Трансформация морфологических свойств почв вследствие закустаривания пятнистой тундры

A study of soil morphological, physical and chemical properties was performed in woodland of different ages, in which spruce (Picea abies), aspen (Populus tremula) and birch (Betula pendula) growing stocks have colonized former agricultural land. The aim of the study was to clarify changes in soil genesis, morphology and properties due to the afforestation of abandoned agricultural land in glacial till deposits. The research showed that soil in these deposits (loamy sand, loam, clay) retains the morphological properties of agricultural land for up to 100 years. Secondary podzolization features in the soil profiles were observed within 100 years of the start of afforestation, whereas the diagnostic properties of Albic and Spodic horizons had not developed in the soil profile after 200 years. This study demonstrated that the morphological and physico-chemical properties of forest litter horizons, including the accumulation of organic substances, are dependent on forest age; however, changes in the properties of mineral soil horizons are mainly related to woodland age. Following the afforestation of agricultural lands, changes in soil pHKCl, organic matter content and extractable Al and Fe concentrations occur more rapidly than changes in soil diagnostic properties and profile formation.

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

Warming induced shifts in tundra vegetation composition and structure, including circumpolar expansion of shrubs, modifies ecosystem structure and functioning with potentially global consequences due to feedback mechanisms between vegetation and climate. Satellite-derived vegetation indices indicate widespread greening of the surface, often associated with regional evidence of shrub expansion obtained from long-term ecological monitoring and repeated orthophotos. However, explicitly quantifying shrub expansion across large scales using satellite observations requires characterising the fine-scale mosaic of Arctic vegetation types beyond index-based approaches. Although previous studies have illustrated the potential of estimating fractional cover of various Plant Functional Types (PFTs) from satellite imagery, limited availability of reference data across space and time has constrained deriving fraction cover time series capable of detecting shrub expansion. We applied regression-based unmixing using synthetic training data to build multitemporal machine learning models in order to estimate fractional cover of shrubs and other surface components in the Mackenzie Delta Region for six time intervals between 1984 and 2020. We trained Kernel Ridge Regression (KRR) and Random Forest Regression (RFR) models using Landsat-derived spectral-temporal-metrics and synthetic training data generated from pure class spectra obtained directly from the imagery. Independent validation using very-high-resolution imagery suggested that KRR outperforms RFR, estimating shrub cover with a MAE of 10.6% and remaining surface components with MAEs between 3.0 and 11.2%. Canopy-forming shrubs were well modelled across all cover densities, coniferous tree cover tended to be overestimated and differentiating between herbaceous and lichen cover was challenging. Shrub cover expanded by on average + 2.2% per decade for the entire study area and + 4.2% per decade within the low Arctic tundra, while relative changes were strongest in the northernmost regions. In conjunction with shrub expansion, we observed herbaceous plant and lichen cover decline. Our results corroborate the perception of the replacement and homogenisation of Arctic vegetation communities facilitated by the competitive advantage of shrub species under a warming climate. The proposed method allows for multidecadal quantitative estimates of fractional cover at 30 m resolution, initiating new opportunities for mapping past and present fractional cover of tundra PFTs and can help advance our understanding of Arctic shrub expansion within the vast and heterogeneous tundra biome.

The encroachment of shrubs into grasslands is common in terrestrial ecosystems dominated by grass. Land abandonment and favourable climatic trends in recent decades have favoured the expansion of shrubs into subalpine grasslands in many mountainous regions across Europe. The advance of the succession from grassland to shrubland is expected to have a major impact on ecosystem functioning. We used DNA metabarcoding to assess whether the structure of soil fungal communities varied along the succession from subalpine grassland to shrubland in the Pyrenees, and investigated whether shrub encroachment was associated with changes in soil properties. The expansion of shrubs increased the soil C:N ratio and/or reduced the N, P or K contents. Plant-driven changes in soil properties were strongly associated with the compositional turnover of fungi, including arbuscular mycorrhizal, ectomycorrhizal, ericoid, root endophytic, saprotrophic, lichenised and pathogenic fungi. Total richness and the richness of most functional groups were correlated with soil P, N and the C:N or N:P ratios. We show that the interplay between abiotic factors (changes in soil properties) and biotic factors (occurrence and identity of shrubs) played a key role in the structure and uniqueness of soil fungal communities along the succession.

