Patterned Ground Features Research Articles

Tundra landform and vegetation productivity trend maps for the Arctic Coastal Plain of northern Alaska

Arctic tundra landscapes are composed of a complex mosaic of patterned ground features, varying in soil moisture, vegetation composition, and surface hydrology over small spatial scales (10–100 m). The importance of microtopography and associated geomorphic landforms in influencing ecosystem structure and function is well founded, however, spatial data products describing local to regional scale distribution of patterned ground or polygonal tundra geomorphology are largely unavailable. Thus, our understanding of local impacts on regional scale processes (e.g., carbon dynamics) may be limited. We produced two key spatiotemporal datasets spanning the Arctic Coastal Plain of northern Alaska (~60,000 km2) to evaluate climate-geomorphological controls on arctic tundra productivity change, using (1) a novel 30 m classification of polygonal tundra geomorphology and (2) decadal-trends in surface greenness using the Landsat archive (1999–2014). These datasets can be easily integrated and adapted in an array of local to regional applications such as (1) upscaling plot-level measurements (e.g., carbon/energy fluxes), (2) mapping of soils, vegetation, or permafrost, and/or (3) initializing ecosystem biogeochemistry, hydrology, and/or habitat modeling.

Tracking rapid landscape change with repeated photography, Gros Morne National Park, Canada

At various coastal and inland sites in and around Gros Morne National Park in western Newfoundland, photographs taken periodically over many decades illustrate the physical stability of landforms. ἀese images provide a convenient, qualitative way to track the development of stone rings and patterned ground, the movement of rocks along intertidal platforms, changes to marine estuaries and to alluvial rivers and fans, temporal trends in late-lying snow beds along mountain tops, and slope failure by landslides and rock falls. ἀis study has established a spatial and temporal photographic record of slope failures along the steep cliḀs of Western Brook Pond, showing that nearly all of the sites identiᴀed in earlier studies as high risk of failure have remained stable. In contrast, thin-skinned landslides along Winter House Brook have remained active for at least 100 years. Little evidence of physical changes in patterned ground features in Trout River Gulch was found, other than frost-heaving in soils disturbed by road construction. Fluctuations from year to year in the level of gravel beaches along parts of the coast are common, and blow-outs continue to modify coastal sand dunes. Apart from certain engineered sites where change was obviously driven by direct human activities, the immediate cause or “driver” of change was natural (non-human), the result of gravitational instability, heavy precipitation, wave and storm action, frost heaving, and other background processes of the sort that long pre-date the coming of people to the region. Continuation of this kind of inexpensive, non-invasive monitoring can assist in assessing ecological integrity, managing public safety, and interpreting landscape processes for Park visitors.

Relative Paleoenvironmental Adjustments Following Deglaciation of the Byers Peninsula (Livingston Island, Antarctica)

ABSTRACTIn the present context of fast warming in the Antarctic Peninsula (AP), understanding past and recent environmental dynamics is crucial to better assess future environmental responses in this region. Very detailed geomorphological maps can help to interpret the interaction between glacial, periglacial, and paraglacial systems. The Holocene environmental sequence on Byers Peninsula, an ice-free area in the westernmost part of Livingston Island (Maritime Antarctica), is still poorly understood. This paper focuses on the geomorphology of the Cerro Negro, a volcanic plug located on the southeast fringe of this peninsula. The distribution of landforms and deposits generated by different geomorphological processes provides insights into the Holocene environmental dynamics on Byers Peninsula. During the fieldwork campaign in January 2014, an accurate geomorphological map of Cerro Negro and its surroundings was generated. Four geomorphological environments were identified: hill, north slope, southern escarpment, and marine terraces and present-day beach. Periglacial landforms are abundant, especially patterned ground features (blockstreams, sorted stone circles, stone stripes). All these cryoturbation landforms, except blockstreams, are active under present-day climate conditions. In addition to a sequence of Holocene marine terraces and slope deposits, such as talus cones and rockfalls, there is a glacial moraine adjoining the northern slope of the hill. From the morphostratigraphic correlation between the active and inactive landforms, we infer three main phases describing the paleoenvironmental evolution in this area: (1) maximum glacial expansion; (2) Holocene glacial retreat, lake formation, and intense periglacial dynamics; and (3) deglaciation of the Byers Peninsula and widespread periglacial processes. The Cerro Negro has been a nunatak for most of the Holocene; the lake located near the summit of this hill appeared when most of the Byers Peninsula was still covered by glacial ice. This study constitutes an example of how an accurate geomorphological characterization of a small area can complement other approaches to generate a better understanding of the paleoenvironmental evolution in the region.

