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Научни трудове на Съюза на учените в България-Пловдив, серия Б. Естествени и хуманитарни науки, т. XVIII, ISSN 1311-9192 (Print), ISSN 2534-9376 (On-line), 2018. Scientific researches of the Union of Scientists in Bulgaria-Plovdiv, series B. Natural Sciences and the Humanities, Vol. XVIII, ISSN 1311-9192 (Print), ISSN 2534-9376 (On-line), 2018.
THICKNESS STRUCTURES OF NATURAL AND ARTIFICIAL SCOTS PINE DENDROCOENOSES
RoNmeS Petrin and Ivaylo Markov Forest ResearRh Institute of the Bulgarian AcDdemy of Sciences, Sofia
Abstract:
On the basis of 195 sample plots have the curves of tree-number distribution according to thickness levels been investigated for two aggregates of dendrocoenoses of different origins. (By 'origin' we mean, on the one hand, Scots pine stands established by seeds, i.e. natural Scots pine dendrocoenoses, and, on the other, Scots pine plantations that Man has established artificially by sowing or planting.) The curves of the distribution in percentages have been transformed into complex, distribution curves by multiplying these percentages by the thickness levels, which makes it possible for the curves to represent the volumes of wood in the dendrocoenoses in a more realistic way. The complex curves have been investigated by means of a special coefficient of asymmetry (Cas) that enables us to find out the asymmetry of each tree-number distribution curve in terms of the average diameter. For the natural and artificial Scots pine dendrocoenoses, the average curves of the normal numbers have been calculated, and the average curves have been compared with A. V. Tyurin's uniform average curve of normal numbers. The investigation has resulted in finding out that the distribution of the sample-plot numbers according to the asymmetry or symmetry of the curves revealing the thickness structures of both aggregates investigated is almost one and the same. Hence, the inference that the origins of Scots pine dendrocoenoses do not influence their thickness structures and that they can be investigated together as a whole. Comparing the average curves of the normal numbers for the natural and artificial Scots pine dendrocoenoses with Tyurin's uniform average curve has resulted in finding the extreme similarity between the curves' shapes and the great proximity of their values, which confirms that the dendrocoenoses' thickness structures are not influenced by either the origin of the Scots pine trees or the very tree species.
Key words: Scots pine dendrocoenoses, thickness structure, symmetry, normal numbers INTRODUCTION:
It is very important for forest managers to be able to estimate the timber volume and assortment structure of each particular forest, yet as easily, quickly and accurately as possible. For this reason, it is necessary to permanently perfect the normative and reference base of forest estimation, i.e. to perfect the respective models and tables, hence, scientist always have to improve their knowledge of the regularities in the structures of forest dendrocoenoses. In connection with this, the present investigation has dealt with the thickness structures of Scots pine stands and plantations while comparing these.
Natural Scots pine dendrocoenoses occupy a comparatively large area - about 51.7% of the coniferous forests in Bulgaria, and they are among the most highly productive natural, lasting stands, whereas Scots pine plantations comprise about 8.4% of the coniferous forests in this
country. These forests are important as for timber production so for recreation, health improvement and amenity, because they occupy sites where they grow under mountain and hill conditions.
A number of authors have carried out studies of forest-stand structures (Tretyakov, 1927, Tretyakov, 1952, Sirakov, 1947, Nedyalkov, 1964 and 1967, Mihov, 1991, Mihov et al., 1993, Dimitrov, 2003, and Tonchev, 2007). The more important inferences the above and other authors have made from their studies of stand structure are as follows:
Tretyakov, 1927, carried out a detailed study of the regularities in the structures and variation of some dendrobiometric indicators in even-aged and pure stands, as well as in uneven-aged ones of mixed compositions and complex sylvicultural systems, on the basis of data as of his own so by Weise, Kuntze and others. He established that forest structure always has a constant nature, regardless of spacing index, age, tree species, growth conditions, and stands - as normal so complex, mixed ones. This gave him the reason to formulate the Law about the Uniformity of Stand Structure.
Tyurin, 1938, while comparing the curves of the distribution of the trees in many, pure, even-aged, normal stands, came to the conclusion that the aspects of the curves were influenced neither by tree species and site conditions nor by spacing index. Age was found to have a certain influence, as well as the kind of thinning. This gave him the reason for developing a uniform curve of the percentage distribution of tree numbers and basal areas according to natural levels of thickness for all tree species.
