Monthly average and mean annual temperatures of air and grounds in the wood (а -2008, b -2009).
The goal of this ongoing study is to examine theimpact of climate change on vegetation and permafrost in ecosystems of West Siberia Subarctic. Results of long-term monitoring of northern taiga ecosystem under impact of climatic changes are presented.
The warming of an observable climate from the end of 20th century was accompanied by changes of vegetation and permafrost degradation, especially in the zone of sporadic permafrost. This important problem is examined in works of many researchers (Tyrtikov, 1969, 1979; Belopukhova, 1973; Brown, Pewe, 1973; Nevecheryaet al, 1975;Yevseyev V.P, 1976.;Nelson et al. 1993; Ershov et al. 1994; Pavlov 1997, 2008; Moskalenko,1999; Osterkamp et al. 1999; Parmuzin&Chepurnov 2001; Izrael et al. 2002, Kakunov&Sulimova 2005; Hollister, Webber &Tweedie, 2005; Walker et al.2006; Perlstein et al. 2006; Oberman 2007; Leibman et al. 2011). They demonstrated that freezing and thawing conditions change in response to the vegetation dynamics.Increases in moss and lichen cover thickness result in the reduction of active layer thickness, and decreases in soil and ground temperatures. However in these works not enough attention was given to estimated impact of climate on the vegetation and permafrost in the ecosystems. In the present report the author tries to fill this deficiency based on long-term monitoring of changes in the northern taiga ecosystem of Western Siberia.
2.Location and parametric considerations
Research on ecosystems were carried out since 1970 on the Nadym stationary site (Fig. 1), located 30 km to a southeast from the town of Nadym (Moskalenko, 2006) in the zone of sporadic permafrost distribution (Melnikov, 1983). Patches of permafrost, occupying up to 50% of areas, are closely associated with peatlands, peat bogs, and frost mounds of III fluvial-lacustrine plain having elevationsranging from 25 to 30m above sea level. The plain is composed of sandy deposits interbedded with clays, with an occasional covering of peat (Andrianov et al. 1973).
During ecosystem monitoring were used remote and cartographical methods. Office studies and field decoding of remote sensing materials from 1970 up to 2009 was added by land route and detail field descriptions on permanent transects and 10x10m plots, fixed on a terrain. Leveling of permanent marks was carried out by electronic level Sprinter 150M every year. Two times for observation period near plots biomass resources were determined. Repeated mapping of vegetation was performed on 1x1m permanent grids for studying of vegetation structure and dynamics. Annual geobotanical descriptions are made on 28 permanent fixed (10 x 10 m) plots. The structure, average height, phenological and vital condition, frequency and coverage of plant species on 50 registered 0.1m2 plots were recorded.
Study of spatial and temporal patterns of active layer thickness, caused with microrelief and vegetation mosaic was carried out on 100x100m CALM (Circumpolar Active Layer Monitoring) grid. On 121-grid nodes detail vegetation descriptions and repeated leveling of microrelief were performed. It would reveal some correlations between active layer thickness, vegetation and microrelief. In 16 10-mboreholes and 1 30-m borehole were established loggers Hobo, and measurements of permafrost temperature were carried out by project TSP (Thermal State of Permafrost).Air and soil temperatures were measured too. Monthly average and mean annual temperatures of air and grounds in a wood and on a peatlandare resulted in tables 1 and 2.
3. Investigations and observations
Ecosystem changes have been revealed as a result of 40-years observation over a microrelief, species composition of a vegetation cover, height, frequency and coverage of dominant species of plants, soil and permafrost temperature, thickness and moisture of active layer on permanent plots and transects.
3.1. Impact of increase in amount of atmospheric precipitation on vegetation and permafrost
The analysis of the received data has allowed to revealing tendencies in development of a natural vegetation cover. In wood communities in connection with increase of atmospheric precipitation amount which is marked last decades, the increase in participation of mosses, and change of green moss-lichen sparse forests by lichen-green moss plant communitieson drained sites is observed. Changes of atmospheric precipitation (Fig. 2) and Cladinarangiferina frequency (Fig.3) in Birch-pine sparse forest are presented. Coverage of Pleurozium Schreberi opposite increases (Fig. 4).