Recent expansion of tall shrubs in Low Arctic tundra is widely seen as a response to climate warming, but shrubification is not occurring as a simple function of regional climate trends. We show that establishment of tall alder (Alnus) is strongly facilitated by small, widely distributed cryogenic disturbances associated with patterned-ground landscapes. We identified expanding and newly established shrub stands at two northwest Siberian sites and observed that virtually all new shrubs occurred on bare microsites (‘circles’) that were disturbed by frost-heave. Frost-heave associated with circles is a widespread, annual phenomenon that maintains mosaics of mineral seedbeds with warm soils and few competitors that are immediately available to shrubs during favorable climatic periods. Circle facilitation of alder recruitment also plausibly explains the development of shrublands in which alders are regularly spaced. We conclude that alder abundance and extent have increased rapidly in the northwest Siberian Low Arctic since at least the mid-20th century, despite a lack of summer warming in recent decades. Our results are consistent with findings in the North American Arctic which emphasize that the responsiveness of Low Arctic landscapes to climate change is largely determined by the frequency and extent of disturbance processes that create mineral-rich seedbeds favorable for tall shrub recruitment. Northwest Siberia has high potential for continued expansion of tall shrubs and concomitant changes to ecosystem function, due to the widespread distribution of patterned-ground landscapes.

Decomposition of plant litter is a key control over carbon (C) storage in the soil. The biochemistry of the litter being produced, the environment in which the decomposition is taking place, and the community composition and metabolism of the decomposer organisms exert a combined influence over decomposition rates. As deciduous shrubs and trees are expanding into tundra ecosystems as a result of regional climate warming, this change in vegetation represents a change in litter input to tundra soils and a change in the environment in which litter decomposes. To test the importance of litter biochemistry and environment in determining litter mass loss, we reciprocally transplanted litter between heath (Empetrum nigrum), shrub (Betula nana), and forest (Betula pubescens) at a sub‐Arctic treeline in Sweden. As expansion of shrubs and trees promotes deeper snow, we also used a snow fence experiment in a tundra heath environment to understand the importance of snow depth, relative to other factors, in the decomposition of litter. Our results show that B. pubescens and B. nana leaf litter decomposed at faster rates than E. nigrum litter across all environments, while all litter species decomposed at faster rates in the forest and shrub environments than in the tundra heath. The effect of increased snow on decomposition was minimal, leading us to conclude that microbial activity over summer in the productive forest and shrub vegetation is driving increased mass loss compared to the heath. Using B. pubescens and E. nigrum litter, we demonstrate that degradation of carbohydrate‐C is a significant driver of mass loss in the forest. This pathway was less prominent in the heath, which is consistent with observations that tundra soils typically have high concentrations of “labile” C. This experiment suggests that further expansion of shrubs and trees may stimulate the loss of undecomposed carbohydrate C in the tundra.

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.

Forest management impacts on the soil carbon pool and soil properties. This study analyzed the changes of soil organic carbon (SOC) fractions, soil properties, and forest floor in a Chinese fir (Cunninghamia lanceolata) plantation after two years of thinning in Eastern China. The experiment consisted of three thinning treatments: unthinned, moderate thinned (stand stem density reduced by approximately 21%), and heavy thinned (stand stem density reduced by approximately 36%) stands. Concentrations of soil dissolved organic carbon (DOC), light fraction carbon (LFOC), and total SOC in the topsoil (0 to 20 cm) increased in the heavy thinned stands, and no significant effect for heavy fraction carbon (HFOC) was detectable in the soil profile. Some soil properties were also altered after thinning, which included a decrease in soil bulk density (BD), and an increase in soil temperature (ST), soil organic matter (SOM), total nitrogen (TN), available nitrogen (AN), available phosphorus (AP), available potassium (AK), and pH. The change of these soil properties mainly occurred in the topsoil layers (0 to 20 cm) in the heavy thinned treatment. The SOC and soil labile carbon fractions were positively correlated with ST, TN, AN, AP, and AK. Moreover, the increase of SOC fractions and the availability of soil nutrients maybe due to the increased input from an abundant well-decomposed forest floor after thinning. These results suggest that a 36% of thinning operations had a marked impact on the soil labile carbon pool and soil fertility in the topsoil in a Chinese fir plantation during a short-time period. Thus, changes to soil carbon stability and soil fertility should be considered when developing forest management plans. Key words: Thinning, soil organic carbon fraction, soil nutrient, soil carbon stability.

