Alder Shrubs Research Articles

Implications of alder shrub growth for alpine tundra soil properties in Interior Alaska

ABSTRACT The increase in deciduous shrub growth in response to climate change throughout the Arctic tundra has uncertain implications, in part due to a lack of field observations. Here we investigate how increasing alder shrub growth in alpine tundra in Interior Alaska corresponds to active layer thickness and soil physical properties. We documented increased alder growth by combining biomass harvests and dendrochronology with the analysis of remotely sensed Normalized Difference Vegetation Index and fire history. Active layer thickness was measured with a tile probe and carbon and nitrogen pools were assessed via elemental analysis. Shallower organic layers under increasing alder growth indicate that nitrogen-rich, deciduous litter inputs may play a role in accelerating decomposition. Despite the observed reduction in organic carbon stocks, active layer thickness was the same under alder and adjacent graminoid tundra, implying deeper thaw of the underlying mineral soil. This study provides further evidence that the widely observed expansion of deciduous shrubs into graminoid tundra will reduce ecosystem carbon stocks and intensify soil–atmosphere thermal coupling.

Plant-moth community relationships at the degraded urban peat-bog in Central Europe.

Peatlands have their own, specific insect fauna. They are a habitat not only for ubiquistic but also stenotopic moths that feed onplants limited to wet, acid and oligotrophic habitats. In the past, raised bogs and fens were widely distributed in Europe. This has changed since 20th c. Due to irrigation, modern forestry, and increasing human settlement, peatlands have become isolated islands in anagricultural and urban landscape. Here, we analyze the flora in a degraded bog situated in a large Lodz city agglomeration in Poland in relation to the diversity and composition of moth fauna. Over the last 40 years since the bog has become protected as a nature reserve, birch, willow, and alder shrubs replaced the typical raised bog plant communities due to the decreased water level. The analysis of moth communities sampled in 2012 and 2013 indicates dominance of ubiquistic taxa associated with deciduous wetland forests and rushes. Tyrphobiotic and tyrphophile moth taxa were not recorded. We conclude that the absence of moths typical of bog habitats and the dominance of common, woodland species are associated with hydrological changes, the expansion of trees and brushes over typical bog plant communities, and light pollution.

High nitrate variability on an Alaskan permafrost hillslope dominated by alder shrubs

Abstract. In Arctic ecosystems, increasing temperatures are driving the expansion of nitrogen (N) fixing shrubs across tundra landscapes. The implications of this expansion to the biogeochemistry of Arctic ecosystems are of critical importance and more work is needed to better understand the form, availability, and transportation potential of N from these shrubs across a variety of Arctic landscapes. To gain insights into the processes controlling N within a permafrost hillslope system, the spatiotemporal variability of nitrate (NO3-) and its environmental controls were investigated at an alder (Alnus viridis spp. fruticosa) dominated permafrost tundra landscape in the Seward Peninsula, Alaska, USA. Soil pore water was collected from locations within alder shrubland growing along a well-drained hillslope and was compared to soil pore water collected from locations outside (upslope, downslope, and between) the alder shrubland. Soil pore water collected within alder shrubland had an average NO3-N (nitrogen from nitrate) concentration of 4.27±8.02 mg L−1 and differed significantly from locations outside alder shrubland (0.23±0.83 mg L−1; p<0.05). Temporal variation in NO3-N within and downslope of alder shrubland co-occurred with precipitation events where NO3- that accumulated in the soil was likely flushed downslope during rainfall. These findings have important implications for nutrient availability and mobility in N-limited permafrost systems that are experiencing shrub expansion in response to a warming Arctic.

Late Quaternary paleoenvironmental reconstructions from sediments of Lake Emanda (Verkhoyansk Mountains, East Siberia)

