Annual growth rhythm of Larix sibirica and Larix gmelinii provenances in a field trial in southern Finland

The aim of this study was to analyse how the growth onset and shoot elongation of seedlings differ in field conditions in Finland for 20 Russian larch provenances and five comparison entries, and if they could be explained by the geographic and climatic conditions of the provenance origins. In this work, the Dahurian larch (Larix gmelinii Rupr.) provenances had the earliest growth onset and the northern Siberian larches (Larix sibirica Ledeb.) slightly earlier bud burst. The temperature sum and latitude of the provenances explained the differences in shoot elongation. The time needed for shoot elongation and the temperature sum needed to obtain 50% of total shoot elongation were quite equal in the years 2008 and 2009 (larger difference with the 90% level). The growth cessation was affected by photoperiod regardless of provenance. However, it was affected in the southern provenances also by declining temperatures in autumn. The final height was in 2009 largest in southern Dahurian larches. Despite our findings, the use of seed sources of domesticated Raivola origin is the safest choice for regeneration in Finland. We should still study more in detail the performance of other provenances and their adaptation capacity and suitability to Finnish forestry.