The snowpack gradient in the alpine generates a temperature and moisture gradient that largely co... more The snowpack gradient in the alpine generates a temperature and moisture gradient that largely controls organic matter decomposition. While low temperatures constrain decomposition and mineralization (chapter 12), moisture appears to be the strongest source of landscape variation in the alpine, with surface decay rates of plant materials highest in moist and wet meadow habitats. Despite a longer snow-free season and higher surface temperatures in dry meadows, decay in these areas is substantially lower than in moist meadows. Studies of decay rates of roots within the soil indicate that decay is uniformly low in all habitats and is limited by low temperatures and perhaps by the absence of certain groups of decomposer invertebrates. As in other ecosystems, substrate quality indices such as nitrogen and lignin content can be shown to be important factors influencing the rate of decay of specific substrates. Alpine ecosystems were overlooked during the flurry of activity associated with...
Aims: An Arctic Vegetation Classification (AVC) is needed to address issues related to rapid Arct... more Aims: An Arctic Vegetation Classification (AVC) is needed to address issues related to rapid Arctic-wide changes to climate, land-use, and biodiversity. Location: The 7.1 million km 2 Arctic tundra biome. Approach and conclusions: The purpose, scope and conceptual framework for an Arctic Vegetation Archive (AVA) and Classification (AVC) were developed during numerous workshops starting in 1992. The AVA and AVC are modeled after the European vegetation archive (EVA) and classification (EVC). The AVA will use Turboveg for data management. The EVC will use a Braun-Blanquet (Br.-Bl.) classification approach. There are approximately 31,000 Arctic plots that could be included in the AVA. An Alaska AVA (AVA-AK, 24 datasets, 3026 plots) is a prototype for archives in other parts of the Arctic. The plan is to eventually merge data from other regions of the Arctic into a single Turboveg v3 database. We present the pros and cons of using the Br.-Bl. classification approach compared to the EcoVeg (US) and Biogeoclimatic Ecological Classification (Canada) approaches. The main advantages are that the Br.-Bl. approach already has been widely used in all regions of the Arctic, and many described, well-accepted vegetation classes have a pan-Arctic distribution. A crosswalk comparison of Dryas octopetala communities described according to the EcoVeg and the Braun-Blanquet approaches indicates that the non-parallel hierarchies of the two approaches make crosswalks difficult above the plantcommunity level. A preliminary Arctic prodromus contains a list of typical Arctic habitat types with associated described syntaxa from Europe, Greenland, western North America, and Alaska. Numerical clustering methods are used to provide an overview of the variability of habitat types across the range of datasets and to determine their relationship to previously described Braun-Blanquet syntaxa. We emphasize the need for continued maintenance of the Pan-Arctic Species List, and additional plot data to fully sample the variability across bioclimatic subzones, phytogeographic regions, and habitats in the Arctic. This will require standardized methods of plot-data collection, inclusion of physiogonomic information in the numeric analysis approaches to create formal definitions for vegetation units, and new methods of data sharing between the AVA and national vegetation-plot databases.
Climate warming leads to more intensive evaporation from the Arctic sea resulting in increased pr... more Climate warming leads to more intensive evaporation from the Arctic sea resulting in increased precipitation in the low Arctic, e.g., higher snowfall during winter. Deeper snow keeps the arctic soils warmer and alters soil attributes and vegetation, e.g., increase in nitrogen availability, expansion of shrubs and decline in shade-intolerant lichens and bryophytes. Changes in soil properties and vegetation are expected to influence on saprotrophic and plant-symbiotic fungi, but how increased snow depth affects their community composition remain unknown. In the present work, we used DNA meta-barcoding to study the effects of long-term experimental manipulations of snow depth on soil fungal communities in dry heath and moist tussock tundra in Arctic Alaska. We report strong changes in fungal community compositions in the two tundra types, with pronounced declines observed in the majority of fungal functional guilds, including ectomycorrhizal, lichenized, plant pathogenic, saprotrophic and bryophyte-associated species. The observed changes in lichenized and bryophyte-associated fungi are in agreement with previously published above-ground changes, i.e. decrease of lichen and bryophyte cover and diversity. However, the majority of observed trends, including the decline of ectomycorrhizal fungi (that were anticipated to benefit from the expansion of their host plants), suggest that changes in fungal communities do not entirely correspond to and are not primarily driven by shifts in vegetation. Instead, arctic fungal communities appear to exhibit faster turnover that may be influenced by dynamic interactions with numerous biotic and abiotic factors, e.g., soil nutrient cycling and community dynamics in other groups of soil microorganisms. We highlight the importance of " below-ground studies " in assessing ecosystem responses to climatic changes, because faster turnover of microbial communities may be applicable for monitoring early-stage alterations caused by climatic changes.