Pedology focuses on understanding soil genesis in the field and includes soil classification and mapping. Digital soil mapping (DSM) has evolved from traditional soil classification and mapping to the creation and population of spatial soil information systems by using field and laboratory observations coupled with environmental covariates. Pedological knowledge of soil distribution and processes can be useful for digital soil mapping. Conversely, digital soil mapping can bring new insights to pedogenesis, detailed information on vertical and lateral soil variation, and can generate research questions that were not considered in traditional pedology. This review highlights the relevance and synergy of pedology in soil spatial prediction through the expansion of pedological knowledge. We also discuss how DSM can support further advances in pedology through improved representation of spatial soil information. Some major findings of this review are as follows: (a) soil classes can be mapped accurately using DSM, (b) the occurrence and thickness of soil horizons, whole soil profiles and soil parent material can be predicted successfully with DSM techniques, (c) DSM can provide valuable information on pedogenic processes (e.g. addition, removal, transformation and translocation), (d) pedological knowledge can be incorporated into DSM, but DSM can also lead to the discovery of knowledge, and (e) there is the potential to use process‐based soil–landscape evolution modelling in DSM. Based on these findings, the combination of data‐driven and knowledge‐based methods promotes even greater interactions between pedology and DSM.Highlights Demonstrates relevance and synergy of pedology in soil spatial prediction, and links pedology and DSM. Indicates the successful application of DSM in mapping soil classes, profiles, pedological features and processes. Shows how DSM can help in forming new hypotheses and gaining new insights about soil and soil processes. Combination of data‐driven and knowledge‐based methods recommended to promote greater interactions between DSM and pedology.

<p>Soil erosion rates frequently exceed the pace at which new soil is formed. This imbalance can lead to soil thinning (i.e., truncation) whereby subsoil horizons, and the underlying parent material, emerge progressively closer to the land surface. These subsurface horizons may have contrasting physical, chemical, and biological properties from those of the original topsoil. Hence, soil thinning can induce changes in topsoil erodibility – a fact that has been largely overlooked in erosion modelling research and could affect long-term projections of soil erosion rates. Here we present a model-based exploration of the potential feedbacks between water erosion and soil thinning, using measured data from 265 agricultural soil profiles in the United Kingdom. We simulated annual erosion rates on these soil profiles with the Modified Morgan-Morgan-Finey model, assuming time-constant land cover, topographic, and rainfall parameters. As the original topsoil was successively removed, our model gradually mixed the subsurface horizons into a 20 cm ploughing layer. We applied this modelling framework on a yearly time-step over a 500-year period, or until the ploughing layer reached the bottom of the lowermost soil horizon. Soil texture, stone cover, and soil organic carbon content for the ploughing layer were recalculated for each time-step through a mass-balance model. Soil bulk density and soil moisture content at field capacity were estimated for each time-step by pedo-transfer functions developed from our own dataset. In addition, we employed a Monte Carlo simulation with 100 iterations per year to provide a forward error assessment of the modelled soil losses. We found that simulated erosion rates on 42 % of the soil profiles were sensitive to truncation-induced changes in soil properties during the analysed period. Among the profiles sensitive to soil thinning, 68 % displayed a negative trend in modelled erosion rates. This was largely explained by decreasing silt contents on the surface soil due to selective removal of this more erodible particle size fraction and the presence of clayey or sandy substrata. Moreover, an increased residual stone cover shielded the surface soils from detachment by raindrop impact and surface runoff. The soil profiles with a positive trend in erosion rates were characterised by the presence of siltier subsoil horizons, which increased topsoil erodibility as they were mixed into the ploughing layer. Overall, our results demonstrated how modelled erosion rates could be sensitive to truncation-induced changes in soil properties, which in turn may accelerate or slow down soil thinning. These feedbacks are likely to affect how we calculate soil lifespans and make long-term projections of land degradation.</p>

