Forest Health
Dramatic changes in ecological conditions, combined with the physiological instability of some forests, are the major factors behind the present decline in forest health. Table 15 presents estimates of the visible damage to tree crowns attributed to air pollution. The data is derived from a long-term program to assess the impacts of air pollution on the forests. This program was initiated in Bulgaria to evaluate the degree of environmental contamination and associated damage (discoloration and defoliation) to forest ecosystems. The program follows the manual prepared by the European Forestry Commission of the United Nations Food and Agriculture Organization (FAO, 1989).
In 1992, 62.8% of the forests were affected by air pollution. For 34.3% of the forest ecosystems, the degree of the damage (discoloration and defoliation) was rated as moderate or severe. The young conifer stands were more strongly affected. There is also great danger, however, for the survival of fir and oak stands in the country.
Table 15. Estimated visible damage to tree crowns attributed to air pollution
Degree of damage
(damage class)1992 Change between 1992 and 1991 percentage of forest (%) Forest damaged
(million ha)Percentage of forest
(%)0 No damage symptoms 1.2382 37.2 +22.0 1 Light damage 0.9471 28.5 +2.6 2 Moderate damage 0.5355 16.1 -9.6 3-4 Severe damage, dead 0.6063 18.2 -15.0 Total wooded land 3.3271 100.0 2-4 Moderate and severe damage, dead 1.1418 34.3 -24.6 1-4 Total damage 2.0889 62.8 -22.0 Ecological Functions of the Forest
By "ecological functions" we mean those forest processes that influence the state of the environment, and that accompany the production of timber. This is the aggregate of infrastructural material and nonmaterial services that:
- conserve and improve the living environment as a condition for the comfortable, wholesome, and spiri-tually complete life of man; and
- conserve and improve the nation's stability and the economic potential of the environment as the basis of society's production within and beyond the forestry sector.
However, there is no doubt that the dominant proportion of our forests shall serve, from now into the predictable future, as multi-function and multi-purpose sources of raw materials, as well as bearers of environmental benefits and influences.
Under current legislation, the forests of Bulgaria are classified into two groups in accordance with their social purposes. The first group includes "forests of commercial purpose," which are managed mainly for the production of timber. The second group includes "forests of special purpose." According to their configuration, the latter are subdivided into shelter forests, recreation forests, protected areas, and other forests of special purpose. The main social purpose of these forests is to produce ecological benefits and other environmental goods. The harvesting of timber and other raw materials in these forests is regulated by strict forestry methods, following environmentally sound standards, or is not allowed at all.
The relative proportion of forests of special purpose has increased from 10.2% in 1960 to 30.4% in 1990. A general impression of the ecological functions of the forests can be drawn from data on the distribution of the forests by area and growing stock, which is presented for the forests of special purposes in Table 16.
