MAJOR RISKS AND TECHNOLOGIES OF ARTIFICIAL FOREST REGENERATION IN

Wildfires occur in the Republic of Mari El (Russian Federation) from time to time, that is why reforestation work is very important in the region. Some risks arise in the course of forest reproduction at fire-sites. Wastelands formation, May beetle outburst (Melolontha melolontha), fire recurrence are the most typical risks. Predominance in the forests (sandy soil) of the Republic of Mari El of Scots pine (Pinus sylvestris) determines regeneration of this very species. Accelerated growth of pine in fire-sites is achievable through artificial forest regeneration. The goal of our research is to study the influence of different technologies of plantation establishment in fire-sites on their development and productivity and assess possible risks mitigation in establishment and cultivation of the plantations. Eight different plots of planted Scots pine (Pinus sylvestris) were studied. These plots are rectangular (Н-1, K-1, К-3, К-4, К-5), square (К-2) and spot planting (Н-2, Н-3) plots. The initial density of the planted trees was different in the plots; it was low (К-1, К-2, К-3), mean (К-4) and high (Н-1, К-5). It was revealed that in the plots where trees were planted with high initial density (more than 10000 trees per hectare) the risk of May beetle outburst was reduced due to quick canopy closure (up to 3-4 years). Two-row spot planting of Scots pine and leaving the wide inter-rows (Н-2, Н-3) makes it possible to carry out the prevention measures and contributes to forest environment preservation and natural regeneration of broadleaved species.


INTRODUCTION
Wildfire is a well known phenomenon throughout the world.Wildfire is one of the most important ecological factors, defining forest forming processes and vegetation development together with temperature, precipitation and soil fertility.Depending on the natural conditions of a region and a community type, wildfires may play both a negative and positive evolutionary role (wood fire) (Kalinin, autoref.).
Many factors define success of natural regeneration in fire-sites.Fire intensity, fire cause class, square of fire-sites, seeds availability are among them.
Study of the 1972 fire-sites (Mari El Republic) made it possible to specify a number of ideas.Thus, L. I. Yashnov (1930), A. I. Druzhinina (1930) and P. K. Guryanova (1930) stated that most natural seeding grew through in 2-3 years after a fire took place and the regeneration process finished in 4-5 years after the fire.А. R. Chistyakov and V. A. Kreyer (1976) considered one of the peculiarities of natural regeneration at the 1972 fire-sites (Mari El Republic) to be pine natural seeding of cones of the burnt trees.А. К. Denisov and А. А. Aleksandrov (1954) studied 30-year old young stands, grown in sandy soil in the Mari El in the 1921 fire-sites.The researchers determined that birch did not displace pine whatever percentage ratio the birch was in a stand.In case of a lack of seeds and grassland vegetation development, natural regeneration slowed down and the fire-sites turned into grass wastelands.
