Effects of volcanic ash chemistry and former agricultural use on the soils and vegetation of naturally regenerated woodlands in the Massif Central, France

In the Chaı̂ne des Puys, a volcanic mountain range in the French Massif Central, stands of silver birch and Scots pine have naturally regenerated during the past five decades. The woodlands have developed on former croplands, pastures and heathlands. Soil properties, species composition and dendrometric stand characteristics were investigated at sites of similar altitude and topographic conditions. Soils from the southern and northern parts of the study area differ in volcanic ash composition. Those of the northern part are afforested by birch and have developed mainly on trachytic ash; they have lower pH values and show accumulation of Fe–Al organic complexes. Soils of the southern part, afforested by Scots pine, are mostly on basaltic ash and have a higher pH, much less organic matter and more allophane. Soils of former croplands have lower C/N ratios, higher δ15N contents and greater potential N mineralization than those of former heathlands and pastures. The flora of the birch woodlands differs from that of the Scots pine woodlands and also varies with former land use, mainly because of different N availabilities. Woodlands established on former heathlands and pastures were more dense but less mature than stands on former croplands. Volcanic ash chemistry and the intensity of former agricultural use are key factors influencing present soil fertility, plant composition and stand development.