G. Sirakov, 1947, developed a method of creating constant curves of heights, for groups, the so-called order curves of heights, which, together with the thickness-structure curve, provide the basis for developing volumetric and assortment tables.
Simeon Nedyalkov, 1964 and 1967, established different curves of the distribution for particular generations in terms of the thickness structures of uneven-aged growing stocks of different species: Scots and Austrian pines, common beech, oak, and spruce. For the generations at particular ages, the distribution curves had bell-shaped or parabolic aspects, with one or two maximums, and the total curve of the distribution had a constantly descending nature and an exponential form.
Mihov and Tsogtbaatar, 1994, on the basis of natural indicators, have found out three types of European larch stand thickness structure: with a left-hand-side, right-hand-side and central asymmetry in terms of average diameter.
Mihov et al., 1996, has found the availability of three types of thickness structure and height structure of mature beech growing stocks: with a right-hand-side (-) asymmetry, left-hand-side (+) asymmetry, and of the normal (symmetric) type.
E. Dimitrov, 2003, having investigated different functions of tree-number distribution according to thickness levels, has found out the availability of three typical distributions: symmetric (or normal), right asymmetric and left asymmetric. This same author has cited investigations by Tishenko, 1926, where the latter, while simultaneously investigating in detail the tree-number distributions in Scots pine, spruce, aspen and birch dendrocoenoses, found out that these distributions did not depend on spacing index, age, site index (stand-quality level) but only on the average diameter and the tree species.
Tonchev, 2007, while investigating the thickness structures of common beech dendrocoenoses, has found out that the function of the normal distribution describes this distribution in the best way. He has established three types of structure depending on the asymmetry of the curve of the tree-number distribution according to thickness levels.
PURPOSE: The purpose of the present work is to investigate the thickness structures of natural and artificial Scots pine dendrocoenoses with a view to solving the following problems: 1. Finding out the different types of thickness structure of natural and artificial Scots pine
dendrocoenoses; investigating the symmetry (or asymmetry) of the thickness-structure curves for both aggregates, and
2. Comparing the parametric, average curves of the normal numbers for the investigated
dendrocoenoses in the two groups with A.V. Tyurin's average curve developed for all tree species, with a view to find a proximity in their values, which could provide reasons for making important inferences.
OBJECTS OF THE INVESTIGATION:
The present investigation pertains to natural Scots pine dendrocoenoses in the Rila Mountains (Samokov, Belovo and Yundola), the Rhodope Mountains (Peshtera, Satovcha, Devin, Velingrad and Ardino) and Sakar Mountain (Svilengrad). A total of 110 sample plots have been laid, 68 of these being in mature and 42 - in young and middle-aged natural Scots pine stands. In the Scots pine plantations, 85 sample plots have been laid in the lands of: the state forest estates of Doupnitsa, Koprivshtitsa, Hvoyna, Godech, Breznik and Belitsa; Plovdiv Regional Forestry Board; Vitosha Nature Park, and the towns of Rila and Sapareva Banya. The investigation has been based on a total of 195 sample plots.
METHODS: For each sample plot, the natural levels of thickness (NLT) have been calculated after Tyurin, 1938. These are obtained by dividing the absolute levels of thickness by the average diameter; this is a methodical approach making it possible to unify the abscissa points of the thickness-structure curves. The natural levels of thickness are relative numbers, each corresponding to a particular number of trees. The respective numbers of trees have been reported in percentages, in a graphical way, for each round level of thickness (0.5, 0.6 etc.). Further on, the curves of the percentage distributions of the trees have been converted into complex curves of thickness structures by multiplying the tree numbers by the natural levels of thickness, and, after their unification to 100%, we have investigated them in terms of their asymmetry in relation to the abscissa point 1.0, which pertains to the average diameter in the stand. It has been necessary to introduce the complex curves so that these will reveal not only the numbers of trees but also tree thicknesses. The complex curves are actually the tree numbers in percentages, though changed according to the trees' relative (or natural) thickness levels. Thus, with lower levels of thickness the tree numbers become smaller and with the higher ones - larger. If the complex curves of the thickness structures are of a prevailing right-hand-side asymmetry in relation to the NLT 1.0, this means larger amounts of wood with thicker trees and, respectively, more wood in the very dendrocoenosis. It is just the opposite with the prevailing left-hand-side asymmetry - the dendrocoenosis will contain less wood and its assortment structure will be of a lower quality. We draw your attention to the fact that we investigate the asymmetry of the complex curves of distribution in relation to the average diameter (NLT = 1.0), which is a point on the abscissa, not in relation to the distribution curve's maximum, as it is with statistical asymmetry. The distribution curves have been investigated within the NLT interval from 0.6 to 1.4, which is an interval of the complex curves of tree-number distribution. Though shortened, it is valid for all the curves and sufficient for reporting the asymmetry of the curves, as well as for making an analysis in comparison with other parametric curves.
