ISSN 1067-4136, Russian Journal of Ecology, 2007, Vol. 38, No. 5, pp. 299–305. © Pleiades Publishing, Ltd., 2007.Original Russian Text © A.Yu. Kudryavtsev, 2007, published in Ekologiya, 2007, Vol. 38, No. 5, pp. 323–330.

299

Kamyshev (1965) was the first to characterize theforest–steppe system as a single genetic and evolution-ary formation. In the Oka–Don Depression, this is asystem of aspen shrubs and meadow steppes; in theCentral Russian Upland, this is a fruit-shrub steppemorphologically resembling savannas of the tropicalzone (Berezhnoi and Berezhnaya, 2000). The distin-guishing of fruit-shrub–steppe vegetation as an invari-ant of the forest–steppe landscape has fundamentalgenetic grounds, confirming Krasheninnikov’s (1951)conclusions that the forest–steppe zonal landscape isancient and was preceded by the savanna landscape inthe Neogene (Mil’kov, 1950, 1977).

As the impact of various factors on ecosystems ofthe forest–steppe zone increases, community dynamicsin these ecosystems attract increasing attention. Themore diverse the factors affecting a community, thelarger the number of states that the system may assumeunder the same ecotope conditions (Ipatov and Gerasi-menko, 1992). Therefore, the study of vegetationdynamics at the ecosystem level in areas that containnumerous biogeocenoses calls for a probabilistic statis-tical approach based on dynamic simulation of land-scapes.

As Vinogradov (1998) notes, spatially distributeddynamics of complex ecosystems best fits Markovmodels. To construct a model of long-term dynamics ofan ecosystem, it is necessary to begin with obtainingreliable, detailed cartographic information on the vege-tation structure in a large area at large time intervals(Aaviksoo and Kaderik, 1989; Vinogradov, 1984;Debussche, 1977). The purpose of this study was to

analyze community dynamics in the succession thatleads to the formation of bird cherry forests.

MATERIAL AND METHODS

A part of the Privolzhskaya Lesostep’ NatureReserve near Ostrovets in southwestern Penza oblastwas used as a model object for studying the structure ofthe forest–steppe vegetation in the Volga basin. Thearea is 352 ha in size and covers part of the watershedand a slope of a ravine along which a stream flows intothe Khoper River. The latitudes above sea level withinthe area vary from 200 to 240 m. The terrain is ruggedbecause of a well-developed network of ravines andgullies. The soil is mostly leached chernozem withspots of typical chernozem. The vegetation is a com-plex mosaic of steppe, meadow, shrub, and forest com-munities of the watershed, the ravine–gully network,and the floodplain. A characteristic feature of the areais distinctive low forests whose stand is formed by spe-cies that typically dominate undergrowth, such as Euro-pean bird cherry (

Padus avium

) and Tatarian maple(

Acer tataricum

) (Kudryavtsev, 2000).In 1999–2000, we performed geobotanical mapping

of a 30-ha key area located on the watershed withleached chernozem as a dominant soil (Fig. 1).We made seven transects with a total length of 4.3 km.Along each transect, adjoining 10

×

10-m test plotswere established, where we performed a complete cen-sus and mapping of trees and shrubs (Kudryavtsev,2003). For each test plot, we determined the speciescomposition of trees, shrubs, and herbs; the mean age,height, and diameter of trees and shrubs; and coverage

Vegetation Restoration Dynamics in the Forest–Steppe Systemof the Middle Volga Region

A. Yu. Kudryavtsev

Privolzhskaya Lesostep’ State Nature Reserve, ul. Lenina 22-51, Penza, 440039 Russiae-mail: zapoved_PLStep@mail.ru

Received December 15, 2006

Abstract

—The current dynamics of ecosystems of the forest–steppe system is most adequately described viadetermining the probable trajectories of changes in its elements in a simple Markov chain. The obtained datahave made it possible to determine the direction of succession and draw its scheme. Theoretically possibleseries of community development are presented. The succession of community restoration from the spread ofshrubs over steppificated fallow lands to the formation of low forests of European bird cherry has been ana-lyzed. The restoration cycle of ecosystem dynamics is described by eight age stages.

DOI:

10.1134/S1067413607050013

Key words

: forest–steppe system, restoration dynamics, succession, simple Markov chains, transition frequencymatrix.

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(measured in square meters per 100 square meters ofthe ground) of each species.

