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Can paludification be stopped in the Taiga?

Kryuchkov, V. V.; National Research Council of Canada. Division of Building Research

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CANADA INS'I'ITUTE

FOR SCIENTIFIC AND TECHNICAL INFORMATION ISSN 0 0 7 7 - 5 6 0 6 l NSTlTllT CANADl EN DE L'INFORMATION SCIENTIFIQLIE ET TECHNIQUE NRC/CNR TT- 1 9 2 2 TECHNICAL TRANSLATION TRADUCTION TECHNIQUE V.V. KRYUCHKOV

CAN PALUDIFICATION BE STOPPED I N THE TAIGA? PRIRODA, (2) : 83-92, 1 9 7 5

TRANSLATED BYITRADUCTION DE V. POPPE

T H I S I S THE TWO HUNDRED AND THIRTY-THIRD I N THE SERIES OF TRANSLATIONS PREPARED FOR THE D I V I S I O N OF BUILDING RESEARCH

TRADUCTION N U M ~ R O 2 3 3 DE L A S~RIE P R ~ P A R ~ E POUR LA DIVISION DES RECHERCHES EN

BATIMENT

OTTAWA 1 9 7 8

National Research Conseil national

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NATIONAL RESEARCH COllNCIL OF CANADA CONSEIL NATIONAL DE RECHERCHES DU CANADA

TECHNICAL TRANSLATION 1922 TRADUCTION TECHNIQUE

T i tl e/Ti t r e : Can p a l u d i f i c a t i o n be stopped i n t h e t a i g a ? (Mozhno 1 i ostanovi t zabolachivanie t a i g i ? ) Au thor/Au t e u r : V.V. Kryuchkov

Ref erence/Ref 6rence: P r i r o d a , ( 2 ) : 83-92, 1975 Trans1 a tor/Traducteur: V. Poppe

Canada I n s t i t u t e f o r I n s t i t u t canadien de

S c i e n t i f i c and Technical 1 ' i n f o r m a t i o n s c i e n t i f i q u e I n f o r m a t i o n e t technique

Ottawa, Canada KIA OS2

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PREFACE

The D i v i s i o n o f B u i l d i n g Research has been c a r r y i n g o u t i n v e s t i g a t i o n s on t h e d i s t r i b u t i o n o f permafrost i n Canada f o r many y e a r s as p a r t o f i t s programme t o g a i n a b e t t e r understanding o f t h i s phenomena i n r e l a t i o n t o n o r t h e r n c o n s t r u c t i o n problems. The t y p e o f t e r r a i n i n which permafrost e x i s t s i s one of t h e i m p o r t a n t aspects of i n v e s t i g a t i o n s i n i t s d i s t r i b u t i o n . The s p e c i a l r e l a t i o n s h i p s e x i s t i n g between t h e occurrence o f permafrost and p e a t bogs i s under continuous study and t h e e x t e n s i v e work by S o v i e t i n v e s t i g a t o r s on t h i s s u b j e c t i s o f c o n s i d e r a b l e i n t e r e s t f o r comparison w i t h Canadian c o n d i t i o n s . T h i s t r a n s l a t i o n o f a paper from a Russian j o u r n a l d e s c r i b e s a s p e c i f i c aspect of t h i s s u b j e c t concerned w i t h t h e f o r m a t i o n o f peat bogs and permafrost i n che d i s c o n t i n u o u s zone o f t h e S i b e r i a n t a i g a ( s u b a r c t i c f o r e s t zone).

The D i v i s i o n o f B u i l d i n g Research i s g r a t e f u l t o

M r . V. Poppe f o r t r a n s l a t i n g t h i s paper and t o D r . R.J.E.

Brown o f t h i s D i v i s i c . who checked t h e t r a n s l a t i o n .

Ottawa,

February, 1 978

C

.

B. Crawford,

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CAN PALUDIFICATION BE STOPPED I N THE TAIGA?

Rapid economic development o f Western S i b e r i a and changes which occur i n t h e t a i g a as a r e s u l t o f i n d u s t r i a l a c t i v i t y make i t i m p o r t a n t t o study t h e e v o l u t i o n o f t h e t a i g a biogeocenoses. Knowledge o f t h e e v o l u t i o n a r y processes w i l l f a c i l i t a t e t h e e x p l o i t a t i o n o f n a t u r a l resources and a t t h e same t i m e w i l l h e l p t o a v o i d an u n d e s i r a b l e development o f t h e environment.

The process of p a l u d i f i c a t i o n and degradation o f f o r e s t s i s one of t h e more obvious aspects o f e v o l u t i o n o f t h e t a i g a i n Western S i b e r i a . I t was r e p e a t e d l y i n v e s t i g a t e d and discussed. Much has been done t o study these phenomena, e s p e c i a l 1y i n t h e l a s t few years, owing t o t h e search f o r o i 1 and n a t u r a l gas and a l s o i n t h e course o f engineering and g e o l o g i c a l i n v e s t i g a t i o n s o f proposed r o u t e s f o r pipe1 ines and roads, i n t h e course of c o n s t r u c t i o n o f towns and settlements

,

e t c .

.

'These e x p l o r a t i o n a c t i v i t i e s y i e l d e d an enormous aniount o f data on t h e 1 it h o l o g y o f rocks, t h e thickness of peat1 ands

,

t h e groundwater 1 eve1

,

t h e s o i 1 temperature, and t h e p r o p e r t i e s o f permafrost. Wood remnants have been found i n t h e peat.

Having p a r t i c i p a t e d i n a number o f e x p e d i t i o n s i n t h e t a i g a , t h i s author has analyzed t h e c o l l e c t e d d a t a and has attempted t o r e c r e a t e t h e h i s t o r y o f degradation o f f o r e s t s i n t h e l a s t few thousand y e a r s s i n c e t h e end of t h e s o - c a l l e d p o s t g l a c i a l thermal maximum (Middle Holocene). The c l imate d u r i n g t h i s p e r i o d can be considered t o have been s t a b l e ; i t f l u c t u a t e d o n l y s i g h t l y about i t s average l e v e l .

