Vegetation and pedogenesis on pyrogenic substrates of former peat soils

12

ISSN 1064-2293, Eurasian Soil Science, 2006, Vol. 39, No. 1, pp. 12–20. © Pleiades Publishing, Inc., 2006.Original Russian Text © F.R. Zaidel’man, D.I. Morozova, A.P. Shvarov, M.V. Batrak, 2006, published in Pochvovedenie, 2006, No. 1, pp. 19–28.

GENERAL STATEMENTS

In the last decades, systematic fires occurred overvast territories with drained peat soils [2, 3], especiallyin the taiga and forest-steppe zones. In the landscapesof forested lowlands (poless’e), organic soils with shal-low peat layers (1 to 2 m) underlain by gleyed sands runinto particular danger. These drained low-moor peatsoils degrade to the greatest degree. They, having ashallow peat horizon, usually burn down to the mineralbottom of the bogs. As a result, in place of potentiallyfertile and rich in organic matter peat soils, pyrogenicformations poor in mineral nutrients and carbon appear.The current fires on the drained peat soils are relatednot only to summer droughts but also mainly to a lossof the control over the groundwater table in drainagesystems because of the destruction or inactivity ofpump stations. Usually, fires on drained peat soils arisewhen the capillary fringe of the groundwater loses con-tact with the lower layers of the organic horizons. Pre-cisely this circumstance is the main reason for the fullburning out of peat soils within hundreds of Russiandrainage systems. After fires, the ground surfacebecomes lower by a depth equal to the thickness of theburned out peat (0.5–1.5 m) and the territory is exposedto secondary bogging; the elevated areas are subjectedto deflation.

As our studies showed [2], after fires, on the surfaceof burned peatlands, pyrogenic formations are formed.These formations differ from the initial organic soils intheir morphology, physical and chemical properties,and type and productivity of vegetation.

The aim of our studies was to analyze the changes inthe plant cover within six years after a fire on drainedpeat soils, to assess the above- and underground biom-

ass of the natural vegetation on pyrogenic formations,and to study the evolution of pyrogenic formations dur-ing the postfire period.

Pyrogenic Formations and Fire-Modified Peat Soils

Usually, four kinds of pyrogenic formations may befound on burned bogs in poless’e landscapes: (1) pyro-genic–mucky, (2) pyrogenic–sandy, (3) sandy, and(4) pyrogenic–woody–sandy. Pyrogenically modifiedpeat soils are also present there [2, 4, 5].

Pyrogenic–mucky formations develop after burningof a relatively thick peat layer (>100 cm). They have ahorizon (10 to 15 cm thick) of bright ocher-colored ashenriched in mineral nutrients. Owing to this nutrientresource, over 1–2 years after fire, pioneer vegetationappears on these pyrogenic–mucky formations. Pyro-genic–sandy formations arise within the areas oforganic soils with a peat horizon less than 1 m thick.Sandy formations are confined to local elevations of themineral bottom of bogs previously composed of shal-low peat soils. After fires, wind and floodwater removethe ash from the surface of the gleyed sandy layers. Theplant cover on these sites is less diverse because of thedeficiency of mineral nutrients. Pyrogenic–woody–sandy formations develop on the areas previously occu-pied by peatlands with the predominance of wood in thepeat composition. In this case, an agglomeration (“sin-tering”) of tree trunks takes place. The thickness ofsuch an agglomerated wood layer is 10 to 20 cm. In 5–7 years after fire, the wood is completely decomposedand disappears. Fire-modified peat soils occupy theareas along collecting canals. Their profiles areexposed to fire to a lesser extent. At the initial state, thebanks of collecting canals are overgrown with perennial

Vegetation and Pedogenesis on Pyrogenic Substratesof Former Peat Soils

F. R. Zaidel’man, D. I. Morozova, A. P. Shvarov, and M. V. Batrak

Faculty of Soil Science, Moscow State University, Leninskie gory, Moscow, 119899 Russia

Received July 31, 2004

Abstract

—The role of vegetation and chemical factors in the development of the primary pedogenesis and evo-lution of pyrogenic formations resulting from fires on drained peat soils was studied. Over four years after thefire, a shallow (1 cm) humus horizon is formed on the surface of the ashy horizon of the pyrogenic formations.For six years, its thickness increases up to 3–4 cm. The dynamics and productivity of the plant cover on thepyrogenic formations were investigated. The dominant plant species were restricted to certain pyrogenic for-mations. The formation of stable phytocenoses and chemical transformation of substrates are the factors gov-erning the primary pedogenesis on pyrogenic substrates. Four stages in the evolution of the pyrogenic forma-tions were revealed. At the fourth stage, some features appeared that permit us to recognize the development ofsoddy soils on the pyrogenic substrates (i.e., soddy pyrogenic–mucky, soddy pyrogenic–sandy soils, etc.).

