Arctic Vegetation Research Articles

Cynodontium luthii sp. nov.: a permineralized moss gametophyte from the Late Cretaceous of the North Slope of Alaska.

Mosses are a major component of Arctic vegetation today, with >500 species known to date. However, the origins of the Arctic moss flora are poorly documented in the fossil record, especially prior to the Pliocene. Here, we present the first anatomically preserved pre-Cenozoic Arctic moss and discuss how the unique biology of bryophytes has facilitated their success in polar environments over geologic time. A permineralized fossil moss gametophyte within a block of Late Cretaceous terrestrial limestone, collected along the Colville River on the North Slope of Alaska, was studied in serial sections prepared using the cellulose acetate peel technique. The moss gametophyte is branched and has leaves with a broad base, narrow blade, and excurrent costa. We describe this fossil as Cynodontium luthii sp. nov., an extinct species of a genus that is known from the High Arctic today. Cynodontium luthii is the oldest evidence of the family Rhabdoweisiaceae (by ≥18 Ma) and reveals that genera of haplolepideous mosses known in the extant Arctic flora also lived in high-latitude temperate deciduous forests during the Late Cretaceous. The occurrence of C. luthii in Cretaceous sediments, together with a rich Pliocene-to-Holocene fossil record of extant moss genera in the High Arctic, suggests that some moss lineages have exploited their poikilohydric, cold- and desiccation-tolerant physiology to live in the region when it experienced both temperate and freezing climates.

Potential palaeoflora of Last Glacial Maximum Eastern Beringia, northwest North America

Potential Last Glacial Maximum (LGM, 26,500–15,000 bp) members of the Eastern Beringia (now Alaska-Yukon, northwest North America) vascular flora were recognized based on their contemporary co-occurrence in easternmost Siberia (formerly part of Western Beringia). Of 1,633 indigenous terrestrial Alaska-Yukon taxa, 835 also occur in easternmost Siberia, including 526 arctic/alpine and 90 subarctic taxa. Archival macrofossil and DNA evidence corroborated the occurrence of 55 LGM taxa and indicated the presence of an additional 13 non–Western Beringian taxa. The total (848) was double the number of taxa previously considered amphi-Beringian, but likely, still an underestimate. Most Eastern Beringian arctic/alpine and subarctic taxa were perennials (94%) and forbs (64%), with herbaceous plants having average median heights of ≤ 37 cm. Arctic/alpine taxa were associated with xeric to submesic environments (54%), whereas the subarctic taxa favoured moister conditions. Both arctic/alpine and subarctic taxa were potentially present in unglaciated Eastern Beringia. However, some subarctic taxa may have migrated from refugial areas peripheral to Western Beringia during the Late Wisconsinan, prior to opening of the Bering Strait (11,000 bp), rather than being migrants from mid-latitude North America because of timing and distance considerations. Currently, former LGM Eastern Beringian taxa dominate (> 80% content) the flora and plant canopy cover of Alaska-Yukon arctic vegetation, but their frequency decreases curvilinearly (~ 0.102 taxon km−1) from Alaska to Hudson Bay, and from Yukon to southern British Columbia (p 1,400 km from Eastern Beringia.

Winter snow and spring temperature have differential effects on vegetation phenology and productivity across Arctic plant communities.

Tundra dominates two-thirds of the unglaciated, terrestrial Arctic. Although this region has experienced rapid and widespread changes in vegetation phenology and productivity over the last several decades, the specific climatic drivers responsible for this change remain poorly understood. Here we quantified the effect of winter snowpack and early spring temperature conditions on growing season vegetation phenology (timing of the start, peak, and end of the growing season) and productivity of the dominant tundra vegetation communities of Arctic Alaska. We used daily remotely sensed normalized difference vegetation index (NDVI), and daily snowpack and temperature variables produced by SnowModel and MicroMet, coupled physically based snow and meteorological modeling tools, to (1) determine the most important snowpack and thermal controls on tundra vegetation phenology and productivity and (2) describe the direction of these relationships within each vegetation community. Our results show that soil temperature under the snowpack, snowmelt timing, and air temperature following snowmelt are the most important drivers of growing season timing and productivity among Arctic vegetation communities. Air temperature after snowmelt was the most important control on timing of season start and end, with warmer conditions contributing to earlier phenology in all vegetation communities. In contrast, the controls on the timing of peak season and productivity also included snowmelt timing and soil temperature under the snowpack, dictated in part by the snow insulating capacity. The results of this novel analysis suggest that while future warming effects on phenology may be consistent across communities of the tundra biome, warming may result in divergent, community-specific productivity responses if coupled with reduced snow insulating capacity lowers winter soil temperature and potential nutrient cycling in the soil.