Small-scale variability of soil properties and soil–vegetation relationships in patterned ground on different lithologies (NW Italian Alps)

Cryogenic patterned ground represents spectacular periglacial landscapes. On the Alps, sorted/nonsorted patterned ground features larger than 1m, formed by deep seasonal cryoturbation with or without permafrost, occupy exposed, stable surfaces at high altitudes and represent a particularly harsh habitat for plant life.We analyzed soils across transects through typical active patterned ground features (sorted/nonsorted circles and stripes) on four common lithotypes (calcschists, serpentinite, gabbros and gneiss) in the Western Italian Alps, in order to observe the small-scale lateral and depth variability in physico-chemical properties, and their association with cryoturbation, plant cover and species distribution.Cryoturbation was correlated with lateral/vertical textural sorting across features, mostly visible on silt and coarse sand, but with opposite trends on sorted and nonsorted patterned ground types. A strong lateral variability in organic carbon was detected, with high values near the better vegetated rims and low contents in the centers. Exchangeable bases, heavy metals and nutrients followed the same distribution. However, the differences inherited from the parent materials were overwhelming.Climate is the main driver of high altitude ecosystems, reducing total plant cover and causing cryoturbation, which in turn creates strong edaphic gradients over small distances. Plant species and communities are well correlated with edaphic properties inherited from the parent materials, such as exchangeable Ca and heavy metals.

Rich and cold: diversity, distribution and drivers of fungal communities in patterned‐ground ecosystems of the North American Arctic

Fungi are abundant and functionally important in the Arctic, yet comprehensive studies of their diversity in relation to geography and environment are not available. We sampled soils in paired plots along the North American Arctic Transect (NAAT), which spans all five bioclimatic subzones of the Arctic. Each pair of plots contrasted relatively bare, cryoturbated patterned-ground features (PGFs) and adjacent vegetated between patterned-ground features (bPGFs). Fungal communities were analysed via sequencing of 7834 ITS-LSU clones. We recorded 1834 OTUs - nearly half the fungal richness previously reported for the entire Arctic. These OTUs spanned eight phyla, 24 classes, 75 orders and 120 families, but were dominated by Ascomycota, with one-fifth belonging to lichens. Species richness did not decline with increasing latitude, although there was a decline in mycorrhizal taxa that was offset by an increase in lichen taxa. The dominant OTUs were widespread even beyond the Arctic, demonstrating no dispersal limitation. Yet fungal communities were distinct in each subzone and were correlated with soil pH, climate and vegetation. Communities in subzone E were distinct from the other subzones, but similar to those of the boreal forest. Fungal communities on disturbed PGFs differed significantly from those of paired stable areas in bPGFs. Indicator species for PGFs included lichens and saprotrophic fungi, while bPGFs were characterized by ectomycorrhizal and pathogenic fungi. Our results suggest that the Arctic does not host a unique mycoflora, while Arctic fungi are highly sensitive to climate and vegetation, with potential to migrate rapidly as global change unfolds.

Microorganisms in Small Patterned Ground Features and Adjacent Vegetated Soils along Topographic and Climatic Gradients in the High Arctic, Canada

In this study, we determine differences in total biomass of soil microorganisms and community structure (using the most probable number of bacteria (MPN) and the number of fungal genera) in patterned ground features (PGF) and adjacent vegetated soils (AVS) in mesic sites from three High Arctic islands in order to characterize microbial dynamics as affected by cryoturbation, and a broad bioclimatic gradient. We also characterize total biomass of soil microorganisms and the most probable number of bacteria along a topographic gradient within each bioclimatic subzone to evaluate whether differences in topography lead to differences in microbial dynamics at a smaller scale. We found total microbial biomass C, the most probable number of heterotrophic bacteria, and fungal genera vary along this bioclimatic gradient. Microbial biomass C decreased with increasing latitude. Overall, microbial biomass C, MPN and the number of fungal isolates were higher in AVS than in PGFs. The effects which topographic position had on microbial biomass C varied across the bioclimatic gradient as there was no effect of topographic position in Isachsen (subzone A) and Mould Bay (subzone B), when compared to Green Cabin (subzone C, warmer site).There was no effect of topographic position on MPN counts at Mould Bay and Green Cabin. However, in Isachsen, MPN counts were highest in the wet topographic position as compared to the mesic and dry. In conclusion, PGFs seem to decouple the effect climate that might have on the total biomass of soil microorganisms along the bioclimatic gradient; and influence gets ameliorated as latitude increases. Similarly, the effect of topography on the total microbial biomass is significant at the warmest bioclimatic zone of the gradient. Thus, climate and topographic effects on total microbial biomass increase with warmer climate.

