Arctic Tussock Tundra Research Articles

Vegetation classification for northwestern Arctic Alaska using an EcoVeg approach: tussock tundra and low and tall willow groups and alliances

Aims: The USNVC is the standard for vegetation classification in the US and is part of the broader IVC. Recent work on the USNVC in Alaska established macrogroups, groups and alliances. Here we incorporate tussock tundra and low and tall willow (Salix) groups and alliances for northwestern Arctic Alaska into the IVC and USNVC classification. Study Area: The study area encompasses the Seward Peninsula, the western Brooks Range, and the northwestern foothills and Arctic coastal plain of Alaska. Methods: We used data from 2,087 relevé plots collected between 1992 and 2019 from northwestern Arctic Alaska to prepare a draft association classification using cluster analysis, ordination, and sorted tables. The draft classification was subject to peer review and subsequently refined. We fit the tussock tundra and low and tall willow associations into the USNVC using NMDS and GAMs to evaluate the patterns of environmental gradients against the ordination axis scores. Results: We identified eight tussock tundra and 37 low and tall willow associations. The associations fit in two classes, two subclasses, two formations, two divisions, three macrogroups, four groups, and 13 alliances. A description of the alliances, and a field guide to the northwestern Arctic Alaska tussock tundra and low and tall willow associations, including a dichotomous key and descriptions, is provided. Conclusions: Many of the tussock tundra and low and tall willow associations fit seamlessly within the USNVC, while some alliances had yet to be defined, and we have proposed new alliances here. In still other cases, we proposed a new group and recommend broadening the concept of an existing group using a data-driven approach. Since not all available data from Arctic Alaska were used in this study, we suggest continuing with a more comprehensive analysis to fulfill the gap at the alliance and association levels for Arctic Alaska. Taxonomic reference: USDA NRCS (2021) for vascular plants, bryophytes, and lichens. Syntaxonomic reference: USNVC (2019). Abbreviations: AVA-AK = Alaska Arctic Vegetation Archive; AVPD = Alaska Vegetation Plots Database; BCP = Beaufort Coastal Plain; CAVM = Circumpolar Arctic Vegetation Map; CBVM = Circumboreal vegetation map; EC = Electrical conductivity; ELD = ELS Legacy Database; ELS = Ecological Land Survey; GAM = Generalized additive model; IVC = International vegetation classification; LPI = line-point intercept; NMDS = Non-metric multidimensional scaling; PAM = Partitioning Around Medoids; PESC = Proportionate ericaceous shrub cover; SM = Supplementary material; US = United States of America; USNVC = U.S. National Vegetation Classification.

Impacts of wildfire and landscape factors on organic soil properties in Arctic tussock tundra

Tundra ecosystems contain some of the largest stores of soil organic carbon among all biomes worldwide. Wildfire, the primary disturbance agent in Arctic tundra, is likely to impact soil properties in ways that enable carbon release and modify ecosystem functioning more broadly through impacts on organic soils, based on evidence from a recent extreme Anaktuvuk River Fire (ARF). However, comparatively little is known about the long-term impacts of typical tundra fires that are short-lived and transient. Here we quantitatively investigated how these transient tundra fires and other landscape factors affected organic soil properties, including soil organic layer (SOL) thickness, soil temperature, and soil moisture, in the tussock tundra. We examined extensive field observations collected from nearly 200 plots across a wide range of fire-impacted tundra regions in AK within the scope of NASA’s Arctic Boreal Vulnerability Experiment. We found an overall shallower SOL in our field regions (∼15 cm on average) compared to areas with no known fire record or the ARF (∼20 cm or thicker), suggesting that estimations based on evidence from the extreme ARF event could result in gross overestimation of soil organic carbon (SOC) stock and fire impacts across the tundra. Typical tundra fires could be too short-lived to result in substantial SOL consumption and yield less robust results of SOL and carbon storage. Yet, repeated fires may amount to a larger amount of SOC loss than one single severe burning. As expected, our study showed that wildfire could affect soil moisture and temperature in the tussock tundra over decades after the fire, with drier and warmer soils found to be associated with more frequent and severe burnings. Soil temperature was also associated with vegetation cover and air temperature.

