Changes In Vegetation Composition Research Articles

Tectonic-climate-wildfire coupling during the Miocene in the northeastern Qinghai-Tibetan Plateau

The uplift of the Qinghai-Tibetan Plateau (QTP) is one of the most significant geological events in the Cenozoic era. While most studies have focused on the latitudinal differences in the uplift process of the QTP, there has been scant attention to its longitudinal differentiation. The Miocene epoch is pivotal for understanding both the uplift of the QTP and associated climatic changes. Wildfire events not only record changes in vegetation composition but also reflect climatic fluctuations and their driving forces. However, investigations into the interactions among these factors remain limited. This study aims to explore the coupling between the uplift of the QTP, climatic changes and wildfire frequency (or intensity) from northeastern QTP by analyzing microcharcoal concentrations and length-to-width ratios from the Miocene Youshashan Formation in Wulan County, Qinghai Province. The results indicate that the development of wildfires could be divided into three stages. Compared with the intervals 18–15 Ma and 11–8.7 Ma, the middle stage (15–11 Ma) experienced the highest wildfire frequency. This finding underscores the synchronous and close relationship between wildfire occurrences, the uplift of the QTP, and consequent climatic fluctuations. The ratio of length-to-width of microcharcoal indicates that Miocene wildfires in the Wulan Basin primarily occurred at the transitional zones between forests and grasslands. Moreover, the highest peak of wildfire events at six sites gradually shifted from the northeastern to the northwestern QTP from 18–8.7 Ma. This fact demonstrates spatiotemporal disparities in wildfire events from northern QTP, likely stemming from asynchronous uplifts there.

Changes in vegetation composition and structure following landslide-induced disturbance in the Himalaya

The Himalaya cover 12% of India’s landmass and are prone to approximately one-seventh of global rainfall-triggered landslides. Still, very few studies have examined the after-effects of landslides on native vegetation structure and composition. This study aims to fulfil this gap by analysing the vegetation structure and composition of 10 landslide-impacted sites in Uttarakhand Himalaya along an elevational gradient between 1400-3500 m. The investigations revealed that physiognomically, the younger landslide-disturbed sites were dominated by herbaceous taxa while shrubs and trees dominated the older landslide-disturbed sites. Shannon-Wiener diversity values were highest at the old-low disturbed site compared to recent and young disturbed sites. Sorensen similarity index values indicated that the older landslide sites had the highest similarity in species composition of disturbed and undisturbed sites. The younger and recently disturbed landslide sites were highly dissimilar in species composition and structure as compared to the adjacent undisturbed sites. Notably, both the landslide-disturbed and undisturbed sites had a high percentage of native species (90-95%). The fundamental understanding developed from this study can have potential applications in evolving management practices for ecological restoration of the degraded ecosystems in the Himalaya and other mountain ecosystems around the world.

Vegetation response to Holocene hydroclimatic variability in the aseasonal forests of the north-western Amazon

Projected warming and intensification of the hydrological cycle across the Amazon threatens the functioning of some of the most biodiverse ecosystems on the planet. Interfluvial wetlands, or wetlands fed directly by precipitation or small streams, may be some of the most vulnerable to future hydroclimatic changes. In this study, we investigated a 7300-year-old sedimentary archive from an upland palm swamp in the Yasuní National Park (Ecuador) to reconstruct past vegetation dynamics, palaeo-hydroclimatic conditions and human history using pollen, charcoal and geochemical analysis. Pollen data revealed: i) a forest composition influenced by dry conditions 6000 years ago, ii) the development of a palm swamp 4500 years ago, and iii) the establishment of the modern closed-canopy Mauritia flexuosa dominated swamp (moretal) 400 years ago. X-ray fluorescence data indicated that changes in vegetation composition were related to fluctuations in relative moisture levels, which occurred coeval to identified regional climatic events, particularly the Mid Holocene Dry Event (MHDE). Analysis of charcoal revealed continuous presence of fire, albeit at very low levels, since 5000 cal yr BP, with increased values during the last millennium. Our results suggest a footprint of hydroclimatic transitions in the mid-to-late Holocene in the aseasonal forests of the northwest Amazon, highlighting the need to better understand the long-term ecology of these systems to better protect them in light of future climatic change.

