Interactions between vegetation and permafrost on some CALM grids in Russia

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1 Permafrost, Phillips, Springman & Arenson (eds) 2003 Swets & Zeitlinger, Lisse, ISBN Interactions between vegetation and permafrost on some CALM grids in Russia N.G. Moskalenko Earth Cryosphere Institute, Russian Academy of Sciences, Siberian Branch, Moscow, Russia ABSTRACT: Interactions between vegetation and permafrost were studied by the author on four sites of the CALM (Circumpolar Active Layer Monitoring) project in different bioclimate zones of Russia. Frequency of plant species and depths of seasonal thaw were measured on these grids at each of the grid nodes. The collected data were subjected to statistical and graphic analysis. The minimum active layer thickness occurred on peatlands with Rubus chamaemorus, Ledum decumbens or Ledum palustre, Sphagnum and Cladina as dominants. Maximum thaw depths in the tundra zone are on bare patches, or patches partially covered by grass-prostrate dwarf shrub-lichen communities. The places with deep thaw in the northern taiga are peatland hollows occupied by sedge-moss mires. The most reliable species indicator of minimum thaw depth ( m) is Rubus chamaemorus. 1 INTRODUCTION The significant influence of vegetation cover dynamics on geocryological conditions was noted long ago (Gorodkov, 1932; Koloskov, 1925; Sumgin, 1937 etc.). The most thorough studies on the interactions between vegetation and permafrost were performed by Tyrtikov (1969, 1979). He proved convincingly that freezing and thawing conditions change in response to the vegetation dynamics. Increases in moss and lichen cover thickness result in the reduction of seasonal thaw depths, and decreases in soil and ground temperatures. However, Tyrtikov did not study spatial variability in seasonal thaw related to the horizontal structure of the vegetation cover. These studies were initiated later. In particular, the author performed such studies in the forest-tundra and tundra zones of Western Siberia (Moskalenko, 1995), and then continued them on four grids of the CALM project in Russia. These studies made it possible to distinguish plant communities and plant species that can be used as phytoindicators of the depth of seasonal thaw. Phenological observations of plants were made as well. The same approach was suggested in the ITEX Manual (Molau, 1993) to estimate the climatic warming. In addition, annual variability in the frequency of plant species was studied related to changes in seasonal thaw depth, thawing index of air temperatures, and summer and winter precipitation. in the European part of Russia; and the fourth, 30 km south from the town of Nadym in Western Siberia (Fig.1). Permanent stakes were installed at distances of 100 m (1 km 2 grid) or 10 m (100 m 2 grid) from one another on these sites to form a regular grid pattern (11 11). A brief description of the observation grids is given in Brown et al., (2000). The frequency of plant species and depths of seasonal thaw were measured at each stake, except for those in lakes. Four to five replicate measurements of thaw depths were made using a metal rod, in the end of August or beginning of September, when the thaw depth was close to the maximum. The frequency of plant species was determined at 100 points in 1 m 2 assessment squares temporarily established near the stakes. The collected data were treated by statistical and graphic analysis using Surfer 7 and Statgraph software. The 1 km 2 CALM grids (Parisento and Marre-Sale) are located in the subzone of typical tundra. The gentle hills dissected by deep gullies, creek valleys, lake 2 DESCRIPTION OF THE OBSERVATION GRIDS In this paper, the results of observations made on two 1km 2 and two 100 m 2 CALM grids are described. The first grid is found on the Gydan Peninsula; the second, in the Yamal Peninsula; the third, in the Pechora delta Figure 1. Location of the observation grids: B.Bolvansky, M.Marre-Sale, P.Parisento, N.Nadym (1:40 M scale). 789

