Dominant Dwarf Shrub Research Articles

Elemental composition of <i>Vaccinium vitis-idaea</i> и <i>V. myrtillus</i> (Ercaceae) leaves in green moss pine forests under aerotechnogenic pollution in the Komi Republic

The paper aims at the impact of aerotechnogenic emissions from the largest in the European North pulp and paper production enterprise, namely JSC «Syktyvkar Timber Processing Complex», on the elemental composition (N, S, C, P, K, Ca, Mg, Na, Al, Fe, Mn) of lingonberry and blueberry leaves as the dominant dwarf shrubs in green moss pine forests. The leaves of blueberry and lingonberry growing in pine stands both in the background and contaminated areas were identified to have similar average values of the mass fraction of ash elements in 2009. The content of ash elements in the leaves of dwarf shrubs from the background pine forests was higher than that in leaves collected from the impact zone in 2018. The average values of the mass fraction of ash elements in blueberry leaves were found to access those in lingonberry leaves by 1,5 time both in the background and contaminated areas. There was no regular change in the content of elements in leaves of dwarf shrubs with distance from the source of emission. The differences in the sulfur content in leaves of dwarf shrubs for 2009 and 2018 were within the error limits. No significant differences were found in the values of the mass fraction of nitrogen in blueberry and lingonberry leaves for pine stands located at different distances from the emission source. The nitrogen content in lingonberry leaves was significantly lower than that in blueberry leaves for both observation periods. There was no significant difference in the total nitrogen content in blueberry and lingonberry leaves between 2009 and 2018.

Changing species dominance patterns of Boreal‐Arctic heathlands: evidence of biotic homogenization

Heathlands are extensive systems often dominated by slow‐growing and long‐lived woody plants. These systems require longer‐term studies to capture if and how they are changing over time. In 2020, we resurveyed species richness and cover of vascular plant communities in 139 heathlands along the coastline of northern Fennoscandia, first surveyed during 1965–1975. The first survey included six heathland types, each with dominance – a cover of 25% or more – of the dwarf shrubs Calluna vulgaris, Kalmia procumbens, Betula nana, Vaccinium myrtillus and Empetrum nigrum. The two latter heathland types made up 29% and 48%, respectively, of all heathlands. In addition to the dominant dwarf shrubs giving their names to the heathland types, a few other species qualified as dominant. In the resurvey, all the heathland types had E. nigrum as the single dominant species, except for the heathland formerly dominated by B. nana. Most other species had low cover both at the time of the original survey and the resurvey. Also, the heathland types were species poor at the time of the original survey, with an average of eight vascular plant species per 4 m2 and were found equally species poor in the resurvey. Species richness differed between heathland types only at the time of the original survey, and the ratio of species exchange between the two surveys was negatively related to the original cover of E. nigrum.Here we provide a half‐century perspective on vegetation change, during which several heathland types in northern Fennoscandia have changed to Empetrum heathlands, reducing the diversity of heathland types across the Boreal to Arctic landscape. As a native plant, E. nigrum cannot be considered invasive, but its allelopathic capacity has likely already modified these heathland ecosystems and will continue to do so, reducing ecosystem multifunctionality across the region.

From tundra to tree-birch; late-glacial and early Holocene environment and vegetation oscillations at the ecotonal positioned Bjerkreim, Dalane, SW Norway