In connection with the increase of atmospheric precipitation process of bog formation on flat poorly drained surfaces of plains becomes more active. As a result hummocky pine cloudberry-wild rosemary-lichen-peat moss open woodlands were replaced by andromeda-cotton grass-sedge-peat moss bogs. Hummocks settled, and the lenses of permafrost under hummocks thawed.
The frequency of wild rosemary (Ledumpalustre) which dominated in a cover of the open woodland fell sharply after 1997 (Fig. 5, 2). The frequency of cotton-grass (Eriophorumangustifolium) for the past decade increased, and it began to dominate the cover (Fig. 5, 1).
Comparison of biomass in wood communities and bog communities shows that by bog formation in wood all aboveground biomass decreases from 2316 to 1715 g/m2 and biomass of graminoid and mosses increases (table 3). Comparison of species composition of wood and bog plant communities presents that biodiversity of vegetation cover in process of bogginess decreases in the result of absence mesophyte species of sedges and shrubs (Carexglobularis, Empetrumnigrum, Vacciniumvitis-idaea), аnd also lichens (Cladinarangiferina, C. stellaris, Cetrariaislandica, Cladoniacoccifera, table 4). Common number of species decreases from 27 to 17.
|Species||Year||Height, cm||Coverage, %||Frequency, %|
|1. Andromeda polifolia||1||7||2||54|
|2. Betula nana||1||45||2||16|
|24. Polytrichum commune||1||3||3||38|
|25. Sphagnum angustifolium||1||1||11||18|
|26. Sphagnum fuscum||1||2||36||52|
|27. Sphagnum lindbergii||1||4||23||34|
3.2. Impact of increase in air temperature on vegetation and permafrost
Last decades in the north of Western Siberia rise in air temperature is observed (Fig. 6). Increase of the air thawing index (the sum monthly mean air temperatures above 0°C) caused the appearance on flat and palsapeat lands separate trees (Betulatortuosa, Pinussibirica, Pinuasilvestris); increase in frequency and height of shrubs (Betula nana, Ledumpalustre, Fig. 7) and coverage them of a soil surface. These plant species can serve as indicators of climate warming.
Long-term studying of plants communities and active layer thickness in northern taiga has allowed calculating of plant communities frequency with active layer thickness. The smallest values of active layer thickness (67.1 cm) are observed under Rubuschamaemorus-Ledumpalustre-Sphagnum-Cladinarangiferina cover on flat peatland (coefficient of correlation -0.71). Areas with deepest active layer thickness (173.7 cm) are confined to large sedge-moss pools within peatlands (coefficient of correlation 0.58).
The analysis of the given measurements of the active layer thickness on palsapeatland (Fig. 8) has shown that it has a trend to the increase, caused by increase in the thawing index of air temperature, which trend for 1970-2010 makes 0.20С in a year. The permafrost temperature at the depth of 10m has increased on 1.40С. Temperature of permafrost at the depth of 10m (layer with minimum annual fluctuations of temperatures) for the period of researches on the palsapeatland has increased from -1.80С up to-0.40С (Fig.9, 2). On flat peatland increase of permafrost temperature was less; here permafrost temperature at the depth of 10m has increased from -0.90С up to -0.20С (Fig.9, 1).
Increase in air temperature and rise in amount of atmospheric precipitation promoted faster recovery of a vegetation cover after a fire.For example, on frost mounds with Pinussibirica- wild rosemary-peat moss-lichen open woodland in 35 years after the fire Betula nana-wild rosemary-peat moss-lichen community with Pinussibirica in height 2mhad developed(Fig.10).
On the permanent plot located on a flat southern slope the frost mound in height of3m. In a well-defined microrelief of tussocks and hummocks height up to 0.8m are characteristic. Pools were usual, sometimes filled with water.
Soil is sandy peat-gley, and frozen at 0.5m depth. Average peat horizon thickness is 30сm. A crown density of Pinussibirica is 0.1, its height 7-8m. Thecoverage of grasses anddwarf shrubs makes up 40-50%.