The d a t a were c o l l e c t e d m a i n l y i n t h e Nadym-Ob i n t e r f l u v e n o r t h of

T y p i c a l t a i g a biogeocenoses

L e t us examine t h e n a t u r a l complexes, o r biogeocenoses (BGC)

,

o f t h e n o r t h e r n t a i g a i n Western S i b e r i a and arrange them i n a s e r i e s as u n i t s o f

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a l o n g e v o l u t i o n a r y chain. The s e r i e s s t a r t w i t h coniferous f o r e s t s , o f t e n c o n t a i n i n g l i c h e n , and ends w i t h d r y r a i s e d scrub-covered peatlands w i t h l i c h e n on t h e ground surface.

Pine-cedar-larch f o r e s t s w i t h 1 ic h e n ( F i g . 1 ) on elevated s e c t i o n s of t h e p l a i n s ( H = 50 m). The diameter of t r e e s a t a h e i g h t of 1.5 m reaches 35 cm. New growth i s normal. Such f o r e s t s (we s h a l l c a l l them BGC-1 ) a r e n o t common and u s u a l l y occur on elevated and w e l l d r a i n e d s e c t i o n s o f t h e p l a i n s . They a r e surrounded by wet, s t u n t e d f o r e s t s , swamps and p e a t bogs. I n p l a n view such s e c t i o n s a r e e i t h e r round (800-1000 m i n diameter) o r elongated (up t o 1000 m i n w i d t h ) .

Stunted spruce-larch f o r e s t s (BGC-2a) ( F i g . 2). These a r e sparse f o r e s t s c o n t a i n i n g some b i r c h , scrubs and moss. The t r e e diameter a t a h e i g h t of 1.5 m ranges from 5 t o 12 cm. New growth i s e i t h e r absent o r i s v e r y sparse. Such f o r e s t s i nclude s e c t i o n s of newly formed permafrost and occur i n t h e e l e v a t e d p a r t s o f t h e p l a i n s , o r as s t r e t c h e s of l a n d surrounding coniferous f o r e s t s (BGC-1)

.

Humocky m i c r o r e l i e f w i t h permafrost 1 enses i s

i n v a r i a b l y p r e s e n t i n these f o r e s t s , as w e l l as i n t h e c o n i f e r o u s - b i r c h f o r e s t s on t h e slopes (BGC-2b).

Sparse larch-spruce f o r e s t s w i t h moss (BGC-3) occur i n l o w - l y i n g areas. There a r e o n l y a few s i n g l e t r e e s i n t h e c e n t r e of t h e depression. T h e i r diameter ranges from 8 t o 15 cm, t h e t r u n k s a r e deformed and t h e tops a r e u s u a l l y d r y . There i s no advance growth. The moss-peat l a y e r i n t h e c e n t r e o f t h e depression i s 30 t o 40 cm t h i c k . The p e a t o f t e n c o n t a i n s b u r i e d t r e e t r u n k s . I n J u l y , permafrost i s a t a depth o f 0.3

-

1.1 m.

Next i n t h e e v o l u t i o n a r y s e r i e s a r e t h e t r a n s i t i o n biogeocenoses which 1 i e halfway between t h e f o r e s t s and t h e peatlands.

Hummocky bogs (BGC-4). These i n c l u d e s e c t i o n s w i t h s i n g l e t r e e s ( t h e remnants o f former f o r e s t s ) and bare s e c t i o n s ( F i g s . 3 and 4). According t o i n f o r m a t i o n from boreholes and e x p l o r a t i o n p i t s , t h e s t r u c t u r e o f t h e hummocks ( t h e y range f r o m 2 t o 8 m i n w i d t h and from 0.8 t o 1.5 m i n h e i g h t ) and o f depressions between them i s as shown i n Figs. 5 and 6.

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Moss-sedge fens (BGC-5). We s h a l l mention o n l y those which 1 i e between t h e f o r e s t s and t h e p e a t bogs (Fig. 7 ) . They a r e u s u a l l y lower t h a n t h e f o r e s t s e c t i o n s by 0.5

-

0.7 m and l o w e r than t h e bottom s u r f a c e o f t h e p e a t by 0.5

-

2 m. Permafrost i s a t a depth o f 0.5 t o 1.0 m.

Dry humnocky peat bogs (BGC-6). Permafrost i s a t a depth o f 0.4 m.

The p e a t hummocks a r e up t o 0.5 m i n h e i g h t and a r e covered w i t h dwarf b i r c h and v a r i o u s 1 ow scrubs (Ledum, Vacci nium, b1 ueberry

,

crowberry). Lichen

(Cladonia) occur between t h e hummocks.

A n t h i l l s occur on d r y p e a t bogs and i n c o n i f e r o u s f o r e s t s . There i s c o n s i d e r a b l e f i r e hazard on such p e a t bogs due t o t h e abundance o f 1 ichen. I n J u l y and i n t h e f i r s t t e n days o f August, t h e temperature a t a depth of 20

0

cm i s 2.0

-

3.5'~; a t a d e p t h o f 8 t o 1 0 m i t ranges from - 1 . 5 ' ~ t o -2.5 C.

The p e a t i s t h i c k e s t i n t h e c e n t r e and t h i n n e s t a t t h e edges. The same i s t r u e of permafrost: i t s t h i c k n e s s reaches several tens of meters i n t h e c e n t r e , e s p e c i a l l y beneath t h e hummocks, f r o m which snow i s swept away by wind. I t decreases t o j u s t a few meters a t t h e edges and then wedges o u t a t t h e c o n t a c t w i t h t h e f o r e s t s .

Now t h a t we have discussed t h e main biogeocenoses o f t h e t a i g a , we s h a l l t r y t o t r a c e t h e i r e v o l u t i o n which i s c l o s e l y r e l a t e d t o t h e development o f permafrost

.

