no soil improvement treatments were considered in this study. Most
of the plots (about 73%) were unmanaged, resulting in 2616
plots in which at least one of the treatments was observed.
363 plots had both regeneration and stand improvement
treatments, but these were analysed as regeneration plots
because regeneration treatments have the largest influence on
stand structure and diversity. The number of plots by
treatment in the 3SNFI was: 81 with clearcutting, 12 with
shelterwood, 1901 with selection cutting, 158 with cleaning,
67 with precommercial thinning, 283 with thinning and 114
with pruning. We estimated and ranked the intensity of each
silvicultural treatment through the percentage of basal area
removed in 8613 of the 3SNFI plots that had also been
inventoried 10 years before in the Second Spanish National
Forest Inventory (2SNFI). This percentage was calculated as
the amount of basal area of those tally trees that had been
inventoried in the 2SNFI but that were not present in the same
permanent plots in the 3SNFI, divided by the total basal area
of the stand. Although management is the main cause of tree
removal from the forest, other natural disturbances different
from forest fires (already excluded from the analyses) may
also cause the natural mortality and loss of stems in the
stands, and therefore forests without human disturbance may
still lose basal area as calculated here.