ABSTRACTContinuous pollen and chironomid records from Lake Emanda (65°17′N, 135°45′E) provide new insights into the Late Quaternary environmental history of the Yana Highlands (Yakutia). Larch forest with shrubs (alders, pines, birches) dominated during the deposition of the lowermost sediments suggesting its Early Weichselian [Marine Isotope Stage (MIS) 5] age. Pollen‐ and chironomid‐based climate reconstructions suggest July temperatures (TJuly) slightly lower than modern. Gradually increasing amounts of herb pollen and cold stenotherm chironomid head capsules reflect cooler and drier environments, probably during the termination of MIS 5. TJuly dropped to 8 °C. Mostly treeless vegetation is reconstructed during MIS 3. Tundra and steppe communities dominated during MIS 2. Shrubs became common after ~14.5 ka bp but herb‐dominated habitats remained until the onset of the Holocene. Larch forests with shrub alder and dwarf birch dominated after the Holocene onset, ca. 11.7 ka bp. Decreasing amounts of shrub pollen during the Lateglacial are assigned to the Older Dryas and Younger Dryas with TJuly ~ 7.5 °C. TJuly increased up to 13 °C. Shrub stone pine was present after ~7.5 ka bp. The vegetation has been similar to modern since ca. 5.8 ka bp. Chironomid diversity and concentration in the sediments increased towards the present day, indicating the development of richer hydrobiological communities in response to the Holocene thermal maximum.

Thinning the thickets: Foraging of hardy cattle, sheep and goats in green alder shrubs

Abstract Green alder shrubs Alnus viridis increasingly overgrow European mountain pastures but hinder natural forest succession. This nitrogen‐fixing, autochthonous invasive species has numerous negative effects including the loss of biodiversity and landscape aesthetic, eutrophication of soils and downstream waters, and greenhouse gas emission. Over centuries, A. viridis encroachment was impeded by grazing livestock, particularly goats. However, in modern agriculture, livestock numbers decreased on remote mountain pastures and goat farming became unprofitable. A grazing experiment tested if hardy breeds of the more economically attractive livestock species, cattle and sheep can replace goats as A. viridis antagonists. On a subalpine pasture heavily encroached by A. viridis, space use and debarking (bark foraging) by Dexter cattle, Engadine sheep and Pfauen goats were analysed using GPS tracking and vegetation mapping. Dexter cattle used space least evenly (Camargo evenness: cattle = 0.39; sheep = 0.52; and goats = 0.47) and preferred flat slopes and open pastures. They spent least time foraging in A. viridis stands (relative presence while foraging: cattle = 0.55; sheep = 0.76; and goats = 0.80). Dexter cattle did not debark any A. viridis, but damaged shrubs by trampling. Engadine sheep visited A. viridis stands nearly as often as goats, but preferred flat slopes, short vegetation and shrub edges more clearly than goats. This sheep breed debarked significantly more A. viridis branches (average 244 branches per paddock; 7.4% of all A. viridis branches) than goats (45; 0.8%). Goats preferred mountain‐ash shrubs Sorbus aucuparia covering only 2% of the shrub layer. Synthesis and applications. Green alder shrubs, controlled by goats traditionally, overgrow valuable mountain pasture ecosystems today. Cattle, kept instead of goats, may slow down but not hinder shrub encroachment, because they avoid shrub stands and do not debark green alder. However, this study is the first to show that Engadine sheep are even better suited for green alder clearance than goats. Moreover, if management goals include forest re‐establishment, Engadine sheep outperform goats, because they debark green alder (which hinders forest regeneration), but do not destroy elderberry—a valuable forest pioneer. Hardy breeds are an important tool to maintain biodiverse, open pastures, restore natural mountain forests and mitigate the negative environmental effects of shrub encroachment.

Трансформация морфологических свойств почв вследствие закустаривания пятнистой тундры

