Zmiana wielkości krzywizn u modrzewi różnych pochodzeń na powierzchni doświadczalnej w Rogowie

The paper describes changes in the size of the curvatures in the fifteen Polish provenances of larch represented at the study site in the Experimental Forests of the Warsaw University of Life Sciences – SGGW in Rogów (Central Poland). The measurements were carried out in 1982 and 2003 (the age of larch trees was 17 and 38 years, respectively). All curvatures occurring in the lower part of the stem (up to 4 metres) of the same trees were measured on both dates using the same method (measurement of the curvature (arrow) at the maximum bend). 30 trees in the first date and 15-22 trees in the second date were selected from each provenance for measurements (some of earlier measured trees were cut during thinning). The obtained data confirmed that larch is a species of relatively high ability to reduce the size of curvatures with age which should be associated with the formation of reaction wood. This ability differs between provenances. The quality of larch stems can improve with age. The absolute change in arrow size was directly proportionally correlated with the initial size of tree curvature. The relative change of tree curvature (percentage reduction) was not related to its initial size; as both small and large curvatures diminished to a similar degree (40%). The reduction of tree curvatures was not correlated with their length, breast height diameter of a tree or its increment.