For investigating the asymmetry of the tree-number distribution curves, we have introduced a special coefficient of asymmetry, which can be written down with the formula:
Kas = N0, x1+ N0,x2+. ■ ■ N0,8+£(N0,9+ N1,0+ NU)/2
N, N etc. are the numbers of trees of the respective thickness levels, starting from the lowest, in %, up to level 0.8, inclusive;
N+N is the sum of the numbers of the trees of the three, central levels of thickness: 0.9, 1.0 and 1.1, in %.
The presented formula reveals the fact that the trees of the central levels of thickness, 0.9, 1.0 and 1.1, i.e. around the average diameter, are in the largest numbers. These numbers are divided by two for estimating with a maximum accuracy their curves' asymmetry in relation to the average diameter (or the natural level of thickness 1.0).
When K, as calculated in percent, is lower than 49%, the curves are of a right-hand-side asymmetry, above 51% - the asymmetry is a left-hand-side one, and when its values are within the interval from 49% to 51% - we have assumed the curves as symmetric.
Further on, the distribution curves have been transformed into total-distribution curves, where the number of trees for each thickness level is calculated in percent with accumulation; in this way the value of 100% is obtained for the last level of thickness. From these curves have the normal numbers' curves been obtained by dividing the percentages for the particular thickness levels by the percentage for the last level, i.e. by 100. The act of obtaining the curves of the normal numbers (also called indicators of quality) is a stage of the calculations done through the Natural Indicators' Method (Douhovnikov, 1966). Based on the curves of the normal numbers has the average curve of the normal numbers been calculated (q) for both investigated aggregates of curves, i.e. for the natural and artificial Scots pine dendrocoenoses.
While comparing the curves of the normal numbers for both Scots pine dendrocoenoses with Tyurin's uniform average curve of normal numbers, we have used correlation coefficients, the standard deviation, a variation coefficient and the error in the arithmetic mean as criteria of the proximity of the curves' values.
RESULTS AND DISCUSSION
1. Types of Thickness Structure
According to the values of the coefficient of asymmetry (Cas), about the thickness structure, we have divided the sample plots into three groups, thus forming three types of thickness level according to the asymmetry of the respective curves in relation to the imaginary vertical line raised from the NLT 1.0. So, all the three types of curves are available: of a left-hand-side asymmetry, of a right-hand-side asymmetry and of symmetry. Figures 1 and 2 illustrate the three types of curves for natural and artificial Scots pine dendrocoenoses, respectively.
35.00
— —Left-hand-asymmetry
nni2, Kas=60.2% ••••O-- Simmetry nn5, Kas=50.4%
30.00
%25.00
— O — Right-hand-asymmetry nni, Kas=26.7
a; a;
£ 20.00
o
£ 15.00
E
J^ 10.00
5.00
0.00
0.4 0.6 0.8 1 1.2 1.4 1.6
Natural Levels of Thickness [NLT]
Fig. 1 Three types of curves based on the asymmetry (or symmetry)
natural Scots pine dendrocoenoses
20
15
£
<4-
с
J 10
S
I
5
0.4 0.6 0.8 1 1.2 1.4 Natural Levels of Tikness [NLT]
■ Left-hand-asymmetry ПП22, Kas=55.3%
■ Symmetry ПП12, Kas=49.5%
■ Right-hand-asymmetry ПП26, Kas=42.8
1.6
Fig. 2 Three types of curves based on the asymmetry (or symmetry) - Scots pine cultures
Figures 1 and 2 reveal that a clearly expressed left-hand-side asymmetry of the complex curves of thickness levels corresponds to the high values of CaS% (SPs 12 and 22), which means prevalence of thin trees and lower volumes of wood; curves of a right-hand-side asymmetry correspond to the lower values of CaS% (SPs 1 and 26), which means prevalence of thicker trees and suggests higher volumes of wood; and when the CaS values are about 50% (SPs 5 and 12), the curves are symmetric, i.e. they occupy a middle position.