Cryoturbation in the Central Brooks Range, Alaska

Cryoturbation in permafrost-affected soils is important to many Arctic biogeochemical processes and critical to the appropriate classification of Gelisols. Standardized methodologies for describing the soils formed from these processes and knowledge regarding the time scales at which they operate continue to evolve. Twenty-six profiles were described across a transect in the Midas Lake region of the Central Brooks Range of Alaska using a modified version of the standard USDA and Turbel description protocol that is appropriate for work in wilderness areas. Profile descriptions and associated field data were aggregated and generalized to reveal major trends and relationships in horizonation between cryoturbated and noncryoturbated soils on the transect. A conceptual model for the geomorphic relationships of cryoturbated and noncryoturbated soils on this landscape was developed. In addition to a landscape-scale perspective, individual profiles were described on patterned ground features at a location where cryoturbated horizons were strongly expressed. Samples from these profiles were analyzed for cesium-137 (137Cs) activity, and it was found that the surficial activity of this fallout radioisotope varied strongly by material type and position on the patterned ground microtopography. These differences suggest that the use of fallout isotopes, such as 137Cs, when combined with quantitative profile descriptions and a standardized description protocol, may significantly improve our understanding of the spatial distribution and mechanisms of cryoturbation.

Soil Nitrogen Transformations Associated with Small Patterned‐Ground Features along a North American Arctic Transect

ABSTRACTSmall patterned‐ground features (PGFs) in the Arctic have unique soil properties that vary with latitude and may greatly affect tundra biogeochemistry. Because nitrogen availability can strongly limit arctic vegetation growth, we examined how soil nitrogen transformations differ between PGFs and the surrounding inter‐PGF tundra along an arctic latitudinal gradient. We collected soils at eight sites from the Alaskan Low Arctic to the Canadian High Arctic. The soils were incubated for 21 days at 9 °C and 15 °C and analysed for changes in total inorganic nitrogen, nitrate and extractable organic nitrogen (EON). We found greater nitrogen immobilisation in the surrounding inter‐PGF soils than in the PGF soils. Along the latitudinal gradient, differences in net nitrogen mineralisation and EON cycling between PGF and inter‐PGF soils were strongly influenced by the presence of a pH boundary within the Low Arctic and the transition between the High and Low Arctic, with greater immobilisation in the nonacidic and Low Arctic sites, respectively. Incubation temperature affected EON flux but did not affect net nitrogen mineralisation or nitrification. These results show that spatial heterogeneity at several scales can influence soil nitrogen dynamics, and is therefore an important influence on arctic ecosystem function. Copyright © 2012 John Wiley & Sons, Ltd.

Statistical Analyses of Active Patterned Ground Occurrence in the Taillon Massif (Pyrénées, France/Spain)

ABSTRACTStatistical approaches were used to describe and explain the presence or absence of active patterned ground features in a mid‐latitude alpine area. The relative rarity of these landforms can be problematic for such analyses but this issue was resolved by a novel spatial sampling strategy that considers only terrain within circles drawn around each observed patterned ground feature, which is then subdivided into a grid. This strategy focuses only on fields with potential patterned ground occurrence and can be used for all statistical studies concerning the occurrence of scattered features over extensive areas. These data were examined using factor analyses (multiple correspondence analysis and hierarchical ascendant classification) blended with a complementary bivariate method to associate patterned ground occurrence with eight environmental variables (elevation, exposure, height‐distance ratio, drift, glacier influence, vegetation cover, slopewash and lithology). The absence of active patterned ground is associated with low elevation, glacier absence, no slopewash, a low height‐distance ratio and talus fans. Zones where active patterned ground features are present are divided into three homogeneous subzones and are mostly associated with glacier influence, a large height‐distance ratio and an absence of vegetation. Their location is controlled by the presence of till from different glacial sequences so that the former and current presence of glaciers favours the development of patterned ground features at the landscape scale. Copyright © 2011 John Wiley & Sons, Ltd.

