Falling Asian elephant numbers may impact forest biodiversity

Declining numbers of endangered Asian elephants, which play a key role in seed dispersal and maintain the diversity of forest ecosystems, may have negative, long-term consequences for sustenance of certain tree species, researchers warn.

These mega-gardeners eat the plant's fruit and defecate the seeds, often far away from the parent plant, and contribute to forest biodiversity.

Some trees in Africa seem to exclusively rely on elephants for the dispersal of their seeds. But much less is known about the role of Asian elephants (Elephas maximus) for seed dispersal of trees in Asia, a team of international researchers has pointed out.

So, the researchers studied the capabilities of Asian elephants to boost dispersal and seed germination for an evergreen tree species, known as elephant apple (Dillenia indica), which is commonly found throughout South and Southeast Asia.

"While we still know relatively little about elephant seed dispersal in Asia it is clear that elephants hold key functions in forest ecosystems. They can help maintain plant diversity and a further decline or local loss of elephants and other large herbivores would likely lead to simpler plant communities and could further trigger negative cascading effects for overall system functioning," Franziska K. Harich, of the Department of Agroecology in the Tropics and Subtropics, University of Hohenheim, Germany, told IANS in an email interaction.

In addition to University of Hohenheim, the study involved researchers from International College for Sustainability Studies, Srinakharinwirot University, Thailand, and Conservation Ecology Program, King Mongkut's University of Technology, Thailand.

They examined whether planting seeds with elephant dung makes a difference to their germination and also mapped the link between the duration the seed stays inside the pachyderm's digestive tract and the seed growth rate and time when planted. Both African and Asian elephants could potentially disperse seeds over distances as large as 54 to 57 km.

"We used six captive elephants from the Golden Triangle Asian Elephant Foundation in northern Thailand for our feeding experiments and offered them as many ripe D. indica fruits as they wanted to eat. We then monitored the elephants and collected all their dung from which we retrieved the seeds," explained Harich.

In total, 1,200 seeds were planted and germination was monitored for six months to see if seeds eaten by elephants had a higher and faster germination rate than those acquired from fresh fruit that was not eaten by elephants.

"Our results show that D. indica does not solely depend on but seems to benefit from being eaten by elephants as ingested seeds were significantly more likely to germinate and to do so earlier than non-ingested seeds.

"Seeds with the longest gut passage time (those that stayed within the elephant gut for the longest duration) and, therefore, the largest potential dispersal distance had the highest germination success," Harich said, adding the declining numbers of these mega-faunal seed dispersers might, therefore, have "long-term negative consequences for the recruitment and dispersal dynamics of populations of certain tree species".

The study underscores the importance of stringent protective measures for the pachyderms, whose habitats have shrunk by 95 percent and population declined by at least 90 per cent over the last century.

Less than 50,000 Asian elephants, according to the International Union for the Conservation of Nature (IUCN), roam the forests of Bangladesh, Bhutan, India, Nepal, and Sri Lanka in South Asia and Cambodia, China, Indonesia (Kalimantan and Sumatra), Lao PDR, Malaysia, Myanmar, Thailand, and Vietnam in Southeast Asia.

In times of climate change, a large dispersal area might become increasingly important as it might help in buffering potential population losses due to adverse environmental conditions, the study notes.

Harich said that to fulfil their ecological role, the animals need sufficient space to roam. Apart from habitat loss and fragmentation, conflicts between humans and elephants are another major concern for conservation efforts.

"India is in the fortunate position to harbour the largest population of wild elephants in Asia that likely accounts for more than 50 per cent of the remaining animals of this species.

"Only if we can maintain viable elephant populations within large enough natural areas will the animals be able to continue fulfilling their important ecological roles in forests, for example as long-distance seed dispersers," Harich said.

According to wildlife biologist Varun Goswami of the Wildlife Conservation Society (WCS), the Asian elephant has been described in the past as "Mega-gardener of the Forest" because of the critical role it plays in the ecosystem as a seed disperser.

"Dillenia indica is a key species that elephants feed on in India as well, and this study makes a valuable contribution in demonstrating through experiments how the ingestion of the plant seeds by Asian elephants significantly improves their germination success," Goswami told IANS.

(Sahana Ghosh can be contacted at sahana.g@ians.in)

--IANS

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