To study the vegetation dynamics, we used aerialphotographs made in 1985 and 1996 (scale 1 : 10000)and a geobotanical map of the region drawn in 1990(scale 1 : 10000). The probability of transition from onestate into another was calculated from the number ofplots whose state changed during the period studied. Toobtain data on spatially distributed vegetation dynam-ics, we used the Markov chain method (Vinogradov,1998), which has already become a traditionalapproach to describing successions (Jeffers, 1981;Aaviksoo, 1993; Usher, 1979, 1981, 1992).

We used dynamic classification approaches (Ipatovand Gerasimenko, 1992; Ipatov and Kirikova, 1999), aswell as guidelines for the study of vegetation dynamics(Razumovskii, 1999; Logofet, 1999), to reconstruct arestoration series of communities that included

P. avium

divided into five-year age stages. Communities withidentical compositions and states of species, age stagesof the edificator, its vitality, and spatial arrangementwere classified with the same stage. The dynamics ofthe phytosociological spectrum of communities wasanalyzed according to the ecomorph system developedby Bel’gard (1950, 1980) with a special emphasis onthe conditions of the steppe zone, taking into accountmodifications proposed by Matveev (1995).

RESULTS AND DISCUSSION

The vegetation of the study area was divided intothree main types: steppes (meadow and shrub steppes),shrubs, and low forests. On the basis of data as of 2000,we distinguished 14 states of vegetation: areas ofmeadow steppes and steppificated meadows (MS) withless than 10% coverage of trees and shrubs; shrub

steppes (SS) with no more than 25% coverage ofshrubs, divided into subareas dominated by

Chamae-cytisus ruthenicus

(SS Ch),

Amygdalus nana

(SS Am),

Cerasus fruticosa

(SS Cer),

Prunus spinosa

(SS Pr),and

Rhamnus cathartica

(SS Rh); shrub communitiesformed by

A. nana

(Am),

C. fruticosa

(Cer),

P. spinosa

(Pr),

R. cathartica

(Rh),

Euonymus verrucosa

(Eu), and

Viburnun opulus

(Vib); and low forest communitiesdominated by

P. avium

(Pad) and

A. tataricum

(Ac).As follows from the matrix of transitions between

vegetation states (Table 1), the main trend in the vege-tation dynamics was the spread of trees and shrubs overmeadow–steppe areas. We did not observe a strictlypredetermined sequence of formations replacing oneanother. Since shrubs spread rapidly, the model con-tained so-called “loops,” where intermediate stages oftransitions were absent because the given intervalbetween aerophotography surveys did not permit theirdetection. This phenomenon was typical of the initialstages of a succession. The probability of transition ofmeadow steppes into shrub steppes was low. Meadowsteppes were most likely to transform directly intoshrub communities, especially those of dwarf shrubs(

A. nana

and

C. fruticosa

) and

P. spinosa.

The probabil-ity of transformation of meadow steppes into

R. cathar-tica

formations was low, and they were entirelyunlikely to transform into formations of mesophilicshrubs (

E. verrucosa

or

V. opulus

). However, meadowsteppes could transit directly into

P. avium

formations.Shrub steppes were extremely unstable during the

study period. They were most likely to transform intoshrubs. For example, 80% of

C. fruticosa

communitiestransited into

P. spinosa

ones, which were considerablymore stable, within that period. The probability of theirtransition into

P. avium

and

R. cathartica

communitieswas high, and that of transition into

A. tataricum com-

Fig. 1.

Map of ecological monitoring transects in the Ostrovets area of the Privolzhskaya Lesostep’ Nature Reserve.

RUSSIAN JOURNAL OF ECOLOGY

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VEGETATION RESTORATION DYNAMICS IN THE FOREST–STEPPE SYSTEM 301

munities

was considerably lower. The probability oftransformation of

P. spinosa

communities into commu-nities of mesophilic shrubs (

E. verrucosa

and

V. opulus

)was very low.

Rhamnus cathartica

communities wereeven more stable. Their most frequent transformationwas that into

P. avium

communities. Transformation

into communities of mesophilic shrubs was also veryprobable. All low forests remained unchanged. A possi-ble reason for this stability was that

P. avium

and

A. tataricum

forests were relatively young (no olderthan 40 years) and, therefore, had not yet reached thedecay stage.

Table 1.

