Restoration induced long‐term vegetation change in oligotrophic peatlands

Global warming has led to significant vegetation changes especially in the past 20 years. Hulun Buir Grassland in Inner Mongolia, one of the world’s three prairies, is undergoing a process of prominent warming and drying. It is essential to investigate the effects of climatic change (temperature and precipitation) on vegetation dynamics for a better understanding of climatic change. NDVI (Normalized Difference Vegetation Index), reflecting characteristics of plant growth, vegetation coverage and biomass, is used as an indicator to monitor vegetation changes. GIMMS NDVI from 1981 to 2006 and MODIS NDVI from 2000 to 2009 were adopted and integrated in this study to extract the time series characteristics of vegetation changes in Hulun Buir Grassland. The responses of vegetation coverage to climatic change on the yearly, seasonal and monthly scales were analyzed combined with temperature and precipitation data of seven meteorological sites. In the past 30 years, vegetation coverage was more correlated with climatic factors, and the correlations were dependent on the time scales. On an inter-annual scale, vegetation change was better correlated with precipitation, suggesting that rainfall was the main factor for driving vegetation changes. On a seasonal-interannual scale, correlations between vegetation coverage change and climatic factors showed that the sensitivity of vegetation growth to the aqueous and thermal condition changes was different in different seasons. The sensitivity of vegetation growth to temperature in summers was higher than in the other seasons, while its sensitivity to rainfall in both summers and autumns was higher, especially in summers. On a monthly-interannual scale, correlations between vegetation coverage change and climatic factors during growth seasons showed that the response of vegetation changes to temperature in both April and May was stronger. This indicates that the temperature effect occurs in the early stage of vegetation growth. Correlations between vegetation growth and precipitation of the month before the current month, were better from May to August, showing a hysteresis response of vegetation growth to rainfall. Grasses get green and begin to grow in April, and the impacts of temperature on grass growth are obvious. The increase of NDVI in April may be due to climatic warming that leads to an advanced growth season. In summary, relationships between monthly-interannual variations of vegetation coverage and climatic factors represent the temporal rhythm controls of temperature and precipitation on grass growth largely.

Northern aapa mire complexes are characterized by patterned fens with flarks (wet fen surfaces) and bog zone margins with Sphagnum moss cover. Evidence exists of a recent increase in Sphagnum over fens that can alter ecosystem functions. Contrast between flarks and Sphagnum moss cover may enable remote sensing of these changes with satellite proxies. We explored recent changes in hydro-morphological patterns and vegetation in a south-boreal aapa mire in Finland and tested the performance of Landsat bands and indices in detecting Sphagnum increase in aapa mires. We combined aerial image analysis and vegetation survey, repeated after 60 years, to support Landsat satellite image analysis. Aerial image analysis revealed a decrease in flark area by 46% between 1947 and 2019. Repeated survey showed increase in Sphagnum mosses (S. pulchrum, S. papillosum) and deep-rooted vascular plants (Menyanthes trifoliata, Carex rostrata). A supervised classification of high-resolution UAV image recognized the legacy of infilled flarks in the patterning of Sphagnum carpets. Among Landsat variables, all separate spectral bands, the Green Difference Vegetation Index (GDVI), and the Automated Water Extraction Index (AWEI) correlated with the flark area. Between 1985 and 2020, near-infrared (NIR) and GDVI increased in the central flark area, and AWEI decreased throughout the mire area. In aapa mire complexes, flark fen and Sphagnum bog zones have contrasting Landsat NIR reflectance, and NIR band is suggested for monitoring changes in flarks. The observed increase in Sphagnum mosses supports the interpretation of ongoing fen–bog transitions in Northern European aapa mires, indicating significant ecosystem-scale changes.