Effects of Nitrogen Fertilization on Plant Communities of Nonsorted Circles in Moist Nonacidic Tundra, Northern Alaska

Nitrogen availability is considered to be a key limiting factor for plant growth in arctic tundra. Freeze-thaw cycles, which can produce patterned-ground features, may also limit the establishment and growth of arctic plants. In this experiment, we fertilized nonsorted circles, a type of patterned-ground feature, and the surrounding more stable vegetation in moist nonacidic tundra of northern Alaska to determine if nitrogen availability limited plant communities on these disturbance-dominated features. Similar to other studies in moist nonacidic tundra, the fertilized stable vegetation showed an increase in graminoid biomass and a decrease in moss biomass, but no total biomass response. The plant communities on nonsorted circles were less responsive to the addition of nitrogen as compared to the well-vegetated rims. The nonsorted circle vegetation may be limited by additional factors, such as frost heave disturbance, availability of buried seeds, and/or other nutrients. This difference in fertilization response shows that the presence of these features creates spatial heterogeneity in tundra plant community dynamics that should be taken into account when studying tundra responses to environmental change.

Effects of Nitrogen Fertilization on Plant Communities of Nonsorted Circles in Moist Nonacidic Tundra, Northern Alaska

Nitrogen availability is considered to be a key limiting factor for plant growth in arctic tundra. Freeze-thaw cycles, which can produce patterned-ground features, may also limit the establishment and growth of arctic plants. In this experiment, we fertilized nonsorted circles, a type of patterned-ground feature, and the surrounding more stable vegetation in moist nonacidic tundra of northern Alaska to determine if nitrogen availability limited plant communities on these disturbance-dominated features. Similar to other studies in moist nonacidic tundra, the fertilized stable vegetation showed an increase in graminoid biomass and a decrease in moss biomass, but no total biomass response. The plant communities on nonsorted circles were less responsive to the addition of nitrogen as compared to the well-vegetated rims. The nonsorted circle vegetation may be limited by additional factors, such as frost heave disturbance, availability of buried seeds, and/or other nutrients. This difference in fertilization response shows that the presence of these features creates spatial heterogeneity in tundra plant community dynamics that should be taken into account when studying tundra responses to environmental change.

Patterned-Ground Plant Communities along a bioclimate gradient in the High Arctic, Canada

Non-sorted circles, non-sorted polygons, and earth hummocks are common ground-surface features ill arctic regions. The), are caused by a variety of physical processes that Occur in permafrost regions including contraction cracking and frost heave. Here we describe the vegetation of patterned-ground forms on zonal sites at three location!: along an N-S transect through the High Arctic of Canada. We made 75 releves on patterned-ground features (circles, polygons, earth hummocks) and adjacent tundra (Interpolygon, intercircle, interhummock areas) and identified and classified the vegetation according to the Braun-Blanquet Method. Environmental factors were correlated with the vegetation data using a nonmetric multidimensional scaling ordination (NMDS). We identified eleven commnunities: (1) Puccinellia angustata-Papaver radicalum community in xeromesic non-sorted polygons of subzone A of the Circumpolar Arctic Vegetation Map; (2) Saxifraga-Parmelia omphalodes ssp. glacialis community in hydromesic interpolygon areas of subzone A; (3) Hypogymnia subobscura-Lecanora epibryon community In xeromesic non-sorted polygons of subzone B; (4) Orthotrichum speciosum-Salix arctica community In xeromesic interpolygon areas of subzone B; (5) Cochlearia groenlandica-Luzula nivalis community in hydromesic earth Mocks Of subzone B; (6) Salix arctica-Eriophorum angustifolium ssp. triste community in hygric earth hummocks of subzone 13; (7) Puccinellia angustata-Potentilla vahliana community in xeromesic non-sorted circles and bare patches of subzone Q (8) Dryas integrifolia-Carex rupestris community in xeromesic intercircle areas and vegetated patches of subzone C; (9) Braya glabella ssp. purpurascens-Dryas integrifolia community In hydromesic non-sorted circles of subzone Q (10) Dryas integrifolia-Carex aquatilis community in hydromesic intercircle areas of subzone C; and (11) Eriophorum angustifolium ssp. triste-Carex aquatilis community ill hygric intercircle areas of subzone C. The NMDS ordination displayed the vegetation types with respect to complex environmental gradients. The first axis of the ordination corresponds to a complex soil moisture gradient and the second axis corresponds to a complex geology/elevation/climate gradient. The tundra plots have a greater moss and graminoid cover than the adjacent frost-heave communities. In general, frost-heave features have greater thaw depths, more bare ground, thinner organic horizons, and lower soil moisture than the surrounding tundra. The morphology of the investigated patterned ground forms changes along the climatic gradient, with non-sorted pollygons dominating in the northernmost sites and non-sorted circles dominating, in the southern sites.