Many arctic ecological processes are regulated by soil temperature that is tightly interconnected... more Many arctic ecological processes are regulated by soil temperature that is tightly interconnected with snow cover distribution and persistence. Recently, various climate-induced changes have been observed in arctic tundra ecosystems, e.g. shrub expansion, resulting in reduction in albedo and greater C fixation in aboveground vegetation as well as increased rates of soil C mobilization by microbes. Importantly, the net effects of these shifts are unknown, in part because our understanding of belowground processes is limited. Here, we focus on the effects of increased snow depth, and as a consequence, increased winter soil temperature on ectomycorrhizal (ECM) fungal communities in dry and moist tundra. We analyzed deep DNA sequence data from soil samples taken at a long-term snow fence experiment in Northern Alaska. Our results indicate that, in contrast to previously observed responses of plants to increased snow depth at the same experimental site, the ECM fungal community of the dr...
Page 1. Impacts of Petroleum Development in the Arctic: Response Author(s): Donald A. Walker, Nan... more Page 1. Impacts of Petroleum Development in the Arctic: Response Author(s): Donald A. Walker, Nancy Lederer, Marilyn D. Walker, Emily Binnian, Kaye R. Everett, Earl Nordstrand, Partick J. Webber Source: Science, New Series, Vol. 245, No. 4919 (Aug. 18, 1989), pp. ...
Field manipulations of environmental conditions have been established in dry tundra sites on Niwo... more Field manipulations of environmental conditions have been established in dry tundra sites on Niwot Ridge, CO, Toolik Lake, AK and on Svalbard, Norway as part of the International Tundra Experiment (ITEX). Dryas octopetala is the dominant species at all three sites where we have examined organismic and ecosystem responses to similar increases in temperature. Leaf and seed mass differ significantly between all sites and warmer temperatures resulted in reductions in leaf mass at both the high and low arctic sites in the initial year, but this was not observed at the alpine site. Reductions in leaf mass were accompanied by changes in leaf demography. Seed masses were inherently different between sites, being largest from plants in the alpine tundra. Plants in the alpine and in the high arctic had higher seed weights when warmed. By the end of the second year, leaf C:N ratios were higher in alpine plants which were warmed. These organismic responses may set the stage for altered coloniza...
Fungi, including symbionts, pathogens and decomposers, play crucial roles in community dynamics a... more Fungi, including symbionts, pathogens and decomposers, play crucial roles in community dynamics and nutrient cycling in terrestrial ecosystems. Despite their ecological importance, the responses of most arctic fungi to climate warming is unknown, so are their potential roles in driving the observed and predicted changes in tundra communities. We carried out deep DNA sequencing of soil samples to study the long-term effects of experimental warming on fungal communities in dry heath and moist tussock tundra in Arctic Alaska. The data presented here indicate that fungal community composition responds strongly to warming in the moist tundra, but not in the dry tundra. While total fungal richness were not significantly affected by warming, there were clear correlations among OTU richness of various ecological and taxonomic groups and long-term warming. Richness of ectomycorrhizal, ericoid mycorrhizal and lichenized fungi generally decreased with warming, while richness of saprotrophic, p...