P e r ~ i i a f r o s t and p a l u d i f ic a t i o n

I t i s p o s s i b l e t o s i n g l e o u t f o u r stages i n t h e h i s t o r y of development o f permafrost i n Western S i b e r i a .

I n t h e f i r s t two stages, t h e sea was r e g r e s s i n g and t h e ground was f r e e z i n g i n t h e n o r t h e r n p a r t o f Western S i b e r i a . The second stage continued u n t i l t h e s t a r t o f t h e thermal maximum .in t h e M i d d l e Holocene. The t h i r d stage c o i n c i d e d w i t h t h e thermal maximum. A t t h a t time, p a r t i a l thawing of pemnafrost was t a k i n g p l a c e from t h e surface and t h e permafrost 1 i m i i was

moving northwards approximately t o 67

-

68'~. Hence t h e permafrost 1 i m i t a t t h e surface was much f a r t h e r n o r t h t h a n a t present. However, permafrost d i d

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n o t thaw c o m p l e t e l y d u r i n g t h i s warmer p e r i o d . I t thawed t o a depth o f 100

-

150 m b u t remained i n t a c t below t h a t t o a depth of 300

-

350 m. T h i s permafrost i s s t i l l i n e x i s t e n c e today. 'The f o u r t h stage s t a r t e d a t t h e end o f t h e c l i m a t i c maximum and continues t o t h e p r e s e n t day. The c h a r a c t e r i s t i c f e a t u r e o f t h i s stage i s f r e e z i n g f r o m t h e surface which leads t o f o r m a t i o n o f a two-1 ayered p e r m a f r o s t mass. The p e r m a f r o s t 1 i m i t i s moving southwards.

I t was t h o u g h t t h a t t h e f o u r t h stage has been i n e x i s t e n c e f o r 2500 years. However, r e c e n t radiocarbon s t u d i e s have e s t a b l i s h e d t h a t t h e c o o l i n g t r e n d i n t h e n o r t h e r n p a r t of Western S i b e r i a s t a r t e d about 4500 years ago, i .e. 2000 y e a r s e a r l i e r t h a n p r e v i o u s l y thought." Therefore, p a l u d i fi c a t i o n and t h e development o f peatlands which a r e r e s p o n s i b l e f o r t h e f o r m a t i o n o f p e r m a f r o s t and degradation o f f o r e s t s have been going on i n t h e n o r t h e r n t a i g a f o r about 4500 years.

P a l u d i f i c a t i o n i n v a r i a b l y s t a r t s i n l o w - l y i n g areas ( F i g . 8 ) . A good i 1 lu s t r a t i o n of t h i s process can be found i n t h e contemporary sparse 1 arch-spruce f o r e s t s on 1 o w - l y i ng t e r r a i n (BGC-3). The r e l a t i v e 1 owering of contemporary depressions amounts t o 1

-

2 m; t h e y occur i n t h e e l e v a t e d p a r t s o f t h e p l a i n s . Deeper depressions and those 1 ocated lower down a r e e i t h e r f i l l e d w i t h p e a t o r t h e process of p e a t f o r m a t i o n i n them i s i n i t s f i n a l stages.

The h e a t exchange between t h e atmosphere and t h e ground changes w i t h t h e growth o f t h e moss and p e a t l a y e r and seasonal f r e e z i n g begins t o exceed summer thawing. Permafrost lenses a r e formed beneath t h e moss-peat l a y e r , which a r e q u i t e t h i n a t f i r s t (10 t o 30 cm). The i n c r e a s e i n t h e t h i c k n e s s of t h e p e a t r e s u l t s i n t h e d e s t r u c t i o n of t r e e s and scrubs; snow i s swept away f r o m such areas and t h i s i n t e n s i f i e s t h e f r e e z i n g process s t i l l f u r t h e r .

W i t h time, a r a i s e d p e a t bog i s formed i n t h e depression. Water f l o w s down f r o m t h e p e a t forming a s t r i p o f swampy ground around i t (BGC-5)

which r e c e i v e s a d d i t i o n a l water from t h e s i d e o f t h e f o r e s t ( F i g s . 7 and 8 ) .

*

N.A. K h o t i n s k i i

-

Paleogeographical r e s u l t s o f t h e c o r r e l a t i o n of stages i n

t h e development o f v e g e t a t i o n i n t h e n o r t h e r n p a r t o f Eurasia d u r i n g t h e Holocene. A u t h o r ' s t h e s i s . Moscow, 1972.

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T h i s swampy area (a moss-sedge bog) i s t h e s i t e o f a r a p i d development o f t h e moss-peat l a y e r . The moss hummocks g r a d u a l l y invade t h e f o r e s t ( F i g . 8 ) .

The moss hummocks freeze more r a p i d l y t h a n t h e ground between them.

A f r o z e n l a y e r i s developing beneath t h e hummock, as if p i e r c i n g through t h e

unfrozen ground. Moi s t u r e from t h e s u r r o u n d i ng unfrozen water1 ogged s o i 1 m i g r a t e s towards t h e f r e e z i n g f r o n t , where i t f r e e z e s which r e s u l t s -in heaving of t h e moss hurnniock. The hummock i s t h e n transformed t o a mound w i t h a m i n e r a l c o r e ( F i g s . 5, 6 and 8 ) . F u r t h e r growth o f t h i s mound depends m a i n l y on t h e abundance o f m o i s t u r e w i t h o u t which i t cannot heave. The m o i s t u r e i s e s p e c i a l l y abundant c l o s e t o a moss-sedge bog w i t h pools o f open water. The biogeocenoses w i t h t h e l a r g e s t mounds up t o 1 . 5

-

2.0 m i n h e i g h t occur n e x t t o such bogs. The f a r t h e r away from t h e bog, t h e s m a l l e r t h e mounds. The s t r i p o f hummocky m i c r o r e l i e f s t r e t c h i n g i n f r o n t o f t h e p e a t bog i s 200 t o 400 ni i n w i d t h . The f l a t t e r t h i s s t r i p , t h e more e x t e n s i v e t h e e f f e c t o f t h e p e a t bog.

