Effect of heat on soil seedbank of three contrasting physiognomies in Shasha forest reserve, Southwestern Nigeria

Abstract

The effects of soil heating which usually occur during forest fires on the floristic composition and seed density of the soil seed bank of Shasha forest reserve in Southwestern Nigeria was investigated and the potential of the soil seedbank in forest restoration process (especially after a fire) was examined. Three distinct sites (Regrowth forest, Gmelina and Pinus plantations) were selected in the forest reserve. Species enumeration, identification and distribution into families of the standing vegetation were carried out. Soil samples were collected at 0–15 cm depth from each plot in March 2012. One set of replicate samples was heated in an oven until the soil reached 80 °C (to simulate typical temperature at soil surface during forest fires) while the other serves as a control. They were subjected to seedling emergence for six months to determine the density and species composition of the seed banks of the study sites. Seedling emergence result for heated and unheated soil samples showed that the seedbank density was higher in control than heated samples in the three sites. Few woody species emerged from the soil seedbank of three study sites and in both control and heated samples. There was a significant difference in total seed density when treatments were compared (P < 0.05) and no significant difference (P > 0.05) when sites were compared. Diversity and evenness indices follow the order Regrowth forest > Pinus plantation > Gmelina plantation. NMDS (non-metric multi-dimensional scaling) ordination revealed low similarity in the species composition of extant vegetation and seedbank. The potential of vegetation restoration of the disturbed forest reserve from seed bank is limited, and heat from fire had negative effects on the seed bank characteristics of the forest but selectively enhanced the emergence of species like Pinus carribaea.