The Dynamics and Variability of Radial Growth in Provenance Trials of Norway Spruce (<i>Picea abies</i> (L.) Karst.) Within and Beyond the Hot Margins of its Natural Range

Abstract

Multi-site field trials provide valuable data for the investigation of possible effects of environmental changes on forest tree species. We analyze the descendants of plus trees from 33 Norway spruce seed sources of Romanian Carpathians, at age 30, in four comparative field trials: two established in the natural range of species and two outside of it. The dynamics and variation of radial growth, earlywood and latewood were analyzed. The influence of populations, site conditions and climatic factors were also quantified. The provenances response in the four comparative trials was asymmetric for mean radial growth, but its dynamics was less favourable outside of the natural range. Analysis of variance showed significant differences (P<0.001) between the testing sites, but non-significant (P<0.05) for the populations. Populations x localities interaction was high (P<0.001) in the first half of the testing period, but decreased over time, becoming not significant at the age of 30. At intra-populational level, the average coefficient of variation for radial growth was higher outside the natural range, whereas the proportion of latewood decreased. The temperature in the first half of the growing season negatively influenced (P<0.001) the radial increment, but in the latewood proportion significat effects (P˂0.05) were recorded only in trials located outside of the natural range. An increased variability of radial growth and a decrease of latewood proportion are expected in Norway spruce stands located at lower altitudes, towards the limits of the natural range. Our results may contribute to the sustainable management of Norway spruce forests within and outside its natural range.