Moist Acidic Tundra Research Articles

Response of CO2 exchange in a tussock tundra ecosystem to permafrost thaw and thermokarst development

Climate change in high latitudes can lead to permafrost thaw, which in ice‐rich soils can result in ground subsidence, or thermokarst. In interior Alaska, we examined seasonal and annual ecosystem CO2 exchange using static and automatic chamber measurements in three areas of a moist acidic tundra ecosystem undergoing varying degrees of permafrost thaw and thermokarst development. One site had extensive thermokarst features, and historic aerial photography indicated it was present at least 50 years prior to this study. A second site had a moderate number of thermokarst features that were known to have developed concurrently with permafrost warming that occurred 15 years prior to this study. A third site had a minimal amount of thermokarst development. The areal extent of thermokarst features reflected the seasonal thaw depth. The “extensive” site had the deepest seasonal thaw depth, and the “moderate” site had thaw depths slightly, but not significantly deeper than the site with “minimal” thermokarst development. Greater permafrost thaw corresponded to significantly greater gross primary productivity (GPP) at the moderate and extensive thaw sites as compared to the minimal thaw site. However, greater ecosystem respiration (Reco) during the spring, fall, and winter resulted in the extensive thaw site being a significant net source of CO2 to the atmosphere over 3 years, while the moderate thaw site was a CO2 sink. The minimal thaw site was near CO2 neutral and not significantly different from the extensive thaw site. Thus after permafrost thaw, initial periods of increased GPP and net CO2 uptake could be offset by elevated Reco during the winter, spring, and fall.

Chemical and isotopic characterization of size‐fractionated organic matter from cryoturbated tundra soils, northern Alaska

Recent studies indicate a second layer of organic matter often accumulates in the lower active layer and upper permafrost in arctic tundra soils as a result of cryoturbation. In this study, cryoturbated organic matter was characterized using a combination of physical size fractionation and modern analytical techniques for elemental composition (C and N), stable isotopes (δ13C and δ15N), radiocarbon content (Δ14C), and molecular fingerprinting (pyrolysis‐gas chromatography/mass spectrometry, Py‐GC/MS). The results indicated that cryoturbated organic matter could be highly bioavailable. Soil organic matter (SOM) associated with fine sand particles was considered to be the organic carbon pool most sensitive to the changing climate. More organic matter is stabilized on clay minerals in arctic tundra soils compared to those in temperate and tropical soils. The bioavailable soluble organic matter extracted from cryoturbated soil was found to have significant long‐term effects on carbon cycling. The similar molecular composition between cryoturbated and surface soil organic matter suggests that the vegetation cover has not significantly changed since the early Holocene. Furthermore, the SOM quality in moist acidic tundra was found to be higher than that of wet nonacidic tundra. With thawing permafrost and a deepening of the active layer, cryotrubated organic matter could reenter the biogeochemical cycles in the Arctic, resulting in a positive feedback to climate change.

Differential frost heave model for patterned ground formation: Corroboration with observations along a North American arctic transect

Frost boils in the Arctic are a manifestation of patterned ground in the form of nonsorted circles. Active frost boils involve convection of water through the soil that can bring basic salts from depth to the surface. As such, active frost boils can mitigate acidification and thereby strongly influence the type of vegetation supported by Arctic soils. The presence or absence of active frost boils is thought to play a pivotal role in establishing the sharp demarcation between moist nonacidic tundra (MNT) and moist acidic tundra (MAT) in the Arctic. The focus of this paper is to corroborate the predictions of a mathematical model that relates observable patterned ground features to ecosystem parameters with observations at the field sites along the North American Arctic Transect (NAAT) established by the Biocomplexity of Patterned‐Ground Ecosystems Project. Model predictions indicate that recurrent one‐dimensional frost heave can become unstable and evolve into multidimensional differential frost heave (DFH). A laboratory frost heave simulation produced a 28‐cm pattern in an active layer of 10 cm, which agrees with linear stability theory predictions. A finite element solution predicts three‐dimensional patterns with approximately 3‐m spacing develop in a 1.0‐m active layer with a surface n factor of 0.35, which agrees well with field observations from the NAAT. The lack of significant frost boil activity in the MAT is a result of suppression of DFH owing to denser surface vegetation characterized by low n factors. Prominent active frost boils are observed in the MNT at higher latitudes with more sparse vegetation characterized by higher n factors that promote DFH. However, at the northernmost field sites frost boils cannot be generated even though the n factors are relatively high owing to very rapid freezing conditions that mitigate DFH.

