Asia

Oak decline in the Middle Povolzhje Region
By I.A. Yakovlev

1. History and state-of-the-art of oak forests in the Middle Povolzhje region

Among the number of forest ecosystems growing on the territory of the Middle Povolzhje region, the one of most valuable are oak forests. The oak forests of the Middle Povolzhje region cover 934,1 thousand ha (5 % of the forested area of the region and 25 % of total oak forests area of Russia). Most significant in a historical plan and economic ratio in of the Middle Povolzhje region are the seed oak forests of region – in Chuvash republic, Republics Tatarstan, Mordovia and Mary El, Kirov, Kostroma, Nizhniy Novgorod, Ulyanovsk, Penza, Samara areas (table 1).

Growing in the basin of Volga, the oak forests fulfill the exclusive environmental, watershield and protective role. They are located in high populated territories with developed agroindustrial complexes of economy. Common oak itself is characterized by a significant economic value, but also it is powerful consort and edificator, ensuring forming richest on specific structure and on variety of ecological functions of forest ecosystems in region, ensuring maintaining of maximum biodiversity.

The oak forests in all times were a national symbol and honor of many peoples occupying the Middle Povolzhje region - chuvash, mordva, cheremis, tatar, etc., part of their culture, source of well-being and development. The huge value and importance of oak forests as natural ecosystem is stipulated also by that irreplaceable aesthetic and culturologic role, which they fulfill in region.

In appropriate growing conditions the oak form mixed on structure and complicated on a structure high-productive, biologically tolerant stands. The last decades are characterized by an amplification decline and wither of oak forests, reduction of its areas. It’s clear a possibility of total loss of oak forests as natural ecosystem in the region. In this connection by a number of the scientists of the Faculty of forestry and ecology of Mary state technical university, together with the forestry workers and ecologists were begun active researches on study of the role of oak forests in the region, gene pool conservation, reasons of decline and tentative works on management and rational use and restoring of oak stands. The principal task to revive former glory of Kazan high plain land (nagorniy) oak forests.

The oak forests of the region for a long times actively exploited by man, that lead to reduction of areas and significant modification of their species composition, structure and productivity. Since 1703 all the forests along Volga river and it confluent were used for timber supplying for the needs of shipbuilding, mainly for supply of Baltic shipyards. Clear cuttings of forests for agricultural uses, multiple selective cuttings of the best ship trees have rendered significant influence on species structure and distribution of oak forests on the territory of region. Only for the period from the first state registration of lands (general mezhevanie of 1763-67) till 1914 in Kazan province the forest area has decreased on 1.4 million ha (nearly almost two times), the degree of forested lands, thus, was reduced to 22.1 % (from 51.2 to 29.1 %). In Simbirsk province from 1856 to 1914 the area of forests were reduced approximately on 1.8 million ha, the degree of forested lands was reduced from 47.6 % to 26.2 %. Similar picture and in others provinces of region [10].

In the beginning of 19 centuries in Kazan province, the amount of forests suitable to provide oak ship timber was nearly 1400 thousand ha (approximately 45.4% of the forested area), till the end of century, due to cutting of oak forests and species change, the share of oak forests has decreased to 15-24%. To 1921-22 in Tatar, Mary and Chuvash republics the share of stands with predominance of an oak has made only 223.5 thousand ha (about 13.6 % from forested area) [1, 12]

The analysis of dynamics oak forest area in soviet time testifies constant trends of decreasing of areas of oak forests and amplification of their decline (tab. 1). Only for 30 years (1966-1993) the area of oak forests was reduced approximately on 430 thousand ha, i.e. almost to one third. The most significant diminution of areas of oak forests is observed in republics forest-steppe and steppe zones, in Tatarstan, Ulyanovsk and Samara areas. In Mary El Republic the area of oak forests has decreased on 7,1 thousand ha (38,4 %) and about 1 million m³ of stock, mainly, in flood-plain oak forests, due to of their cutting down in zone of flooding of reservoir Cheboksary hydroelectric station and in placorniy oak forests which have been cut down per World War II.

