Boreal Vegetation Research Articles

Can EVI-derived land-surface phenology be used as a surrogate for phenology of canopy photosynthesis?

Canopy phenology plays a prominent role in determining the timing and magnitude of carbon uptake by many ecosystems. The Moderate Resolution Imaging Spectroradiometer (MODIS) Global Land Cover Dynamics product developed from the enhanced vegetation index (EVI) provides broad spatial and temporal coverage of land-surface phenology (LSP), and may serve as a useful proxy for the phenology of canopy photosynthesis. Here, we compare the MODIS growing season start and end dates (SOS and EOS) with the seasonal phenology of canopy photosynthesis estimated using the eddy covariance approach. Using 153 site-years obtained from the Ameriflux database, we calculated the SOS and EOS of gross primary production (GPP) and canopy photosynthesis capacity (CPC) for seven different boreal and temperate vegetation types. CPC is GPP at maximum radiation, estimated by fitting half-hourly GPP and radiation to a rectangular hyperbolic function. We found large mean absolute differences of up to 53 days, depending on vegetation type, between the phenology of canopy development and photosynthesis, indicating that remotely sensed LSP is not a robust surrogate of seasonal changes in GPP, particularly for evergreen needleleaf forests. This limited correspondence of ecosystem carbon uptake with the MODIS LSP product points to the need for improved remotely sensed proxies of GPP phenology.

Paleoenvironmental Studies in Southwestern Yukon

The St. Elias Mountain region has occupied an important place in the study of the Quaternary because it presents a relatively accessible non-polar icefield and an array of environments from tundra to boreal forest. Paleoenvironmental studies in southwestern Yukon have documented the broad-scale climatic changes of the past 20 000 years, although few studies exist with well-dated sequences at high temporal resolution. Picea glauca arrived across the entire region around 10 000 years ago; however, the details regarding its migration pathways are not well known. Available records indicate few major changes in the composition of the boreal forest vegetation since that time. A slightly more intense fire regime in the early to mid Holocene has been suggested, but this conclusion is based on only a few studies. Variations in the tree line during the Holocene have been examined, but these studies also lack details. There is no evidence for more extensive grasslands in the area during the Holocene. Paleolimnological studies indicate that changes in populations of aquatic organisms have occurred in response to either Holocene climates or watershed variability.

Pyrogenic carbon stocks and storage mechanisms in podzolic soils of fire-affected Quebec black spruce forests

Wildfire, a recurrent disturbance in the boreal, converts part of the forest floor into pyrogenic carbon (PyC). The latter is an important component of the global soil carbon pool, yet knowledge of its stocks and storage mechanisms in these boreal ecosystems is scarce. Podzolization processes, which are frequent under boreal vegetation, result in distinctive patterns of soil organic carbon (SOC) accumulation in the mineral subsoil; how this may affect PyC storage remains largely unknown. The objectives of this study were to estimate SOC and PyC stocks in podzolic soils from fire-affected black spruce forests, and to explore the storage mechanisms taking place in their mineral horizons. We also compared PyC stocks in mineral soils to forest floor stocks. Samples were collected from 23 soil profiles under black spruce forests located throughout the province of Quebec. To further explore the relationship between podzolization and PyC storage mechanisms, we measured SOC and PyC contents in size and density fractions of a subset of 11 podzolic B horizons. Total SOC stocks in the mineral horizons and forest floors were comparable. Pyrogenic carbon stocks in the mineral soils, estimated by a H2O2/dilute HNO3 digestion, averaged 0.2(±0.1)kgCm−2. This was significantly lower than forest floor stocks, which ranged from 0.2 to 1.2kgCm−2. Consequently, PyC constituted a smaller fraction of total SOC (2–15%) in mineral soils than in forest floors, where it was as high as 68% (±5) in some horizons. In the mineral soils, SOC and PyC concentrations were strongly correlated. While some PyC was found in unprotected particulate organic matter (POM), the rest was associated with organo-mineral and organo-metallic complexes in the micro-aggregate protected POM and fine fraction. Patterns of PyC accumulation in mineral soils were similar to SOC, and the greater PyC stocks were found in podzolic B horizons.