Climate warming in the Subarctic leads to the expansion of shrub ecosystems. The most common upland tundra shrubification is by alder in combination with dwarf birch and willows. However, the nature and rate of changes in the morphological properties of soils in the low arctic tundra during shrubification remain unknown. To study the impact of new shrub ecosystems on tundra soils, we studied alder shrubs in the south of the Western Siberian tundra. The key site is located between the rivers Taz and Pur. The village of Tazovsky, Yamalo-Nenets Autonomous Okrug (Russia) is located nearby. This area is called the Taz tundra, near its transition to the forest tundra. The coordinates of the center of alder shrubs are N67°22'17.4'', E78°42'11.7'' (Fig. 1). The formation of alder shrubs at the study site began no later than 1957. We studied 34 soil profiles. Of these, eight soil profiles were studied in the tundra, eight more in the tundra ecotone and alder shrubs. Eighteen soil profiles characterized the periphery or central zone of alder shrubs (Fig. 2, 3). In the field, we studied the vegetation, the depth of permafrost, photographed soil profiles, and took samples of soil horizons and a micromonolith. We quantified soil morphological parameters such as soil horizon boundary depth, soil horizon thickness, thixotropy index, gley patch percentage, root penetration depth, charcoal abundance, and horizon coloration in the CIE-L*a*b* system. A topographic survey was made within the key site. The age of shrubs and the relief form for each soil profile were determined. The obtained values were processed using the methods of basic statistics and the method of principal components. The studied alder shrubs in the Taz Tundra are located in the upper part of the slopes of stream valleys. The expansion of shrubs at the key site has been observed since the beginning of the second half of the 20th century. For the key site with alder, the succession stages of transformation of tundra into a shrub ecosystem are described. At the first stage, only a few young shoots of alder are observed in tundra (Fig. 10). Alder appears as a result of seed germination on devoid of vegetation areas of cryoturbated soils (patterned-ground). Alder actively colonizes the territory adjacent to the original places of germination, which leads to the expansion of the original range and the concentric structure of shrubs. The second stage is represented by tundra and alder ecotone. In this ecotone, the cover and height of alder increase, and so does the habitus of the original shrubs (dwarf birch and wild rosemary). The main transformations of soil properties are associated with an increase in the active layer thickness. The third stage is the peripheral part of the alder shrubs, where the height of the alder is maximum and reaches 4.5 m. The fourth stage is the central zone of the alder shrubs, where there appear reed-sedge meadows with fireweed. Meadows form in places where the alder bushes died out. The main changes at the third and fourth stages are associated with a radical improvement in the hydrothermal conditions of soil formation, which leads to deepening of the permafrost surface to 3-4.5 m, and a talik is formed. Soil fertility increases due to its enrichment with nitrogen by nitrogen-fixing alder. Alder leaves susceptible to decomposition fall on the soil surface, which is important for earthworms and has a priming effect for the decomposition of tundra litter. The depth of the root system increases. An increase in evapotranspiration leads to a decrease in soil moisture and disappearance of their thixotropic properties. The area of gley patches in soils decreases (Fig. 6). The thickness of peat and litter horizons decreases (Fig. 7). Initially, thixotropic horizons are structured according to the ooid type (Fig. 8). Root and animal tunnels, which are stable in seasonal cycles, are formed in the soil. The resulting pores and soil aggregates allow the development of soil mesofauna. All the above mentioned cause formation of humus-accumulative horizons on convex slopes under alder. Reductaquic Cryosols and Folic Reductaquic Cryosols evolve into Gleyic Cambisol, Stagnic Cambisol (Ochric), and Gleysol (Ochric). Thus, our study confirmed the hypothesis that the radical change of tundra vegetation during the expansion of shrubs causes significant classificatory changes in the morphological properties of soils over several decades. The article contains 10 figures, 79 references. The Authors declare no conflict of interest.

Tussocks Enduring or Shrubs Greening: Alternate Responses to Changing Fire Regimes in the Noatak River Valley, Alaska

AbstractAs the Arctic warms, tundra wildfires are expected to become more frequent and severe. Assessing how the most flammable regions of the tundra respond to burning can inform us about how the rest of the Arctic may be affected by climate change. Here we describe ecosystem responses to tundra fires in the Noatak River watershed of northwestern Alaska using shrub dendrochronology, active‐layer depth monitoring, and remotely sensed vegetation productivity. Results show that relatively productive tundra is more likely to experience fires and to burn more severely, suggesting that fuel loads currently limit tundra fire distribution in the Noatak Valley. Within three years of burning, most alder shrubs sampled had either germinated or resprouted, and vegetation productivity inside 60 burn perimeters had recovered to prefire values. Tundra fires resulted in two phases of increased primary productivity as manifested by increased landscape greening. Phase one occurred in most burned areas 3–10 years after fires, and phase two occurred 16–44 years after fire at sites where tundra fires triggered near‐surface permafrost thaw resulting in shrub proliferation. A fire‐shrub‐greening positive feedback is currently operating in the Noatak Valley and this feedback could expand northward as air temperatures, fire frequencies, and permafrost degradation increase. This feedback will not occur at all locations. In the Noatak Valley, the fire‐shrub‐greening process is relatively limited in tussock tundra communities, where low‐severity fires and shallow active layers exclude shrub proliferation. Climate warming and enhanced fire occurrence will likely shift fire‐poor landscapes into either the tussock tundra or erect‐shrub‐tundra ecological attractor states that now dominate the fire‐rich Noatak Valley.