The 1972 wildfires (Mari El Republic) had a number of peculiarities which had an impact on natural regeneration.The wildfires were of high intensity, they coincided with the seed pine year; they occupied the largest area in late August (the period of ripening of seeds in cones).Successful natural regeneration of Scots pine (Pinus sylvestris) from parent trees as well as regeneration of broadleaved trees (European white birch (Betula betula) and Aspen (Populus tremula)) was observed in almost all studied fire-sites.Regeneration was insufficient or there was practically no regeneration in the lichen pine forest growing in poor dry sandy soil (small creeping fire took place in the forest) and in the cowberry pine forest growing in fresh sandy soil (crown fire) (see Table 1).Other researchers (Chistyakov, Kreyer, 1976;Denisov, 1979) came to these very conclusions.
Natural regeneration of the main species (К.К. Kalinin, 2002) is assured only if there are seed trees.The nature of regeneration depends on the forest type and the fire cause class.Studies of S. А. Denisov (1979Denisov ( , 2012)), К. К. Kalinin, Yu. P. Demakov (1978, 2002) prove the idea (see Table 1).Kalinin (2002) defined that regeneration of pine in the fire-sites and clearances occured in 1-2 years after the fire due to stands seeding before the fire; than it was ceased for the next 5 years due to the lack of cones with seeds.
In cowberry pine forest, bilberry pine forest, polytric pine forest, and bog moss pine forest growing in fresh, moist and wet sandy soil, conversion of species to birch and aspen takes place in the course of regeneration (Kalinin, 2002).He also determined that a considerable (up to 37,5%) mortality of young growth and natural seeding of Scots pine took place in the fire-sites.It was mostly observed in the area with dry soil and in sites covered with bush grass (Calamagróstis epigéios) or adder-spit (Pterídium aquilínum).
Summarizing the results of the study of natural regeneration in fire-sites, it should be noted that the process of natural regeneration in firesites depends on the type of fire, level of damage of trees, forest growth conditions, as well as the square of fire-sites.Natural regeneration of Scots pine in fire-sites is assured by successful establishment of Scots pine plantations.The idea was proved by G. К. Nezabudkin (1958Nezabudkin ( , 1961)).He was the first researcher in the Republic of Mari El who Table 1.Natural regeneration in fire-sites in the middle-aged and old stands in 5 years after the 1972 wildlife (Denisov, 1979)  elaborated on the types of plantations in fire-sites (Nezabudkin, 1961, Nezabudkin, Eremin, 1969).They were implemented into production.Much attention was paid to quicker canopy closure in rows and inter-row spacing as the fire-sites existence provoked May beetle outburst, so that high density of planting was recommended (Romanov, Karaseva, Nureeva et al., 2011).Plantations, established at the 1921 and 1972 fire-sites, were studied both at the beginning and later on (Demakov, Ivanov, Elmekeeva, 1998).Different types of soil tillage, schemes of mixture and schemes of arrangement, ways of density of planting were used in the establishment of Pine plantations in the 1921 and 1972 fire-sites.Today, it gives us possible grounds for the accumulated experience, reveals more effective technologies, allowing to assure the best sustainability of artificial stands and saves the main species in it, and creates highproductive artificial stands with the lowest labor costs (Romanov, Karaseva, Nureeva et al., 2011).