Monitoring Changes in Composition and Diversity of Forest Vegetation Layers after the Cessation of Management for Renaturalization

Overstory and understory vegetation play a vital role in forest ecosystem functionality. However, it is necessary to enhance the knowledge of their diversity and compositional dynamics following cessation of disturbance, which is required to inform restoration approaches and the mechanisms required for maintaining disturbance cessation. We conducted a chronosequence spanning 0–1, 5–6, 11–12, 20–24, and 28–34 years since disturbance cessation, and old-growth forests to investigate the dynamic changes in overstory and understory vegetation diversity and composition, as well as maintenance mechanisms following the cessation of anthropogenic disturbances in subtropical regions of Eastern China. The current study results indicated a decrease in understory cover and periodic fluctuations in the diversity of overstorey and understory vegetation following disturbance cessation efforts. Specifically, the shrub layer exhibited the highest richness in 28–34 years, while the herb layer showed the lowest evenness. Multivariate analysis using multiple-response permutation procedures indicated that the species composition and interspecific quantity ratio of understory plants in the forest at 28–34 years significantly differ from those in the early closure stage. An indicator species analysis revealed that more support was given to sun-loving plants after 0–1 years of the enclosure, while species with shade tolerance and low nutrient requirements were supported after 28–34 years. The structural equation model results show that 38.8% of the impact on herb evenness was related to light and substrate diversity. The ecological restoration time mainly indirectly affects understory vegetation by influencing the upper vegetation, light availability, and substrate heterogeneity. Overall, this study revealed that cessation of anthropogenic disturbance can maintain and care for understorey plant diversity and contribute to the sustainable management of forests.

Upscaling vascular aboveground biomass and topsoil moisture of subarctic fens from Unoccupied Aerial Vehicles (UAVs) to satellite level

Arctic and subarctic ecosystems are experiencing rapid changes in vegetation composition and productivity due to global warming. Tundra wetlands are especially susceptible to these changes, which may trigger shifts in soil moisture dynamics. It is therefore essential to accurately map plant biomass and topsoil moisture. In this study, we mapped total, wood, and leaf above ground biomass and topsoil moisture in subarctic tundra wetlands located between Norway and Finland by linking models derived from Unoccupied Aerial Vehicles with multiple satellite data sources using the Extreme Gradient Boosting algorithm. The most accurate predictions for topsoil moisture (R2 = 0.73) used a set of red edge-based vegetation indices with a spatial resolution of 20 m per pixel. On the contrary, wood biomass showed the lowest accuracies across all tested models (R2 = 0.38). We found a trade-off between the spatial resolution and the performance of upscaling models, where smaller pixel sizes generally led to lower accuracies. However, we were able to compensate for reduced accuracy at smaller pixel sizes using Copernicus phenology metrics. A modelling uncertainty assessment revealed that the uncertainty of predictions increased with decreasing pixel sizes and increasing number of co-predictors. Our approach could improve efforts to map and monitor changes in vegetation at regional to pan-Arctic scales.

Seventy-five years of vegetation change after fire in Tasmanian alpine heathland

Context Alpine ecosystems are threatened by warming and an associated increase in fire frequency. There is a gap in our knowledge of succession in Tasmanian alpine heath more than 50 years after fire. The literature suggests that the alpine successional progression usually involves decreasing rates of change, decreasing differences among fire ages, ongoing transitions among shrub species, ongoing transitions from some lifeforms/species to others, and that warming results in increases in species richness. Aims We test for these tendencies up to 75 years from fire in alpine vegetation on kunanyi/Mount Wellington, Tasmania, Australia. Methods We documented the changes in vegetation structure and composition between 1998 and 2022 in plots on either side of an alpine fire boundary in the alpine heathland and used earlier data and observations to extend the record of change after fire to 75 years. We put these changes in the context of the only area of alpine vegetation that was not burnt in 1947 or later. Key results The area last burnt in 1947 exhibited declines in all lifeform covers between 1998 and 2022. All lifeforms except tall shrubs and mat shrubs declined in cover in the area last burnt in 1962. By 2022, shrub cover in the 1962-burnt area had not attained equivalence with the area last burnt in 1947. Herbs had the most dramatic decline in both fire-age classes. There were few shrub seedlings in 2022. All but six taxa, three being exotic, were observed in both the plots and previous broader surveys. Increases in species richness caused by the upward migration of lower-elevation species were not observed. The long-unburnt patch lacked the major dominant of the 1947-burnt plots, namely Orites acicularis, and was dominated by a gymnosperm absent from most of the mountain. Conclusions Succession follows the initial floristic composition model. The differences in trajectories from the 1947 and 1962 fires could possibly be due to desiccation or abrasion damage from increasing wind speeds and temperatures. There are strong indications of further potential change in the absence of fire. Implications The slow rate of recovery and its on-going nature emphasise the importance of keeping fire out of this vegetation type.