Spatial heterogeneity of tundra vegetation response to recent temperature changes

AbstractThe spatial heterogeneity of recent decadal dynamics in vegetation greenness and biomass in response to changes in summer warmth index (SWI) was investigated along spatial gradients on the Arctic Slope of Alaska. Image spatial analysis was used to examine the spatial pattern of greenness dynamics from 1991 to 2000 as indicated by variations of the maximum normalized difference vegetation index (Peak NDVI) and time‐integrated NDVI (TI‐NDVI) along latitudinal gradients. Spatial gradients for both the means and temporal variances of the NDVI indices for 0.1° latitude intervals crossing three bioclimate subzones were analyzed along two north–south Arctic transects. NDVI indices were generally highly variable over the decade, with great heterogeneity across the transects. The greatest variance in TI‐NDVI was found in low shrub vegetation to the south (68.7–68.8°N) and corresponded to high fractional cover of shrub tundra and moist acidic tundra (MAT), while the greatest variance in Peak‐NDVI predominately occurred in areas dominated by wet tundra (WT) and moist nonacidic tundra (MNT). Relatively high NDVI temporal variances were also related to specific transitional areas between dominant vegetation types. The regional temporal variances of NDVI from 1991 to 2000 were largely driven by meso‐scale climate dynamics. The spatial heterogeneity of the NDVI variance was mostly explained by the fractional land cover composition, different responses of each vegetation type to climate change, and patterned ground features. Aboveground plant biomass exhibited similar spatial heterogeneity as TI‐NDVI; however, spatial patterns are slightly different from NDVI because of their nonlinear relationship.

Differences in Surface Roughness, Energy, and CO2 Fluxes in Two Moist Tundra Vegetation Types, Kuparuk Watershed, Alaska, U.S.A

Roughly 70% of the tundra north of the Brooks Range, Alaska, can be classified as moist nonacidic (39%) and moist acidic tundra (31%). We investigated the differences in energy partitioning and carbon balance among these two important landscape types. Despite structural differences in plant growth forms, moss cover, and soil pH, the sensible and latent heat fluxes were quite similar. However, aerodynamic properties (i.e. roughness length), ground heat flux, and CO2 flux were significantly different: aerodynamic roughness of moist acidic tundra was 2.1 times higher than, and ground heat flux was 36% lower than the values obtained from moist nonacidic tundra. Daily carbon balance showed 26% more net CO2 uptake (with 34% greater ecosystem respiration and 30% greater gross primary production) in moist acidic tundra. The greater respiration rate in moist acidic tundra was explained by differences in surface soil temperatures, whereas the rate of gross primary production was only half of what was expected from observed differences in leaf area index. These differences suggest that understanding the controls of CO2 exchange in nonacidic moist tundra vegetation will be critical for determining the carbon budget of the Low Arctic region.

Spatial and Temporal Heterogeneity of Vegetation Properties among Four Tundra Plant Communities at Ivotuk, Alaska, U.S.A.

Intraseasonal patterns of normalized difference vegetation index (NDVI), leaf area index (LAI), and phytomass were compared for four tundra vegetation types at Ivotuk, Alaska, during summer 1999. The vegetation types included moist acidic tundra (MAT), moist nonacidic tundra (MNT), mossy tussock tundra, and shrub tundra. The seasonal curves of NDVI were similar among the vegetation types but with varying magnitudes of the peak values. Peak NDVI in the shrub tundra (0.83) was significantly greater than in MAT (0.76), which was significantly greater than in MNT (0.71) and mossy tussock tundra (0.70). LAI and phytomass exhibited high temporal variability with distinct seasonality only in shrub tundra. Seasonal LAI and NDVI patterns were therefore correlated only in shrub tundra, which was attributed to the high quantity of deciduous shrub foliage present in this community and absent in the other vegetation types. Shrub tundra peak live above-ground phytomass (1256 ± 123 g m−2) was significantly greater than peak live above-ground phytomass for MAT, MNT, and mossy tussock tundra (722 ± 71, 773 ± 53, 703 ± 39 g m−2 respectively, P < 0.05). Relative abundances of deciduous shrubs, mosses, and graminoids were revealed as key components controlling differences in NDVI, LAI, and phytomass among tundra vegetation types.