Soil -humidity
Making a decision on the choice of the way of forest regeneration in fire-sites, it is important to take into account all the possible risks.They are conversion of coniferous stands of high economic value to broadleaved stands, open forest formation, insufficient stand density and wastelands formation which will probably lead to May beetle outbreak.
Many questions on forest restoration at the fire-sites are still to be answered.The lack of long-term studies in fire-sites is one of the possible explanations of this problem.The risks of usage of different ways of forest restoration in firesites and the technologies of artificial regeneration are not well studied in particular.This is the reason why we chose "forest regeneration in firesites" to be the problem of our research.To find the problem solution is of high scientific and practical importance.

MATERIALS AND METHODS
The work was carried out in summer 1994, summer 2008 and summer 2013 in the territory of Nolkinskoe forestry (a part of scientific and experimental forestry of Volga State University of Technology (Mari El Republic)) and Kuyarskoe for-estry in Medvedevskiy administrative district (Mari El Republic), which is on the left-bank of the Volga (Zavolzhskiy sandy lowland plain).
The data of 15 sampling areas (size no less than 0,06 ha) with planted Scots pine (Pinus sylvestris) were the data to study.They were established in the dry and fresh sandy soil (А 1-2 forest growth conditions).The main elements of technology of pine plantations establishment are given in Table 2.All plantations are young pure pine stands.The forest inventory with a specification of location in the canopy of the growing stand and the main morphometric characteristics was carried out in the sampling areas.The age of stand is defined by the materials of mensurational description of forestries and data from the book of records of artificial forests of Kuyarskiy and Research and Scientific forestry.
All the sampling areas of planted Scots pine were established in the 1972 fire-sites (fresh and dry sandy soils) with the aim to study the problems of productivity improvement and fire resistance of trees growing in fresh and dry sandy soil.Н-1, Н-2 and Н-3 sampling areas are located in the Scientific and Experimental forestry of the Volga State University of Technology.The students under the guidance of their lecturers of the Chair of Plantations and Mechanization of Forestry Activities (Volga State University of Technology) planted trees at the Н-1, Н-2 and Н-3 sampling areas in 1974 year.The technology was elaborated by G.К. Nezabudkin (1961).Different schemes of pine arrangement were used.Stump extraction and sweeping them into rolls, broadcast tillage with the ПН-4-35 plough and planting the trees by means of the mechanical tree planter which was designed by the director of the Scientific and Experimental forestry V.M. Bochkarev were carried out.
Forest trials at the К-1, К-2, К-3, К-4, К-5 sampling areas were established in spring of 1977 under the guidance of Mari Division of the Tatar forest experiment station.Forty-Fifty-year old pine stand of natural origin grew in that territory before the 1972 fire took place.The area is plain.The soil is sod weak podzolic sandy dry, forest growth conditions -А1-2, forest type -rich in herbs, lichenous pine forest.The object is pure pine stand planted with different density (500 -13,300 trees/ha).Two-year old standard seedlings of pine were used as a planting material.There were no agrotechnical and silvicultural tendings.
Sampling areas with planted Scots pine (Pinus sylvestris) were established using the methods of G.К. Nezabudkin (1971) and Е.L. Maslakov (1978).No less than 300 trees were examined in each sampling area.Diameter at a 1,3 m height (calliper) and a height (Suunto hypsometer) were measured; kraft dominance class was defined.All the trees were divided into the following groups: healthy trees, injured trees, partly mortal trees, dead trees.The position of trees in the canopy of a stand was taken into account.Besides, trees were divided into dominant trees (trees-leaders and trees of upper canopy), trees of medium canopy and trees of lower canopy.Several types of trees were chosen in each sampling area of plantations; crown diameter, height to the living crown, branch wood diameter were measured together with the diameter and height of the trees.Annual increment of the branches of crowns were measured in 1994 at the experimental plantations of Scots pine established with the density of 500-13,3 thousand trees/ha.Russian pine forests have always been one of the most important plant formation.In the Republic of Mari El, most pine forests grow in sands, formed by large rivers.Thus, there are 41% of pine forests in the region (Denisov, Kalinin, et. al., 2012).In accordance with the geo-botanical position, the territory is located in the subzone of mixed forests (European part of Russia).
Sands is the most widely spread type of soil in the Republic of Mari El (39,2%).A1 forest conditions (dry sandy soils) are the most complex conditions for forest regeneration.The share of dry pine forests in the Republic of Mari El is about 6,3%.
The climate in the region is moderately continental.Annual average yearly temperature of the air in the central part of the Republic of Mari El (Yoshkar-Ola city) is 2,8 0 С.January and February are the coldest months (-13,2 0 С), July is the warmest month (+19 0 С).The maximum temperature in summer is 36-38 0 С and the minimum temperature in January-February is 28-37 0 С (47-49 0 С sometimes).The frostless season lasts 4 months (May 18 -September 18).However, late spring frosts may occur in early June, early autumn frosts -in early September (Chistyakov, Nezabudkin, Malochka, 1964).The annual average precipitation is about 457 mm, including April-October period (346 mm).Climate and forest growth conditions in the Republic of Mari El (Smirnov, 1968, Kolobov, 1968) are rather good for coniferous and broadleaved forest.The central lowland, which is located along the left bank of the Volga River (20-70 кm wide), is the largest geomorphic district.
The lowland is a so-called third terrace of the Volga; it towers above the river-valley (30-40 m) (Chistyakov, 1964).The studied Scots pine plantations were established in the area.Quaternary deposits of ice age, represented by the deposits of glacial waters -light-yellow sands, sandy loam and yellow-brown clay loam -lie in the lowland.
According to the professor V. N. Smirnov, sodpodzol soil of different mechanical composition and different level of podzol is typical of the area (Smirnov, 1953).

