Shrub Tundra Vegetation Research Articles

Stratigraphy and paleontology (plant and arthropod fossils) from the Late Neogene Niguanak site, Arctic Slope, Northern Alaska

ABSTRACT Motivated by the need for more paleodata for Pliocene paleoclimate data-model comparison, we revisited unpublished investigations of a fossiliferous site on the Niguanak River in Arctic North America. Analyses of the samples indicates forested conditions during an early phase of sedimentation in which environments were perhaps similar to those near tree line in the modern Anchorage area or farther south along the Pacific coast, whereas during a later phase of sedimentation, environments were characterized by shrub tundra vegetation and were possibly similar to the present-day conditions in the interior of southern Seward Peninsula. We describe the site stratigraphy and discuss the macrofossils and pollen recovered from the sediments, their paleoecological implications, and their significance for paleoclimate and sea ice. Mean annual temperatures were found to be 12.7°C warmer than current, with a pattern of much warmer winters, and less difference in summer warming as observed at other Pliocene Arctic sites. Finally, we discuss possible age assignments for the sediments, based on regional stratigraphy and geomorphology, and the probable sequence of evolution of arctic borderland climate and ecosystems.

Climate Predicts NDVI Better Than Plant Functional Group Attributes Along a Latitudinal Gradient in Nunavik

ABSTRACTAimThis study aims to describe the latitudinal pattern in plant functional groups' (PFGs') biomass and cover in Nunavik to test whether PFG attributes are better Normalized Difference Vegetation Index (NDVI) predictors than climate.LocationThe study spans a 700‐km latitudinal gradient from the lichen woodland to prostrate shrub tundra vegetation zones across Nunavik, Canada.TaxonOur analysis focuses on the following PFGs: erect and prostrate shrubs, herbaceous plants, bryophytes, and lichens.MethodsBiomass and cover data of the different PFGs were sampled in 40 sites distributed across the latitudinal gradient. NDVI data were obtained through remote sensing, while climatic, permafrost depth, and surficial deposits were derived from various databases. The PFG models were built to explore relationships between average NDVI (2016–2020) at the sampling site and ecological attributes such as PFG biomass or cover but also other variables such as surficial deposits and permafrost depth. A second series of models, the climatic models, were built using only climatic variables such as seasonal temperature and precipitation.ResultsThe most parsimonious PFG model was built with the biomass data of erect shrubs, herbaceous plants, bryophytes, and lichens and included surficial deposits and permafrost depth (R2 = 0.74). This biomass model performed better than the most parsimonious cover model (cover of erect shrubs and herbaceous, surficial deposits, permafrost depth; R2 = 0.63). However, the most parsimonious climatic model (fall temperature, annual, and winter precipitations) exhibited superior predictive power compared to the ecological ones (R2 = 0.87).ConclusionsPFG models built with PFGs aboveground biomass or cover are good predictors of NDVI of the plant formations sampled along the latitudinal gradient in Nunavik. Despite the intrinsic association between NDVI and vegetation attributes, our study emphasizes the importance of the regional climate in the control of primary productivity in Arctic and subarctic ecosystems. This study provides new insights into the interpretation of NDVI data and enhances our understanding of Arctic vegetation responses under rapid climate change. Furthermore, it underscores the balance between climatic drivers and ecological dynamics in shaping fragile Arctic ecosystems.

Paleo-Ecology of the Yedoma Ice Complex on Sobo-Sise Island (EasternLena Delta, Siberian Arctic)