Large spruce seedling responses to the interacting effects of vegetation zone, competing vegetation dominance and year of mechanical release

It is necessary to evaluate how large seedling stock, used as an alternative to chemical herbicide for vegetation management, interacts with the timing of mechanical release (MR) and if use of such stock offers a broader window of intervention for release than conventional stock. Such a context is present in Quebec (Canada), where chemical herbicides were banned from use on public lands in 2001. We thus evaluated the impact of delaying MR on the performance of large spruce seedlings established in a gradient of vegetation zones and competition environments. Fourteen experiments were conducted in Picea glauca or P. mariana plantations in the temperate hardwood (TH), temperate mixedwood or boreal mixedwood vegetation zones. On each site, we established a completely randomized block design with 5 –8 replicates, each divided into four plots: (1) control; (2) MR applied the year during which light availability to the planted seedlings averaged 60 per cent of full sunlight (EARLY); (3) MR at EARLY + 1 year (LATE1); and (4) MR at EARLY + 2 years (LATE2). Vegetation data collected in controls 8 years after MR was submitted to a correspondence analysis to group the sites according to their competing species dominance. Seedling responses to the timing of MR, 5 –8 years after treatment, varied across competing vegetation dominance, vegetation zone or a combination of both. On sites where intolerant hardwoods were dominant, postponing MR 1 year after light availability had reached 60 per cent of full sunlight had a positive effect on seedling dimensions, especially in the TH zone. However, the LATE2 treatment resulted in significant stem volume losses on these sites. Whereas treatment effects were limited on ericaceous dominated sites, MR promoted seedling growth on sites dominated by shrub/herbaceous species, with no difference between EARLY, LATE1 and LATE2.

Real and simulated waveform-recording LiDAR data in juvenile boreal forest vegetation

Airborne small-footprint LiDAR is replacing field measurements in regional-level forest inventories, but auxiliary fieldwork is still required for the optimal management of young stands. Waveform (WF) -recording sensors can provide a more detailed description of the vegetation than discrete return (DR) systems through accurate characterization of the backscattered signal. Furthermore, knowing the signal shape facilitates comparisons between real data and those obtained with simulation tools. We performed calibration and quantitative validation of a Monte Carlo ray tracing (MCRT) -based LiDAR simulator against real data, and used simulations and real data to study small-footprint WF-recording LiDAR for the classification of juvenile boreal forest vegetation. The simulations were based on geometric-optical models of three species: birch (Betula pendula Roth), raspberry (Rubus idaeus L.), and fireweed (Chamerion angustifolium (L.) Holub). Simulated WF features were in good agreement with the real data (differences of −19% to 11% in radiometric features, −0.23m to 0.45m in mean height), and relative interspecies differences were preserved. We used simulated data to study the effects of sensor parameters on the classification among the three species. An increase in footprint size improved the classification accuracy up to 0.30–0.36m in diameter, while the emitted pulse width and the WF sampling rate showed minor effects. Finally, we used real data to classify four silviculturally important vegetation functional groups (conifers, broad-leaved trees, low vegetation (green), low vegetation (barren)+abiotic material). Classification accuracies of 68.1–86.7% (kappa 0.50–0.80) showed slight improvement compared with existing studies on DR LiDAR and passive optical data. The results of simulator validation serve as a basis for the future use of simulation models, e.g. in LiDAR survey planning or in the simulation of synthetic training data, while the other findings clarify the potential of small-footprint WF data for characterizing vegetation in intensively managed forest stands at seedling and sapling stages in the boreal region.

Can thinning alleviate negative effects of fertilization on boreal forest floor vegetation?