Impact of long-term fertilizer and summer warming treatments on bulk soil and birch rhizosphere microbial communities in mesic arctic tundra

ABSTRACT Recent climate warming in the Arctic is enhancing microbial decomposition of soil organic matter, which may result in globally significant greenhouse gas releases to the atmosphere. To better predict future impacts, bacterial and fungal community structures in both the bulk soil and the rhizosphere of Arctic birch, Betula glandulosa, were determined in control, greenhouse summer warming, and annual factorial nitrogen (N) and phosphate (P) addition treatments twelve years after their establishment. DNA sequence analyses at multiple taxonomic levels consistently indicated substantial bulk soil and rhizosphere microbial community differences among the fertilization treatments but no significant greenhouse effects. These results suggest that climate warming will likely increase the activity rates of soil microbial decomposers but without substantially altering the structure of either the bacterial or fungal communities. Differential abundance testing revealed changes in ectomycorrhizal fungal species of the genus Thelephora in both bulk soil and rhizosphere, with increases in their relative abundance in P and N + P amended plots compared with warming and controls. Because birch is the principal low Arctic ectomycorrhizal host, our results suggest that these fungi may promote this shrub’s competitiveness where tundra soil nutrient availability is enhanced by warming or other means, ultimately contributing to arctic vegetation “greening.”

Чек-лист синтаксонов Российской Арктики: текущее состояние классификации растительности

Чек-лист синтаксонов Российской Арктики: текущее состояние классификации растительности

Растительность класса Scheuchzerio–Caricetea fuscae Tx. 1937 в районе горного массива Янганапэ (восточный макросклон Полярного Урала)

Растительность класса Scheuchzerio–Caricetea fuscae Tx. 1937 в районе горного массива Янганапэ (восточный макросклон Полярного Урала)

Imprint of Climate Change on Pan-Arctic Marine Vegetation

The Arctic climate is changing rapidly. The warming and resultant longer open water periods suggest a potential for expansion of marine vegetation along the vast Arctic coastline. We compiled and reviewed the scattered time series on Arctic marine vegetation and explored trends for macroalgae and eelgrass (Zostera marina). We identified a total of 38 sites, distributed between Arctic coastal regions in Alaska, Canada, Greenland, Iceland, Norway/Svalbard, and Russia, having time series extending into the 21st Century. The majority of these exhibited increase in abundance, productivity or species richness, and/or expansion of geographical distribution limits, several time series showed no significant trend. Only four time series displayed a negative trend, largely due to urchin grazing or increased turbidity. Overall, the observations support with medium confidence (i.e., 5–8 in 10 chance of being correct, adopting the IPCC confidence scale) the prediction that macrophytes are expanding in the Arctic. Species distribution modeling was challenged by limited observations and lack of information on substrate, but suggested a current (2000–2017) potential pan-Arctic brown macroalgal distribution area of 655,111 km2(140,433 km2intertidal, 514,679 km2subtidal), representing an increase of about 45% for subtidal- and 8% for intertidal macroalgae since 1940–1950, and associated polar migration rates averaging 18–23 km decade–1. Adjusting the potential macroalgal distribution area by the fraction of shores represented by cliffs halves the estimate (340,658 km2). Warming and reduced sea ice cover along the Arctic coastlines are expected to stimulate further expansion of marine vegetation from boreal latitudes. The changes likely affect the functioning of coastal Arctic ecosystems because of the vegetation’s roles as habitat, and for carbon and nutrient cycling and storage. We encourage a pan-Arctic science- and management agenda to incorporate marine vegetation into a coherent understanding of Arctic changes by quantifying distribution and status beyond the scattered studies now available to develop sustainable management strategies for these important ecosystems.