The grass-dwarf shrub cover has two-layer structure: the upper layer in height is 0.3-0.35m composed of wild rosemary and Betula nana, and the lower layer in height is 0.05-0.15m with abundant cowberry (Vacciniumvitis-idaea), Chamaedaphnecalyculata, cloudberry and sedge (Carexglobularis). Peat mosses and lichens make up the continuous ground cover.
In June 1976 the plot of grass-dwarf shrub cover, and a forest stand was completely burned. Within two months following the fire the surface cover of 25% consisted of shoots of Carexglobularis, Betula nana, wild rosemary, and cloudberry. In pools the moss coverage of up to 30% was maintained.
One year following the fire the sedge-cloudberry-peat moss grouping was formed, and the next year it was replaced by cloudberry-sedge-wild rosemary-peat moss community. This was the result of the fast recovery of a former role of wild rosemary (Fig.11, 1). In this community the coverage of grasses and dwarf shrubs increased up to 35%, and mosses up to 40%.The next years the coverage of grasses and dwarf shrubs reached its initial value (40-50%), but mosses still covered less than half of plot surface.The frequencyof Betula nana has increased in 3 times, probably, in connection with the rise in air temperature (Fig. 11, 2).
The occurrence of lichens sharply decreased after the fire, and within 16 years had considerably increased. Only the frequency of Cladoniacoccifera strongly increased after the fire. The frequency ofCladinastellaris was recovered (Fig. 12, 1), and its reduction last decade is connected to increase of amount of atmospheric precipitation that is observed and in undisturbed conditions. The frequencyof Sphagnum fuscum(Fig. 12, 2) while remains in 2 times less than in initial community. The increase in height of shrubs (Betula nana, Chamaedaphnecalyculata, Ledumpalustre) is marked also. Changes in species composition, height, coverage and frequency of plants on frost mound are presented in the table 5.
On the cloudberry-wild rosemary-lichen palsapeatlands n 40 years after the fire the cloudberry-Betula nana- wild rosemary-lichen-Polytrichumcommunities are found. These communities differ from the initial communities by ground vegetation composition (smaller percentage of lichens) and increase in presence of Betula nana. The last, apparently, is connection to the increase of the air thawing index and a snow thickness over the last decades.
In 1971, plot onpalsapeatland on which in 1970 were carried out the detailed description of a vegetation cover, measurements of active layer thickness and permafrost temperature, was burned.
This plot is located at top of peat hillocky with height of 2m and with cloudberry-wild rosemary-lichen plant community. In the microrelief of plot are characteristic small Dicranum hummocks with heights of 0.1-0.3m and pools with bog dwarf shrubs (Andromeda polifolia, Chamaedaphnecalyculata) and mosses. The soil of the plot is peaty, and maximum thickness of the active layer is 0.6m. The coverage of grasses and dwarf shrubs equaled 45 %; mosses and lichens - 90%. In a grass-shrub cover two layers are found: an upper layer in height of 0.2-0.4m made up of wild rosemary and Betula nana, and a lower layer in height up to 0.15m formed of cloudberry and cowberry. In ground vegetation, lichens preedominated over a Cladinagenus and frequent Dicranum mosses but with low coverage.
In 1975, four years after the fire at the top of the peaty hillocky where the vegetation had been described in 1970, a permanent 10 x 10m plot on the soil surface was established. On this plot, since 1975 on present time, annual geobotanical descriptions are performed.
A 10-meter borehole was drilled at the hillocky top near to the geobotanical plot. According to the drilling the peat thickness is 1m, below lies sand with layers of the clay, underlaying with depth 3,75m by clay. From 1975 year-round temperature measurements of soil and permafrost were observed (Fig. 13). Since 2001 year-round measurements of temperature by loggers are obtained. Thickness and moisture of the active layer were measured.
