The article presents the results of studies on the population of curly (or Karelian) birch Betula pendulaRoth var.carelica(Mercklin)Hämet-Ahti created in the Kivach State Nature Reserve since the 1950s–1970s. Seed- and vegetative (produced by clonal micropropagation) progenies were sampled (108 trees in total) to study growth parameters in six tree groups of different ages growing not far from one another. In seed progeny, the average height was 12.5 m in young, 24-year-old trees, 16.0 m in 52-year-old trees, and a mere 11.6 m in 65-year-old trees. It is hypothesized that the reduction in illumination in older plantations due to different reasons has affected the growth of trees of all growth forms in one case and primarily of short-stemmed and shrub-like forms in the other. The variability of the growth parameters was comparatively analyzed. Thus, the coefficient of variation of the “plant height” attribute in seed progeny ranged from high or very high (34–45 %) in young generative-stage plants (g1) to elevated (27 %) in the late generative stage (g3). This index in vegetative progeny was at a much lower (ca. 8 %) or an interim (ca. 16 %) level. The height and diameter distributions of trees generally conform to the normal law, while the coefficient of variation, as analysis has shown, mainly depends on the tree age, ontogenetic status, illumination and, most significantly, on the origin-controlled level of genetic heterogeneity in each of the six plant groups. A conclusion drawn from this study is that the conditions in the Kivach Nature Reserve are quite favorable for curly birch growth, and the general state of the population can be recognized as satisfactory except the need to remove some “hazardous” trees and implement regular tending in all the six sites harboring the trees that form this population.