Evaluation of methods used to improve grasslands as ring‐necked pheasant brood habitat

AbstractRing‐necked pheasant (Phasianus colchicus) demographic response is sensitive to chick survival and nest success. The establishment and management of grasslands within agricultural landscapes, often through cropland conversion programs (e.g., Conservation Reserve Program [CRP]), have positive impacts on survival and nest success. Newly established CRP and early successional habitat can provide vegetative structure selected by pheasant chicks. Ideal brood habitat provides an abundance of arthropods, an open understory promoting efficient chick movement, and a protective canopy cover. However, the natural succession of grasslands changes desired vegetative structure and challenges managers with providing adequate habitat for pheasant chicks. We investigated the efficacy of different methods of CRP management, including haying, burning, herbicide application, interseeding, and grazing, to provide adequate brood rearing habitat in cool‐ and warm‐season grasslands. We assessed chick body mass change using human‐imprinted ring‐necked pheasant chicks and investigated changes in vegetation composition and structure in relation to various habitat treatments in north‐central and north‐eastern South Dakota during mid‐June and mid‐July of 2013, 2014, and 2015. Generally, treatments that incorporated interseeding, herbicide application, or their combination had the greatest chick mass gain, reduced litter cover and depth, and increased bare ground and forb cover. Effective management for brood habitat may require more aggressive techniques than simple haying or prescribed fire techniques.

Surface-atmosphere energy exchanges and their effects on surface climate and atmospheric boundary layer characteristics in the forest-tundra ecotone in northwestern Canada

The circumpolar forest-tundra ecotone is experiencing rapid changes in vegetation composition and structure. Collectively, these changes modify surface-atmosphere energy exchanges and thus characteristics of the atmospheric boundary layer (ABL). Here, we characterize differences in bulk surface properties and resulting energy balance components using multi-year eddy covariance and supporting measurements made at a mineral upland tundra and a nearby subarctic woodland site between 2013 and 2022. The two sites are characteristic of the forest-tundra ecotone of northwestern Canada. A mixed-layer slab model, in combination with radiosonde observations, was used to gain more insights into differences in ABL characteristics. Compared to the tundra, the tree cover of the woodland led to an enhanced ability to transfer heat into the atmosphere, a higher resistance to evapotranspiration and a stronger coupling between surface and atmosphere. Sensible heat flux (H) was generally higher at the woodland than at the tundra. The largest difference in daily mean H was observed in late winter and spring when the albedo of the snow-covered landscape at the woodland was reduced by 45% compared to the tundra. Both sites experienced similar latent heat flux throughout the year. At the woodland, modelled afternoon air temperature in the mixed layer was up to 9 °C higher in spring and up to 3 °C higher in summer compared to the tundra. In accordance with model results, radiosonde observations indicated a deeper ABL and higher air temperature at the woodland. The presence of trees in the southern part of the forest-tundra ecotone increases air temperature throughout the year and has a drying effect in spring. Consequently, vegetation shifts in the forest-tundra ecotone can be expected to modify local surface climate change patterns, which must be considered when assessing climate change impacts in the region.

Latitude or altitude as the future refugium? A case for the future of forests in Asia Minor and its surroundings.

Anatolian Peninsula and its surroundings, longitudes 24-50° E, latitudes 33-46° N. Time Period: 1961-2100. Major Taxa Studied: 25 woody species and a C3 grass-type. Keeping a spatial window large enough to track potential changes in the vegetation range and composition especially in the mountain ranges within the study area, we parameterized a process-based regional-to-global dynamic vegetation model (LPJ-GUESS v 4.1), forced it with ERA5-Land reanalysis for the historical period, and five different bias-corrected centennial global circulation model (GCM) datasets under SSP5-8.5, and simulated the dynamic responses of key forest species. Bivariate spatio-temporal maps from the simulation results were constructed for final analysis. A significant increase in woody taxa biomass for the majority of our study area, towards the end of the century was simulated, where temperate taxa with high tolerance for drought and a wider range of temperatures took dominance. The mountain ranges in our study area stood out as critical potential refugia for cold favoring species. There were no regional extinctions of taxa, however, important changes in areal dominance and potential future forest composition were simulated. Our simulation results suggest a high potential for future forest cover in our study region by the end of the century under a high emissions scenario, sans human presence, with important changes in vegetation composition, including encroachment of grasslands ecosystems by woody taxa.