Transition frequency matrix for the states of vegetation in the Ostrovets forest–steppe between 1990 and 2000(in percent)

Class of states1990

MS SS Am SS Cer Am Cer Pr Rh Pad Ac

MS

2000

26.3 – – – – – – – –

SS Cer 3.0 9.3 4.9 – – – – – –

SS Am 2.0 2.3 2.4 – – – – – –

SS Pr 2.0 2.3 1.2 – – – – – –

SS Ch 1.0 – – – – – – – –

SS Rh 1.0 – – – – – – – –

Cer 17.2 18.6 17.1 – 20.0 – – – –

Am 14.1 23.3 11.0 – – – – – –

Pr 28.4 37.2 48.7 – 80.0 42.4 – – –

Rh 2.0 4.7 3.7 – – 19.8 46.7 – –

Eu – – – – – 2.8 13.3 – –

Vib – – – – – 1.7 6.7 – –

Pad 3.0 – 9.8 – – 22.6 33.3 100 –

Ac – 2.3 1.2 – – 10.7 – – 100

3.0

22.6

10.7

3.33

1.2

2.3

9.848.7

37.2

80.0

19.8

2.8

6.7

13.3

2.0

4.7 3.7 1.7

11.0

14.1

17.218.6 2.3

1.2

2.03.0

2.4

9.3

17.1

2.0

23.3

1.0

28.4

MS

26.3

SS Ch SS Am

2.3

SS Cer

4.9

SS Pr SS Rh

Am Cer

20.0

Pr

42.4

Pad

100.0

Ac

100.0

Rh

46.7

Eu Vib

Fig. 2.

Graph of transitions between the states of the forest–steppe system between 1990 and 2000. The probabilities of preservationduring the survey period are indicated within the blocks; the probabilities of transition into another state, at the arrows. See the textfor designations.

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We used the matrix and graph of transition frequen-cies (Fig. 2) to determine the succession trend and con-struct six generalized variants of a succession leadingfrom meadow steppe to low forests (Fig. 3). When con-structing the succession scheme, shrub steppe was clas-sified with meadow steppes, because the herbaceouscover at this stage was practically the same as that ofmeadow steppes.

The complete variant of the succession (Fig. 3a)comprised the following stages: meadow steppe, steppedwarf shrubs dominated by

A. nana

and

C. fruticosa

;

P. spinosa

formations;

R. cathartica

formations; forestmesophilic shrub communities dominated by

V. opulus

and

E. verrucosa

; and low forests of

P. avium

and

A. tataricum.

In this scheme, communities of meso-philic shrubs are regarded as a side branch of the suc-cession, because the trend of their transformation isunknown. In the second variant (Fig. 3b), the stage of

R. cathartica

(and mesophilic shrub) formations areexcluded from the succession, and

P. spinosa

forma-tions are transformed directly into low forests. Thethird variant (Fig. 3c) has no stage of

P. spinosa

forma-tion, and dwarf shrub communities are directly trans-formed into

R. cathartica

formations. The fourth andfifth variants (Figs. 3d, 3e), where steppe is transformedinto

P. spinosa

communities without passing throughthe stage of dwarf shrubs, are the most frequent. Thefifth variant lacks the

R. cathartica

stage. In the sixthvariant (Fig. 3f), steppe vegetation is directly trans-

formed into low forests. The succession is unlikely tooccur according to this variant.

Table 2 shows a possible general pattern of changesin the community composition in the succession lead-ing to low forests dominated by

P. avium.

At the first stage (within five years), trees and shrubsspread over the area. Shrubs, having appeared theresimultaneously with trees, rapidly cover the area andinterfere with the spread of trees. Sparse communitiesdominated by

C. fruticosa

, with

P. spinosa

as a codom-inant species, are formed. After that, the density of thetree–shrub layer dramatically increases, and, within thefirst ten years, communities with a high degree of close-ness appear, where

P. spinosa

remains dominant for along time. As the community develops, differences ingrowth rates of trees and shrubs lead to the replacementof one-layer phytocenoses by two- and three-layer phy-tocenoses. The communities have the greatest speciesdiversity and a well-developed structure in the periodfrom 16 to 30 years. They may be generally describedas polydominant. Afterwards, as the populations ofshrubs in lower layers become extinct, the communitystructure is simplified. Within 40 years, a practicallyone-layer stand absolutely dominated by low trees isformed. Although high trees are present at late stages,their contribution into the communities remains insig-nificant. This suggests that, under these conditions,low-tree communities are close to climax.

The main changes in herbaceous vegetation occur atearly stages of succession. In this period, the herba-ceous layer considerably degrades. Later, a decrease inthe density of the upper layer and a considerably weak-ening competition with the root systems of aging shrubpopulations favor its rapid restoration. Gaps appearingin the upper layer favor the growth of herbs with highlight requirements, and the species composition is con-siderably enriched. However, the herbaceous vegeta-tion is changed: meadow species disappear, and forestplants appear, the vegetation gradually becoming moremesophilic.

