A chronosequence study of soil nutrient status under oak and Corsican pine with Ellenberg assessed ground vegetation changes

Ellenberg indices (light, nitrogen, reaction and water) were derived from the Environmental Change Network groundflorasurveyunderpedunculateoak(Quercus robur(L.) ,200years)andCorsicanpine(Pinus nigra var maritima ((Ait.) Melville) ,60 years) at Alice Holt Forest and compared with soil factors analysed for moisture, pH and nutrients,NH4-N,NO3-Nandwater-solublenitrogen(N)(TsolN).Resultsfromreplicateplotsweregroupedbystand age.SoilpHrosewithageexceptundertheoldestoak.JulyNH4-Nlevelsunderoldoakonallclaysoilsweredouble those under old pine on sandier surface deposits, but NO3-N levels were halved under the oak. Floristic indices showed an N increase with age under both species, as soil N stock also significantly rose (oak: P , 0.01, pine, P , 0.05). Ellenberg N values were significantly correlated with Tsol N under oak (P , 0.01), and loss on ignition per cent under pine (P , 0.001). There was direct relation between Ellenberg R and soil pH across both communities (P , 0.05), but Ellenberg R and N values were highly inter-correlated (P , 0.001). The combined values (Ellenberg RandN)weresignificantlycorrelatedwithlevelsofmid-summerTsolN(P , 0.01),indicatingwater-solubleorganic N to be a good measure of N availability to ground flora plants. Ellenberg L values rose under pine with age but decreased under oak. Measured leaf area index of oak understorey shrubs increased from 10 to 20 per cent of the total with age, contributing to the loss of floristic diversity beyond middle age.