353 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 Ekológia (Bratislava) Vol. 23, No. 4, p. 1-2, 2004 INCREMENT AND ENVIRONMENTAL CONDITIONS IN TWO SLOVENIAN PEDUNCULATE-OAK FOREST COMPLEXES MATJAŽ ČATER, TOM LEVANIČ Slovenian Forestry Institute, Večna pot 2, 1000 Ljubljana, Slovenia, e-mail: matjaz.cater@gozdis.si Abstract Čater M., Levanič T.: Increment and environmental conditions in two Slovenian pedunculate- oak forest complexes. Ekológia (Bratislava), Vol. 23, No. 4, , 2004. In Slovenian lowlands there has been a noticeable decline and physiological weakening of pe- dunculate oak, connected with dry climate, unfavourable precipitation patterns and human in- fluence through hydromeliorations and changes in water table. Dendrochronological comparison was made to compare past growth patterns of oak trees in two different pedunculate oak forest complexes. An experiment with seedlings was also performed to evaluate regeneration ability of planted and natural seedlings in different light conditions on plots with different water supply (groundwater table) and to give possible perspective for the species in the future. Analysis confirmed differences in growth patterns of older oak trees between complexes and indicated light conditions of planted seedlings where relative height and relative diameter incre- ment were reaching their maximum in specific site conditions. Comparison of crown defoliation for both forests (1995-2000) confirmed gradual increase of crown defoliation between years. Correlations between crown defoliation and cumulative preci- pitation and between average air temperatures in August on both plots indicated a strong connec- tion. Key words: pedunculate oak, growth, light conditions, water conditions, increment Introduction Declining of oaks is a process, which has been periodically repeating ever since the end of last century. Several theories tried to explain the decline as the combined effect of several factors (Führer, 1992; Rösel, Reuther, 1995; Donaubauer, 1995, Siwecki, Ufnalski, 1995) and some have indicated possible causes in parts of Europe (Hartmann et al., 1989; Hämmerli, Stadler ,1989; Näveke, Meyer, 1990; Harapin, Androić, 1996). In depth studies