Spatial patterns of arctic tundra vegetation properties on different soils along the Eurasia Arctic Transect, and insights for a changing Arctic

Vegetation properties of arctic tundra vary dramatically across its full latitudinal extent, yet few studies have quantified tundra ecosystem properties across latitudinal gradients with field-based observations that can be related to remotely sensed proxies. Here we present data from field sampling of six locations along the Eurasia Arctic Transect in northwestern Siberia. We collected data on the aboveground vegetation biomass, the normalized difference vegetation index (NDVI), and the leaf area index (LAI) for both sandy and loamy soil types, and analyzed their spatial patterns. Aboveground biomass, NDVI, and LAI all increased with increasing summer warmth index (SWI—sum of monthly mean temperatures > 0 °C), although functions differed, as did sandy vs. loamy sites. Shrub biomass increased non-linearly with SWI, although shrub type biomass diverged with soil texture in the southernmost locations, with greater evergreen shrub biomass on sandy sites, and greater deciduous shrub biomass on loamy sites. Moss biomass peaked in the center of the gradient, whereas lichen biomass generally increased with SWI. Total aboveground biomass varied by two orders of magnitude, and shrubs increased from 0 g m−2 at the northernmost sites to >500 g m−2 at the forest-tundra ecotone. Current observations and estimates of increases in total aboveground and shrub biomass with climate warming in the Arctic fall short of what would represent a ‘subzonal shift’ based on our spatial data. Non-vascular (moss and lichen) biomass is a dominant component (>90% of the photosynthetic biomass) of the vegetation across the full extent of arctic tundra, and should continue to be recognized as crucial for Earth system modeling. This study is one of only a few that present data on tundra vegetation across the temperature extent of the biome, providing (a) key links to satellite-based vegetation indices, (b) baseline field-data for ecosystem change studies, and (c) context for the ongoing changes in arctic tundra vegetation.

Disjunctions of Needle-leaved Sedge (<i>Carex duriuscula</i>) and Thread-leaved Sedge (<i>Carex filifolia</i>) in the Husky Lakes area of Northwest Territories—first records for the Canadian true Arctic and possible Pleistocene relicts

Disjunctions are reported for Needle-leaved Sedge (Carex duriuscula) and Thread-leaved Sedge (Carex filifolia) into the Arctic region of Northwest Territories at the Husky Lakes south of Tuktoyaktuk. These are significant additions to the Canadian Arctic flora and may be part of a group of relicts of the Arctic vegetation of the Pleistocene, specifically the Tundra-steppe. The occurrence of relict vegetation east of the Mackenzie Delta is east of its frequently cited eastern limit in North America.

Late Paleocene–early Eocene Arctic Ocean sea surface temperatures: reassessing biomarker paleothermometry at Lomonosov Ridge

Abstract. A series of papers published shortly after the Integrated Ocean Drilling Program Arctic Coring Expedition (ACEX, 2004) on Lomonosov Ridge indicated remarkably high early Eocene sea surface temperatures (SSTs; ca. 23 to 27 ∘C) and land air temperatures (ca. 17 to 25 ∘C) based on the distribution of isoprenoid and branched glycerol dialkyl glycerol tetraether (isoGDGT and brGDGT) lipids, respectively. Here, we revisit these results using recent analytical developments – which have led to improved temperature calibrations and the discovery of new temperature-sensitive glycerol monoalkyl glycerol tetraethers (GMGTs) – and currently available proxy constraints. The isoGDGT assemblages support temperature as the dominant variable controlling TEX86 values for most samples. However, contributions of isoGDGTs from land, which we characterize in detail, complicate TEX86 paleothermometry in the late Paleocene and part of the interval between the Paleocene–Eocene Thermal Maximum (PETM; ∼ 56 Ma) and the Eocene Thermal Maximum 2 (ETM2; ∼ 54 Ma). Background early Eocene SSTs generally exceeded 20 ∘C, with peak warmth during the PETM (∼ 26 ∘C) and ETM2 (∼ 27 ∘C). We find abundant branched GMGTs, likely dominantly marine in origin, and their distribution responds to environmental change. Further modern work is required to test to what extent temperature and other environmental factors determine their distribution. Published Arctic vegetation reconstructions indicate coldest-month mean continental air temperatures of 6–13 ∘C, which reinforces the question of whether TEX86-derived SSTs in the Paleogene Arctic are skewed towards the summer season. The exact meaning of TEX86 in the Paleogene Arctic thus remains a fundamental issue, and it is one that limits our assessment of the performance of fully coupled climate models under greenhouse conditions.

