Changes of Humus Features along with a Successional Gradient of Rhododendron ferrugineum (L.) Populations (Subalpine Level, Northwestern Alps, France)

Abstract

The modifications of humus characteristics as a result of the establishment and the increasing cover of Rhododendron ferrugineum L. (Ericaceae) in a subalpine meadow were studied in three sites in the northwestern French Alps corresponding to a west–east transect between wet and dry Alps (“Chaîne de Belledonne,” “Massif du Taillefer,” “Briançonnais”). The physical and chemical parameters of humus and biological parameters were studied during the successive studies.As opposed to other Ericaceae heathlands on siliceous soils (Vaccinium sp., Erica sp., Calluna vulgaris), with an increasing Rhododendron cover, the humus structure changed while some other parameters remain stable or increased. The development of Rhododendron populations on calcareous soils (Briançonnais) with maintenance of a calcareous humus has never been checked before.The modifications of the Rhododendron environment under its canopy led to an improvement in its growth conditions (positive feedback).