Late Pleistocene permafrost of the Yedoma type constitutes a valuable paleo-environmental archive due to the presence of numerous and well-preserved floral and faunal fossils. The study of the fossil Yedoma inventory allows for qualitative and quantitative reconstructions of past ecosystem and climate conditions and variations over time. Here, we present the results of combined paleo-proxy studies including pollen, chironomid, diatom and mammal fossil analyses from a prominent Yedoma cliff on Sobo-Sise Island in the eastern Lena Delta, NE Siberia to complement previous and ongoing paleo-ecological research in western Beringia. The Yedoma Ice Complex (IC) cliff on Sobo-Sise Island (up to 28 m high, 1.7 km long) was continuously sampled at 0.5 m resolution. The entire sequence covers the last about 52 cal kyr BP, but is not continuous as it shows substantial hiatuses at 36–29 cal kyr BP, at 20–17 cal kyr BP and at 15–7 cal kyr BP. The Marine Isotope Stage (MIS) 3 Yedoma IC (52–28 cal kyr BP) pollen spectra show typical features of tundra–steppe vegetation. Green algae remains indicate freshwater conditions. The chironomid assemblages vary considerably in abundance and diversity. Chironomid-based TJuly reconstructions during MIS 3 reveal warmer-than-today TJuly at about 51 cal kyr BP, 46-44 and 41 cal kyr BP. The MIS 2 Yedoma IC (28–15 cal kyr BP) pollen spectra represent tundra-steppe vegetation as during MIS 3, but higher abundance of Artemisia and lower abundances of algae remains indicate drier summer conditions. The chironomid records are poor. The MIS 1 (7–0 cal kyr BP) pollen spectra indicate shrub-tundra vegetation. The chironomid fauna is sparse and not diverse. The chironomid-based TJuly reconstruction supports similar-as-today temperatures at 6.4–4.4 cal kyr BP. Diatoms were recorded only after about 6.4 cal kyr BP. The Sobo-Sise Yedoma record preserves traces of the West Beringian tundra-steppe that maintained the Mammoth fauna including rare evidence for woolly rhinoceros’ presence. Chironomid-based TJuly reconstructions complement previous plant-macrofossil based TJuly of regional MIS 3 records. Our study from the eastern Lena Delta fits into and extends previous paleo-ecological Yedoma studies to characterize Beringian paleo-environments in the Laptev Sea coastal region.

Tundra shrub expansion may amplify permafrost thaw by advancing snowmelt timing

The overall spatial and temporal influence of shrub expansion on permafrost is largely unknown due to uncertainty in estimating the magnitude of many counteracting processes. For example, shrubs shade the ground during the snow-free season, which can reduce active layer thickness. At the same time, shrubs advance the timing of snowmelt when they protrude through the snow surface, thereby exposing the active layer to thawing earlier in spring. Here, we compare 3056 in situ frost table depth measurements split between mineral earth hummocks and organic inter-hummock zones across four dominant shrub–tundra vegetation types. Snow-free date, snow depth, hummock development, topography, and vegetation cover were compared to frost table depth measurements using a structural equation modeling approach that quantifies the direct and combined interacting influence of these variables. Areas of birch shrubs became snow free earlier regardless of snow depth or hillslope aspect because they protruded through the snow surface, leading to deeper hummock frost table depths. Projected increases in shrub height and extent combined with projected decreases in snowfall would lead to increased shrub protrusion across the Arctic, potentially deepening the active layer in areas where shrub protrusion advances the snow-free date.

Environmental history of the northwestern Québec Treeline

Latitudinal treeline in northwestern Québec, Canada, is a broad band of forest-tundra between 56 and 58°N. Three new pollen records from the forest-tundra zone were combined with ten previously-published records to form a transect of paleoecological data across this treeline. The area was deglaciated ∼6–7 ka, with only a brief period of shrub tundra vegetation in the oldest sediments of all sites. Noticeable values of Populus, Juniperus and Larix pollen percentages were found during this time in the southernmost sites, suggesting they comprised part of the initial plant migration. Maximum Picea pollen percentages were found between 2 and 4 ka across the boreal forest and forest-tundra, with values remaining constant in the boreal forest and decreasing in the forest-tundra in the past 3 ka. Across the entire area, pollen influx decreased in the past 4 ka, and non-arboreal pollen increased in the forest-tundra, suggesting an opening of the forest and decrease in terrestrial production. Charcoal influx also declined, indicating a reduction in fire activity in the past 2–4 ka. Although the treeline has remained in the same average location in the region over the past 6 ka, the strength of the temperature gradient across the frontal zone changed over the course of the Holocene.

