The phenology of Rhododendron ferrugineum L. (Ericaceae) in correlation totemperature, frost, insolation, and snow cover duration

The phenology of Rhododendron ferrugineum L. has been studied during five y ears (1994 to 1998) in two sites in the Alps of Valais (Switzerland). The f irst site is the Val d'Arpette and the second one is Belalp. Observation pl ots have been set up according to a subalpine-alpine altitudinal transect. Several climatic factors such as air temperature, soil temperature, relativ e air humidity insolation and snow cover duration have been measured. The c orrelation between the phenological development and these factors has been determined. The results show that the floral development of this species is mainly correlated with the sum of the mean daily air temperature. But fros t, insolation and snow cover duration have also shown a significant influen ce. A phenoclimatic model including all these factors is proposed.