Understory species diversity, regeneration and recruitment potential of sacred groves in south west Nigeria

Abstract

Global species extinction rates due to forest conversions are increasing. Ecologists, conservationists and governments have adopted various conservation methods. Sacred grove is one conservation option that has gained attention in recent time. We assessed understory species diversity, regeneration and recruitment potentials of four sacred groves in southwestern Nigeria. Overstory tree species were inventoried in eight 800 m2 temporary sample plots, systematically laid along two transects of 1000 m each. Understory tree species were assessed in 100 m2 plots for saplings and 25 m2 plots for seedlings in all sample plots. Shannon–Wiener diversity index (1.8–3.46 (overstory); 2.65–3.55 (understory)), number of species (32–58 (overstory); 39–78 (understory)) and tree density (309–417 individuals/ha (overstory); 775–1445 individuals/ha (understory)) were comparable and/or higher at the understories than the overstories. Dbh distribution curves showed highest stand density at the lowest class (10–20 cm) and decreased with increasing dbh, indicating good regeneration status and healthy ecosystem. Regeneration was considered good and fair, because in most cases, number of seedlings > saplings > overstory trees or number of seedlings > saplings ≤ overstory trees. The good regeneration status was further confirmed by the good species recruitment in the understory. However, the high influx of people into sacred groves for festivals and rituals, which results in trampling and burning of seedlings, is a threat to the diversity, regeneration and recruitment potentials of the groves. High regeneration and recruitment status maintained in all the sacred groves in this study were achieved using taboos, cultural and traditional methods. These methods could be incorporated in managing forest reserves in Southwestern Nigeria.