UBD calls for proper management of invasive Acacias

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PROPER management and close monitoring of soil seed banks are to be adopted as best practices in minimising the spread of invasive Acacias into the tropical heath (kerangas) forests of Borneo, according to recommendation by researchers following a Universiti Brunei Darussalam (UBD) study.

The invasive plant has been globally recognised as a major threat towards biodiversity and is considered one of the most destructive invasive plants within the tropics.

About 23 of its species have been listed as top invaders worldwide, said the study’s authors.

The study, ‘Soil Seed Bank of an Exotic Acacia sp. Plantation and an Adjacent Tropical Heath Forest in Brunei Darussalam’ was published last year in the journal of BIOTROPIA.

Its authors, Adrian Lee Rahman Suhaili, Kushan U Tennakoon and Rahayu Sukmaria Sukri, collected soil samples from 10 plots set up in contrasting habitats.

These were the Acacia mangium plantation, the adjacent tropical kerangas forest in the Andulau Forest Reserve and the transition zone in between.

“As such, the invasions of Acacias are a threat to these rare and vulnerable tropical ecosystems in Borneo,” said the study’s authors, who noted that tropical kerangas accounts for less than one per cent of all forests in Brunei and that Acacias effectively outcompetes the native kerangas forest species.

“Invasive Acacias reduce species richness, diversity and composition of soil seed banks of invaded ecosystems, thus changing the vertical structure of above-ground vegetation and community composition of the invaded ecosystems,” said the authors.

“Furthermore, Acacia-enriched soil seed banks act as reservoirs that allow for the persistence of the invasive behaviour,” explained the authors.

As a result of the study, the authors found that a comparison between the soil seed banks between the Acacia mangium plantation and the adjacent heath forests has shown higher seed density, viability and species richness in the heath forest than in the plantation.

The clearing of the intact forests for the Acacia mangium plantations would have a detrimental effect on seed bank diversity, concluded the authors, who added that it can have “negative knock-on effects on native plant regeneration”.

“Though Acacia mangium is a known invasive species, due to its shade intolerant nature, it appears to have some difficulty of spreading into intact tropical forests,” explained the researchers.

“It is therefore, recommended close monitoring of escaping Acacia seedlings from the intact parent plantations to mitigate further spread of Acacias into natural habitats,” they concluded.

The Brunei Times