Climate warming is driving tundra shrub expansion with implications for ecosystem function and regional climate. Understanding associations between shrub ecophysiological function, distribution and environment is necessary for predicting consequences of expansion. We evaluated the role of topographic gradients on upland shrub productivity to understand potential constraints on shrub expansion. At a low arctic tundra site near Inuvik, Northwest Territories, Canada, we measured sap flow, stem water potential and productivity-related functional traits in green alder, and environmental predictors (water and nutrient availability and seasonal thaw depth) across a toposequence in alder patches. Seasonal thaw reduced stem sap flow whereas topographic position predicted stem water potential and productivity-related functional traits. Upslope shrubs were more water-limited than those downslope. Shrubs in drainage channels had traits associated with greater productivity than those on the tops of slopes. The effect of thaw depth on sap flow has implications for seasonal water-use patterns and warming impacts on tundra ecohydrology. Topographic variation in functional traits corresponds with observed spatial patterns of tundra shrub expansion along floodplains and concave hillslopes rather than in upland areas. Green alder is expanding rapidly across the low arctic tundra in northwestern North America; thus, anticipating the implications of its expansion is essential for predicting tundra function.

Implementation of effective soil conservation management is required in order to rehabilitate and manage degraded forest land in the tropics. For the humid tropics of Sarawak, Malaysia, extensive information on the soil characteristics for rehabilitation of degraded forest lands is essential to guide future forest management programme. In this study, a preliminary assessment on the current status of the soil morphological and physicochemical properties at one of the reforestation sites in Sarawak which was established after enrichment planting of Shorea macrophylla in comparison to an adjacent secondary forest was conducted. The soil profiles in the study sites were established at the reforestation areas of different age stand (year 1996; SM96, 1997; SM97, 1998; SM98 and 1999; SM99) planted with Shorea macrophylla located in Sampadi Forest Reserve as well as existing secondary forest adjacent to the reforestation sites (secondary forest, SF). Soil profile description was conducted at each study sites and soil samples were collected from each identified soil horizon for determination of the soil physicochemical properties. The results showed that the soils in the study area consisted of mainly grey-white podzolic soils which derived from combination of sandstone, coarse-grained, humult ultisols and sandy residual parent material. According to the Sarawak Soil Classification, the morphological properties in the studied sites resemble of Bako soil series as a dominant unit in association with Saratok series in which, corresponds to Typic Paleaquults of Soil Taxonomy by USDA-NRCS Classification. The general soil physicochemical properties indicated that the soils at both reforestation sites and secondary forest were strongly acidic in nature with pH (H2O) of less than (pH < 5.5) with low nutrient status. The acidic nature of the soils might be ascribed to the presence of high exchangeable Al which concomitantly, increased the level of Al saturation of the studied soils. Observation within each soil profiles indicated that soil acidity decreased with depth, resulting in higher pH (H2O) at deeper horizons for all studied sites. For the soil total carbon and total nitrogen, soils at secondary forest depicted higher values in total carbon and total nitrogen at surface soils as compared to the reforestation sites which indicate large pool of organic matter at surface soil derived from the above vegetation. In terms of the soil physical properties, the soils observed were relatively of sandy texture and did not varied widely among the studied sites. In addition, the soil bulk density at reforestation sites was relatively higher than secondary forest due to higher penetration of roots and accumulation of organic matter contents in secondary forest. Based on the current progress of this study, it is recommended that determination on the soil characteristics should be taken into consideration as an important indicator prior or during the establishment of reforestation area in order to ensure the success of reforestation activity in tropical rainforests.

