Figure 2. Location of the three study sites namely Palomäki, Pollari,
and Vesijako and vegetation zones in Finland (left) and study sites on
top of satellite imagery © 2020 TerraMetrics.
The plots were measured and thinning treatments performed at the time of
the establishment (in 2005 at Palomäki and in 2006 at Pollari and
Vesijako). The most recent field measurements were carried out in
October 2018 and in April 2019. Tree species, crown layer, DBH from two
perpendicular directions, and health status were recorded from each tree
within a plot (i.e. tally trees). At the time of the latest
measurements, the proportion of Norway spruce and deciduous trees (i.e.Betula sp and Alnus sp) from the total stem volume of all
trees within the 9 sample plots was 3.02% and 0.07%, respectively.
Approximately half of the trees (n=318) were selected as sample trees
from which tree height, crown base height, and height of the lowest dead
branch were also measured. Height of the tally trees was estimated using
an allometric model calibrated for each sample plot with the information
from the sample trees. Stem volume of individual trees was produced by
using the existing nationwide, species-specific volume equations with
DBH and height as predictors (Laasasenaho 1982) to obtain corresponding
information from different field measurements. Plot-level attributes
before and after thinning treatments are presented in Table 1, and the
development of tree-level attributes for each thinning treatment can be
found in Table 2.
Table 1. Mean stand characteristics by treatments before and after
thinning and thinning removal. N = stem number per hectare, G = basal
area, Dw = mean diameter weighted by basal area,
Hw = mean height weighted by basal area,
H100 = dominant height, and V = volume.