RESULTS AND DISCUSSION
More than 40 thousand ha of the 1921 firesites (Mari El Republic) turned into wastelands which became the habitat of May beetle and other pests.Taking into account the actual mean increment of wood in 1956 (2,42 m 3 /ha), the deficiency in the increment of pine wood in the Republic of Mari El was 3,87 million m 3 .Intensive reforestation was started 40 years after the fire and it was finished in early 1970s (see Fig. 1).
The 1972 fire-sites were mainly artificially restored (see Figure 1).Usage of the means of mechanization, existence of large nurseries, sufficient financing made it possible restore the forest in the shortest terms (10 years) (Romanov, Eremin et al., 2008).Usage of the technologies of artificial forest regeneration after the 1972 wildfires led to food resources supply and to reduction of the May beetle outburst (see Figure 2) (Demakov, Smykov, 2009).
Many studies of wildfires in Russian forests let us conclude that the fires are associated with certain types of landscape and stands.The type of a stand is defined by the level of soil moisture, the soil type and human impact.In the area of mixed forests of the Republic of Mari El, pine forests with different share of birch and aspen predominate (see Fig. 3, Map А).These forests belong to the high class of fire danger.
Predominance of pine forests on the left-bank of the Volga River and low density of population in this territory complicate quick access to the fire area and extinction of wildfires which occur in drought season in time.The 1972 and 2010 firesites prove the idea (see Fig. 1, В).
According to the researches of А. P. Tolskiy (1941), the climate in the Republic of Mari El has its peculiarities.Irregular precipitation during the vegetation period and a risk of long-term droughts Mass propagation of May beetle (Melolontha melolontha) is caused by untimely deforestation of clearances, fire-sites, and wastelands; young plantations and natural young stands with an unclosed canopy are also vulnerable to May beetle.In case of large population of May beetle, its grubs gnaw the roots of young trees.As a result, forest regeneration is complicated or even impossible.Pines, growing in dry sandy lands (А 1 , А 2 ), are especially vulnerable to May beetle attacks (Recommendations for the integrated struggle with May beetle, 1981).Reduction of the risk of propagation of May beetle may be achieved if trees are planted with higher density (the density when the canopy closure takes place in the shorter terms).As a result, the land is shaded and it is less heated in spring and summer, which is bad for the pests.
G. K. Nezabudkin elaborated the terms of canopy closure for the Republic of Mari El for fresh sandy soils (1961).We are offering the obtained data as a mathematical relation: Equation periods calculated by this of canopy closure in the stands, planted with different density and different arrangement are given in Figure 4.According to the offered relation, 12 years is the longest period for canopy closure.At that, the terms of canopy closure influence trees arrangement.In case of even square arrangement (К-2, k=1,0) canopy closure in plantations takes place simultaneously 11 years after planting.Researchers (Nezabudkin, 1961) consider this type of closure undesirable, if it takes place very late (our case).In case of rectangular row arrangement (Н-1, К-4, 5), canopy closure of pine takes place in 2 stages: 1) in the rows of the planted trees; 2) between the rows of planted trees.Canopy closure in the rows in 4 years after planting shows resistance of the plantation beginning from a young age.Speaking about two-row spot planting of trees (Н-2 and Н-3), it should be noted that canopy closure takes place in 3 stages: 1-in a row, 2 -between the rows of a spot, 3-between two spots.Usage of this type of planting helps avoid inter-oppressive differentiation of trees and contributes to the selection of the strongest trees.In case of dense plantations (Н-1, К-4, К-5), canopy closure takes place in shorter terms, the land is earlier shaded, and the risk of May beetle propagation reduces.Thus, it is possible to recommend to establish them in the locus of May beetle (Melolontha melolontha).
The research results of the branches length of Scots pine crown in 20-year-old plantations with the minimum density of 500 trees per hectare (К-1) and 5000 trees per hectare (К-4) are proved to be true.The crown radius is to a high precision described in the equation: 3).K characterizes the critical length of crown branches, а reflects the speed of branches growth, b shows the extent of environmental resistance to the growth of the branches of the crown.Dynamics of the crown growth in the artificial stands planted with different density has its own peculiarities.Augmentation of critical length of the crown in the artificial stands with low initial density (500 trees/ha) is regular.At that, the space per one tree is 20 m 2 .If density is higher (5000 trees/ha), it reduces by 10 times.
Considering the diagram of growth of crown branches of the artificial pine stand planted with different density, we should pay special attention to the curves which are close to each other till the plantations are 7-years old (see Figure 5).At this age, the crown grows 0,5 m every two years, shadowing the land under the trees and decreasing the risk of May beetle (Melolontha melolontha) propagation.In subsequent years, taking into account the early canopy closure and differentiation in case of rectangular allocation and the density of trees 5000 trees per 1 hectare (К-4), the growth crown branches is declining and the of accelerated of the stem in height begins.
