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

This study describes how crown density changes were distributed within moni toring plots, in order to determine whether the reduced crown density obser ved could be explained as a worsening of a limited number of unhealthy or s mall and slightly suppressed trees. Crown density, yellowing, coning and st em diameter data were available from 447 selected plots comprising 22 560 s ingle trees all having a complete 1990-97 series of crown condition data. T he 8-year record of crown density for each tree was recalculated to two med ian 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. Relationship s between variables were described by graphs and examined by correlation an alyses of the indices. The trees tended to retain their internal ranking. G enerally, 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 ch anges, but apart from that the trees were equally affected regardless of th eir yellowing, number of cones, and their size. The results demonstrate tha t any effects from competition between the trees were sufficiently removed in the assessments even in densely stocked stands.