2 basins and drained lakes are characteristic. They are on sandy sediments overlain by peat in some places. The Parisento grid is on the Gydan Peninsula, 70 km from the settlement of Tadibijacha near Lake Parisento. A series of lake terraces (I-III) with gentle hill topography and elevations varying from 10 to 30 m, are distinguished around the lake. These surfaces are occupied by polygonal dry grass-prostrate dwarf shrub-lichen tundra combined with windblown sandy patches, and sands with polygonal moist sedge-hemiprostrate dwarf shrublichen-moss tundra. Flat terrace surfaces are covered by complexes of hemiprostrate dwarf shrub-sedge-moss bogs with fragments of peatlands and tundra. Bogs in combination with shrublands are found in creek valleys. Measurements of the active layer thickness on this grid were made in 1992, 1993 and Maximum thaw depths were registered in 1995, which was the warmest year for this period. In this year, the average thaw depth reached 95 cm. The minimum thaw depths were registered in 1992, the coldest summer season. The mean thaw depth in this year was only 82 cm. The frequency of plant species was determined in For each grid node, the interannual node variability (%) was calculated using data on spatial variability of thaw depths ([(Z I Zm)/Zm]), where Z I is a nodespecific thaw depth for a given year, and Zm is the mean thaw depth for the whole grid in the same year. The comparison of these values for different for a given node makes it possible to determine the degree of variability of this parameter for particular landscape conditions. On average, the interannual node variability was small (13%). The minimum values of this parameter are characteristic of boggy sites, whereas the highest ones are typical of tundra and valleys with significantly complex vegetation cover. The maximum seasonal thaw depth at the Parisento grid is observed on the tops and slopes of hills with windblown sands. The minimum active layer thickness is typical of flat surfaces with fragments of peatlands on which Rubus chamaemorus, Eriophorum vaginatum, Ledum decumbens, Sphagnum angustifolium, Cladina stellaris, and Cladina rangiferina predominate. The Marre-Sale grid is located on the Kara Sea coast near the polar weather station of the same name. The observation grid encompasses the areas of the second and third alluvial-marine plains with elevations ranging from 10 to 25 m a.s.l. On gentle hills, polygonal dry grass-prostrate dwarf shrub-moss-lichen tundra predominates in combination with windblown sands, and moist sedge-hemiprostrate dwarf shrub-lichen-moss tundra. Sedge-moss mires with fragments of peatlands occupy the bottoms of gullies and drained lakes. Measurements of seasonal thaw depths were performed from 1995 to For the 7-year-long period of our studies (Vasiliev et al., 1998), 1995 was the warmest year, and the mean thaw depth reached cm. In the coldest year, 1999, it decreased to 91.6 cm. Places with deep thaw are most common at this grid: polygonal dry tundra with a mean thaw depth of 119 cm. The places with shallow thaw are confined to mires with fragments of peatlands, and occupy just small patches. The estimated mean thaw depth for them is 76 cm. The mean value of interannual node variability (25%) at the Marre-Sale grid is almost two times higher than that at the Parisento grid (13%). This is explained by the greater ruggedness of the topography at the Marre-Sale grid and the prevalence of deeply thawing dry tundra with the greatest interannual node variability. The Bolvansky grid (100 m 2 ), located in the Pechora River delta was established in the southern tundra subzone on the marine plain IY ( m a.s.l). This plain is composed of Late Quaternary marine deposits represented by loamy sands and clay loams, less often by sands. It has a gentle hilly topography and is dissected by lake basins and drainages. It is the most western CALM grid in the Russian sector of the Arctic region (Fig.1). The gentle hills are covered by sedge-low shrub-moss-lichen spotty and hummocky tundra. Forbmoss willow stands with Betula nana are found on the foothills. Sedge-Hypnum mires develop in boggy bottoms of lake basins. Observations of seasonal thaw depth at the Bolvansky grid were made in The frequency of plant species was determined in The mean thaw depth reached 70 cm in cold 1999, and it increased to 111 cm in warm The comparison of plots covered by different vegetation shows that the minimum active layer thickness is observed under Rubus chamaemorus-hemiprostrate dwarf shrub-moss-lichen communities confined to poorly drained peaty pools, cryogenic