DOI:

10.1134/S1064229306010029

GENESIS AND GEOGRAPHYOF SOILS

EURASIAN SOIL SCIENCE

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2006

VEGETATION AND PEDOGENESIS ON PYROGENIC SUBSTRATES 13

macropodus grasses, which weaken the intensity offires affecting organic soils. The upper compact (sin-tered) horizon of hydrophobic peat of up to 40 cm thickis typical for fire-modified peat soils. The deeper layersof the organic horizons remain practically unchanged.More detailed descriptions of all the pyrogenic forma-tions and fire-modified peat soils were published earlier[2, 3].

STUDY OBJECTS

The plant cover after the fires was studied in the PraRiver floodplain (the Oka–Meshchera Poles’e, Ryazandistrict). The pyrogenic formations that appeared afterthe destructive fire of 1996 in the territory of the polderdrainage–irrigation ameliorative system “MakeevskiiMys” were the direct objects of the investigations. Thepeat soils occupied the entire (2000 ha) polder territorybefore the fire and were drained in 1978. The thicknessof the peat horizons in these soils (before the fire) was80 to 160 cm. Gleyed fine and medium sands underliethe organic soils. The ground water is fresh bicarbon-ate–calcium with a low iron content (the FeO content is1–3 mg/l). Formerly, the entire polder territory wasused for cropping of cereals, perennial grasses, pota-toes, and vegetables. Before the fire, the annual yield ofthese crops was high.

Presently, the pyrogenic formations in place of theburned out shallow- and medium-thick peat soils arenot used in agriculture because of (1) the secondarywaterlogging of the whole area due to a drastic lower-ing of the surface level by 70–120 cm after the fire and(2) the sharp reduction in the fertility of the pyrogenicformations as compared to the initial peat soils. Thespecies composition of the plant cover and the proper-ties of the pyrogenic formations changed over six yearsfrom the fire. As our investigations showed, the phyto-cenoses developed were differentiated among the areasof the pyrogenic formations.

RESULTS AND DISCUSSION

Changes in the Species Composition of the Vegetation

In 1996, in the zone of the fire on the drained bog,the plant cover was completely eliminated. Over 1–2 years after the fire, the pioneer vegetation appeared.During the first years after the fire, under extreme con-ditions (high pH values, excessive moistening, etc.),plants and their vegetative organs were depressed. Thedepression of the plants was manifested in their smallsizes, the changes in the shape and size of their leavesand flowers, and in the weak development of their rootsystems. The height of most of the plants was less than10 cm irrespectively of the species. The exceptionswere woodreed (

Calamagrostis epigeios

(L.) Roth) andmugwort (

Artemisia vulgaris

L.), which predominatedover the territories studied during the entire postfireperiod.

Since 1997, every year we monitored the plant coveron the pyrogenic formations (Table 1). The year afterthe fire, single pioneer species of

Artemisia vulgaris

L.,rose bay (

Chamaenerion angustifolium

Holub.), andweeds (coltsfoot,

Tussilago farfara

L., and dandelion(

Taraxacum officinale

Wigg.)) were recorded there. Asis usual, the pioneer communities did not completelyoccupy the ecotope. With time, the structure of thepyrogenic formations changed considerably (Fig. 1). In2001, the pyrogenic–woody–sandy formations werenot found. The wood layer of these formations wasfully decomposed under the influence of the weatherconditions and floods. In 2002, the second fire occurredin the polder territory. During this fire, the organic lay-ers of the peat soils that were preserved after the fire of1996 mainly along the banks of the canals burned downto the mineral layers. As a result, in 2002 (6 years afterthe fire), over the entire area studied, the number ofpyrogenic formations decreased to two kinds. Thepyrogenic–mucky formations with an ash layer of 10–15 cm thick occupied depressions and the pyrogenic–sandy ones with an ash layer <6 cm thick were found inelevated areas. Locally, the mineral horizons outcropped.