Therefore t h e f i r s t s i g n s o f t h e suppressing e f f e c t o f a p e a t bog on t h e f o r e s t manifest themselves i n t h e growth o f moss humniocks on waterlogged s o i l a l r e a d y a t a d i s t a n c e o f 200 t o 400 m from t h e bog. Once e s t a b l i s h e d t h e hummocks themselves become t h e f o c i of development o f moss which begins t o spread over t h e a d j o i n i n g areas. Because of t o o much m o i s t u r e and poor a e r a t i o n o f t h e s o i 1, t h e t r e e s i n such areas a r e suppressed s t i 11 f u r t h e r . The advance growth i s reduced o r s t o p s a1 together. I n such places one can u s u a l l y see how Sphagnum moss 1 i t e r a l l y encroaches upon t h e 1 i c h e n cover. The C l i d o n i a l i c h e n beneath t h e moss hummocks a r e i n v a r i o u s stages of decomposition. I n t h i s way, a c o n i f e r o u s f o r e s t (BGC-1) i s r e p l a c e d by a s t u n t e d f o r e s t w i t h moss and p e a t hummocks, hummocky m i c r o r e l i e f

,

e t c . (BGC-2, F i g s . 2, 8 and 9).

C l o s e r t o a p e a t bog, t h e ground i s waterlogged f o r a l o n g e r p e r i o d of t i m e , t h e mounds a r e l a r g e r and t h e r e a r e 1 enses o f permafrost which remain f r o z e n throughout t h e sunwner. S i n g l e s t u n t e d t r e e s can be seen here avd t h e r e , w h i l e n e x t t o t h e p e a t bog t h e r e a r e no t r e e s a t a l l . T h i s i s -the domain o f t h e hurnrnocky bogs (BGC-4, F i g s . 3, 4, 8 and 9 ) . As moss begins t o

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p e a t bog. The peat l a y e r i s q u i t e t h i n a t f i r s t b u t becomes t h i c k e r l a t e r and t h e ground beneath t h e p e a t freezes t o a depth o f several tens o f meters. As a r e s u l t o f t h i s transformation, t h e s t u n t e d c o n i f e r o u s f o r e s t w i t h hummocky m i c r o r e l i e f (BGC-2) i s r e p l a c e d by hummocky bogs (BGC-4). As t h e peat bog continues t o expand, t h e swampy s t r e t c h o f l a n d w i t h moss humnocks and a hummocky m i c r o r e l i e f i n f r o n t of i t moves i n t h e d i r e c t i o n o f t h e f o r e s t ( F i g s . 8 and 9 ) . Thus a BGC w i t h hunimocky m i c r o r e l i e f -in f r o n t of t h e p e a t bog i s a s i g n o f an advancing bog and approaching d e s t r u c t i o n o f t h e f o r e s t .

With t i m e , small p e a t occurrences coalesce t o form a 1 arge peatland s t r e t c h i n g f o r tens of k i l o m e t e r s ( F i g s . 9 and 10). A t t h e same time, t h e p e r m a f r o s t i s l a n d s merge a l s o t o form a continuous permafrost mass t h e boundary of which moves southwards (Fig. 1 0 ) . The area occupied by f o r e s t s i s c o n t i n u o u s l y decreasing.

Changes i n t h e environmental components

We have seen how growth o f t h e moss cover and subsequent f o r m a t i o n o f a moss-peat l a y e r l e a d t o a t w o f o l d r e s u l t .

F i r s t l y t h e r e i s a d e t e r i o r a t i o n i n t h e growth c o n d i t i o n s o f t r e e s : t h e s o i l temperature drops; t h e s o i l pores a r e f i l l e d w i t h water which reduces t h e a e r a t i o n ; no new t r e e s appear on t h e moss-peat l a y e r ; t h e t r e e s b e g i n t o r o t mcre r a p i d l y . A1 1 t h i s leads t o t h e d e g r a d a t i o n o f t h e f o r e s t s .

Secondly, t h e r e i s a change i n t h e h e a t exchange between t h e s o i l and t h e atmosphere. As a r e s u l t o f t h i s , seasonal f r e e z i n g exceeds seasonal thawing, even if t h e c l i m a t e reniains unchanged. T h i s leads t o f o r m a t i o n o f small permafrost 1 enses, and l a t e r (once t h e t r e e s a r e destroyed, and t h e snow c o v e r i s g r e a t l y reduced and compacted) t o f o r m a t i o n o f a permafrost mass s e v e r a l t e n s o f meters i n t h i c k n e s s , which i n t u r n , a c c e l e r a t e s t h e d e g r a d a t i o n of t h e f o r e s t s . Once a p e a t bog has been e s t a b l i s h e d ( w i t h permafrost beneath i t ) , t h e r e i s a sharp i n c r e a s e i n p a l u d i f i c a t i o n , s i n c e p e r m a f r o s t c o n s t i t u t e s an impervious 1 ayer

.

The wind v e l o c i t y i ncreases

u n

t h e p e a t bog which i s d e v o i d of t r e e s . I f i n t h e f o r e s t t h e wind v e l o c i t y a t a h e i g h t o f 2

-

3 m i s 2

-

3 m/sec, on t h e p e a t bog t h e average v e l o c i t y

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increases t o 5

-

6 ni/sec o r even 1 0

-

1 2 m/sec. The t r e e s growing a t t h e boundary between t h e p e a t bog and t h e f o r e s t a r e o f t e n deformed by wind.

The i n c r e a s e i n t h e area of w e t bogs and p e a t bogs reduces t h e area o f t h e h a b i t a t o f t h e t a i g a animals, as w e l l as t h e number o f t h e animals themselves, such as moose, bear, s q u i r r e l

,

sable, chipmunk, grouse, woodpecker, c r o s s b i l l

,

cuckoo, e t c .

