This study of the Kanna calcareous spring fen on Saaremaa, the largest island of Estonia, elucidates its history of fen development and vegetation diversity over the last 9,200 years. Pollen, spores, ...non-pollen palynomorphs, macrofossils, loss-on-ignition and humification index analyses were carried out to reconstruct fen succession, vegetation development, environmental changes and human impact. Hierarchical clustering, ordination analysis and linear regression were applied to examine the vegetation composition and richness patterns through time and to identify the potential environmental drivers underlying these patterns. Our results suggest reverse mire development from bog to fen, a rare occurrence and contrary to typical mire autogenic succession from groundwater fed to rainwater fed. Kanna developed as a small bog for the first 2,000 years from 9,200 to 7,200 cal yrs
bp
. Changes to the hydrological regime around 7,200 cal yrs
bp
, due to a warmer and drier climate and land uplift, caused a change from an ombrotrophic to a minerotrophic environment. Typical spring fen characteristics developed ca. 5,000 cal yrs
bp
and continued until ca. 400 cal yrs
bp
, when the fen was fed by calcareous mineral-rich groundwater and reached very high floristic diversity with various calciphilous and relict plant taxa. We conclude that general changes in the Kanna fen succession, vegetation community and diversity are associated with climatic changes. The present high diversity of the fen is a result of a long-term stable fen environment, which may have been even higher in the past. However, the pollen richness has decreased during the last 400 years, possibly due to human or natural factors.
Predicting the trajectory of ongoing diversity loss requires knowledge of historical development of community assemblages. Long-term data from palaeoecological investigations combined with key ...biodiversity measures in ecology such as taxonomic richness, functional diversity (FD), phylogenetic diversity (PD) and environmental factors expressed as Ellenberg indicator values (EIVs) could provide that knowledge. We explored the modern pollen–plant (moss polster pollen vs. surrounding vegetation) diversity relationships for herbaceous and woody taxa in calcareous fens from two different regions in Estonia, NE Europe. Associations of taxonomic richness, vegetation composition, FD (including functional alpha diversity and trait composition), PD and EIVs in modern pollen vs. plant data were studied with correlation analysis, Procrustes analysis and linear regression models. To test their potential use in palaeoreconstructions, diversity measures were applied on pollen data from Kanna spring fen reflecting fen vegetation development over the last nine millennia and diversity changes through time were studied using generalized additive models. Results showed significant pollen–plant richness correlations for herbaceous taxa at vegetation estimate scales up to 6 m radius and Procrustes analysis showed significant compositional associations at all plant estimate scales (up to 100 m). Woody taxa had no significant pollen–plant richness correlations but composition relationships were significant at plant estimate scales of 6–100 m. Traits that were best reflected by pollen data (both in terms of trait composition and functional alpha diversity) among woody and herbaceous taxa were seed number, clonality, SLA and LDMC. PD of herbaceous species was reflected by pollen data. Among the EIVs, Ellenberg L and T were significantly reflected by pollen data for both woody and herbaceous communities. Palaeoreconstruction from Kanna fen indicates that trends of woody taxa are mostly related to long-term changes in climate while diversity variables of herbaceous taxa closely follow autogenic processes within the fen. We suggest that pollen-based diversity estimates should be calculated separately for woody and herbaceous taxa as they clearly represent different spatial scales. Present study suggests that linking sedimentary pollen data with FD, PD and EIVs provides possibilities to examine long-term trends in community assembly and ecosystem processes that would be undetectable from traditional pollen diagrams.
Non-biting midges (Chironomidae) are the most diverse and abundant invertebrate group in boreal lakes and are strongly responsive to climate change, thus they are a valuable palaeoecological proxy ...for studying aquatic biodiversity response in the face of climate change. Here, we aim to decipher the influence of climate-induced changes on temporal patterns in chironomid assemblages. We apply a novel approach combining traditional taxon-based analysis and species-trait framework to subfossil chironomid assemblages in a sediment core covering the Late Glacial–Holocene transition in Northern Europe. We produce pollen-based July and January temperature reconstructions to characterize past climate fluctuations that show a distinct Early Holocene warming for continuous 1700 years with considerably greater warming in winter (ca. 10 °C) than summer (ca. 4 °C) temperature. Overall, chironomid taxonomic changes were mainly induced by the temperature tolerances and optima of species, as temporal dynamics showed agreement with temperature reconstructions. Our results suggest that vegetation dynamics could also play a role in structuring chironomid assemblages by selecting taxa with the highest ability to exploit available food resources, thus potentially confounding chironomid-based summer climate reconstructions. We demonstrate that the study of the hidden chironomid functional composition could help to identify secondary drivers and thus strengthen the reliability of climate reconstruction based on subfossil chironomids.
•Climate change drives chironomid taxon selection towards the highest ability to exploit existing food resources.•Additional drivers of chironomid diversity could potentially confound climate reconstructions.•Lateglacial and early-Holocene climate change was mostly a winter phenomenon.