Society’s increased interest in renewable energy and materials put pressure on forest biomass production. Intensive fertilization of young Norway spruce (Picea abies) forest has a considerable potential to increase the production of tree biomass, but there are concerns about negative side-effects on forest ecosystem structure and function. Fertilization of young forest has a strong negative impact on light availability below the tree canopy and reduces the abundance of the forest floor vegetation. The silvicultural practice of thinning has been shown to affect composition and diversity of forest floor vegetation, and it has been proposed, but rarely tested, that the effects of fertilization are interdependent on the type of thinning performed. Here we present responses on the forest floor vegetation following 25years of fertilization and eighth years after thinning (removing 30% or 60% of the tree basal area) in a Norway spruce forest in northern Sweden. Fertilization without thinning led to a considerable reduction in abundance of most forest floor plants. It did not affect species richness but resulted in an increased evenness. Thinning reduced the fertilization effects so that the total abundance of the vegetation was comparable to the unfertilized control plots. A considerable change in species composition had, however, taken place. Thinning favored early-successional species and pteridophytes on the account of dwarf-shrubs. Thinning also increased species richness and functional richness, while none, or negative effects were seen on evenness and functional evenness, respectively. A comparison with data from the National Forest Inventory revealed that the type of vegetation generated by fertilization, without or in combination with thinning, is a type of vegetation very uncommon in Swedish boreal forests. First, we conclude that the effects of fertilization on forest floor vegetation in young stands of Norway spruce are largely dependent on thinning regime. Secondly, fertilization will, independently of thinning, lead to considerable changes in the vegetation, including a functional shift from dwarf-shrubs with ericoid mycorrhiza to ferns and grasses with arbuscular mycorrhiza, resulting in a functional type of vegetation that is rare in this part of the boreal forest biome. Finally, in contrast to what previously has been suggested for unfertilized forests, thinning of fertilized forests may not promote late-successional species.

Assessing global biome exposure to climate change through the Holocene–Anthropocene transition

AbstractAimTo analyse global patterns of climate during the mid‐Holocene and conduct comparisons with pre‐industrial and projected future climates. In particular, to assess the exposure of terrestrial biomes and ecoregions to climate‐related risks during the Holocene–Anthropocene transition starting at the pre‐industrial period.LocationTerrestrial ecosystems of the Earth.MethodsWe calculated long‐term climate differences (anomalies) between the mid‐Holocene (6 ka cal bp, mH), pre‐industrial conditions and projections for 2100 (middle‐strength A1B scenario) using six global circulation models available for all periods. Climate differences were synthesized with multivariate statistics and average principal component loadings of temperature and precipitation differences (an estimate of climate‐related risks) were calculated on 14 biomes and 766 ecoregions.ResultsOur results suggest that most of the Earth's biomes will probably undergo changes beyond the mH recorded levels of community turnover and range shifts because the magnitude of climate anomalies expected in the future are greater than observed during the mH. A few biomes, like the remnants of North American and Euro‐Asian prairies, may experience only slightly greater degrees of climate change in the future as compared with the mH. In addition to recent studies that have identified equatorial regions as the most sensitive to future climate change, we find that boreal forest, tundra and vegetation of the Equatorial Andes could be at greatest risk, since these regions will be exposed to future climates that are well outside natural climate variation during the Holocene.ConclusionsThe Holocene–Anthropocene climate transition, even for a middle‐strength future climate change scenario, appears to be of greater magnitude and different from that between the mH and the pre‐industrial period. As a consequence, community‐ and biome‐level changes due to of expected climate change may be different in the future from those observed during the mH.

REAL AND SIMULATED WAVEFORM RECORDING LIDAR DATA IN BOREAL JUVENILE FOREST VEGETATION

Abstract. Airborne small-footprint LiDAR is replacing field measurements in regional-level forest inventories, but auxiliary field work is still required for the optimal management of young stands. Waveform (WF) recording sensors can provide a more detailed description of the vegetation compared to discrete return (DR) systems. Furthermore, knowing the shape of the signal facilitates comparisons between real data and those obtained with simulation tools. We performed a quantitative validation of a Monte Carlo ray tracing (MCRT) -based LiDAR simulator against real data and used simulations and empirical data to study the WF recording LiDAR for the classification of boreal juvenile forest vegetation. Geometric-optical models of three common species were used as input for the MCRT model. Simulated radiometric and geometric WF features were in good agreement with the real data, and interspecies differences were preserved. We used the simulator to study the effects of sensor parameters on species classification performance. An increase in footprint size improved the classification accuracy up to a certain footprint size, while the emitted pulse width and the WF sampling rate had minor effects. Analyses on empirical data showed small improvement in performance compared to existing studies, when classifying seedling stand vegetation to four operational classes. The results on simulator validation serve as a basis for the future use of simulation models e.g. in LiDAR survey planning or in the simulation of synthetic training data, while the empirical findings clarify the potential of WF LiDAR data in the inventory chain for the operational forest management planning in Finland.