In four years since the fire on hillocky the cotton-grass-cloudberry-Polytrichumcommunity is found in which the coverage of grasses made 15%, and mosses 50 %. After the fire the number of species on the plot was 42% of their common number in 1970. Change of species number could be still large, but appearance of new grass species (Erophorumrusseolum, Carexlimosa, Chamaeneriumangustifolium) and shoots of a birch (Betulatortuosa) compensated for significant decrease of species number.It has been related to disappearance of five dwarf shrubs (Vacciniumuliginosum, V. vitis-idaea, Empetrumnigrum, Andromeda polifoliaand Chamaedaphnecalyculata), Eriophorumvaginatum, one species of lichens (Alectoriaochroleuca) and three species of mosses (Sphagnum fuscum, Pleuroziumschreberi, Hylocomiumsplendens). In the first years of vegetation recovery the frequency and coverage of Polytrichum mosses strongly increased (Table 6). Occurrence of dwarf shrubs has decreased, bog grasses have appeared absent earlier, and the occurrence of shrubs increased.
In five years after the fire on hillocky landscape with cotton-grass-cloudberry-Polytrichumcommunity the coverage of grasses was 20%, and mosses 50%. The next year there was an appreciable increase in occurrence of Betula nana that led to changes of the grass-moss community with Betula nana- cloudberry-cotton-grass-Polytrichumcommunity.The coverage of grasses and dwarf shrubs in this community gradually grew and in 14 years after the fire had reached its initial value. At this time an appreciable role of wild rosemary began to occur. The ground vegetation by this time covered up to 85% of a plot surface, but it still has consisted of Polytrichum mosses. The thickness of the active layer in this plant community has increased up to 65-70сm.
The frequency of lichens though has increased, but the coverage on the surface did not exceed 1-3 %. However the coverage of lichens gradually continued to increase, and in 23 years after the fire it has reached 8.5 %. The coverage of lichens has increased for 40th year up to 18.5%, and includes Betula nana-wild rosemary-cloudberry-Cladina-Polytrichum community in which the occurrence of cotton-grass has decreased. The number of dwarf shrubs and mosses by this time has appreciably increased, but remained less than in undisturbed cover due to the absence of bog dwarf shrubs (Andromeda polifolia, Chamaedaphnecalyculata) and one species of mosses (Hylocomiumsplendens). The bog grasses whichhave appeared at early stages of plant community recovery in 2005 have disappeared from the plant community.
|Species||Year||Height, cm||Coverage, %||Frequency, %|
|1. Andromeda polifolia||1||10||1||18|
|2. Betula nana||1||45||2||22|
|22. Polytrichum commune||1||5||0.1||4|
|23. Sphagnum angustifolium||1||2||0.1||2|
|24. Sphagnum fuscum||1||2||23||52|
Negatively reacted to a fire some shrubs (Vacciniumvitis-idaea, Ledumpalustre), lichens, green mosses and Sphagnum fuscum. In 15 years after a fire at the cowberry, the wild rosemary and all before plentiful species of lichens (Cladina, Cetraria), the frequency and the coverage strongly differed from initial sizes. This distinction was kept and in 23 years after fire. Participation of some species of lichens (Cladoniacoccifera and Cladoniaamaurocraea) and blueberries for the investigated period was recovered. At cloudberries sizes of the coverage were made even to initial sizes, but it frequency still was more than in 2 times smaller.
In 30 years after the fire the frequency of Betula nana has exceeded initial size, the frequency of Ledumpalustre too has considerably increased and for 40-th year was only a little less, than in not disturbed community. Only at the cowberry and dominant species of lichens (Cladinastellaris and Cladinarangiferina) the frequency for all period of observations was not recovered. The analysis of frequency diagrams of Betula nana and Ledumpalustre (Fig. 14)shows, that there is a positive trend which will be coordinated to increase of summer air temperatures.
Plant species.Vascular plants: Andpol – Andromeda polifolia, Betnan – Betula nana, Bettor – Betulatortuosa, Callap – Calamagrostislapponica, Carglo – Carexglobularis, Carlim – Carexlimosa, Carrot – Carexrotundata, Chaang – Chamaeneriumangustifolium, Empnig – Empetrumnigrum, Eriang – Eriophorumangustifolium, Erirus – Eriophorumrusseolum, Erisch – Eriophorumscheucheri, Erivag – Eriohorumvaginatum, Ledpal – Ledumpalustre, Pinsib – Pinussibirica, Pinsil – Pinussilvestris, Rubcha – Rubuschamaemorus, Vaculi – Vacciniumuliginosum, Vacvit – Vacciniumvitis-idaea.