Table 16. Distribution of the Bulgarian forests according to their purposes
Purpose Total area Afforested area Growing stock ha % ha % ha % I. Commercial forests 2694249 69.6 2364539 70.6 259175 64.0 II. Special forests: 1. Shelter forests 546264 14.1 430253 12.9 58066 14.3 incl. water protective 308705 8.0 254204 7.6 40277 9.9 erosion protective 216139 5.6 157897 4.7 16148 4.0 meliorative 21420 0.5 18152 0.6 1641 0.4 2. Recreation forests 248161 6.3 221615 6.6 31118 7.7 incl. resort forests 145144 3.7 132765 4.0 21895 5.4 green zones and systems 97700 2.5 84422 2.5 8735 2.2 parks out of settlements 5317 0.1 4428 0.1 488 0.1 3. Protected areas 164232 4.2 131551 3.9 21950 5.4 incl. natural reserves 58279 1.5 47309 1.4 10175 2.5 national parks 77389 2.0 60819 1.8 8098 2.0 beauty spots 9321 0.2 6852 0.2 967 0.3 protected places 9887 0.3 8441 0.3 1356 0.3 historical sites 8891 0.2 8069 0.2 1350 0.3 protected landscapes 465 0.0 61 0.0 4 0.0 4. Others 218541 5.6 200074 6.0 34563 8.6 incl. resort resources 3150 0.1 2421 0.1 218 0.1 resort places 648 0.0 583 0.0 191 0.0 monuments of the culture 12 0.0 10 0.0 5 0.0 hunting territories 142095 3.7 128195 3.8 18229 4.5 seed lots and plantations 43672 1.1 43613 1.3 12606 3.1 arboretums 1619 0.0 1321 0.1 149 0.0 botanical and zoo gardens 100 0.0 80 0.0 36 0.0 200 m around hats 1082 0.0 1028 0.0 195 0.1 buffer zones 7841 0.2 6611 0.2 1203 0.3 of other institutions 18322 0.5 16212 0.5 1731 0.5 TOTAL II 1177198 30.4 983493 29.4 145697 36.0 TOTAL (I + II) 3871447 100.0 3348032 100.0 404872 100.0 Level of Economic Importance of Tree Species, Endemism, and Fragility Under Human Activities
The species composition of the forests in Bulgaria is quite varied, but a fairly limited number of species are of economic (commercial) importance. In Table 17, the 135 tree species are separated into 3 levels according to their economic importance. The assessments of the relative level of importance of the species is based on their distribution and on their area of origin. The most important are those of autochthonous origin. The tree species of endemic origin and those that have been introduced from other parts of the world are also noted (Stefanov and Ganchev, 1958; Delkov, 1988).
The fragility of tree species under different human activities is expressed in terms of the resistance of tree species to air pollutants. In the last column of Table 17, the tree species most tolerant of harmful air pollutants are labeled with "++"; those that are tolerant are marked "+"; those that are not tolerant are marked "0"; and species for which information is lacking are marked "-" (Prokopiev, 1978). It should be mentioned that this scale is relative, since the tree species have different levels of tolerance for different pollutants.
Table 17. Economic importance of tree species, place of origin (endemism), and fragility
Tree Species Importance Origin Fragility 1 2 3 1 2 3 Coniferous Abies alba Mill. X X 0
Abies borisii-regis Mattf. X X - Abies cephalonica Loud. X X - Abies concolor Lindl. X X 0 Abies nordmanniana (Stev.) Spach. X X - Abies numidica De Lannoy X X - Abies pinsapo Boiss. X X - Cedrus atlantica Manetti X X - Cedrus deodara Loud. X X - Cedrus libani Laws. X X - Chamaecyparis lawsoniana Parl. X X ++ Cryptomeria japonica D. Don X X - Cupressus arizonica Mill. X X - Cupressus sempervirens L. X X - Juniperus virginiana L. X X ++ Larix europea DC X X + Metasequoia gymtostroboides Hu at Cheng X X - Picea exelsa Link. X X 0 Picea omorica (Panc.) Purk. X X + Picea orientalis (L.) Link. X X + Picea pungens Engelm. X X ++ Pinus aristata Engelm. X X 0 Pinus cembra L. X X 0