Soil bacterial communities vary more by season than with over two decades of experimental warming in Arctic tussock tundra

High latitude ecosystems are characterized by cold soils and long winters, with much of their biogeochemistry directly or indirectly controlled by temperature. Climate warming has led to an expansion of shrubby plant communities across tussock tundra, but whether these clear aboveground shifts correspond to changes in the microbial community belowground remains less certain. Using bromodeoxyuridine to label growing cells, we evaluated how total and actively growing bacterial communities varied throughout a year and following 22 years of passive summer warming. We found that changes in total and actively growing bacterial community structures were correlated with edaphic factors and time point sampled, but were unaffected by warming. The aboveground plant community had become more shrub-dominated with warming at this site, and so our results indicate that belowground bacterial communities did not track changes in the aboveground plant community. As such, studies that have used space-for-time methods to predict how increased shrub cover has altered bacterial communities may not be representative of how the microbial community will be affected by in situ changes in the plant community as the Arctic continues to warm.

Estimating decay dynamics for enzyme activities in soils from different ecosystems

Extracellular enzymes in soil are central to the decomposition of plant and microbial detritus and they are increasingly incorporated into soil biogeochemical models as drivers of detritus breakdown. In enzyme-driven models, a critical parameter is the functional lifespan of the enzymes, yet this is poorly constrained by experimental data. We evaluated how long soil enzymes remain active in five soils spanning from arctic tussock tundra to a tropical forest/grassland soil. We incubated soils under continuous fumigation with CHCl3 vapor to kill microbes and prevent the synthesis of new enzymes. We monitored the activities of six hydrolytic and two oxidative enzymes over a 12-week incubation. Initial activities of the various soil enzymes varied substantially across the ecosystems; they were generally highest (per gram soil) in the tussock tundra, followed by temperate hardwood forest, grassland, tropical forest/grassland, and then chaparral. In tussock tundra organic soil, activities of all enzymes decreased rapidly following first-order decay curves; the half-lives of enzyme activity were typically several weeks. In the mineral soils, the time course of loss of hydrolytic enzyme activities could always be described by a first-order decay curve, but in many cases, activity could equally be described by a zero-order, linear, decay function because the rate of loss was slow. Although α-glucosidase lost activity rapidly, for other enzymes substantial activity remained even after 12 weeks of incubation. This likely resulted from stabilization by mineral surfaces, stabilization that might constrain activity against native polymeric substrates. Measured turnover rate constants fell within the broad range that model have used, but that range remains exceedingly broad.

Identifying the sources and uncertainties of ecosystem respiration in Arctic tussock tundra

Ecosystem respiration (ER) is the largest flux of carbon (C) from terrestrial ecosystems to the atmosphere, yet our ability to model this aggregate flux lags considerably behind our ability to model photosynthesis. Arctic ecosystems hold large stocks of potentially labile soil C and are dominated by plants with high root: shoot ratios. However, simple models of Arctic tundra ER typically use only aboveground drivers, such as air temperature and leaf area index. To investigate this apparent discrepancy, we partitioned ER into its component fluxes in moist acidic tussock tundra, which is among the most widespread of Arctic ecosystems. To partition ER, we combined tissue-scale measurements of leaf, wood, moss, lichen, and root respiration with seasonal biomass estimates. Simple respiration models were fit to the data for each tissue type. Our results suggest that belowground respiration is a large proportion of ER and that its contribution increases over the course of the growing season with soil thaw. We estimated that bulk soil heterotrophic respiration made up approximately 40 %, root respiration made up 35 %, mosses contributed 8.5 % and all vascular plant leaves combined made up a mere 13.5 % of ER during the 2012 growing season. Our ability to model aboveground tissue respiration exceeded our ability to model belowground respiration. We hypothesize that effects of the aboveground climate on rhizosphere respiration, mediated by the production and delivery of photosynthate, may be a critical determinant of ER, as this would reconcile our results with simple models of ER.

