Soil seed bank of an exotic acacia sp. plantation and an adjacent tropical heath forest in brunei darussalam

Abstract

Acacias are some of themost successful invasive plants in the tropics, causing significant negative impacts on the biodiversity and ecosystem services of invaded habitats. Their successful invasiveness is partly attributed to the ability to accumulate large soil seed banks in the areas that they invade. Seedling emergence and soil seed bank composition were compared under an Acacia mangium plantation and an adjacent tropical heath (kerangas) forest in the Andulau Forest Reserve, BruneiDarussalam. Soil sampleswere collected fromten 20 x 20mplots set up in three contrasting habitats: theAcacia plantation, the adjacent heath forest and the transition zone in between. Soil samples were subjected to smoke and heat treatments, following seedling emergencewhichwas observed daily over a 12-week period. In a parallel investigation, variations in species richness, seed density and seed viability of the soil seed banks of the ten plots were investigated. Seedling emergence was the highest in the plantation and the lowest in the heath forest plots, respectively. However, no significant differences among treatments and no significant treatment-habitat interactions were detected. Species richness, seed density and seed viability in the plantation plots were significantly lower than those in the transition zone and intact heath forest plots. Acacia mangium seeds were not recorded in the heath forest soil seed banks, butwere detected in the plantation and transition zone plots. Lower native plant species richness, seed density and viability in the A. mangium plantation could imply higher regeneration potential for the heath forest habitat if severe habitat destruction was to occur in this forest reserve. It is suggested that proper plantationmanagement practices and closemonitoring of soil seed banks are the best practices that could be adopted tominimize the gradual spread of invasiveAcacias into tropical heath forests of Borneo.