The nature of spatial transitions in the Arctic

AbstractAim Describe the spatial and temporal properties of transitions in the Arctic and develop a conceptual understanding of the nature of these spatial transitions in the face of directional environmental change.Location Arctic tundra ecosystems of the North Slope of Alaska and the tundra‐forest region of the Seward Peninsula, AlaskaMethods We synthesize information from numerous studies on tundra and treeline ecosystems in an effort to document the spatial changes that occur across four arctic transitions. These transitions are: (i) the transition between High‐Arctic and Low‐Arctic systems, (ii) the transition between moist non‐acidic tundra (MNT) and moist acidic tundra (MAT, also referred to as tussock tundra), (iii) the transition between tussock tundra and shrub tundra, (iv) the transition between tundra and forested systems. By documenting the nature of these spatial transitions, in terms of their environmental controls and vegetation patterns, we develop a conceptual model of temporal dynamics of arctic ecotones in response to environmental change.Results Our observations suggest that each transition is sensitive to a unique combination of controlling factors. The transition between High and Low Arctic is sensitive primarily to climate, whereas the MNT/MAT transition is also controlled by soil parent material, permafrost and hydrology. The tussock/shrub tundra transition appears to be responsive to several factors, including climate, topography and hydrology. Finally, the tundra/forest boundary responds primarily to climate and to climatically associated changes in permafrost. There were also important differences in the demography and distribution of the dominant plant species across the four vegetation transitions. The shrubs that characterize the tussock/shrub transition can achieve dominance potentially within a decade, whereas spruce trees often require several decades to centuries to achieve dominance within tundra, and Sphagnum moss colonization of non‐acidic sites at the MNT/MAT boundary may require centuries to millennia of soil development.Main conclusions We suggest that vegetation will respond most rapidly to climatic change when (i) the vegetation transition correlates more strongly with climate than with other environmental variables, (ii) dominant species exhibit gradual changes in abundance across spatial transitions, and/or (iii) the dominant species have demographic properties that allow rapid increases in abundance following climatic shifts. All three of these properties characterize the transition between tussock tundra and low shrub tundra. It is therefore not surprising that of the four transitions studied this is the one that appears to be responding most rapidly to climatic warming.

Litter decomposition in moist acidic and non-acidic tundra with different glacial histories.

Plant species composition is a potentially important source of variation in soil processes, including decomposition rates. We compared litter decomposition in two common and compositionally distinct tundra vegetation types in the northern foothills of the Brooks Range, Alaska: moist acidic tundra (soil pH 3-4), which occurs primarily on older landscapes, and moist non-acidic tundra (soil pH 6-7), which occurs primarily on landscapes with a more recent history of glaciation and has higher graminoid and forb abundance and lower woody shrub abundance than acidic tundra. To separate the influence of plant community composition from that of the soil environment, we decomposed the same nine substrates at a moist acidic and a moist non-acidic site located less than 2 km apart. Substrates included leaf litter of the dominant species in each growth form (graminoid, deciduous shrub, evergreen shrub, forb, moss) as well as woody stems of the deciduous shrub Betula nana. Then, we estimated above-ground community-level decomposition by weighting the decay rate of each species in the community by its proportional contribution to overall above-ground net primary production (ANPP). In contrast to our expectations, community-level decomposition rates estimated using the site-average decay rate for each substrate were similar between the two sites, likely because growth forms differed little in their leaf litter decay. By contrast, when site-specific decay rates were used to estimate community-level decomposition, it was nearly twice as fast at the older, moist acidic tundra site because most substrates decayed faster at that site, indicating a more favorable environment for decomposition in acidic tundra. Site differences in soil moisture and temperature could not explain site differences in decomposition. However, higher soil N availability at the moist acidic tundra may have contributed to faster decomposition since, in a separate experiment, fertilization with N stimulated decomposition of a common substrate at both sites. In addition, lower pH in acidic tundra may promote greater abundance of soil fungi, perhaps explaining faster decomposition rates at that site. In summary, the large differences in plant species composition between moist acidic and non-acidic tundra are likely to not contribute to site differences in decomposition. Nevertheless, decomposition is much more rapid in moist acidic tundra. Thus, landscape age and associated differences in soil pH and nutrient availability are important sources of variation in decomposition rate in upland Alaskan tundra.