Mosses: Aulpal – Aulacomniumpalustre, Diccon – Dicranumcongestum, Hylspl – Hylocomiumsplendens, Plesch – Pleuroziumschreberi, Polcom - Polytrichum commune, Sphfus – Sphagnum fuscum.
Lichens: Aleoch – Alectoriaochroleuca, Cetcuc – Cetrariacucullata, Cetisl – Cetrariaislandica, Cetniv – Cetrarianivalis, Claama – Cladoniaamaurocraea, Clacoc – Cladoniacoccifera, Claran – Cladinarangiferina, Claste – Cladinastellaris.
Stages of vegetation recovery after the fire on the frost mound and the palsapeatland are presented in Table 7. Comparison of rates of vegetation cover restoration in these ecosystems demonstrate that on flat weakly drained top of frost mound the vegetation recovery is faster than on better drained palsapeatland. The domination in ground vegetation of Polytrichum mosses and the lower occurrence of lichens persists longer.
|Stages and their duration(years)||Ecosystems|
Ecosystems: I – cloudberry-wild rosemary-lichenpalsapeatland, II – frost mound with Pinussibiricawild rosemary- peat moss-Cladina open woodland.
Plant communities: 1а – cotton grass-cloudberry-Polytrichum, 1б–sedge-cloudberry-peat moss, 2а – Betula nana-cloudberry-cotton- grass-Polytrichum, 2б – cloudberry-sedge-wild rosemary-peat moss, 3а – cloudberry-Betula nana--wild rosemary-Cladina-Polytrichum, 3б – Betula nana-wild rosemary-peat moss-Cladina, 4а - cloudberry-Betula nana-wild rosemary-Cladina-Polytrichum, 4б – Pinussibirica-Betula nana-wild rosemary-peat moss-Cladina.
3.3. Impact of vegetation dynamics on permafrost
On the dwarf shrub-cotton grass-peat moss bogs in the result of vegetation dynamics itis possible to observe formation of new frost heavy hummocks (Fig.16). The height of one of young frost mound, which beginning of formation concerns to 1973, makes by the present moment 80 cm.
The ecosystems are detected, in which the local temperature decrease observed on a background of the general tendency of temperature increase, caused by dynamics of a vegetation cover. It is necessary to allow a possibility of such different tendencies of temperature changes in ecosystems at for the same changes of a climate at geocrylogical monitoring.
For example, such downturn of permafrost temperatures was observed on dwarf shrub-sedge-peat moss bog, replaced through 25 years by sedge-dwarf shrub- lichen-peat moss peatland as a result of increase in moss thickness, accumulation of peat and growths of dwarf shrubs (Andromeda polifolia, Chamaedaphnecalyculata). Here permafrost temperatures for the investigated period have gone down on0.30С (Fig.15)though in the next flat peatlands surrounding a drained up bog, the permafrost temperature became higher.
On cotton grass-peat moss bogs with the lowered permafrost table on formed on it dwarf shrub-peat moss hummocksafter cold winters it is observed formation of new frozen ground. Mean active layer thickness on these hummocks is 80 cm.
4. Results and discussions
Long-term monitoring of the northern taiga ecosystem changes has allowed revealing impact of climatic changes on a vegetation cover and permafrost.
During the last decades in the north of West Siberia the rise in air temperature and the increase in amount of atmospheric precipitation are observed. In wood communities in connection with increase of atmospheric precipitation amount which is marked last decades, the increase in participation of mosses, and change of green moss-lichen sparse forests by lichen-green moss plant communities on drained sites is marked.
On flat poorly drained surfaces of plains process of bog development became more active. As a result of it hummocky pine cloudberry-wild rosemary-lichen-peat moss open woodlands with lenses of permafrost under the hummocks are replaced by andromeda-cotton grass-sedge-peat moss thawed bogs. Comparison wood communities and bog communities show that by bog formation in wood all aboveground biomass decreases on 26% and biodiversity in process of bogginess decreases on 37%.