Different Fire Frequency Impacts Over 27 Years on Vegetation Succession in an Infertile Old-Field Grassland

Investigations of past biotic responses to rapid climate shifts are useful for developing biological scenarios that may result from future climate change. Vegetation responses to the Younger Dryas (YD) cold climatic reversal, the 8.2 ka cooling event, and the 4.2 ka event are of considerable interest. In this paper, we conduct model simulations of vegetation responses to these rapid climate changes over East Asia, and compare them with pollen-based vegetation records. Our aims were to investigate the vegetation responses to rapid climate changes with different magnitudes and to analyze dominant impact factors on vegetation in East Asia. Our results reveal that all major Plant Functional Types responded to the climate changes, but the magnitude, timing, and impact of their responses varied, with most changes in vegetation composition rather than vegetation type succession. In addition, it was found that after the abrupt cooling events the vegetation did not always recover to the state simulated before the perturbation, suggesting that different vegetation compositions may occur under similar climate conditions. Notably, there was a latitudinal gradient in the magnitude of these cold events in East Asia and in the resulting vegetation response, indicating a more pronounced vegetation responses to the severe cooling in the north and weaker responses to less cooling in the south. Changes in temperature exerted a major influence on the vegetation dynamics in the most high latitude regions, and changes in both temperature and precipitation were responsible for the vegetation changes at mid-to-high-latitudes. Vegetation compositions show a long-lasting effect of abrupt climate changes through eco-physiological and ecosystem demographic processes.

Vegetation response in subtropical southwest China to rapid climate change during the Younger Dryas

QuestionPlant communities will change along environmental gradients, even in “azonal” vegetation such as wetlands. It is hypothesized that functional community composition of wetland vegetation changes along a natural gradient from dry low‐lying areas to wet high‐lying areas. We wanted to know how the functional groups that make up wetland plant communities change along such aridity and altitudinal gradients.LocationHighveld area of Central South Africa, covering four provinces of the country: Northern Cape, Free State, North West and Mpumalanga.MethodsThe community composition of 201 vegetation plots was obtained from a compilation of South African wetland vegetation types of the study area. Functional traits were collected for the dominant plant species and community‐weighted means of plant functional traits were calculated for wetland vegetation plots. Redundancy analysis was performed to plot these against environmental and climatic gradients.ResultsThe ordination results showed that the community‐weighted plant functional traits were correlated with environmental and climatic variables. For example, specific correlations reveal that root/shoot biomass ratio, leaf nitrogen and specific leaf area are associated with high temperature and evaporation, conditions that prevail in the driest end of the gradient. On the opposite end, wetland vegetation in mesic areas has adaptations for fast growth and high productivity, as it is composed of tall plants with wide stems and deep roots. A hierarchical cluster analysis (HCA) resulted in nine plant functional groups, with different representation along the aridity gradient in the Highveld Plateau of South Africa.ConclusionsWetlands in dry areas have plant functional groups different from those in mesic areas. Changes in community composition show how wetlands are responding to climatic variability and environmental change. Thus, the study of changes in plant functional groups can be useful for detecting the impacts of climate change on wetland vegetation.

Accelerated vegetative growth measured by gross primary productivity in China from 1980 to 2018

Boreal peatlands harbour large stores of carbon as peat below their surfaces. Climate change is expected to cause drying in northern peatlands, which will in turn impact the carbon balance of these ecosystems that is maintained by high water tables and the hydrologically sensitive plants growing there. This study aims to quantify how vegetation will be structured (I) and photosynthesize (II, III) in a future climate as emulated by long-term water level drawdown (WLD). To do this, changes in the vegetation and its photosynthesis after WLD are linked, and the response of Sphagnum mosses to periodic drought is investigated. Field measurements were done at a long-term WLD field experiment that contained a rich (mesotrophic) fen, a poor (oligotrophic) fen and a bog (ombrotrophic) site. Measurements included vegetation surveys from existing permanent sample plots and leaf-level carbon dioxide exchange measurements. For an experiment in controlled conditions peatland surface cores from this field experiment were transported to a greenhouse where the photosynthesis of lawn Sphagna during and after an experimental periodic drought was measured. The field study revealed that the response of peatland vegetation to WLD depend on peatland type. The species composition in the rich fen was the most impacted by WLD, while the bog vegetation demonstrated stability. Similarly, large increases in photosynthesis occurred following WLD on the vascular plant-covered rich fen, while changes were negligible on the Sphagnum-carpeted bog. The vegetation on the two fens shifted from an open sedge-, or sedge and Sphagnum-dominated ecosystem, to a tree-dominated ecosystem. Canopy development following WLD further accelerated vegetation changes by shading and sheltering the understorey vegetation. Vascular plants were the most likely to increase productivity from WLD as they are best suited to utilize the nutrients made available by peat mineralization, while Sphagnum moss photosynthesis was impacted little. The greenhouse study revealed that lawn Sphagnum mosses exposed to long-term WLD were more vulnerable to drought compared to those from wet sites. Large capitula typical to fen Sphagnum species appeared to be beneficial for surviving periodic drought. This work demonstrated that climate change as emulated by long-term WLD will have a large impact on the vegetation composition of northern peatlands and increase photosynthetic function of these ecosystems, fens in particular. To better predict climate feedbacks from these changes, carbon dynamics including peatland vegetation dynamics should be updated in global process models. Future research to better understand the tipping point of different peatland types after WLD in different climatic regions will help us to predict changes in these diverse and globally important systems.