The distribution of the sample plots according to types of asymmetry for both aggregates of dendrocoenoses investigated has been presented in Table 1.
Table 1. Distribution of Scots Pine Natural and Artificial Dendrocoenoses according to Types of Asymmetry of the Complex Curves of Thickness Levels
Types of asymmetry Natural Scots pine dendrocoenoses % Scots pine plantations % Total sample plots %
Left-hand-side asymmetry 16 14.5 13 15.3 29 14.9
Right-hand-side asymmetry 76 69.1 59 69.4 135 69.2
Symmetry 18 16.4 13 15.3 31 15.9
Total 110 100 85 100 195 100
0
Table 1 clearly reveals the great similarity and correspondence in the distribution of tree numbers according to types of asymmetry for the natural Scots pine dendrocoenoses, the plantations, and both aggregates. One can see that the percentages have very close values - the right-hand-side asymmetry dominates with about 69% everywhere, next followed by the left-hand-side one -about 15%, and the symmetry - with 15% - 16%. It can be talked, therefore, about a similarity or proximity in the structures of the investigated natural and artificial Scots pine dendrocoenoses. It is also possible to establish the total structure, by means of a common study.
2. Comparison between the average curves of normal numbers (qx)
The average curves of the normal numbers for the natural and artificial Scots pine dendrocoenoses have been compared with Tyurin's uniform average curve, established for all tree species. The results have been presented in Table 2.
Table 2. Comparing the Two Average Curves of the Normal Numbers with Tyurin's Uniform Average Curve of Normal Numbers
Natural levels of thickness Indicators for accuracy
0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 Correla Stand Varia Error
, tion ard tion in Curves's
b l . coetti- devi- coetti aritmet
Average curves of normal numbers for cient ation cient ic
construction in thickness (qualitative indicators) [R] [S] [V%] means
[%]
Natural
Scot,s pine 0.06 0.14 °.2 0.45 0.63 0.79 0.90 0.96 1.00 0.998 0.02 4.17 1.39 dendrocoen 8
oses
Scots pine 0.07 0.17 0.3 0.47 0.63 0.79 0.90 0.96 1.00 0.999 0.02 4.02 1.34 plantations 1
Total
average 0.04 0.14 a3 0.49 0^ 0.81 0.90 0.97 1.00 - - - -
curve of 0
Tyurin_
As one can see in Table 3, the indicators of accuracy, or of the closeness of our two rows to Tyurin's average curve established for all tree species, are too high: the correlation coefficient equals almost 1, the standard deviation - 0.02, the variation coefficient is low (from 3.83% up to 4.17%), and the error in the arithmetic mean is much below 5% (from 1.28% up to 1.39%) thus meeting the requirements to the accuracy of such investigations completely. The proximity of the rows of the normal numbers for the thickness structures of the investigated Scots pine dendrocoenoses to the values of Tyurin's curve suggests the conclusion that the thickness structures of the investigated Scots pine stands and plantations are similar to those of all other tree species.
INFERENCES
The following inferences can be made as a result of our investigation:
• Three types of thickness structure have been found to exist with the investigated Scots pine stands and plantations: of a right-hand-side asymmetry, of a left-hand-side asymmetry, and of symmetry.
• For both groups of dendrocoenoses, one and the same trend has been noticed as of distribution of the sample plots according to asymmetry. For this reason, it does not matter whether we shall study the natural dendrocoenoses separately from the plantations or together with them; it does not affect the total asymmetry of the curves. The origin of the dendrocoenoses does not influence their thickness structures.
• The comparisons of the average curves of the normal numbers (or indicators of quality) of the thickness structures of natural and artificial Scots pine dendrocoenoses with Tyurin's uniform average curve show close proximities in the aspects of the curves. This fact shows quite convincingly that it is possible to develop uniform models of the volumes and assortment structures of such stands and plantations, as long as these models depend on thickness structure.