A Borehole Record of Late Quaternary Permafrost on Kurungnakh Island (Lena Delta, Northeastern Siberia): Reconstruction of Deposition Environments

Abstract —Paleoenvironmenal reconstructions have been made from a multidisciplinary study of a borehole permafrost record on Kurungnakh Island (Lena delta). According to data on palynomorphs and ostracods, the clay silt units from the 10.58 to 13.54 m and 1.58 to 10.3 m core depth intervals were deposited in the Late Pleistocene (during the Karginian interstadial) and Early–Middle Holocene, respectively. The sediments were studied in terms of moisture contents, grain size distribution, mineralogy, and magnetic susceptibility, and the results were compared with published evidence from nearby natural outcrops. Quite a cold oligotrophic lake existed in the area during the Karginian period, and the deposition was interrupted by a gap recorded at a core depth of about 11 m. In the Early and Middle Holocene, the area was covered with shrub tundra vegetation.

Dune stabilization in central and southern Yukon in relation to early Holocene environmental change, northwestern North America

Eolian deposits of central and southern Yukon, northwestern Canada, consist of loess mantles, small areas of active dunes, and larger stabilized dune fields. Dune fields in valley settings within the region are situated both within and beyond the limit of the last glaciation. Infrared stimulation luminescence (IRSL) dating in central and southern Yukon reveals that these dune fields stabilized as late as 9–8.5 ka, well after the retreat of Cordilleran glaciers. These findings are comparable to other valley-setting dune fields and loess from central Alaska, which record activity during the period from the Lateglacial to the Holocene Thermal Maximum (HTM), and reduced or altered activity after 9–8 ka. Post-glacial dune activity was most likely related to warm, dry conditions during the HTM, under predominantly shrub-tundra vegetation. Early Holocene stabilization of these dunes probably occurred in response to cooler, moister conditions, and replacement of predominantly tundra by boreal forest cover, dominated by spruce. Stabilization of dune fields in southern Yukon and Alaska most likely represented an extension of the time-transgressive stabilization of dune fields that occurred across northwestern North America with the post-glacial expansion of the boreal forest.

Daily MODIS products for analyzing early season vegetation dynamics across the North Slope of Alaska

Monitoring the growth and distribution of Arctic tundra vegetation is important for understanding changes in early growing season conditions in Arctic ecosystems in response to a warming climate. The primary objective of this study is to examine the utility of computed Daily Moderate Resolution Imaging Spectroradiometer (MODIS) Normalized Difference Vegetation Index (NDVI) products relative to 16-day maximum value composite (MVC) datasets for observing early season green-up dynamics of Arctic tundra vegetation across the North Slope of Alaska. Greening in the Arctic typically occurs shortly after snowmelt and can potentially be captured by using satellite observations that are available on a daily basis. Daily MODIS Snow Cover products were employed to retrieve dates of complete snowmelt (DOCS) for 2003–2005 for pixels that were cloud free at the time of complete snowmelt. Given the sparseness of cloud-free observations in both space and time, early season NDVI trajectories for cloud-free pixels were derived using daily MODIS data based on two approaches: a chronosequence (temporally continuous but aspatial) and a pixel trajectory (temporally discontinuous but spatial explicit) approach. On average during the three-year period, 12.5% of the North Slope region was cloud free at the time of complete snowmelt and a majority of these cloud-free pixels (65%) were associated with the Coastal Plain province. In contrast, the Foothills region was relatively less cloudy from the time following complete snowmelt until peak greenness (56%) than the Coastal Plain province (61%). As a result, vegetation communities that lie mostly in the Foothills province such as shrub tundra and moist acidic tundra classes had more cloud-free observations available to characterize NDVI trajectories using the pixel trajectory approach. Complete snowmelt in the North Slope generally occurred between day of year (DOY) 140 and 170 over the three years with areas covered by the shrub tundra vegetation community (Foothills province) experiencing snowmelt first in all three years with mean DOCS ranging from DOY 148 in 2004 to DOY 158 in 2003. For approximately two weeks following complete snowmelt (Phase I, a period of rapid NDVI increase), the Daily NDVI derived trajectories were substantially different from the MVC NDVI trajectories. Early season integrated NDVI (ESINDVI) values computed for Phase I were 7% higher using the Daily NDVI approaches relative to those derived from the MVC MODIS data for the North Slope region. Following this initial period, until peak greenness (Phase 2, a period of gradual NDVI increase), the Daily and MVC trajectories were similar in shape and magnitude. This study demonstrates the utility of the Daily MODIS Snow product for assessing cloud cover and snowmelt patterns and Daily MODIS NDVI data for observing and detecting sharp and rapid changes in early season vegetation phenology as seen during Phase I.

