Crown density changes of Norway spruce and the influence from increased age on permanent monitoring plots in Norway during 1988-1997.

摘要

A study was carried out to determine whether changes in crown density in local county monitoring plots in Norway during 1988-97 could be attributed to normal effects due the increasing age of trees in the plots. The dataset comprised around 580 plots and 27 000 single trees of Norway spruce (Picea abies), with 10 years of crown density measurements available for each tree. Highly significant correlations were found between crown density and age. The relationship suggested an annual reduction of crown density of around 0.12%. However, the relationship varied both between years and between regions, and it was not possible to determine whether the relationship was best described by linear or non-linear models. The relationship appeared to be influenced by the presence of stresses, with effects generally more severe in old stands. It was determined that the mean crown density change of -0.41% annually could not be attributed to normal ageing, as it was clearly below all the suggested expectancies from various models. It is suggested that the amount of stress in the period under study was higher than normal. The results were valid for most of Norway, with the exception of western and northern regions.