Annual patterns and budget of CO2 flux in an Arctic tussock tundra ecosystem

AbstractThe functioning of Arctic ecosystems is not only critically affected by climate change, but it also has the potential for major positive feedback on climate. There is, however, relatively little information on the role, patterns, and vulnerabilities of CO2 fluxes during the nonsummer seasons in Arctic ecosystems. Presented here is a year‐round study of CO2 fluxes in an Alaskan Arctic tussock tundra ecosystem, and key environmental controls on these fluxes. Important controls on fluxes vary by season. This paper also presents a new empirical quantification of seasons in the Arctic based on net radiation. The fluxes were computed using standard FluxNet methodology and corrected using standard Webb‐Pearman‐Leuning density terms adjusted for influences of open‐path instrument surface heating. The results showed that the nonsummer season comprises a significant source of carbon to the atmosphere. The summer period was a net sink of 24.3 g C m−2, while the nonsummer seasons released 37.9 g C m−2. This release is 1.6 times the summer uptake, resulting in a net annual source of +13.6 g C m−2 to the atmosphere. These findings support early observations of a change in this particular region of the Arctic from a long‐term annual sink of CO2 to an annual source from the terrestrial ecosystem and soils to the atmosphere. The results presented here demonstrate that nearly continuous observations may be required in order to accurately calculate the annual net ecosystem CO2 exchange of Arctic ecosystems and to build predictive understanding that can be used to estimate, with confidence, Arctic fluxes under future conditions.

Evidence for spatially inaccessible labile N from a comparison of soil core extractions and soil pore water lysimetry

NH4+, NO3−, and amino acids are generally thought to be either mobile in the soil solution or adsorbed to ion exchange sites on soil surfaces. Here we examine a third possibility: some labile N compounds may be spatially inaccessible to plants and microbes due to isolation in soil microsites with low water potential. We tested this hypothesis in Arctic tussock tundra soils by comparing soil NH4+, NO3−, and amino acid concentrations using tension lysimetry, water extractions, and salt extractions. We used lysimeters to measure labile N that is in the mobile soil solution, and water extracts and salt extracts as combined measurements of mobile, adsorbed, and spatially inaccessible labile N. Averaged through the 2011 growing season, 37 ± 28% of labile N was adsorbed to ion exchange sites, 10 ± 4% was in the mobile soil solution, and the remaining 52 ± 26% was neither mobile nor on exchange sites. Labile N concentrations in water extractions were, on average, ∼5 times higher than those in lysimeters. These results suggest that a large quantity of the water-extractable N is not available in the mobile soil solution. The estimated quantity of spatially inaccessible labile N declined over the course of the season, suggesting that these pools can be gradually drawn down by plant or microbial uptake. To place these results in context, we reviewed published labile N concentrations in lysimeters and extractions in other ecosystems and these published values were consistent with our results, showing much higher concentrations of labile N in extractions than in lysimeters. Overall, our study supports the hypothesis that soils can contain a substantial spatially inaccessible pool of extractable labile N that is not immediately available to plants and soil microbes.

Detecting microbial N-limitation in tussock tundra soil: Implications for Arctic soil organic carbon cycling

More than a third of the global soil organic carbon (SOC) pool is estimated to be stored in northern latitudes. While the primary regulators of microbially-mediated decomposition in physically unprotected organic soils are typically attributed to abiotic factors ( e.g. temperature and moisture), in extremely nutrient-poor environments such as the Alaskan Arctic tussock tundra, evidence from field studies suggests that low N-availability may also strongly limit microbial growth, and thus the rate of SOC decomposition. However, there have been few direct tests of microbial nutrient-limitation, particularly in Arctic systems. We predicted that during the Arctic summer growing season, when both plants and microbes are competing for mineralized nutrients, N-availability in tussock tundra soil is so low that it will limit microbial biomass production, and thus decomposition potential. We tested this prediction by adding N and C to tussock tundra organic soil and tracking microbial responses to these additions. We used a combination of approaches to identify microbial N-limitation, including changes in microbial biomass, C-mineralization, substrate use efficiency, and extracellular enzyme activity. The Arctic soil's microbial community demonstrated strong signals of N-limitation, with N-addition increasing all aspects of decomposition tested, including extracellular enzyme activity, the rate-limiting step in decomposition. The corresponding C-addition experiment did not similarly influence the microbial activity of the tundra soil. These results suggest that tundra SOC decomposition is at least seasonally constrained by N-availability through microbial N-limitation. Therefore, explicitly including N as a regulator of microbial growth in this N-poor system is critical to accurately modeling the effects of climatic warming on Arctic SOC decomposition rates.