Acknowledgements:
We thank Prof. Ivan Mihov and Assoc. Prof. Tatyana Stankova for commending to us the sample plots in the stands and plantations, respectively.
LITERATURE CITED:
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Dimitrov, E., 2003. Modelling the Structure, Volume and Assortments of Middle-Aged and Maturing Dendrocoenoses of Scots Pine, Norway Spruce and Silver Fur. Simolini 94, Sofia: 1322. (In Bulgarian)
Douhovnikov, Yu., 1966. The Morphological Classification as the Basis of Increasing Forest Productivity. Sofia: 25-40. (In Bulgarian)
Goossev, I. I., 1960. On the Structures of Spruce Forests in Arkhangelsk Region. Lessnoy Zhournal /Forestry Journal/, Book 2, p. 22. (In Russian)
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Korostelev, I. F., 1976. Variation in the Heights and Diameters of Boles in Pine Growing Stocks in Chelyabinsk Region. Lessnoy Zhournal /Forestry Journal/, Book 3, pp. 16-18. (In Russian) Mihov, I., Poryazov, Ya. and Dobrichov, I., 1993. Height-Order, Tapering and Assortment Tables about Hungarian Oak, Durmast and Turkey Oak of the Re-Growing (Transformation) Class. NIS /Unions of Scientists and Researchers/, University of Forestry: 3-5. (In Bulgarian) Mihov, I. and Zhansramghiin Tsogtbaatar, 1994. Some Peculiarities of the Thickness and Height Structures of Siberian Larch in Western Mongolia. Naouka za Gorata (Forest Science), Book 4, pp. 80-89 (in Bulgarian)
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Mihov, I., 2005. Forest Mensuration. Sofia, pp. 101-111. (In Bulgarian)
Mihov, I. and T. Tonchev. 2010. Growth Model for Macedonian Pine (Pinus peuce Griseb.) Stands in Bulgaria. Silva Balcanica (Bulgarian Forest), Issue 11(1), pp. 59-66 Nedyalkov, S., 1964. Basic Principles of the Organisation of Forestry in Mountain Forests. Zemizdat Publishing House, Sofia: 80-92. (In Bulgarian)
Nedyalkov, S., 1967. Organisation of the Forestry in Norway Spruce Forests. Publishing House of the Bulgarian Academy of Sciences, Sofia: 68-78. (In Bulgarian)
Petrin, R., 1988. Regularities in the Growth of Common Beech Stands and Using These in Forest-Management Planning. Dissertation, Sofia: 128-137. (In Bulgarian)
Petrin, R., Markov, I. and Mihov, I., 2013. Structures of Natural, Seed-Tree Common Beech Dendrocoenoses in Bulgaria According to Thickness and Height. Management and Sustainable Development, Book 3, Year 15th (in press). (In Bulgarian)
Petrin, R., Markov, I. and Mihov, I., 2014. Comparative Investigations of the Structure According to Height of Mature and Middle-Aged Natural Common Beech Dendrocoenoses. Management and Sustainable Development, Book 3, Year 15th (in press). (In Bulgarian)
Petrin, R., 2014. Investigations of the Structure According to Thickness of Scots Pine Dendrocoenoses. Digest '145 Years since the Establishment of the Bulgarian Academy of Sciences', p. 81. (In Bulgarian)
Sirakov, G., 1947. Improved Permanent Curves of Heights, Form-Factor Tables and Volumetric Tables for Scots Pine in Our Country. Digest of the CGI Institute, Book 3, pp. 20-25. (In Bulgarian)
Tonchev, T., 2007. Studies of the Structure and Growth of Coppice Common Beech Stands in the Balkan Mountains. Doctoral Thesis, Sofia, pp. 49-60. (In Bulgarian)
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Tretyakov, N. V., 1952. Some Principles of Soviet Forest Mensuration. Reference Book for the Forest-Mensuration Specialist. Goslesboumizdat, Moscow-Leningrad, pp. 5-15. (In Russian) Tyurin, A. V., 1938. Forest Mensuration. Goslestehizdat Publishing House, Moscow, pp. 13-25. (In Russian)