Controls over intra-seasonal dynamics of AVHRR NDVI for the Arctic tundra in northern Alaska

We analysed the Normalized Difference Vegetation Index (NDVI), calculated from biweekly NOAA Advanced Very High Resolution Radiometer (AVHRR) images for northern Alaska at both regional (latitudinal gradients) and site scales. Our objectives were to determine if tundra types and arctic subzones could be differentiated in terms of intra-seasonal patterns of greenness, and to construct the relationships between NDVI and air and soil temperatures. There were common intra-seasonal patterns of NDVI along two latitudinal transects, and a general latitudinal gradient of time of greenness onset and length of growing season was observed. At the site scale, in most cases, wet tundra (WT) had the lowest NDVI values throughout the year, while shrub tundra (ST) had the highest values. The peak NDVI appeared in the period of 22 July to 4 August, with mean values of 0.552 for ST, 0.495 for moist acidic tundra (MAT), 0.434 for sandy tundra (Sandy), 0.426 for moist non-acidic tundra (MNT) and 0.343 for WT. The earliest onset of greenness occurred in ST, followed by MAT, Sandy and MNT, while WT had the latest onset. There were positive linear relationships between bi-weekly NDVI anomalies and air temperature, soil surface temperature, and 20 cm depth soil temperature anomalies in the region. Plant functional type abundances, tundra type, air and soil temperatures all appeared to influence the seasonal dynamics of NDVI.

Characterizing soil organic matter quality in arctic soil by cover type and depth

In the past 30 years, the arctic climate has warmed appreciably. Mounting evidence suggests that climate warming is being amplified at the earth's polar regions. A warmer Arctic could lead to the gradual loss of circumpolar permafrost. Northern soils are estimated to contain 25–33% of the world's soil carbon, much of which is frozen in permafrost as poorly decomposed plant remains. A warming and thawing of northern permafrost would result in an increase in soil organic matter (SOM) exposed to decomposition. Carbon dioxide (CO 2) or methane (CH 4) released from decomposing SOM would likely result in a positive feedback to climate warming. The rate that SOM decomposes in soil depends on many variables, including temperature, soil moisture, nutrient availability, pH, oxidation–reduction potential, and chemical composition of the SOM. This paper addresses the effect of regional scale ecosystem differences on SOM composition and the potential for CO 2 to be respired from these soils under SOM-limiting conditions. In previous research, an empirical model was developed to predict CO 2 flux from arctic soils based on specific compounds in the SOM. The model was built using an incubation designed to create SOM-limiting conditions and pyrolysis-gas chromatography/mass spectrometry (py-GC/MS) analysis of SOM. SOM-limiting conditions were defined as the state in which microbial respiration was limited only by the SOM quality. That is, during the incubation, ample nutrients were available to microorganisms, the pH was neutral, and the system was kept aerobic, mixed, and at 20 °C. SOM that was rapidly mineralized was defined as being of high quality. SOM that was slowly mineralized was defined as being of low quality. With an understanding of SOM quality in different soil types, one can better understand the relative potential for different soils to contribute to atmospheric CO 2 in a warmer, drier arctic environment. In the research described herein, soils from across the Western and Northern Alaska transects were analyzed to determine if SOM quality could be tied to cover class, a parameter that can be remotely sensed. In nearly all cases, SOM quality under similar cover classes was of similar quality regardless of its geographic origin. The clearest trend observed was that SOM quality was highest in soil under moist acidic tundra, followed by tussock tundra and tundra/shrub transitions, shrubs, and nonacidic tundra, respectively.

Responses of moist non‐acidic arctic tundra to altered environment: productivity, biomass, and species richness

In arctic Alaska, researchers have manipulated air temperature, light availability, and soil nutrient availability in several tundra communities over the past two decades. These communities responded quite differently to the same manipulations, and species responded individualistically within communities and among sites. For example, moist acidic tundra is primarily nitrogen (N)‐limited, whereas wet sedge tundra is primarily phosphorus (P)‐limited, and the magnitude of growth responses varies across sites within communities. Here we report results of four years of manipulated nutrients (N and/or P) and/or air temperature in an understudied, diverse plant community, moist non‐acidic tussock tundra, in northern Alaska. Our goals were to determine which factors limit above‐ground net primary productivity (ANPP) and biomass, how community composition changes may affect ecosystem attributes, and to compare these results with those from other communities to determine their generality.Although relative abundance of functional groups shifted in several treatments, the only significant change in community‐level ANPP and biomass occurred in plots that received both N and P, driven by an increase in graminoid biomass and production resulting from a positive effect of adding N. There was no difference in community biomass among any other treatments; however, some growth forms and individual species did respond. After four years no one species has come to dominate the treatment plots and species richness has not changed. These results are similar to studies in dry heath, wet sedge, and moist acidic tundra where community biomass had the greatest response to both N and P and warming results were more subtle. Unlike in moist acidic tundra where shrub biomass increased markedly with fertilization, our results suggest that in non‐acidic tundra carbon sequestration in plant biomass will not increase substantially under increased soil nutrient conditions because of the lack of overstory shrub species.