Changes in species richness with climate change in subalpine communities are dependent on regional environmental conditions and local functional composition

AbstractQuestionsClimate change may have different effects on species richness depending on regional climates, soil types and the functional composition of local communities.LocationSubalpine belt of the Grandes Rousses (Alps) and Sancy mountain ranges (the Massif Central), France.MethodsWe compared changes in species richness in response to recent climate change in communities from two mountain ranges subjected to contrasting environmental conditions, with a more continental climate and drier soils in the Alps than in the Massif Central. Vegetation composition of 189 and 157 plots was assessed in 1997 and 2017–2018 in the Alps and 1988–1989 and 2022 in the Massif Central, respectively. Five species traits (height, lateral spread, leaf area, specific leaf area and leaf dry matter content) were measured on 108 and 144 species, respectively. Changes in vegetation composition and species richness along spatial environmental gradients were analysed with correspondence analysis at the Sancy site and canonical correspondence analysis at the Alpe d'Huez site. Changes in functional composition across sites were analysed with principal components analysis. Changes in species richness with climate change were analysed with repeated‐measure ANOVAs.ResultsIn both mountain ranges summer temperatures increased and the hydric balance decreased over the past three decades, but snow cover duration decreased in the Alps only, whereas irradiance strongly increased in the Massif Central only. Functional composition was characterized by shorter and more conservative species in the Alps than in the Massif Central, which was dominated by tall exploitative species. Species richness overall decreased with climate change by ca 10% in the Alps but overall increased by ca 10% in the Massif Central. Species richness decreased in the Alps probably because of increasing competition induced by dwarf shrub encroachment due to decreasing snow cover duration, whereas species richness increased in the Massif Central probably due to increasing irradiance in a very nebulous climate.ConclusionThe opposite changes in species richness observed in the two mountain ranges with recent climate change were likely to be explained by their contrasting climate and soil conditions driving different functional compositions and diversity–environment relationships.

Changes in climate, vegetation cover and vegetation composition affect runoff generation in the Gulf of Guinea Basin

AbstractAlthough considerable effort has been deployed to understand the impact of climate variability and vegetation change on runoff in major basins across Africa, such studies are scarce in the Gulf of Guinea Basin (GGB). This study combines the Budyko framework and elasticity concept along with geospatial data to fill this research gap in 44 nested sub‐basins in the GGB. Annual rainfall from 1982 to 2021 show significant decreasing and increasing trends in the northern and southern parts of the GGB, respectively. Annual potential evapotranspiration (PET) also shows significant increasing trends with higher magnitudes observed in the northern parts of the GGB. Changing trends in climate variables corroborates with shift to arid and wetter conditions in the north and south, respectively. From 2000 to 2020 vegetation cover estimated using enhanced vegetation index (EVI) shows significant increasing trends in all sub‐basins including those experiencing a decline in annual rainfall. Vegetation composition measured using vegetation continuous fields (VCFs) from 2000 to 2020 show an increase in tree canopy cover (TC), a decline in short vegetation cover and marginal changes in bare ground cover (BG). Elasticity coefficients show that a 10% increase in annual rainfall and PET may lead to a 33% increase and 24% decline in runoff, respectively. On the other hand, a 10% increase in EVI may lead to a 4% decline in runoff while a 10% increase in TC, SV and BG may reduce runoff by 4% and increase runoff by 3% and 2%, respectively. Even though changes are marginal, decomposing vegetation into different parameters using EVI and VCFs may lead to different hydrological effects on runoff which is one of the novelties of this study that may be used for implementing nature‐based solutions. The study also demonstrates that freely available geospatial data together with analytical methods are a promising approach for understanding the impact of climate variability and vegetation change on hydrology in data‐scarce regions.