Simulating nonsorted circle development in arctic tundra ecosystems

Nonsorted circles, ubiquitous to the Arctic Tundra region, are patterned ground features with circular semibarren areas surrounded by vegetation. These circles are formed and persist as an ecosystem due to complex soil‐water‐energy‐ice‐plant relationships and dynamics in the Arctic. In this paper, we present the first model that captures the dynamics of the physical and biological components of the nonsorted circle ecosystem in order to understand its formation and persistence, especially in a changing climatic environment. We have applied a coupled model describing (1) vegetation dynamics (ArcVeg) and (2) coupled heat and moisture transport with phase change (WIT) in the active layer of the soil where such circles are initiated and developed. We simulated the system behavior during the formation process starting with a random vegetation development. The vegetation provided heterogeneous insulation to the soil surface. During freezing, the noninsulated areas froze first, resulting in preferential ice accumulation in those areas. The ice prevented the vegetation from developing further in those areas and thus developed and stabilized the nonsorted circle pattern. The model produced a nonsorted circle pattern that was well compared to those observed in the field. The model also illustrated that the availability of water was critical for the sustenance and stability of the nonsorted circle. The effect of climatic variations on the freezing process on the other hand did not seem to affect the formation and sustenance of nonsorted circles.

Arctic patterned‐ground ecosystems: A synthesis of field studies and models along a North American Arctic Transect

Arctic landscapes have visually striking patterns of small polygons, circles, and hummocks. The linkages between the geophysical and biological components of these systems and their responses to climate changes are not well understood. The “Biocomplexity of Patterned Ground Ecosystems” project examined patterned‐ground features (PGFs) in all five Arctic bioclimate subzones along an 1800‐km trans‐Arctic temperature gradient in northern Alaska and northwestern Canada. This paper provides an overview of the transect to illustrate the trends in climate, PGFs, vegetation, n‐factors, soils, active‐layer depth, and frost heave along the climate gradient. We emphasize the thermal effects of the vegetation and snow on the heat and water fluxes within patterned‐ground systems. Four new modeling approaches build on the theme that vegetation controls microscale soil temperature differences between the centers and margins of the PGFs, and these in turn drive the movement of water, affect the formation of aggradation ice, promote differential soil heave, and regulate a host of system properties that affect the ability of plants to colonize the centers of these features. We conclude with an examination of the possible effects of a climate warming on patterned‐ground ecosystems.

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.

Experimental Alteration of Vegetation on Nonsorted Circles: Effects on Cryogenic Activity and Implications for Climate Change in The Arctic

ABSTRACTNonsorted circles are relatively barren patterned-ground features common in most arctic tundra regions. We studied how vegetation changes on nonsorted circles might affect cryogenic processes, which is of relevance as arctic vegetation responds to climate change. Twenty-eight circles at a moist nonacidic tundra site in northern Alaska received one of four treatments: (a) vegetation removal; (b) vegetation removal and sedge transplants; (c) vegetation removal and moss transplants; or (d) no manipulation. We monitored soil-surface temperatures, thaw depth, frost heave, and soil-surface instability as indicators of cryogenic processes for three years.Vegetation removal led to 1.5 °C (22.3%) warmer summer soil-surface temperatures, 4.8 cm (6.2%) deeper mean thaw depth, 3.5 cm (26.2%) greater frost heave and a drastic increase in an index of soil instability when compared to the control. In contrast, moss additions lowered soil-surface temperatures by 2.8 °C (41.8%) in the summer, delayed freezing by almost two weeks and thawing by one week, decreased mean thaw depth by 10.3 cm (14.9%), and decreased frost heave by 6.6 cm (52.4%) when compared to the control. The sedge treatment had intermediate effects on thaw and heave. This study indicates that increases in plant cover and particularly moss cover on nonsorted circles due to a warming climate would decrease the heat flux between the atmosphere and the mineral soil and result in shallower thaw and less frost heave, leading to regional reductions in the activities of nonsorted circles.