Structural traits of woody plants and geomorphological conditions to the vegetation recovery at Ksudach caldera (Southern Kamchatka) since the explosive eruption in 1907

This study considers the restoration of the plant cover destroyed by a catastrophic volcano eruption in the south of Kamchatka Peninsula (the Ksudach caldera, Shtyubel cone), with a particular attention to the role of woody plants. It aims to qualitatively estimate (at a qualitative level) the rate of the primary succession development depending on the microrelief and the modern relief-forming processes. The vegetation recovery in the caldera after the Shtyubel cone eruption 109 years ago proceeds slowly and irregularly. It proceeds most slowly on a thick tephra mantle continuously disturbed by water and wind erosion, lahars, debris flows, landslides, etc. Such conditions are most typical of the western part of the caldera dominated by pumice fields with occasional patches of pioneer herbs and dwarf shrubs. Alpine tundra communities with gradually expanding patches of shrub alder develop in the southern, eastern and northeastern parts of the Ksudach caldera. Since 1997 the area of the shrub alder communities has increased by 1.9 times, while the alpine tundra — by 1.3 times only. The woody plants (dwarf shrubs and prostrate shrubs) are of particular importance in the process of the vegetation recovery on pumice fields. We suggest that the bark thickness of woody plants is an integrated indicator, which may serve for estimating the state of ecosystem in the course of the primary succession development on juvenile sediments. The extremely inhospitable environments cause changes in physiological processes in the plant body and in its bark in particular. The results show that woody plants have a “thin” bark and develop some structural-functional arrangements for keeping bark tissues at their minimum. So, the woody plant structure and the rate of changes in plant communities are under control of the geomorphic conditions and primarily — of physicochemical features of the pyroclastic cover.

Mapping tall shrub biomass in Alaska at landscape scale using structure-from-motion photogrammetry and lidar

Warming in arctic and boreal regions is increasing shrub cover and biomass. In southcentral Alaska, willow (Salix spp.) and alder (Alnus spp.) shrubs grow taller than many tree species and account for a substantial proportion of aboveground biomass, yet they are not individually measured as part of the operational Forest Inventory and Analysis (FIA) Program. The goal of this research was to test methods for landscape-scale mapping of tall shrub biomass in upper montane and subalpine environments using FIA-type plot measurements (n = 51) and predictor variables from imagery-based structure-from-motion (SfM) and airborne lidar. Specifically, we compared biomass models constructed from imagery acquired by unmanned aerial vehicle (UAV; ~1.7 cm pixels), imagery from the NASA Goddard's Lidar, Hyperspectral, and Thermal Airborne Imager (G-LiHT; ~3.1 cm pixels), and concomitant G-LiHT small-footprint lidar. Tall shrub biomass was most accurately predicted at 5 m resolution (R2 = 0.81, RMSE = 1.09 kg m−2) using G-LiHT SfM color and structure variables. Lidar-only models had lower precision (R2 = 0.74, RMSE = 1.26 kg m−2), possibly due to reduced model information content from variable multicollinearity or lower data density. Separate models for upper montane zones with trees and shrubs and subalpine zones with only shrubs were always chosen over single models based on minimization of Akaike's Information Criterion, indicating the need for variable sets robust to overhanging tree canopy. Decreasing point density from UAV (5000–8000 pts. m−2) to the G-LiHT SfM point cloud (500–2000 pts. m−2) had little impact on model fit, suggesting that high-resolution airborne imagery can extend SfM approaches well beyond line-of-sight restrictions for UAV platforms. Overall, our results confirmed that SfM from high-resolution imagery is a viable approach to estimate shrub biomass in the boreal region, especially when an existing lidar terrain model and local field calibration data are available to quantify uncertainty in the SfM point cloud and landscape-scale estimates of shrub biomass.

Experience of applying plant and animal fluctuating asymmetry in assessment of environmental quality in terrestrial ecosystems: Results of 20-year studies of wildlife and anthropogenically transformed territories