Arctic and alpine tundra, defined as those areas that lie to the north of the latitudinally or al... more Arctic and alpine tundra, defined as those areas that lie to the north of the latitudinally or altitudinally controlled limits of tree growth (Gabriel and Talbot 1984), currently occupies approximately 8.3 × 106km2. The tundra biome is characterized by low biomass and species diversity relative to other biomes, and the spatial distribution of species of all groups is strongly structured
Arctic tundra regions have been responding to global warming with visible changes in plant commun... more Arctic tundra regions have been responding to global warming with visible changes in plant community composition, including expansion of shrubs and declines in lichens and bryophytes. Even though it is well known that the majority of arctic plants are associated with their symbiotic fungi, how fungal community composition will be different with climate warming remains largely unknown. In this study, we addressed the effects of long-term (18Â years) experimental warming on the community composition and taxonomic richness of soil ascomycetes in dry and moist tundra types. Using deep Ion Torrent sequencing, we quantified how OTU assemblage and richness of different orders of Ascomycota changed in response to summer warming. Experimental warming significantly altered ascomycete communities with stronger responses observed in the moist tundra compared with dry tundra. The proportion of several lichenized and moss-associated fungi decreased with warming, while the proportion of several pla...
Arctic regions are experiencing the greatest rates of climate warming on the planet and marked ch... more Arctic regions are experiencing the greatest rates of climate warming on the planet and marked changes have already been observed in terrestrial arctic ecosystems. While most studies have focused on the effects of warming on arctic vegetation and nutrient cycling, little is known about how belowground communities, such as fungi root-associated, respond to warming. Here, we investigate how long-term summer warming affects ectomycorrhizal (ECM) fungal communities. We used Ion Torrent sequencing of the rDNA internal transcribed spacer 2 (ITS2) region to compare ECM fungal communities in plots with and without long-term experimental warming in both dry and moist tussock tundra. Cortinarius was the most OTU-rich genus in the moist tundra, while the most diverse genus in the dry tundra was Tomentella. On the diversity level, in the moist tundra we found significant differences in community composition, and a sharp decrease in the richness of ECM fungi due to warming. On the functional lev...
Two distinctive types of small dome-shaped hills occur in the Prudhoe Bay region. One type has sm... more Two distinctive types of small dome-shaped hills occur in the Prudhoe Bay region. One type has small basal diameters, steep side slopes, and occurs primarily in drained thaw-lake basins; the other type consists of mounds of larger diameter and commonly occurs outside modern lake basins. The U.S. Army Cold Regions Research and Engineering Laboratory drilled three of the mounds including one broad-based mound and encountered massive ice in all of them. It is thus likely that all of the steep-sided mounds and at least the larger broad-based mounds are pingos. It is clear that the largest of the broad-based mounds are neither dunes, unmodified remnants, nor highly eroded steep-sided pingos of the type common in the region today. Discriminant analysis of topographic-map data indicates that mean slope and length of the longest axis are the clearest discriminators between the two groups of mounds. The broad-based mounds are limited to older surfaces in the region and are thus likely to be quite old (< 12,000 yr). Explanations for the large size of many of the broad-based mounds and their occurrence outside lake basins will have to await detailed drilling studies.
The hypothesized presence of large regions of grass and forb-dominated "steppe tundra" across Ala... more The hypothesized presence of large regions of grass and forb-dominated "steppe tundra" across Alaska and Siberia during the Pleistocene glacial epochs has led to a search for modern analogs. Evidence is presented for the presence of steppe vegetation on south-facing slopes and summits of pingos within the central Arctic Coastal Plain of Alaska. Vegetation, floristics, soils, and climatic factors are each considered, and together support the idea of an ecologicallyphysiognomically defined steppe on these sites. Grasses and forbs dominate this vegetation, and Dryas integrifolia, which is dominant in most dry sites regionally, is absent or has only minimal cover. Although the floristic evidence indicates that the pingo vegetation is most strongly related to the circumpolar arctic vegetation, the steppe-like vegetation has more North American-Asian and low arctic taxa than do other sites. Soils are Pergelic Cryoborolls, and the microclimates on south slopes have greater daily and annual fluctuations than do other microsites. Other pingo vegetation is related to fellfield and snowbeds. These communities represent the northernmost known examples of steppe in North America, and help explain the complex relationships that can exist within the vegetation of well-drained arctic sites. 'Joint Facility for Regional Ecosystem Analysis, 2Institute of Arctic and Alpine Research, and
The snowpack gradient in the alpine generates a temperature and moisture gradient that largely co... more The snowpack gradient in the alpine generates a temperature and moisture gradient that largely controls organic matter decomposition. While low temperatures constrain decomposition and mineralization (chapter 12), moisture appears to be the strongest source of landscape variation in the alpine, with surface decay rates of plant materials highest in moist and wet meadow habitats. Despite a longer snow-free season and higher surface temperatures in dry meadows, decay in these areas is substantially lower than in moist meadows. Studies of decay rates of roots within the soil indicate that decay is uniformly low in all habitats and is limited by low temperatures and perhaps by the absence of certain groups of decomposer invertebrates. As in other ecosystems, substrate quality indices such as nitrogen and lignin content can be shown to be important factors influencing the rate of decay of specific substrates. Alpine ecosystems were overlooked during the flurry of activity associated with...
