Arctic Forests Research Articles

An Analytical Model of Active Layer Depth Under Changing Ground Heat Flux

AbstractImproved modeling of permafrost active layer freeze‐thaw plays a crucial role in understanding the response of the Arctic ecosystem to the accelerating warming trend in the region over the past decades. However, modeling the dynamics of the active layer at diurnal time scale remains challenging using the traditional models of freeze‐thaw processes. In this study, a physically based analytical model is formulated to simulate the thaw depth of the active layer under changing boundary conditions of soil heat flux. Conservation of energy for the active layer leads to a nonlinear integral equation of the thaw depth using a temperature profile approximated from the analytical solution of the heat transfer equation forced by ground heat flux. Temporally variable ground heat flux is estimated using non‐gradient models when field observations are not available. Validation of the proposed model conducted against field data obtained from three Arctic forest and tundra sites demonstrates that the model is able to simulate both thaw depth and soil temperature profiles accurately. The model has the potential to estimate regional variability of the thaw depth for permafrost related applications.

High Productivity at High Latitudes? Photosynthesis and Leaf Ecophysiology in Arctic Forests of the Eocene

AbstractThe Arctic forests of the Eocene, which thrived under elevated CO2, a temperate climate, high precipitation and annually extremely different daylengths, represent a quite spectacular no‐analogue habitat of Earth's greenhouse past. The aim of this study was to improve our understanding of the ecophysiology of Arctic broad‐leaved deciduous forests of the Eocene, by analyzing leaf photosynthesis and tree productivity based on gas exchange modeling for two fossil Eocene sites, Svalbard and Ellesmere Island. For this, a single‐leaf photosynthesis model that includes heat transfer and leaf senescence was derived. Environmental conditions were based on available palaeoclimate data and a CO2 level of 800 μmol/mol. Additionally, different light regimes (diffusivity and transmissivity) were considered. With this model, annual photosynthesis was calculated on the basis of annual temperature and day lengths (derived by celestial mechanics). To obtain productivity of a whole deciduous broad‐leaved tree, the single leaf data were then upscaled by a canopy model. The results indicate that productivity was enhanced at both high latitude sites by elevated CO2, temperature of the growing season and high maximum daylength (24 hr) during late spring and early summer. With productivity values about 30%–60% higher as for a mid‐latitude continental European forest, the results indicate a potential for high productivity at the Eocene polar sites which is in the range of extant tropical forests. In contrast to speculations, no evidence for a selective advantage of large leaf size—as shown by various fossil leaves from high latitude sites—could be found.

Two- and three-dimensional territories and territory overlap of Willow Warblers Phylloscopus trochilus in Arctic forests

Two- and three-dimensional territories and territory overlap of Willow Warblers Phylloscopus trochilus in Arctic forests

Flushing or mixing? Stable water isotopes reveal differences in arctic forest and peatland soil water seasonality

AbstractUnderstanding the relative importance of different water sources that replenish soil water storage is necessary to assess the vulnerability of sub‐arctic areas to changes in climate and altered rain and snow conditions, reflected in the timing and magnitude of water infiltration. We examine spatiotemporal variability and seasonal origin of soil water at the soil‐vegetation interface in Pallas catchment, located in northern Finland. The field study was conducted from May 2019 to June 2020 over two snowmelt seasons and one summer growing season. We sampled soil cores up to a 1‐m depth and stem water of dominant tree species at four sites located in forests and forested peatlands for stable water isotopes. Seasonal rainfall variation and late snowmelt events were well identifiable in the well‐drained soils of forested areas, while this input signal is heavily attenuated in wetter, forested peatland areas. Spatiotemporal variability of soil water in two forest sites was similar, whereas soil water storage in peatland sites was controlled by the extent of hydrologic connectivity to the adjoining water pools. A mixture of both summer and winter precipitation was present in peatlands during the entire study period, while forest mineral soils showed an ephemeral response to water input and got nearly fully flushed twice during the hydrological year. Meltwater signal in forest soils was dominant after snowmelt and in early spring but became displaced by isotopically enriched rainfall during the summer. Seasonal evolution of soil water pools was not reflected in tree stem dynamics but offset between soil and stem water isotopic signals was less pronounced in forested peatlands. This field data set uncovered seasonal changes of soil water isotopic signal at high depth‐resolution, quantifying the importance of snowmelt water in replenishing and sustaining soil water storage in sub‐arctic conditions.