Pinus coulteri D. Don X X 0 Pinus exelsa Wall. X X 0 Pinus halepensis Mill. X X 0 Pinus heldreichii Christ. X X + Pinus montana Mill. X X + Pinus nigra Arn. X X + Pinus peuce Gris. X X + Pinus pinaster Alt. X X 0 Pinus ponderosa Dougl. X X 0 Pinus radiata Don. X X 0 Pinus rigida Mill. X X 0 Pinus sylvestris L. X X 0 Pinus strobus L. X X 0 Pseudotsuga menziesii (Mirb.) Franco X X + Sequoia sempervirens (D.Don) Endl. X X - Sequoiadendron giganteum (Lindl.) Buchh. X X + Taxus baccata L. X X ++ Taxodium disticum (L.) Rich. X X - Thuja gigantea Nitt. X X ++ Thuja gigantea Nitt. X X ++ Thuja occidentalis L. X X ++ Thuja orientalis L. X X ++ Tsuga canadensis (L.) Carr. X X + Tsuga caroliniana Engelm. X X + Non-coniferous Acer campestre L. X X + Acer dasycarpum Ehrt. X X + Acer heldreichii Orch. X X + Acer hyrcanum Fisch. et C.A. Mey X X + Acer negundo L. X X + Acer palmatum Thunb. X X 0 Acer platanoides L. X X 0 Acer tataricum L. X X + Aesculus hippocastanum L. X X 0 Aesculus carnea Hayne X X 0 Ailanthus altissima (Mill.) Swingle X X + Alnus glutinosa (L.) Gaertn. X X 0 Alnus incana (L.) Moench. X X 0 Alnus viridis (Chaix) DC X X 0 Betula pendula Roth. X X + Betula Maximowiczii Rgl. X X + Carpinus betulus L. X X + Carpinus orientalis L. X X ++ Castanea sativa Mill. X X 0 Celtis australis L. X X + Celtis caucasica Willd. X X + Celtis occidentalis L. X X + Cerasus avium (L.) Moench. X X + Cerasus vulgaris Mill. X X + Corylus colurna L. X X - Fagus orientalis Lipsky X X + Fagus silvatica L. X X + Fraxinus americana L. X X + Fraxinus excelsior L. X X + Fraxinus ornus L. X X + Fraxinus oxycarpa Willd. X X + Fraxinus pensylvanica Marsh. X X + Gleditshia triacanthos L. X X ++ Juglans nigra L. X X + Juglans regia L. X X + Lirodendron tuipifera L. X X 0 Magnolia denudata Desr. X X + Magnolia kobus DC X X + Magnolia liliiflora Desr. X X + Magnolia stellata Maxim. X X + Morus alba L. X X + Morus nigra L. X X + Ostria carpinifolia Scop. X X - Platanus acerifolia Willd. X X ++ Platanus occidentalis L. X X ++ Platanus orientalis L. X X ++ Populus alba L. X X + Populus canescens Sm. X X + Populus deltoides Marsh. X X + Populus euramericana (Dode) Guinier X X + Populus nigra L. X X + Populus piramidalis Rozier X X + Populus tacamahaca Mill. X X + Populus tremula L. X X + Populus trichocarpa Torr. X X + Prunus serasifera Ehrt. X X + Quercus aegilops L. X X ++ Quercus cerris L. X X ++ Quercus coccifera L. X X ++ Quercus frainetto Ten. X X ++ Quercus hartwissiana Stev. X X ++ Quercus petraea Liebl. X X ++ Quercus pubescens Willd. X X ++ Quercus robur L. X X ++ Quercus rubra L. X X X ++ Quercus suber L. X X ++ Quercus tracica Stev. et Ned. X X ++ Robinia pseudoacacia L. X X ++ Salix alba L. X X + Salix babylonica L. X X + Salix caprea L. X X + Salix fragilis L. X X + Salix puntandra L. X X + Salix purpurea L. X X + Salix triandra L. X X + Sophora japonica L. X ++ Sorbus aucoparia L. X + Sorbus aria (L.) Crantz. + Sorbus domestica L. + Sorbus torminalis (L.) Crantz. + Tilia cordata Mill. X X 0 Tilia platypholios Scop. X X 0 Tilia rubra DC X X 0 Tilia tomentosa Moench. X X + Ulmus minor Mill. X X + Ulmus laevis Pall. X X + Ulmus glabra Huds. X X +
Legend:
Importance of the tree species
1) Of primary economic importance,
2) Of secondary economic importance,
3) Of lowest economic importance (widely distributed in the parks).Origin of the tree species
1) Autochthonous,
2) Endemic to the Balkan Peninsula,
3) Introduced from other parts of the world.