Outbreaks by canopy-feeding geometrid moth cause state-dependent shifts in understorey plant communities.

The increased spread of insect outbreaks is among the most severe impacts of climate warming predicted for northern boreal forest ecosystems. Compound disturbances by insect herbivores can cause sharp transitions between vegetation states with implications for ecosystem productivity and climate feedbacks. By analysing vegetation plots prior to and immediately after a severe and widespread outbreak by geometrid moths in the birch forest-tundra ecotone, we document a shift in forest understorey community composition in response to the moth outbreak. Prior to the moth outbreak, the plots divided into two oligotrophic and one eutrophic plant community. The moth outbreak caused a vegetation state shift in the two oligotrophic communities, but only minor changes in the eutrophic community. In the spatially most widespread communities, oligotrophic dwarf shrub birch forest, dominance by the allelopathic dwarf shrub Empetrum nigrum ssp. hermaphroditum, was effectively broken and replaced by a community dominated by the graminoid Avenella flexuosa, in a manner qualitatively similar to the effect of wild fires in E. nigrum communities in coniferous boreal forest further south. As dominance by E. nigrum is associated with retrogressive succession the observed vegetation state shift has widespread implications for ecosystem productivity on a regional scale. Our findings reveal that the impact of moth outbreaks on the northern boreal birch forest system is highly initial-state dependent, and that the widespread oligotrophic communities have a low resistance to such disturbances. This provides a case for the notion that climate impacts on arctic and northern boreal vegetation may take place most abruptly when conveyed by changed dynamics of irruptive herbivores.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-013-2648-1) contains supplementary material, which is available to authorized users.

Does background nitrogen deposition affect the response of boreal vegetation to fertilization?

Forest floor vegetation is an important component of forest biodiversity, and numerous studies have shown that N input alters the vegetation. In some cases, however, the effects of experimental N addition have been small or absent. Two alternative hypotheses have been suggested: (a) competition from the tree layer confounds the response to N, or (b) N response in areas with high background deposition is limited by N saturation. Neither of these hypotheses has so far been explicitly tested. Here, we compile data on forest floor vegetation from N addition experiments, in which the forest had been clear-cut, along an N deposition gradient ranging from 4 to 16 kg ha(-1) year(-1) in Sweden. We analyzed the effects of N addition and its interaction with N deposition on common species and thereby tested the second hypothesis in an environment without the confounding effects of the tree layer. The results show that the effects of the experimental N addition are significantly influenced by background N deposition: the N addition effects are smaller in areas with high N deposition than in areas with low N deposition, despite the fact that the highest N deposition in this study can be considered moderate from an international perspective. The results are important when assessing the reliability of results from N addition experiments on forest floor vegetation in areas with moderate to high background N deposition. We conclude that the interacting effects of N addition and N deposition need to be included when assessing long-term N sensitivity of plant communities.

Tracing the origin of Arctic driftwood

Arctic environments, where surface temperatures increase and sea ice cover and permafrost depth decrease, are very sensitive to even slight climatic variations. Placing recent environmental change of the high‐northern latitudes in a long‐term context is, however, complicated by too short meteorological observations and too few proxy records. Driftwood may represent a unique cross‐disciplinary archive at the interface of marine and terrestrial processes. Here, we introduce 1445 driftwood remains from coastal East Greenland and Svalbard. Macroscopy and microscopy were applied for wood anatomical classification; a multi‐species subset was used for detecting fungi; and information on boreal vegetation patterns, circumpolar river systems, and ocean current dynamics was reviewed and evaluated. Four conifer (Pinus,Larix,Picea, andAbies) and three deciduous (Populus,Salix, andBetula) genera were differentiated. Species‐specific identification also separatedPinus sylvestrisandPinus sibirica, which account for ~40% of all driftwood and predominantly originate from western and central Siberia. Larch and spruce from Siberia or North America represents ~26% and ~18% of all materials, respectively. Fungal colonization caused different levels of driftwood staining and/or decay. Our results demonstrate the importance of combining wood anatomical knowledge with insight on boreal forest composition for successfully tracing the origin of Arctic driftwood. To ultimately reconstruct spatiotemporal variations in ocean currents, and to better quantify postglacial uplift rates, we recommend consideration of dendrochronologically dated material from many more circumpolar sites.

