Age distribution patterns in open boreal Dahurican larch forests of Central Siberia

Abstract

Tree age distribution determines stand size structure and is related to disturbance history and stand dynamics. Data are presented from 40 pure larch stands from six locations on the Taimyr peninsula and Evenk region in the northern open forests of Russian Siberia. A Weibull density function was used to describe actual age distribution and to simulate age distribution. Larch age distributions have similar patterns in different locations over the study area. All stands were found to have a multi-aged structure. The average coefficient of variation for age is about 48%. The range of tree ages exceed 400 years in the oldest forests. The patterns of age distribution change for different age groups. For the youngest stands (40–80 years old) the age distribution was leptokurtic and positively skewed, whereas for middle-aged forests (80–180 years old) it tended to be more mesokurtic and symmetric. In the oldest stands (more than 180 years old) the distribution had a platykurtic form. A high correlation was found between the Weibull function coefficients and the coefficient of age variation and for the mean age. The oldest forests were found in river valleys. Middle-aged forests occur more commonly on middle slopes and the youngest forests occupy top slopes and uplands. A more normal tree age distribution assumes a study area less damaged by forest fires than in the more southern parts of the boreal forest.