After fires, how long does it take for the forest to grow back?

Fires in Gironde, Brittany, Spain, Portugal, Morocco, Australia: this summer is disastrous for forests, which, like previous years in Europe and elsewhere, go up in smoke. These fires have been gaining frequency in recent years, destroying fauna and flora. How many years does nature take to regenerate trees, find animals?

There is no single answer to this question, as regeneration depends on multiple factors: forest type, species, soil, climate. But one thing is certain: after a fire, it takes at least 30 years to find the beginning of a forest, in some cases several hundred years old.

  • After 20 years, only a third of the plant species originally present can be found there. Biodiversity is impoverished, dominated by fire resistant grasses. The absence of shade limits the growth of many other species.
  • To find the diversity of species, including the rarest, it is necessary to wait much longer, not to mention that some never reappear.
  • After about fifty years, the number of species can reach ancient forest level.
  • But it takes centuries to recover a composition similar to the original.

Natural regeneration is therefore long, but it works: thus most of today’s forests have grown back after fire, flood, logging or deforestation), in Europe in the 18th and 19th centuries and in the first half of the 20th century in eastern United States. In the northeast of this country, the forest cover is even greater than it was 100 or 200 years ago. Half of tropical forests are secondary forests, which have regenerated after deforestation for agricultural or livestock purposes.

Erosion, disappearance of fauna and maquis

It should be noted that natural regeneration is not guaranteed, especially in case of repeated fires. we saw it in the Russian Federation, with the serious fires of 1998: more than 2 million hectares of forest lost their main ecological functions for a period of 50 to 100 years. Some plants, fungi, lichens and mosses sometimes disappear in dozens of species. Mammals and fish were severely affected: the mortality of squirrels and weasels was 70 to 80% and that of wild boars between 15 and 25%.

In the Mediterranean area, consecutive fires can transform the forest into scrub or maquis.

In the mountains, fires cause soil instability on steep slopes, causing erosion and rockfall. IFire can leave a layer of ash that repels water, and for one to two years, rainwater has difficulty penetrating the soil and runs to the surface, causing erosion.

Finally, the fires increase carbon dioxide levels in the atmosphere, contributing to the greenhouse effect and climate change. And the use of chemicals like flame retardants in firefighting can add an additional problem. The accumulation of ammonium polyphosphate alters soil fertility.

Fire may have played a role in maintaining the health of certain forest ecosystems: the most resilient species survive by showing adaptive capabilities such as thickening of the bark, the ability to heal burns, the ability to grow again… fires are, above all, a threat to biodiversity.

There is also the option of a artificial regeneration, that is, planting the forest from nurseries or even seeding in some rare cases. For this, the plants must be selected according to the soil, this is what the Comptoir Forestier de Marche-en-Famenne does for Wallonia. In other places we also plant, such as in Chile, where millions of hectares of industrial forests provide wood for construction and pulp. Some countries, like Uruguay, insist on cultivating these forest plantations only on agricultural land and not at the expense of the natural forest.

You should know that the logging continues in the world, even if it slows down in some places, it always progresses in Sub-Saharan Africa, Latin America and Southeast Asia.

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