L i m i t s of southward m i g r a t i o n of permafrost

T h e o r e t i c a l c a l c u l a t i o n s i n c l u d i ng model 1 i ng i n a h y d r o i n t e g r a t o r showed* t h a t t h e southern '1 'imi t o f p o t e n t i a l development o f permafrost 1 ie s 400 t o 450 km s o u t h o f t h e present boundary o f permafrost i n t h e peatlands.

Freezing may o c c u r under p r e s e n t c l i m a t i c c o n d i t i o n s , i f t h e r e i s a change i n t h e h e a t exchange between t h e s o i l and t h e atmosphere which i s c o n t r o l l e d by t h e moss ( o r r a t h e r p l a n t ) and t h e snow covers. I n t h i s zone o f p o t e n t i a l f r e e z i n g , a 1 arge-scale development o f pennafrost w i l l n o t t a k e p l a c e o n l y under c o n d i t i o n s o f d i s s e c t e d r e 1 i e f

,

where good drainage prevents i n t e n s i v e p a l u d i f i c a t i o n , w h i l e i s o l a t e d small p e a t bogs cannot expand l a t e r a l l y and coalesce. Permafrost can develop here o n l y i f t h e area i s d e f o r e s t e d by man, as a r e s u l t of which snow i s swept away t h u s i n c r e a s i n g t h e depth o f w i n t e r f r e e z i n g . I t i s known t h a t t h e l i m i t o f p o s s i b l e thawing of permafrost l i e s

0

approximately a t 68 N, i .e. 580

-

620 km n o r t h o f t h e present southern boundary o f permafrost. T h i s thawing may a l s o occur under present c l i m a t i c c o n d i t i o n s , i f t h e moss cover i s s y s t e m a t i c a l l y removed and snow accumulation i s c o n t r o l l e d .

A.P. T y r t i kov** a r r i v e d a t s i m i l a r conclusions. He t h i n k s t h a t i n t h e 300 t o 500 km wide b e l t a d j o i n i n g t h e southern boundary of permafrost, systematic removal o f peat, o r i t s m i n e r a l i z a t i o n , and accumulation o f snow t o a depth of a t l e a s t 1 m may r e s u l t i n thawing o f a 1 0 m t h i c k permafrost l a y e r i n 10 t o 20 years. I t i s known t h a t a f t e r t h e removal o f moss t h e s o i l temperature a t a depth of 20 cm w i l l r i s e by 11

-

1 5 ' ~ i n t h e sumner; a 20 cm t h i c k snow l a y e r w i l l i n c r e a s e t h e s o i l temperature by 2

-

~ O C , w h i l e a snow

c o v e r 60 t o 70 cm i n depth w i l l r e s u l t i n a temperature r i s e o f 6

-

7 ' ~ .

*

V.P. Chernyad'ev

-

"Trudy PNIIS,It Vol. 2, 1970.

(12)

Such a r e t h e s c a l e and p o s s i b l e r e s u l t s o f changes i n t h e h e a t exchange between t h e s o i l and t h e atmosphere, which can be achieved by c o n t r o l 1 in g t h e moss and t h e snow covers.

Causes of p a l u d i f i c a t i o n and degradation of f o r e s t s i n Western S i b e r i a

Some i n v e s t i g a t o r s r e l a t e t h e p a l u d i f i c a t i o n process and t h e degradation of f o r e s t s t o a c o o l e r c 1 imate, assuming t h a t permafrost i s degraded d u r i n g warmer p e r i o d s and i s r e s t o r e d when a c o o l i n g t r e n d s e t s i n again. There i s no doubt t h a t c l i m a t i c f l u c t u a t i o n s , and c o o l i n g t r e n d s i n p a r t i c u l a r , a f f e c t t h e processes o f p a l u d i f i c a t i o n and permafrost f o r m a t i o n . However, t h e y cannot be regarded as t h e d e t e r m i n i n g f a c t o r s . The mosses a r e s u f f i c i e n t l y aggressive under t h e physico-geographical c o n d i t i o n s p r e v a i l i n g i n t h e n o r t h e r n p a r t o f Western S i b e r i a ( c o o l summers, more p r e c i p i t a t i o n t h a n evaporation, poor drainage owing t o f l a t t e r r a i n , e t c .)

.

The e c o l o g i c a l amp1 i tude o f mosses i s c o n s i d e r a b l e and i t i s u n l i k e l y t h a t t h e temperature r i s e o f 1 .0

-

1

.!iOc,

which occurred between t h e beginning o f t h e c e n t u r y and a b o u t 1950, had a d e t r i m e n t a l e f f e c t o n t h e i r growth. Q u i t e t h e c o n t r a r y , perhaps. I n t h e n o r t h e r n t a i g a o f Western S i b e r i a , t h e growth o f moss i n v a r i a b l y c r e a t e s c o n d i t i o n s under which seasonal f r e e z i ng exceeds seasonal thawing. The f i n a l outcome o f t h i s i s f o r m a t i o n o f permafrost. I n t h i s r e g i o n t h e thicknesses o f t h e moss, moss-peat and peat l a y e r s a r e q u i t e d i f f e r e n t and range from a few c e n t i m e t e r s ( t h e moss l a y e r ) t o several meters ( p e a t ) . The t h i c k n e s s of permafrost i s n o t u n i f o r m e i t h e r . I t ranges f r o m s e v e r a l t e n s o f c e n t i m e t e r s t o several t e n s o f meters. We have a l r e a d y seen t h a t t h e r e i s a d i s t i n c t g e n e t i c r e l a t i o n s h i p between t h e biogeocenoses w i t h d i f f e r e n t thicknesses o f moss, p e a t and permafrost. A l l t h i s i n d i c a t e s t h a t t h e growth o f moss, p a l u d i f i c a t i o n , f o r m a t i o n o f p e a t bogs and formation of p e r m a f r o s t a r e we1 1 -defined and continuous processes, which may slow down under unfavourable c o n d i t i o n s . It was p o i n t e d o u t e a r l i e r t h a t , depending o n t h e moss-peat 1 ayer and t h e amount o f snow, t h e r e i s a d i s t a n c e o f 1000 km between t h e southern 1 i m i t o f p o t e n t i a l f o r m a t i o n of permafrost and t h e southern l i m i t o f i t s p o t e n t i a l thawing. T h i s v e r y f a c t i n d i c a t e s t h a t

In

t h e t a i g a s l i g h t temperature changes o v e r a p e r i o d o f several decades cannot be t h e d e c i s i v e f a c t o r a f f e c t i n g t h e changes i n permafrost w i t h time.

