PALAEOECOLOGY AND RESILIENCE OF GRAZING ECOSYSTEMS IN NORTHWEST EURASIA, A PALYNOLOGICAL PERSPECTIVE

Resilience refers to the overall capacity to adapt to change within a social-ecological system. Social-ecological systems or SESs can be described as complex adaptive systems where social and biophysical agents interact at multiple temporal and spatial scales. The concept of humans in nature is emphasized and the delineation between social and ecological systems is considered artificial and arbitrary (Chapin et al., 2006).

During the recent decades many regions at northern high latitudes have experienced a significant and rapid climate warming. This presents challenges to different SESs when they are facing the need to adapt to short — and long-term systemic changes. In Northern Fennoscandia and the Yamal-Nenets Autonomous Okrug (YNAO), Western Siberia, air temperatures have increased ca. 2°C over the past 35 years, with warming taking place year round (NASA-GISS, 2011). During the same time period the North American Arctic has warmed to a similarly high level. The predicted and observed ecosystem responses in different reports include the advance of treeline to the higher latitudes/elevations and an increase in shrub abundance within the existing tundra zones (ACIA, 2005; IPCC, 2007; SWIPA, 2011). Since the early 1980‘s it has been possible to detect the ‗greening‘ of the Arctic from satellite images, which itself indicates an increase in biological productivity and changes in land cover on a biome level (Raynolds et al., 2008; Forbes et al., 2010). Despite the recent warming, the late Holocene and especially the last millennium have had some clear and rapid climate changes, which have been recorded in different archives and well documented (the Medieval Warm Period and the Little Ice Age) (ACIA, 2005; IPCC, 2007; SWIPA, 2011).

The ecosystem structure and function may take decades or centuries to fully respond to anthropogenic disturbance or environmental change. This is even more accurate in the high Arctic where the growing season is short. Still the ecological studies almost exclusively examine ecosystem dynamics over intervals of only a few days to a few years (Redman, 2005; Fisher et al., 2009). Palynological data provides information about the changes in local and regional vegetation over centuries and millennia. The data can also be used to interpret possible grazing pressure and local herbivore densities when the non-pollen palynomorphs such as coprophilous fungal spores are counted alongside pollen. If the aim is to detect the

short term anthropogenic disturbance or environmental change as a whole from the palynological record, the high temporal resolution of the record and a contiguous sampling without gaps in the record are imperative. The temporal resolution of a pollen record is affected by the thickness of the sample, the rate of sediment accumulation, and the accuracy of the age-depth model used to produce the chronology. In the Arctic the use of peat rather than lake sediment is advised since the former accumulates much more rapidly than the latter and so offers a higher temporal resolution (Hicks and Hyvärinen, 1999). A robust age-depth chronology and precise measurement of the sample volume allow the calculation of pollen accumulation rates (PAR, grains cm-2 year-1) which generally provide a better record of vegetation changes than the more traditional percentage representation since the representation of each taxon is unaffected by the changes in the abundance of other taxa (Davis and Deevey, 1964).

It is important to understand the spatial resolution that the pollen assemblages represent. Also, the separation of the local pollen from the regional elements is crucial when making vegetation reconstructions. One way to quantify the spatial scale of pollen representation of vegetation is to assess the ‗relevant source area of pollen‘ (RSAP: Sugita, 1994). It has been shown that as much as 60% of the total pollen loading at a site can come from outside the radius of the RSAP and can be considered as a background component (Sugita, 1994; Von Stedingk et al., 2008). PARs are also influenced by the spatial resolution of the pollen record but cannot, in themselves, quantify it. However, some assessment of local (within-site) events can be distinguished from more regional ones on the basis of the stratigraphy (macrofossil record) and through the contribution to the pollen record of the local plants. Moreover, local hydrological events are often preserved in the peat stratigraphy and recorded by other microfossils present in the peat such as testate amoebae (Borgmark and Schoning, 2006), just as an increase in the amount of mineral matter can indicate wind erosion of exposed mineral soil around the site (Kuoppamaa et al., 2009).

There has been an ongoing discussion about overgrazing by reindeer in Fennoscandia for years (Mysterud, 2006). Partly as a byproduct of this discussion, different groups have established ecological experiments, which have demonstrated the speed with which graminoid-dominated ‗lawns‘ can replace shrub-dominated vegetation when reindeer activities (grazing, trampling, faeces deposition) are concentrated in tundra areas (van der Wal et al., 2004; Olofsson, 2006). Such graminoid-dominated swards can develop under both anthropogenic and zoogenic disturbance regimes and may persist after decades or even centuries of disuse, effectively functioning as alternative stable states (Forbes, 1996; Forbes et al., 2001; Potthoff, 2007). Key questions are 1) to what extent have reindeer and people been responsible for managing these transitions, and 2) how stable have the so-called ‗stable states‘ actually been through periods of significant climate change that have simultaneously driven, for example, regional shifts in treeline. Palynological and other evidence from sites in Fennoscandia suggests that humans and herbivores, such as reindeer, can override the effects of climate change, at least locally, and prevent the advance of shrubs and trees in periods of favourable climate (Emanuelsson, 1987; Karlsson et al., 2007; Olofsson et al., 2009; Potthoff,

2009).

There are very few integrative ecological studies of anthropogenic/zoogenic changes in land cover at time scales that are longer than a century (Redman, 2005; Fisher et al., 2009). This research aims also to link archaeological materials and cultural residues to contemporary oral histories and palaeoecology to construct more complete narratives that encompass both the social and environmental drivers of change over the long term and at the regional scale. A key aim is, therefore, to understand how resilient the SESs of the western Eurasian North actually have been throughout the well-known periods of dramatic climate change that characterize the late Holocene and to produce quantitative reconstructions of regional and

local environmental change for the last ~1200 years, comprising the Medieval Warm Period, Little Ice Age, and the late 20th century warming. In order to study the long-term interactions between tundra ecosystems, herbivory and climate, the study presents a spatiotemporal evaluation of climate-reindeer-vegetation dynamics in Northwestern Eurasia, taking into account local (temperature, snowfall, rainfall, wind) and regional-to-global (Arctic/North Atlantic Oscillation) climate processes. Reconstructions will focus on 1) land cover, 2) ancient plant and animal community composition, 3) grazing intensity, and 4) past reindeer diet. Palynological investigations will be based on pollen and coprophilous fungal spores which will be used to investigate the intensity of contemporary and historical reindeer herding in Fennoscandia and Yamal. One aim is also to produce relative pollen productivity estimates and fall speed of pollen grains for the key taxa in the area, that are needed for the purpose of estimating the past vegetation cover with Landscape Reconstruction Algorithm (LRA; Sugita,

2007 a, b). This information is not available for tundra species and needs to be obtained during the course of this study by collecting a representative set of moss surface pollen samples from a range of locations with varying degrees of land use. Fossil reindeer faeces will be used to investigate reindeer diet and analyse the adaptability of reindeer herds to changing plant communities.

Материал взят из: Интеграция археологических и этнографических исследований: сборник научных трудов: в 2 т.