Arctic warming on two continents has consistent negative effects on lichen diversity and mixed effects on bryophyte diversity

AbstractLittle is known about the impact of changing temperature regimes on composition and diversity of cryptogam communities in the Arctic and Subarctic, despite the well‐known importance of lichens and bryophytes to the functioning and climate feedbacks of northern ecosystems. We investigated changes in diversity and abundance of lichens and bryophytes within long‐term (9–16 years) warming experiments and along natural climatic gradients, ranging from Swedish subarctic birch forest and subarctic/subalpine tundra to Alaskan arctic tussock tundra. In both Sweden and Alaska, lichen diversity responded negatively to experimental warming (with the exception of a birch forest) and to higher temperatures along climatic gradients. Bryophytes were less sensitive to experimental warming than lichens, but depending on the length of the gradient, bryophyte diversity decreased both with increasing temperatures and at extremely low temperatures. Among bryophytes, Sphagnum mosses were particularly resistant to experimental warming in terms of both abundance and diversity. Temperature, on both continents, was the main driver of species composition within experiments and along gradients, with the exception of the Swedish subarctic birch forest where amount of litter constituted the best explanatory variable. In a warming experiment in moist acidic tussock tundra in Alaska, temperature together with soil ammonium availability were the most important factors influencing species composition. Overall, dwarf shrub abundance (deciduous and evergreen) was positively related to warming but so were the bryophytes Sphagnum girgensohnii, Hylocomium splendens and Pleurozium schreberi; the majority of other cryptogams showed a negative relationship to warming. This unique combination of intercontinental comparison, natural gradient studies and experimental studies shows that cryptogam diversity and abundance, especially within lichens, is likely to decrease under arctic climate warming. Given the many ecosystem processes affected by cryptogams in high latitudes (e.g. carbon sequestration, N2‐fixation, trophic interactions), these changes will have important feedback consequences for ecosystem functions and climate.

X-ray μCT imaging technique reveals corm microstructures of an arctic-boreal cotton-sedge, Eriophorum vaginatum

X-ray computed tomography (CT), a non-destructive imaging technique, has recently been effectively applied to botanical research. In this study an X-ray microCT technique was developed to allow for anatomical study of the overwintering corms of Eriophorum vaginatum, an ecologically important sedge species in arctic tussock-tundra and boreal peatlands. Using a GE Medical MS8X-130 X-ray microCT scanner, optimal imaging parameters included scanning isolated corms at 80 k Vp and 100 microA with a 3500 ms exposure time and an isotropic voxel size of 10 microm. A Gaussian blur image filter with a blur radius (sigma) of two pixels was applied to the optimal dataset to improve visual detection and contrast of tissues while removing 99.2% of image noise. Using the developed X-ray microCT technique several undocumented anatomical characteristics of the corm were identified including the vascular connection between a parent corm and branching cormel and the 3D shape of sclereid clusters. The 3D structure of sclereid clusters was determined whereby the perimeter of their lance shape is greatly reinforced by sclereids with thicker secondary cell walls as compared to those of the interior of the cluster. The structure of sclereid clusters and their association with leaf traces suggests they may be stabilizing the corm-leaf connection to protect vascular tissues from physical damage. The proposed X-ray microCT technique is an excellent tool for determination of the 3D structure of E. vaginatum corms and may be used to detect alterations in tissue structure and chemistry in response to environmental change in this and other Cyperaceous species.