Branched glycerol dialkyl glycerol tetraethers (brGDGTs) preserved in lake sediments are increasingly used to investigate past terrestrial temperatures. brGDGTs are ubiquitous in sedimentary ...environments, well-preserved, and the number of methyl groups in different brGDGTs is generally controlled by temperature. Current brGDGT calibrations largely rely on empirical correlations between the relative abundances of different brGDGTs in surface sediments and either mean annual or warm season air temperatures. These approaches may introduce complications in global temperature calibrations due to differences in the seasonality of temperature and variations in brGDGT production with latitude that are difficult to constrain. Here, we report new brGDGTs data from lake surface sediments obtained throughout the tropics including South America (n = 57), East Africa (n = 21), and Southeast Asia (n = 13), and revisit globally distributed brGDGT data. We find a uniform response of brGDGTs to mean annual air temperature across the tropics despite differences in the environmental and geological conditions in different regions highlighting the dominant influence of temperature on brGDGT distributions. brGDGTs in mid- and high latitude sediment show a qualitatively similar but quantitatively different response to those in the tropics. We show that temperature seasonality can partially explain the latitudinal differences, implying the need for latitudinally-dependent brGDGT calibrations and/or improved observations and models to constrain seasonal effects on brGDGTs. Combining our new data with previously published brGDGT data, we develop and apply improved temperature calibrations.
•brGDGT distributions were measured in 91 tropical lakes' surface sediments.•Tropical brGDGTs show uniform response to mean annual air temperature.•We observe a different response of brGDGTs to temperature in high latitude lakes.•Seasonality causes different brGDGT responses in the tropics and mid-to high latitudes.•We provide improved regional and global lacustrine brGDGT temperature calibrations.
Mires or peatlands host unique biodiversity and provide many valuable ecosystem services. Mires often undergo different development phases during their evolution. Two mire phases that have clearly ...divergent hydrological regimes and characteristic biotas are minerotrophic fen and ombrotrophic bog. Open mires can be overgrown by trees and develop into peatland forests. Mire development trajectories are expected to be associated with three major factors—post‐glacial isostatic uplift, autogenic succession and climate‐induced changes. Understanding long‐term mire development is important for the conservation planning of these threatened habitats.
We use data from modern pollen samples to characterize differences between the pollen signal and to identify indicator pollen taxa for three mire development phases—open fens, forested fens and bogs. The modern reference samples are then used to support the interpretation of the sediment records in terms of mire development phases and related biodiversity changes in six mires within a 20 × 30 km area in western Saaremaa, Estonia. Palynological richness and phylogenetic diversity (PD) as well as Ellenberg indicator values are compared throughout the 10,000‐year history of the Saaremaa mires.
Pollen of herbaceous taxa discriminates between open fens, forested fens and bogs, and indicator pollen taxa can be associated with each mire phase. In general, the fen phases of the mires show higher richness and PD than the bog phases but there is considerable variation between the sites. The mire diversity peaks are often associated with transitional periods when high local community heterogeneity allows the coexistence of high numbers of taxa from different phylogenetic lineages.
Synthesis. When the initiation of mires in isostatic land uplift areas is closely related to water‐level changes and the position of the sites in relation to the sea, the development of mires and their biodiversity in the late Holocene is associated with local conditions but mediated by climate. The ongoing rapid climate change is likely to accelerate changes in existing mires, and while the transitional periods are characterized by high diversity, these periods are temporary, and the overall diversity of mires can be expected to decrease.
When the initiation of mires in isostatic land uplift areas is closely related to water‐level changes and the position of the sites in relation to the sea, the development of mires and their biodiversity in the late Holocene is associated with local conditions but mediated by climate. The ongoing rapid climate change is likely to accelerate changes in existing mires, and while the transitional periods are characterized by high diversity, these periods are temporary, and the overall diversity of mires can be expected to decrease.
Pollen-based quantitative vegetation reconstructions using multiple sedimentary basins from the same area, along with their quantified relevant pollen source areas, are a powerful means to study how ...long-term human impact has affected vegetation and shaped the currently protected heritage landscapes at different spatial scales. Our study presents the outcome of a palynological investigation in Karula Upland, south Estonia, for the last 6500 years. Centennial-resolution pollen records from one large (175 ha) and three small (5 ha) lakes, and one small bog (0.1 ha) were used to reconstruct the vegetation at different spatial scales using the Landscape Reconstruction Algorithm. The results are discussed in combination with archaeological sites and historical knowledge.
The first signs of small-scale forest clearings connected to local human settlements are already visible in the Middle Stone Age (3100–4100 BCE). The first finds of cereal pollen (2500 BCE) from Lake Ähijärv suggest that grain crops were introduced to south Estonia during the Late Stone Age. The evidence of local crop farming in Karula is traceable since the Bronze Age. The widespread practice of slash-and-burn agriculture led to a major shift in land-cover with replacement of old-growth forests with the early-successional birch, occupying long-term fallows, during Late Bronze Age and Early Iron Age (700–250 BCE). A notable regression in farming is visible during the second part of the Early Iron Age (100–600 CE), with the most prominent change taking place around 500 CE, roughly coinciding with the 6th century Northern Hemisphere climate cooling and Migration Period. Permanent fields gained importance alongside slash-and-burn cultivation, during the Late Iron Age, ca 600–700 CE, shifting the vegetation composition towards more open land-cover. The ∼50 % open mosaic land-cover of the heritage landscape, protected today in Karula Upland, was formed during the Late Iron Age.