Basin sediments from Bjerkreim, SW Norway, have been analyzed regarding pollen, plant macrofossils, chironomids, palaeomagnetism, elements, volcanic ash, and loss-on-ignition. The chronology is based on the Vedde Ash and Saksunarvatn ash layers and radiocarbon dates of plant and insect macrofossils. The records spanning the period from local deglaciation around 16 ka BP to the early Holocene ca 10.2 ka BP, have given new detailed information of the late-glacial environments. In the cold pre-Bølling (prior to 14.6 ka BP), open pioneer vegetation on unstable mineral soils was dominant. After the Bølling warming, climate became moister and reached the late-glacial thermal maximum (July mean of 12–13 °C), and dominant dwarf shrubs and snow beds established. Shallow soils, strong winds, and drought may have restricted vegetation development. Despite colder summers (July mean of 9.5–11 °C) in Allerød 13.9–12.8 ka BP, fertile humus-soils developed, and shrub vegetation and open birch-forests established. Snow beds regained dominance in Younger Dryas (July mean of 6.5–9 °C). The early Holocene warming initiated rapid establishment of early Betula/Populus-forests and the later Corylus forests around 10.7 ka BP. Three cooling events in the Bølling-Allerød interstadial (Older Dryas/GI-1d, G1-1c2, GI-1b/Gerzensee) temporarily increased open-ground vegetation showing the ecotonal position of Bjerkreim with low resistance to these changes. The Empetrum expansion was delayed (from 14.5 to 13.7 ka BP) towards the east along the coast of Rogaland. This could point to a precipitation/outwash gradient decreasing towards the east and developing the acid soils necessary for Empetrum to expand. For the first time, macrofossils show the late-glacial presence of tree-birch in Norway. Tree-birch were sparse in Bølling and formed patches of open-forests in Allerød. Several pollen taxa previously thought to reflect long-distance dispersal, such as Populus, Hippohaë, Jasione, and Sanguisorba ssp., most probably were present in Rogaland during Late-glacial. Doggerland seem to have been important for the late-glacial northwards migration of plants into South Norway.

Carbohydrates and secondary compounds of alpine tundra shrubs in relation to experimental warming

BackgroundIt is critical to understand the sensitivity, response direction and magnitude of carbohydrates and secondary compounds to warming for predicting the structure and function of the tundra ecosystem towards future climate change.ResultsOpen-top chambers (OTCs) were used to passively increase air and soil temperatures on Changbai Mountain alpine tundra. After seven years’ continuous warming (+ 1.5 °C), the vegetation coverage, nonstructural carbohydrates (soluble sugars and starch) and secondary compounds (total phenols, flavonoids and triterpenes) of leaves and roots in three dominant dwarf shrubs, Dryas octopetala var. asiatica, Rhododendron confertissimum and Vaccinium uliginosum, were investigated during the growing season. Warming did not significantly affect the concentrations of carbohydrates but decreased total phenols for the three species. Carbohydrates and secondary compounds showed significantly seasonal pattern and species-specific variation. No significant trade-off or negative relationship between carbohydrates and secondary compounds was observed. Compared to Dr. octopetala var. asiatica, V. uliginosum allocated more carbon on secondary compounds. Warming significantly increased the coverage of Dr. octopetala var. asiatica, did not change it for V. uliginosum and decreased it for Rh. confertissimum. Rh. confertissimum had significantly lower carbohydrates and invested more carbon on secondary compounds than the other two species.ConclusionsEnhanced dominance and competitiveness of Dr. octopetala var. asiatica was companied by increased trend in carbohydrate concentrations and decreased ratio of secondary compounds to total carbon in the warming OTCs. We, therefore, predict that Dr. octopetala var. asiatica will continue to maintain dominant status, but the competition ability of V. uliginosum could gradually decrease with warming, leading to changes in species composition and community structure of the Changbai tundra ecosystem under future climate warming.

Shrub and dwarf shrub communities of Sangilen Plateau

The paper presents a detailed ecological and caenotic characteristic of dwarf shrub and shrub communities growing in the highmountain belt of the Sangilen Plateau. The communities investigated were referred to the class of Loiseleurio-Vaccinietea Eggler 1952. The dwarf birch thickets with prevalence of Betula rotundifolia and the high incidence of Caragana jubata, Juniperus pseudosabina, J. sibirica, Pentaphylloides fruticosa, Salix glauca, Spiraea alpina were referred to the union of Carici tristis–Betulion rotundifoliae Zibzeev et al. 2018 of the order of Betuletalia rotundifoliae Mirkin at al. ex Chytrý Pešout et Anenkhonov 1993. Communities with dominant calciphilous shrubs and dwarf shrubs, such as Rhododendron adamsii, Caragana jubata, Salix berberifolia, S. reticulata, were referred to the union of Saxifrago oppositifoliae–Rhododendrion adamsii Zibzeev et al. 2018 of the order of Rhododendro-Vaccinietalia Br.-Bl. ex Daniels 1994.

