Diversity and distribution of vascular cryptogams in relation to elevation gradient in Osomba range of the Cross River National Park, Cross River State, Nigeria

Abstract

Vascular cryptogams also known as Pteridophytes have been found to colonize the lower altitudes of world’s tropical forest regions. Hence, a study to establish the relationship existing between elevation gradient and Pteridophytes heterogeneity and distribution within Osomba Range, Cross River State, Nigeria was carried out. In this study, we delineated four elevation classes and enumerated the vascular cryptogam communities found at each level within the range using standard scientific protocol. Shannon-Wiener's (3.434 and 2.833) and Simpson’s indices of diversity (0.968 and 0.941) as well as Taxa (31 and 17) assumed a dump bell pattern with peak values associated with the mid-elevation classes (178 -205m and 232 – 240m) respectively. On the contrary, dominance followed an inverted dump bell distribution with its optimum (0.1667 and 0.2500) skewed towards the extreme elevation classes (297 – 295 m and 347- 405 m). Correlation analysis imprinted a significant (P<0.05) positive relationship between altitude and dominance (0.867*) but an inverse relationship between elevation and Simpson diversity (-0.867*). 178- 205 m and 232-240 m elevation classes were more comparable with lesser species heterogeneity judging from Bray and Curtis (0.458), Simpson (0.647) and Jaccard (0.297) similarity indices respectively. Conclusively, forty-nine (49) species of vascular cryptogams were identified and their occurrence seemed patchy in distribution along the gradient. This is an indication that elevation is an important factor amongst the suite of ecological drivers which determine the diversity of this critical group of plants. Further investigation on individual species response to ecological gradient is recommended as this will enhance the conservation of these vascular cryptogams within and outside the study area.