Ecological and evolutionary responses of an arctic plant to variation in microclimate and soil

The arctic and alpine regions are predicted to experience some of the highest rates of climate change, and the arctic vegetation is expected to be especially sensitive to such changes. Understanding the ecological and evolutionary responses of arctic plant species to changes in climate is therefore a key objective. Geothermal areas, where natural temperature gradients occur over small spatial scales, and without many of the confounding environmental factors present in latitudinal and other gradient studies, provide a natural experimental setting in which to examine the response of arctic–alpine plants to increasing temperatures. To test the ecological and evolutionary response of the circumpolar alpine bistort Persicaria vivipara to temperature, we collected plant material and soil from areas with low, intermediate and high soil temperatures and grew them at three different temperatures in a three‐factorial growth chamber experiment. At higher experimental soil temperatures, sprouting was earlier and plants had more leaves. Sprouting was earlier in soil originating from intermediate temperature and plants had more leaves when grown in soil originating from low temperatures. We did not find evidence of local adaptation or genetic variation in reaction norms among plants originating from areas with low, intermediate and high soil temperature. Our findings suggest that the alpine bistort has a strong plastic response to warming, but that differences in soil temperature have not resulted in genetic differentiation. The lack of an observed evolutionary response may, for example, be due to the absence of temperature‐mediated selection on P. vivipara, the low rate of sexual recombination, or high levels of gene flow balancing differences in selection. When placed within the context of other studies, we conclude that arctic–alpine plant species often show strong plastic responses to spring warming, while evidence of evolutionary responses varies among species.

Biochemical composition and productivity of reindeer pastures in the Arctic tundra subzone of the Republic of Sakha (Yakutia)

Northern domestic reindeer breeding in the Arctic zone of the Republic of Sakha (Yakutia) is a traditional and ethnos-preserving industry of the indigenous peoples of the North living there. Anabarsky national (Dolgan-Evenki) district is a place of compact residence of one of the small peoples of the North – the Dolgans. They have preserved their unique traditional method of keeping and breeding of domestic reindeer. Northern vegetation, especially Arctic vegetation is very vulnerable and tender. The problem of ecological and floristic researches of pasture plants in the North-East of the Republic of Sakha (Yakutia) is one of the most important tasks. Domestic reindeer are kept on natural pasture feed, so the urgent task is the rational exploitation of reindeer pastures, which is based on the study of productivity, changes in plant diversity under the influence of grazing and man-made impacts. These factors of influence on the state of deer pastures (degradation and loss of the main feed of deer-lichens) remain poorly studied at present. The purpose of the researches was to provide scientific justification for the rational use and protection of reindeer pastures, to study the feed supply of natural reindeer pastures in the Arctic tundra subzone of the Anabarsky national (Dolgan-Evenki) district of the Republic of Sakha (Yakutia). The results of researches have shown that the maximum yield has been observed in the camp #2: willow-grass meadow – 38 centner/ha DM and grass meadow – 41,3 centner/ha DM. Herbages 5 camps (herb-cotton-grass meadow, mixed grass-meadow of mossy plants, willow-grass meadow, grass meadow, forb-grass meadow, sedge meadow of mossy plants) reindeer pastures have been characterized by a high nutritional value feed, allowing to develop and strengthen the feed base for the development of reindeer breeding in the subzone of the Arctic tundra of the Sakha Republic (Yakutia).

Winter in a warming Arctic

Winter conditions have typically been downplayed or oversimplified in past estimations of terrestrial Arctic vegetation shifts in relation to climate change. A study now demonstrates the importance of fine-scale variation in winter temperature in explaining the composition and diversity of Arctic plant communities.

Comparison of Empirical and Physical Modelling for Estimation of Biochemical and Biophysical Vegetation Properties: Field Scale Analysis across an Arctic Bioclimatic Gradient

To evaluate the potential of multi-angle hyperspectral sensors for monitoring vegetation variables in Arctic environments, empirical and physical modelling using field data was implemented for the retrieval of leaf and canopy chlorophyll content (LCC, CCC) and plant area index (PAI) measured at four sites situated across a bioclimatic gradient in the Western Canadian Arctic. Field reflectance data were acquired with an ASD FieldSpec (305–1075 nm) and used to simulate CHRIS Mode1 spectra (411–997 nm). Multi-angle measurements were taken corresponding to CHRIS view zenith angles (VZA) (−55°, −36°, 0°, +36°, +55°). Empirical modelling compared parametric regression based on vegetation indices (VIs) to non-parametric Gaussian Processes Regression (GPR). In physical modelling, PROSAIL was inverted using numerical optimization and look-up table (LUT) approaches. Cross-validation of the empirical models ranked GPR as best, followed by simple ratio (SR) with optimally selected NIR and red wavelengths, and then ROSAVI using its published wavelengths (mean r2cv = 0.62, 0.58, and 0.54, respectively across all sites, variables, and VZAs). However, the best predictive performance was achieved by SR followed by GPR and ROSAVI (NRMSEcv = 0.12, 0.16, 0.16, respectively). PROSAIL simulated the multi-angle top-of-canopy reflectance well with numerical optimization (r2 = ~0.99, RMSE = 0.004 ± 0.002), but best performing LUT models of LCC, CCC and PAI were poorer than the empirical approaches (mean r2 = 0.48, mean NRMSE = 0.22). PROSAIL performed best at the high Arctic sparsely vegetated site (r2 = 0.57–0.86 for all parameters). Overall, the best performing VZA was −55° for empirical modelling and 0° and ±55° for physical modelling; however, these were not significantly better than the other VZAs. Overall, this study demonstrates that, for Arctic vegetation, nadir narrowband reflectance data used to derive simple empirical VIs with optimally selected bands is a more efficient approach for modelling chlorophyll and PAI than more complex empirical and physical approaches.

