The vegetation is deciduous oak forest: both sessile oaks ("Quercus petraea") and pedunculate oaks ("Quercus robur"), with European ash ("Fraxinus excelsior") and hazels in the coolest and deepest soil at the bottom of the valley. The mountain layer is characterised by the presence of beeches and at times, in the Pyrenees, by silver firs ("Abies alba"); these beeches and silver firs occupy the cool slopes with shallow soil. The Mediterranean influence is felt in the presence of Holm oaks ("Quercus rotundifolia") with bay laurel, which are situated on the warmest crests and slopes, especially above chalky soil, where the dryness becomes more pronounced.