Reactivity of hydroxyproline-rich glycoproteins and their potential as biochemical tracers of plant-derived nitrogen

The amino acid hydroxyproline (Hyp) has potential for tracing plant N because Hyp-rich glycoproteins (HRGPs), structural proteins in the cell walls of plants, are its only major biochemical source in soil. The reactivity of Hyp in tissue from three vascular plants (black mangrove leaves, smooth cordgrass and cypress needles) was investigated in a 4yr decomposition study to test its suitability as a tracer of plant N. The reactivity was similar to that of bulk plant N in cordgrass and cypress needles, but Hyp was more resistant to decomposition in mangrove leaves. This was likely due to increased cross liking between peptides in HRGPs from dicotyledons vs. other plants. These cross links involve stable diphenyl ether and biphenyl linkages that may protect the HRGP from degradation. The results suggest that Hyp can provide a quantitative estimate of the contribution of plant residues to the detrital N pool in systems dominated by gymnosperm and monocotyledon inputs. A mixing model using litter input representative of boreal forest vegetation demonstrated the potential of Hyp for tracing plant N in soil.

Растительность севера Дальнего Востока России в картографических моделях

Distribution, configuration of vegetation zones and distribution of altitudinal belts on the North of the Russian Far East are characterized by their peculiarities caused by marginal position of the region on Eurasian continent, surrounding seas influence, altitude of the place. Areas types of vegetation complexes are established on the base of cartometric analysis of data-base of digital geobotanic large-scale map. The main regularities of differentiation of vegetation cover are revealed that are confirmed earlier known data. Types of arctic vegetation complexes are distributed through the whole territory of the region. Correlation between boreal and arctic vegetation complexes are characterized by zonal peculiarities. North-east boundary of boreal vegetation types is the important botanic-geographic frontier. To the south of this frontier wide zone of ecotone is noticed. In this zone forest vegetation types and tundra vegetation existed side by side on the placors habitats. The most distributed types are mountain vegetation type complexes with dominance of stone deserts, tundra siberian dwarf-pine. Vertical differentiation of mountain vegetation territories (taking in account zonalty) is reflected in subsequent change altitudinal belts where vegetation types complexes with dominance lichens mountain stone deserts, mountain tundra, siberian dwarf-pine (Pinus pumila), mountain open forests and larch (Larix cajanderi) and birch (Betula ermanii) forests are represented. Degree of revealing of vertical belts depends not only zonal conditions but also the altitude of the place above sea level, landscape peculiarities. Therefore separate belts, for example, mountain tundra, siberian dwarf-pine can be represented fragmentally. The stripe of ecotone usually can be noticed between alpine and subalpine belts. Vertical vegetation belts are evidently connected with horizontal zones of vegetation cover. In tundra zone 2 altitudinal belts can be noticed – alpine that is represented by lichens stone deserts, and subalpine that is formed mostly by mountain tundra. Mountain siberian dwarf-pine play big role in forest zone in formation of subalpine belt altogether with mountain tundra. Lower on the slopes prostrate shrubs are changed by forest belt (subzone of Larch open forests and forests, subzone of birch open forests and forests) or exist side by side with zonal prostrate shrubs and subarctic tundra (subzone of prostrate shrubs). Zonal vegetation complexes types (inhabit on placors and close to them habitats – plain low watershed areas, not steep mountain slopes, valleys between mountains, terraces near sea shore) are represented by arctic and subarctic tundra, siberian dwarf-pine (Pinus pumila), open forests and Larch (Larix cajanderi) and Birch (Betula ermanii) forests. Mires are dominated among zonal-interzonal vegetation type complexes. Valley forests, shrubs, tundra are distributed quite widely. Transitional structures, for example tundra-bogs are referred to this group of vegetation complexes. Vegetation that is transformed by strong stress factors (mostly natural and anthropogenic) is represented communities of plants formed under influence birds colonies, reindeer grazing, fire places, after technogenic disturbance as well as agricultural phytocoenosis.

