How climate change impacts tree growth and wood quality?

Trees are feasting on decades of carbon dioxide emissions and growing taller as a result, according to a new study. The scientists tracked the volume of wood in 10 different tree groups from 1997 to 2017, finding that all but the aspen grew larger.

Recent studies examining the effects of climate change on tree growth and wood quality have highlighted worrying trends. Rising global temperatures and lengthening growing seasons have accelerated tree growth in temperate regions of North America and Europe.

This accelerated growth comes at a cost. Researchers have discovered that as trees grow, the quality of their wood decreases, making them structurally weaker and more prone to breaking. Let's dive into the details of these studies and explore their implications for our forests.

Increased growth & decreased wood quality

According to a study by the Technical University of Munich, the growth rate of trees in temperate regions has increased by a staggering 77% compared to the previous century.

While this may initially seem like a positive result, the researchers observed an inverse relationship between growth rate and wood density. As the growth rate increased, the wood density decreased by 8-12%. This phenomenon indicates a drop in the structural strength of trees, as weaker wood makes them more susceptible to breakage.

The decrease in wood density also affects the carbon sequestration capacity of trees. Thinner cell walls result in a reduced ability to accumulate carbon dioxide (CO2) from the atmosphere.

The study found that the carbon content in the wood decreased by about 50%, suggesting that the trees extract less CO2, a crucial greenhouse gas, from the atmosphere. This reduction in carbon sequestration has significant implications for combating climate change, as forests play a vital role in sequestering carbon.

It's all because of carbon fertilization

Although other factors, such as weather and pests, can somewhat affect a tree's volume, the study found that elevated carbon levels consistently led to an increase in wood volume in 10 different groups of temperate forests. in all the country. This suggests that the trees are helping to protect the Earth's ecosystem from the impacts of global warming through their rapid growth.

"Forests are removing carbon from the atmosphere at a rate of about 13 per cent of our gross emissions," said Brent Sohngen, a co-author of the study and a professor of environmental and resource economics at The Ohio State University. "While we're putting billions of tons of carbon dioxide into the atmosphere, we're actually removing much of it just by letting our forests grow."

However, it has not been clear whether this increase was primarily driven by forest management and its recovery from the previous land uses such as agriculture, or other environmental factors such as elevated carbon dioxide, nitrogen deposition, or climate change.

Quality of wood

To further complicate the picture, another recent study established a correlation between growth rate and tree lifespan. Fast-growing trees were found to have a shorter life expectancy. This interconnectedness means that the rapid growth observed in some trees may be unsustainable in the long term, leading to premature death and affecting the health of the forest.

A recent study focusing on balsam fir shed light on the relationship between growing season length, productivity, and wood cell characteristics. The research showed that trees with longer growing seasons produce more wood cells and thicker growth rings.

However, this higher growth was accompanied by changes in the ratio of earlywood to latewood. Each additional day in the growing season led to the production of an extra cell of early wood, resulting in a decrease in wood density. This finding highlights that higher volume growth does not necessarily translate into higher biomass production.

With average global temperatures exceeding pre-industrial levels and further increases projected, longer growing seasons could become a widespread phenomenon.

While this may contribute to forest expansion, studies indicate a potential decrease in the rate of carbon uptake by trees. The implications of these findings are significant and emphasize the need for direct action to address the underlying causes of global climate change.

During that same period, carbon dioxide levels went from 363 parts per million to 405 parts per million, due in large part to the burning of fossil fuels. More abundant CO2 speeds up photosynthesis, causing plants to grow faster, a phenomenon known as "carbon fertilization." The findings were published in the journal Nature Communications.

Carbon fertilization

Research has also shown that through a phenomenon called carbon fertilization, plants use an influx of carbon dioxide from the atmosphere to increase their rate of photosynthesis, a process by which plants combine energy from the sun, water and other nutrients to stimulate their growth.

“It's well known that when you put a ton of carbon dioxide into the atmosphere, it doesn't stay there forever. A lot of it falls into the oceans, while the rest is taken up by trees, wetlands and those kinds of areas,” explained Dr. Sohngen.

In the study, the researchers noted that forests in the US have sequestered between 700 and 800 million tons of carbon dioxide each year, which represents about a tenth of the country's total carbon emissions.

Scientists say that compared to trees that lived about 30 years ago, modern trees in US forests have 20 to 30 per cent more biomass.

Even the oldest large trees, they say, continue to add biomass as they age due to elevated carbon dioxide levels.

Unlike the effects of climate change, which varies by location and time, the amount of carbon dioxide in the atmosphere mixes almost evenly, so every place on Earth has about the same amount, Sohngen said.

The team used old data

So, to test whether the chemical compound was responsible for reinforcing our biome, Sohngen's team used historical data from the US Forest Service's Forest Inventory and Analysis Program (USFS-FIA) to compare how the volume of wood from certain groups of forests in the past few decades. The study estimates that between 1970 and 2015 there was a significant increase in the volume of wood from trees, which correlates with a clear increase in carbon emissions.

The researchers were also able to use this method to test whether there were differences between natural trees and planted trees. Sohngen thought that the planted trees would experience a greater fertilization effect since they have the advantage that planters often choose the best seeds to plant only in the best locations. Instead, he was surprised to find that planted trees respond to carbon dioxide levels in the same way natural trees do.

These findings, according to the researchers, highlight the value of trees in mitigating climate change.

“Carbon fertilization certainly makes it cheaper to plant trees, avoid deforestation or do other activities related to trying to improve the carbon sink in forests. We should be planting more trees and preserving the oldest ones because, at the end of the day, they are probably our best bet for mitigating climate change,” Dr. Sohngen said.

The scientists say the findings can help policymakers and other stakeholders better explain the role of forests in helping to reduce global warming within the 1.5 degree Celsius target that was agreed upon in the Paris Climate Agreements in 2015.

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