Long-term responses of understory vegetation in boreal Scots pine stands after nitrogen fertilization

ABSTRACT Nitrogen fertilization can increase above- and belowground forest growth and carbon storage in low nitrogen (N) environments. However, it may also induce changes in other parts of the ecosystem, such as altered composition and diversity of the ground vegetation. These changes may occur, for example, because of increased availability of nitrogen and light depletion due to a denser tree canopy. We studied vegetation changes at 11 experimental sites in Pinus sylvestris stands with low N-deposition, along a south–north gradient in Sweden. We estimated the relative cover of individual species and the data were analysed with a linear model, using total amount of fertilizer-N added, years since last fertilization, site and site index as independent variables. The relative cover of the dominant dwarf shrubs (Vaccinium myrtillus and Vaccinium vitis-idaea) increased following fertilization. In the bottom layer, N significantly increased the total cover of two of the three dominant species (Pleurozium schreberi and Dicranum spp.). For the third species (Hylocomium splendens) no detectable effect was found. For lichens as a group, the cover decreased following N fertilization. No effect of N fertilization on species diversity was detected at any of the sites, and the forest vegetation types remained unchanged.

Climate synchronises shrub growth across a high‐arctic archipelago: contrasting implications of summer and winter warming

Climate change is most pronounced at high latitudes, where plant and animal populations are often strongly influenced by environmental fluctuations related to climate and weather. Environmental conditions can co‐fluctuate over large distances and thereby synchronise primary production in space. However, large‐scale studies of such spatiotemporal patterns remain rare in the Arctic, where short time‐series and poor spatial replication have characterised the data available on both biotic and abiotic parameters. Here, we use dendrochronological tools to measure ring growth of a dominant dwarf shrub, the polar willow Salix polaris, previously found to reliably trace community‐level vascular plant biomass production. We investigated climate drivers of vegetation growth and their role in the synchronisation of primary production across the rapidly warming archipelago of Svalbard (n = 8 sites, composed of 17 sub‐sites, 0.06–293 km apart). We found contrasting effects of summer versus winter weather on ring growth and its spatial synchrony. Although an overall positive effect of summer temperature caused spatially synchronous growth, negative impacts of winter rain‐on‐snow events occurred only locally, potentially counteracting such synchrony. However, the anticipated increase in both summer temperature and spatial extent of rain‐on‐snow events, causing basal ice encapsulation of the vegetation, could change the relative importance of seasons for spatiotemporal dynamics of shrub growth. Because these shrub ring growth chronologies reflect annual fluctuations in total vascular plant biomass, fuelling the bottom–up controlled food‐web, these results have large implications for our understanding of how climate change shapes tundra ecosystem productivity in time and space.

Accumulation of heavy metals in forest dwarf shrubs and dominant mosses as bioindicators of atmospheric pollution

This article discusses the environmental concerns about heavy metal accumulation in dominant forest mosses and dwarf shrubs. Samples of two different species of mosses, such as glittering wood moss ...

Impact of Multiple Ecological Stressors on a Sub-Arctic Ecosystem: No Interaction Between Extreme Winter Warming Events, Nitrogen Addition and Grazing.

Climate change is one of many ongoing human-induced environmental changes, but few studies consider interactive effects between multiple anthropogenic disturbances. In coastal sub-arctic heathland, we quantified the impact of a factorial design simulating extreme winter warming (WW) events (7 days at 6–7°C) combined with episodic summer nitrogen (+N) depositions (5 kg N ha-1) on plant winter physiology, plant community composition and ecosystem CO2 fluxes of an Empetrum nigrum dominated heathland during 3 consecutive years in northern Norway. We expected that the +N would exacerbate any stress effects caused by the WW treatment. During WW events, ecosystem respiration doubled, leaf respiration declined (-58%), efficiency of Photosystem II (Fv/Fm) increased (between 26 and 88%), while cell membrane fatty acids showed strong compositional changes as a result of the warming and freezing. In particular, longer fatty acid chains increased as a result of WW events, and eicosadienoic acid (C20:2) was lower when plants were exposed to the combination of WW and +N. A larval outbreak of geometrid moths (Epirrita autumnata and Operophtera brumata) following the first WW led to a near-complete leaf defoliation of the dominant dwarf shrubs E. nigrum (-87%) and Vaccinium myrtillus (-81%) across all experimental plots. Leaf emergence timing, plant biomass or composition, NDVI and growing season ecosystem CO2 fluxes were unresponsive to the WW and +N treatments. The limited plant community response reflected the relative mild winter freezing temperatures (-6.6°C to -11.8°C) recorded after the WW events, and that the grazing pressure probably overshadowed any potential treatment effects. The grazing pressure and WW both induce damage to the evergreen shrubs and their combination should therefore be even stronger. In addition, +N could have exacerbated the impact of both extreme events, but the ecosystem responses did not support this. Therefore, our results indicate that these sub-arctic Empetrum-dominated ecosystems are highly resilient and that their responses may be limited to the event with the strongest impact.

