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Trees aren’t a climate change cure-all – 2 new studies on the life and death of trees in a warming world show why

Trees aren’t a climate change cure-all – 2 new studies on the life and death of trees in a warming world show why

A female forestry technician cuts a fallen tree with a chainsaw in a forest with dead and dying pine trees whose needles have turned brown.

When people speak of ways to slow climate changes, They often mention treesIt is a good thing. Forests occupy a Large amountsThe carbon dioxide that fossil fuel combustion emits into the atmosphere causes global warming. As global temperatures rise, will trees be able to keep up this pace? With companies As an offset, forests are being increasingly invested in, saying it cancels out their continuing greenhouse gas emissions, that’s a multibillion-dollar question.

The results of two studies published in the journals Science and Ecology Letters on May 12, 2022 – One that is focused upon growth, Other on death – raise new questions about how much the world can rely on forests to store increasing amounts of carbon in a warming future. Ecologist William AndereggThe reason is explained by, who was involved with both studies.

What can new research tell us about trees’ ability to store carbon?

The future of forests is on a knife’s edge, with a tug of war between two very important forces: the benefits trees get from increasing levels of carbon dioxide and the stresses they face from the climate, such as heat, drought, fires, pests and pathogens.

These climate stresses are growing faster than scientists expected as the planet heats. We’re seeing Wildfires erupted in great numbers Drought-driven forest die-offsMuch sooner than anyone expected. Carbon from these trees goes back into our atmosphere when they die. We’re also seeing evidence that the benefits trees get from higher levels of carbon dioxide in a warming world It may be less.People realize this more than they realize.

This tells us it’s probably not a great idea to count on forests for a widespread carbon sink through the 21st century, particularly if societies don’t Reduce their emissions.

A female forestry technician cuts a fallen tree with a chainsaw in a forest with dead and dying pine trees whose needles have turned brown.
Droughts make trees more vulnerable to fires or beetle attack.
Phillippe Diederich/Getty Images

Trees and forests do all sorts of other amazing things – they clean the air and water, and they provide economic value in terms of timber and tourism and pollination. It is important to understand how they will grow for many reasons.

There’s an argument that, with more carbon dioxide in the atmosphere, trees will simply grow more and lock that carbon away. What did your research reveal?

Two things are key to tree growth: photosynthesisThis is how trees transform sunlight and carbon dioxide to food. Cell divisionExpanding.

There’s been a long-standing debate about which is the biggest driver of tree growth.

Two horses and a cart are a good metaphor. The cart moving down the road is the tree growing, and there are two horses attached, but we don’t know which is actually doing the work of pulling the cart. One horse is photosynthesis. That makes a lot of intuitive sense – it’s where all the carbon comes from for building cells. But we know there’s another horse – in order to grow more wood, trees have to grow layers of cells, and the cells have to expand and divide. Cell growth is very sensitive and will shut down when the conditions are dry.

Map of drought in the U.S. showing the western half of the country under drought conditions
Many areas of the Western U.S. have been in severe drought for many years. About half of the contiguous U.S. were in drought in May 2022.
Drought Monitor/UNL/NOAA/USDA

Many people assume that photosynthesis is the dominant process everywhere. We found that photosynthesis is not the dominant process everywhere. stronger evidenceThese cellular processes that are sensitive and sensitive to drought actually do more for growth.

We used tree ring data taken from thousands of trees in Europe and the U.S. Measurements of photosynthesis taken from towers located in nearby forestsTo determine if tree growth and photosynthesis are correlated over time. If they had followed the same pattern of increasing or decreasing in the years, that would have suggested that photosynthesis was pulling the cart. We found no correlation.

This suggests that droughts may have a greater impact on the speed of future tree growth than carbon dioxide levels in the atmosphere. We’re already Severe droughts are becoming more frequent and severe.Many regions.

What have you learned about the risk of tree deaths in the future?

In the second study, we found out that lowering global greenhouse gases emissions could have a significant impact on our ability to reduce global warming. huge impact for avoiding damageForests from drought, wildfires, and insects

We used satellite observations and climate data for years. A networkThere are approximately 450,000 tree plots in the U.S., where each tree is monitored for survival and climate stress. We used historical data to create statistical models of the risks that trees in the United States face from wildfires and insects, as well as climate stress. This is mainly due to drought. Next, we examined what might happen in future climate scenarios with high carbon emissions as well as medium and low emissions. The results can be viewed at Interactive map.

The images above, from CarbonPlan.org’s interactive maps, show how risks to forests from wildfire (orange), drought (pink) and insects (blue) increase over time in a medium-emissions scenario of the future. Slide the slider to compare 2020 and 2090.

The big picture Risiko increasesParticularly in the Western U.S., the rate of wildfires has increased significantly over the past century. Wildfire risk is expected to rise by four in a scenario of medium emissions. Drought, insect and disease risks increase by 50% to 80%.

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What does this mean regarding carbon offsets?

Together these studies suggest that the benefits carbon dioxide has for growth won’t be nearly as large as people thought, and the risk of climate stress, particularly wildfire, drought and insects, will be much larger than people anticipate.

This has enormous implications for forest use Carbon offsets.

This new scientific understanding has not been fully incorporated into carbon offset markets and protocols. Forests face risksFrom climate change. This shows that climate policymakers and offset designers need to be very careful about counting forest offsets as a source of benefits.

The good news is that actions taken in the next ten years will make a difference. If we can slow down climate change’s pace and choose a lower-emissions route, it will make a significant difference in reducing risk and increasing the benefits. This isn’t a “throw up our hands and panic” situation – it is our chance to take steps that make sure resilient and sustainable forests last for the future.

It is vital that we take action to reduce our carbon emissions and slow climate change. This will have a huge impact on the future of forests.

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