Aims: An Arctic Vegetation Classification (AVC) is needed to address issues related to rapid Arct... more Aims: An Arctic Vegetation Classification (AVC) is needed to address issues related to rapid Arctic-wide changes to climate, land-use, and biodiversity. Location: The 7.1 million km 2 Arctic tundra biome. Approach and conclusions: The purpose, scope and conceptual framework for an Arctic Vegetation Archive (AVA) and Classification (AVC) were developed during numerous workshops starting in 1992. The AVA and AVC are modeled after the European vegetation archive (EVA) and classification (EVC). The AVA will use Turboveg for data management. The EVC will use a Braun-Blanquet (Br.-Bl.) classification approach. There are approximately 31,000 Arctic plots that could be included in the AVA. An Alaska AVA (AVA-AK, 24 datasets, 3026 plots) is a prototype for archives in other parts of the Arctic. The plan is to eventually merge data from other regions of the Arctic into a single Turboveg v3 database. We present the pros and cons of using the Br.-Bl. classification approach compared to the EcoVeg (US) and Biogeoclimatic Ecological Classification (Canada) approaches. The main advantages are that the Br.-Bl. approach already has been widely used in all regions of the Arctic, and many described, well-accepted vegetation classes have a pan-Arctic distribution. A crosswalk comparison of Dryas octopetala communities described according to the EcoVeg and the Braun-Blanquet approaches indicates that the non-parallel hierarchies of the two approaches make crosswalks difficult above the plantcommunity level. A preliminary Arctic prodromus contains a list of typical Arctic habitat types with associated described syntaxa from Europe, Greenland, western North America, and Alaska. Numerical clustering methods are used to provide an overview of the variability of habitat types across the range of datasets and to determine their relationship to previously described Braun-Blanquet syntaxa. We emphasize the need for continued maintenance of the Pan-Arctic Species List, and additional plot data to fully sample the variability across bioclimatic subzones, phytogeographic regions, and habitats in the Arctic. This will require standardized methods of plot-data collection, inclusion of physiogonomic information in the numeric analysis approaches to create formal definitions for vegetation units, and new methods of data sharing between the AVA and national vegetation-plot databases.
Climate warming leads to more intensive evaporation from the Arctic sea resulting in increased pr... more Climate warming leads to more intensive evaporation from the Arctic sea resulting in increased precipitation in the low Arctic, e.g., higher snowfall during winter. Deeper snow keeps the arctic soils warmer and alters soil attributes and vegetation, e.g., increase in nitrogen availability, expansion of shrubs and decline in shade-intolerant lichens and bryophytes. Changes in soil properties and vegetation are expected to influence on saprotrophic and plant-symbiotic fungi, but how increased snow depth affects their community composition remain unknown. In the present work, we used DNA meta-barcoding to study the effects of long-term experimental manipulations of snow depth on soil fungal communities in dry heath and moist tussock tundra in Arctic Alaska. We report strong changes in fungal community compositions in the two tundra types, with pronounced declines observed in the majority of fungal functional guilds, including ectomycorrhizal, lichenized, plant pathogenic, saprotrophic and bryophyte-associated species. The observed changes in lichenized and bryophyte-associated fungi are in agreement with previously published above-ground changes, i.e. decrease of lichen and bryophyte cover and diversity. However, the majority of observed trends, including the decline of ectomycorrhizal fungi (that were anticipated to benefit from the expansion of their host plants), suggest that changes in fungal communities do not entirely correspond to and are not primarily driven by shifts in vegetation. Instead, arctic fungal communities appear to exhibit faster turnover that may be influenced by dynamic interactions with numerous biotic and abiotic factors, e.g., soil nutrient cycling and community dynamics in other groups of soil microorganisms. We highlight the importance of &quot; below-ground studies &quot; in assessing ecosystem responses to climatic changes, because faster turnover of microbial communities may be applicable for monitoring early-stage alterations caused by climatic changes.