Recent spring warming limits near‐treeline deciduous and evergreen alpine dwarf shrub growth

AbstractWarming may lead to a cover increase of tundra shrubs and a north‐ and upward shift of treelines. The latter may be inhibited by a densification of shrub stands. However, the climatic drivers of near‐treeline shrub growth are relatively unexplored, especially that of shrub species from different functional groups growing intertwined, in competition for light and resources. We measured ring widths from two dominant dwarf shrubs species, the deciduous Betula nana and the evergreen Empetrum nigrum ssp. hermaphroditum from a near‐treeline alpine ridge in the Central Norwegian Scandes, and tested the influence of on‐site and regional climate, and changes therein, over the past 55 yr. Radial growth of B. nana was found to be negatively influenced by early summer (June–July) precipitation, possibly related to low amounts of photosynthetically active radiation and nitrogen leaching, and positively by July temperatures. That of E. hermaphroditum was positively correlated with late summer (July–August) temperatures. In recent decades, the influence of summer climate on both species’ growth has declined and been replaced by a negative influence of May temperatures. Rising spring temperatures in recent decades have likely advanced key phenology events in B. nana and E. hermaphroditum, such as budburst and flowering. This may have left the shrubs’ soft tissues vulnerable to late frost events, which in recent decades occur more frequently after the advanced start of the growing season, resulting in suppressed growth.

Short-term carbon allocation dynamics in subalpine dwarf shrubs and their responses to experimental summer drought

Carbon (C) allocation is a key determinant of plant functioning and ecosystem processes. Its dynamic responses to environmental conditions and global change are still poorly understood. This holds particularly true for dwarf shrubs, which are an important component of high mountain vegetation. We studied the short-term C allocation dynamics in two dominant dwarf shrub species, Vaccinium myrtillus and Vaccinium uliginosum, at two subalpine sites, in the Pyrenees and in the Alps, and additionally performed an experimental rain exclusion to simulate summer drought at the site in the Alps. We compared net assimilation rates (Amax), stomatal conductance (gs) and shoot water potentials (ΨS) between the two species and carried out a 13C pulse labelling experiment to trace their C allocation dynamics, both under natural conditions and in the drought experiment. Under ambient conditions, V. uliginosum showed higher Amax and gs and used recent assimilates as a respiratory substrate more slowly than V. myrtillus. C allocation dynamics in current-year shoots differed significantly between the species, showing a progressive decrease after the pulse labelling in V. uliginosum shoots but a progressive increase in V. myrtillus shoots. In the drought experiment, a significant reduction of soil moisture caused predawn ΨS below −1.2MPa in both species, which is considered close to the turgor loss point. However, the stomatal conductance and the speed of transfer of newly assimilated C to belowground organs decreased in V. uliginosum only. We found a strong coupling in C allocation dynamics between xylem and phloem tissues of the rhizome, which was maintained under drought. Although both species were largely tolerant to the drought imposed, our results indicate a higher drought sensitivity of V. uliginosum compared to V. myrtillus, with potential implications for community composition and ecosystem C cycling in a future climate.

A dominant dwarf shrub increases diversity of herbaceous plant communities in a Trans-Himalayan rangeland