Human Aactivities in the Forest
Afforestation, the tending of young stands, forest protection, and the tending and final cutting of trees are the main human activities in the forests. Afforestation has been the main instrument for developing and improving the nation's forestland area. In recent years, about 40-45,000 ha have been afforested annually (Table 18).
Afforestation policies are elaborated on the basis of the condition of forestlands and the need for the quickest and most effective production of wood and other forest utilities.
Table 18 shows data regarding afforestation work over the course of the last decade. The data illustrate that about 25% of the entire annually afforested area involves the reconstruction of low-value stands, i.e., replacing the existing species composition as quickly as possible with quick-growing valuable species. About 15% of the annually afforested land involves the conversion of waste and eroded bare lands. Active intervention in the process of regeneration, and in filling out open canopy stands, through afforestation takes place on about 60% of the annually afforested area. Priority in afforestation is given to Scots pine, Austrian black pine, spruce, fir, Douglas fir, and other coniferous trees (about 70% of the total), and to oaks, lindens, birches, and others broad-leaved species (about 30% of the total).
Forest protection measures include the control of pests, diseases, weeds, and forest fires, and protection of the forests from infringement. Table 18 shows that pest and disease control using biological preparations is the pre-ferred method. There are plans to expand biological control programs, and to investigate other concepts and prognoses for the prevention of damage by pests, diseases, and abiotic factors. Also envisioned in fire control programs are special methods of conditioning forest areas: creation of new mineralized median strips, proper maintenance of existing strips, cleaning of forested sites along railroad lines, construction of a considerable number of fire towers, etc. The number of fires over the past few years has gone as high as 200. They have devastated areas up to 1000 ha. The prevention of unauthorized cutting and grazing in for-ested areas has become an important task of the forest enterprises, as well as local people, councils, and public organizations. Checkpoints and mobile forestry guards have been established by each Regional Forestry Board.
The respective Forest Enterprises have the task of regenerating and managing the forests and forestlands with a view to increasing their productivity. This means a planned silvicultural program: plowing under the canopy with a view toward improving the structure and quality of the soil; taking advantage of natural regeneration; accelerating the rate of growth of existing stands and young stands; converting coppices into high-stem forests; thinnings; cuttings to allow for the reconstruction of species composition; and final cutting.
Table 18. Extent of some human activities in the forests in the period 1980-1989
Activities Area, hectares 1980 1984 1985 1986 1987 1988 1989 1. Soil preparation for afforestation 36100 29913 30397 29436 35212 28888 32942 2. Afforestation, including: 47313 39441 39798 40590 46041 46434 45799 - on bar lands 7598 7936 7916 8921 7915 6251 6463 - on lands after clear cut for reconstruction 14258 9573 9132 9001 10215 10115 9131 - for filling out open canopy stands after final felling 25457 21932 22750 22668 27911 30068 30205 3. Simulating of natural forest regeneration 2.2 0.5 1.4 0.4 0.2 0.1 0.7 4. Forestry car of young stands 145.1 125.0 115.1 113.1 108.7 104.2 108.6 5. Pest and disease control, including: 38.5 121.7 91.9 50.6 57.5 70.9 75.2 - with chemical preparations 12.6 10.1 7.7 5.8 7.2 5.4 9.5 - with biological preparations 9.0 69.5 47.4 19.2 14.0 17.2 21.9 Natural forest regeneration is simulated by plowing under the canopy (see Table 18), preserving seed trees and young growth during felling and timber hauling operations, clearing of felling sites, controlling grazing, and other practices.
Careful forestry can do much for the survival and early growth of new stands (Table 18). Systematic weed control and scarification can solve to a very large degree the problems of moisture conservation and survival of the seedlings.