Table 1. Dynamics(changes) of areas of oak forests on areas and republics of the Middle Povolzhje region
<The html version of this figure still under construction>

Only for last 5 years (by the data of forest inventory in 1988 and 1993) the area of oak forests has decreased on 58 thousand ha, including in Tatarstan - on 22.3 thousand ha (almost on 10 %), Penza area - 14.8 thousand ha (8.1 %), in Ulyanovsk area - 21.9 thousand ha (16 %). The area high forests, from the total area of oak forests (January 1, 1993) - 934,1 thousand ha, is only 304 thousand ha or 32.5 %, and coppice - 630,1 thousand ha (67.5 % of common area of oak forests (tab. 1). All this testifies to proceeding processes of reduction of areas and decline of oak forests of the Middle Povolzhje region.

2. Reasons of oak decline in the Middle Povolzhje region

Decline and intensive withering of oak forests is to a greater or lesser extent marked already in many European countries, in Central Asia and in USA. The oak decline seems to be a periodical process and have a different width of a spanning and degree of damage of stands. The first separate facts of oak decline were marked already in the middle and the end of 19 centuries, however, they did not carry such mass and universal character. For last 100 years on the territory of our country they repeated approximately 7 times, with periodicity about 10-15 years, and especially waves of hard oak decline happen with periodicity in 25 - 30 years [7].

All authors of numerous works on oak decline converge in the judgement, that decline of oak forests is stipulated not by one factor, but the complex of the interconnected factors, which complicatedly and differently are combined in various natural-climatic zones and frequently are exhibited during a long phase of time [2 - 9, 14, 16]. Decline of oak forests is a complicated phenomenon. Shutt [18] has named it as a "complex of complex deceases". The rather precise regional association of action of the initiating factors both with intensities and periodicity of oak forests decline is marked.

There are two models explaining processes of oak forests decline. First is offered by Houston [17]. He considered oak decline as more straight-line and linear process, when decline and dieback of a population will happen when the action of the unfavorable factor(s) will become too numerous and/or intensive. The important value thus have those pest and decease or factors, which lead to dieback of trees.

Other model was offered by Manion [15]. Within the framework of the given model a basic meaning has the history of a population up to decline, and factor or factors, which immediately have caused decline and dieback of oak trees can vary in the dependence with the concrete growing conditions and the aspect of the factor has not the special value. In our interpretation the given model can be expressed as follows (picture). It’s determined, that the principal reason (predisposition factor), at least for oak forests of the Middle Povolzhje region, is the rough interference of the human in oak ecosystem, non-rational forestry management in oak stands, their intensive exploitation within almost three centuries, without sufficient care of recover of oak. Due to outcome reduction of forest areas, the subdivisions of massive and continuous in past oak forests, modifications of a hydrological condition of the rivers the tolerance of oak forest ecosystems was broken. The oak forests have gained different quality exhibited in inability to resist natural abiotic and biotic influences. Forming of structure of oak forests inappropriate to the ecological requirement of an oak (simplification of the form, structure and lowing of density of oak stands, the deleting of oak’s companion species) in a combination with both anomalous climatic factors (drought, hard frosts) and air and ground pollution - initializing factors – leads to depression of trees. Depression of oak forests by critical temperatures promote the development of mildew, vascular decease, rots and reproduction leaf-eating pests, in turn defoliation by insects has lowered drought and frost resistance (strengthening factor). All this leads in further, to massive, and dispersible depression and dieback of oak trees, and in turn, to further lowing of density of oak stands, destruction of complex interrelations in ecosystem ensuring it’s stability and tolerance. The depression of trees reduces acorn production in stands, magnification of an interval between seed years, that considerably reduces a possibility of natural recover of oak forests. The process becomes cycle, being completed with full dying of stand. Therefore, all the factors are the links of a common chain, mutual stipulating each other, in direct and inversive relation among themselves.

The important singularity of oak forests dieback, practically on the whole territory of Russia, is the fast modification of a structure phytocoenosis. With a lack of intensive anthropogenic influence, liberated space in canopy is fast filling by oak companion species, including earlier drop behind in growth, by intensive growth undergrowth and shrubs layer. Oak phytocoenosis is rebuilt from monoprepotent and unstable (formed due to non-rational forest management and oak trees dieback) to polyprepotent and uneven-aged, more stable biological system. The diminution of participation of an oak in a stand composition or it full disappearing happens, these decrease the value of stands from an economic and ecological point of view.

In case of an intensive anthropogenic load (cattle greasing, making hay and etc.) the liberated space is filled by nothing, on a place of oak stand is formed open woodland with intensive soding of a soil cover or all area heavily grows with hazelnut and hazel coppice with single oak trees is formed, i.e. happens complete decline of oak stand. Such stands have not any more any ecological or economic value and should be reconstructed by forest methods.

