Floristic Composition and Structure in Relation to Elevation in the Togo Plateau Forest Reserve in Ghana

Abstract

Plateau ecosystems are of special scientific and conservation interests as they harbour rich plant diversity and exhibit considerable spatial variability along elevation gradients. In this study, variations in floristic composition and structure in relation to elevation were studied in six-fringed communities Hohoe (HH), Alavanyo (AL), Santrokofi (SA), Akpafu (AK), Bowuri (BO), and Nkonya (NK) of the Togo Plateau Forest Reserve in Ghana to help provide explicit and effective management of this ecological hotspot. A total of 180 plots (each measuring 25m × 25m) were demarcated across the six communities for sampling of trees (DBH measured at 1.3 m above ground ≥10 cm). Smaller nested plots, measuring 5m × 5m and 1m × 1m, were used for sampling saplings (DBH < 10 cm, height > 1.5 m) and seedlings (DBH < 3 cm, height < 1.5 m), respectively. Species identity and abundance and elevation were recorded for each plot. Relationships of elevation gradient with vegetation attributes were analysed using simple linear regression. A total of 281 plant species (164 trees, 60 saplings and 57 seedlings) belonging to 66 families were recorded in the study. Leguminosae, Apocynaceae and Euphorbiaceae were the most dominant families across and along the elevation gradient. Average basal area of trees across the six communities was 44.72 m2/ha (ranged from 57.10 m2/ha at BO to 33.10 m2/ha at AL) whereas the Shannon-Weiner Index (H’) averaged 3.99 (ranged from 4.14 m2/ha at BO to 3.89 m2/ha at AL) and evenness index averaged 0.96 (ranged from 1.00 at BO to 0.92 at AL). The saplings and seedlings showed a similar pattern of composition and structure as the trees. The geographical locations of the study communities, which somehow correspond with different elevations of the plateau (i.e., BO, NK occur in lower elevations, SA, AL in mid elevations and HH, AL in higher elevations), was observed to have marginally influenced the composition and structure of the vegetation on the landscape. The most important trees listed in the study were Ceiba pentandra, Albizia zygia, and Terminalia superba. The saplings were Acacia camerunensis, Microdesmis puberula and Cnestis ferruginea. The seedlings were Chromoleana odorata, Palisota hirsuta and Costus affer. The most important tree species listed were distributed along a broad range of elevations. These results generally demonstrate the high floristic diversity of the Topo Plateau and the influence of elevation gradient on this, which should help in understanding of the composition and structure of several plateau ecosystems in Ghana and elsewhere.