WOOD JAMS OR BEAVER DAMS? PLIOCENE LIFE, SEDIMENT AND LANDSCAPE INTERACTIONS IN THE CANADIAN HIGH ARCTIC

ABSTRACT During the mid-Pliocene (Zanclean, ca. ∼ 3.9 Ma), parts of the Canadian High Arctic experienced mean annual temperatures that were 14–22°C warmer than today and supported diverse boreal-type forests. The landscapes of this vegetated polar region left behind a fragmented sedimentary record that crops out across several islands in the Canadian Arctic Archipelago as the Beaufort Formation and correlative strata. Paleoecological information from these strata provides a high-fidelity window onto Pliocene environments, and prominent fossil sites yield unparalleled insights into Cenozoic mammal evolution. Significantly, many of the strata reveal evidence for life-sediment interactions in a warm-climate Arctic, most notably in the form of extensive woody debris and phytoclast deposits. This paper presents original field data that refines the sedimentological context of plant debris accumulations from the anactualistic High Arctic forests, most notably at the ‘Fyles Leaf Beds' and ‘Beaver Pond' fossil-bearing sites in the ‘high terrace deposits' of central Ellesmere Island. The former is a remarkably well-preserved, leaf-rich deposit that is part of a complex of facies associations representing lacustrine, fluvio-deltaic and mire deposition above a paleotopographic unconformity. The latter yields tooth-marked woody debris within a peat layer that also contains a rich assemblage of vertebrate and plant fossils including abundant remains from the extinct beaver-group Dipoides. Here we present sedimentological data that provide circumstantial evidence that the woody debris deposit at Beaver Pond could record dam-building in the genus, by comparing the facies motif with new data from known Holocene beaver dam facies in England. Across the Pliocene of the High Arctic region, woody debris accumulations are shown to represent an array of biosedimentary deposits and landforms including mires, driftcretions, woody bedforms, and possible beaver dams, which help to contextualize mammal fossil sites, provide facies models for high-latitude forests, and reveal interactions between life and sedimentation in a vanished world that may be an analogue to that of the near-future.

The Impact of Global Warming on Russia’s Ecological Environment

The Russian ecosystem is a complex consisting of the Arctic marine ecosystem, the tundra, forest, steppe, mountain and island ecosystems, as well as the terrestrial and water ecosystems, the spatial ecosystem, the atmospheric ecosystem, the soil ecosystem, etc. Rather than being independent, these ecosystems are interactive. Global warming, so destructive to the global ecosystem, particularly affects Russia due to the country’s unique geographical position. It is a double-edged sword for the Russian ecosystem; it does have some beneficial effects, but on the whole, its negative consequences outweigh the benefits. Specific negative effects are the decrease in the Arctic sea ice, the increase in carbon emissions, the lessening of biodiversity, an increase in forest pests and diseases, the spread of contagious diseases, the frequency of forest fires, changes in the habitat conditions of biological species, and environmental degradation. In recent years, coping with these negative effects has become a major challenge for Russia’s sustainable development. Therefore, Russia is actively participating in international cooperation to deal with global warming and is optimizing the relevant domestic mechanisms. To ensure the stable and balanced development of society and the economy, Russia has been striving to reduce Russian greenhouse gas emissions by 30 percent by 2030 compared to 1990, in order to further improve the country’s ecosystems.

