Snow is a critically important and rapidly changing feature of the Arctic. However, snow-cover and snowpack conditions change through time pose challenges for measuring and prediction of snow. Plausible scenarios of how Arctic snow cover will respond to changing Arctic climate are important for impact assessments and adaptation strategies. Although much progress has been made in understanding and predicting snow-cover changes and their multiple consequences, many uncertainties remain. In this paper, we review advances in snow monitoring and modelling, and the impact of snow changes on ecosystems and society in Arctic regions. Interdisciplinary activities are required to resolve the current limitations on measuring and modelling snow characteristics through the cold season and at different spatial scales to assure human well-being, economic stability, and improve the ability to predict manage and adapt to natural hazards in the Arctic region.
Climate change impacts are not uniform across the Arctic region because interacting factors causes large variations in local ecosystem change. Extreme climatic events and population cycles of herbivores occur simultaneously against a background of gradual climate warming trends and can redirect ecosystem change along routes that are difficult to predict. Here, we present the results from sub-Arctic heath vegetation and its belowground micro-arthropod community in response to the two main drivers of vegetation damage in this region: extreme winter warming events and subsequent outbreaks of the defoliating autumnal moth caterpillar (Epirrita autumnata). Evergreen dwarf shrub biomass decreased (30%) following extreme winter warming events and again by moth caterpillar grazing. Deciduous shrubs that were previously exposed to an extreme winter warming event were not affected by the moth caterpillar grazing while those that were not exposed to warming events (control plots) showed reduced (23%) biomass from grazing. Cryptogam cover increased irrespective of grazing or winter warming events. Micro-arthropods declined (46%) following winter warming but did not respond to changes in plant community. Extreme winter warming and caterpillar grazing suppressed the CO2 fluxes of the ecosystem. This article is protected by copyright. All rights reserved.
The tundra-taiga boundary stretches for more than 13,400 km around the Northern Hemisphere and is probably the Earth's greatest vegetation transition. The trees that define the boundary have been sensitive to climate changes in the past and models of future vegetation distribution suggest a rapid and dramatic invasion of the tundra by the taiga. Such changes would generate both positive and negative feedbacks to the climate system and the balance could result in a net warming effect. However, the boundary is becoming increasingly affected by human activities that remove trees and degrade forest-tundra into tundra-like areas. Because of the vastness and remoteness of the tundra-taiga boundary, and of methodological problems such as problematic definitions and lack of standardized methods to record the location and characteristics of the ecotone, a project group has been established under the auspices of the International Arctic Science Committee (IASC). This paper summarizes the initial output of the group and focuses on our uncertainties in understanding the current processes at the tundra-taiga boundary and the conflicts between model predictions of changes in the location of the boundary and contrasting recently observed changes due to human activities. Finally, we present recommendations for a coordinated international approach to the problem and invite the international community to join us in reducing the uncertainties about the dynamics of the ecotone and their consequences.
The lands surrounding the North Atlantic Region (the SCANNET Region) cover a wide range of climate regimes, physical environments and availability of natural resources. Except in the extreme North, they have supported human populations and various cultures since at least the end of the last ice age. However, the region is also important at a wider geographical scale in that it influences the global climate and supports animals that migrate between the Arctic and all the other continents of the world. Climate, environment and land use in the region are changing rapidly and projections suggest that global warming will be amplified there while increasing land use might dramatically reduce the remaining wilderness areas. Because much of the region is sparsely populated--if populated at all--observational records of past environmental changes and their impacts are both few and of short duration. However, it is becoming very important to record the changes that are now in progress, to understand the drivers of these changes, and to predict future consequences of the changes. To facilitate research into understanding impacts of global change on the lands of the North Atlantic Regions, and also to monitor changes in real time, an EU-funded network of research sites and infrastructures was formed in 2000: this was called SCANNET--SCANdinavian/North European NETwork of Terrestrial Field Bases. SCANNET currently consists of 9 core sites and 5 sites within local networks that together cover the broad range of current climate and predicted change in the region. Climate observations are well replicated across the network, whereas each site has tended to select particular environmental and ecological subjects for intensive observation. This provides diversity of both subject coverage and expertise. In this paper, we summarize the findings of SCANNET to-date and outline its information bases in order to increase awareness of data on environmental change in the North Atlantic Region. We also identify important gaps in our understanding and identify where the roles of existing infrastructures and activities represented by SCANNET can facilitate future research, monitoring and ground-truthing activities.
Insulation provided by snow cover and tolerance of freezing by physiological acclimation allows Arctic plants to survive cold winter temperatures. However, both the protection mechanisms may be lost with winter climate change, especially during extreme winter warming events where loss of snow cover from snow melt results in exposure of plants to warm temperatures and then returning extreme cold in the absence of insulating snow. These events cause considerable damage to Arctic plants, but physiological responses behind such damage remain unknown. Here, we report simulations of extreme winter warming events using infrared heating lamps and soil warming cables in a sub-Arctic heathland. During these events, we measured maximum quantum yield of photosystem II (PSII), photosynthesis, respiration, bud swelling and associated bud carbohydrate changes and lipid peroxidation to identify physiological responses during and after the winter warming events in three dwarf shrub species: Empetrum hermaphroditum, Vaccinium vitis-idaea and Vaccinium myrtillus. Winter warming increased maximum quantum yield of PSII, and photosynthesis was initiated for E. hermaphroditum and V. vitis-idaea. Bud swelling, bud carbohydrate decreases and lipid peroxidation were largest for E. hermaphroditum, whereas V. myrtillus and V. vitis-idaea showed no or less strong responses. Increased physiological activity and bud swelling suggest that sub-Arctic plants can initiate spring-like development in response to a short winter warming event. Lipid peroxidation suggests that plants experience increased winter stress. The observed differences between species in physiological responses are broadly consistent with interspecific differences in damage seen in previous studies, with E. hermaphroditum and V. myrtillus tending to be most sensitive. This suggests that initiation of spring-like development may be a major driver in the damage caused by winter warming events that are predicted to become more frequent in some regions of the Arctic and that may ultimately drive plant community shifts.