The value of fluctuating asymmetry (FA) of trees and small mammals is considered as an indicator of developmental instability. The urban territories with recreation zones, sites with increased radiation background, and the areas affected by mining facilities have been analyzed as anthropogenically transformed areas. The following tree and small mammalian species are the objects of the study: Siberian silver birch (Betula platyphylla), spreading birch (B. divaricata), dwarf birch (B. exilis), shrub alder (Duschekia fruticosa), basket willow (Salix viminalis), northern red-backed vole (Clethrionomys rutilus), tundra vole (Microtus oeconomus), Laxmann’s shrew (Sorex caecutiens), and tundra shrew (S. tundrensis). In total, 60000 leaves have been measured and 3500 rodent sculls have been examined. The issues of selection of bioindicator species and the factors distorting the results of environmental quality assessment according to developmental instability are discussed. A statistically significant increase in FA of plants is recorded in urban territories as compared with the wildlife biotopes. A positive correlation of FA value with transport load, concentration of heavy metals in soil, and atmospheric air pollution is observed. The proximity to a roadway and the state of road pavement influence the FA value. The main source of pollution in the administrative center (Yakutsk) is motor vehicles; correspondingly, large streets and crossroads with a high transport load are the most polluted sites. As for the industrial center (city of Mirnyi), pollution spreads from the areas affected by mining to the residential area. The main pollution source in a small administrative center (city of Aldan) is the federal highway. It is recommended to concurrently use the FA characteristics of plant and animals in the area affected by the mining industry. Characteristic of this industry is withdrawal of large areas of natural landscapes; typically, transformed plots alternate weakly affected plots. The specific features of the effects of diamond, gold, and coalmining industries, as well as oil and gas field development, are discussed, which should be taken into account in sampling for bioindication. The problem of bioindication in the areas completely devoid of soil and plant cover can be solved by biotesting via assessment of bunching onion seed germination rate and the rate of mitotic aberrations. An increase in the FA level in trees and small mammals is observed in the areas transformed by the mining industry displaying a chronically increased radiation background and oil-polluted as a result of technogenic accidents. The use of FA index makes it possible to estimate the environmental quality and to compare the state of territories located under different natural and climatic conditions and influenced by multicomponent anthropogenic impacts differing in their strength and genesis, which interferes with their comparison.

Green alder (Alnus viridis) encroachment shapes microbial communities in subalpine soils and impacts its bacterial or fungal symbionts differently.

Since the mid-twentieth century, subalpine grasslands undergo a progressive encroachment by Alnus viridis shrubs. Thanks to its rapid vegetative reproduction, its nitrogen fixing symbiosis with Frankia and its ectomycorrhizal cohorts, green alders are vigorous colonizers that quickly form mosaic of alder patches that evolves into a close canopy shrub community. To better understand how alder encroachment might influence microbial communities in this successional sequence, symbiont distribution, microbial richness and community structure in both soils and nodules were analyzed at three successional stages: grassland, mosaic and forest. Soil analyses were performed in association with measures of nitrification and denitrification, as well as DNA metabarcoding of three bacterial genes (16S rDNA, nifH and amoA) and one fungal gene (ITS1). Our results show that (i) A. viridis encroachment is associated with soil microbial community changes that are in turn, linked to certain soil properties (i.e., pH, C/N ratio and organic matter content), (ii) both taxonomic and N related functional gene structures of bacteria are modified by alder encroachment and (iii) the distribution in soils of its bacterial symbionts (Frankia) is apparently weakly influenced by alder establishment while Alnus-specific ectomyccorrhizae increase with the increase in alder shrub density.

Seasonal and Long-Term Changes to Active-Layer Temperatures after Tall Shrubland Expansion and Succession in Arctic Tundra

Vegetation, active-layer soils, and snow cover regulate energy exchange between the atmosphere and permafrost. Therefore, interactions between changes to tundra vegetation and soil thermal regime will fundamentally affect permafrost in a warmer world. We recorded soil temperatures for approximately 1 year in a Siberian Low Arctic landscape with a known history of alder (Alnus) shrub expansion on disturbed microsites in patterned ground. We recorded near-surface soil temperatures and measured physical properties of soils and vegetation on sorted-circle microsites in four stages of shrubland development: (1) tundra lacking tall shrubs; (2) shrub colonization zones; (3) mature shrublands; and (4) paludified, long-established shrublands with thick soil organic layers. Summer soil temperatures declined with increasing shrub cover and soil organic thickness; shrub colonization suppressed cryoturbation, facilitating the development of continuous vegetation and a surface organic mat on circles. Compared to open tundra, mature shrubs cooled soils by up to 9 °C during summer, but warmed soils by greater than 10 °C in winter presumably because they developed highly insulative snowpacks. Paludified shrublands had the coldest summer active layers, but winter soil temperatures were much colder than mature shrublands and were similar to earlier stages. Our results indicate that although tall shrub establishment dramatically warms winter soils within decades, much of this warming is transient at paludification-prone sites because the buildup of wet peat favors cooling in winter and the stature and snow-trapping capacity of shrubs diminish over time. In the ecosystem we studied, shrub expansion has contrasting effects on active-layer temperatures both seasonally and over longer timescales due to successional processes.