Exploring the role of High Arctic Large Igneous Province volcanism on Early Cretaceous Arctic forests

The Hauterivian–Aptian Isachsen Formation at Glacier Fiord, Axel Heiberg Island, in the Sverdrup Basin of the Canadian Arctic Archipelago was deposited contemporaneous with initiation of the High Arctic Large Igneous Province (HALIP). New palynological biostratigraphy and paleoenvironmental reconstruction, in coordination with the emerging geochronology of HALIP igneous rocks, permits exploration of the effects of volcanism on Arctic vegetation during the Early Cretaceous. Four informal terrestrial palynofloral zones are defined and used to reconstruct vegetation change over the Isachsen Formation's ca. 17 million year history and explore the role of the HALIP in these changes. Climate warming during the Hauterivian promoted expansion of a hinterland community dominated by members of the Pinaceae. By the middle Barremian, this community was replaced by mixed heathland and mire, represented by up to 70% fern spores in the uppermost Paterson Island Member, that may be, in part, in response to environmental disturbance associated with volcanic flows of the HALIP. Above the fern spore spike, dinoflagellate cyst assemblages suggest an early Aptian age and a marine setting for mudstones of the Rondon Member in which Ocean Anoxic Event 1a is recorded. An interval of floral instability is recorded in the overlying Walker Island Member, characterized by fluctuations in Pinaceae and Cupressaceae pollen and fern spores, possibly as a result of post-OAE 1a temperature variabilty and landscape disturbance associated with lava flows of the HALIP that were repeatedly extruded onto the subsiding delta plain during deposition of the member.

Evidence for widespread wildfires and their environmental impact in the Late Cretaceous Canadian Arctic

Wildfires are important in modern ecology but the complex interplay between wildfires and vegetation or climate is less well understood in ancient environments, in particular those of the Arctic regions. This includes the impacts of paleo-wildfires on surrounding marine basins by affecting sedimentation rates and nutrient input via soil degeneration and intensification of continental run-off. The Late Cretaceous was an important time of global climate shift, with the rise of angiosperm vegetation marking a turning point in global flora, and globally abundant wildfires due to high atmospheric oxygen levels and elevated temperatures. This study investigates Late Cretaceous samples from the Canadian Arctic Islands to examine the evidence for widespread wildfires and how these wildfires may have influenced or been influenced by contemporaneous climate and vegetation shifts. Organic geochemical, and organic petrological data show evidence of enhanced wildfires beginning in the Turonian, including increases in semi-fusinite macerals and pyrogenic PAH (polycyclic aromatic hydrocarbon) indicators of natural combustion. This increasing wildfire influence corresponds with a rise in broad-leafed Arctic forests, as evidenced by angiosperm-derived terpenoid biomarkers, with both wildfire and angiosperm abundances peaking in the Early Campanian. Additionally, geochemical and petrographic data shows a shift in the type of organic matter deposited over time, correlating to the evidence of increased wildfire activity. This study proposes that the distance between wildfire region and marine depocenter is assessed via a new provenance method based on the degree of photo-oxic degradation of selected PAH isomers upon airborne transport. The increasing effects of wildfires on the Arctic ecosystem over the Turonian-Campanian were likely driven by relatively warm temperatures, elevated atmospheric oxygen, volcanism related to the High Arctic Large Igneous Province (HALIP), and abundant fuel availability. Widespread wildfires are proposed to have fostered the expansion of angiosperm vegetation into the Canadian Arctic in the Late Cretaceous by allowing them to outcompete gymnosperms in post-fire regrowth. Intensified erosion and continental run-off associated with the destruction of the vegetation cover by wildfires is thought to have acted as a driving force in the increasing terrigenous organic matter deposition in the Sverdrup Basin during the Late Cretaceous. Taken together, the results of this study suggest that increasing wildfires related to global climatic conditions in the Late Cretaceous contributed to the expansion of angiosperm flora in the Arctic, and had a substantial impact on the deposition of sediments in the surrounding Sverdrup Basin.