Coppice stands that are in a better state, with greater density and on better soils, are designated for conversion into high-stem forests on a 50-80 year rotation basis. In these stands, thinning and other silvicultural treatments begin in the earliest ages so that the greatest possible number of trees may grow to a size suitable for the production of mine shaft supports, girders, etc. The area of these stands was 784,000 ha in 1990. Thinning and other silvicultural practices increase productivity, improve the quality of the stands (primarily the high-stem ones), reduce the time necessary for the growth of mature timber, improve the health standards of the forests and their resistance to adverse factors, and aid in soil and water conservation and other functions. The basic methods depend on the age of the stands and can involve forest thinning and cleaning, selective cutting, and the creation of more open spaces.
Stands dedicated to the reconstruction of their species composition totalled 608,000 ha in 1990. Their status, species composition, and productivity are inversely proportional to the quality of their soil and climatic site conditions. The problems with these poor value and low-productivity stands can be solved only through clear-cutting and afforestation using valuable and highly productive species. Regeneration felling is applied to mature forests in accordance with their respective rotation plans. This solves the forester's problems of forest regeneration, soil conservation, and declining increments, and facilitates exploitation through mechanized logging. Regeneration felling requires competent evaluation of each particular site and forest type, and proper setting of priorities. In the Bulgarian context, the selection of regeneration felling normally gives priority to forest development projects that require the most efficient regeneration of stands, without leading to deterioration of the landscape, and taking into account the ecological functions of the forests. Two basic systems of final cutting or harvest are applied in Bulgaria: systems based on natural regeneration (progressive cuttings, selective cuttings, group selection, etc), and systems based on artificial regeneration (clear-cutting, group-progressive cuttings, etc.).
Results after the thinnings, clear-cuts for reconstruction of low-productivity stands, and final cuttings are given in Table 19. The total yield in 1990 was 4755 m3. This was 71.4% of the volume provided for in the forest management plans, and 1.17% according to the total growing stock volume of the forests in the same year.
Table 19. Cuttings and timber yield in 1990
Kind of forest Project/actual report Annual cutting area Timber yield (standing) 1000X m3 o.b. With natural regeneration last phase with artificial regeneration Tending felling 1000X hectares Coniferous project
actual3.2
2.50.7
0.62.1
2.056.2
28.21749
1524Broadleaved project
actual15.8
8.92.1
1.76.8
4.882.9
40.73872
2469For "reconstruction" project
actual- - 21.6
9.4- 1040
762Total project
actual19.0
11.42.8
2.330.5
16.2139.0
69.06661
4755Economic Analysis and Analyses of the Development of the Bulgarian Forests
The expenditures in the forestry sector that are not met through cash inflow from direct commercial exchange are compensated for through governmental subsidies. Expenditures for implementation of some forest activities in the period 1980-1989 are presented in Table 20.
The number of people working in the field of forestry totals 25,160 (20,334 workers). Those who work in logging and in the wood industry number 64,476 (53,682 workers). These data are for 1989. The amount of construction investments in the forestry sector is negligible. Bulgaria is an importer of wood and wood products.
The value of the forests' ecological functions is determined on the basis of social expenditures made for the production of environmental benefits and goods from forests. Preliminary investigations in Bulgaria (Vassilev and Petkov, 1993) indicate that, at present, the harvesting of timber has become more than twice as expensive due to the application of environmentally sound forest management regimes and technologies. This alone provides evidence that the value of the environmental functions of the forests in Bulgaria, which is now recognized by society, is at least equal to the profitability of timber harvesting. If the government subsidies, which were in place until two years ago, are added to the annual value of the environmental functions, the total environmental value will appear to be more than twice as the profit value of timber harvesting. Under such conditions, it is logical to accept that the capital value of the ecological functions of the forests in Bulgaria is approximately twice as high as the value of forestland and tree resources, and amounts to approximately 33% of the total value of the country's tangible assets.
