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

摘要

Ellenberg indices (light, nitrogen, reaction and water) were derived from the Environmental Change Network ground flora survey under pedunculate oak (Quercus robur (L.) <200 years) and Corsican pine (Pinus nigra varmar-itima ((Ait.) Melville) <60 years) at Alice Holt Forest and compared with soil factors analysed for moisture, pH and nutrients, NH4-N, N03-N and water-soluble nitrogen (N) (Tsol N). Results from replicate plots were grouped by stand age. Soil pH rose with age except under the oldest oak. July NH4-N levels under old oak on all clay soils were double those under old pine on sandier surface deposits, but N03-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 R and N) were significantly correlated with levels of mid-summer Tsol N (P < 0.01), indicating water-soluble organic N to be a goodmeasure 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 offloristic diversity beyond middle age.