QuestionsRising temperatures are predicted to cause upward shifts and reorganisation of mountain vegetation. This study analyses how field layer vegetation across the forest–tundra ecotone has responded over a 22‐year period. Main questions are: (a) have vegetation composition, richness and diversity changed; (b) have abundance of functional plant groups and individual species changed; and (c) which environmental factors regulate vegetation distribution and composition?LocationCentral Norway.MethodsThe study uses vascular plant species recordings and environmental data from permanent 1 m × 1 m quadrats (n = 266), established in 1994 and revisited in 2016, along transects from forest to high alpine areas (750–1,500 m a.s.l.). Changes in vegetation composition (species and functional group levels) and influence of environmental factors are analysed using ordination and mixed‐effect models.ResultsOrdination shows an overall upward vegetation movement corresponding to 0.5 ± 0.1 m/y, and compositional homogenisation across the ecotone over time. Changes at species and functional group levels vary across the ecotone. Species richness and diversity increase over time due mainly to an increase of herbs and graminoids in the forested part of the ecotone. Evergreen woody species increase in abundance across the entire ecotone and most strongly above the forest. Deciduous woody species abundance is stable at group level but shows large variation at species level. Species‐level responses deviate from group‐level responses in all functional groups. Vegetation distribution and composition are environmentally explained by altitudinal distance to the treeline and microtopography.ConclusionsOur results show how increased temperature impacts vegetation movements and reorganisation through mainly species‐specific responses with low within‐functional‐group coherency. The apparent upward shift is moderate compared to the increase in temperature over the study period, but larger than in similar studies, although grazing pressure might co‐control change rate. Species‐specific responses and response rates highlight the need for detailed empirical data to predict and understand vegetation responses in a warming climate.

Global patterns of vegetation response to millennial-scale variability and rapid climate change during the last glacial period

Large-scale vegetation response to the 8.2 ka BP cooling event in East Asia

Plant functional group controls litter decomposition rate and its temperature sensitivity: An incubation experiment on litters from a boreal peatland in northeast China

Anthropogenic nitrogen (N) loading has the potential to affect plant community structure and function, and the carbon dioxide (CO2) sink of peatlands. Our aim is to study how vegetation changes, induced by nutrient input, affect the CO2 exchange of a nutrient-limited bog. We conducted 9- and 4-year fertilization experiments at Mer Bleue bog, where we applied N addition levels of 1.6, 3.2, and 6.4 g N m -2 a -1 , upon a background deposition of about 0.8 g N m -2 a -1 , with or without phosphorus and potassium (PK). Only the treatments 3.2 and 6.4 g N m -2 a -1 with PK significantly affected CO2 fluxes. These treatments shifted the Sphagnum moss and dwarf shrub community to taller dwarf shrub thickets without moss, and the CO2 responses depended on the phase of vegetation transition. Overall, compared to the large observed changes in the vegetation, the changes in CO2 fluxes were small. Following Sphagnum loss after 5 years, maximum ecosystem photosynthesis (Pgmax) and net CO2 exchange (NEEmax) were lowered (-19 and -46%, respectively) in the highest NPK treatment. In the following years, while shrub height increased, the vascular foliar biomass did not fully compensate for the loss of moss biomass; yet, by year 8 there were no significant differences in Pgmax and NEEmax between the nutrient and the control treatments. At the same time, an increase (24‐32%) in ecosystem respiration (ER) became evident. Trends in the N-only experiment resembled those in the older NPK experiment by the fourth year. The increasing ER with increasing vascular plant and decreasing Sphagnum moss biomass across the experimental plots suggest that high N deposition may lessen the CO2 sink of a bog.