(13)

It f o l l o w s t h a t degradation o f f o r e s t s and t h e accompanying d e t e r i o r a t i o n i n t h e environmental c o n d i t i o n s a r e n o t due t o general c l i m a t i c f a c t o r s (a d r o p i n t h e ambient temperature, s h o r t e r summers, i ncreased atmospheric p r e c i p i t a t i o n ) , which a r e s t i l l beyond t h e grasps of human i n f l uence, b u t t o 1 ocal causes: t h e growth o f moss ; t h e development o f p e a t bogs, f o r m a t i o n and i n c r e a s e i n t h e area and t h i c k n e s s of permafrost. Development o f permafrost leads i n t u r n t o an i n t e n s i f i c a t i o n o f p a l u d i f i c a t i o n , etc.. What we have here i s " s e l f - i n t e n s i f i c a t i o n " of processes, t h e f i n a l outcome o f which i s development of p e a t bogs w i t h u n d e r l y i n g permafrost and t h e d e s t r u c t i o n o f f o r e s t s . I t i s now p o s s i b l e t o s t o p these processes. The n e c e s s i t y t o c o n t r o l f r e e z i n g and thawing o f s o i l by agro- engineering methods was p o i n t e d o u t by M . I . Sumgin*, t h e founder of g eocryo 1 ogy

.

P

.

I. Koloskov** developed t h e main p r i n c i p l e s of c o n t r o l 1 i ng t h e h e a t exchange between t h e s o i l and t h e atmosphere, which a r e e s s e n t i a l l y as f o l l o w s . By c o n t r o l l i n g t h e s o i l and v e g e t a t i o n cover, i t i s p o s s i b l e t o i n c r e a s e t h e i n f l o w o f h e a t i n t h e sumner and t o reduce t h e heat l o s s i n w i n t e r . Removal o f nioss increases t h e s o i l temperature by 10

-

1 5 ' ~ i n t h e summer. T h i s p o i n t s t o t h e n e c e s s i t y t o develop methods o f moss removal. The s i m p l e s t method i s 1 iming. Lime d e s t r o y s t h e moss, n e u t r a l i z e s t h e s o i l a c i d s , and i n t e n s i f i e s t h e development o f microorganis~ns which decompose t h e p l a n t remains. The h e a t i n g o f s o i l irr~proves once moss i s destroyed. It i s p o s s i b l e t h a t i n some cases moss can be burned.

I n some p a r t s o f t h e n o r t h e r n t a i g a i n Western S i b e r i a on f l a t t e r r a i n w i t h o u t ground i c e , t h e b u r n i n g o f moss may c r e a t e f a v o u r a b l e c o n d i t i o n s f o r a renewed growth of f o r e s t s . I n o t h e r p a r t s , where t h e r e i s ground i c e , f i r e s l e a d t o an i n t e n s i f i c a t i o n o f p a l u d i f i c a t i o n , and sparse f o r e s t s w i t h c o t t o n grass and hummocks a r e r e p l a c e d by moss-sedge bogs. I n sparse f o r e s t s t h e r e i s u s u a l l y a t h i c k c o v e r o f l o o s e snow which p r o t e c t s t h e ground f r o m severe c o o l i n g i n w i n t e r . The bare s e c t i o n s remaining a f t e r a f i r e o f f e r 1 i t t l e p r o t e c t i o n a g a i n s t wind, t h e snow cover becomes t h i n n e r and

*

M. I . Sumgin

-

Vechnaya merzlota pochvy v predelakh SSSR (Permafrost i n t h e

U

.

S. S. R. )

.

Moscow-Leni ngrad, 1937.

**

P. I. Koloskov

-

I s s l edovaniya vechnoi nierzl o t y v Yakuti i (Permafrost research i n Yakutiya).

Issue 2,

MOSCOW, 1950.

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more compact, which i n t e n s i f i e s t h e f r e e z i n g process and f o r m a t i o n o f permafrost. O c c a s i o n a l l y t h i s n a t u r a l process i s aggravated by i r r a t i o n a l a c t i v i t i e s of man ( t r e e f e l l i n g , tramp1 i n g down). For example, a sparse f o r e s t was growing near t h e s e t t l e m e n t o f Nyda i n t h e e a r l y p a r t o f t h i s c e n t u r y . NOW, however, t h e r e i s a t u n d r a - l i k e swampy area. The same a p p l i e s t o t h e surroundings o f T a z o v s k i i

,

Nadym, Salekhard, and o t h e r s e t t l e m e n t s l o c a t e d 'in t h e zone o f sparse l a r c h f o r e s t s * .

Uncompacted snow p r o t e c t s t h e s o i l f r o m f r e e z i n g : a snow cover 60

t o 70 cm i n d e p t h r a i s e s t h e s o i l temperature by 6

-

7 ' ~ . T h i s p o i n t s t o t h e n e c e s s i t y t o develop methods of snow accumulation i n w i n t e r . Here again, t h e s i r n p l e s t method i s t o determine t h e optimum p r o p o r t i o n o f f o r e s t s e c t i o n s w i t h scrubs (dwarf b i r c h , a l d e r scrubs, w i l l o w ) and t r e e l e s s s e c t i o n s w i t h grass and scrubs, which would ensure a u n i f o r m accumulation o f snow several tens o f c e n t i m e t e r s i n depth. Blackening of snow i n t h e s p r i n g would reduce t h e me1 t i n g p e r i o d by two o r t h r e e weeks, which would i n c r e a s e t h e i n f l o w o f h e a t

i n t h e s p r i n g and sunnner.