Table 20. Expenditures, labor force, and construction investments in the period 1980-1989
Units 1980 1984 1985 1986 1987 1988 1989 Expenditures Simulating of natural forest regeneration th. leva 115 44 148 42 46 62 103 Forestry care of young stands th. leva 8728 9037 8389 8607 8702 9267 9773 Pest and disease control th. leva 651 1181 1170 1445 1535 2018 2075 Labor force People working in the field of forestry persons 17771 16721 16335 24261 25846 26782 25160 including workers persons 14484 13437 13038 19538 20521 21694 20334 Construction investments Investments mil. leva 8.6 10.8 13.5 8.7 9.0 6.7 4.1 Percentage of the investments in the forestry branch % 0.1 0.1 0.1 0.4 0.1 0.1 0.0 Table 21. Trade balance (+ = import; - = export) of wood and wood products
Wood and wood products Balance (+ imports, - exports)
1000X m3 equivalent in round wood1. Round wood +1555 2. Mine-wood (props) +31 3. Wood pulp and paper +1283 4. Wood base panel: particle board, fiberboard -65 Total +2804 The development of the Bulgarian forests in the period 1955-2035 has been analyzed for this paper. Statistically reliable data for the years 1955-1985 were used (Central Statistical Bureau, 1962, 1967, 1978, 1988). The future development of the forests was determined through the computerized Model of Forest Lands (Bojinov, 1988). In the Model of Forest Lands, the natural processes in forests are simulated and concepts about the future management of these forests are expressed in numbers.
These estimates and concepts, which were jointly determined by a team of scientists and experts in the field of forestry, involve: the potential of forest sites to produce timber; the natural/artificial regeneration ratio; the conversion of coppice forests into high-stem forest; the reconstruction of some broad-leaved forests of low productivity; the establishment of two-storied stands; thinnings; the future composition of tree species in conformity with probable changes in the environment; improvement in the protective, water-conserving, and other special functions of forest; and material, technical, financial, and human resources.
The changes in the main characteristics of the forests in the period 1955-2035 are presented in Table 22.
As regards species composition, the proportion of coniferous species is expected to increase considerably (Table 22, line 1*). The total area under conifers is expected to increase from 441,400 ha in 1955 to about 1700 thousand ha in 2035, mainly as a result of reforestation of poor sites that are now occupied by tree species of low value and productivity (i.e., stands of the "for reconstruction" class) and afforestation of bare ground.
The increase in tree resources during the period under investigation is impressive. From 214.4 million m3 in 1955, they reached 344.8 million m3 in 1985, and are expected to exceed 470 million m3 by 2035 (Table 22, line 2.1) - thus attaining an increment of 137 m3/ha in the same year. This increase in volume is due mainly to the enormous growth potential of widely established young, mainly coniferous forests (Table 22, line 2.1*), as well as activities that have already been carried out and that have resulted in improvements in the state of the forests.
The total afforested area of our national forestlands is unlikely to rise much. It is expected to increase from 3153.3 thousand ha in 1955 up to 3443.3 thousand ha after 2015, when there will be no more bare grounds suitable for afforestation within the forest lands (Table 22, line 1). The mean annual increment (Table 22, line 3), after a decrease in 1965, is expected to be about 10 million m3 by 2035, or about 3 m3/ha by this same year, when the increment will be accumulated in growing stocks of assorted structures of higher quality. The future annual cut is predicted to be about 9 million m3 of standing timber (Table 22, line 6.1), including about 6 million m3 from the main cuttings (Table 22, line 4) and about 3 million m3 from thinnings (Table 22, line 5). The increase in the total amount of harvested timber by the end of the period of investigation is expected to be due to the increased harvest from thinnings. Statistical data on the nature of harvesting (Table 22, lines 6.2., 6.3) serve to characterize two periods in the past. Until the 1970s, timber harvests had been increasing; i.e. the percentage of annual cut of the total timber volume had been 3.61% and 3.31%, and of the mean annual increment 118.2% and 137.1%, in 1955 and 1965 respectively. Even though the average age of the forests was comparatively young (about 35 years) for the period of investigation, the above figures indicate a considerable exceeding of the "normal" cut on a 100-year rotation, i.e. an annual cut of 2% of the volume or 100% of the increment. After the 1970s, a tendency toward incom-plete utilization of forest tree resources is observed. By 1985, the percentage of the annual cut amounts to 1.63% of the total timber volume, and only 63.3% of the mean annual increment.