For six years, the species composition of the vegeta-tion changed to a great extent. In 2000 (the 4th yearafter the fire), a continuous plant cover was formed onall the pyrogenic formations. The dominant specieswere woodreed (


(L.) Roth) andmugwort (

Artemisia vulgaris

L.) on the pyrogenic–sandy formations. These species formed distinct areas;they might be easily recognized upon a visual analysisof the territories.

In the grass layer on the pyrogenic formations,diverse weeds were found. They were represented byannual, biennial, and perennial species whose appear-ance or disappearance is related to the weather condi-tions. In this grass layer, marsh watercress (

Rorippapalustris

(L.) Bess), white goosefoot (

Chenopodiumalbum

L.), coltsfoot (

Tussilago farfara

L.), dandelion(


Wigg.), greater plantain (

Plan-tago major

L.),

Tripleurospermum inodorum

Sch., etc.,were widely spread. The species diversity of the annualand biennial plants and its annual variability indicatedthe initial development stage of a phytocenosis. Amongthe meadow grasses were cocksfoot (

Dactylis glomer-ata

L.), different species of foxtail (

Alopecurus praten-sis

L.,

A. aequalis

Sobol), red fescue (

Festuca rubra

L.),awnless (

Bromus mollis

L.). All these species weremainly found on the pyrogenic–mucky formations,which, as our investigations showed, were richer inmineral nutrients as compared to the other kinds ofpyrogenic formations [4].

A group of hygrophilous species (Table 1) was anindicator of the water regime over the studied territo-ries. In the spring, water flooded the pyrogenic forma-tions for 1- to 2-month-long periods. In the summerperiods, the ground water table was at a depth of 40 to

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ZAIDEL’MAN

et al

.

Table 1.

The dynamics of the species composition of the vegetation on the pyrogenic formations and fire-modified peat soils

Species

Pyrogenic formationFire-modified

peat soilpyrogenic–mucky pyrogenic–sandy pyrogenic–wood–sandy

Years

1997

1998

2000

2001

2002

1997

1998

2000

2001

2002

1997

1998

2000

1997

1998

2000

2001

Shrub layerWhite birch (

Betula pubescens

Ehrh.) + + + + + + + + + + +Great sallow willow (

Salix caprea

L.) + +Osier (

S. viminalis

L.) + + + +Grey sallow (

S. cinerea

L.) + + + + + + + + + + + + + +Bay willow (

S. pentandra

L.) + + + + +French willow (

S. triandra

L.) + +Aspen (

Populus tremula

L.) + + + + + + + + + +Scotch pine (

Pinus sylvestris

L.) +Grass layer

Dominant speciesBush grass (


(L.) Roth) + + + + + + +Mugwort (

Artemisia vulgaris

L.) + + + + + + + + + + + + + + +Weeds

Knotweed (

Polygonum aviculare

L.) +Marsh thistle (

Cirsium palustre

(L.) Scop. +Creeping thistle (

C. arvense

(L.) + +

Polygonum scabrum

Moench. + +

P. lapathifolium

L. + + + + +Treacle mustard (

Erysimum cheiranthoides

L.) + + + + + +Marsh watercress (

Roripa islandica

(geder) Borbas)

+ + + + +

Common stinging nettlt (

Urtica dioica

L.) + + +Prickly lettuce (

Lactuca serriola

L.) +Spear-leaved orache (

Atriplex hastata

L.) +Yellow toadflux (

Linaria vulgaris

Mill.) + + + +White goosefoot (

Chenopodium album

L. + + + + + + +Oak-leaved goosefoot (

Ch. glaucum

L.) + + +Coltsfoot (

Tussilago farfara

L.) + + + + +Canadian fleabane (

Erigeron canadensis

L.) + +Loose silky bent (

Apera spica-venti

(L.) Beauv.)

+ + + +

Dandelion (


Wigg.) + + + + + +Corn sowthistle (

Sonchus arvensis

L.) + + + + + + +Tansy (

Tanacetum vulgare

L.) + + + + +Large-flowered hemp-nettle (

Galeopsis speciosa

Mill.)