I t should a l s o be considered t h a t pumping o u t o i l from t h e i n t e r i o r o f t h e E a r t h may r e s u l t i n subsidence and may i n t e n s i f y t h e p a l u d i f i c a t i o n process. I t i s known f r o m experience t h a t i n j e c t i o n of water i n t o t h e v o i d s f o r m e r l y occupied by o i l prevents subsidence. Since t h e r e i s an excess of m o i s t u r e i n t h i s r e g i o n , t h e removal o f water would slow down t h e p a l u d < f i c a t i o n process.

Development of p e a t d e p o s i t s can be doubly p r o f i t a b l e : i t would p r o v i d e o r g a n i c raw m a t e r i a l s and would l e a d t o degradation o f permafrost on s e c t i o n s f r o m which p e a t has been removed. With t i m e an a f o r e s t a t i o n programme can be s t a r t e d on such s e c t i o n s .

T h i s b r i e f o u t 1 i n e o f measures may he1 p t o s t o p t h e pal u d i f i c a t i o n and d e s t r u c t i o n o f f o r e s t s and p r e v e n t a general d e t e r i o r a t i o n o f n a t u r a l environment

.

*

V. V. Kryuchkov

-

K r a i n i i Severa: Probl emy r a t s i o n a l 'nogo i spol 'zovaniya p r i r o d n y k h resursov. (Far North: Problems o f r a t i o n a l u t i l i z a t i o n o f n a t u r a l resources). "Mysl ,I1 Moscow, 1973.

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- a m tn

e03.-lz

-,

( D o - 3 - 3 3 3 . ID-ID 4,s i D 1 - 7 W O C O W P t n S t n S S I D 0 3 * 3 3-0 3 P r D 0- T * w S 7 w 3 - w t n "' -hE!

E

3, 3 - 5 0 7 -4, -h$Z. s 3 0 0 1

Zrn

2 . Z P I D 0 sul J U S I I 0 ID 1 - 1 . m I D + t n Q 0 3 X - - " w 3 n * t n I tn ID - 0 1 - * 3 w -1.0

-

I D = - I < w d . 3 t n 0 r D I tn73 w 3 - 5 0 I D * " I D 3 - - I o n - P . w ID c n l - l - w o w -h r * t n S O I I P S d.7 ID ID *ID N U O O 3 t n w l - l - - h 5 l-l- 0 d - 3 o N - - O O W 0 -1. -1. 0 l-l- 0- - h I * J J I D - o t n m U ' 3 3 e m 3

-

s 3- - I 0 I I a3 D 0 3 - h N C 0 0 3 t n x - mb=,qcr< 1 3 0 - r < N - 3 w 3 ID 3 u J 3 tn I n o w -

- = g

3 I D O W w I D U O - 1 . - 0 I W I P O 0 3 2.5 w A. O w 3 - ID < P 3, w ID c n - 5 m u - l ID 0 - S - U P S rD w O O N I D I G ) -h O U I D O -ID I d - c t - 1 - I w

-

5 0 0 7 I -ID % I D .

(16)

Figure 2

Stunted coniferous f o r e s t on an elevated section of a plain (BGC-2a) surrounded

on

a1 1 sides by advancing hummocky bog and peat bog. Peaty-gleyed-podzolic, sandy s o i l . Peat layer 5

-

12 cm i n thickness. Snow depth 70

-

80 cm. Ground generally unfrozen b u t frozen lenses a r e occasionally present beneath l a r g e r hummocks 70 t o 80 cm in height. The lenses a r e 0.5

-

1.5

m

thick and do not thawoevery summer. Ground temperature a t a depth of 8

-

9

m

ranges from 0.2 t o 0.5 C.

Figure 3

Hummocky bog with dying t r e e s and lenses of frozen ground u p t o 1 . 5

-

2.0

m

i n thickness (BGC-4a). Formed in an area formerly covered by a stunted coniferous f o r e s t ( BGC-2a)

.

(17)

1,

F i g u r e 4

-

a

.-

.

mc**

Hummocky bog (BGC-4a) formed i n an area f o r m e r l y covered by f o r e s t as i n d i c a t e d by stumps and t r e e t r u n k s b u r i e d i n t h e peat.

Figure

5

Cross s e c t i o n through a hummock i n a hummocky bog. The moss-peat l a y e r i s about 20 cm t h i c k near t h e t o p o f t h e humnock and about 10 cm a t t h e

I edges. The e x p l a n a t i o n i s t h a t t h i s hummock w i t h i t s mineral core was formed from a p e a t hummock which was 10 cm h i g h e r than t h e surrounding moss cover. The p e a t hummock f r o z e more r a p i d l y than i t s surroundings, which l e d t o heaving and e v e n t u a l l y t o f o r m a t i o n o f a hummock w i t h a mineral c o r e ( f o r more d e t a i l see t e x t ) .

(18)

F i q u r e 6

I Y

Cross s e c t i o n through mounds and a depression between them i n a hummocky bog (BGC-4a). 1

-

boreholes, 2

-

moss-peat l a y e r , 3

-

medium-grained sand and supes, 4

-

peaty sand, 5

-

t o p and base of

permafrost, 6

-

b u r i e d remnants of t r e e s , 7

-

i c e 1 enses. The mounds f r e e z e more e x t e n s i v e l y than t h e depressions. T h i s leads t o m i g r a t i o n o f m o i s t u r e towards t h e freezing f r o n t and increases t h e i c e c o n t e n t t o 30

-

40%. As a r e s u l t t h e mounds c o n t i n u e t o heave. The i c e content i s lower i n t h e depressions. If t h e w i d t h of t h e depressions exceeds 8

-

10 m, t h e f r o z e n l a y e r beneath them w i l l thaw completely.