Palynostratigraphy of the lower Paleogene Margaret Formation at Stenkul Fiord, Ellesmere Island, Nunavut, Canada

The upper Paleocene to lower Eocene Margaret Formation exposed at Stenkul Fiord on southern Ellesmere Island, Nunavut, Canada, represents a nearly continuous terrestrial succession of microfossil-rich clastic sediments and coal. These strata were deposited at a time of extensive tectonic activity associated with Eurekan deformation. The precise chronology of the Eurekan deformation is poorly known. Prior studies at Stenkul Fiord provided a stratigraphic overview and relative age estimates for exposed strata but lack the absolute age control required to investigate the timing of deformation events. Strata at Stenkul Fiord preserve evidence of Arctic forests that may have grown during hyperthermal events that characterized the Paleogene, namely, the Paleocene-Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (ETM2). A quantitative palynological approach is herein used to define a new higher-resolution biostratigraphic framework for the Margaret Formation strata at Stenkul Fiord. This resulting improved biostratigraphic framework is integrated with new absolute age control of 53.7 ± 0.06 Ma provided by U-Pb ID-TIMS of zircon preserved in an ash bed within the studied succession. Nine pollen zones are defined based on cluster analysis, NMDS ordination, first- and last occurrences of taxa, and angiosperm pollen taxa diversity (H′). The presence of thermophilic pollen taxa at Stenkul Fiord provides evidence of climates related to the globally warm climates during the early Paleogene.

Thermal desorption treatment of petroleum hydrocarbon-contaminated soils of tundra, taiga, and forest steppe landscapes

The results of field, analytical, and experimental research at a number of production facilities reflect the properties of oil-contaminated soils in 3 landscapes: the permafrost treeless Arctic ecosystem, boreal forest, and temperate-climate grassland-woodland ecotone. Laboratory studies have revealed the concentrations of petroleum hydrocarbons in soils, ranging from medium levels of 2000–3000 mg/kg to critical figures over 5000 mg/kg, being 2–25 times higher than the permissible content of oil products in soils. The experimentally applied thermal effects for the oil products desorption from the soil allowed finding an optimal regime: the treatment temperature from 25 to 250 °C reduces the concentrations to an acceptable value. The conditions are environmentally sound, given that the complete combustion point of humates is ca. 450 °C. The outcomes suggest the eco-friendly solution for soil remediation, preserving the soil fertility in fragile cold environments and in more resilient temperate climates, where revitalized brownfields are essential for food production.

Using tooth enamel microstructure to identify mammalian fossils at an Eocene Arctic forest.

Lower Eocene (Wasatchian-aged) sediments of the Margaret Formation on Ellesmere Island in Canada's High Arctic preserve evidence of a rainforest inhabited by alligators, turtles, and a diverse mammalian fauna. The mammalian fossils are fragmentary and often poorly preserved. Here, we offer an alternative method for their identification. Among the best preserved and extensive of the Eocene Arctic forests is the Strathcona Fiord Fossil Forest, which contains permineralized in situ tree stumps protruding from a prominent coal seam, but a paucity of vertebrate fossils. In 2010 and 2018, we recovered mammalian tooth fragments at the fossil forest, but they are so incomplete as to be undiagnostic by using their external morphology. We used a combination of light microscopy and SEM analysis to study the enamel microstructure of two tooth fragments from the fossil forest-NUFV2092B and 2092E. The results of our analysis indicate that NUFV2092B and 2092E have Coryphodon-enamel, which is characterized by vertical bodies that manifest as bands of nested chevrons or treelike structures visible in the tangential section under light microscopy. This enamel type is not found in other mammals known from the Arctic. Additionally, when studied under SEM, the enamel of NUFV2092B and 2092E has rounded prisms that open to one side and are surrounded by interprismatic matrix that is nearly parallel to the prisms, which also occurs in Coryphodon enamel, based on prior studies. The tooth fragments reported here, along with some poorly preserved bone fragments, thus far are the only documented vertebrate fossils from the Strathcona Fiord Fossil Forest. However, fossils of Coryphodon occur elsewhere in the Margaret Formation, so its presence at the fossil forest is not surprising. What is novel in our study is the way in which we identified the fossils using their enamel microstructure.