According to the a 25 cm-increase in the distance between the trees of Scots pine (Pinus sylvestris) leads to prolongation of the term of canopy closure for a year.It means, the higher risk of May beetle propagation the higher density the trees should be planted in fire- sites.We presume the term of canopy closure of pines planted with the density of 5000 trees per hectare and 2,7 m between the rows (К-4) will take place in 10 years after planting, in a row where the distance between the trees is 0,65 m -in 2-3 years.In case of 500 planted Scots pine per hectare (К-1), canopy closure will take place in 16 years minimum.These figures are similar to the figures, obtained in 1961 (G.К.Nezabudkin, 1961).Taking into account the fact that the period of May beetle generation development is 4-5 years, it is important to assure the canopy closure of the plantations the earlier the better.
The number o survived trees of Scots pine is correlated with the initial density (correlation index is r=0,918) by the age of 35-years old.Twenty-twenty five percent of the total number of planted trees took part in the stand formation in dense plantations (Н-1 and К-5 plots).Other trees carried out their function in improvement of stand resistance against May beetle and died.These variants have a very high coefficient of variation (V= 32,1%), which shows high interspecific competitiveness (see Table 4).Mean diameter of Scots pine (plantations) depends on the quality of growing trees per hectare.The connection between them is inverse (r=-0,939).It is evident, К-1 and К-2 plots (the least density of planting) will show the highest diameter of trees.The trees of spot planting (Н-2, Н-3) have less diameter (12,8 and 14,4 сm) in comparison with К-1 and К-2 plots, but it is higher than the diameter of the trees planted in even rectangular (Н-1, К-3, К-4, К-5).
The studied pine plantations were established in the forests of exploitation function; the final goal was to increase the stands productivity and obtain the timber of high quality in shorter terms.The artificial forest of two-row spot planting (Н-2, Н-3), established in rectangular with the initial density no less than 3000 trees per 1 hectare, is of high stock (Н-1, К-3, К-4, К-5) (see Table 5).
Analyzing the risks which provoke the fire break out in the studied stands, we should pay attention to the low down crown and a considerable width of knots in the artificial forest planted with the density of 500 and 1000 trees per hectare (К-1, К-2).These characteristics lower the quality of timber.Young coniferous trees with low down crown are the most dangerous, they can provoke the risk of conversion of the creeping fire to the crown fire (Romanov, Karaseva, et al., 2011).
The risks of the repeated wildfires are minimized when the plantations are established in accordance with the two-row spot planting technology (Н-2, Н-3).The width of narrow inter-rows was 1,3 m.The distance between the different groups of spot planting depends on soil fertility, water content of soil, and the designated purpose of the stands.Natural regeneration of the broadleaved trees, serving the fire stop barrier and the source of organic substance and forming in decomposition of the fallen leaves, was mainly remained in the non-logged land.Fire lines, protecting the plantations of the fire and assuring the accessibility of the equipment for fire-fighting operations were made in the wide strips between the double rows.Besides, application of this technology makes it possible reduce the costs to planting material, contributes to conservation of forest environment and natural regeneration of the broadleaved species.The researches showed that the plantations established in spot planting were of high productivity and resistance to different diseases and pests (Romanov, Karaseva, et al., 2011).
Formation of resistant plant community is connected with the self-regulation process, when the structural organization of stands takes place.6 and Table 6).
The dominant trees were defined by sight by height and crown position in crown space of stand.The biggest number of trees, occupying the upper canopy, were found in the plantations with the initial density of 5000 and current density of 2270 trees per hectare (К-4).At that, in this case the diameter of the dominant trees is lower in 1,2-2,0 times in comparison with all the plots, but for the К-5 plot.The trees of upper canopy in the plantations, established by spot planting (Н-2, Н-3) are characterized with the good height and diameter, prevailing the diameter of the plantations established in rectangular and square (Н-1, К-1, К-2, К-3, К-4, К-5) in 1,1-2,6 times (see Table 6).Spot planting allows to avoid sudden differentiation.As a result, the process of young pine stands (35-year old) formation is characterized with high rates for diameter, height and standing timber both of all the stand and the dominant trees.
Thus, artificial forest regeneration at the firesites reduces the risks of the wastelands formation and May beetle (Melolontha Melolontha) outburst.Establishing Scots pine plantations in conditions of dry sandy soils, it is important to assure high productivity of plantations and the conditions for their accelerated growth.It improves their fire resistance, prevents from May beetle and pests outburst by cultivation of healthy stands with the optimum structural organization and prevailing of the dominant trees.
To accelerate the restoration of the large areas of fire-sites in the Republic of Mari El and some other Russian regions, realization of the strategy, based on an integrated approach (elaboration of fire arrangement of forests and the choice of the way of forest generation on the basis of the landscape-typological principal) is important (Fig. 7).