MULTITEMPORAL HISTOGRAM MATCHING – A NEW APPROACH OF MOSS AND LICHEN CHANGE DETECTION FROM LANDSAT IN DATA-POOR ANTARCTICA ENVIRONMENTS

Mosses and lichens are important components of Antarctic ecosystems. Maps of these vegetation are needed to improve our understanding of ecosystem dynamics. This requires species distribution to be mapped repeatedly over time, a critical task that becomes extremely challenging in data-poor Antarctic regions, where the lack of field data, logistics, coupled with scarcity of cloud free, quality multitemporal Landsat imagery are major intrinsic constraints to time-series analysis for change detection. This study firstly analyzes the spectral curves of moss and lichen generated by field-based spectroradiometer and then proposes an innovative histogram matching technique where historical Landsat data is modified such that its histogram matches that of present (reference) dataset. This has made it possible to mapping multitemporal Landsat data in the Antarctic Peninsula. The results demonstrate an overall accuracy of 90.5%. Mapping of Arctic vegetation facilitated by histogram matching of Landsat image, according to the results, seems to be an advisable image processing technique for application in a data-poor context.

A Multi-Sensor Unoccupied Aerial System Improves Characterization of Vegetation Composition and Canopy Properties in the Arctic Tundra

Changes in vegetation distribution, structure, and function can modify the canopy properties of terrestrial ecosystems, with potential consequences for regional and global climate feedbacks. In the Arctic, climate is warming twice as fast as compared to the global average (known as ‘Arctic amplification’), likely having stronger impacts on arctic tundra vegetation. In order to quantify these changes and assess their impacts on ecosystem structure and function, methods are needed to accurately characterize the canopy properties of tundra vegetation types. However, commonly used ground-based measurements are limited in spatial and temporal coverage, and differentiating low-lying tundra plant species is challenging with coarse-resolution satellite remote sensing. The collection and processing of multi-sensor data from unoccupied aerial systems (UASs) has the potential to fill the gap between ground-based and satellite observations. To address the critical need for such data in the Arctic, we developed a cost-effective multi-sensor UAS (the ‘Osprey’) using off-the-shelf instrumentation. The Osprey simultaneously produces high-resolution optical, thermal, and structural images, as well as collecting point-based hyperspectral measurements, over vegetation canopies. In this paper, we describe the setup and deployment of the Osprey system in the Arctic to a tundra study site located in the Seward Peninsula, Alaska. We present a case study demonstrating the processing and application of Osprey data products for characterizing the key biophysical properties of tundra vegetation canopies. In this study, plant functional types (PFTs) representative of arctic tundra ecosystems were mapped with an overall accuracy of 87.4%. The Osprey image products identified significant differences in canopy-scale greenness, canopy height, and surface temperature among PFTs, with deciduous low to tall shrubs having the lowest canopy temperatures while non-vascular lichens had the warmest. The analysis of our hyperspectral data showed that variation in the fractional cover of deciduous low to tall shrubs was effectively characterized by Osprey reflectance measurements across the range of visible to near-infrared wavelengths. Therefore, the development and deployment of the Osprey UAS, as a state-of-the-art methodology, has the potential to be widely used for characterizing tundra vegetation composition and canopy properties to improve our understanding of ecosystem dynamics in the Arctic, and to address scale issues between ground-based and airborne/satellite observations.