GEM-AQ/EC, an on-line global multi-scale chemical weather modelling system: model development and evaluation of global aerosol climatology

Abstract. A global air quality modeling system GEM-AQ/EC was developed by implementing tropospheric chemistry and aerosol processes on-line into the Global Environmental Multiscale weather prediction model – GEM. Due to the multi-scale features of the GEM, the integrated model, GEM-AQ/EC, is able to investigate chemical weather at scales from global to urban domains. The current chemical mechanism is comprised of 50 gas-phase species, 116 chemical and 19 photolysis reactions, and is complemented by a sectional aerosol module CAM (The Canadian Aerosol Module) with 5 aerosols types: sulphate, black carbon, organic carbon, sea-salt and soil dust. Monthly emission inventories of black carbon and organic carbon from boreal and temperate vegetation fires were assembled using the most reliable areas burned datasets by countries, from statistical databases and derived from remote sensing products of 1995–2004. The model was run for ten years from from 1995–2004 with re-analyzed meteorology on a global uniform 1° × 1° horizontal resolution domain and 28 hybrid levels extending up to 10 hPa. The simulating results were compared with various observations including surface network around the globe and satellite data. Regional features of global aerosols are reasonably captured including emission, surface concentrations and aerosol optical depth. For various types of aerosols, satisfactory correlations were achieved between modeled and observed with some degree of systematic bias possibly due to large uncertainties in the emissions used in this study. A global distribution of natural aerosol contributions to the total aerosols is obtained and compared with observations.

Vegetation responses to long‐term alkaline cement dust pollution in Pinus sylvestris‐dominated boreal forests – niche breadth along the soil pH gradient

AbstractQuestionsHow resilient is boreal forest vegetation growing on acidic podzols to the environmental change caused by alkaline kiln dust pollution? How adaptive is the vegetation, when species pool and time for dispersal do not limit? How constant is the species niche breadth along the soil pH gradient?LocationRegion of 30 km around the Kunda cement plant, northern Estonia (59°30′ N, 26°32′ E), which has been continuously polluted last 140 years.MethodsWe sampled 20 forest stands on sandy gleyic podzols at various distances from the pollution source, leeward and windward of prevailing winds. Data processing: principal components analysis for gradient generalization, indicator species analysis for grouping species along the pollution gradient and generalized linear model analyses to estimate species reaction to pollution, considering covariates.ResultsThe impact of alkaline dust accumulated over a century persisted despite resolute reductions of pollution. Forest soil conditions changed 10 km leeward and 5 km windward from the source: the litter pH level changed from 3.6 to 4.5 in unpolluted forests to 7.1–7.4 in the heavily polluted forests, and soil Ca content increased ten‐fold. Soil alkalization has induced a remarkable succession from typical boreal vegetation toward vegetation of boreo‐nemoral or calcareous habitats. We detected a linear increase of species richness from habitats on acidic soils (unpolluted) to newly formed alkaline soils (polluted habitats), reflecting the species pool composition and size, which is known to be large for calcicolous species. The establishment of several endangered calcicolous species shows the lack of dispersal limitation and points on their narrow soil pH niche. The niche breadth of species along the pH gradient varied among species, but only a few species appeared to be pH generalists.ConclusionsSpecies ranking along the pH and/or Ca gradients indicates (1) the existence of different ecological guilds in terms of ecological niche use, and (2) the formation of a new community is dictated by the tolerance level of each species. This supports the individualistic community assembly rule suggested by Gleason. We find that such polluted regions with disturbed communities have high scientific value as long‐term ecological experiments, but this might lead to conflict between the peculiar biodiversity complex and human well‐being.