Diversity of Peloppiidae (Oribatida) in North America

Members of the oribatid mite family Peloppiidae are found throughout the Holarctic in subarctic and arctic habitats, and temperate and boreal forests, and while common, are rarely collected in high abundance. Pacific Northwest forest habitats of western Canada have high relative diversity of peloppiid mites representing species of the genera Ceratoppia, Dendrozetes, and Metrioppia. Many of these are newly described species that are seemingly endemic to the region. Here I review the status and diversity of Peloppiidae from North America, and summarize the distributions of described species. Despite recent efforts, significant work remains. Within Ceratoppia two widely-distributed and established species have considerable morphological variation, while the type specimens are missing or destroyed, making confirmation of new specimens difficult. For other genera, extensive review of the Canadian National Collections in Ottawa, Canada suggest there are at least four undescribed species of North American Peloppiidae - two potentially new species of Paenoppia, and new species each of Parapyroppia and Pyroppia.

Potential contributions of root decomposition to the nitrogen cycle in arctic forest and tundra.

Plant contributions to the nitrogen (N) cycle from decomposition are likely to be altered by vegetation shifts associated with climate change. Roots account for the majority of soil organic matter input from vegetation, but little is known about differences between vegetation types in their root contributions to nutrient cycling. Here, we examine the potential contribution of fine roots to the N cycle in forest and tundra to gain insight into belowground consequences of the widely observed increase in woody vegetation that accompanies climate change in the Arctic. We combined measurements of root production from minirhizotron images with tissue analysis of roots from differing root diameter and color classes to obtain potential N input following decomposition. In addition, we tested for changes in N concentration of roots during early stages of decomposition, and investigated whether vegetation type (forest or tundra) affected changes in tissue N concentration during decomposition. For completeness, we also present respective measurements of leaves. The potential N input from roots was twofold greater in forest than in tundra, mainly due to greater root production in forest. Potential N input varied with root diameter and color, but this variation tended to be similar in forest and tundra. As for roots, the potential N input from leaves was significantly greater in forest than in tundra. Vegetation type had no effect on changes in root or leaf N concentration after 1 year of decomposition. Our results suggest that shifts in vegetation that accompany climate change in the Arctic will likely increase plant‐associated potential N input both belowground and aboveground. In contrast, shifts in vegetation might not alter changes in tissue N concentration during early stages of decomposition. Overall, differences between forest and tundra in potential contribution of decomposing roots to the N cycle reinforce differences between habitats that occur for leaves.

Dispersal of thermophilic beetles across the intercontinental Arctic forest belt during the early Eocene

Massive biotic change occurred during the Eocene as the climate shifted from warm and equable to seasonal and latitudinally stratified. Mild winter temperatures across Arctic intercontinental land bridges permitted dispersal of frost-intolerant groups until the Eocene-Oligocene boundary, while trans-Arctic dispersal in thermophilic groups may have been limited to the early Eocene, especially during short-lived hyperthermals. Some of these lineages are now disjunct between continents of the northern hemisphere. Although Eocene climate change may have been one of the most important drivers of these ancient patterns in modern animal and plant distributions, its particular events are rarely implicated or correlated with group-specific climatic requirements. Here we explored the climatic and geological drivers of a particularly striking Neotropical-Oriental disjunct distribution in the rove beetle Bolitogyrus, a suspected Eocene relict. We integrated evidence from Eocene fossils, distributional and climate data, paleoclimate, paleogeography, and phylogenetic divergence dating to show that intercontinental dispersal of Bolitogyrus ceased in the early Eocene, consistent with the termination of conditions required by thermophilic lineages. These results provide new insight into the poorly known and short-lived Arctic forest community of the Early Eocene and its surviving lineages.