troughs and microhollows. Somewhat deeper active layer is characteristic of boggy sedge-hemiprostrate dwarf shrubmoss tundra and sedge-hypnum bogs. The maximum thaw is registered on bare patches, or patches partially covered by prostrate dwarf shrub-lichen communities. The margins of a hill in the southeastern part of this grid are covered by shrubs and have very deep thaw. In some places, lowering of the permafrost table was observed. The average interannual node variability of thaw depth at this grid was 17%. Like the other grids, the highest values of this parameter are typical of dry tundra and places with shrubland. The Nadym grid (100 m 2 ) is found in the northern taiga, on a flat boggy surface of the lacustrine-alluvial plain (third terrace) with elevations of m a.s.l. The plain is composed of sands with loamy interlayers and a peat layer on the top in some places (Melnikov, 1983). The CALM grid includes flat (Rubus chamaemorus-ledum palustre-sphagnum-cladina) and hummocky (Betula nana-ledum palustre-moss-lichen) 790

3 peatland. This peatland is bordered by a sedge-moss mire on the south and east. The mire surface is complicated by small (up to 50 cm in height) growing frost mounds resulting from both seasonal and long-term heaving. Measurements of the active layer thickness on the grid were made in the beginning of September in Additional data are available from monitoring seasonal thaw depths in similar conditions, performed since 1972 on permanent 10-m 2 plots (Moskalenko et al., 2001). For the period of observations on the CALM grid, the maximum thaw depth (137 cm) was registered in This year had the greatest sum of summer air temperatures, which is tightly correlated to thaw depth (Pavlov, 1998). As well as at the Marre-Sale grid, minimal thaw depths were registered in 1999, when the mean thaw depth at the Nadym grid decreased to 125 cm. The frequency of plant species at this grid was determined in The minimum thaw depth (67 cm) is typical of a flat surface of the peatland with Rubus chamaemorus-ledum palustre-sphagnum-cladina, which occupies the northwestern part of the grid. The places with deep thaw are allocated to hollows occupied by sedge-moss mires. The interannual node variability of thaw depths at this grid averaged 20%. The minimum values of this parameter are characteristic of the flat peatland. The same regularity was observed on the plots where observations were made since For the period of , the value of interannual variability of thaw depths at the peatland reached 14%. The greatest values of interannual variability (34%) are typical of the peat bog. Hence, small values for interannual variability of thaw depths are observed on peatlands, the active layer of which consists of peat with a well-developed moss-lichen cover cm thick. On the contrary, significant interannual variations in the thaw depth are characteristic of excessively moistened mires. In the latter, the depth of seasonal thawing varies significantly depending on meteorological conditions of a particular year. In peatlands, a thick layer of peat and relatively thick moss-lichen cover play a stabilizing role and smooth the influence of weather conditions on the active layer thickness. 3 ANALYSIS OF THE RESULTS This investigation shows that the minimum values of seasonal thaw depths are observed under Rubus chamaemorus-ledum palustre-sphagnum-cladina cover on peatlands (Table 1). The maximum thaw depth is found in the tundra zone on sandy dry sites deprived of vegetation cover, or covered by prostrate dwarf shrub-lichen communities. Areas with deep thaw in the northern taiga (Nadym) are confined to large sedge-moss pools within peatlands, and to bogs. The highest coefficients of correlation between the Table 1. Vegetation and thawing depths (h th ) on the grids. Grid Vegetation h th in cm *K Parisento Rubus chamaemorus Eriophorum vaginatum- ( ) Cladina rangiferina Salix nummularia Alectoria ochroleuca ( ) Sphaerophorus globosus Marre-Sale Rubus chamaemorus Eriophorum angustifolium- ( ) Sphagnum balticum Salix nummularia Polytrichum strictum ( ) Bolvansky Rubus chamaemorus Ledum palustre- ( ) Spagnum angustifolium Dryas octopetala Alectoria ochroleuca ( ) Nadym Rubus chamaemorus Ledum palustre- ( ) Cladina rangiferina Carex rotundata Sphagnum lindbergii ( ) *K Coefficient of correlation (confidence level). 791

