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ŠUMARSKI LIST 11-12/2009 str. 28     <-- 28 -->        PDF

S.Andrašev, M. Bobinac, S. Orlović: DIAMETER STRUCTURE MODELS OF BLACK POPLAR SELECTED ... Šumarski list br. 11–12, CXXXIII (2009), 589-603

increases in the dendromass quantity and value. By the
establishment of intensive plantations after the Second
World War in Serbia, in a relatively short period (20–25
years), annual poplar and willow felling volume increased
12 times, and by improving the assortment
structure, the value of wood volume increased almost
20 times compared to the pre-war period (Marković,
et al., 1995). However, plantation establishment with
one clone over large areas soon resulted in susceptibility
to pathogen and pest attacks. For this reason, one of
the strategic directions of further poplar research was
the continuing creation (selection) of new poplar clones
and their putting to production. These processes
were accompanied by the quantification of productivity
at the designated sites and for the selected plantations
management procedures.

The quantification of differences between genotypes
is usually defined by mean values of growth elements:
diameter (d), height (h), and the derived elements, basal
area (G), and volume (V).Also, the study of internal
stand (plantation) structure makes it possible to analyse
the state and to project the future development which
leads to a more reliable identification of productivity
differences. In this process, modern forest management
planning applies the models of tree and stand (plantation)
growth, based on real and testable data which also
include the data on ecological conditions and growth
characteristics of forest trees.The first step in the design
of stand models is the model of diameter structure.

Diameter structure modelling in even-aged stands
(and plantations) applies theWeibull probability density
function.The mathematical model of the function was
defined by Weibull,(1951) in his study of the reliability
of material hardness. It was introduced to forestry by
Bailey andDell (1973) who constructed the model
of stand diameter structure. Since then, theWeibull distribution
has been widely implemented in forestry because
it can describe a wide range of unimodal
distributions and it can be adapted to both negative and
positive skewness (Bailey and Dell, 1973; ......,
1984;Zarnoch andDell,1985;Knowe, et al.,
1994;Kotar,2005). AccordingtoBailey andDell,
(1973), ...... (1984), a special characteristic of
Weibull distributionis the fact that its parameters have a
biological interpretation. The significance of the Wei-
bull distribution in the construction of diameter structure
model in poplar plantations was reported by Andraševet
al.(2003, 2004),Andrašev(2008).

The objective of this study was to investigate the
suitability of theWeibull distribution for the construction
of diameter structure models of newly selectedpoplar
clones, SectionAigeiros(Duby), by applying the
so-called “hybrid system”of predicting the model parameters
from the sample.Also, the objective was to
study the change in model parameters depending on
plantation age and poplar clone, and also their relation
to plantation growth elements (dg ,G).

2. MATERIAL – Objekt istraživanja

The research was performed in a 20-year-old test
plantation consisting of several clones (cultivars) of
black poplar in the SectionAigeiros(Duby). Theplantation
is located on the experimental field of the Institute
for Lowland Forestry and Environment (former
Poplar Research Institute) near Novi Sad, planting
space 5 × 5 m (400 trees per hectare), plant type 2+0.
The plantation soil is fluvisol, sandy-loamy form (Škorić
et al.,1985) and can be considered as medium suitable
for poplar growing. The following poplar clones
(cultivars) were researched:
1S (Populus deltoidesBartr. ex Marsh.) – cultivar


registered in Serbia in 1987;
2NS (Populus deltoidesBartr. ex Marsh.) – cultivar


registered in Serbia in 1998;

3NS (Populus × euramericana (Dode) Guinier)


× (Populus deltoidesBartr. ex Marsh.) – cultivar registered
in Serbia in 1998;
3 Pannonia (Populus × euramericana (Dode) Guinier)
– cultivar registered in Serbia in 1998;
5 PE 19/66 (Populus deltoidesBartr. ex Marsh.) – in
selection procedure;
6S(Populus deltoidesBartr. ex Marsh.) – in selec


tion procedure.
Each clone in the test plantation consisted of six
rows, with 20–25 trees per row.The fringe rows were
not included in measurement and processing, because
of the mutual influences. From the aspect of the experiment,
each row represents a replicate (altogether 4 replicates)
for the statistical processing of the results.

3. METHOD – Metoda rada

Diameters at breast height of all trees were periodically
measured (to the nearest 1mm) after one, two, five,
eight, twelve, seventeen and twenty years from the test
plantation establishment. The number of trees in the
plantation decreased over time due to different causes:
after 20 years, minimum 85%of the initial num ber of
trees remained in each row (replicate) (Table 1). Their
diameters measured at the above ages were used for the
construction of the diameter structure model.This was
done to avoid the impact of changes in parameters due to
the decrease in the number of trees.As the same trees
were measured throughout the study period, the parameter
changes in diameter structure models can mostly be
assigned to the process of tree growth, i.e. to the specific