High Arctic forests during the middle Eocene supported by moderate levels of atmospheric CO2

Fossils from Paleogene High Arctic deposits provide some of the clearest evidence for greenhouse climates in the past and offer the potential to improve our understanding of Earth system dynamics in a largely ice-free world. One of the most well-known and stunningly preserved polar forest sites, Napartulik, crops out of middle Eocene (47.9–37.8 Ma) sediments on eastern Axel Heiberg Island, Nunavut, Canada (∼78°N paleolatitude). An abundance of data from Napartulik suggests mean annual temperatures at least 30 °C warmer than today and atmospheric water loads 2× current levels. Despite this wealth of paleontological and paleoclimatological data, there are currently no direct constraints on atmospheric CO 2 levels for Napartulik or any other polar forest site. Here we apply a new plant gas-exchange model to Metasequoia (dawn redwood) leaves to reconstruct atmospheric CO 2 from six fossil forest horizons at Napartulik. Individual reconstructions vary between 392 ppm and 474 ppm, with a site median of 424 ppm (351–523 ppm at 95% confidence). These estimates represent the first direct constraints on CO 2 for a High Arctic forest and suggest that the temperate conditions present at Napartulik during the middle Eocene were maintained under CO 2 concentrations ∼1.5× pre-industrial levels. Our results support the case that long-term climate sensitivity to CO 2 in the past was sometimes high, even during largely ice-free periods, highlighting the need to better understand the climate forcings and feedbacks responsible for this amplification.

Latitudinal forest advance in northernmost Norway since the early 20th century

AbstractAimThe arctic forest–tundra boundary is expected to advance rapidly northwards in response to climate warming. The purpose of this study was: (1) to analyse region‐wide changes in the positions of the latitudinal forest line and tree line since the early 20th century; (2) to calculate rates of northward movement and to estimate uncertainties from different sources of data; (3) to analyse how rates of advance differ between two common tree species, Betula pubescens (downy birch) and Pinus sylvestris (Scots pine); and (4) to place the results in the context of dynamic global vegetation models.LocationThe study covers Finnmark county in northern Norway, which has warmed by 1–2 °C since the early 20th century.MethodsHistorical forest maps, topographic maps, aerial photographs and satellite imagery were used to delineate region‐wide, species‐specific and time‐specific subarctic forest lines and tree lines. Rates of advance were calculated using two geometrical methods, placing different emphases on the shape and mean position of the lines, but yielding similar results.ResultsThe analyses revealed an average northward advance of the birch and pine forest lines of 156 and 71 m year−1, respectively. Both showed considerable spatial and temporal variation. The birch tree line showed the most pronounced advance (340 m year−1), whereas the pine tree line showed very limited advance (10 m year−1). Data sources contributed an uncertainty of around 10 m year−1 to these rates.Main conclusionsThe analysis of historical and recent forest delineation data showed a very restricted advance rate compared to the predictions of dynamic global vegetation models. If these results are representative of the behaviour of the entire circumarctic forest–tundra zone over the present century, they suggest that the modelled prediction of the loss of 40% of the current tundra is a serious overestimate. A stronger focus on factors limiting the response of the forest–tundra ecotone to climate change is needed to refine the output from dynamic global vegetation models.

The role of the circumarctic forest–tundra ecotone for Arctic biodiversity

The arctic forest–tundra ecotone (FTE), which links species communities of the boreal forest with those of the arctic tundra, is expected to respond swiftly to climate change with a profound reduction of tundra as the dominating scenario. With its circumarctic expanse and up to several hundred kilometres in width, the zone occupies a large part of the vegetated surface at high latitudes. Relocation and structural changes of the ecotone vegetation will affect not only plant but also animal and other biological diversity. A large number of arctic species are dependent on the FTE in terms of food and habitat during parts of their life cycle or annual migration. In the ‘Arctic Species Trend Index’, developed to provide trends in arctic vertebrates, more than half of the species and data are from the FTE. However, in assessments of arctic biodiversity, only the northernmost tundra-dominated areas of the ecotone are included. This is unfortunate and somewhat problematic since the treed part that serves as a source of seeds for new seedlings and saplings in the tundra-dominated part is excluded. This inconsistency hampers monitoring efficiency and biodiversity conservation efforts. During the International Polar Year, a large international research project on the FTE established numerous sites around the circumpolar north where causes and consequences of vegetation change were analysed. This network of sites and data forms an excellent basis for necessary monitoring of the spatial and temporal complexity of forest encroachment into tundra and its relation to arctic biodiversity.

