Dead trees are piling up faster than forests can break them down, climate change is speeding up the cycle. Warmer forests rot faster. That has always been the working assumption among scientists. When dead trees hit a heated forest floor, they should break down more quickly, keeping pace with whatever kills them. Higher temperatures feed the fungi and beetles that eat dead timber.
Researchers tested that assumption with a full accounting of global forests through 2099. Their analysis showed that dead wood is arriving faster than it can decompose. The gap was the widest in the cold north, where trees are already dying in growing numbers. All that fallen timber adds up to a quiet giant in the climate system. Deadwood holds roughly 80 billion tons of carbon worldwide (73 billion tonnes). This accounts for about eight percent of all the carbon stored in forests. That stockpile rises and falls through two competing forces.
New dead wood forms whenever trees die, and old dead wood vanishes as organisms release its carbon back into the air. Climate change affects both. Pascal Edelmann, an ecologist at the Technical University of Munich (TUM), wanted to know which force would win. Would forests accumulate dead wood, or lose it? No one had settled the question.
Gaining new insight Edelmann’s team built their answer from three pieces. They started with a map of dead wood stocks in the world’s forests in 2010. Then, they layered on projections of tree growth and death from five vegetation models. For the breakdown side, the team drew on a global experiment tracking rotting logs at 55 sites on six continents. Each site measured how fast wood decayed under local heat and rainfall.
Running the whole picture forward to 2099, they compared the carbon flowing into dead wood against the carbon leaving it. A score above one meant dead wood was piling up, and below one meant it was shrinking. Two opposing forces Warming pushes both sides upward at once. When more trees are dying and forests are growing faster, more wood accumulates on the forest floor.
A recent study found drought, fire, and insect outbreaks are already killing more trees worldwide. More death means more supply. Heat works the other end too. Warmer conditions drive faster decomposition rates that are measured across forest sites worldwide. This suggests that the fungi, beetles, and other organisms that eat dead wood become more active as temperatures climb.
Those two forces could cancel each other out, leaving the global pile roughly steady. Or one could pull ahead. That gap, however small, decides whether the world’s forests gain or lose dead wood across the century. Evidence from models Until this study, no one had pinned down the winner. Edelmann’s results landed on one conclusion.
Dead wood formation outran breakdown by about five percent across every model and climate scenario tested. This was a small lead, but a consistent one. Both sides increased through the century, yet formation outpaced decomposition. New dead wood produced each year rose by around 15 percent on average, while breakdown climbed about eight percent. By the late 2080s, the amount of new dead wood entering forests climbs significantly per year.
That global average hides sharp regional contrasts. The biggest accumulation shows up in the cold north, in the boreal forests and Arctic edge stretching across Canada and Russia. The temperate zones are not far behind. But in the tropics, the picture is very different. Formation barely outpaced breakdown there, since the same heat and moisture that help trees grow quickly also cause them to decay quickly.
Over time, that split could redraw where the world’s dead wood lives. About two-thirds of it currently sits in tropical forests. However, with northern forests gaining fastest, dead wood may spread more evenly worldwide in coming decades. Some messy variations None of this is locked in. About one in five simulations showed dead wood declining, not growing, by the end of the century. Decomposition is especially tricky to forecast.
One study found that termites speed wood decay sharply as temperatures rise, and warming could let such decomposers expand into regions where they were once rare. The team also left out two big wild cards. Wildfires can burn dead wood away entirely, and human choices could swamp the climate signal in either direction. Dead wood counts Decaying lumber is far from being waste. It serves as home and food for roughly a quarter of all forest species, and it anchors biodiversity across the world’s forests.
Climate change will profoundly accelerate deadwood dynamics in the forests of the world, Edelmann and his colleagues write. Many insects that depend on dead wood are now threatened with extinction. Warming will likely leave forests with more dead wood, not less, with the cold north gaining most. For foresters and policymakers, that turns dead wood into something worth keeping rather than clearing.
The study is published in Communications Earth & Environment. Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.
