Source: Haut-Languedoc Regional Nature Park
Haut-Languedoc Regional Nature Park (PNRHL), located on the southern limit of the Massif Central, sits in a unique area of meeting point for three climates (Mediterranean, Atlantic, Alpine), thus in a place where the environment will be very sensitive to any shifting of climate ranges.
Therefore, in some areas, the Mediterranean climate is very close to the Alpine climate. This geographical proximity induces a stronger sensitivity to climate change in the PNRHL territory because a small change there can have a huge impact.The effects of climate change will most certainly be visible on the vegetation, which is vulnerable to sudden changes, especially if the intensity of the climate crisis is high. The rise of the Mediterranean climate should happen in successive waves towards the higher elevation zones, and not in a gradual way.
In France, we are not seeing yet a strong trend in the changes of precipitation regime, even though in the PNRHL there is already a decrease in Summer rainfall. This decline, combined with an increase of winter temperatures and rainfalls, seems to indicate that the Mediterranean climate is becoming stronger throughout the territory.
In 2003, in some areas of the Tarn department, we observed a climate similar to the one in Marseille. As a result of this exceptional heat wave, many Douglas fir stands underwent decay after 90 days with an average daily temperature of 30°C in the shade and no rain.
2001 and 2003 orthophotographs taken on the PNRHL territory (Source : IGN)
Just after the heat wave, the IGN did an aerial photography campaign, which made it possible to highlight areas of dying forest stands, because the crown of dead Douglas trees immediately turned red in some plots.
After studying stand maps and aerial photographs, a study found that 65% of the inventoried stands were affected by mortality, distributed in spots in the plots. However this mortality was rather diffuse given that tree dieback occurred in only 3 to 5% of the global surface of Douglas fir in the PNRHL territory.