4 thaw depth and plant communities are obtained for the Nadym grid, distinguished by flat relief and less vegetation cover complexity in comparison with the other grids (Table 1). The lowest coefficients of correlation are found for the Marre-Sale grid (Table 1) with significant ruggedness of the topography and high complexity of the vegetation. The correlation between separate plant species and seasonal thaw depth is lower than that between plant communities and the thaw depth. Among the investigated plant species, Rubus chamaemorus is the most reliable indicator of the minimal thaw depth at all studied grids. Figure 2 presents an example of spatial variations in the seasonal thaw depths for 1992 and the frequency of separate plant species at the Parisento grid. In contrast to Eriophorum vaginatum and Rubus chamaemorus found on poorly drained peaty sites with shallow thaw depths, Salix nummularia, Alectoria ochroleuca, A. nigricans and Sphaerophorus globosus are characteristic of deeply thawing dry places. Salix nummularia grows in similar conditions at the Marre-Sale grid, and Alectoria at the Bolvansky grid. Within the latter grid, places with minimum thaw are occupied by Ledum palustre. In the northern taiga (the Nadym grid), poorly drained peat sites with shallow thaw are occupied not only by Rubus chamaemorus and Ledum palustre but also Cladina stellaris and Cladina rangiferina. Nondrained excessively moistened pools with deep thaw are characterized by Sphagnum lindbergii. Temporal variability in the frequency of separate plant species depends on seasonal thaw depths, thawing index of air temperature, summer and winter precipitation. This conclusion is derived from the results of longterm (since 1972) studies at the Nadym station. The correlation between frequency of separate plant species in different and thaw depth is weak (less than 0.25). Frequency of separate plant species (e.g., Betula nana, Fig. 3) is much better correlated with thawing index of air temperature. According to records at the Nadym weather station, the sum of positive air temperatures has increased somewhat from 1972 to 2000; this increase is estimated to be on average 0.14 C per year. The Betula nana frequency has also increased in the same period, at an average rate of 0.4% per year. Among the species whose frequency depends distinctly on summer air temperatures, deciduous shrubs (Betula nana) and herbs (Carex globularis, Rubus chamaemorus) predominate. The relationship between the frequency of separate plant species and air temperatures is affected by particular landscape conditions. For example, the coefficient of correlation between the frequency of Betula Figure 2. Active layer thickness and frequency of indicator species on Parisento station (scale 1:1000). 792

5 frequency (%) t A 0 B trend line trend line 30 Figure 3. Changes of the Betula nana frequency (A) and thawing index ( C month) of air temperature (B). frequency (%) precipitation (mm) A 0 B trend line 300 Figure 4. Changes of the Cladonia amaurocraea frequency (A) and annual precipitation (B). nana and the sum of positive air temperatures, is higher on a flat surface of peatland than for a frost mound. Significant influence on the frequency of some species (eg., Cladonia amaurocraea, Fig. 4) is caused by the annual precipitation. The coefficient of correlation between these values equals The annual precipitations for the study period has somewhat decreased (this trend is approximated 1.4 mm per year). Accordingly, the frequency of Cladonia amaurocraea, for which this factor is decisive, has also decreased; moreover, this decrease is much more distinct than the decrease in precipitation. Evergreen dwarf shrubs (Andromeda polifolia, Ledum palustre, Vaccinium vitis-idaea) and lichens (Cetraria cucullata, Cladonia amaurocraea, Cladonia coccifera) are the species, whose frequency depends significantly on the annual precipitation. The data on vegetation dynamics obtained in the course of our studies and processed using Statgraph make it possible to calculate autocorrelation coefficients between the frequencies of separate plant species in different and to define the character of interannual changes in plant communities and their species composition (Vasilevich, 1970). For natural plant