Continuous estimates of CO2 efflux from arctic and boreal soils during the snow‐covered season in Alaska

Soils in arctic and boreal ecosystems hold large stocks of soil carbon (C), which may be sensitive to changes in climate. Recent studies suggest that winter CO2 efflux from the subnivean environment may be an important component of annual C budgets in arctic and boreal ecosystems. The present study was designed to examine the seasonal patterns and magnitudes of winter CO2 efflux from arctic tussock tundra near Toolik Lake, Alaska, and upland boreal forest in Anchorage, Alaska. The seasonal pattern of winter CO2 efflux differed strongly between the two sites. Tussock tundra showed a prolonged period with very low flux rates between late December and mid‐April. In contrast, rates of CO2 efflux were relatively high, but variable, throughout the winter at the boreal site. Estimates of C efflux for the snow‐covered season were within the range of previous studies in tussock tundra (24 g C m−2) and upland boreal forest (75 g C m−2). A simple exponential model, using shallow soil temperatures, explained much of the variation in CO2 efflux from tussock tundra. In contrast, air temperature was an important secondary control on winter CO2 efflux from the boreal forest, suggesting that trees became active during prolonged winter thaws. Results of the study imply that warmer winters may increase rates of C efflux from high‐latitude ecosystems. Changes in the depth or duration of snow cover will, however, modulate the relationship between air and soil temperatures and could amplify or dampen the effects of climate warming.

Detecting changes in arctic tundra plant communities in response to warming over decadal time scales

AbstractDetecting the response of vegetation to climate forcing as distinct from spatial and temporal variability may be difficult, if not impossible, over the typical duration of most field studies. We analyzed the spatial and interannual variability of plant functional type biomass from field studies in low arctic tussock tundra and compared these to climate change simulations of plant community composition using a dynamic tundra vegetation model (ArcVeg). Spatial heterogeneity of peak season live aboveground biomass was estimated using field samples taken from low arctic tundra at Ivotuk, Alaska (68.5°N, 155.7°W) in 1999. Coefficients of variation for live aboveground biomass at the 1 m2 scale ranged from 14.6% for deciduous shrubs, 18.5% for graminoids and 25.3% for mosses to over 57% for forbs and lichens. Spatial heterogeneity in the ArcVeg dynamic vegetation model was simulated to be greater than the field data, ranging from 37.1% for deciduous shrubs to 107.9% for forbs. Disturbances in the model, such as caribou grazing and freezing–thawing of soil, as well as demographic stochasticity, led to the greater variability in the simulated results. Temporal variances of aboveground live biomass over a 19‐year period using data from Toolik Lake, AK fell within the range of field and simulation spatial variances. However, simulations using ArcVeg suggest that temporal variability can be substantially less than site‐scale spatial variability. Field data coupled with ArcVeg simulations of climate change scenarios indicate that some changes in plant community composition may be detectable within two decades following the onset of warming, and shrubs and mosses might be the key indicators of community change. Model simulations also project increasing landscape scale spatial heterogeneity (particularly of shrubs) with increasing temperatures.

Climate and litter quality controls on decomposition: An analysis of modeling approaches

Four mathematical models simulated decay of two litter types of contrasting quality over a 2‐year period at four sites in North America. The litter types were Drypetes glauca and Triticum aestivum, representing litter with high and low nitrogen:lignin ratios, respectively. The field sites were an Arctic tussock tundra (Alaska, United States), a warm desert (New Mexico, United States), a temperate deciduous forest (New York, United States) and a tropical rain forest (Puerto Rico). Models captured the overall patterns of site and litter quality controls on decomposition; both simulated and observed mass losses were higher in warm, moist environments (both forests) than in cold (tundra) or dry sites (desert), and simulated and observed decay was more rapid for Drypetes than Triticum. However, predictions tended to underestimate litter mass loss in the tropical forest and overestimate decay in the desert and tundra, suggesting that site controls in model formulations require refinement for use under such a broad range of conditions. Also, predicted nitrogen content of litter residues was lower than observed in Drypetes litter and higher than observed for Triticum. Thus mechanisms describing loss of nitrogen from high‐quality litter and nitrogen immobilization by low‐quality litter were not captured by model structure. Individual model behaviors revealed different sensitivities to controlling factors that were related to differences in model formulation. As these models represent working hypotheses regarding the process of litter decay, results emphasize the need for greater resolution of climate and litter quality controls. Results also demonstrate the need for finer resolution of the relationships between carbon and nitrogen dynamics during decomposition.

