Background 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 800m2 temporary sample plots, systematically laid along two transects of 1000m each. Understory tree species were assessed in 100m2 plots for saplings and 25m2 plots for seedlings in all sample plots.
Results 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. Some tree species were found to be unique to some sacred groves while some species that were absent in protected forests existed in the groves. The presence of these unique tree species indicated the potential of sacred groves in conserving important tree species. The high regeneration could be attributed to strict access restrictions in the groves, and the taboos and myths feared by the people. 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.
Conclusion 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.