Kempas trees here have retained genetic health

SINGAPORE - More than 150 years of development has led to the disappearance of most of Singapore's primary forests.

When populations of plants and animals shrink as a result of deforestation, these species lose their genetic diversity over successive generations as fewer among them are left to breed with one other.

But one tree species here has managed to withstand the diversity loss - for now.

There are just 179 or so of the tall and long-lived adult Koompassia malaccensis trees, commonly known as Kempas trees, left on the island. Kempas trees, which can grow up to 60m tall, are a key part of the tropical rainforest canopy.

In addition, there are 200 or so Kempas saplings of less than a year old, and nearly 2,000 seedlings in Singapore's forests.

National University of Singapore plant ecology researchers Edward Webb and Annika Noreen have been pondering whether the younger generations of Kempas trees show less genetic diversity than the older ones.

Their initial thought was that this might be so because of the genetic "bottleneck" caused by the removal of a big proportion of the original adult trees.

But when the researchers painstakingly sampled each and every Kempas tree on the island, they found that the younger trees were as genetically diverse as the older ones.

They explained that because the trees can live for several hundred years, a number of them may date back to before deforestation began and preserved some of their earlier genetic variation.

In addition, Kempas trees are pollinated by wild honey bees which can travel far and wide, said Associate Professor Webb. These bees probably play a key role in helping distant trees to breed, he added.

The researchers' work was published in the journal PLoS One on Wednesday.

But the Kempas trees' genetic diversity here could still be lost over time, said Dr Noreen, who is now based in Canada.

"With long-lived species such as trees, the genetic consequences from the loss of individuals can sometimes take a long time to carry on through to future generations. Adult Koompassia trees can potentially contribute their genes to the next generation for several hundred years.

"Hence, slow and ongoing loss of genetic diversity in a small population such as Singapore's Koompassia malaccensis should not be ruled out," she said in an e-mail.

The findings on Kempas trees should not be applied to other species that have different reproduction processes.

Prof Webb said: "Other species, particularly those with less mobile pollinators, extinct pollinators or seed dispersers, or which do not reproduce frequently, are probably less likely to have such optimistic results.

"So, we should not apply the somewhat good news of Koompassia to other species."

caiwj@sph.com.sg

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