Satellite‐based evidence for shrub and graminoid tundra expansion in northern Quebec from 1986 to 2010

AbstractGlobal vegetation models predict rapid poleward migration of tundra and boreal forest vegetation in response to climate warming. Local plot and air‐photo studies have documented recent changes in high‐latitude vegetation composition and structure, consistent with warming trends. To bridge these two scales of inference, we analyzed a 24‐year (1986–2010) Landsat time series in a latitudinal transect across the boreal forest‐tundra biome boundary in northern Quebec province, Canada. This region has experienced rapid warming during both winter and summer months during the last 40 years. Using a per‐pixel (30 m) trend analysis, 30% of the observable (cloud‐free) land area experienced a significant (P < 0.05) positive trend in the Normalized Difference Vegetation Index (NDVI). However, greening trends were not evenly split among cover types. Low shrub and graminoid tundra contributed preferentially to the greening trend, while forested areas were less likely to show significant trends in NDVI. These trends reflect increasing leaf area, rather than an increase in growing season length, because Landsat data were restricted to peak‐summer conditions. The average NDVI trend (0.007 yr−1) corresponds to a leaf‐area index (LAI) increase of ~0.6 based on the regional relationship between LAI and NDVI from the Moderate Resolution Spectroradiometer. Across the entire transect, the area‐averaged LAI increase was ~0.2 during 1986–2010. A higher area‐averaged LAI change (~0.3) within the shrub‐tundra portion of the transect represents a 20–60% relative increase in LAI during the last two decades. Our Landsat‐based analysis subdivides the overall high‐latitude greening trend into changes in peak‐summer greenness by cover type. Different responses within and among shrub, graminoid, and tree‐dominated cover types in this study indicate important fine‐scale heterogeneity in vegetation growth. Although our findings are consistent with community shifts in low‐biomass vegetation types over multi‐decadal time scales, the response in tundra and forest ecosystems to recent warming was not uniform.

Boreal rich fen vegetation formerly used for haymaking

In the present study, we describe the variation in rich fen (brown moss‐dominated) vegetation of boreal uplands in Norway, based on studies in two nature reserves representing an oceanic and a more continental area. The vegetation description included 134 sample plots and 200 taxa, using TWINSPAN classification and DCA ordination. The main aims were to describe the rich fen vegetation used for traditional haymaking, to find important ecological gradients and to compare the fen vegetation to the main European classification systems. We classified the fen vegetation into six plant communities. Rich (including extremely rich) fen vegetation of lawns and open margins were most common, representing the alliances Caricion atrofuscae, including alpine/continental species like Equisetum variegatum and Pedicularis oederi and Schoenion ferruginei (Caricion davallianae), including lowland/oceanic species like Drosera longifolia and Narthecium ossifragum. A majority of the constant species were in common for the two alliances, e.g. Thalictrum alpinum, Trichophorum cespitosum, Campylium stellatum and Gymnocolea borealis. The lawn communities included 30–38 species per plot (12.5 m2). We classified the flat fens with carpet communities dominated by Scorpidium cossonii and S. scorpioides to the alliances Stygio–Caricion limosae and Caricion lasiocarpae. The carpets contained ca 30 species per plot. Shrub‐dominated fen margin represents Sphagno–Tomentypnion, with the highest species number, more than 50 species per plot, including Molinia caerulea as a constant and abundant species, and a large number of herbs as constants. The plots of the margin community were in an overgrowing process, invaded by shrubs and wet grassland species. The peak in floristic diversity in abandoned margin communities fits well with both the humped‐back model of species richness and the intermediate disturbance hypothesis.

Growth of aspen and white spruce on naturally saline sites in northern Alberta: Implications for development of boreal forest vegetation on reclaimed saline soils