An analysis of changes in the phytosociologicalspectrum of communities in the succession (Table 3)demonstrated that the expansion of forest vegetationwas distinctly predominant. Absolute dominance ofsteppe shrubs (

P. spinosa, C. fruticosa

, and

A. nana

) atthe initial stages was replaced, 30 years later, by abso-lute dominance of forest species (

P. avium, A. tatari-cum

, and

R. cathartica

). The presence of forest speciesin the herbaceous layer was noticeable as early as at thefirst succession stage. The phytosociological spectrumof this layer changed considerably more rapidly thanthat of the tree–shrub synusia. Forest species began todominate the herbaceous layer as early as at the stage ofsix to ten years. Within the first 20 years, the entire her-baceous vegetation was of the forest type.

Thus, the analysis of the development of plant com-munities allows us to subdivide the succession intothree distinct periods (Fig. 4).

MS

MS

MS

MS

MS

MS

Am

Cer

Pr Rh

Eu

Vib

Pad

Ac

Am

Am

Cer

Cer

Pr

Pr

Pr

Rh

Rh

Pad

Pad

Pad

Pad

Pad

Ac

Ac

Ac

(a)

(c)

(d)

(e)

(f)

(b)

Fig. 3.

Variants of the restoration series of vegetation in theforest–steppe system. See the text for designations.

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VEGETATION RESTORATION DYNAMICS IN THE FOREST–STEPPE SYSTEM 303

Table 2.

Changes in community composition in the course of succession (the most stable species are indicated)

CompositionTime from the start of the succession, years

5 10 15 20 25 30 35 40

Trees and shrubs

Acer

tataricum

L. 0.2 0.1 0.5 0.2 1.4 5.6 26.1

Padus

avium

Mill. 0.5 1.0 13.1 12.8 27.2 44.6 79.1 71.0

Cerasus

fruticosa

Pall. 61.4 0.7 0.8 1.4 0.1

Prunus

spinosa

L. 32.5 88.9 79.7 74.6 46.7 17.9

Rosa

majalis

Herrm. 3.0 5.3 1.6 0.8 0.8

Euonymus

verrucosa

Scop. 0.1 0.4 1.9 10.6 2.8

Rhamnus

cathartica

L. 1.0 2.0 7.3 16.0 21.5 9.5 1.9

Sambucus

racemosa

L. 0.3 1.2 1.8 0.9 0.7

Viburnum opulus L. 0.1 0.4 1.7 1.4 0.8

Total coverage of trees and shrubs 41.0 252.0 171.0 246.0 156.0 141.0 109.0 98.0

Number of tree and shrub species 5 8 8 15 16 11 10 7

Herbaceous layer

Stipa pennata L. 7.2 1.7 2.6

Nepeta pannonica L. 6.3 1.2

Calamagrostis epigeios (L.) Roth 40.7 4.1 13.2 0.4 0.3

Brachypodium pinnatum (L.) Beauv. 22.9 0.8

Bromopsis inermis (Leyss.) Holub 16.4 21.1

Bromopsis riparia (Rehm.) Holub 9.0 0.8 3.9 0.2

Elytrigia repens (L.) Nevski 4.5 2.6 0.6 0.5 0.2

Phlomis tuberosa L. 3.7 2.6 0.3 0.1

Seseli libanotis (L.) Koch 3.6 2.5 0.7

Vicia tenuifolia Roth 3.6 3.3 1.6 1.8

Melica altissima L. 8.2 5.9 2.1 2.6 3.1 1.0

Aegopodium podagraria L. 18.2 22.1 9.1 19.3 1.0

Arabis pendula L. 1.6 0.4 0.3 5.2

Chelidonium majus L. 1.7 26.3 50.7 45.2 49.4 57.1 71.2

Convallaria majalis L. 0.8 2.6 2.9 5.0 3.3 3.1 2.1

Elymus caninus L. 1.3 1.6 1.6 2.6 1.8 0.5

Galium aparine L. 3.9 3.3 1.8 3.8 5.7

Geum urbanum L. 2.4 1.2 2.6 0.5

Glechoma hederacea L. 3.2 1.5 2.3

Leonurus quinquelobatus Gilib. 0.8 1.3 1.2 1.0

Rubus caesius L. 4.2 5.3

Urtica dioica L. 9.4 10.5 10.8 5.7

Coverage of herbaceous layer 55.3 17.5 38.0 17.1 27.2 30.4 29.8 26.5

Number of herbaceous species 24 38 24 23 20 51 24 17

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(1) Dominance of shrubs (the first 20 years). Twodistinct phases can be distinguished: the first (within5 years) is characterized by the dominance of C. fruti-cosa and a mixed herbaceous layer dominated bymeadow species; at the second phase (6–20 years),P. spinosa is dominant, and the mixed herbaceous layeris dominated by forest species.

