Between 1860 and 1930, the RTM service reforested approximately 280,000 hectares of the Southern Prealps with the Austrian black pine to combat erosion and floods. This species, chosen for its powerful root system, has turned out to be one of the most flammable in the Mediterranean region due to its resin and needles rich in volatile compounds. As early as 1981, foresters noted a lack of natural regeneration in these uniform stands, while certain species such as the Scots pine or the fir now show signs of decline due to climate warming. A forest planted to tame water has become a time bomb in the face of fire. One must go back to the 19th century to understand the scale of the problem that the state engineers were facing. In the Southern Alps and the Cévennes, decades of deforestation and overgrazing had left entire slopes bare. Without roots to hold the soil, storms turned streams into mudflows capable of swallowing entire hamlets. The valleys downstream suffered catastrophic floods, and both harvests and homes paid the price of these denuded soils. It was in this context that the Mountain Terrain Restoration Service, better known by its acronym RTM, was born. Its mission was clear: to reforest extensively to stabilize the soil and stop erosion. What no one imagined at the time was that the solution chosen to eliminate one disaster would, a century and a half later, ignite another. Between 1860 and 1950, the RTM reforested more than a million hectares of Mediterranean mountains. A titanic project, carried out at a time when mechanization did not yet exist, when each sapling had to be planted by hand on sometimes vertiginous slopes. Faced with urgency, forest engineers did not seek diversity: they bet on a single species capable of adapting quickly to poor soils and harsh climates. This choice, as pragmatic as it was, created an unprecedented forest uniformity over tens of thousands of hectares. It is estimated that approximately 280,000 hectares of the Southern Alps were thus reforested with the same species between 1860 and 1930, a figure that shows the scale of the ambition of the time, but also its relatively bold ecological daring. The Austrian black pine, the star imposed by a 19th-century forest bet. Its main advantage: a particularly powerful root system capable of anchoring deeply in unstable terrain and resisting erosion. From a purely agronomic point of view, the bet was an undeniable success. The tree has adapted perfectly to the Mediterranean climate, it has colonized the slopes assigned to it, and it continues today to cover about 33,000 hectares in Languedoc-Roussillon. The torrents have calmed, the devastating floods have become rarer, and the valleys have been able to develop peacefully. From the initial perspective of the fight against erosion, the history of the Austrian black pine is a success still taught in forestry schools. But this same tree that saved the soil hides a structural flaw. The Austrian black pine is now classified among the most flammable species in the Mediterranean region. Its resin, precious for its resistance and rapid growth, becomes a dangerous fuel as soon as heat and drought set in. The needles, rich in volatile compounds, ignite easily and spread the fire from branch to branch with a disconcerting speed. The result is an almost ironic superposition: the areas that were most carefully reforested in the 19th century to avoid a catastrophe are today among the most exposed to forest fires. It is not nature that created this risk, but a human decision made in a context where climate change was obviously not anticipated. The problem is not new to specialists. As early as the end of the 20th century, foresters themselves began to document the flaws of these uniform stands. An analysis conducted in 1981 on the reforestation of the Southern Alps already pointed out the uncertainty surrounding the future of these forests, due to a lack of sufficient natural regeneration. In other words, these pines are aging without being naturally replaced by young shoots, which further weakens already homogeneous stands. In the Hautes-Alpes, the local RTM service continues to defend some of these historical species. The larch and the Austrian black pine are still considered compatible with the IPCC climate scenarios, which slightly nuances the picture. On the other hand, other trees planted at the same time, such as the Scots pine or the fir, already show signs of decline related to warming, proof that the 19th-century forest equation must now be completely rethought. What this story ultimately reveals is the difficulty of reconciling decisions made to respond to an immediate emergency with the challenges of a future that could not be predicted at the time. The 19th-century engineers solved a vital problem for their generation, that of erosion and floods, without being able to imagine that their solution would become, a century and a half later, an aggravating factor for the fire risk. As the Southern Prealps continue to suffer from increasingly hot and dry summers, the question that now arises is that of the diversification of forest species: how to correct the legacy of a unique choice without losing the benefits it brought in terms of soil stability?