Stand structure and regeneration in a Kamchatka mixed boreal forest

A 1-ha plot was established in a Betula platyphylla-Picea ajanensis mixed boreal forest in the central Kamchatka peninsula in Russia to investigate stand structure and regeneration. This forest was relatively sparse: total density and stand basal area were 1071 /ha and 25.8 m(2)/ha, respectively, for trees > 2.0 cm in trunk diameter at breast height (DBH). 25% of Betula regenerated by sprouting, and its frequency distribution of DBH had a reverse J-shaped pattern. In contrast, Picea had a bimodal distribution. The growth rates of both species were high, reaching 20 m in ca. 120 yr. The two species had clumped distributions. especially for saplings. Benda saplings were not distributed in canopy gaps. Small Picea saplings were distributed irrespective of the presence/ absence of gaps. while larger saplings aggregated in gaps. At the examined spatial scales (6.25 - 400 m(2)) the spatial distribution of Benda saplings was positively correlated with living Betula canopy trees and negatively with dead Picea canopy trees. This suggests that Benda saplings regenerated under the crowns of Benda canopy trees and did not invade the gaps created by Picea canopy trees. The spatial distribution of Picea saplings was negatively correlated with living and dead Betula canopy trees and positively with dead Picea canopy trees, Most small Picea seedlings were distributed under (he crowns of Picea trees but not under the crowns of Betula trees or in gaps. This suggests that Picea seedlings establish under the crowns of Picea canopy trees and can grow to large sizes after the death of overhead Picea canopy trees. Evidence of competitive exclusion between the two species was not found. At a 20 m x 20 m scale both skewness and the coefficient of variation of DBH frequency distribution of Picea decreased with an increase in total basal area of Picea while those of Betula were unchanged irrespective of the increase in total basal area of Benda. This indicates that the size structure of Picea is more variable with stand development than that of Betula on a small scale. This study suggests that Benda regenerates continuously by sprouting and Picea regenerates discontinuously after gap formation and that the species do not exclude each other.