Short-term Periglacial Processes, Vegetation Succession, and Soil Development within Sorted Patterned Ground: Jotunheimen, Norway

Small (1 ≤ m diameter) sorted patterned ground features were studied on the Little Ice Age forelands of three Jotunheimen glaciers. Patterned ground appears to be most active near the ice margins, declining in intensity of activity with distance from the glaciers. Vegetation and soil development are negligible within patterned ground that is “Recent” (decadal time frame). Significant (P < 0.05) fine scale differences in vegetation and soil development occur within patterned ground on terrain ∼70 yr in age, with patterned ground borders having higher values of vegetation cover and thicker soils than that in patterned ground centers. With increasing age of terrain and patterned ground, soil development and vegetation encroach inward toward patterned ground centers, implying that a short-term, active periglacial zone exists near the ice margin, decaying with time and glacier retreat. Specifically, terrain that has been deglaciated for ∼70 years and is approximately ∼350–500 m from the ice margin shows a significant decline in frost activity, allowing for the initiation of pedogenesis and vegetation colonization.

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.

Temporal and Spatial Variability of Soil pH in Patterned-Ground Chronosequences: Jotunheimen, Norway

Glacier foregrounds of Jotunheimen, Norway are characterized by the occurrence of Little Ice Age end moraines, dating to approximately the mid 18th century. Patterned-ground features occurring within chronologically established time units were studied. Young patterned-ground features, forming ~ 10-20 years after deglaciation, are frost active with minimal soil development. With time and distance from the ice margin, frost activity declines within the patterned ground. Frost activity initially decreases at the borders of the features, with the centers later stabilizing. Sorted circles and sorted nets showed significant changes in soil pH across the chronosequences. Temporal thresholds were recognized on two of the chronosequences where patterned-ground features on terrain deglaciated ~ 1930 A.D. show increased acidification rates, suggesting a decline in frost activity and disturbance. Microsite variability was noted on one of the chronosequences with patterned-ground borders being more acidic than that of center positions. All glacier forelands showed a higher soil pH with depth in patterned-ground features. The importance of microsite variability and associated disturbance is stressed and should be incorporated when studying environmental change at traditional landscape scales.

Vegetation establishment, succession and microsite frost disturbance on glacier forelands within patterned ground chronosequences

AbstractAim The impact of microscale frost disturbance on vegetation colonization and successionary trends was examined within patterned ground features of Little Ice Age chronosequences. The goal was to investigate and compare vegetation response to micro‐site frost disturbance with that of previous studies done at a coarser landscape scale.Location The study sites occur on Little Ice Age glacier forelands within Jotunheimen, Norway (61°–62° N). The forelands of the glaciers Slettmarkbreen, Styggedalsbreen and Vestre Memurubreen have been well studied providing chronological controls for landscape studies. Sorted patterned ground features are found within the chronosequences, typically declining with frost intensity and disturbance with increasing terrain age.Methods Micro‐plots (8.3 × 8.3 cm) were placed at the inner borders and centres of patterned ground features. Species were identified and per cent species cover and per cent cover of life‐form category were noted. Nonparametric Kruskal–Wallis and Mann–Whitney U‐tests were used to test for differences between percent cover of life‐form categories within patterned ground features as well as to identify thresholds of successional change across the chronosequences.Results Significant relationships between life‐from groups and patterned ground positions of varying ages were deduced using nonparametric statistics. Findings were then used to discuss trends of succession within patterned ground features and across the chronosequences. Vegetation establishment occurs at the border positions of young (&lt; 30 years) patterned ground features. With time and distance from the ice margin, vegetation encroaches inwards toward the disturbed centres. Succession within patterned ground exhibits several stages: (1) bryophytes/crusts and lichens, (2) grasses/sedges and (3) woody shrubs. The occurrence of forbs was sporadic and generally non‐significant.Main conclusions Frost disturbance in patterned ground appears to delay successional trends of vegetation communities when compared with previous studies on ‘stable’ terrain, producing micro‐site lag effects. These small patches of disturbed ground are therefore important regarding vegetation assemblages across the landscape and are unlikely to be detected at the landscape scale.