Temporal pattern of tree community dynamics in a secondary forest in Southwestern Nigeria,29 years after a ground fire.
The study determined successional replacement model among the functional groups in the forest, the changes in floristic composition and community structure and tree mortality and recruitment rates in a secondary forest at Ile-Ife, 29 years after fire. It also determined if change in basal area of the tree community within time period results from recruitment and mortality of all tree species and assessed whether changes in rainfall and temperature were the major drivers of change in the forest. This was with a view to determining the stand temporal pattern of tree community dynamics in a moist forest regenerating after fire disturbance. Two sample plots, 0.25 ha each, were established in burnt and unburnt parts of the secondary forest. In each plot, woody plant species ≥ 1 cm in girth and 1m and above in height were completely enumerated, identified to species level, labelled with a permanent tag and girth size measured at breast height (gbh). The number of species, genera and families were established for each plot. The data collected were used to calculate species diversity indices, basal area, species evenness, density, similarity and dissimilarity indices for the plots. Tree mortality and recruitment rates were calculated using data from this study and previous studies in the burnt plot in 1983, 1984, 1997 and 2008. Correlation and regression analyses were used to assess whether decadal changes in rainfall and temperature were major drivers of changes in the forest after calculating decadal temperature and rainfalldata for 29 years collected from various Meteorological Stations on the campus. The results showed that a total of 380 trees were present in the 0.25 ha of the burnt plot, representing 63 species, 46 genera and 22 families. Stem density decreased from 4332 stem haˉˡ to haˉˡ, 29 years after the fire. The species diversity (H¹) which decreased to 2.50 in 2008 has increased to 3.50 in 2012. The species evenness which peaked (0.80) in 1997 decreased to 0.48 in 2012. The basal area which increased to 20.18 m² hˉ¹in 1997 and dropped to 14.62 m²hˉ¹in 2008 has increased to 21.34 m² hˉ¹in 2012. The tree annual mortality rates which continued todecrease one year after the fire (-2.02% y-1in 1984-1997, -5.16 % y-1 in 1997 -2008) had increased to 25.7% y-1 in2008-2012.The annual recruitment rates continued to decrease since the fire, decreasing to the lowest rate of-25.7 % y-1in 2008 -2012. There was a non-significant positive correlation between basal area and mortality ratesbut a non-significant negative correlation between basal area and recruitment rates.There was a non-significant positive correlation between decadal mean minimum temperature, decadal mean maximum temperature, decadal mean annual rainfall and density but a non-significant negative correlation between these climatic data and basal area, species richness and species diversity. The changes in community parameters in the forest as it recovers from the fire disturbance followed the tolerance model of succession. The study concluded that changes in the floristic, structural character, mortality and recruitment rates were still going on in the forest, 29 years after the fire disturbance. Changes in decadal rainfall and temperature since the fire seemed to be part of the drivers of the changes in the forest.