Many arctic ecological processes are regulated by soil temperature that is tightly interconnected... more Many arctic ecological processes are regulated by soil temperature that is tightly interconnected with snow cover distribution and persistence. Recently, various climate-induced changes have been observed in arctic tundra ecosystems, e.g. shrub expansion, resulting in reduction in albedo and greater C fixation in aboveground vegetation as well as increased rates of soil C mobilization by microbes. Importantly, the net effects of these shifts are unknown, in part because our understanding of belowground processes is limited. Here, we focus on the effects of increased snow depth, and as a consequence, increased winter soil temperature on ectomycorrhizal (ECM) fungal communities in dry and moist tundra. We analyzed deep DNA sequence data from soil samples taken at a long-term snow fence experiment in Northern Alaska. Our results indicate that, in contrast to previously observed responses of plants to increased snow depth at the same experimental site, the ECM fungal community of the dr...
Page 1. Impacts of Petroleum Development in the Arctic: Response Author(s): Donald A. Walker, Nan... more Page 1. Impacts of Petroleum Development in the Arctic: Response Author(s): Donald A. Walker, Nancy Lederer, Marilyn D. Walker, Emily Binnian, Kaye R. Everett, Earl Nordstrand, Partick J. Webber Source: Science, New Series, Vol. 245, No. 4919 (Aug. 18, 1989), pp. ...
Field manipulations of environmental conditions have been established in dry tundra sites on Niwo... more Field manipulations of environmental conditions have been established in dry tundra sites on Niwot Ridge, CO, Toolik Lake, AK and on Svalbard, Norway as part of the International Tundra Experiment (ITEX). Dryas octopetala is the dominant species at all three sites where we have examined organismic and ecosystem responses to similar increases in temperature. Leaf and seed mass differ significantly between all sites and warmer temperatures resulted in reductions in leaf mass at both the high and low arctic sites in the initial year, but this was not observed at the alpine site. Reductions in leaf mass were accompanied by changes in leaf demography. Seed masses were inherently different between sites, being largest from plants in the alpine tundra. Plants in the alpine and in the high arctic had higher seed weights when warmed. By the end of the second year, leaf C:N ratios were higher in alpine plants which were warmed. These organismic responses may set the stage for altered coloniza...
Fungi, including symbionts, pathogens and decomposers, play crucial roles in community dynamics a... more Fungi, including symbionts, pathogens and decomposers, play crucial roles in community dynamics and nutrient cycling in terrestrial ecosystems. Despite their ecological importance, the responses of most arctic fungi to climate warming is unknown, so are their potential roles in driving the observed and predicted changes in tundra communities. We carried out deep DNA sequencing of soil samples to study the long-term effects of experimental warming on fungal communities in dry heath and moist tussock tundra in Arctic Alaska. The data presented here indicate that fungal community composition responds strongly to warming in the moist tundra, but not in the dry tundra. While total fungal richness were not significantly affected by warming, there were clear correlations among OTU richness of various ecological and taxonomic groups and long-term warming. Richness of ectomycorrhizal, ericoid mycorrhizal and lichenized fungi generally decreased with warming, while richness of saprotrophic, p...