Lilles, E. B., Purdy, B. G., Macdonald, S. E. and Chang, S. X. 2012. Growth of aspen and white spruce on naturally saline sites in northern Alberta: Implications for development of boreal forest vegetation on reclaimed saline soils. Can. J. Soil Sci. 92: 213-227. We examined height and basal area growth over time for trembling aspen and white spruce in plots along a salinity gradient at six naturally saline sites in northern Alberta, as a benchmark for forest productivity on reclaimed saline sites. We measured root distributions and analyzed foliage for ions, nutrients and carbon and nitrogen stable isotope ratios. Both species grew on soil conditions previously considered unsuitable for forest vegetation [pH>8.5; electrical conductivity>10 dS m-1, sodium adsorption ratio>13 at depth (50-100 cm)] yet there was little evidence of nutritional toxicities or deficiencies. Aspen basal area growth decreased 50% as salinity increased, but aspen was commercially productive (site index=22) on soils with electrical conductivity of 7.8 dS m-1 at 50-100 cm depth. Growth of white spruce seemed to be unaffected by salinity level differences, but 78% of white spruce site indexes were less than 13 and would be considered non-productive. Both species showed growth declines over time, compared with non-saline reference growth curves, and rooted primarily in the forest floor and top 20 cm of soil. This suggests that rooting limitations may constrain longer-term productivity of forests established on sites with salinity at depth.

Growth of aspen and white spruce on naturally saline sites in northern Alberta: Implications for development of boreal forest vegetation on reclaimed saline soils

Lilles, E. B., Purdy, B. G., Macdonald, S. E. and Chang, S. X. 2012. Growth of aspen and white spruce on naturally saline sites in northern Alberta: Implications for development of boreal forest vegetation on reclaimed saline soils. Can. J. Soil Sci. 92: 213–227. We examined height and basal area growth over time for trembling aspen and white spruce in plots along a salinity gradient at six naturally saline sites in northern Alberta, as a benchmark for forest productivity on reclaimed saline sites. We measured root distributions and analyzed foliage for ions, nutrients and carbon and nitrogen stable isotope ratios. Both species grew on soil conditions previously considered unsuitable for forest vegetation [pH>8.5; electrical conductivity>10 dS m−1, sodium adsorption ratio>13 at depth (50–100 cm)] yet there was little evidence of nutritional toxicities or deficiencies. Aspen basal area growth decreased 50% as salinity increased, but aspen was commercially productive (site index=22) on soils with electrical conductivity of 7.8 dS m−1at 50–100 cm depth. Growth of white spruce seemed to be unaffected by salinity level differences, but 78% of white spruce site indexes were less than 13 and would be considered non-productive. Both species showed growth declines over time, compared with non-saline reference growth curves, and rooted primarily in the forest floor and top 20 cm of soil. This suggests that rooting limitations may constrain longer-term productivity of forests established on sites with salinity at depth.

Analysis of human impact on boreal vegetation around Monchegorsk, Kola peninsula, using automated remote sensing technique

ABSTRACTThe boreal vegetation of the sub-Arctic comprises more than 30% of the Earth's forest area and plays a major role in controlling the global environment. In the 20th century the boreal vegetation of Fennoscandia was significantly changed by heavy industrialisation leaving many forest areas damaged or dying. Due to severe climate conditions of the sub-Arctic such vegetation changes are traceable over long periods of time. This provides an opportunity to study all types of human impact on vegetation in time and to develop methods to monitor geographical and structural changes in the vegetation cover. Here we present the first part of a larger study in which we use the remote sensing technique to investigate the dynamics of the boreal vegetation in Fennoscandia in context of human impact. We have developed a novel method for an automated analysis and mapping of vegetation and of all types of human impact based on a single support-vector-machines classifier (for the whole area). Implemented with free and open source software the method uses Landsat TM and ETM+ band data (for which it automatically performs atmospheric correction) and a number of indices like NDVI, NBR, etc. The accuracy of the 16-class classification has been assessed using field data and literature sources and determined to be 74.1%. The method has been successfully applied to a study area around Monchegorsk, Kola peninsula, Russia, the most industrialised part of northern Europe. We have characterised all major types of human impact on the boreal forest and tundra vegetation performing the change detection analysis in an area of 1750 km2 between 1986 and 2005. The analysis has confirmed industrial atmospheric pollutions as the primary type of human impact here. We have discussed the role of forest fires and uncovered temporal trends in the vegetation cover. We have found that during the 19 years covered by the study more than one third of all coniferous forest in the area was transformed primarily to wetland, deciduous forest and typical tundra vegetation. The success of the method in this area allows us to extend the study to the rest of Fennoscandia and look at large scale changes in the boreal vegetation cover.