The Bering Land Bridge: a moisture barrier to the dispersal of steppe–tundra biota?

The Bering Land Bridge (BLB) connected the two principal arctic biological refugia, Western and Eastern Beringia, during intervals of lowered sea level in the Pleistocene. Fossil evidence from lowland BLB organic deposits dating to the Last Glaciation indicates that this broad region was dominated by shrub tundra vegetation, and had a mesic climate. The dominant ecosystem in Western Beringia and the interior regions of Eastern Beringia was steppe–tundra, with herbaceous plant communities and arid climate. Although Western and Eastern Beringia shared many species in common during the Late Pleistocene, there were a number of species that were restricted to only one side of the BLB. Among the vertebrate fauna, the woolly rhinoceros was found only to the west of the BLB, North American camels, bonnet-horned musk-oxen and some horse species were found only to the east of the land bridge. These were all steppe–tundra inhabitants, adapted to grazing. The same phenomenon can be seen in the insect faunas of the Western and Eastern Beringia. The steppe–tundra beetle fauna of Western Beringia was dominated by weevils of the genus Stephanocleonus, a group that was virtually absent from Eastern Beringia. The dry-adapted weevils, Lepidophorus lineaticollis and Vitavitus thulius were important members of steppe–tundra communities in Eastern Beringia, but were either absent or rare in Western Beringia. The leaf beetles Chrysolina arctica, C. brunnicornis bermani, and Galeruca interrupta circumdata were typical members of the Pleistocene steppe–tundra communities of Western Beringia, but absent from Eastern Beringia. On the other hand, some steppe tundra-adapted leaf beetles managed to occupy both sides of the BLB, such as Phaedon armoraciae. Much of the BLB remains unstudied, but on biogeographic grounds, it appears that there was some kind of biological filter that blocked the movements of some steppe–tundra plants and animals across the BLB.

Modelling spatially distributed snowmelt and meltwater runoff in a small Arctic catchment with a hydrology land‐surface scheme (WATCLASS)

The fully distributed hydrology land‐surface scheme WATCLASS is used to simulate spring snowmelt runoff in a small Arctic basin, Trail Valley Creek, dominated by open tundra and shrub tundra vegetation. The model calculates snowmelt rates from a full surface energy balance, and a three‐layer soil model is used to simulate the infiltration into and the exchange of heat and moisture within the ground. The generated meltwater is delivered to the stream channel network by overland flow, interflow, and baseflow and subsequently routed out of the catchment. Subgrid spatial variability is handled by the model through the use of grouped response units (GRUs). The GRUs in WATCLASS are chosen according to vegetation land cover. Five spring snowmelt periods with a variety of initial end‐of‐winter snow cover and melt conditions were simulated and compared with observed runoff data. In a second step, the model's ability to simulate spatially variable snow covered area (SCA) within the basin was tested by comparing model predictions to remotely sensed SCA. WATCLASS was able to predict runoff volumes (on average within 15% over five years of modelling) as well as timing of snowmelt and meltwater runoff for open tundra fairly accurately. However, the model underestimated melt in the energetically more complex shrub tundra areas of the basin. Furthermore, the observed high spatial variability of the SCA at a 1‐km resolution was not captured well by the model. Several recommendations are made to improve model performance in Arctic basins, including a more realistic implementation of the gradual deepening of the thawed layer during the spring, and the use of topographic information in the definition of land cover classes for the GRU approach.