Arctic and alpine tundra, defined as those areas that lie to the north of the latitudinally or al... more Arctic and alpine tundra, defined as those areas that lie to the north of the latitudinally or altitudinally controlled limits of tree growth (Gabriel and Talbot 1984), currently occupies approximately 8.3 × 106km2. The tundra biome is characterized by low biomass and species diversity relative to other biomes, and the spatial distribution of species of all groups is strongly structured
Arctic tundra regions have been responding to global warming with visible changes in plant commun... more Arctic tundra regions have been responding to global warming with visible changes in plant community composition, including expansion of shrubs and declines in lichens and bryophytes. Even though it is well known that the majority of arctic plants are associated with their symbiotic fungi, how fungal community composition will be different with climate warming remains largely unknown. In this study, we addressed the effects of long-term (18Â years) experimental warming on the community composition and taxonomic richness of soil ascomycetes in dry and moist tundra types. Using deep Ion Torrent sequencing, we quantified how OTU assemblage and richness of different orders of Ascomycota changed in response to summer warming. Experimental warming significantly altered ascomycete communities with stronger responses observed in the moist tundra compared with dry tundra. The proportion of several lichenized and moss-associated fungi decreased with warming, while the proportion of several pla...
Arctic regions are experiencing the greatest rates of climate warming on the planet and marked ch... more Arctic regions are experiencing the greatest rates of climate warming on the planet and marked changes have already been observed in terrestrial arctic ecosystems. While most studies have focused on the effects of warming on arctic vegetation and nutrient cycling, little is known about how belowground communities, such as fungi root-associated, respond to warming. Here, we investigate how long-term summer warming affects ectomycorrhizal (ECM) fungal communities. We used Ion Torrent sequencing of the rDNA internal transcribed spacer 2 (ITS2) region to compare ECM fungal communities in plots with and without long-term experimental warming in both dry and moist tussock tundra. Cortinarius was the most OTU-rich genus in the moist tundra, while the most diverse genus in the dry tundra was Tomentella. On the diversity level, in the moist tundra we found significant differences in community composition, and a sharp decrease in the richness of ECM fungi due to warming. On the functional lev...
Two distinctive types of small dome-shaped hills occur in the Prudhoe Bay region. One type has sm... more Two distinctive types of small dome-shaped hills occur in the Prudhoe Bay region. One type has small basal diameters, steep side slopes, and occurs primarily in drained thaw-lake basins; the other type consists of mounds of larger diameter and commonly occurs outside modern lake basins. The U.S. Army Cold Regions Research and Engineering Laboratory drilled three of the mounds including one broad-based mound and encountered massive ice in all of them. It is thus likely that all of the steep-sided mounds and at least the larger broad-based mounds are pingos. It is clear that the largest of the broad-based mounds are neither dunes, unmodified remnants, nor highly eroded steep-sided pingos of the type common in the region today. Discriminant analysis of topographic-map data indicates that mean slope and length of the longest axis are the clearest discriminators between the two groups of mounds. The broad-based mounds are limited to older surfaces in the region and are thus likely to be quite old (< 12,000 yr). Explanations for the large size of many of the broad-based mounds and their occurrence outside lake basins will have to await detailed drilling studies.
The hypothesized presence of large regions of grass and forb-dominated "steppe tundra" across Ala... more The hypothesized presence of large regions of grass and forb-dominated "steppe tundra" across Alaska and Siberia during the Pleistocene glacial epochs has led to a search for modern analogs. Evidence is presented for the presence of steppe vegetation on south-facing slopes and summits of pingos within the central Arctic Coastal Plain of Alaska. Vegetation, floristics, soils, and climatic factors are each considered, and together support the idea of an ecologicallyphysiognomically defined steppe on these sites. Grasses and forbs dominate this vegetation, and Dryas integrifolia, which is dominant in most dry sites regionally, is absent or has only minimal cover. Although the floristic evidence indicates that the pingo vegetation is most strongly related to the circumpolar arctic vegetation, the steppe-like vegetation has more North American-Asian and low arctic taxa than do other sites. Soils are Pergelic Cryoborolls, and the microclimates on south slopes have greater daily and annual fluctuations than do other microsites. Other pingo vegetation is related to fellfield and snowbeds. These communities represent the northernmost known examples of steppe in North America, and help explain the complex relationships that can exist within the vegetation of well-drained arctic sites. 'Joint Facility for Regional Ecosystem Analysis, 2Institute of Arctic and Alpine Research, and
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Papers by M. Walker