Let's consider influence of the separate most important factors on oak decline in the Middle Povolzhje.

2.1. Influence of forest management on oak decline

The human activity, as the main reason of modern decline of oak forests, derives from the past. Studying a history of forest management in oak forests, the state of stands in the past and nowadays, is possible to make a conclusion, that the structure and form of modern oak stands does not answer the ecological requirements of an oak. The significant qualitative modifications in structure of oak woods, have taken place from a beginning of intensive exploitation of oak forests (first quarter of 19 centuries). Multiple selective cuttings have led to deterioration of a breeding-genetic potential of oak forests, decreasing of gene pool of populations. The cuttings of the best trees should undermine a biological stability of oak forests to the unfavorable factors. It is possible to determine following forest management measure, which have stipulated current decline of oak forests: 1) Selective cuttings of the best, most qualitative and steady trees of oak in stands without measures for their regeneration. Deterioration of a breeding structure of existing stands and their progeny. 2) Applications of continuous wide-strips clear cuttings, violation of cuttings and thinning terms. Damage of the roots, squeeze of soils during the clear cuttings. 3) Lacks of care for natural regeneration of oak on felling sites, limited application of measures on oak self-seedlings and young growth maintenance, priority of growing of forest plantations (forest cultures). 4) Errors in technology of growing of forest plantations (forest cultures) and thinning in young stands of an oak. Too dense plantings, creation in all forest culture sites of pure plantations of oak with narrow distance between rows. Unsuccessfully selected companion species. 5) Violations of a shadow structure of oak forests. An extermination of a 2-nd layer and undergrowth of attendant species and shrubs due to intensive thinning in young forests. 6) Cattle greasing in forests, high recreation levels, eating of oak younf forests by elks.

In a current phase of economic development the negative anthropogenic influence on surrounded ecosystems considerably has increased, part of which are the oak forests.

2.2. Modification of a hydrological condition of the Volga river

It is rather authentic determined, that the modification of a level of water in the rivers and level of ground waters of enclosing territories renders significant influence to a condition and stability of oak stands [11]. Volga, on which the cascade of hydroelectric power stations is created, is one of the most regulated flat river of Europe. Construction of reservoirs Kuibyshev and Cheboksary hydroelectric station, has rendered significant influence to a level of water in Volga. The Kuibyshev reservoir was filled up to a design mark 53 ? in 1957. The annual amplitude of a level of water more than 6-8 ?, that lead to instability of a hydrological condition of surrounded territories. Cheboksary reservoir are beginning to be filled in 1980. Under the project the water level should be arisen up to NPU 68 ? (volume of water 14 cubic km, area of a mirror of water 2190 ??²). Nowadays level of water is arisen on mark of 63 m. Cheboksary hydroelectric station has become the property of Chuvash republic therefore any of hopes for completion of reservoir preparing did not remain. "Samarahydroproekt" in 1995 has presented a substantiation of necessity of a raising NPU up to 65 and then up to 68 m. The association "Large Volga " does not render any active action on settling of a problem of reservoir. It’s clear a sharp inconsistency of economic and industrial interests of the subjects of federation in region, region and federal center to the detriment of ecological stability.

The filling of reservoir up to a mark of 63 m. has reduced in a raising of a level of water in Volga near Koz’modem’jansk and in all it tributaries - Sura, Vetluga, etc. From 85 thousand ha of the flooded coastal territory 45 is situated in the Mary El Republic, 25 - in Nizhniy Novgorod area and only 15 thousand ha in Chuvashiya. With a raise of water level up to 65 ? in Mary El Republic will be flooded additionally 62, 4 thousand ha of lands, from which 41 thousand ha forest lands. In right-bank elevated plain area part of territory have amplified abrasion- landslide processes. In left-bank part of Volga and Kama rivers first (flood-plain) terrace has been flooded. Even if didn’t take into consideration all cut down flood-plain oak forest in a bed of reservoir, which mainly situated on territory of left-bank lowland part of Mary El Republic, the rise of a level of ground waters from affluent of Cheboksary reservoir negatively influences pine and oak forests on a distance of 10-12 kms from the bank of Volga. Such sharp modification of growing conditions of stands should have a negative effect on growth and condition of all forests and first of all of oak and spruce forests. The modification of a hydrological condition has led to depression of oak trees, dying of tops of crowns of trees. If a water level will be risen up to design mark the state of forests could significantly worsen.

