Resumen
This study presents results on the growth and nutritional status of Quercus petraea trees underplanted in an artificial pine stand as a conversion strategy. A total of 162 plots of 400 to 800 m2 were established in underplanted pine stands (130 plots), naturally regenerated oaks in pine stands (23 plots) and pure oak plantations (9 plots). The age of the oak stands was 7 to 14 years where they were planted, and 25 to 60 years in the natural regenerations. Biomass growth and nutrition of the oaks was studied by means of foliar analysis, soil analysis, biomass evaluation and regression techniques, considering site variables, meteorological parameters and pine cover as explicative variables. The vegetation structure of the stands in the forest-transforming areas is still dominated by the species spectrum of the original pure pine stands. As the quality of a site decreases, so the dominance of a few species increases and the diversity decreases. The manipulative effect upon the vegetation of underplanting with oaks is less severe than that of underplanting with beeches. With the progressing development of the ecological system, more demanding deciduous tree types replace the undemanding pine forest vegetation. On principle, the pine-tree canopy influences the supply of nutritional elements to the under-planted oaks. However, neither in average weather periods nor during droughts could any symptoms of nutrient deficiency or growth-impeding nutritional element disharmonies be detected by the naked eye. Only in the «Summer of the Century», 2003, did the laboratory analysed macro-element leaf-index reveal slight deficiencies of Ca- und S. The modelling of the above-ground increase in oak biomass growth, differentiated according to site and depending on time and the canopy of pine trees revealed increasing increment losses the greater the canopy cover, which even lead to stagnation in growth as the quality of the site deteriorates.