Increase of the thawing index of air temperature caused the appearance on the flat and pals apeat lands separate trees (Betulatortuosa, Pinussibirica, Pinussilvestris), increase in the frequency and the height of shrubs (Betula nana, Ledumpalustre) and in the coverage them of a soil surface. These plant species can serve as indicators of climate warming.
The analysis of the given measurements of the active layer thickness on palsapeat land has shown that it has a trend to the increase, caused by increase in the air thawing index, which trend for 1970-2010 makes 0.20С in a year.
The permafrost temperature at the depth of 10m has increased on 1.40С. Temperature of permafrost at the depth of10m for the period of research on the palsapeatland has increased from -1.80С up to-0.40С. On the flat peatland increase of the perma frost temperature was less; here the permafrost temperature at the depth of 10mhas increased from-0.90Сupto -0.20С.
In conditions of climate warming fires began to be observed more often. On cloudberry-wild rosemary-lichen palsapeat lands 40 years after a fire are formed cloudberry-Betulanana-wild rosemary-lichen-Polytrichim plant communities. These plant communities differ from initial communities by ground vegetation composition (smaller participation of lichens) and increase in occurrence of Betula nana connected with increase of the air thawing index.
On flat weakly drained top of frost mound the vegetation recovery after the fire is faster than on better drained palsapeat land. Here Pinussibirica- wild rosemary-peat moss-lichen open woodland in 35 years after the fire changed by Betula nana-wild rosemary-peat moss-lichen community with Pinussibirica in height 2m.
Stages and rate of vegetation recovery after thefire were revealed.
The ecosystems are established, in which the local temperature decrease observed on a background of the general tendency of temperature increase, caused by dynamics of the vegetation cover.
The carried out researches prove observations of A.P. Tyrtikov (1969), E.B. Belopukhova (1973), V.L. Nevecheryaet all. (1975). These researchers marked, that in modern climatic conditions of Western Siberia northern taiga during dynamics of bog vegetation are formed new frost mounds which are considered as some researchers relic formations (Yevseyev, 1976; Brown, Pewe, 1973) for which formation now there are no necessary conditions.
In my research the vegetation cover is considered as one of components of the natural ecosystems, closely connected with other components and first of all with soils,underground waters and permafrost for which indication it is used. As the mobile component of ecosystem easily broken at external impact, but capable to self-recovery, vegetation is one of critical components of ecosystems and the major factor of their stabilization.
Long-term monitoring of vegetation cover show that main environmental factors in development of plant communities in the North of West Siberia are water and thermal regime of soil.
Studying of interactions of vegetation with other ecosystem components and revealing of leading factors in vegetation dynamics of region allows more proved to approach to compiling the prediction of vegetation changes in conditions of a varying climate on materials received as a result of long-term monitoring. Use of the interactions existing between the vegetation cover and permafrost, enables to predict on expected tendencies of vegetation development changes of geocryological conditions and to recommend necessary actions on preservation of natural balance in environment.
In all territory of the north of Western Siberia climate changes in time have oscillatory character on a background of the general warming which have begun since 1970th years. On data of Nadym weather station for 1970-2011 the trend to increase of mean-annualair temperature is revealed. Increase of mean-annual temperature has made 0.040С in a year.
The steady increase in active layer thickness is connected to rise in air temperature in all natural complexes. Extreme reaction to climatic changes natural complexes of bogs and peatlands in the north of Western Siberia possess. Active layer thickness in palsapeatlands for the 40-years period has increased on 30 %.
Despite of climate warming and observed rise in permafrost temperature single instances of permafrost transition in a thawed condition on all thickness of annual heat turn layer are fixed only.
The research was supported by Land-Cover Land-Use Change program, project Circumpolar Active Layer Monitoring (CALM, National Science Foundation, Grant NSF OPP-9732051, 0PP-0225603); project Thermal State of Permafrost (TSP, NSF RC-0632400, ARC-0520578)and Council undergrant of the President of the Russian Federation (grant NSH-5582.2012.5).
Aleksandar Lazinica is acknowledged for their very useful comments in improving my chapter.