In 1996 the scientists of MarSTU prepared a reciprocal ecological evaluation of the project represented by "Samarahydroproekt", the inference about inadmissibility of further rise of a level of water and necessity of reconstruction of stands in the prepared bed is made. Nowadays is begun constant monitoring of a state of coastal stands.

2.3. Air and soil pollution

The Middle Povolzhje region with rather small territory is one of most high populated regions of Russia. The region has turned from agrarian into agrarian-industrial, where the enterprises, polluting an environment - chemical, electrotechnical, power, electronic, machine-building and other industries function. In Mary El Republic the level of contamination has made - 0,92 ton per square km., and in Chuvashiya - 4,3 ton per square km. So in Chuvash republic the greatest level of contamination is marked in Cheboksary (38 %) and Kanash areas (10 % from a common level of contamination). Main pollutants are PO "Himprom", JSC "ChZPT", PO named by Chapaev, etc. A geographical situation of basic enterprises - polluters and rose of winds cause intensive contamination and deposition of pollutants mainly in oak forests of republic and significant transposition of pollutants in Mary El Republic. The forest located to the east and north-east from industrial enterprises are subject of most hart action of polluting substances. In particular, the oak forests of Marposadskiy forest enterprise have appeared in the zone of polluting action of chemical firms of Novochebiksarsk, the share is conditional healthy stands makes only 16 %, oak forest of Yadrin forest enterprise, located to the south-west significantly in the best state - the share of conditional healthy stands makes 85%. The problem is complicated by necessity of closing of manufactures of army poisoning substances and lack of safe process of their processing and deactivation.

For agricultural time former continuous large oak forests areas have turned out totally fragmented and are surrounded by agricultural lands. Agrotechnics of crop cultivation and used chemicals (fertilizer, poisons for controlling of pests), though immediately is not used in territory of woods, however indirectly render significant action on their condition. The forests enclosed by agricultural fields directly or indirectly suffer from consequences of application of various chemical substances (through dispersion in an air, contamination of ground waters, etc). The comparison agrochemical load and state of forests allows to trace rather precise regularity - decline of oak forests more heavily flows in areas with a high level of application of chemical substances in an agriculture (in Chuvashiya – Morgaush, Tcivil, Cheboksary and Kanash areas).

Thus, it is necessary to recognize, that oak forests as the natural complexes are not isolated, and open systems for all types of pollutants, so technological and agrochemical load on an environment and agricultural fields represents also load on oak forests of region.

2.4. Influence of the extreme climatic factors on oak decline

Above was already marked, that there is a rather precise regional dependence of the initializing factors of oak decline. Middle Povolzhje region concerns to be among the most dangerous regions regarding of damage of oak by early and late frosts and hard winter frosts. Extreme low temperature in a winter phase, which oak is capable to bear, for steppe zone (-39-40^o?, for northern forest-steppe zone and Near Ural zone (-41^o?). The tolerance of oak to winter frosts, mainly depends on a state of trees and stands, weather in the second half of a summer and preparedness of plants to winter.

Two waves intensive dieback of oak in region were caused by extremely low temperatures of winters 1941-42 and 1978-79. Especially the processes of dying of oak forests on large areas were came out after winter of 1978-79. This winter temperature in a forest was dropped to -43^o?, and on open places - to -53^o?. Dying of oak was reinforced by partial depression of oak stands after a durable drought in 1972. Mostly have suffered premature, mature and old-growing oak stands on Privolzhskaja elevated area. Areas of the cutted down oak forests during continuous sanitary cuttings in 1985 has made in Tatarstan - 4.3 thousand ha, in Ulyanovsk area - 36.6 thousand ha, in Chuvashiya - 4.0 thousand ha, in Mordovia - 1.1 thousand ha. Till 1993 continuous dying of oak forests in Republic Tatarstan has taken place on area 19 thousand ha, and the area of stands damaged by frosts has reached 127 thousand ha. Decline proceeds till now. Totally for 15 years from 1978 to 1993 the area of oak forests of Tatarstan has decreased on 30 % - from 286.1 to 186 thousand ha. Especially noticeably died oak forests in left-bank between rivers area of Volga and Kama, that also can be stipulated by influence of two reservoirs. In many forest enterprises oak managerial unit is not represented any more.