Carbon cycling in the Kuparuk basin: Plant production, carbon storage, and sensitivity to future changes

The Marine Biological Laboratory General Ecosystem Model was calibrated for an arctic tussock tundra system using data from long‐term observations and experiments at Toolik Lake, Alaska. These experiments include the effects of changes in temperature, light, CO2, and nutrients, so the model could be applied to five regions comprising the entire Kuparuk River basin. Net primary production, averaged for the entire basin, was 92 g C m−2 yr−1. A 150 year simulation of carbon storage under a doubling of CO2 (slow ramp‐up) and a temperature increase of 3.5°C gave an estimate of +400 g C m−2 when soil moisture increased and +500 g C m−2 when soil moisture decreased. Drier soils stimulated decomposition producing an increase in nitrogen availability; the increased N led to increased net primary production. If this result is applicable to other arctic ecosystems, then it is unlikely that warming will enhance carbon loss to the atmosphere to further enhance warming.

CLIMATIC EFFECTS ON TUNDRA CARBON STORAGE INFERRED FROM EXPERIMENTAL DATA AND A MODEL

We used a process-based model of ecosystem carbon (C) and nitrogen (N) dynamics, MBL-GEM (Marine Biological Laboratory General Ecosystem Model), to integrate and analyze the results of several experiments that examined the response of arctic tussock tundra to manipulations of CO2, temperature, light, and soil nutrients. The experiments manipulated these variables over 3- to 9-yr periods and were intended to simulate anticipated changes in the arctic environment. Our objective was to use the model to extend the analysis of the experimental data so that unmeasured changes in ecosystem C storage and the underlying mechanisms controlling those changes could be estimated and compared. Using an inverse calibration method, we derived a single parameter set for the model that closely simulated the measured responses of tussock tundra to all of the experimental treatments. This parameterization allowed us to infer confidence limits for ecosystem components and processes that were not directly measured in the experiments. Thus, we used the model to estimate changes in ecosystem C storage by inferring key soil processes within the constraints imposed by measured components of the ecosystem C budget. Because tussock tundra is strongly N limited, we hypothesized that changes in ecosystem C storage in response to the experimental treatments would be constrained by several key aspects of C–N interactions: (1) changes in the amount of N in the ecosystem, (2) changes in the C:N ratios of vegetation and soil, and (3) redistribution of N between soil (with a low C:N ratio) and vegetation (with a high C:N ratio). The model results reveal widely differing patterns of change in C–N interactions and constraints on change in ecosystem C storage among treatments. For example, after 9 yr the elevated CO2 (2 × ambient) treatment and the N fertilized (10 g N·m−2·yr−1) treatment increased ecosystem C stocks by 1.4 and 2.9%, respectively. Whereas the increase in the CO2 treatment was due solely to an increase in the C:N ratios of vegetation and soil, the increase in the fertilized treatment was due to increased ecosystem N content and a shift of N from soil to vegetation. In contrast, the greenhouse (3.5°C above ambient) and shade (one-half ambient light) treatments decreased ecosystem C stocks by 1.9 and 2.7%, respectively. The primary reason for the net C losses in these treatments was an increase in respiration relative to photosynthesis, with a consequent decrease in the ecosystem C:N ratio. However, when we simulated the elevated temperatures in the greenhouse treatment without the confounding effects of decreased light intensity (an artifact of the greenhouse structures), there was a long-term increase in ecosystem C stocks because of increased photosynthetic response to the temperature-induced shift of N from soil to vegetation. If our simulated changes in ecosystem C storage are extrapolated for the ≈43 Pg C contained in arctic tundras globally, the maximum net gain or loss (≈0.3% per yr) from tundra would be equivalent to 0.13 Pg C/yr. Although fluxes of this magnitude would have a relatively minor impact on current changes in atmospheric CO2, the long-term impact on tundra C stores could be significant. The synthesis and insights provided by the model should make it possible to extrapolate into the future with a better understanding of the processes governing long-term changes in tundra C storage.

