Prethodno priopćenje

Circular Sample Plot Size Impact on Structure Elements Estimation in Selected Pedunculate Oak Stands

Krunoslav Indir orcid.org/0000-0002-8824-1487 ; Hrvatski šumarski institut Jastrebarsko
Vladimir Novotny ; Hrvatski šumarski institut Jastrebarsko

Sažetak

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.

Ključne riječi

pedunculate oak; sample plots; stand structure elements; estimation precision

Hrčak ID:

72329

URI

https://hrcak.srce.hr/72329

Datum izdavanja:

14.10.2011.

Podaci na drugim jezicima: hrvatski

Posjeta: 1.498 *