Utilizing treated wastewater for pasture irrigation: Effects on productivity, plant community structure and soil properties

AbstractSurplus wastewater accumulates in winter and requires a discharging solution. In our study we examined the effects of using treated wastewater (TWW) as supplemental pasture irrigation in winter. To test the effect of TWW irrigation on the vegetation and soil, 10 grazing prevention exclosures were established at Ramat‐Hanadiv Park, Israel, with half of them irrigated with TWW. Soil and vegetation were sampled during 2 years of irrigation and 1 year after cessation of irrigation. Vegetation composition, species richness, and productivity were sampled at the peak of the growing season and various indices of herbage quality were measured. Our results show that irrigation with wastewater increased herbage production by an average of 38% and total pasture protein production by 9% relative to the control subplots. Conversely, TWW irrigation decreased plant protein content while increasing herbage fibre content and lowering its digestibility. Over a period of 2 years, species richness decreased in the irrigated subplots. Most of the soil indices examined were not affected by irrigation, but in the irrigation subplots, sodium values and the sodium adsorption‐ratio were higher than in areas without irrigation. Additional resources in winter enabled the plants to grow rapidly and increased interplant competition. Changes in vegetation composition were revealed through functional group reshuffling and species richness decline. The results of our study show that wastewater irrigation causes an increase in productivity but a decrease in forage quality. At the pastoral system level, the significant increase in productivity leads to increased availability of protein and herbage for animals.

Wild mice in an urbanized world: Effects of light at night under natural and laboratory conditions in the single-striped grass mouse (Lemniscomys rosalia)

ABSTRACT Urbanization, and the accompanying artificial light at night (ALAN), can disrupt the activity of animals. Such disruptions at the base of a food web can ripple through the ecosystem. Most studies of ALAN are performed in the laboratory. Thus, we lack basic information about the circadian responses of animals under natural environmental conditions to fully evaluate the impact of ALAN. We studied the behaviour and activity of wild-caught, peri-urban single-striped grass mice (Lemniscomys rosalia) under a natural treatment and in a standard laboratory treatment, including dim light at night to mimic conditions that they could experience. The species exhibited predominantly crepuscular activity under all experimental treatments. It showed the highest level of activity under the natural treatment, whereas ALAN significantly suppressed its activity. Males were more active than females under all experimental treatments. The marked changes in activity under ALAN is of particular concern since global change in combination with urbanization can lead to a change in vegetation density and composition that will decrease the number of suitable microhabitats and expose small mammals to novel habitat changes. We suggest that the single-striped mice could become vulnerable because of urbanization, leading to impacts on its ecosystem broadly.

Tracking floristic archetypes of Patagonian steppes

AbstractQuestionsThe classification of plant communities is a well‐established practice in ecology. However, the factors that determine the distribution of common species and the extent of their dominance and overlap are still being debated. Large‐scale studies based on field data are of great interest in the face of biodiversity changes and climate change impacts. This research was designed to answer the following two questions: What are the dominant plant communities in the Patagonian steppes and how do they relate to environmental features, as measured by latitude, longitude, altitude, mean annual precipitation and mean temperature? What have been the recent changes in plant communities in terms of expansion and contraction of different types of communities?LocationPatagonian steppes (South America).MethodsWe used a large database of species‐by‐species vegetation cover from 426 monitoring plots in the South American Patagonian steppes, surveyed between 2007 and 2019, with two different assessment dates at least 5 years apart. We applied archetypal analysis to identify different vegetation compositions at a regional scale (called floristic archetypes) and to track their changes over time. In addition, we analyzed the relationship between floristic archetypes and spatial and meteorological variables to assess the association between floristic composition and the environmental context.ResultsSeven floristic archetypes were identified in the Patagonian steppes. The dominant and most widespread floristic archetype showed an expanding pattern in floristic trajectories and was positively associated with mean annual temperature. This floristic archetype was characterized by both drought‐ and grazing‐tolerant species. Two floristic archetypes located at the longitudinal extremes showed decreasing relative participation in the vegetation configurations, and the archetype located towards the west showed a positive relationship with annual precipitation, suggesting a threatened scenario in the face of drier conditions. Southern floristic archetypes either showed a slight decrease or remained stable.ConclusionsPatagonian steppes are dominated by both drought‐ and grazing‐tolerant species communities and their spatial distribution is expanding across different biomes, whereas the more forage‐preferred species were associated with a decreasing floristic archetype. A projected drier and hotter climate scenario may potentiate this pattern. The floristic archetypes framework has potential as a monitoring tool for tracking changes in vegetation composition at a mesoscale and for identifying hotspots of vulnerable vegetation in the face of environmental changes.