EFFECTS OF ROADSIDE DISTURBANCE ON SUBSTRATE AND VEGETATION PROPERTIES IN ARCTIC TUNDRA

Tundra adjacent to the gravel Dalton Highway in northern Alaska was examined for effects of 15 yr of chronic road and road dust disturbance. Road effects at a nonacidic site (soil pH ≥ 5.0) and an acidic site (soil pH < 5.0) were compared to examine differential susceptibility. Overall, effects on vegetation were more pronounced in acidic tundra. Initial substrate pH appears to control the degree of response to disturbance by road and calcareous road dust. Soil at the acidic site is normally pH 4.0, whereas in the disturbed area next to the road soil pH was as high as 7.3 ± 0.07 (at 2 m from the road edge). Soils next to the road had lower nutrient levels, altered organic horizon depth, higher bulk density, and lower moisture. Effects on snowpack include both increased drifting in the lee of the road and earlier meltout near the road due to dust-induced change in albedo. Permafrost thaw was deeper next to the road at both sites, and potentially could affect road structure detrimentally. Vegetation biomass of most taxa was reduced near the road at both sites. Total aboveground biomass of nonacidic tundra ranged from 330.0 ± 34.72 g/m2 (mean ± 1 se) at 2 m from the road to 690.7 ± 94.52 g/m2 at 100 m away from the road. Total biomass of acidic tundra ranged from 150.5 ± 16.60 g/m2 at 5 m from the road to 743.1 ± 168.98 g/m2 at 100 m from the road. Species richness in acidic tundra next to the road was less than half of that at 100 m away from the road. Community composition was altered most noticeably in acidic tundra. The moss Tomentypnum nitens, dominant in nonacidic arctic tussock tundra, was nearly equally abundant at all distances from the road at the nonacidic tundra site, whereas Sphagnum mosses, dominant in acidic low arctic tussock tundra, were virtually eliminated near the road at the acidic tundra site. Salix lanata was more abundant next to the road at the nonacidic site. Ordinations indicate that variation in vegetation cover is explained by distance from the road. Knowledge of differential effects of road construction and use, including the long-term effects of hydrological alterations and dust mobilization on local corridors, is key information for planning development in areas of arctic tundra. Planned placement of roads in the future should consider the impact of such changes to sensitive (acidic) tundra areas in the Arctic.

Effects of Roadside Disturbance on Substrate and Vegetation Properties in Arctic Tundra

Tundra adjacent to the gravel Dalton Highway in northern Alaska was examined for effects of 15 yr of chronic road and road dust disturbance. Road effects at a nonacidic site (soil pH ≥ 5.0) and an acidic site (soil pH < 5.0) were compared to examine differential susceptibility. Overall, effects on vegetation were more pronounced in acidic tundra. Initial substrate pH appears to control the degree of response to disturbance by road and calcareous road dust. Soil at the acidic site is normally pH 4.0, whereas in the disturbed area next to the road soil pH was as high as 7.3 ± 0.07 (at 2 m from the road edge). Soils next to the road had lower nutrient levels, altered organic horizon depth, higher bulk density, and lower moisture. Effects on snowpack include both increased drifting in the lee of the road and earlier meltout near the road due to dust-induced change in albedo. Permafrost thaw was deeper next to the road at both sites, and potentially could affect road structure detrimentally. Vegetation biomass of most taxa was reduced near the road at both sites. Total aboveground biomass of nonacidic tundra ranged from 330.0 ± 34.72 g/m2 (mean ± 1 se) at 2 m from the road to 690.7 ± 94.52 g/m2 at 100 m away from the road. Total biomass of acidic tundra ranged from 150.5 ± 16.60 g/m2 at 5 m from the road to 743.1 ± 168.98 g/m2 at 100 m from the road. Species richness in acidic tundra next to the road was less than half of that at 100 m away from the road. Community composition was altered most noticeably in acidic tundra. The moss Tomentypnum nitens, dominant in nonacidic arctic tussock tundra, was nearly equally abundant at all distances from the road at the nonacidic tundra site, whereas Sphagnum mosses, dominant in acidic low arctic tussock tundra, were virtually eliminated near the road at the acidic tundra site. Salix lanata was more abundant next to the road at the nonacidic site. Ordinations indicate that variation in vegetation cover is explained by distance from the road. Knowledge of differential effects of road construction and use, including the long-term effects of hydrological alterations and dust mobilization on local corridors, is key information for planning development in areas of arctic tundra. Planned placement of roads in the future should consider the impact of such changes to sensitive (acidic) tundra areas in the Arctic.