Recent Pan‐Arctic shrub expansion has been interpreted as a response to a warmer climate. However, herbivores can also influence the abundance of shrubs in arctic ecosystems. We addressed these alternative explanations by following the changes in plant community composition during the last 10 years in permanent plots inside and outside exclosures with different mesh sizes that exclude either only reindeer or all mammalian herbivores including voles and lemmings. The exclosures were replicated at three forest and tundra sites at four different locations along a climatic gradient (oceanic to continental) in northern Fennoscandia. Since the last 10 years have been exceptionally warm, we could study how warming has influenced the vegetation in different grazing treatments. Our results show that the abundance of the dominant shrub, Betula nana, has increased during the last decade, but that the increase was more pronounced when herbivores were excluded. Reindeer have the largest effect on shrubs in tundra, while voles and lemmings have a larger effect in the forest. The positive relationship between annual mean temperature and shrub growth in the absence of herbivores and the lack of relationships in grazed controls is another indication that shrub abundance is controlled by an interaction between herbivores and climate. In addition to their effects on taller shrubs (>0.3 m), reindeer reduced the abundance of lichens, whereas microtine rodents reduced the abundance of dwarf shrubs (<0.3 m) and mosses. In contrast to short‐term responses, competitive interactions between dwarf shrubs and lichens were evident in the long term. These results show that herbivores have to be considered in order to understand how a changing climate will influence tundra ecosystems.

Shrub expansion at high latitudes has been implicated in driving vegetation ‘greening’ trends and may partially offset CO2 emissions from warming soils. However, we do not yet know how Arctic shrub expansion will impact ecosystem carbon (C) cycling and this limits our ability to forecast changes in net C storage and resulting climate feedbacks. Here we quantify the allocation of photosynthate between different ecosystem components for two common deciduous Arctic shrubs, both of which are increasing in abundance in the study region; green alder (Alnus viridis (Chaix) DC.) and dwarf birch (Betula glandulosa Michx., B.). Using 13C isotopic labelling, we show that carbon use efficiency (i.e. the fraction of gross photosynthesis remaining after subtracting respiration) in peak growing season is similar between the two shrubs (56 ± 12% for A. viridis, 59 ± 6% for B. glandulosa), but that biomass production efficiency (plant C uptake allocated to biomass production, per unit gross photosynthesis) is 56 ± 14% for A. viridis, versus 31 ± 2% for B. glandulosa. A significantly greater proportion of recent photosynthate is allocated to woody biomass in A. viridis dominated plots (27 ± 5%), compared to plots dominated by B. glandulosa (4 ± 1%). Allocation of C to belowground pools also differs significantly; after 2.5 weeks we recovered 28 ± 6% of recent photosynthate in root-free soil under B. glandulosa, but under A. viridis we were unable to detect recent photosynthate in the soil. We provide the first evidence that the impact of shrub expansion on Arctic C cycling will be species dependant. Where Betula dominates, ~1/3 of recently photosynthesised C will be rapidly allocated belowground to soil and microbial pools. Where Alnus dominates, more recently fixed C will be allocated to woody biomass. We conclude that models driven by remotely-sensed aboveground canopy characteristics alone (i.e. greenness) will be unable to accurately represent the impact of vegetation change on Arctic C storage.

The physicochemical properties of soil profiles in the Luohui Irrigation Scheme located along the southeastern edge of the Loess Plateau in China were investigated. The scheme covers part of a river terrace system along the Luohe River. The study area was approximately 31 × 16 km with a north–south gradient and a difference in altitude of about 40 m. The terrace system was divided into a high terrace (HT; 371–389 m), an intermediate terrace (IT; 360–370 m), and a low terrace (LT; 344–359 m). The HT and LT soils showed different trends in salt accumulation in their surface horizons and overall soil profiles. Surface soils and soil profiles on the HT contained a greater amount of clay and silt than those on the LT, which had coarser soil textures. The IT had soils with characteristics intermediate between those of the HT and LT. A negative relationship was found between soil pH and soil electrical conductivity, and positive ones between soil electrical conductivity and silt contents and between water electrical conductivity and the sodium adsorption ratio. Soil morphological characteristics and soil salinization were related to the topographic sequence of the soils. Soil salinization showed spatial pattern within this irrigation scheme and subsoil texture was a useful indicator of the state of salt accumulation. This information may help in developing guidelines for agricultural soil management that are based on the underground water dynamics and soil morphological properties.