Millennial-scale vegetation changes in the north-eastern Russian Arctic during the Pliocene/Pleistocene transition (2.7–2.5 Ma) inferred from the pollen record of Lake El’gygytgyn

Abstract The sediment record of Lake El’gygytgyn (67°30′N, 172°05′E) spans the past 3.6 Ma and provides unique opportunities for qualitative and quantitative reconstructions of the regional paleoenvironmental history of the terrestrial Arctic. Millennial-scale pollen studies of the sediments that accumulated during the Late Pliocene and Early Pleistocene (ca. 2.7 to 2.5 Ma) demonstrate orbitally-driven vegetation and climate changes during this transitional interval. Pollen spectra show a significant vegetation shift at the Pliocene/Pleistocene boundary that is, however, delayed by a few thousand years compared to lacustrine response. About 2.70–2.68 Ma the vegetation at Lake El’gygytgyn, currently a tundra area was mostly dominated by larch forests with some shrub pine, shrub alder and dwarf birch in understory. During the marine isotope stages G3 and G1, ca. 2.665–2.647 and 2.625–2.617 Ma, some spruce trees grew in the local larch-pine forests, pointing to relatively warm climate conditions. At the beginning of the Pleistocene, around 2.588 Ma, a prominent climatic deterioration led to a change from larch-dominated forests to predominantly treeless steppe- and tundra-like habitats. Between ca. 2.56–2.53 Ma some climate amelioration is reflected by the higher presence of coniferous taxa (mostly pine and larch, but probably also spruce) in the area. After 2.53 Ma a relatively cold and dry climate became dominant again, leading to open steppe-like and shrubby environments followed by climate amelioration between ca. 2.510 and 2.495 Ma, when pollen assemblages show that larch forests with dwarf birch and shrub alder still grew in the lake’s vicinity. Increased contents of green algae colonies (Botryococcus) remains and Zygnema cysts around 2.691–2.689, 2.679–2.677, 2.601–2.594, 2.564–2.545, and 2.532–2.510 Ma suggest a spread of shallow-water environments most likely due to a lake-level lowering. These events occurred simultaneously with dry climate conditions inferred from broad distribution of steppe habitats with Artemisia and other herbs.

Water and solute dynamics during rainfall events in headwater catchments in the Central Swiss Alps under the influence of green alder shrubs and wetland soils

AbstractIn the Swiss Alps, shrubs (e.g. Alnus viridis (Chaix) DC) are encroaching into formerly open habitats. The shrub encroachment might affect soil hydrological properties, which in turn influence runoff generation. Moreover, alder species (Alnus spp.) are known to affect chemical soil properties (e.g. increase of nitrate concentrations in the soil solution) and can therefore alter the water quality of stream water. In our study, we investigated four small alpine headwater catchments to assess the influence of shrub encroachment and wetland soils on stream water geochemistry during storm runoff. Stream water was sampled in the growing season of 2010 at hourly intervals during one single rainfall event. Stable isotope values (δ18O) of stream water (ranging from −13.8 to −8.5‰) and rainfall (bulk mean δ18O value of about −5.6‰) during the single event were used to estimate the fraction of event water in stream discharge. Continuously measured electrical conductivity in the growing seasons of 2010 and 2011 was used to infer information on runoff generation during 15 rainfall events. Riparian wetland soils were flushed by a high fraction of event water of up to 72% during peak discharge, which increased the dissolved organic carbon export during the single rainfall event. Besides the atmospheric input through nitrate in rainwater, the expected expansion of green alder shrubs in the region, associated with increasing number and intensity of summer rainfall events in the future, might increase the episodic export of nutrients such as dissolved organic carbon and NO3− from these catchments. Copyright © 2015 John Wiley & Sons, Ltd.