+

Greater plantain (

Plantago major

L.) + + +Couch (

Elytrigia repens

(L.) Nevski) + + + +

Tripleurospermum inodorum

Sch. + + + + + + + + +Dog violet (

Viola canina

L.) + + + +Welted thistle (

Carduus crispus

L.) + +Dead nettle (

Lamium album

L.) +


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Table 1.

(Contd.)

Species

Pyrogenic formationFire-modified

peat soilpyrogenic–mucky pyrogenic–sandy pyrogenic–wood–sandy

Years

1997

1998

2000

2001

2002

1997

1998

2000

2001

2002

1997

1998

2000

1997

1998

2000

2001

Meadow plants

Cocksfoot (

Dactylis glomerata

L.) +

Hungarian brome (

Bromus mollis

. L.) +

Autumn hawkbit (

Leontodon autumnalis

L.) +

Common foxtail (

Alopecurus pratensis

L.) +

Orange foxtail (

A. aequalis

Sobol.) +

Tufted hair grass (

Deschampsia caespitosa

(L.) Beauv.)

+

Meadow-grass (

Poa pratensis

. L.) + + +

Red fescue (

Festuca rubra

L.) + +

Rough hawk’s-beard (

Crepis biennis

L.) +

Timothy grass (

Phleum pratense

. L.) + +

Hygrophilous plants

Reed grass (

Phalaris arundinacea

L. Rausch.) +

Purple loosestrife (

Lythrium salicaria

L.) +

Rose bay (

Chamaenerion angustifolium

(L.) + + + + + +

Willow-herb (

Epilobium rubescens

Rydb.) +

Marsh willow-herb (

E. palustre

L.) + +

Pale willow-herb (

E. roseum

Schreb.) + +

Tormentil (

Potentilla erecta

(L.) +

Creeping buttercup (

Ranunculus repens

. L.) + +

Plicate sweet-grass (

Glyceria plicata

Fries.) +

Corn mint (

Mentha arvensis

L.s.l.) + +

Sedge (

Carex acuta

L.) +

Great reedmace (

Typha latifolia

L.) + + + +

Common reed (

Phragmites communis

Trin.) + + + + + + +

Yarrow (

Achillea cartilaginea

Ledeb. ex Re-ichenb.)

+

Three-lobed bur marigold (

Bidens tripartita

L.) +

Marsh woundwort (

Stachys palustris

. L.) +

Golden dock (

Rumex maritimus

L.) + + + + +

Mosses

Leptobrium pyriforme

L. + + + + + + + +

Funaria hygrometrica

Hedw. + +

Bryum argenteum

Hedw. + +

Marshancia polymorfa

L. + + + +

Ceratodon purpureus

(Hedw.) Brid + +

Bryum caespiticum

Hedw. + +

Note: The sign + designates the presence of a species.

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ZAIDEL’MAN et al.

50 cm in the profiles of the pyrogenic–mucky forma-tions and at a depth of 80 to 100 cm in the pyrogenic–sandy ones. As a result of excessive moistening, theplant cover on the territories investigated was repre-sented by diverse hygrophilous and peat-formingplants, such as creeping buttercup (Ranunculus repens L.),sedge (Carex acuta L.), common reed (Phragmites aus-tralis Trin.), golden dock (Rumex maritimus L.), andmarsh woundwort (Stachys palustris L.), and so on.

The shrub layer in the territory of the pyrogenic for-mations was dominated by different willow species.The young growth of white birch (Betula pubescensEhrh.), aspen (Aspen tremula L.), and single Scotchpine (Pinus sylvestris L.) seedlings were also present

there. Small depressions on the surface of the pyro-genic formations were occupied by different speciesof green mosses (Leptobrium pyriforme Wils.,Bryum arventeum Hedw., and Marshancia polymor-pha L.) (Table 1).

The plant cover was the most diverse on the pyro-genic–mucky formations due to their higher supplywith nutrients as compared to the vegetation on theother pyrogenic formations. We found earlier [4, 5] thatplants that intensely settled on the pyrogenic forma-tions actively affected the ash layer and promoted theorganic matter accumulation there. As a result, in 2000,a shallow (1.0–1.5 cm) humus horizon (A1) appeared.By 2002, its thickness increased up to 3–4 cm due to thegradual organic matter accumulation in the upper partof the ash layer. A shallow (1 cm) sod horizon haddeveloped by this time. The humus accumulation beganwhen the potash (K2CO3) was washed off the ash layerand its reaction became less alkaline (Table 2). Within4 years after the fire, the pH of the ash layer changedfrom 11.2 to 8.1 and the contents of organic matter andavailable phosphorus in the newly formed humus hori-zon increased.