: Waters of the United States (WoUS) are regulated by the U.S. Army Corps of Engineers under Section 404 of the Clean Water Act (33 U.S.C. 1344). The Corps lateral jurisdictional extent in Arid West stream channels is the upper level of the ordinary high water (OHW). The channel shape, fluvial textures, and vegetation patterns of these arid stream channels are heavily influenced by short-term, high-intensity or flashy events, which create distinctive physical features and vegetation responses. To determine vegetation and channel morphology responses, sequential aerial photos and stream gauge data for eight ephemeral and intermittent stream channels in the Arid West were analyzed. The observed patterns associated with various discharge event levels are consistent with the Corps OHW delineation manual. The use of remote sensing resources provides another critical support tool for delineating the extent of the OHW in Arid West stream channels. The results of this study consistently show that the majority of work, whether it affects vegetation or channel morphology, occurs within the bankfull channel and active floodplain. This study also showed that the terrace floodplain maintained its vegetative and morphology composition with discharges as large as an 18.7-year flood event, the largest we studied. Data analyzed by flood events support the theory that the bankfull and active channels of intermittent and ephemeral streams in the Arid West function as one channel and that the outer boundary of this single channel represents the extent of the OHW.

A core recovered from a thick sedimentary sequence in the Ioannina basin, on the western flank of the Pindus M ountain Range, northwest Greece, presents the opportunity to observe multiple changes in vegetational communities at one locality through a series of glacial-interglacial Q uaternary cycles. The Ioannina 249 record adds to the knowledge of vegetation history of areas of increased topographical variability and precipitation of the western Balkans and provides a complete stratigraphical record that can be compared with that of other long terrestrial sequences and with the marine record. Pollen analytical results are presented as percentages and concentrations, the former providing information on the composition and structure of vegetation, while the latter is considered here to be a reliable indication of vegetation density when changes differing by an order of magnitude are documented. The record shows an hierarchical order of variation in the response of vegetation to environmental change. Higher order of magnitude changes are alternations between forest and open vegetation communities, a reflection of major climatic shifts from interglacial to glacial modes. Superimposed on these oscillations is a lower order variability associated with vegetation changes within interglacial and glacial periods. During forest periods a succession is recorded withQuercusandUlmus/Zelkovaexpanding early, followed byCarpinus betulusand alsoOstrya carpinifolia/Carpinus orientalis, and finallyAbiesoften accompanied byFagus. Although individual periods may be characterized by dominance of one or more taxa, the underlying pattern of differential expansion is usually distinct and consistent. Nine forested intervals are distinguished and are assigned local names to facilitate longdistance comparisons and correlations. During open vegetation periods a series of changes is also observed from transitional steppe—forest or forest-steppe vegetation, through grassland steppe communities, culminating in a discontinuous desert-steppe vegetation. In addition to the two ends of the spectrum (forest and desert—steppe), attention is drawn to the intermediate phases representing ‘average’ Quaternary conditions. The Ioannina record is correlated with that of other long sequences from Europe and variation in the response of vegetation with site characteristics is considered. A strategy for long-distance correlations relying on the primary structure of vegetation and relative stratigraphical position of individual periods is described. The last interglacial period followed by two interstadials is recorded in much the same fashion in all records. Correlation of earlier periods was also in general agreement although only two continuous records that extend beyond the last interglacial are at present available for comparison. To minimize elements of circularity, similarities in the behaviour of individual taxa during particular periods are not part of the correlation criteria so that if their chronostratigraphical equivalence is independently corroborated their significance can be examined. On this basis, the importance ofCarpinus betulusand the almost complete absence ofFaguson a subcontinental scale during the last interglacial are noted. Possible effects of climate, competition and disease are discussed. Cross-correlation with the deepsea oxygen isotope record provides a tentative chronology for the Ioannina record. Based on this, the sequence down to a depth of 162.75 m is considered to represent a record of approximately the past 423 000 years. Aspects of land-sea correlations are discussed in the light of the Ioannina 249 record and the importance of long sequences in the development of European Quaternary stratigraphy is emphasized.