Plant communities are structured by both competition and facilitation. The interplay between the two interactions can vary depending on environmental factors, nature of stress, and plant traits. However, whether positive or negative interactions dominate in regions of high biotic and abiotic stress remains unclear. We studied herbaceous plant communities associated with a dwarf shrub Caragana versicolor in semi-arid, high altitude Trans-Himalayan rangelands of Spiti, India. We surveyed 120 pairs of plots (within and outside shrub canopies) across four watersheds differing in altitude, aspect, and dominant herbivores. Herbaceous communities within shrub canopies had 25% higher species richness, but similar abundance when compared to communities outside the canopy, with the shrub edge having higher diversity than the centre of the canopy. Grasses and erect forbs showed positive associations with the shrub, while prostrate plants occurred at much lower abundance within the canopy. Rare species showed stronger positive associations with Caragana than abundant species. Experimental removal of herbaceous vegetation from within shrub canopies led to 42% increase in flowering in Caragana, indicating a cost to the host shrubs. Our study indicates a robust pattern of a dwarf shrub facilitating local community diversity across this alpine landscape, increasing diversity at the plot level, facilitating rare species, and yet incurring a cost to hosts from the presence of herbaceous plants. Given these large influences of this shrub on the vegetation of these high altitude rangelands, we suggest that the shrub microhabitat be explicitly considered in any analyses of ecosystem health in such rangelands.

The fate of nitrogen inputs in a warmer alpine treeline ecosystem: a 15N labelling study

Summary Global warming may accelerate nitrogen (N) transformations in the soil, with potentially large effects in N‐poor high‐elevation ecosystems. To gain insight into the partitioning of inorganic and organic N inputs within the plant–soil system and how warming influences these patterns, we applied a 15N label (15NH4Cl or 15N‐glycine) shortly after snowmelt during the sixth year of experimental soil warming (+4 °C) at treeline in the Swiss Alps. Seven weeks after labelling, approximately 60% of the applied label remained in the soil organic layer to 10 cm depth, whereas label recovery summed over all measured plant pools was <10% of the added label. Soil warming led to a weaker Δ15N signal in plants and no change in the amount of added label recovered in plants. This 15N dilution resulted from a greater N pool size of some plant species in warmed plots as well as enhanced availability of (unlabelled) N under warming. Temporal dynamics of foliar Δ15N in dominant dwarf shrub species suggested that these plants primarily take up N early in the season. In a subset of plots labelled with 13C‐enriched glycine (U‐13C2‐15N‐glycine), the labelled glycine was mineralized rapidly, with approximately 50% of the applied 13C respired as CO2 during the first 99 h, suggesting that effects of warmer soils on N dynamics in this treeline system are only slightly modulated by the preferences of different plant species for inorganic and organic N forms. Synthesis. Plants growing in warmer soils acquired more unlabelled, soil‐derived N in the sixth year of treatment, implying a sustained increase in N mineralization and availability in alpine treeline ecosystems with higher soil temperatures predicted for the future. Wide variation in the ability of plant species and functional groups to compete for early‐summer N inputs means that there is a feedback between plant community shifts and N dynamics under environmental change at the treeline.

Ecosystem functions as indicators for heathland responses to nitrogen fertilisation

Anthropogenic deposition of reactive nitrogen (N) has increased during the 20th century, and is considered an important driver of shifts in ecosystem functions and biodiversity loss. The objective of the present study was to identify those ecosystem functions that best evidence a target ecosystem’s sensitivity to N deposition, taking coastal heathlands as an example. We conducted a three-year field experiment in heathlands of the island Fehmarn (Baltic Sea, North Germany), which currently are subject to a background deposition of 9kgNha−1 yr−1. We experimentally applied six levels of N fertilisation (application of 0, 2.5, 5, 10, 20, and 50kgNha−1 yr−1), and quantified the growth responses of different plant species of different life forms (dwarf shrubs, graminoids, bryophytes, lichens) as well as shifts in the C:N ratios of plant tissue and humus horizons. For an applicability of the experimental findings (in terms of heathland management and critical load assessment) fertilisation effects on response variables were visualised by calculating the treatment ‘effect sizes’. The current year’s shoot increment of the dominant dwarf shrub Calluna vulgaris proved to be the most sensitive indicator to N fertilisation. Shoot increment significantly responded to additions of ≥ 5kgNha−1 yr−1 already in the first year, whereas flower formation of Calluna vulgaris increased only in the high-N treatments. Similarly, tissue C:N ratios of vascular plants (Calluna vulgaris and the graminoids Carex arenaria and Festuca ovina agg.) only decreased in the highest N treatments (50 and 20kgNha−1 yr−1, respectively). In contrast, tissue C:N ratios of cryptogams responded more quickly and sensitively than vascular plants. For example, Cladonia spp. tissue C:N ratios responded to N additions ≥ 5kgNha−1 yr−1 in the second study year. After three years we observed an increase in cover of graminoids and a corresponding decrease of cryptogams at N fertilisation rates of ≥ 10kgNha−1 yr−1. Soil C:N ratios proved to be an inappropriate indicator for N fertilisation at least within our three-year study period. Although current critical N loads for heathlands (10−20kgNha−1 yr−1) were confirmed in our experiment, the immediate and highly sensitive response of the current year’s shoots of Calluna vulgaris suggests that at least some ecosystem functions (e.g. dwarf shrub growth) also might respond to low (i.e.<10kgNha−1 yr−1) but chronic inputs of N.