At the last glacial maximum, vast ice sheets covered many continental areas. The beds of some shallow seas were exposed thereby connecting previously separated landmasses. Although some areas were ice-free and supported a flora and fauna, mean annual temperatures were 10-13 degrees C colder than during the Holocene. Within a few millennia of the glacial maximum, deglaciation started, characterized by a series of climatic fluctuations between about 18,000 and 11,400 years ago. Following the general thermal maximum in the Holocene, there has been a modest overall cooling trend, superimposed upon which have been a series of millennial and centennial fluctuations in climate such as the "Little Ice Age spanning approximately the late 13th to early 19th centuries. Throughout the climatic fluctuations of the last 150,000 years, Arctic ecosystems and biota have been close to their minimum extent within the most recent 10,000 years. They suffered loss of diversity as a result of extinctions during the most recent large-magnitude rapid global warming at the end of the last glacial stage. Consequently, Arctic ecosystems and biota such as large vertebrates are already under pressure and are particularly vulnerable to current and projected future global warming. Evidence from the past indicates that the treeline will very probably advance, perhaps rapidly, into tundra areas, as it did during the early Holocene, reducing the extent of tundra and increasing the risk of species extinction. Species will very probably extend their ranges northwards, displacing Arctic species as in the past. However, unlike the early Holocene, when lower relative sea level allowed a belt of tundra to persist around at least some parts of the Arctic basin when treelines advanced to the present coast, sea level is very likely to rise in future, further restricting the area of tundra and other treeless Arctic ecosystems. The negative response of current Arctic ecosystems to global climatic conditions that are apparently without precedent during the Pleistocene is likely to be considerable, particularly as their exposure to co-occurring environmental changes (such as enhanced levels of UV-B, deposition of nitrogen compounds from the atmosphere, heavy metal and acidic pollution, radioactive contamination, increased habitat fragmentation) is also without precedent.
Several studies have reported significant emission of greenhouse gasses (GHG) from beaver dams, suggesting that ponds created by beavers are a net source of CO2 and CH4. However, most evidence come from studies conducted in North America (on Castor canadensis) without a parallel comparison with the Eurasian beaver's (Castor fiber) impacts and a critical consideration of the importance of the carbon deposition in dam sediments. The most abundant population of the Eurasian beaver lives in Russia, notably within the River Ob watershed in Western Siberia which is the second largest floodplain on Earth. Consequently, we assessed the holistic impact of Eurasian beavers on the multiple carbon pools in water and on other related biogeochemical parameters of the Ob's floodplain streams. We compared dammed and flowing streams in a floodplain of the middle course of the river. We found that beavers in western Siberia increase the stream emission of methane by about 15 times by building their dams. This is similar to what has been documented in North America. A new finding from the present study is that Siberian beavers facilitate 1) nutrient recycling by speeding up the nutrient release from particulate organic matter; and 2) carbon sequestration by increasing the amount of dissolved organic carbon. This carbon becomes in part recalcitrant when buried in sediments and is, therefore, removed from the short-term carbon cycle. These new results should be taken into consideration in river management and provide a further reason for the conservation and management of Eurasian Beavers.
Shrubs and trees are expected to expand in the sub-Arctic due to global warming. Our study was conducted in Abisko, sub-arctic Sweden. We recorded the change in coverage of shrub and tree species over a 32- to 34-year period, in three 50 x 50 m plots; in the alpine-tree-line ecotone. The cover of shrubs and trees ( or =3.5 cm) were noted and positions determined. There has been a substantial increase of cover of shrubs and trees, particularly dwarf birch (Betula nana), and mountain birch (Betula pubescens ssp. czerepanovii), and an establishment of aspen (Populus tremula). The other species willows (Salix spp.), juniper (Juniperus communis), and rowan (Sorbus aucuparia) revealed inconsistent changes among the plots. Although this study was unable to identify the causes for the change in shrubs and small trees, they are consistent with anticipated changes due to climate change and reduced herbivory.
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The tundra-taiga interface is a dominant vegetation boundary that is related to climate and has an importance at a global level for its contribution to land atmosphere interactions, biodiversity and land use. However, our understanding of the precise location, dynamics and characteristics of the boundary, and its environmental and biotic drivers at a circumpolar level is poor. Our understanding has been constrained for various reasons, perhaps including a quest by researchers to denote 2- or even 3-dimensional tree distribution limits to a single line on a map. Current rapid sociological and environmental changes in the north necessitate better definitions to be made of characteristics associated with the tundra-taiga interface so that changes can be monitored and identified, and implications of these changes can be assessed. This concept paper introduces some of the complexities of adequately defining the boundary and suggests characteristics and processes that could focus future research at a collaborative, circumpolar level to create baseline data and to monitor and predict changes in the boundary zone.