Fungal colonization of attached beech branches. II. Spatial and temporal organization of communities arising from latent invaders in bark and functional sapwood, under different moisture regimes

summary Fungal colonization of healthy beech (Fogus sylvatica L.) branches was studied by sectioning branch lengths and drying the sections under controlled regimes. Maintaining water saturation prevented any fungal development in the wood, while active mycelium was isolated as soon as 14 days after the start of the drying period. Fungi developing in these sections were naturally established in healthy branches in the field and formed a floristically denned group, dominated by Hypoxylon fragiforme (Scop.) Kickx., H. nummularium Buill.: Fr., Nectria coccinea (Pers.: Fr.) Fr., and Coniophora putaena (Fr.) P. Karst., and also included coelomycete species. This group was obtained independently of position of the branch in the canopy, season of sampling over an 11 -month period, and site, sampling including four sites in south-west Britain and one in the French Pyrenees. Several species in this group are specific or show a preference for beech as a host. Direct observations and isolation from sections with time indicated that whereas most species developed inwards from the bark, H. fragiforme and H. nummularium grew out from pockets within the wood. Each pocket contained a genetically different individual, as revealed by colony morphology and vegetative incompatibility tests. It was established that water content of the wood is the major determinant for the initial development of fungi in the xylem of beech, and that these early colonizers derive from inoculum latent in the healthy, living branches.