Palynology of Lake Motykino in the Holocene (Vologda region, Northwestern part of European Russia)

This work is dedicated to studying the dynamics of vegetation and natural-climatic conditions in the Mologo-Sheksninskaya lowland in the north of the East European Plain during the Holocene. Lake Motykino, located in the Darwin Nature Biosphere Reserve, was chosen as the research object due to its unique location and preservation of relic lake deposits. Radiocarbon dating and pollen analysis were conducted. The research results are presented in the form of a lithological description of the sediment column, stratigraphic analysis, and a pollen diagram divided into five local pollen zones, reflecting the succession of plant communities from periglacial landscapes in the Late Glacial to the formation of boreal forests in the Holocene. Analysis of pollen spectra allowed for the identification of key periods in the vegetation history of the region, from 13,300 cal BP to 400 cal BP, and to track changes in vegetation composition and peat formation processes.

Drivers of contemporary and future changes in Arctic seasonal transition dates for a tundra site in coastal Greenland.

Climate change has had a significant impact on the seasonal transition dates of Arctic tundra ecosystems, causing diverse variations between distinct land surface classes. However, the combined effect of multiple controls as well as their individual effects on these dates remains unclear at various scales and across diverse land surface classes. Here we quantified spatiotemporal variations of three seasonal transition dates (start of spring, maximum normalized difference vegetation index (NDVImax ) day, end of fall) for five dominating land surface classes in the ice-free Greenland. Using a distributed snow model, structural equation modeling, and a random forest model, based on ground observations and remote sensing data, we assessed the indirect and direct effects of climate, snow, and terrain on seasonal transition dates. We then presented new projections of likely changes in seasonal transition dates under six future climate scenarios. The coupled climate, snow cover, and terrain conditions explained up to 61% of seasonal transition dates across different land surface classes. Snow ending day played a crucial role in the start of spring and timing of NDVImax . A warmer June and a decline in wind could advance the NDVImax day. Increased precipitation and temperature during July-August are the most important for delaying the end of fall. We projected that a 1-4.5°C increase in temperature and a 5%-20% increase in precipitation would lengthen the spring-to-fall period for all five land surface classes by 2050, thus the current order of spring-to-fall lengths for the five land surface classes could undergo notable changes. Tall shrubs and fens would have a longer spring-to-fall period under the warmest and wettest scenario, suggesting a competitive advantage for these vegetation communities. This study's results illustrate controls on seasonal transition dates and portend potential changes in vegetation composition in the Arctic under climate change.

Environmental assessment of the state of fallow drained meadow-soddy-gley and brown mountain-forest soils to involve them into a new agricultural turnover (on the example of the Jewish autonomous region)

Relevance. In the context of ever-increasing anthropogenic influence, the importance of agricultural land reclamation increases and becomes more complicated. Involvement of new virgin soils in agricultural circulation requires large financial investments and huge labor resources, which the local administration does not have. The secondary return to agricultural circulation of fallow reclaimed lands that are not used in agriculture may be a less costly method of increasing the area of agricultural arable land. Aim. To analyze the changes in vegetation and aggregate composition on drained fallow soils of different ages. Object. Drained fallow meadow-soddy-gley and brown mountain-forest soils of different ages. Methods. Standard geobotanical methods were used to describe the vegetation of the polygons. The granulometric analysis of soils was carried out by the method of dry sieving. Soil density was determined by the cutting cylinder method. Results. The study showed that reclaimed arable land, after being withdrawn from agricultural use, enters into a long process of self-recovery. In the course of a long-term transformation, a noticeable accumulation of humus is observed in fallow brown mountain-forest soils in comparison with adjacent arable lands. In the 20-year-old deposit, the highest content of humus is noted, while there is a decrease in saline and hydrolytic acidity. In fallows, the density of the upper soil horizon decreases, which favorably affects the structure of soils. On brown mountain-forest soils, in a 20-year-old fallow, there is a noticeable increase in the proportion of mesoaggregates (0,25–10 mm), including agronomically valuable ones. The number of micro- (<0,25 mm) and macro-aggregates (>10 mm) decreases, which indicates an improvement in the agronomic properties of fallow soils. The results of dry screening indicate that the fallow period of drained meadow-soddy-gley soils adversely affects their structure.

