Boiser and reboiser are two distinct forestry practices. Boiser refers to the act of planting trees on land that previously lacked forest cover, such as heaths or eroded slopes. Between 1860 and 1950, the French government implemented a large-scale boiser program in the Mediterranean mountains through the RTM (Restoration of Mountain Terrains) service. This initiative aimed to prevent soil erosion, which had become a major issue due to centuries of deforestation, overgrazing, and agricultural activity. The Austrian black pine was selected for its ability to thrive in harsh conditions, including poor soil, steep slopes, and dry climates. Today, this species covers about 33,000 hectares in the Languedoc-Roussillon region. The RTM service was established in the mid-19th century to address the environmental degradation of southern French mountains. The Austrian black pine was introduced in large quantities and became a dominant species in areas such as the borders of the causses and the western Corbières. After World War II, the National Forest Fund was created to support even more extensive planting campaigns. The Austrian black pine proved effective in stabilizing the soil and adapting to the Mediterranean climate, often regenerating naturally without human assistance. Despite its success in preventing erosion, the Austrian black pine has a drawback: it is highly flammable. Its resinous structure contains compounds that ignite easily, making it particularly vulnerable to wildfires. When planted in dense, single-species stands, these pines create conditions that allow fires to spread rapidly. This has led to a growing concern among forest managers, especially in regions like the Hautes-Alpes, where these plantations have been in place for over a century. Today, the legacy of the RTM continues to shape the French Mediterranean landscape. While some tree species, like the Austrian black pine and larch, are seen as relatively resilient to climate change, others such as the Scots pine and fir are struggling with rising temperatures and prolonged droughts. The overlap between historically planted areas and regions most at risk of wildfires is particularly evident in the southern medium mountains, stretching from the Southern Alps to the Cévennes. This case illustrates how a solution to one environmental problem can lead to unforeseen challenges in the future.