Holocene climate and environmental change in north-eastern Kamchatka (Russian Far East), inferred from a multi-proxy study of lake sediments

A sediment record from a small lake in the north-eastern part of the Kamchatka Peninsula has been investigated in a multi-proxy study to gain knowledge of Holocene climatic and environmental change. Pollen, diatoms, chironomids and selected geochemical parameters were analysed and the sediment record was dated with radiocarbon. The study shows Holocene changes in the terrestrial vegetation as well as responses of the lake ecosystem to catchment maturity and multiple stressors, such as climate change and volcanic eruptions. Climate change is the major driving force resulting in the recorded environmental changes in the lake, although recurrent tephra deposition events also contributed. The sediment record has an age at the base of about 10,000calyrs BP, and during the first 400years the climate was cold and the lake exhibited extensive ice-cover during winter and relatively low primary production. Soils in the catchment were poor with shrub alder and birches dominating the vegetation surrounding the lake. At about 9600–8900calyrs BP the climate was cold and moist, and strong seasonal wind stress resulted in reduced ice-cover and increased primary production. After ca. 8900calyrs BP the forest density increased around the lake, runoff decreased in a generally drier climate resulting in decreased primary production in the lake until ca. 7000calyrs BP. This generally dry climate was interrupted by a brief climatic perturbation, possibly attributed to the 8.2ka event, indicating increasingly windy conditions with thick snow cover, reduced ice-cover and slightly elevated primary production in the lake. The diatom record shows maximum thermal stratification at ca. 6300–5800calyrs BP and indicates together with the geochemical proxies a dry and slightly warmer climate resulting in a high productive lake. The most remarkably change in the catchment vegetation occurred at ca. 4200calyrs BP in the form of a conspicuous increase in Siberian dwarf pine (Pinus pumila), indicating a shift to a cooler climate with a thicker and more long-lasting snow cover. This vegetational change was accompanied by marked shifts in the diatom and chironomid stratigraphies, which are also indicative of colder climate and more extensive ice-cover.

Cumulative Impacts and Feedbacks of a Gravel Road on Shrub Tundra Ecosystems in the Peel Plateau, Northwest Territories, Canada

Gravel highways in the continuous permafrost zone provide critical transportation links that are increasingly vulnerable to the impacts of climate warming and permafrost thaw. To examine if the physical effects associated with the construction, maintenance, and use of gravel roads alter vegetation and permafrost conditions, we measured vegetation, soils, and near-surface ground temperatures at tall and dwarf shrub tundra sites adjacent to and distant from the Dempster Highway in the Northwest Territories of Canada. We found that alder growth and recruitment were significantly enhanced adjacent to the highway. Where alder shrubs had formed closed canopies, we observed dramatic alterations to plant community composition, soil properties, and ground temperatures. Tall shrub sites adjacent to the road exhibited less understory vegetation, greater litter and organic layer thickness, higher nutrient availability, and thicker snowpack than all other site types. Our results show that in shrub tundra ecosystems the conditions generated by the maintenance and use of a gravel road can drive ecological feedbacks that magnify changes to vegetation communities and soils. We found that where the road facilitated shrub dominance, feedbacks were initiated that enhanced snow accumulation and altered ground temperatures and soil chemistry. In turn, these changes likely promoted enhanced shrub recruitment and growth. Shrub proliferation adjacent to highways is an important consideration for the planning and maintenance of this form of infrastructure. To improve our understanding of the spatial heterogeneity of shrub proliferation, research exploring the relationships between biophysical landscape features and shrub development is also needed.

Impact of elevated CO2 on metal homeostasis and the actinorhizal symbiosis in early successional alder shrubs

The increasing atmospheric CO2 concentration could stimulate terrestrial ecosystem and create an important carbon (C) sink that could slow down climate change due to anthropogenic activities. The extent of this enhanced growth will strongly depends upon the availability of nitrogen (N) to plant. In alder, the predominant N2 fixing tree in boreal forest, the ability to establish actinorhizal symbiosis will thus be key. How high CO2 concentration and exogenous N impact actinorhizal symbiosis remains poorly known. In this study on speckled alder and green alder, we evaluated the effect of CO2 and exogenous N availability on (i) the efficiency and development of the actinorhizal symbiosis and (ii) on the homeostasis of eleven elements, including essential nutrients for N2 fixation such as phosphorus (P) and molybdenum (Mo). We report that Frankia sp. infection is the primary factor controlling nutrient homeostasis (allocation and concentration) in plant. P and Mo, and in a less extend magnesium (Mg) and manganese (Mn), are the elements which homeostasis was the most affected by Frankia sp. infection. Exogenous N and CO2 concentrations had limiting or no impact on the homeostasis of most elements. We also show that actinorhizal symbiosis could be critical to alder response to elevated CO2. In absence of Frankia sp. infection neither speckled alder nor green alder responded to elevated CO2. On the contrary, in presence of Frankia sp., the biomass production was significant stimulated by increasing CO2 and independent to exogenous N.

