Fires and warming rapidly changing ecosystems in Canada

MADRID, (EUROPA PRESS). – The proliferation of large forest fires in recent summers due to accelerated warming is increasing photosynthesis rates in Canada and Alaska.

New research published in Global Change Biology finds that increasing wildfires are wiping out black spruce forests that grow relatively slowly and contribute to the organic layer of underlying soils. In many areas, deciduous shrubs and trees, such as willows and poplars, are arriving after a fire. These plants have a much faster metabolism, meaning they can establish themselves faster than spruce.

In 2023, Canada experienced its most devastating wildfire season, with more than 186,000 square kilometers burned. The authors’ work suggests that these fires may accelerate changes in northern forests that are already underway due to climate change.

“We are seeing higher levels of photosynthesis persisting for decades after the fire,” Kim said in a statement. “Rather than evergreen coniferous forests returning immediately, in some regions we see a long-term replacement of these forests with faster-growing species.”

The more photosynthesis there is, the more plants can remove carbon dioxide from the atmosphere. One hypothesis is that this could create a carbon dioxide sink and help moderate global warming.

“But because carbon stored in plants and their organic soils has been burned up, even the increase in photosynthesis we observed does not necessarily translate into greater long-term carbon storage,” said Jinhyuk Kim, a Ph.D. Earth by the University of California Irvine. “Increasing wildfire trends have significant implications for forest species composition and ecosystem function, but are likely to negatively impact the terrestrial carbon sink. It is therefore important to study how the changing landscape due to wildfires and “Warming influences different aspects of the terrestrial carbon cycle.”

To measure the changing rate of photosynthesis in boreal plants, Kim and his team used data from the Orbiting Carbon Observatory 2 satellites that track plant fluorescence to use as an indicator of photosynthesis.

“It’s a more recent measurement that we’ve been able to observe globally,” said Kim, who explained that using fluorescence measurements is a novel approach to measuring photosynthesis. “We also have this long land cover time series from Landsat, and we can look at how fires are changing land vegetation cover and then link that to changes in the sun-induced fluorescence signal. We found that wildfires are changing land cover. which, in turn, can improve the seasonality of carbon fluxes at large spatial scales.

Kim added that it is a sign of unstable ecosystems in which the region’s plant types are changing rapidly.

In another study from a team led by Earth system science doctoral candidate Allison Welch, researchers describe what types of plants are expanding into the arctic and alpine tundra.

“With rising temperatures and wildfire activity, we’re seeing increased growth of larger deciduous shrubs,” said Welch, whose team studied five different alpine tundra sites for the research, which appears in Arctic and Alpine Research. .

“We found increased growth of shrubs of a specific species called alder,” said Welch, who works in the lab of Claudia Czimczik, a professor of Earth system science. “And it just increased the productivity of the overall vegetation on these sites.”

Welch’s team also reported a decrease in the thickness of the organic layer (the top layer of soil characterized by high organic carbon content) at their tundra sites. Shallower organic layers, Welch explained, mean there is less insulation for the underlying Arctic permafrost. Permafrost contains vast reserves of frozen organic matter that, if thawed, can decompose and release planet-warming gases such as carbon dioxide into the atmosphere. “If you have a healthy organic layer, you’re probably going to promote permafrost stability,” Welch said.

In the third study, published in Geophysical Research Letters, a team led by PhD candidate Hui Wang, who works in the Department of Earth System Sciences with Prof. Alex Guenther, obtained field measurements and then performed computer simulations to describe how, as Arctic ecosystems experience a warmer climate, emissions of the molecule isoprene are increasing at a much faster rate than predicted.

“This change will indirectly change the climate,” Wang said. This is because isoprene affects the formation of ozone, aerosols and methane levels in the air. Aerosols influence cloud formation, which in turn can influence local weather. And plants, Wang explained, release more isoprene when the weather is warmer.

The changes reported in the studies point to arctic-boreal ecosystems that are changing rapidly in response to wildfires and warm temperatures.