Measurement of Carbon Dioxide Emissions Plumes from Prudhoe Bay, Alaska Oil Fields

Large carbon dioxide plumes with concentrations up to 45 ppm aboveambient levels were measured about 15 km downwind of the Prudhoe Bay, Alaskamajor oil production facilities, located at 70° N Lat. above the ArcticCircle. The measured emissions were 1.3 × 103 metrictons (C) hour-1 (11.4× 106 metric tons(C) year-1), six times greater than the combustion emissionsassumed by Jaffe and coworkers in J. Atmos. Chem. 20 (1995), 213–227,based on 1989 reported Prudhoe Bay oil facility fuel consumption data, andfour times greater than the total C emissions reported by the oil facilitiesfor the same months as the measurement time periods. Variations in theemissions were estimated by extrapolating the observed emissions at a singlealtitude for all tundra research transect flights conducted downwind of theoil fields. These 30 flights yielded an average emission rate of1.02 × 103 metric tons (C) hour-1 with astandard deviation of 0.33 × 103. These quantity ofemissions are roughly equivalent to the carbon dioxide emissions of7–10 million hectares of arctic tussock tundra (Oechel and Vourlitis,Trends in Ecol. Evolution 9 (1994), 324–329).

Effects of drainage and temperature on carbon balance of tussock tundra micrososms

We examined the importance of temperature (7°C or 15°C) and soil moisture regime (saturated or field capacity) on the carbon (C) balance of arctic tussock tundra microcosms (intact blocks of soil and vegetation) in growth chambers over an 81-day simulated growing season. We measured gaseous CO2 exchanges, methane (CH4) emissions, and dissolved C losses on intact blocks of tussock (Eriophorum vaginatum) and intertussock (moss-dominated). We hypothesized that under increased temperature and/or enhanced drainage, C losses from ecosystem respiration (CO2 respired by plants and heterotrophs) would exceed gains from gross photosynthesis causing tussock tundra to become a net source of C to the atmosphere. The field capacity moisture regime caused a decrease in net CO2 storage (NEP) in tussock tundra micrososms. This resulted from a stimulation of ecosystem respiration (probably mostly microbial) with enhanced drainage, rather than a decrease in gross photosynthesis. Elevated temperature alone had no effect on NEP because CO2 losses from increased ecosystem respiration at elevated temperature were compensated by increased CO2 uptake (gross photosynthesis). Although CO2 losses from ecosystem respiration were primarily limited by drainage, CH4 emissions, in contrast, were dependent on temperature. Furthermore, substantial dissolved C losses, especially organic C, and important microhabitat differences must be considered in estimating C balance for the tussock tundra system. As much as ∼ 20% of total C fixed in photosynthesis was lost as dissolved organic C. Tussocks stored ∼ 2x more C and emitted 5x more methane than intertussocks. In spite of the limitations of this microcosm experiment, this study has further elucidated the critical role of soil moisture regime and dissolved C losses in regulating net C balance of arctic tussock tundra.

Effects of Climate Change on Decomposition in Arctic Tussock Tundra: A Modeling Synthesis

A model of litter decomposition (GENDEC; Moorhead and Reynolds, 1991) is used to examine the potential effects of changing soil climate on the decay of dead organic matter in a tussock tundra soil ...