(2) The transitional period (21–30 years). Trees andshrubs make approximately equal contributions, with-out distinct dominance of individual species. Duringthis period, shrubs are replaced by low trees. Forestspecies entirely dominate the herb layer.

(3) Dominance of low trees (31–40 years). Forestspecies absolutely dominate the herbaceous layer.

CONCLUSIONS

Analysis of the vegetation restoration dynamics in aforest–steppe system protected under strict regulationsof a nature reserve has demonstrated that succession ispolyvariant under the plakor conditions. In general, thesuccession scheme agrees with the population patternconcept regarding a climax community as numerouspopulation mosaics of key species and related popula-tion mosaics of subordinate species cyclically develop-ing in the spontaneous mode (Whittaker, 1953; Whit-taker and Levin, 1977). Succession variants displaysuch a diversity because the initial conditions of theecotope favor the growth of tree and shrub speciesbelonging to different ecological groups. Therefore, thevegetation dynamics are largely determined by the pos-sibilities of dispersal (the presence of seed sources,ways of dispersal, and vegetative mobility) and the bio-logical characteristics of the species (growth rate, shadetolerance, and lifespan).

At the initial stages of succession, species with ahigh vegetative mobility, which can actively spreadover the area, have an advantage. Subsequent develop-ment of trees and shrubs is governed by the conditionsdetermining the sizes of the plants and the period dur-ing which the species can hold the area that it has occu-pied (the annual increase in height and the life span ofthe skeletal axis). Low steppe shrubs are soon replacedby taller shrubs, which, in turn, give way to low trees.Two stages with a drastic change in species composi-tion (6–10 and 26–30 years) and two periods with grad-ual changes in vegetation (11–25 and 31–40 years) canbe distinguished in the succession.

Table 3. Changes in the phytosociological spectrum of forest–steppe communities in the course of succession (percentageof total coverage)

Ecocenotic group ofspecies

Succession stage

<5 years 6–10 years 11–15 years 16–20 years 21–25 years 26–30 years 31–35 years 36–40 years

Trees and shrubs

Forest 3.6 9.5 16.9 23.1 53.1 82.1 100.0 100.0

Steppe 96.4 90.5 83.1 76.9 46.9 17.9 – –

Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

Herbs

Steppe 23.8 12.1 16.0 1.0 – 0.8 0.1 –

Meadow 51.0 11.0 27.0 2.5 0.5 0.5 0.2 0.5

Forest 19.4 57.9 52.5 92.1 96.1 92.5 95.3 97.6

Forest-margin 0.8 10.0 1.8 2.7 2.1 2.7 2.9 0.9

Ruderal 5.0 9.0 2.7 1.7 1.3 3.5 1.5 1.0

Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

10

5

Composition, % of the sum of crown projection areas

Succession stage, years

90

20

80

70

60

50

40

30

20

10 15 25 30 35 40

100

1 Phase

1 Stage

Ac

Eu

Pad

Rh

2 Phase

2 Stage 3 Stage

Cer

Pr

Fig. 4. Scheme of the succession leading to the formation ofbird cherry forests. Designations: Cer, Cerasus fruticosa;Pr, Prunus spinosa; Rh, Rhamnus cathartica; Eu, Euony-mus verrucosa; Pad, Padus avium; Ac, Acer tataricum.

RUSSIAN JOURNAL OF ECOLOGY Vol. 38 No. 5 2007

VEGETATION RESTORATION DYNAMICS IN THE FOREST–STEPPE SYSTEM 305

Thus, the detailed analysis of succession resulting inforests dominated by P. avium has led us to the conclu-sion that the restoration dynamics of forest–steppe veg-etation fits the tolerance model best (Connel and Stay-ter, 1977). According to this model, the succession ofspecies is determined by their biological competitivecharacteristics. The rate of diaspore dispersal is animportant factor in this case: species with heavy seedsdispersed by animals appear at later stages of succes-sion (Horn, 1974; Christensen and Peet, 1981).

Simultaneous growth of plants from different eco-logical groups (steppe, meadow, and forest species) is aspecific feature of forest–steppe communities. Duringthe succession, the proportions of these groups change;however, since the populations of key species do notdevelop uniformly, conditions favorable for all specieswill always exist within the area. The dynamic equilib-rium of communities ensures stable existence of theforest–steppe system as an integrated whole.

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