Hétérogénéité d'une lande haute à Ulex europaeus en relation avec la propagation du feu (Bretagne, France)

Abstract

This study analyzes plant material in a high Ulex europaeus heath to provide information on the partitioning of this ecosystem for fire propagation models. The aboveground biomass, followed for 15 months, has a spatially heterogeneous distribution that is a result of the layered pattern of the various branches. This pattern creates an internal moisture gradient that decreases from the apex to the base of the plant. This gradient also varies according to the species phenology. New, green branches with a high moisture content are at the top of the plant (upper strata), whereas woody branches with a lower moisture content are found near the ground (lower strata). Dry branches and spines, which produce most of the litter, are homogeneously distributed throughout the plant. Temporally, the layered pattern is homogeneous through the year and thus creates a constant fire risk. Soil organic horizons are temporally, spatially, and compositionally heterogeneous. The L layer is always two to three times thinner and drier than the duff layer (F+H). The total depth, weight, and moisture content of the organic horizons vary considerably across both the plot and square metre scales. The distance from a plant has a significant influence on the depth distribution of the soil organic horizons. Fuel distribution on both the soil surface and the plant must be considered to understand fire behaviour in this ecosystem.Key words: architecture, biomass, fire, fuel, humus, moisture content.