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ŠUMARSKI LIST 13/2011 str. 223     <-- 223 -->        PDF

K. Indir, V. Novotny: UTJECAJ VELIČINE KRUŽNIH PRIMJERNIH PLOHANAPROCJENU STRUKTURNIH ... Šumarski list – Posebni broj (2011), 211-221


SUMMARY: Data collecting in forest inventory in Croatia are carried out
on a temporary sample plots (circles or strips). In this article, sample of
86 circular plots established in Repaš-Gabajeva Greda management unit
(Fig. 1), Repaš forest office, Koprivnica regional forest office, is used to see
how the basic structural elements (stem number – N, basal area – G and stand
volume –V) are changing when the sample plot radius is decreasing. Research
area is typical lowland pedunculate oak and hornbeam stand (Carpino betuli


- Quercetum roboris (Anić 1959) Rauš 1969. Sample plots covered the whole
management unit area and stands older than 40 years, from 3rd to 7th age
class. Sample units were circular, with radius 15 to 30 m, bigger than in regular
forest inventory (Table 1) which are usually 12,62 m and 18 m in radius.


All trees above 10 cm in dbh within circular plot were measured. Plot center
was marked with iron bolt below ground level. Position of each tree is determined
with distance and angle from plot center. Haglof caliper was used to
measure two dbh of each tree. Total tree height was taken with Suunto hypsometer.


Data collected in a field, were entered to database created in Microsoft Access.
For each plot, number of trees per hectare, basal area per hectare, and
volume per hectare, were calculated, separately for tree species and total.
These basic structure elements were calculated for different plot sizes, lower
than taken in field. It has been done using database queries, thanks to recorded
position of each tree. For a particular criteria (distance from plot center),
only trees that are within required radius were selected. In 3rd and 4thage
class, plot radius from 5 to 15 m, with 1 m step, is used to calculate structure
elements (Table 2). In 5thage class, examined plot radius range was 15–25 m,
and in 6thand 7thage class 20–30 m (Table 3).


Calculated elements were examined with simple statistical analyses in
order to get variation coefficient (CV), and precision (SP). The results showed
that in 3rd, 4thand 7thage class there is not enough sample plots to bring conclusions
because variation coefficient values are high and precision is at poor
level. (Fig. 3–8). In 5th and 6th age class for all examined plot radii, estimated
precision of basal area and stand volume is better than 5 % (Fig.7, Fig.8),
and variation coefficient is in range of 15,3–26,4 % (Fig. 4, Fig. 5). Stem
number estimation shows precision of 5,3–6,0 % (Fig. 6).


In given research area and stand conditions, conclusions are:


– in 3rd, 4thand 7thage class variability in small amount of sample plots is
too high to bring resolute conclusion
– regarding to variation coefficient and estimation precision values, there is
no need to use sample plot radius greater than 15 m in 5thage class, and
20 m in 6thage class
– with more sample plots in 3rd, 4thand 7thage class, and use of lower sample
plot sizes in 5thand 6thage class, optimal plot radius that gives reliable and
precise stand structure elements estimation could be reached.


Key words:Pedunculate oak, sample plots, stand structure elements,
estimation precision