communities, the separation of the groups of species with different character of interannual variability in the frequency allows us to distinguish between phytocoenoses developing in relatively stable and considerably varying ecological conditions. Plant communities in stable conditions, show typically a small number of species with succession changes of frequency and are dominated by species with irregularly cyclic changes. Figure 5A presents an example of the autocorrelation coefficients between the Polytrichum commune frequencies in successive on Rubus chamaemorus-ledum-sphagnum-cladonia flat peatland. The cycle of frequency changes for this species is 4 7, and the relationship between the frequency changes and deviations of mean annual air temperature (Fig. 5B) is seen, especially in the last ten. In phytocoenoses, confined to frost mounds and bogs, in which moisture conditions change (by the development of water pools on frost mounds as a result of thermokarst, or by drainage of bogs), a role of species with succession changes of frequency essentially increases and the participation of species with irregularly cyclic changes decreases. The autocorrelation coefficients of species with frequency succession changes permanently decrease for the study period in connection with objective decreasing of frequency for these species. For the majority of plant species in the destroyed conditions succession changes of frequency is characteristic. 793

6 Interannual variability in the frequency of plant species is much better correlated with the thawing index of air temperature and annual precipitation. Natural plant communities are dominated by species with irregular cyclic changes of frequency for study period. For plant communities in destroyed and unstable conditions considerable participation by species with succession changes of frequency is typical. REFERENCES Figure 5. Autocorrelation coefficient (K) for Polytrichum commune and air temperature. A coefficient; B temperature (t C) deviations from mean perennial at the Nadym station. 4 CONCLUSIONS The study of interactions between permafrost and vegetation on the CALM grids in Russia made it possible to identify plant communities and plant species that can be used as indicators of seasonal thaw depths. The correlation between the thaw depth and distribution of plant communities is higher than that between the thaw depth and frequency of separate species. The correlation between the thaw depth and distribution of plant communities at the CALM grids is higher on flat surfaces of plains with smooth topography and relatively small complexity of the vegetation cover. The correlation of interannual variability in the frequency of plant species with the thaw depth is low. B Brown, J., Hinkel K.M., Nelson F.E The Circumpolar Active Layer Monitoring (CALM) Program: Research Designs and Initial Results. Polar Geography 24 (3): Gorodkov, B.N Permafrost and Vegetation. Permafrost: Leningrad: Izd-vo Akad. Nauk SSSR. Koloskov, P.I Climatic Foundations of Agriculture in the Amur Area. Blagoveshensk: Soviet for Eastern Meteorological Service. Melnikov E.S. (ed.) Landscapes of Permafrost Zone of the West Siberian Gas Province. Novosibirsk : Nauka. Molau U. (ed.) ITEX Manual. Copenhagen, Danish Polar Center. Moskalenko, N.G Role of vegetation cover in the Permafrost. Russian Geocryological Research 1: {Moscow} Moskalenko, N.G Anthropogenic Vegetation Dynamics in the Permafrost Plains of Russia. Novosibirsk: Nauka. Moskalenko, N.G., Korostelev Yu. V., Chervova E.I Monitoring of Active Layer in Northern Taiga of West Siberia. Cryosphere. V(1): Pavlov, A.V Active layer monitoring in Northern West Siberia.Permafrost :Proceedings, Seventh International Conference, June 23 27,1998, Yelloknife, Canada: Yelloknife: University La val. Sumgin M.I., Permafrost in the USSR. Moscow: Izdvo Akad. Nauk SSSR. Tyrtikov, A.P Effects of the Plant Cover on Ground Freezing and Thawing. Moscow: Mosk. Gos. Univ. Tyrtikov, A.P Plant Cover Dynamics and Evolution of Permafrost Elements of Relief. Moscow: Nauka. Vasilevich V.I Method of autocorrelation with study of vegetation dynamics. Trudy MOIP. Dep. biol. 38: Vasiliev A.A., Korostelev Yu. V., Moskalenko N.G., Dubrovin V.A Active layer monitoring in West Siberia under the CALM program (database). Cryosphere. II (3):