Oak decline is still a characterised by symptoms of canopy transparency, bark cracks and reduced root biomass. Decline causes losses of fine root length, and a moderate recovery can be achieved by thinning, allowing better soil exploration by roots. Mosca et al. investigate fine root and ectomycorrhizal colonisation dynamics using sequential soil coring over two years in a 60-year-old declining Quercus robur forest adjoining the Italian Pre-Alps.
A thinning treatment was applied around affected trees resulting in a recovery of root length and tip density, but a reduction in tip ectomycorrhizal colonisation and vitality. These findings exclude the hypothesis of limited water and nutrient availability as a possible cause of oak dieback. The close correlation between root vitality and mycorrhizal colonisation and their deterioration after thinning indicates that decline does not benefit from reduced root competition.