Decreasing snow cover alters functional composition and diversity of Arctic tundra

The Arctic is one of the least human-impacted parts of the world, but, in turn, tundra biome is facing the most rapid climate change on Earth. These perturbations may cause major reshuffling of Arctic species compositions and functional trait profiles and diversity, thereby affecting ecosystem processes of the whole tundra region. Earlier research has detected important drivers of the change in plant functional traits under warming climate, but studies on one key factor, snow cover, are almost totally lacking. Here we integrate plot-scale vegetation data with detailed climate and snow information using machine learning methods to model the responsiveness of tundra communities to different scenarios of warming and snow cover duration. Our results show that decreasing snow cover, together with warming temperatures, can substantially modify biotic communities and their trait compositions, with future plant communities projected to be occupied by taller plants with larger leaves and faster resource acquisition strategies. As another finding, we show that, while the local functional diversity may increase, simultaneous biotic homogenization across tundra communities is likely to occur. The manifestation of climate warming on tundra vegetation is highly dependent on the evolution of snow conditions. Given this, realistic assessments of future ecosystem functioning require acknowledging the role of snow in tundra vegetation models.

Understanding the spring phenology of Arctic tundra using multiple satellite data products and ground observations

The Arctic is highly sensitive to climate change, and the rise in its near-surface air temperatures has been almost twice the global average. The increased growth of the Arctic tundra and its changing seasonality have been observed, largely in response to the impacts of climate change. In this study, we investigated the temporal and spatial variations of the start of the growing season (SOS) using various remote sensing indices, including Normalized Difference Vegetation Index, Normalized Difference Water Index, and Normalized Difference Snow Index from 2000 to 2018 in Arctic tundra regions. The SOS was derived at 29 sites from ground observations, including CO2 flux data, phenological images, and field records that were used to validate the SOS from remote sensing indices. Our results revealed that the SOS was delayed by approximately 3.86 days per degree of latitude along the northward latitudinal gradient. From 2000 to 2018, the start of the growing season and the interannual variability differed greatly among tundra types. Although the overall trends were not significant from 2000 to 2018, the start of the growing season in different plant communities was consistently delayed after 2016. High Arctic vegetation, including (1) low wetland complexes (5–10 cm) dominated by sedges, grasses, and mosses, and (2) slightly higher prostrate and hemi-prostrate shrubs ( 15 cm), experienced a delayed start of the growing season. The start of the growing season of Low Arctic vegetation, comprising (1) wetland complexes (10–40 cm) dominated by sedges, grasses, mosses, and dwarf shrubs, (2) moist tundra (20–50 cm) dominated by tussock cottongrass and dwarf shrubs, and (3) transition zones containing tundra and taiga, displayed no obvious trend.

Leading‐edge disequilibrium in alder and spruce populations across the forest–tundra ecotone

AbstractThe distribution and composition of Arctic vegetation are expected to shift with ongoing climate change. Global models generally predict northward shifts in high‐latitude ecotones, and analysis of remote sensing data shows widespread greening and changes in vegetation structure across the circumpolar Arctic. However, there are still uncertainties related to the timing of these shifts and variation among different plant functional types. In this paper, we investigate disequilibrium dynamics of green alder and white spruce in the Tuktoyaktuk Coastal Plain, NWT. We used high‐resolution air photographs captured in the 1970s and 2000s to quantify changes in the distribution and abundance of alder and spruce near their northern limits. We found increases in alder and spruce stem density over time, but no change in their range limits, indicating that both species are affected by leading‐edge disequilibrium. Low stand density and temperature limitation of reproduction along the northern margin likely contributed to observed disequilibrium in both species. We also observed the greatest change in species occupancy within a burned area, suggesting that the increased frequency of fire will play a significant role in the timing and magnitude of near‐term vegetation change.

High Arctic Vegetation Change Mediated by Hydrological Conditions

Increasing air temperatures are driving widespread changes to Arctic vegetation. In the high Arctic, these changes are patchy and the causes of heterogeneity are not well understood. In this study, we explore the determinants of high Arctic vegetation change over the last three decades on Banks Island, Northwest Territories. We used Landsat imagery (1984–2014) to map long-term trends in vegetation productivity and regional spatial data to investigate the relationships between trends in productivity and terrain position. Field sampling investigated vegetation community composition in different habitat types. Our analysis shows that vegetation productivity changes are substantial on Banks Island, where productivity has increased across about 80% of the study area. Rising productivity levels can be attributed to increasing biomass of the plant communities in both upland and lowland habitats. Our analysis also shows that the magnitude of greening is mediated by terrain characteristics related to soil moisture. Shifts in tundra vegetation will impact wildlife habitat quality, surface energy balance, permafrost dynamics, and the carbon cycle; additional research is needed to explore the effects of more productive vegetation communities on these processes in the high Arctic.