Vegetation response to climate change and human activity in southwestern China since the Last Glacial Maximum

Southwestern China, a biodiversity hotspot, underwent dramatic climate change following the Last Glacial Maximum and intensive human activity also exerted a major impact since the late Holocene. In this paper, we report a pollen record from Yilong Lake in Yunnan Province, southwestern China, to understand vegetation response to long-term climatic variation and human activities at a regional-level over the last 27,000 years. Findings show that temperate and coniferous taxa were dominant before 18 cal kyr BP reflecting the glacial climate. Between 18 and 14 cal kyr BP, thermophilic taxa increased in response to global deglaciation. A notable shift from deciduous to evergreen forests occurred at approximately 14 cal kyr BP, after which pollen concentration increased but pollen diversity decreased. Pollen assemblages indicated dense forests, primarily composed of evergreen oaks developed under warm and strong summer monsoon conditions from 13 to 8 cal kyr BP. High rates of vegetation change occurred during the middle Holocene before vegetation diversity gradually increased during the Holocene Thermal Optimum, with high variability of precipitation in the Yilong Lake region. Anthropogenic forcing progressively became the main factor affecting vegetation composition and vegetation change rates over the past three millennia.

Arctic tundra shrubification can obscure increasing levels of soil erosion in NDVI assessments of land cover derived from satellite imagery

Monitoring soil erosion in the Arctic tundra is complicated by the highly fragmentated nature of the landscape and the limited spatial resolution of even high-resolution satellite data. The expansion of shrubs across the Arctic has led to substantial changes in vegetation composition that alter the spectral reflectance and directly affect vegetation indices such as the normalized difference vegetation index (NDVI), which is widely applied for environmental monitoring. This change can mask soil erosion if datasets with too coarse spatial resolutions are used, as increases in NDVI driven by shrub expansion can obscure concurrent increases in barren land cover. Here we created land cover maps from a multispectral uncrewed aerial vehicle (UAV) and land cover survey and assessed satellite imagery from PlanetScope, Sentinel-2 and Landsat-8 for several areas in north-eastern Iceland. Additionally, we used a novel application of the Shannon evenness index (SHEI) to evaluate levels of pixel mixing. Our results show that shrub expansion can lead to spectral confusion, which can obscure soil erosion processes and emphasize the importance of considering spatial resolution when monitoring highly fragmented landscapes. We demonstrate that remote sensing data with a resolution < 3 m greatly improves the amount of information captured in an Icelandic tundra environment. The spatial resolution of Landsat data (30 m) is inadequate for environmental monitoring in our study area. We found that the best platform for monitoring tundra land cover is Sentinel-2 when used in combination with multispectral UAV acquisitions for validation. Our study has the potential to improve environmental monitoring capabilities by introducing the use of SHEI to assess pixel mixing and determine optimal spatial resolutions. This approach combined with comparing remote sensing imagery of different spatial and time scales significantly advances our comprehension of land cover changes, including greening and soil degradation, in the Arctic tundra.

Vegetation composition regulates the interaction of warming and nitrogen deposition on net carbon dioxide uptake in a boreal peatland

Abstract Peatlands are carbon sinks and have the potential to mitigate global warming. However, it is unclear whether peatlands will remain carbon sinks or switch to carbon sources under global changes, such as climate warming, elevated nitrogen (N) deposition and vegetation composition change. In this study, these global changes were mimicked in a boreal peatland for 7 years to explore the interactions of climate warming, elevated N deposition and vegetation composition on the carbon sink function of peatlands. The results showed that warming has a limited effect on net ecosystem production (NEP), while N addition decreased NEP by 65% owing to the detrimental effect on Sphagnum mosses. The negative impact of N addition on NEP could be mitigated by warming under intact vegetation. Under the treatment of graminoid removal, warming and elevated N addition (WN) decreased NEP by 80%–106%. Under the treatment of shrub removal, 7 years of WN treatment did not affect NEP. These results highlight the importance of vegetation composition in regulating net CO2 flux in peatlands. If peatlands shift to shrub‐dominated ecosystems, the net CO2 uptake in peatlands would be decreased under climate warming and elevated N deposition. If peatlands shift to graminoid‐dominated ecosystems, the net CO2 uptake in peatlands would be unaltered under climate warming and elevated N deposition. This study sheds new light on the interactions of climate warming, elevated N deposition, and vegetation composition change on the CO2 uptake of peatlands; and could help accurately evaluate the carbon sink function of peatlands under future global change. Read the free Plain Language Summary for this article on the Journal blog.