A comparative assessment of species diversity and structural characteristics in undisturbed forest reserve and protected forest in the humid tropical rainforests of Southwestern Nigeria

Abstract The study compared the structural characteristics of woody species in Ise Ekiti’s relatively undisturbed forest reserve (UFR) and Ikogosi warm spring protected forest (PF) in humid tropical rainforests of southwestern Nigeria. Plot sizes of 25 m × 25 m were randomly mapped out in each plot of the study site. Results revealed Celtis zenkeri has a higher value of basal area-BA (12.857 m 2 ha −1 ), Important value index -IVI (29.26), and stem density-SD (1216 trees ha −1) in the UFR compared with the values recorded in PF (1.3 m 2 ha −1 , 5.03 IVI, 80 trees ha −1 ). While the Sterculiaceae family is dominant in UFR, the Fabaceae family is dominant in PF. The results showed that values of BA (118.833 m 2 ha −1 and SD (15,008 trees ha −1 ) in UFR were higher than the values in PF (97.8 m 2 ha −1 , 3,312 trees ha −1 ). The results revealed the value of Simpson_1-D, Shannon, Pielou’s evenness index (E), and Margalef’s index of species richness (M) (1.86, 6.2, 1.98, 14.75) in the UFR was higher compared to the PA (0.033, 3.7, 1.04, 9.94), respectively. Findings showed that the value of SD in UFR is significantly higher ( P < 0.05) than in PA. While there is a robust positive correlation between BA and SD, SD and IVI in UFR ( p < 0.05), the results indicated that there is a strong positive correlation (ρ = 0.745) between BA and SD in PF. It can be concluded from this study that essential metrics for comprehending structural characteristics of forest ecology, which offer valuable information on past forest protection strategies, have higher values in relatively undisturbed forest reserves compared to protected forests. These findings underscore the importance of minimizing disturbances in forest management practices to enhance sustainable silvicultural management and strengthen conservation efforts for maintaining biodiversity and ecosystem integrity, which are critical for climate change mitigation.