CONCLUSIONS
Fire-sites restoration in conditions of the Middle Volga Region is a long-term process, which is connected with many risks.The main risks are wastelands formation, loss of lands productivity, May beetle and pine fungus outburst, and outbreak of diseases.There are three ways of forest regeneration in the fire-sites: natural, artificial and combined.Natural regeneration of Scots pine is assured by the following factors: land square, land fertility, soil moisture and speed of colonization by birch and aspen.To prevent from large areas of nonproductive lands formation after the fires, some parts of the fire-sites should be restored by means of plantations establishment.The share of plantations in the overall forest regeneration depends on the forest growth conditions and the intended use of plantations.
To prevent May beetle (Melolontha Melolontha) outburst in the forests of the Republic of Mari El growing in poor dry and fresh sandy soils, it is obligatory to establish plantations of Scots pine with the spacing of no more than 5000 trees per hectare (H-1, K-4, K-5).By the age of 35 years old, the plantations with the predominance of pine will show good silvicultural characteristics.Pine plantations established in two rows are of good biometric characteristics.This planting technology allows us to decrease the initial density by means of close-together planting of pine in two-rows and assure the accelerated growth of trees with a better growth index.
To accelerate the restoration of large areas of fire-sites in the Republic of Mari El and in some other Russian regions, realization of the strategy, based on an integrated approach is important to elaborate.
Acknowledgement.The authors want to acknowledge their colleagues V. G. Krasnov, T. F. Miftakhov, M. N. Chefranova, (Chair of Forest Plantations and Mechanization of Forestry Works, Volga State University of Technology); and the student of the Division of Forestry and Ecology (Volga State University of Technology) N. V. Guseva for their help and assistance in field research as well as to acknowledge Mrs. N. A. Kuklina for the diagrams design.We want to say special "thank you" to Mrs. M. A. Shalagina, translator of the Department of International Cooperation for the translation of our manuscript in short terms.

Figure 1 .Figure 2 .
Figure 1.Dynamics of plantations development in firesites in the Republic of Mari El

Figure 6 .
Figure 6.Number of dominant trees of Scots pine and their parameters (diameter -numerator, height -denominator) depending on the density and arrangement

Figure 7 .
Figure 7. Strategy of forest restoration in fire sites

Table 2 .
The main elements of the technology of pine plantations establishment and cultivation in fire-sites (forest growth conditions А1-2)

Table 3 .
Dependence of crown radius of Scots pine on the age in of planting trees with different density (even rectangular arrangement of

Table 4 .
Statistical characteristics of the diameter of Scots pine (35-year old plantations) Note: Student's t-test =1,964 for 0,95 probability belief with the degree of freedom of more than 500.Actual meaning of Student's t-test (t actual) was found by t actual = (M1-M2)/√(m1 2 +m2 2 )

Table 5 .
Mean silvicultural characteristics of Scots pine planted trees(35-years old)