Synchronous flowering despite differences in snowmelt timing among habitats of Empetrum hermaphroditum

The topography within arctic-alpine landscapes is very heterogeneous, resulting in diverse snow distribution patterns, with different snowmelt timing in spring. This may influence the phenological development of arctic and alpine plant species and asynchronous flowering may promote adaptation of plants to their local environments.We studied how flowering phenology of the dominant dwarf shrub Empetrum hermaphroditum varied among three habitats (exposed ridges, sheltered depressions and birch forest) differing in winter snow depth and thus snowmelt timing in spring, and whether the observed patterns were consistent across three different study areas.Despite significant differences in snowmelt timing between habitats, full flowering of E. hermaphroditum was nearly synchronous between the habitats, and implies a high flowering overlap. Our data show that exposed ridges, which had a long lag phase between snowmelt and flowering, experienced different temperature and light conditions than the two late melting habitats between snowmelt and flowering.Our study demonstrates that small scale variation seems matter less to flowering of Empetrum than interannual differences in snowmelt timing.

Snow cover consistently affects growth and reproduction of Empetrum hermaphroditum across latitudinal and local climatic gradients

Arctic ecosystems face strong changes in snow conditions due to global warming. In contrast to habitat specialists, species occupying a wide range of microhabitats under different snow conditions may better cope with such changes. We studied how growth and reproduction of the dominant dwarf shrub Empetrum hermaphroditum varied among three habitat types differing in winter snow depth and summer irradiation, and whether the observed patterns were consistent along a local climatic gradient (sub-continental vs. sub-oceanic climates) and along a latitudinal gradient (northern Sweden vs. central Norway). Habitat type explained most of the variation in growth and reproduction. Shoots from shallow snow cover and high summer irradiation habitats had higher numbers of flowers and fruits, lower ramet heights, shorter shoot segments, lower numbers of lateral shoots and total biomass but higher leaf density and higher relative leaf allocation than shoots from habitats with higher snow depth and lower summer irradiation. In addition, biomass, leaf allocation and leaf life expectancy were strongly affected by latitude, whereas local climate had strong effects on seed number and seed mass. Empetrum showed high phenotypic trait variation, with a consistent match between local habitat conditions and its growth and reproduction. Although study areas varied strongly with respect to latitude and local climatic conditions, response patterns of growth and reproduction to habitats with different environmental conditions were consistent. Large elasticity of traits suggests that Empetrum may have the potential to cope with changing snow conditions expected in the course of climate change.

Impact of early and late winter icing events on sub‐arctic dwarf shrubs

Polar regions are predicted to undergo large increases in winter temperature and an increased frequency of freeze-thaw cycles, which can cause ice layers in the snow pack and ice encasement of vegetation. Early or late winter timing of ice encasement could, however, modify the extent of damage caused to plants. To determine impacts of the date of ice encasement, a novel field experiment was established in sub-arctic Sweden, with icing events simulated in January and March 2008 and 2009. In the subsequent summers, reproduction, phenology, growth and mortality, as well as physiological indicators of leaf damage were measured in the three dominant dwarf shrubs: Vaccinium uliginosum, Vaccinium vitis-idaea and Empetrum nigrum. It was hypothesised that January icing would be more damaging compared to March icing due to the longer duration of ice encasement. Following 2 years of icing, E. nigrum berry production was 83% lower in January-iced plots compared to controls, and V. vitis-idaea electrolyte leakage was increased by 69%. Conversely, electrolyte leakage of E. nigrum was 25% lower and leaf emergence of V. vitis-idaea commenced 11 days earlier in March-iced plots compared to control plots in 2009. There was no effect of icing on any of the other parameters measured, indicating that overall these study species have moderate to high tolerance to ice encasement. Even much longer exposure under the January icing treatment does not clearly increase damage.