The present statistical characteristics of our forests reveal the need for an enormous amount of work in thinning the young, mainly coniferous stands; in converting coppice stands, suitable for such purposes, into high-stem stands over an area of 784,000 ha; in reconstructing stands of low value and productivity over an area of 608,000 ha, and replacing them with high-stem stands of suitable composition. Solving these problems will require the application of various forestry and organizational technologies. The general approach to solving these problems involves investments of credit for building forest roads and facilities; for converting undersized stands of oak (mainly Turkey oak) and poplar; for increasing the production of seedlings in nurseries; and for improving the effectiveness of afforestation and reforestation work.
At present, one can hardly estimate the degree to which the necessary work is going to be undertaken. Any predictions, given the conditions of economic collapse that have affected all branches of industry in the transition from a centralized to a market economy, should be accepted with a large degree of uncertainty, due to the unspecified structure and functions of forest management and the lack of up-to-date forest legislation. This uncertainly also pertains to the data on future developments presented in this work. But by understanding the concepts upon which this work is based, the goals on which foresters in Bulgaria have, to a considerable degree, reached consensus, can be achieved. These goals are: the permanent reproduction of forest resources, the steady harvesting of timber, and the preservation and complete utilization of the special functions of forests. In this sense, the direction presented here is the most expedient and favorable for the development of the forests in Bulgaria. If develop-ment is diverted in a certain direction away from this one, the degree of such deviation could be ascertained.
Table 22. Development of Bulgarian forests in the period 1955-2035
Year 1955 1965 1975 1985 1995 2005 2015 2025 2035 1. Afforested (woody) forest area (thousand hectares) 3153.3 3144.3 3228.1 3320.2 3361.1 3402.2 3443.3 3443.3 3443.3 Available data are on coniferous forest 441.4 722.6 936.6 1098.2 1266.3 1447.7 1635.4 1673.8 1695.3 2. Growing stock's volume (thousand cubic meters) 2.1. Total - thousand cubic meters 214361 252191 274626 344752 375992 407798 432491 449691 471404 Available data are on coniferous forest 68776 86819 95315 123305 159219 199891 240481 265483 280991 2.2. Per 1 hectare (cubic meters) 68.0 80.2 85.1 103.8 111.9 119.9 125.6 130.6 136.9 Available data are on coniferous forest 115.8 120.1 101.2 112.3 125.7 138.1 147.0 158.6 165.7 3. Mean increment: 3.1. Total (thousand cubic meters) 6552.4 6079.2 7069.3 8879.8 9400.0 9709.8 9829.3 9775.8 9820.9 3.2. Per 1 hectare (cubic meters) 2.08 1.93 2.19 2.67 2.80 2.85 2.85 2.84 2.85 4. Yield from main fallings (thousand cubic meters) 5960.0 6680.4 5004.9 4202.0 5610.8 6277.1 5960.0 5662.3 5862.9 5. Yield from thinnings (thousand cubic meters) 1780.9 1656.1 1412.4 1423.0 2024.6 2274.8 2868.0 3061.9 3091.4 6. Total yield (standing) 6.1. Volume - thousand cubic meters 7741.8 8336.5 6417.3 5625.0 7635.1 8551.9 8828.0 8724.2 8954.3 6.2. Rate from the growing stock's volume (%) 3.61 3.31 2.33 1.63 2.03 2.09 2.04 1.94 1.90 6.3. Rate from the mean increment (%) 118.2 137.1 90.8 63.3 81.2 88.1 89.8 89.2 91.2 Bibliography
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