Reacción a "The rapid spread of extreme fires can lead to long-term changes in vegetation"

Are the research findings supported by robust data?

“The article is of high scientific quality and methodologically sound, and is consistent with other research in the same geographical area. It is written in a precise and objective manner.”

Are there any limitations to the analysis?

“There are limitations to the approach, as it does not pay sufficient attention to variables other than climatic ones (such as historical factors, for example). Throughout North America, the indigenous population, from the time of their arrival—which coincided with the end of the last ice age—carried out systematic controlled burns across the entire territory. It was white colonisation that brought these burns to a halt for reasons such as the spread of disease, confinement to reserves, conflicts, the erosion of rights, and so on.

This led to more than a century of neglect of prescribed burning and the indigenous peoples’ traditional knowledge, resulting in forest management being limited to intensive exploitation, where access was minimal but neither reforestation nor subsequent silvicultural treatments were carried out. The increase in fires gave rise to a systematic fire suppression policy from the 1960s onwards.

Added to all this were policies regarding strictly protected areas, where fuel accumulation was even greater, particularly as a result of the campaigns in the late 1980s to save the spotted owl, which prohibited logging across vast tracts of land.

At the same time, the effects of climate change reached North American forests in the 1980s and 1990s, bringing severe infestations of bark beetles (coleoptera), which led to enormous accumulations of dead fine fuel—the ideal fuel for megafires. It should be noted that, unlike in Europe, the influence of the sea is felt only on the Pacific coast and in Alaska. In the rest of boreal North America, the climate is much drier during the growing season than in Eurasia, both in terms of precipitation and ambient humidity.

The observation period used in the article (between 2002 and 2021) is relatively short for this type of analysis, probably due to a lack of precise data of the required quality.

Regarding the trend towards a concentration of the largest burnt areas in a very small number of fires, this had already been predicted 20 years ago as part of the FIRE PARADOX project, highlighting that a policy focused solely on fire suppression is not only costly but also has very limited scope.

Finally, it should be noted that the national forest inventories of Canada and the United States do not confirm a reduction in stocks of forest biomass in either country to date.”

How do these findings relate to fires in Spain?

“Spain has a different climate and a much higher population density, which means the study’s conclusions cannot be directly applied. It is true, however, that climate change is extending the windows of opportunity for large fires, so maintaining managed land by reducing vertical and horizontal continuity is key.

The fact that North America is the continent with the highest incidence of lightning strikes as a cause of fires is of particular relevance to the mountainous interior of Spain, especially in the north-east, where this cause lies behind many of the largest fires and requires greater attention due to its clear upward trend”.

How do tree species (conifers in this case) influence the spread of fires or subsequent recovery?

“In boreal climates, conifers are the most mature (climax) species due to their resistance to the cold, whilst the few species of broad-leaved trees either colonise humid areas or play a purely pioneer role (birch), which is somewhat less pronounced in North America due to lower ambient humidity.

On the other hand, a significant proportion of North American boreal forests consist of larch (Larix), which is considerably less combustible. One specific point in the article is the mention of a single species (Populus tremuloides) as a possible alternative. However, it does not consider that a determined expansion beyond its natural range might be highly forced and could entail other types of risks, including a possible lack of viability.”