Impacts of winter icing events on the growth, phenology and physiology of sub‐arctic dwarf shrubs

The Arctic is experiencing the greatest climate change in winter, including increases in freeze-thaw cycles that can result in ice encasement of vegetation. Ice encasement can expose plants to hypoxia and greater temperature extremes, but currently the impacts of icing on plants in the field remain little understood. With this in mind, a unique field manipulation experiment was established in heathland in northern Sweden with ice encasement simulated in early March 2008, 2009 and 2010 until natural thaw each spring. In the following summers we assessed the impacts on flowering, bud phenology, shoot growth and mortality and leaf damage (measured by chlorophyll fluorescence and electrolyte leakage) of the three dominant dwarf shrub species Empetrum nigrum, Vaccinium vitis-idaea (both evergreen) and Vaccinium myrtillus (deciduous). Two consecutive winters of icing decreased V. vitis-idaea flowering by 57%, while flowering of V. myrtillus and E. nigrum remained unaffected. Vaccinium myrtillus showed earlier budburst but shoot growth for all species was unchanged. Shoot mortality of V. myrtillus and V. vitis-idaea increased after the first year (by 70 and 165%, respectively) and again for V. myrtillus following the third year (by 67%), while E. nigrum shoot mortality remained unaffected, as were chlorophyll fluorescence and electrolyte leakage in all species. Overall, the sub-arctic heathland was relatively tolerant to icing, but the considerable shoot mortality of V. myrtillus contrasting with the general tolerance of E. nigrum suggests plant community structure in the longer term could change if winters continue to see a greater frequency of icing events.

Volume–biomass functions reveal the effect of browsing on three Moroccan dwarf shrubs

We studied the effects of browsing on the plant architecture and volume-biomass relationships of three dominant dwarf shrubs – Artemisia herba-alba, A. mesatlantica and Teucrium mideltense – in a sagebrush steppe in the Central High Atlas Mountains, southern Morocco. For this purpose, we developed power-law volume-biomass functions based on nonlinear regressions for each of these species, under both browsed and unbrowsed conditions. These functions were then applied to individual-based annual monitoring data from inside and outside a browsing exclosure to calculate standing biomass for each of the years from 2004 to 2009. The biomass of the three species was well predicted by the allometric functions, and different functions for the browsed and unbrowsed conditions reflected changes in plant architecture. Browsing had a significant negative impact on biomass for A. herba-alba but not for A. mesatlantica, whereas its effects on T. mideltense were inconsistent between years. The fact that the latter two species hardly benefited from browsing exclusion might be because of increased competition from the more dominant A. herba-alba. During the study period, the standing biomass increased whether or not there was browsing, which might be because of the recovery of the shrubs after a preceding severe drought. Further studies are needed in order to investigate the generality of the findings.

Vegetation recovery following extreme winter warming events in the sub-Arctic estimated using NDVI from remote sensing and handheld passive proximal sensors

Extreme winter warming events in the sub-Arctic have caused considerable vegetation damage due to rapid changes in temperature and loss of snow cover. The frequency of extreme weather is expected to increase due to climate change thereby increasing the potential for recurring vegetation damage in Arctic regions. Here we present data on vegetation recovery from one such natural event and multiple experimental simulations in the sub-Arctic using remote sensing, handheld passive proximal sensors and ground surveys.Normalized difference vegetation index (NDVI) recovered fast (2 years), from the 26% decline following one natural extreme winter warming event. Recovery was associated with declines in dead Empetrum nigrum (dominant dwarf shrub) from ground surveys. However, E. nigrum healthy leaf NDVI was also reduced (16%) following this winter warming event in experimental plots (both control and treatments), suggesting that non-obvious plant damage (i.e., physiological stress) had occurred in addition to the dead E. nigrum shoots that was considered responsible for the regional 26% NDVI decline. Plot and leaf level NDVI provided useful additional information that could not be obtained from vegetation surveys and regional remote sensing (MODIS) alone.The major damage of an extreme winter warming event appears to be relatively transitory. However, potential knock-on effects on higher trophic levels (e.g., rodents, reindeer, and bear) could be unpredictable and large. Repeated warming events year after year, which can be expected under winter climate warming, could result in damage that may take much longer to recover.