A summertime rainy season in the Arctic forests of the Eocene

The discovery of exceptionally well-preserved fossil wood revealed that extensive forests existed north of the Arctic Circle during the Eocene (ca. 45–55 Ma). Subsequent paleobotanical studies led researchers to suggest eastern Asia as a modern analog, based on the distribution of nearest living relatives. During the last decade, proxy-based reconstructions of mean annual paleoprecipitation, productivity, and relative humidity have led workers to characterize the climate of the Arctic forests as similar to today9s temperate forests of the Pacific Northwest. Using a new model, we reconstructed the seasonal timing of paleoprecipitation from high-resolution intra-ring carbon isotope measurements of fossil wood. We showed that the Eocene Arctic forests experienced, on average, 3.1 times more precipitation during summer than winter, entirely dissimilar to the Pacific Northwest where summer precipitation is only one-half to one-sixth of the winter precipitation. This new result shows that although mean annual climate conditions may have been similar to the mean annual conditions the Pacific Northwest, consideration of seasonality implies that the temperate forests of eastern Asia represent the best overall modern analog for the Eocene Arctic forests.

Life at the top of the greenhouse Eocene world--A review of the Eocene flora and vertebrate fauna from Canada's High Arctic

Early–middle Eocene (ca. 53–38 Ma) sediments of the Eureka Sound Group in Canada’s Arctic Archipelago preserve evidence of lush mixed conifer-broadleaf rain forests, inhabited at times by alligators, turtles, and diverse mammals, including primates, tapirs, brontotheres, and hippo-like Coryphodon. This biota reflects a greenhouse world, offering a climatic and ecologic deep time analog of a mild ice-free Arctic that may be our best means to predict what is in store for the future Arctic if current climate change goes unchecked. In our review of the early–middle Eocene Arctic flora and vertebrate fauna, we place the Arctic fossil localities in historic, geographic, and stratigraphic context, and we provide an integrated synthesis and discussion of the paleobiology and paleoecology of these Eocene Arctic forests and their vertebrate inhabitants. The abundance and diversity of tapirs and plagiomenids (both rare elements in midlatitude faunas), and the absence of artiodactyls, early horses, and the hyopsodontid “condylarth” Hyopsodus (well represented at midlatitude localities) are peculiar to the Eocene Arctic. The Eocene Arctic macrofloras reveal a forested landscape analogous to the swamp-cypress and broadleaf floodplain forests of the modern southeastern United States. Multiple climate proxies indicate a mild temperate early–middle Eocene Arctic with winter temperatures at or just above freezing and summer temperatures of 20 °C (or higher), and high precipitation. At times, this high precipitation resulted in freshwater discharge into a nearly enclosed Arctic Ocean basin, sufficient to cause surface freshening of the Arctic Ocean, supporting mats of the floating fern Azolla . Fluctuating Arctic Ocean sea level due to freshwater inputs as well as tectonics produced temporary land bridges, allowing land plants and animals to disperse between North America and both Europe and Asia.

Herbivory in early Tertiary Arctic forests

Early Tertiary High Arctic forest ecosystems are unique in that they have no equivalent among modern forests. Today, no forest ecosystem exists at such high latitudes. To assess the potential role of herbivory during the early Tertiary warm period at high latitudes, we have surveyed 1567 fossil angiosperm leaves from Svalbard for the presence or absence of 35 insect damage types (DTs). Our investigation for the first time uncovered a wealth of insect trace fossils from the early Tertiary northern high latitudes. These include galls, mines, and feeding traces on fossil leaves. Most of the folivory includes unspecific external foliage feeding that cannot be ascribed to a particular group of insects. Exceptions are the mining damage types that are most similar to those made by leaf-mining moths (Lepidoptera: Gracillaroidea). Nevertheless, the abundance of folivory indicates that herbivorous insects were an important component of the forests thriving in the Arctic realm. The observed change in insect herbivory from the Middle Paleocene to the Late Eocene/Early Oligocene in Spitsbergen may be attributed to climatic variables because they influence insect life-cycle timing, population density, and geographic range.