Figure 7

I n f r o n t : a hummocky bog on a g e n t l e slope (BGC-4b) advancing on a f o r e s t . I n t h e d i s t a n c e (below BGC-4b) : a 1 ow moss-sedge bog (BGC-5) w i t h an a d j a c e n t p e a t bog which r i s e s above t h e moss and sedge bog by about 3 m (see a l s o Fig. 8 ) .

(19)
(20)

F i g u r e 8

P a l u d i f i c a t i o n i n a depression and development o f a p e a t bog. I

-

The growth of t h e moss-peat l a y e r l e a d s t o a d e t e r i o r a t i o n of t h e hydrothermal and a e r a t i o n regimes of t h e s o i l , so t h a t t h e t r e e r o o t s can no l o n g e r e x i s t t h e r e . A t t h e same time, t h e moss-peat l a y e r r a d i c a l l y changes t h e h e a t exchange between t h e atmosphere and t h e s o i l . As a r e s u l t o f t h i s , t h e depth o f f r e e z i n g exceeds t h a t o f thawing which leads t o formation o f permafrost lenses. 'The water f l o w i s d i r e c t e d towards t h e depression which r e s u l t s i n w a t e r l o g g i n g and a r a p i d growth o f moss which i s subsequently transformed t o peat. I 1

-

P a l u d i f i c a t i o n l e a d s t o f o r m a t i o n o f a r a i s e d peat bog i n p l a c e of t h e depression. Snow i s swept away f r o m t h e bog. T h i s i n t e n s i f i e s t h e f r e e z i n g process and r e s u l t s i n f o r m a t i o n o f permafrost several t e n s o f meters i n thickness. A depression i s formed between t h e p e a t bog and t h e f o r e s t which r e c e i v e s w a t e r b o t h fro111 t h e s i d e o f t h e f o r e s t ( l o c a t e d i n t h e h i g h e r p a r t of t h e p l a i n ) and from t h e p e a t bog. T h i s l e a d s t o f o r m a t i o n o f a waterlogged s t r e t c h o f l a n d between t h e bog and t h e f o r e s t , i .e., a moss-sedge bog (BGC-5), which i n t u r n p a l u d i f i e s t h e zone b o r d e r i n g t h e f o r e s t , where a hum~iiocky bog (BGC-4b) and a s t u n t e d c o n i f e r o u s f o r e s t w i t h moss-peat humniocks and a hummocky r e l i e f a r e formed (BGC-2b). Once t h e r a i s e d p e a t bog i s formed, p a l u d i f i c a t i o n o f t h e a d j a c e n t f o r e s t i n t e n s i f i e s . I11

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r a i s e d , d r y , f r o z e i , p e a t bog w i t h scrubs and l i c h e n . Water f l o w i n one d i r e c t i o n o n l y

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towards t h e f o r e s t . The upward growth o f t h e p e a t bog stops, i t spreads sideways, which g r e a t l y i n t e n s i f i e s p a l u d i f i c a t i o n and d e s t r u c t i o n of t h e f o r e s t as w e l l as f o r m a t i o n o f permafrost.

1

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d i r e c t i o n of t h e water f l o w , 2

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t h e permafrost boundary, 3

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b u r i e d t r e e t r u n k s , 4

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p e a t hummocks, 5

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peat,

(21)
(22)

F i g u r e 9

Degradation of f o r e s t s and development of p e a t bogs and permafrost i n t h e n o r t h e r n t a i g a o f Western S i b e r i a .

I

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f o r e s t s a t t h e end o f t h e p o s t - g l a c i a l thermal maximum i n t h e M i d d l e Holocene. M o s t l y normal, well-developed t r e e stands a l t e r n a t i n g w i t h wet and swampy depressions. Unfrozen ground everywhere. I I

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p a l u d i f i c a t i o n o f 1 o w - l y i ng areas 1 eads t o f o r m a t i o n o f permafrost and d e s t r u c t i o n o f f o r e s t s

i n t h e more severe c l i m a t e which f o l l o w e d t h e thermal maximum. I11

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water f l o w i n g from r a i s e d p e a t bogs i n t e n s i f i e s t h e p a l u d i f i c a t i o n of surrounding f o r e s t s , which i s accompanied by a sharp i n c r e a s e i n t h e area and t h i c k n e s s of permafrost. I V

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a t p r e s e n t many i s o l a t e d occurrencies of p e a t have coalesced t o form continuous peatlands which occupy up t o 60

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70% o f t h e area o f t h e n o r t h e r n t a i g a i n Western S i b e r i a . 'The f o r e s t s which a t one t i m e covered most of t h e t e r r i t o r y a r e now represented by i s o l a t e d t r e e stands i n t h e upper p a r t s o f t h e p l a i n s ; t h e y a r e doomed t o d e s t r u c t i o n . The numbers above t h e drawings i n d i c a t e t h e biogeocenoses (BGC). The s c a l e a t t h e r i g h t margin i n d i c a t e s t h e a l t i t u d e s above t h e sea l e v e l . The o t h e r symbols a r e as i n F i g . 8.

(23)

Formation of two-layered p e r m a f r o s t i n t h e n o r t h e r n t a i g a o f Western S i b e r i a .

I

-

permafrost occurrence a t t h e end o f t h e thermal maximum i n t h e M i d d l e Holocene. Most o f t h e t e r r i t o r y was covered by f o r e s t s . I 1

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permafrost occurrence a t present: l a

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small peat hogs ( t h e p e a t l a y e r 0.5

-

1

.0

m i n t h i c k n e s s ) ; 2a

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1 arge p e a t bogs ( t h e p e a t 1 ayer several meters t h i c k ) ; 2

-

t h e 1 i m i t o f occurrence o f permafrost. The s c a l e a t t h e l e f t margin i n d i c a t e s t h e depth ( i n m).

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