On the whole, the plants growing on all the pyro-genic formations continued to colonize the territory andform a dense cover. In the first postfire years, the spe-cies composition of the plant cover markedly changes,

00.51.01.52.0

400 m

00.51.01.52.0

00.51.01.52.0

0 I I III II I

1 0.3–0.5

1 0.3–0.5 0.4–0.7 0.5–0.9

0 V I III II IV

Ä

B

C

Dep

th, c

m

1

7

2

8

3

9

4

10

5

11

6

12

Gr Gr

Go

GrGo

Gr Gr Go

Gr Go

Go

Gr

Go

GrGrGr

Fig. 1. A schematic profile of the burned peatland in the polder territory “Makeevskii Mys” and the structure of the pyrogenic for-mations: A—territory before the fire; B, C—territory after the fire, 1996 and 2002, respectively. Pyrogenic formations: I—pyro-genic–mucky; II—pyrogenic–sandy; III—sandy; IV—pyrogenic–woody–sandy; V—fire-modified peat soils; 0—shallow peat soilsbefore the fire; 1—surface before the fire; 2—ground water table; 3—peat horizon; 4—horizon of agglomerated (sintered) peat; 5—gleyed sand; 6—loam; 7—sandy loam; 8—ash horizon; 9—charcoal horizon; 10—mucky horizon; 11—layer of burnt wood; 12—sapropel.

Table 2. Productivity of natural vegetation on the pyrogenicformations in the dry (2002) and wet (2003) periods. “Ma-keevskii Mys,” Ryazan

Type of pyrogen-ic formation

Dominant plant species

Dry mass, n × 100 kg/ha

2002 2003

Pyrogenic–mucky


45 ± 3 67 ± 3

Pyrogenic–sandy

Artemisia vul-garis L.

31 ± 2 56 ± 3

EURASIAN SOIL SCIENCE Vol. 39 No. 1 2006


thus, indicating an actively developing biocenosis.However, 4–5 years after the fire, the plant cover wasdominated by the species that also predominate at thepresent time.

The Aboveground and Underground Biomass

In order to assess the productivity of the natural veg-etation developed on the pyrogenic formations, theaboveground mass of the plants was determined onplots of 1 m2 in 2002 (5 replicates). On the pyrogenic–mucky formations, the dominant species in the plantcover was woodreed (Calamagrostis epigeios (L.)Roth); on the pyrogenic–sandy formations, mugwortwas the dominant species (Artemisia vulgaris L.). Thedata obtained shows the high biological productivity ofthe pyrogenic–mucky formations (Table 2). Calama-grostis epigeios is a coarse forage crop. This plantgrows successfully on the pyrogenic–mucky forma-tions and produces considerable green mass withoutessential expenditures for its cultivation. Thus, thepyrogenic–mucky formations may be used as a naturalsource for hay production. In this case, the applicationof mineral fertilizers (firstly, containing potassium) isexpedient (Table 3). However, under the shallowground water conditions, hay harvesting is possibleonly by hand. On the pyrogenic–sandy formations withthe predominance of Artemisia vulgaris L., the arrange-ment of hayfields is impossible. Preliminary measuresfor raising the fertility of these mineral substrates areneeded.

The root mass was measured in monoliths taken bylayers from plots 20 × 20 cm in area for the whole thick-ness of the horizons. The roots were washed with waterand divided into dead and living ones. The dataobtained confirmed our conclusion that, on the pyro-genic–mucky formations, a humus–accumulative hori-zon began to develop (Fig. 2, I). Plant roots activelyaffect the ash horizon and create conditions for organic

matter accumulation. In its turn, the latter activatesmicroorganisms and promotes increasing of the rootmass and development of primary pedogenesis. In theupper layers (0–3 cm) of the pyrogenic–mucky forma-tions (Fig. 2), the mass of living roots (2.83 t/ha) wasgreater than that of dead ones (0.63 t/ha). The develop-ing soddy process in this layer was distinctly revealedand resulted in the formation of a friable shallow (1–2 cm) sod horizon. In the 0- to 3-cm-thick layer of the

