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Forest Fires: Natural or Human-Made?


https://pixabay.com/de/images/search/waldbrand/,

Pictures of raging forest fires in Canada are currently making their way around the world. The sky over New York is dark orange, and the air quality in some cities in the US and Canada is abysmal. Here in Québec, the air is hazy, and there were times when we couldn't even enter the forest for our fieldwork. Although Québec City has largely been spared from smoke and flames so far, it feels strange to have forest fires suddenly at our doorstep. This year, Canada has already burned more forest than in the years 2016, 2019, 2020, and 2022 combined. And in Germany, too, forest fires are no longer a rarity.


Is this normal? Is it natural for the forest to burn, or are humans to blame?


Sequoia giganteum, https://pixabay.com/de/photos/baum-mammutbaum-sequoia-holz-rinde-4890/

In North America, the majority of forest fires are naturally ignited by lightning. Some tree species have adapted to forest fires over the years. For example, the giant sequoia (Sequoiadendron giganteum) has a very thick bark, which can measure up to 0.6 meters in some individuals! This layer protects the cambium (the cells beneath the bark) from the heat of the fire. Other tree species, such as lodgepole pine (Pinus contorta), have cones sealed with resin that only open when exposed to the heat of the fire, causing the resin to melt. The next generation of saplings thus has an advantage because the seeds fall onto the burned forest floor, where they find many nutrients and face little competition, as the competition has been burned away. However, this adaptation only works up to a certain point. Forest fires in Canada are crucial for ecosystem renewal, but in their current intensity, they are more of a stressor for the ecosystem.


https://stephaniemirocha.com/blog-1/f/jack-pine-and-fire

When we think of a forest fire, logically, we think of burning trees. However, in the boreal forests of Canada, peatlands and permafrost ecosystems also burn, which store large amounts of carbon. Furthermore, in a forest fire, most of the fuel is on the ground. Mosses, peat, and litter burn, releasing significant amounts of carbon.


How can it burn so intensely?


As with many natural disasters we've experienced recently, the climate crisis plays a significant role. Increased temperatures lead to faster soil drying, and in some regions, there is much less rainfall. All of this increases the likelihood of a forest fire outbreak. Especially in the boreal forests of North America, climate warming is exceeding the global average.



And what about Germany?


For Germany as well, an increasing wildfire risk is projected in the coming years. However, our forests are not adapted to it. Wildfires here are more unnatural, often triggered by human negligence, such as discarding cigarette butts. From 2001 to 2020, only 5% of wildfires in Germany were caused by lightning. But here, too, an increase in the frequency of lightning strikes is forecasted for Northern Europe if we do not reduce our CO2 emissions, and if climate change continues unabated.



citations:

Alexander, M. E., & Cruz, M. G. (2012). Modelling the effects of surface and crown fire behaviour on serotinous cone opening in jack pine and lodgepole pine forests. International Journal of Wildland Fire, 21(6), 709-721.


Abdullah Kahraman et al 2022 Environ. Res. Lett. 17 114023

Gnilke, Anne, and T. G. M. Sanders. "Forest fire history in Germany (2001-2020)." Eberswalde: Thünen Institute of Forest Ecosystems 2 (2021).


Prestemon, Jeffrey P.; Hawbaker, Todd J.; Bowden, Michael [and others]. 2013. Wildfire Ignitions: A Review of the Science and Recommendations for Empirical Modeling. Gen. Tech. Rep. SRS-171. Asheville, NC: U.S. Department of Agriculture Forest Service, Southern Research Station, 20 p.


Shive, K. L., Wuenschel, A., Hardlund, L. J., Morris, S., Meyer, M. D., & Hood, S. M. (2022). Ancient trees and modern wildfires: Declining resilience to wildfire in the highly fire-adapted giant sequoia. Forest Ecology and Management, 511, 120110.


Thonicke, Kirsten, and Wolfgang Cramer. "Long-term trends in vegetation dynamics and forest fires in Brandenburg (Germany) under a changing climate." Natural Hazards 38.1-2 (2006): 283.





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