Can forest plantations harbour biodiversity similar to natural forest ecosystems over time?

摘要

This study assessed and compared tree species diversity in a 26-year-old Gmelina arborea plantation with tree diversities in primary and degraded natural forests in southwestern Nigeria. In each forest type, a one-hectare block was divided into 400 m2sample plots from which 4 were randomly selected, which was repeated on another one-hectare block, yielding eight 400 m2 plots per forest type. A 25 m2 quadrat was laid at the centre of each 400 m2 plot while a 4 m2 sub-quadrat was laid at the centre ofeach quadrat. Overstory, sapling and seedling species were inventoried in all 400 m2 plots, 25 m2 quadrats, and 4 m2 sub-quadrats, respectively. Family and species richness were significantly lower in G. arborea plantation overstory (7 families, 8 species) than in primary (8, 28) and degraded (18, 30) forest overstories. Diversity indices were also significantly lower for G. arborea plantation overstory than for primary and degraded forests. However, in the sapling layer, family and species richness inthe G. arborea plantation (10, 13) were similar to those of primary (9, 15) and degraded (9, 16) forests. The species richness of G. arborea plantation seedling layer (24) was similar with that of degraded forest (25) but significantly higher than thatof primary forest (18). primary (18 species), and degraded forests (25 species). Species diversity of the G. arborea sapling layerwct 2 (2.07) was significantly higher than that of its overstory (0.26) but significantly lower than those of primary (2.26)and degraded (2.44) forests. Of the species found in the G. arborea plantation seedling layer, 25% were absent in natural forests. Thus, this plantation understory harbours high biodiversity and can conserve biodiversity over time. Understory species diversity should be considered in biodiversity comparisons between plantations and natural forest.