Termites love global warming, the pace of their wood nibbling gets much faster in hot weather

Wood feeding termites (Microcerotermes spp) inside their nest. Credit: Johan Larson, author provided

When we consider termites, we can think of the danger they can pose to our homes once they take up residence and start eating wood. But in fact, only about 4% of termite species around the world are considered pests that could, at some point, eat your home.

In nature, wood-eating termites play a large and important role in tropical and warm subtropical ecosystems. By feeding on wood, they recycle essential nutrients in the soil and release carbon into the atmosphere.

Our new research, published today in Science, quantified for the first time how heat-loving termites are. The results are striking: we found that termites eat dead wood much faster in warmer conditions. For example, termites in a region with temperatures of 30℃ will eat wood seven times faster than in a place with temperatures of 20℃.

Our results also indicate an increasing role for termites in the coming decades as climate change increases their potential habitat across the planet. And that, in turn, could see more carbon stored in dead wood released into the atmosphere.

Dead wood in the global carbon cycle

Trees play a central role in the global carbon cycle. They absorb carbon dioxide from the atmosphere through photosynthesis, and roughly half of this carbon is incorporated into the new plant mass.

While most trees slowly grow in height and diameter each year, a small proportion die. Their remains then enter the Deadwood Pool.

Here the carbon accumulates until the dead wood is either burnt or rotten by consumption by microbes (fungi and bacteria), or insects such as termites.

If the dead wood pool is consumed quickly, the carbon stored there will be quickly released into the atmosphere. But if decomposition is slow, the size of the pool of dead wood can increase, slowing the buildup of carbon dioxide and methane in the atmosphere.

For this reason, understanding the community dynamics of organisms that decompose dead wood is vital, as it can help scientists predict the impacts of climate change on the carbon stored in terrestrial ecosystems.

This is important because the release of carbon from dead wood into the atmosphere could accelerate the rate of climate change. Storing it longer could slow climate change.

Testing how fast termites eat dead wood

Scientists generally understand the conditions that favor the consumption of dead wood by microbes. We know their typical activity double at every 10℃ increase in temperature. Microbial decomposition of dead wood is also generally faster in moist conditions.

On the other hand, scientists knew relatively little about the global distribution of deadwood-eating termites, or how that distribution would react to different temperatures and humidity levels in different parts of the world.

To better understand this, we first developed a protocol for assessing rates of deadwood consumption by termites, and tested it in a savannah and rainforest ecosystem. in North East Queensland.

Termites love global warming - the pace of their wood-munching speeds up dramatically in hot weather

Amy Zanne with graduate student Mariana Nardi and postdoctoral fellow Paulo Negri of Universidade Estadual de Campinas near termite mounds in the tropical cerrado savannah in Chapada dos Veadieros National Park. Credit: Rafael Oliveira

Our method was to place a series of mesh-covered wooden blocks on the ground surface in a few places. Half of the blocks had small holes in the mesh, giving access to termites. The other half had no such holes, so only microbes could access the blocks through the mesh.

We collected wood blocks every six months and found that the mesh-covered blocks with holes decayed faster than those without, meaning that the contribution of termites to this decomposition was, in fact, significant.

But while the test told us about termites in Queensland, it didn’t tell us what they might be doing elsewhere. Our next step was to contact colleagues who could deploy the woodblock protocol at their study sites around the world, and they enthusiastically accepted the invitation.

In the end, more than 100 collaborators joined the effort at more than 130 sites in a variety of habitats, spanning six continents. This broad coverage allowed us to assess how termite wood consumption rates varied with climatic factors, such as mean annual temperature and precipitation.

Termites like heat and not too much rain

For wooden blocks accessible only to microbes, we confirmed what scientists already knew, which was that decomposition rates approximately doubled from site to site for every 10℃ increase in mean annual temperature. Decay rates increased further when sites had higher annual rainfall, such as in the rainforests of Queensland.

For termite wood blocks, we observed a much stronger relationship between decomposition rates and temperature – dead wood typically decayed almost seven times faster at sites that were 10℃ warmer than others.

To put this into context, termite activity meant that wooden blocks near tropical Darwin, on the northern edge of Australia, were decaying more than ten times faster than those in temperate Tasmania.

Our analyzes also showed that termite consumption of wooden blocks was highest in warm areas with low to intermediate average annual rainfall. For example, termite decomposition was five times faster in a subtropical desert in South Africa than in a tropical rainforest in Puerto Rico.

This may be because termites secure in their mounds can access water deep in the ground during dry periods, while waterlogging may limit their ability to forage for dead wood.

Termites and climate change

Our results were synthesized into a model to predict how termite consumption of dead wood might change globally in response to climate change.

Over the next several decades, we expect greater termite activity, as climate change projections show that suitable termite habitat will expand north and south of the equator.

This will mean that the carbon cycle through the deadwood pool will accelerate, returning the carbon dioxide fixed by the trees to the atmosphere, which could limit carbon storage in these ecosystems. Reducing the amount of carbon stored on land could then trigger a feedback loop to accelerate the rate of climate change.

We have long known that human-caused climate change would favor a few winners but leave many losers. It would seem that the humble termite is likely one of those winners, on the verge of a significant global expansion into its primary habitat.

Termites could play a bigger role in future ecosystems

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Teresa H. Sadler