Table 3. Some chemical and physicochemical properties of the different-aged ash horizons and humus horizon (2000) of thepyrogenic–mucky formations

HorizonpH

AvailableSupply of plants with Corg, %

K2O P2O5

water salt mg/100 g soil K P %

Fresh ash sampled afterthe fire, 1996

11.40 8.10 24.6 18.8 High High 4.18

Pyrogenic–mucky formation 4 years after the fire, 2000

A1, 0–1 cm 8.05 7.41 0.6 17.5 Very low High 5.03

Ash, 1–10 cm 8.20 8.00 0.3 6.1 Very low High 1.47

Pyrogenic–sandy formation 4 years after the fire, 2000

As, 0–1 cm 7.20 6.33 11.3 9.8 Medium Very low 1.50

Am1, 1–8 cm 7.18 6.15 2.1 9.3 Very low Very low 1.39

Note: A1 is the humus horizon formed on ash; Ash is the ash horizon; As is the soddy horizon; Am1 is the pyrogenic–sandy horizon.

28.36.3

15.59.5

11.024.0

12.873.3

0 20 40 60

Depth, cm

Mass of dry matter, n × 100 kg/ha

Amg, 13–28

Cn, 10–13

Ash, 3–10

A1, 0–3

Amg, 3–20

A1, 0–311.0

34.3

24.85.5

0 10 20 4030

12

I

II

Fig. 2. Distribution of plant roots in the (I) pyrogenic–mucky and (II) pyrogenic–sandy formations. The ground-water table: I—40, II—110 cm. Roots: 1—living, 2—dead.

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ZAIDEL’MAN et al.

pyrogenic–sandy formations (Fig. 2, II), the mass ofdead roots (3.43 t/ha) was higher than that of livingroots (1.10 t/ha).

Evolution of the Pyrogenic Formations

Fires on drained bogs cause local ecological catas-trophes that disturb the most important natural pro-cesses: the cycling of biogenic elements and the water,heat, and air regimes. The terrestrial and soil fauna, thevegetation, and the soil microflora responsible for thesoil fertility are destroyed. However, even in 1–2 yearsafter a fire, the development of a new biogeocenosisbegins. The lost equilibrium is gradually restored as aresult of the plant succession, and a new stable biogeo-cenosis whose properties differ from the prefire biogeo-cenosis develops.

The results of long-term studies of the pyrogenicformations developed in place of burned out peat soilsshow that, over the postfire period, the evolution of

these formations proceeds under the influence of anumber of factors.

Firstly, the organic matter accumulated during theprefire period continues to degrade. First of all, this pro-cess is displayed in the transformation of the pyro-genic–woody–sandy formations. The wood is decom-posed under the influence of insolation, precipitation,and temperature and removed by floodwater. The fire-modified peat soils are repeatedly burned out, and soonthey turn to pyrogenic–mucky and pyrogenic–sandyformations. The profiles presented in Fig. 1 reflect suchchanges of the pyrogenic formations in the polder terri-tory. Secondly, the main widely spread kinds of mineralpyrogenic formations—pyrogenic–mucky and pyro-genic–sandy—continue to change. The following fourevolutionary stages of this transformation wererevealed (Table 4).

As a result of the grass cover development and accu-mulation of considerable above- and underground bio-mass and organic matter in the topsoil, the soddy pro-cess is activated. Humus is accumulated, the sod layer

Table 4. Evolution of mineral pyrogenic formations and fire-modified peat soils on burned out drained peat soils in poless’eterritories of the East-European Plain

Evolutionary stage Main processes

Durationof stages,

years

Changes in soil properties and fertility

Pyrogenic formations and fire-modified peat soils. Soddy soils

on pyrogenic formations

1. Leaching Leaching of alkalinecompounds

1–2 Reduction of high alkalinity in ash horizons (frompH 10.5–11 to 8.0–8.5),infertile substrate

Alkaline and weakly alkaline:(1) pyrogenic–mucky,(2) pyrogenic–sandy,(3) sandy,(4) pyrogenic–woody–sandy,(5) fire-modified peat soils

2. Formationof unstablephytocenoses

Colonization of pyrogenic formations by plants

1–2 Appearance of pioneervegetation

Weakly alkaline and neutral:(1) pyrogenic–mucky,(2) pyrogenic–sandy,(3) sandy,(4) pyrogenic–wood–sandy,(5) fire-modified peat soils

