Phenol and Tannin Contents of Fresh Phyllodes and Leaf Litter Materials from Three Acacia Species in Brunei Darussalam

Invasive Acacia species are increasingly spreading into degraded forests in Brunei Darussalam since their initial planting in the 1990s. Information on the secondary metabolites of these invasive Acacia species is important in understanding their effects on leaf litter decomposition rates of invaded forests in Brunei. This study aimed to quantify the pH, total phenolic, and total tannin content of three invasive Acacia species (Acacia auriculiformis A. cunn ex Benth., Acacia holosericea A. Cunn. Ex G. Don and Acacia mangium Willd.) and one co-occurring native heath tree species (Buchanania arborescens (Blume) Blume) in Brunei Darussalam. pH, total phenolic and total tannin contents were measured and compared between leaves of the four species, as well as between leaf types (fresh phyllodes vs. leaf litter samples). All three invasive Acacia species recorded higher pH, total phenolic and total tannin contents than the native species. High pH and total phenolic content were observed in fresh phyllodes than leaf litter samples of all studied species but no differences were observed in total tannin contents for both fresh phyllodes and leaf litter samples. Higher pH, total phenolic and total tannin contents in all Acacia species may reduce leaf palatability to herbivores and detritivores, resulting in slower degradation processes compared to the native tree species, thus potentially affecting leaf litter decomposition rates in Acacia-invaded heath forests. Overall, the study on differences in secondary compounds between species and leaf types has provided insights into the decomposition rate of Acacia species compared to the native tree species.