Structure Formation of Forest Tree Species Coenopopulations During Post-Fire Recovery of Northern Taiga Forest

Abstract

The goal of this study was to compare the coenopopulation structure of two main stand-forming tree species of European northern taiga forest – Picea obovata Ledeb. and Pinus sylvestris L. at different stages of post-fire successions. Investigations were carried out in the Kola Peninsula (67°30ʹ–68°10ʹ N, 33°57ʹ–34°21ʹ E) in Siberian spruce forest of the true moss site type with fire age of 82 and 146, Scots pine forest of the lichen-true moss site type with a similar fire age (83 and 155), and in mixed pine-spruce forest of the true moss site type with fire age of 376. Five 0.1–0.2-ha permanent sample plots were surveyed. In order to register living tree individuals > 0.1 m high, the sample plots were divided into 5 x 5 m squares. Tree individuals 1 yr.) were sampled from 40–100 1x1 m squares. To analyze the age and size distributions we chose three key parameters: range of values, skewness and kurtosis. The vitality of the trees was determined on the basis of relative crown density, using a five-category classification: I – healthy individuals, II – moderately weak individuals, III – very weak individuals, IV – declining individuals, V – dead individuals. According to our data, Picea obovata and Pinus sylvestris showed similar patterns in the formation of the age, size and vitality structure of the coenopopulations during post-fire succession despite the differences in biological and ecological properties. Hence, there exist common mechanisms of coenopopulation structure transformation, based on the laws of competition among tree individuals within a population and coenotic regulation of regeneration processes. The established structural differences are not significant and mostly manifest themselves during the first half of the succession. The distinctive feature of pine coenopopulations is discontinuity of the age and diameter class distribution over a period from ~100–150 to at least 400–500 yrs. after a fire. At later stages of a post-fire succession (>350 yrs. after the fire) one observes a convergence of the age, size and vitality structure of coenopopulations of the two species. This result can be regarded as evidence of uniformity of the main tree species structural organization in subclimax and climax northern taiga forest.