The Symbiosis between Frankia and Alder Shrubs Results in a Tolerance of the Environmental Stress Associated With Tailings from the Canadian Oil Sands Industry

Alders are well recognized for their ability to colonize the harsh environments created by either natural processes or human activity. They establish symbiosis with the actinomycete Frankia which supplies 70 to 100 % of the plant’s nitrogen requirements. An important challenge facing the oil sands industry in Alberta, Canada, is management of the toxicity of Tailing Sands (TS) that are alkaline, saline and contain Naphthenic Acids (NA).In order to begin to understand how alders, Frankia and their symbiosis perform and adapt to these challenging environmental conditions, the tolerance of the microsymbiont (Frankia), the host plants (alders) and their symbiosis to specific compounds found in TS was studied. In addition, the metabolic response of Frankiaalni ACN14a to the presence of NA was characterized. The Frankia strains tested tolerated both high pH and NA levels in addition to salts near or at the concentrations found in TS. Furthermore, actinorhizal symbiosis can establish itself under these conditions. NaCl was observed to exert the greatest stress on the establishment of symbiosis, decreasing the efficiency of the actinorhizal symbiosis. Inoculation of the alder plants with Frankia induced a significant increase in aerial biomass allocation. Finally, intracellular proteins in Frankiaalni ACN14a whose expression level were influenced by naphthenic acids were identified. Together, these results demonstrate that actinorhizal alders show significant promise for use in the revegetation of lands affected by the mine tailings of the Canadian petroleum industry.

The Younger Dryas in the Neotropics: paleoecological evidence from Venezuela

A continuous lacustrine sequence from the western part of Lama Lake (69°32′N, 90°12′E), complemented by a peat sequence from the lake catchment provides the first detailed environmental reconstruction for the Late Glacial and Holocene on the Taymyr Peninsula. Scarce steppe-like communities with Artemisia, Poaceae, and Cyperaceae dominated during the Late Glacial. Tundra-like communities with Betula nana, Dryas, and Salix grew on more mesic sites. There are distinct climatic signals, which may be correlated with the Bølling and Allerød warming and Middle and Younger Dryas cooling. The Late Glacial/Preboreal transition, at about 10,000 14C yr BP, was characterized by changes from predominantly open herb communities to shrub tundra ones. Larch forest might have been established as early as 9700–9600 14C yr BP, whilst shrub alder came to the area ca 9500–9400 14C yr BP, and spruce did not reach area before ca 9200 14C yr BP. Spruce-larch forests with shrub alder and tree birch dominated the vegetation around the Lama Lake from ca 9000 14C yr BP. Dwarf birch communities were also broadly distributed. The role of spruce in the forest gradually decreased after 4500 14C yr BP. The vegetation cover in the Lama Lake area became similar to the modern larch-spruce forest ca 2500 14C yr BP. A pollen-based biome reconstruction supports a quantitative interpretation of the pollen spectra. Climate reconstructions obtained with information-statistical and plan-functional-type methods show very similar trends in reconstructed July temperature since ca 12,300 14C yr BP, while precipitation anomalies are less coherent, especially during the Late Glacial–Holocene transition.

Vegetation history of central Chukotka deduced from permafrost paleoenvironmental records of the El'gygytgyn Impact Crater

Abstract. Frozen sediments from three cores bored in the permafrost surrounding the El'gygytgyn Impact Crater Lake have been studied for pollen, non-pollen palynomorphs, plant macrofossils and rhizopods. The palynological study of these cores contributes to a higher resolution of time intervals presented in a poor temporal resolution in the lacustrine sediments; namely the Allerød and succeeding periods. Moreover, the permafrost records better reflect local environmental changes, allowing a more reliable reconstruction of the local paleoenvironments. The new data confirm that shrub tundra with dwarf birch, shrub alder and willow dominated the lake surroundings during the Allerød warming. Younger Dryas pollen assemblages reflect abrupt changes to grass-sedge-herb dominated environments reflecting significantly drier and cooler climate. Low shrub tundra with dwarf birch and willow dominate the lake vicinity at the onset of the Holocene. The find of larch seeds indicate its local presence around 11 000 cal yr BP and, thus a northward shift of treeline by about 100 km during the early Holocene thermal optimum. Forest tundra with larch and shrub alder stands grew in the area during the early Holocene. After ca. 3500 cal yr BP similar-to-modern plant communities became common in the lake vicinity.