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Termites Protect Tropical Rainforests During Drought

termites on bark
Termites in Khao Yai National Park in Thailand. The insects become more active and abundant during times of drought, protecting tropical ecosystems. | Bernard Dupont

The tireless army of rainforest termites that toils beneath leaf litter and inside the rotting husks of long fallen trees may play a much larger role in tropical rainforest ecosystems than previously thought. According to a new study, the tiny insects' combined efforts have a big impact on shielding tropical forests from the harmful effects of drought.

During periods of drought, termites' abundance and activity nearly double, which has the overall effect of helping to maintain crucial ecosystem processes such as organic decomposition, soil moisture regulation and nutrient mixing. These activities greatly bolster seedling survival, researchers report in the January 11 issue of Science.

The study reveals the integral role that insects have in maintaining a functional ecosystem — particularly one under environmental duress — and illustrates how a single community of tiny invertebrates can help safeguard an entire forest during times of rapid environmental change. The study also demonstrates the need to conserve and protect intact biological communities, both large and small. According to Hannah Griffiths, a University of Liverpool researcher and co-author of the study, rainforest disturbances like logging can greatly impact the termite communities they host, which results in less resilient ecosystems overall.

"This is particularly important given that drought is projected to increase as a result of climate change — termites are going to become increasingly more important," said Griffiths.

Termites, often regarded as common pests by most homeowners, are common in tropical environments worldwide and known to be among the most effective ecosystem engineers. By tunneling below and consuming the dead and decaying leaves and wood scattered across the rainforest floor, termite communities mix, maintain and regulate soil properties like nutrients and moisture — each of which is a key factor in maintaining rainforest ecosystems. Extended periods of droughts can change or disrupt these important ecosystem functions, which can greatly impact tree mortality and the health of the rainforest.

Despite their abundance and recognized importance, the overall ecological contributions of forest termites have remained largely unquantified in real-world environments, according to the study authors. They say little is known about how drought-mediated changes to termite communities affect rainforest ecosystems during periods of environmental stress.

"Up to now it hasn't been possible to separate out the effects of termites from other taxa," such as fungi and microbes, said Louise Ashton, a researcher at the University of Hong Kong and lead author of the study.

To address these questions, the researchers designed a large-scale ecosystem manipulation experiment deep in the old-growth tropical rainforest of Malaysian Borneo, which occurred during and after the 2015 "super El Niño" climate event. Ashton and the other researchers removed termite mounds and suppressed termite activity in discrete sections of the forest, while leaving other plots unmodified. The approach allowed for the research team to directly assess the insect's impact.

Suppressing and monitoring the termites over time was one of the study's biggest challenges, said Ashton, and their primary tool to do so was rolls of toilet paper.

According to Ashton, with its easy to digest cellulose, toilet paper is one of the favorite foods of termites, which will quickly devour it if given the opportunity.

"We treated some of the toilet paper rolls with a targeted insecticide and used non-treated rolls to continuously monitor the activity of termites in the plots," said Ashton. As soon as the researchers observed an increase in toilet paper consumption, the plot was re-poisoned, which effectively kept populations suppressed.

Ashton and the team discovered an increase in both the activity and abundance of termite activity in plots where communities were present during drought, nearly doubling when compared to that of post-drought conditions in the same plots. The termite surge resulted in overall increases in litter decomposition rates, soil nutrient mixing and increases in soil moisture. Furthermore, the researchers found that seedling survivability was higher in these areas, likely due to the preservation of soil moisture dry periods.

"Only where the full termite communities were present did ecosystem processes continue during drought," said Griffiths, suggesting that the increased activity during drought helps buffer important soil processes crucial for tropical forest survival.

"The increase in termite activity during drought will be something of a surprise for many people," said study co-author Theo Evans of the University of Western Australia.

Although researchers have considered the influence of water availability on termite populations, the presumption has long been that less water meant less termite activity. However, this understanding is largely based on observational and often anecdotal studies, said Evans.

According to the authors, it isn't certain why termites become more abundant during times of drought. Ashton and her colleagues speculate that the drier conditions make it easier for the insects to tunnel underground, which would normally be difficult in waterlogged soil, or that the absence of precipitation or reduced predation from ants allows for safer and more fruitful above-ground foraging activities.

Droughts may also represent competitor-free periods during which termites enjoy reduced competition for food. According to Evans, various types of fungi feed on dead and decaying plant matter and use toxins to kill, scare or make food unpalatable for would-be competitors like termites. However, unlike termites, fungi cannot transport nor store their own water. Because of this, the survival of one of the insect's main food competitors depends on regular rainfall, said Evans.

"Termite activity increasing during a drought is an interesting result and requires further work to understand what drought conditions may be more favorable for termite activity," said Ashton.