3. Formationof unstablephytocenoses

Development of shallow humus horizons

2 Formation of stable phyto-cenoses with well-ex-pressed dominant species. Appearance of humus hori-zons 2–3 cm thick (witha humus content of 3–4%).Natural plant associations are well-developed

Neutral soils:(1) pyrogenic–mucky,(2) pyrogenic–sandy,(3) sandy

4. Formationof soddy soilsand shallowsoddy horizons

Formation of well-devel-oped humus horizon,appearance of sod

2 Complete formation of sod-dy soils on the base of initial pyrogenic formations.Transformation of pyrogenic formations into soils of dif-ferent fertility. Increase in the thickness of the humus hori-zons (2–3 cm). The organic matter content is about 5%

Neutral soils:(1) soddy pyrogenic–mucky,(2) soddy pyrogenic–sandy,(3) low-humus soddy sandy



is gradually formed, and the enzymatic activity is inten-sified. The shallow sod and humus horizons are wellexpressed. The pyrogenic formations are substituted forsoddy soils on the pyrogenic substrates. Beginningfrom the third evolutionary stage, the degraded pyro-genic formations gain properties favorable for thegrowth and development of plant associations. There-fore, at the third stage, the pyrogenic formationsacquire the characteristic features of soils. They sup-port plants, the species composition and mass of whichare stipulated by the properties and particularities of thesoil and ground water regimes.

4–6 years after a destructive fire, the features of theactive primary pedogenesis are distinctly revealed,especially in the ashy topsoil. Four stages of transfor-mation of pyrogenic formations into soils may be rec-ognized according to the following features.

The first stage is leaching. For 1–2 years, potash(and other toxic compounds and elements) is activelyleached from the ash horizons. After the first and/orsecond flooding, the reaction in the upper layer of thepyrogenic formations changes from pH 10.5–11.0 to7.5–8.2.

The second stage is the formation of unstable bio-cenoses. In the 2nd to 3rd years, grass and woody plantssettle the pyrogenic formations. The accumulation oforganic matter and humus is activated in the upper ashlayer.

The third stage is the formation of stable biocenosesadapted to the ecological conditions of the pyrogenicformations. In the 5th to 6th years, a shallow (1–2 cm)sod horizon is formed on the surface of the pyrogenic–mucky formations.

The fourth stage is marked by the formation ofsoddy soils with well-expressed humus horizons andsods. This stage is characterized by organic matteraccumulation in the topsoil, which greatly affects themigration activity of metals with variable valence(mainly iron and manganese). At this stage, the pyro-genic horizons should be considered as soddy soils, andtheir names should reflect their evolution. In the caseconsidered, soddy pyrogenic–mucky and soddy pyro-genic–sandy soils (with a shallow (<3 cm) ash horizon)are distinguished.

Since the territory of the floodplain is flooded everyyear, the accumulation of humus and weakly decom-posed organic matter becomes a reason for the develop-ing anaerobiosis in the upper layers of the pyrogenicformations. Under anaerobic conditions, immobiletrivalent iron is transformed to mobile bivalent iron (thelatter may be removed from the soil profile), as well asretrograded phosphorus, to available mobile forms.

The following experiment was performed in order toassess the migration capacity of iron upon flooding.Cylinders with a water outlet in their bottoms werefilled with: (1) fresh ash without organic matter justafter the fire, (2) the fine earth of the humus–accumula-tive horizon that appeared within 4 years in the 0- to

1-cm-thick layer of the pyrogenic–mucky formations,and (3) ash from the ash horizon of the pyrogenic–mucky formations sampled from the 1- to 10-cm-thicklayer of the ash horizon 4 years after the fire.

The samples were taken in three replicates.In the cylinder with the fine earth, there was a water

layer 10 cm thick above the substrate. After a month offlooding, the water was poured out of each cylinder toa flash where the iron content was determined. Theredox potential was continuously measured using a pH-340 potentiometer.

The data obtained (Table 5) show that within thewhole period of the observations, the ash substratewithout humus that was sampled after the fire was char-acterized by a relatively high redox potential and weakiron mobilization.