Satellite image analysis of human caused changes in the tundra vegetation around the city of Vorkuta, north-European Russia

In this paper we present what kind of human impacted changes can be found in dwarf birch ( Betula nana) dominated shrub tundra vegetation around the large industrial complex of Vorkuta in the north-European Russian tundra. Using fieldwork data and Landsat TM satellite image we could identify two impact zones: (1) Pollution zone (150–200 km 2). In this zone most of the lichen species are absent. Changes in vegetation communities' species composition in all main plant groups are obvious. Willows especially are more dominant than in the unpolluted sites. (2) Slight pollution/disturbance zone (600–900 km 2). Here vegetation changes are mainly similar but less so than the changes in the first zone. Particularly, the amount of herbs and grasses is increased when compared to unpolluted areas. The pollution zones are spatially connected to the main emission sources in the area. Zones spread furthest to the northeast, matching the prevailing winds during winter.

Ecology of a steppe‐tundra gradient in interior Alaska

Abstract. Subarctic steppe is currently restricted in interior Alaska and the Yukon Territory to steep, south‐facing river bluffs. Paleoecological and biogeographic evidence suggests that some steppe taxa may have been more widespread during the Full‐Glacial. We examined factors controlling the distribution of steppe taxa on an elevation gradient across a steppetundra ecotone; such analyses may help define potential Full‐Glacial distributions of these taxa. Multivariate analyses suggest that species can be divided into four spatially distinct groups, but individualistic species distributions create considerable overlap among these groups. The steppe‐tundra ecotone comprises a broad zone of mixing between steppe taxa and drought‐tolerant alpine tundra taxa, followed by an abrupt shift to alpine shrub tundra. The transition from low steppe to tundra vegetation is primarily associated with a gradient of decreasing soil temperature. The more abrupt transition from mixed steppe‐tundra to alpine shrub tundra vegetation is primarily associated with changes in soil depth and soil moisture. Variation in vegetation within steppe is associated with gradients in soil phosphorus and moisture. Greenhouse experiments on drought tolerance of two steppe and two tundra taxa suggest that the individualistic distribution of species along the ecotone is partly a function of physiological differences among species. Our analyses of vegetation‐environment relationships support the hypothesis that some components of the steppe community could have been more widespread during the colder Full‐Glacial.

Palynostratigraphy of the last interglacial/glacial cycle in Germany

The last interglacial/glacial cycle comprises the Eemian and the Weichselian (in the area of the Scandinavian Glaciation), respectively the Riss/Würm and the Würm (in southern Germany). Drastic changes of the vegetation have occurred several times during this period in Europe. The best known in Germany is the development of the forests of the last interglacial stage and of the two succeeding early-glacial interstadial phases, the Brørup and the Odderade. Above the Odderade, sediments of two more (Middle Weichselian) interstadials, the Oerel and the Glinde, with a shrub-tundra vegetation have been found at one site in northern Germany. In southern Germany the palynological record ends somewhat earlier, i.e. with the equivalent of the Oerel interstadial, which here in the south had a forest vegetation. Numerous single occurrences of interstadial sediments of different age and vegetation have been studied, but unfortunately their stratigraphic position is most frequently unclear. Therefore a general survey can only rely on few, but long sequences. Their comparison shows that vegetational gradients of different steepness existed at different times, which mirror the changing climatic gradients of this period. The main points of the vegetational zonation as far as it is known from Germany for the cycle are summarized.