Carbon and Nitrogen Cycling in Soils from Acidic and Nonacidic Tundra with Different Glacial Histories in Northern Alaska

Moist acidic and nonacidic tundra are two of the most common vegetation types of the tundra in the northern foothills of the Brooks Range, Alaska, and they differ considerably in vegetation, soil nutrient availability, and soil pH. Both occur on mesic, gentle slopes, but acidic tundra is more common on older glacial surfaces whereas nonacidic tundra is more common on younger surfaces. Although much prior research has focused on moist acidic tundra, nonacidic tundra is still relatively unstudied. We compared rates of soil carbon (C) and nitrogen (N) cycling and their response to warming and changes in moisture in moist acidic tundra on Itkillik I glacial drift (50,000 –120,000 years old, pH 3– 4) and moist nonacidic tundra on Itkillik II glacial drift (11,500 – 60,000 year old, pH 6 –7). We hypothesized that rates of soil C and N cycling would be faster at the nonacidic site because it has a more favorable pH for microbial activity and higher-quality organic matter inputs arising from its greater herbaceous plant production relative to the acidic site. However, in contrast to our hypothesis, in situ soil respiration, as well as respiration, dissolved organic C production, and net N mineralization in laboratory incubations, was greater for soils from the acidic site. Nevertheless, the sites responded similarly to manipulations of temperature and moisture, exhibiting exponential increases in respiration with warming between 4°C and 15°C but surprisingly little sensitivity to changes in moisture between 300% and 700%. Slower soil organic matter decomposition at the nonacidic site likely results from the stabilization of soil organic matter by high concentrations of calcium.

Spatial characteristics of AVHRR‐NDVI along latitudinal transects in northern Alaska

Abstract. Two‐weekly AVHRR images were used to examine spatial patterns of the normalized difference vegetation index (NDVI) and their relationships with environmental variables for moist acidic tundra (MAT) and moist non‐acidic tundra (MNT) along two latitudinal transects in northern Alaska. The NDVI database was derived from a 5‐yr time series (1995–1999) of two‐weekly AVHRR composites for Alaska. A digital climate map, digital elevation map and vegetation map were processed and overlain with the NDVI grid. Homogeneous vegetation patches for both MAT and MNT were defined as sample sites using infrared aerial photos, MSS images and the vegetation map along the transects. Linear and non‐linear regression modeling were performed between NDVI indices and environmental variables, total summer warmth (TSW) and elevation. It was demonstrated that along both western and eastern transects, there were obvious latitudinal trends of peak NDVI (AP‐NDVI), average growing season NDVI (GS‐NDVI), and early June NDVI (EJ‐NDVI). In most cases, MNT had lower NDVI values than MAT throughout the year. There were significant (p&lt;0.01) relations between NDVI (AP‐NDVI, GS‐NDVI and EJ‐NDVI) and total summer warmth (TSW) and elevation in the region. EJ‐NDVI showed the strongest correlation with TSW or elevation, making it the most sensitive NDVI indicator along environmental gradients in northern Alaska. NDVI was likely controlled by TSW and elevation, with the former being dominant.

