest reserves and four free areas distributed in 4 Local Government Areas (LGA) of the state were selected for data collection, out of the total 6 LGAs in the bitumen belt of the state. The two forest reserves are Oluwa FR at Legge in Odigbo LGA and Eba Island FR in Ese-Odo LGA while the four free areas are located close to each of Omotoso community (Odigbo LGA), Ode-Aye community (Okitipupa), Igbo-Egunrin community (Ilaje) and Igbotako community (Okitipupa). Eight plots of equal size (20 9 20 m) were located in each of the selected location, using systematic line transect sampling design. In each plot, all living trees with dbh C 10 cm were identified with their botanical names and their dbhs were also measured. The results of the study reveal that there were ninety nine (99) tropical hardwood timber species (range: 21 to 48 species per selected forest). These species were distributed among twenty nine (29) families. While Funtumia elastica has the highest population distribution across the selected communities' forest, Euphorbiaceae was the dominant family in the entire area. Although there was a moderate variation in the biodiversity indices among the selected communities' forest, the Shannon-Weiner diversity index of H 1 = 4.02 and species evenness of E = 0.88 were obtained for the entire study area. Tree density summing up to 2,740 trees/6 ha varied moderately, with a range of 361-609 tree/ha, among the communities. Though most of the trees encountered belonged to the lowest diameter size class, the mean basal area and biovolume were 26.69 m 2 /ha and 262.36 m 3 /ha respectively. Recommendations guiding the decision on the allocation of the communities' forest to the bitumen exploratory industries are made and the need for good forest management of the prospective area of bitumen exploration of Ondo state is emphasized. This is to prevent the imminent loss of biological diversity that would eventually accompany the exploration.

Logging Impacts in Tropical Lowland Humid Forest on Tree Species Diversity and Environmental Conservation

“…Several researchers have adopted the use of Shannon-Weiner diversity index to investigate ecosystem diversity as it takes into consideration both the species richness and evenness in a community (Onyekwelu et al, 2005). The overall diversity index (Shannon-Weiner diversity (H 1 )) of 3.04 for logged forest, 3.16 for inviolate forest and 3.38 obtained when the species encountered from both sites were pooled is very close to the range of values (3.34-3.66) reported for some tropical rainforest sites in southern Nigeria by Adekunle (2006) and Adekunle and Olagoke (2007). This result is an indication that biological diversity is adequately conserved through the establishment of SNR especially for native species, keystone species and species with narrow range.…”

Phytoecological studies of some protected and degraded forest areas of Lowland Humid forest, Ondo state Nigeria: a Comparative approach

“…This is due to more frequent and heavy extraction of forest resources such as collection of fuel wood and NTFPs by the Local people. The number of family (30), number of Species (78) and Species Evenness (0.69) in this study corresponds to the results of Adekunle & Olagoke (2008) as well as Onyekwelu et al (2007) but lesser when compared to the studies of Lu et al (2010), Rajkumar & Parthasarathy (2008). These researchers reported a total of 95 species and 105 species in Xishuangbana, Chain tropical rainforest and India evergreen forest of Andaman Giant respectively.…”

“…These researchers reported a total of 95 species and 105 species in Xishuangbana, Chain tropical rainforest and India evergreen forest of Andaman Giant respectively. Various researchers have considered the use of Shannon wiener diversity index for the determination of forest community diversity in the tropics (Onyekwelu et al 2007, Adekunle & Olagoke 2008, Borah et al 2014, Boboye & Jimoh 2016. Shannon Diversity Index values for this study ranged between 2.79 and 3.55.…”

Appropriate Volume Functions for Leguminosae Family in Two Tropical Rainforests in Cross River State, Nigeria

“…The volume per hectare values recorded in this studies is an indication that the reserves are probably one of the richest of the tropical rainforest left in Nigeria when compare to the values reported by previous related researches carried out in other tropical rainforests of Nigeria (e.g. Adekunle et al, 2004;Adekunle and Olagoke, 2008). This may also be indication that, the reserves are probably well protected.…”

“…10 tree species were identified as belonging to caesalpinioideae, while 7 and 5 tree species belong to mimosoideae and papilionoideae respectively (Table 1). (Adekunle et al, 2004;Adekunle and Olagoke, 2008). The reason for relatively fewer number of tree individuals of larger dbh values greater than 0.50m (dbh > 0.50m) can be attributed to limited number of species that naturally grow up to this diameters class (Hartshorn, 1980) and the numbers of certain big tree species could have been already reduced by selective extraction for some uses in the past (Hadi et al, 2009).…”