Reactions of different populations of Corylus avellana L. and Prunus spinosa L. to drought and frost stress under controlled conditions Area of origin biomarkers Federal Nature Conservation Act phenology frost damage populations predawn water potential relative water content stomata conductance. Biomarker Bundesnaturschutzgesetz Frostschäden Phänologie predawn Wasserpotenzial relativer Wassergehalt stomatäre Leitfähigkeit Vorkommen Vorkommensgebiete