Spatial characteristics of AVHRR-NDVI along latitudinal transects in northern Alaska

Two-weekly AVHRR images were used to exam- ine spatial patterns of the normalized difference vegetation index (NDVI) and their relationships with environmental vari- ables for moist acidic tundra (MAT) and moist non-acidic tundra (MNT) along two latitudinal transects in northern Alaska. The NDVI database was derived from a 5-yr time series (1995-1999) of two-weekly AVHRR composites for Alaska. A digital climate map, digital elevation map and vegetation map were processed and overlain with the NDVI grid. Homo- geneous vegetation patches for both MAT and MNT were defined as sample sites using infrared aerial photos, MSS images and the vegetation map along the transects. Linear and non-linear regression modeling were performed between NDVI indices and environmental variables, total summer warmth (TSW) and elevation. It was demonstrated that along both western and eastern transects, there were obvious latitudinal trends of peak NDVI (AP-NDVI), average growing season NDVI (GS-NDVI), and early June NDVI (EJ-NDVI). In most cases, MNT had lower NDVI values than MAT throughout the year. There were significant (p < 0.01) relations between NDVI (AP-NDVI, GS-NDVI and EJ-NDVI) and total summer warmth (TSW) and elevation in the region. EJ-NDVI showed the strongest correlation with TSW or elevation, making it the most sensitive NDVI indicator along environmental gradients in northern Alaska. NDVI was likely controlled by TSW and elevation, with the former being dominant.

Responses of an arctic landscape to Lateglacial and early Holocene climatic changes: the importance of moisture

Many of the physical and biological processes that characterize arctic ecosystems are unique to high latitudes, and their sensitivities to climate change are poorly understood. Stratigraphic records of land–surface processes and vegetation change in the Arctic Foothills of northern Alaska reveal how tundra landscapes responded to climatic changes between 13,000 and 8000 14C yr BP. Peat deposition began and shrub vegetation became widespread ca. 12,500 14C yr BP, probably in response to the advent of warmer and wetter climate. Increased slope erosion caused rapid alluviation in valleys, and Populus trees spread northward along braided floodplains before 11,000 14C yr BP. Lake levels fell and streams incised their floodplains during the Younger Dryas (YD) (11,000–10,000 14C yr BP). A hiatus in records of Populus suggest that its geographic range contracted, and pollen records of other species suggest a cooler and drier climate during this interval. Basal peats dating to the YD are rare, suggesting that rates of paludification slowed. Immediately after 10,000 14C yr BP, lake levels rose, streams aggraded rapidly again, intense solifluction occurred, and Populus re-invaded the area. Moist acidic tundra vegetation was widespread by 8500 14C yr BP along with wet, organic-rich soils. Most of these landscape-scale effects of climatic change involved changes in moisture. Although low temperature is the most conspicuous feature of arctic climate, shifts in effective moisture may be the proximate cause for many of the impacts that climate change has in arctic regions.

Calcium-rich tundra, wildlife, and the “Mammoth Steppe”

Moist calcareous tundra has many ecosystem properties analogous to those of the hypothesized “Mammoth Steppe” or steppe tundra of glacial Beringia, and today it is an important range land for arctic wildlife. Moist calcium-rich tundras are associated with moderately drained fine-grained arctic soils with relatively high soil pH. Compared to tussock tundra, moist calcareous tundra has 10 times the extractable Ca in the active layer, half the organic layer thickness, and 30% deeper active layers. The vegetation is less shrubby than that of tussock tundra, has twice the vascular-plant species richness, greater habitat diversity at multiple scales, and contains plants with fewer antiherbivory chemicals and more nutrients (particularly calcium). It has some properties that are unlike the hypothesized steppe tundras, including abundant sedges and a mossy understory. Moist calcium-rich tundra is common north of the acidic shrubby southern tundras and south of the sparsely vegetated polar deserts. Successionally, this tundra type occurs between the present-day dry calcareous dune vegetation and tussock tundra. Thus, at least conceptually, moist calcareous tundra is intermediate between the steppe tundra and tussock tundra and provides insights regarding the transitions from cold arid Beringian ecosystems to present-day moist acidic tundra.

Landsat MSS-derived land-cover map of northern Alaska: Extrapolation methods and a comparison with photo-interpreted and AVHRR-derived maps