Basic damages of an oak caused by frosts are formation of "frost rings" and frost cracks. "Frost rings" - one or several dyed annual rings, on the cross-section of oak trunks they are shown as dark non-wide rings with/without of decoy. It was determined that nearly 90% of oak trees have frost rings. The forming of frost rings are caused by the freezing and consequent dying of non-matured sapwood.

Frost cracks are the most common and widespread damage of oak stands in this region. The share of trees damaged with frost crack in stands varies from 20-46 % in middle-aged forest stands to 77% in mature forests. The damage of trees by frost cracks depends on site grows conditions and stand structure and individual (genetical) peculiarities of trees. The highest share of damaged trees in flood plain grows conditions. The degree of damage grows with increasing of breast-high diameter of trees and decreases with increasing of stand basal area. The main reason of frost crack formation seems to be the thermal tension is emerged after abrupt and deep temperature decreasing due to the anyzothropy of wood and the existence of broad heart rays.

The main unfavorable consequences of hard frost damage are lowering the vitality of separate oak trees and the stands at a whole. The frost cracks one of the main ways by which wood decoying fungi are infecting trees. We found the direct correlation between the presence of oak cracks and infection by fungi. Also frost cracks and frost rings are mechanically decreasing the quality of oak timber. The buds and branches freeze lead to initiation of lateral buds and epicormics grows, forming of secondary crown with enlarged leaves, more vulnerable to fungi decease and insect pests. The weakened stands then are damaged by leaf-eating insects and by mildew on leaves. All these events lead to continue decline or dying of oak stands.

3. Measure on preservation and recover of oak forests of region.

The attitude to a problem of oak forests decline recently mostly was passive. Foresters have carried out intensive sanitary cuttings of died trees, protect forests from defoliating insects, etc. At present tome the situation began to change. It was possible to achieve mutual understanding between forestry organizations and governmental authority of republics and regions regarding the problem on a disastrous state of oak forests of region and possibility of their full loss with current rates dying without active forest management measures. The realization of the complex of measures directed on improvement and recover of oak forests, raise of their tolerance and productivity and on a diminution of unfavorable anthropogenic influence are necessary.

Therefore, taking into account restoring oak forests and growing of stable stands for a perspective, the purpose of forest management in oak forests should consist in creation of complicated mixed stands of an oak with natural attendant species, forming protective "fur coat" and promotion. The main preference should be returned to measures promoting and/or strengthening natural regeneration processes which are taken place in forest ecosystems. The harvest cuttings in oak forests are necessary to carry out by methods and technologies ensuring preservation of young growth of oak and accompanying attendant species (step-to-step and narrow stripes cuttings). As a rule after seed years in oak forests there are enough of self-sowing of oak under the canopy. The best method of regeneration of oak stands is the promotion of natural regeneration by forming (cutting) small windows (open spaces) area about 400-600 ?2 or bands with breadth of 12-15 m.

For creation of forest cultures it is necessary to use technological process ensuring forming of mixed stands, in particular technology of partial - continuous of cultures of an oak [13]. The successful creation of forest cultures of oak and establishing of young forests are impossible without proper thinning, which should be included in the technological process of recover an oak.

The monitoring and regular struggle with wreckers and illnesses of oak forests is necessary.

The establishing of oak seed production base on the basis of the best saved oak populations with the taking into account of phenological and morphological varieties and edaphical forms is necessary. To carry out selection of the forms and varieties, steady against influence of the unfavorable factors, formation of frost cracks and damage by mildew.

It is necessary to decide the problem of Cheboksary hydroelectric station reservoir, to be defined with a mark on which a level of water will be supported and to begin measures on reconstruction and recultivation of forests in the not flooded part of the bed of reservoir. The connection of administrations and presidents of all interested legs together with RAO "EEC Russia" for a final decision on reservoir is necessary.

Very complicated problem remains utilization of wastes of chemical manufactures, decreasing the level of ejection of harmful and polluting substances. Without support of central organs, only by forces of republics and areas to solve this problem practically is not impossible, though the technological developments in this direction are carried on.

The decline of oak forests represents a complicated complex phenomenon and solution of this problem is possible only by combining of efforts of all parts: foresters, industrialists, ecologists and authorities.

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