An addition to our discussions of forest carbon and the management practices that impact carbon storage and ems, and calls for preservation, rather than active management. A new study from Cambridge University: “Fire effects on the persistence of soil organic matter and long-term carbon storage,” Nature ($), Dec. 23, 2021.
A Cambridge press release boils it down:
“Using controlled burns in forests to mitigate future wildfire severity is a relatively well-known process. But we’ve found that in ecosystems including temperate forests, savannahs and grasslands, fire can stabilise or even increase soil carbon,” said Dr Adam Pellegrini in the University of Cambridge’s Department of Plant Sciences, first author of the report.
He added: “Most of the fires in natural ecosystems around the globe are controlled burns, so we should see this as an opportunity. Humans are manipulating a process, so we may as well figure out how to manipulate it to maximise carbon storage in the soil.”
Fire burns plant matter and organic layers within the soil, and in severe wildfires this leads to erosion and leaching of carbon. It can take years or even decades for lost soil carbon to re-accumulate. But the researchers say that fires can also cause other transformations within soils that can offset these immediate carbon losses, and may stabilise ecosystem carbon.
Fire stabilises carbon within the soil in several ways. It creates charcoal, which is very resistant to decomposition, and forms ‘aggregates’ – physical clumps of soil that can protect carbon-rich organic matter at the centre. Fire can also increase the amount of carbon bound tightly to minerals in the soil.
“Ecosystems can store huge amounts of carbon when the frequency and intensity of fires is just right. It’s all about the balance of carbon going into soils from dead plant biomass, and carbon going out of soils from decomposition, erosion, and leaching,” said Pellegrini.
When fires are too frequent or intense – as is often the case in densely planted forests – they burn all the dead plant material that would otherwise decompose and release carbon into the soil. High-intensity fires can also destabilise the soil, breaking off carbon-based organic matter from minerals and killing soil bacteria and fungi.
Without fire, soil carbon is recycled – organic matter from plants is consumed by microbes and released as carbon dioxide or methane. But infrequent, cooler fires can increase the retention of soil carbon through the formation of charcoal and soil aggregates that protect from decomposition.
“Stabilizing” forest carbon is becoming a buzzword and a new goal for forest management, but it is NOT a climate solution. The atmosphere is well-mixed. It does not matter if carbon booms and busts at the scale of stands or even landscapes. What matters is the total amount of carbon in the atmosphere. From a climate perspective, it might make more sense to accumulate carbon in forests and soils (let forest carbon boom), even if it is not “sustainable” over the long term because it will eventually burn (the carbon might go bust), because every day, week, month, year that carbon stays in forests and soils is a day, week, month, year with less solar forcing.
Of course, forest carbon is a minor issue when you include ALL the other issues. Of course, most climate ideas don’t “save the forests” over the longterm course of climate ‘treatments’. Apparently, some climate ‘warriors’ are just fine with burned up forests, accelerated erosion and losses of endangered species habitats, as long as their climate ideas are enacted.
I don’t think that you can separate out the desire for carbon accumulation of unknown time periods with the need for building materials (with varying levels of GHGs from production) and the need to protect communities. All those needs require consideration simultaneously IMHO.
Another study: “Innovative wood use can enable carbon-beneficial forest management in California.”
https://www.pnas.org/content/118/49/e2019073118
And an article about it: “Clever Wood Use Could Mitigate Wildfires and Climate Change.”
https://eos.org/articles/clever-wood-use-could-mitigate-wildfires-and-climate-change
From the study:
Significance
Natural carbon sinks can help mitigate climate change, but climate risks—like increased wildfire—threaten forests’ capacity to store carbon. California has recently set ambitious forest management goals to reduce these risks. However, management can incur carbon losses because wood residues are often burnt or left to decay. This study applies a systems approach to assess climate change mitigation potential and wildfire outcomes across forest management scenarios and several wood products. We find that innovative use of wood residues supports extensive wildfire hazard reduction and maximizes carbon benefits. Long-lived products that displace carbon-intensive alternatives have the greatest benefits, including wood building products. Our results suggest a low-cost pathway to reduce carbon emissions and support climate adaptation in temperate forests.