Vegetation maps of Arctic areas are needed for a variety of tundra ecosystem and climate change studies and for extrapolating from relatively small, well-known sites to broader regions. We made a preliminary land-cover map of northern Alaska by extrapolating a Landsat Multi-Spectral Scanner (MSS) derived classification of the Kuparuk River Region (KRR) to all of northern Alaska. We used a 26-scene mosaic that was previously made by the EROS Data Center, and a K-means unsupervised classification algorithm to produce eight broad land-cover categories. The northern Alaska-MSS map (NA-MSS) has the following land-cover categories and respective percentage coverage within the 200000km2 Arctic Slope: Dry Prostrate-shrub Tundra and Barrens, 8%; Moist Graminoid, Prostrate-shrub Tundra, 22%; Moist Tussock-graminoid, Dwarf-shrub Tundra, 4%; Moist Dwarf-shrub, Tussock-graminoid, Tundra, 28%; Moist Lowshrub Tundra and other Shrublands, 19%; Wet Graminoid Tundra, 9%; Water, 6%; Clouds and ice, <1%; Shadows, 4%. Ancillary data were used to improve the classification for a region of sandy tundra not encountered in the KRR and to separate shadows in the mountains from water and wetlands elsewhere. The NA-MSS map helps to define the distribution of a recently described moist nonacidic (calcareous) tundra and areas of shrublands that are of broad interest to the tundra- and climate-change modelling communities. A boundary separating moist acidic tundra from moist nonacidic tundra stretches across all of northern Alaska (about 850km). Shrub-dominated tundra is prevalent in the southern and western (warmer, wetter) portions of the map. We created difference maps for comparing the northern Alaska-MSS (NA-MSS) map to the Major Ecosystems of Alaska (MEA) map and a map derived from a time series of Advanced Very High Resolution Radiometer images (NA-AVHRR). Compared to the other maps, the NA-MSS map provides more detailed information for moist tundra areas and shows more shrub-dominated vegetation with different spatial distributions than the other two maps. An accuracy assessment of the map will be performed in 1999.

Characteristics of cryogenic soils along a latitudinal transect in arctic Alaska

The morphological, chemical, and physical properties of arctic tundra soils were examined along a 200‐km latitudinal gradient in northern Alaska which includes two major physiographic provinces; the Arctic Coastal Plain and the Arctic Foothills. Annual air temperature and precipitation increase along the gradient from north to south. Soils on the Arctic Coastal Plain support wet, nonacidic tundra vegetation and have high carbonate contents. Soil on the Arctic Foothills support moist, nonacidic tundra in the northern part and moist acidic tundra in the southern part. Most arctic tundra soils are characterized by medium texture, poor drainage, and high organic matter content. From north to south along the transect, the base saturation of the active layer decreases and exchangeable aluminum increases from north to south. Most soils have strongly developed cryogenic features, including warped and broken horizons, ice lenses, thin platy structure, and organic matter frost‐churned into the ice‐rich upper permafrost horizons.

Energy and trace-gas fluxes across a soil pH boundary in the Arctic

Studies and models of trace-gas flux in the Arctic consider temperature and moisture to be the dominant controls over land–atmosphere exchange1,2, with little attention having been paid to the effects of different substrates. Likewise, current Arctic vegetation maps for models of vegetation change recognize one or two tundra types3,4 and do not portray the extensive regions with different soils within the Arctic. Here we show that rapid changes to ecosystem processes (such as photosynthesis and respiration) that are related to changes in climate and land usage will be superimposed upon and modulated by differences in substrate pH. A sharp soil pH boundary along the northern front of the Arctic Foothills in Alaska separates non-acidic (pH > 6.5) ecosystems to the north from predominantly acidic (pH < 5.5) ecosystems to the south. Moist non-acidic tundra has greater heat flux, deeper summer thaw (active layer), is less of a carbon sink, and is a smaller source of methane than moist acidic tundra.

Soils and Cryoturbation in Moist Nonacidic and Acidic Tundra in the Kuparuk River Basin, Arctic Alaska, U.S.A.

We compared 22 pedons derived from silty materials in moist nonacidic tundra (MNT) and moist acidic tundra (MAT) in the arctic foothills of the 9200-km2 Kuparuk River basin in northern Alaska. Soils in MNT have thinner organic horizons, a significantly thicker active layer, and greater cryoturbation than soils in MAT. The quantities of clay and organic-plus-inorganic C in the upper 100 cm are comparable; however, soils in MNT have significantly greater amounts of extractable Ca, Mg, and sum of base cations and significantly lower amounts of exchangeable acidity and Al than soils in MAT. Tissues from forbs, sedges, and woody shrubs in MNT have two to three times as much Ca as the same or similar species in MAT. The area of nonsorted circles was significantly greater in MNT (9.6%) than in MAT (0.9%). Although the existence of nonacidic tundra in the Arctic has been known for some time, its origin and distribution have not been fully explained. Our data link soil and vegetation properties and indicate that cryoturbation plays an important role in maintaining MNT in arctic Alaska.