Termites help protect rainforests from climate change

The researchers, from the Museum and the University of Liverpool, initially set out just to measure the effect that termites had on rainforests in general.

Dr Paul Eggleton, Merit Researcher at the Museum and senior co-author of the study, says, 'We've always known that in tropical rainforests ants and termites are really important players, but they have been underestimated as ecological agents in these systems.

'I think this is because of a northern temperate bias. Temperate forests in the northern hemisphere have been studied much more thoroughly than tropical areas in the southern hemisphere. Because of this, everybody had assumed in the past that microbes are responsible for the majority of decomposition in tropical forests, because they are in the northern temperate regions.'

To demonstrate the insects' vital role in tropical ecosystems, the researchers carried out the first-ever experimental removal of termites from a small patch of rainforest, using new methods to lower the number of termites in the process.

Termite chocolate

To pluck out the termites from the 2,500-metre-square plots, the researchers used over 4,000 toilet rolls.

'Fortunately for us, termites love the cellulose parts of loo rolls,' says Paul, referring to the white paper that surrounds the core. 'It's like giving them chocolate.

'We were able to poison a whole host of loo rolls and put them out onto our plots, managing to reduce the termite activity by about three quarters.'

The poison has been rigorously tested to be certain that only termites are affected by it, resulting in the impressive three-quarter drop in activity.

This then allowed the researchers to measure the decomposition rate of wood and leaf litter, the distribution of nutrients in the soil, whether the termites had any effect on seedling survival, the moisture levels in the soil and also the depth of the leaf litter between plots with and without termites.    

'For all of those things, we saw a very big difference between the plots where we had supressed termites and those where we hadn't,' says Paul. Leaf litter, for example, was 22% lower when termites were present, while seedling survival increased by over 50%.

While the huge benefit of termites to the forest was hardly unexpected, what happened during the experiment really took the team by surprise.

Extreme weather bites

It just so happened that as the experiment was ongoing, the Pacific Ocean experienced the largest El Niño on record. This is the massive weather event that occurs in the Pacific every few years.

Normally, winds across the Pacific blow from South America towards Asia. This means that the warmer water builds up in the western side of the ocean while colder water is uplifted along the eastern edge. It is this temperature difference that drives the weather system.

During El Niño, however, these winds are weakened, meaning the warm water that is usually found off the coasts of Asia and Oceania shifts further east, warming the waters around South America. This unbalances the weather systems and leads to drought across Indonesia and Borneo.

In 2015, while the termite experiments were in full swing the largest ever El Niño hit Borneo plunging the rainforest into a severe drought.  

'At first, we thought the drought would ruin the experiment,' explains Paul. 'But much to our surprise we found that the termites did better in the drought conditions than in the wet conditions.

'That was not what we were expecting at all.'

It turned out that while the researchers predicted that the dry weather would hinder all decomposition in the forest, the opposite was actually true. The termites massively ramped up their activity. Why this was the case is still not fully understood, but Paul thinks it is likely to do with how water-logged the soil is.

He explains, 'They move around in tunnels in the soil, and so when it is very wet they can't move about much, as many of their tunnels will be full of water. But when it is nice and dry they can make their tunnels more easily, resulting in much higher activity levels.'

Buffering climate change

The result is of this activity is not only an increase in the decomposition of leaf litter and wood, but also an increase in the overall level of moisture in the soil and the rate of nutrient cycling within the environment.   

This has a knock-on effect for the plants growing in the rainforest, increasing the survival of seedlings by half during harsh droughts, and providing a mosaic of nutrients that in turn bumps up the overall biodiversity of the forest.   

'They mitigated the effect of drought,' says Paul. 'Of course, we're expecting more droughts in the future, so systems that keep their natural level of termites should be provided with some defence.'

As more and more tropical rainforest is being cut down as the insatiable demand for resources grows, however, the outcome is not favourable for the termites.

According to Paul, even the slightest disturbance to a forest can have a serious impact on the number and diversity of termites that live there. It is now likely that this will affect the resilience of these forests to extreme weather events, which are only predicted to get more frequent and harsher in the future.