Crown condition of Norway spruce: Within-stand relationships and competition

Abstract

This study describes how crown density changes were distributed within monitoring plots, in order to determine whether the reduced crown density observed could be explained as a worsening of a limited number of unhealthy or small and slightly suppressed trees. Crown density, yellowing, coning and stem diameter data were available from 447 selected plots comprising 22 560 single trees all having a complete 1990-97 series of crown condition data. The 8-year record of crown density for each tree was recalculated to two median values, for 1990-93 and 1994-97, in order to reduce the influence from short-term variations including random errors. The scores for yellowing and number of cones were averaged over the years 1990-93. These variables, and diameter, were recalculated to rank indices within each plot. Relationships between variables were described by graphs and examined by correlation analyses of the indices. The trees tended to retain their internal ranking. Generally, when crown density for a plot has changed, most of the trees were affected. The most defoliated trees in each plot had the least negative changes, but apart from that the trees were equally affected regardless of their yellowing, number of cones, and their size. The results demonstrate that any effects from competition between the trees were sufficiently removed in the assessments even in densely stocked stands.