Unlike in the control variant, in the variant with anash substrate enriched in organic matter and humus, theredox potential decreased during the entire period offlooding. As a result, the considerable content of immo-bile trivalent iron was transformed to its mobile biva-lent form. Under the conditions of the experimentalmodeling, the amounts of bivalent iron extracted fromthe humus–accumulative horizon developed on ashwere 34 times higher than those from the fresh ashtaken just after the fire. The contents of organic carbon

Table 5. The influence of humus accumulation in the courseof primary soil formation on the redox potential, mV (modelexperiment)

Days A1, 0–1 cm, 2000

As, 1–10,2000

As, fresh,1996

1 68 65 133

2 –43 143 166

3 –80 108 96

4 –285 103 146

5 –253 251 68

6 –205 66 113

7 –220 80 116

8 –160 175 221

9 –86 165 223

10 –191 278 210

11 –183 226 216

12 –200 120 200

13 –226 110 153

14 –216 115 106

15 –216 155 171

16 –260 251 126

17 –173 200 205

18 –188 203 180

19 –230 176 245

20


ZAIDEL’MAN et al.

in the substrates analyzed were 5.03 and 0.03% of thesubstrate mass, respectively (Table 6).

CONCLUSIONS

(1) In the postfire period, the pyrogenic–woody–sandy formations and fire-modified peat soils degraded.In the wood–sandy formations, within 4–5 years afterthe fire, the wood fully disappeared; in the fire-modifiedsoils, the organic horizons burned again.

(2) Within 3–4 years after the fire in the poless’e ter-ritories, the mineral pyrogenic–mucky and pyrogenic–sandy formations predominated in place of the drainedpeat soils.

(3) In the 4th to 5th years after the fire, the plantcover became dense and was dominated by Calama-grostis epigeios on the pyrogenic–mucky formationsand by Artemisia vulgaris on the pyrogenic–sandyones.

(4) A humus-accumulative horizon was formed inthe upper layer of the ash horizon as a result of the

developing plant cover. This horizon (1.0–1.5 cm)appeared the 4th year after the fire; in the 5th to 6thyears after the fire, the thickness of the humus horizonincreased up to 3 cm and a shallow (1 cm) sod devel-oped.

(5) Under natural conditions, the pyrogenic–muckyformations might be used for cultivation of Calama-grostis epigeios on the assumption of its harvesting byhand.

(6) Four stages were revealed in the evolution of thepyrogenic formations to soddy soils: leaching, forma-tion of unstable biocenoses, formation of stable bio-cenoses, and formation of soddy soils with wellexpressed humus horizon and sod.

REFERENCES1. V. N. Efimov, Peat Soils and Their Fertility, Leningrad:

Agropromizdat, 1986.2. F. R. Zaidel’man and A. P. Shvarov, Pyrogenic and

Hydrothermal Degradation of Peat Soils, Their Agro-ecology, Sand Cultures, and Remediation (Mosk. Gos.Univ., Moscow, 2002) [in Russian].

3. F. R. Zaidel’man, M. V. Bannikov, and A. P. Shvarov,“Structure and Ecological Assessment of Pyrogenic For-mations on Burnt Drained Peat Soils,” Vestn. Mosk.Univ., Ser. 17: Pochvoved., No. 2, 26–31 (1998).

4. F. R. Zaidel’man, D. I. Morozova, and A. P. Shvarov,“Changes in the Properties of Pyrogenic Formations andVegetation on Burnt Previously Drained Peat Soils ofPoles’ie Landscapes,” Pochvovedenie, No. 11, 1300–1309 (2003) [Eur. Soil Sci. 36 (11), 1159–1167 (2003)].

5. F. R. Zaidel’man, D. I. Morozova, and A. P. Shvarov,“Changes in the Chemical Properties of Pyrogenic For-mations after Fires on Drained Low Peat Soils,” Vestn.Mosk. Univ., Ser. 17: Pochvoved., No. 1, 25–29 (2004).

Table 6. The iron yield depending on the organic mattercontent under conditions of flooding

Horizons of pyrogen-ic formations

Iron content,mg Corg, %

Pyrogenic–mucky formation 4 years after the fire

A1, 0–1 cm 3.05 5.03

Ash, 1–10 cm 0.70 1.47

Pyrogenic–mucky formation 4 years after the fire

Ash 0.09 0.03

Documents

Vegetation and pedogenesis on pyrogenic substrates of former peat soils