Phenology and diameter increment in seedlings of European beech (Fagus sylvatica L.) as affected by different soil water contents:: variation between and within provenances

The effect of different soil water levels on phenology and growth of 14 provenances of European beech (Fagus sylvatica L.) was investigated in a glasshouse experiment. The genetic variation within one provenance was further studied by including 10 half-sib families from a Danish stand in the experiment. Flushing and the time for onset of diameter growth were significantly different between provenances. Length of the growing season varied significantly among provenances and was highly affected by the soil water content. Root collar diameter increment during the experimental treatment was reduced by 43% in plants at low compared to plants at medium and high soil water content. The corresponding reduction in height was 53%. Differences between provenances and the interaction between provenances and the soil water treatments were significant for growth response. This interaction term was not significant in the material of 10 half-sib families. Linear geographic and clinal trends were revealed for growth and phenological parameters, but these relationships depended on the soil water levels. The provenances from northern Europe had a fairly homeostatic expression on a low growth level across the soil water gradient, whereas the southern provenances showed a much stronger positive response to increase in soil water content. Consequently, the south European provenances had a greater adaptability to the changing growth conditions. The genetic variation in growth response within one Danish provenance was comparable with the variation between provenance under dry soil conditions, whereas this was not the case under moist and wet soil conditions. The results indicate that a substantial gain in evolutionary adaptability is possible for north European forestry by choice of material from central and southern Europe or by mixing autochton plant material with more southern seed sources. (C) 2002 Elsevier Science B.V. All rights reserved.