The current study shows that sedimentary basins as close as ca 2 km from each other sometimes tell different stories, highlighting the need to quantify the size of the pollen source area to combine successfully archaeological, historical, and palynological evidence. Quantitative pollen-based vegetation reconstructions provide an environmental context for known, and possibly unknown, archaeological evidence within the pollen source area.
•Multidisciplinary approach provides reconstruction of human habitation history.•Pollen-based land-cover reconstruction defines area for archaeological finds.•The arrival of the Corded Ware culture in the Stone Age is evidenced by cereal pollen.•Slash-and-burn practice is indicated by charcoal and early-successional trees.•Land-cover reached the basic structure similar to that of today during the Iron Age.
Human‐induced activities around Lake Lilaste in the central Latvian sandy coastal area have been reconstructed over a 1300‐year period. We use a combination of well‐established geoarchaeological ...research methods (14C dating, pollen, nonpollen palynomorphs, REVEALS modeling, diatoms, C/N ratio, magnetic susceptibility, loss on ignition) to study the human impact on the environment. Historical context aids focus on records of resource (e.g., timber) exploitation in the area. The continuous record of human indicator pollen and agricultural landscape suggests this area was suitable for habitation well before the studied time period, likely due to the ecosystem services it provided. Our proxy‐based study, combined with historical background, reveals a significant human impact on the terrestrial environment since the 14th century. Deficiency of trees in the northern outskirts of Riga during the 17th–19th century was likely. Anthropogenic activity has led to both deforestation and change in species composition. Our paleo records indicate recognizable human‐driven legacy in current seacoast landscape.
Sedimentary pollen offers excellent opportunities to reconstruct vegetation changes over past millennia. Number of different pollen taxa or pollen richness is used to characterise past plant ...richness. To improve the interpretation of sedimentary pollen richness, it is essential to understand the relationship between pollen and plant richness in contemporary landscapes. This study presents a regional‐scale comparison of pollen and plant richness from northern Europe and evaluates the importance of environmental variables on pollen and plant richness.
We use a pollen dataset of 511 lake‐surface pollen samples ranging through temperate, boreal and tundra biomes. To characterise plant diversity, we use a dataset formulated from the two largest plant atlases available in Europe. We compare pollen and plant richness estimates in different groups of taxa (wind‐pollinated vs. non‐wind‐pollinated, trees and shrubs vs. herbs and grasses) and test their relationships with climate and landscape variables.
Pollen richness is significantly positively correlated with plant richness (r = 0.53). The pollen plant richness correlation improves (r = 0.63) when high pollen producers are downweighted prior to estimating richness minimising the influence of pollen production on the pollen richness estimate. This suggests that methods accommodating pollen‐production differences in richness estimates deserve further attention and should become more widely used in Quaternary pollen diversity studies.
The highest correlations are found between pollen and plant richness of trees and shrubs (r = 0.83) and of wind‐pollinated taxa (r = 0.75) suggesting that these are the best measures of broad‐scale plant richness over several thousands of square kilometres.
Mean annual temperature is the strongest predictor of both pollen and plant richness. Landscape openness is positively associated with pollen richness but not with plant richness. Pollen richness values from extremely open and/or cold areas where pollen production is low should be interpreted with caution because low local pollen production increases the proportion of extra‐regional pollen.
Synthesis. Our results confirm that pollen data can provide insights into past plant richness changes in northern Europe, and with careful consideration of pollen‐production differences and spatial scale represented, pollen data make it possible to investigate vegetation diversity trends over long time‐scales and under changing climatic and habitat conditions.
Our results confirm that pollen data can provide insights into past plant richness changes in northern Europe, and with careful consideration of pollen‐production differences and spatial scale represented, pollen data make it possible to investigate vegetation diversity trends over long time‐scales and under changing climatic and habitat conditions.
Kokkuvõte
Taimede ja õietolmu liigirikkuse seosed Põhja‐Euroopas
Järvede ja soode settes leiduva õietolmu abil rekonstrueeritakse viimaste kümnete tuhandete aastate taimkatte muutusi. Soontaimede liigirikkust minevikus hinnatakse tihti erinevate õietolmutüüpide arvu alusel. Õietolmu ja taimede liigirikkuse seoste uurimine tänapäeva maastikes aitab sette õietolmuandmeid paremini tõlgendada. Käesolevas uuringus keskendume õietolmu ja taimede liigirikkuse seostele Põhja‐Euroopas ja hindame erinevate keskkonnategurite mõju nii taimede ja kui õietolmu liigirikkusele.
Uuringus kasutatav õietolmu andmestik pärineb 511 järve pinnasettest ja vaadeldav piirkond ulatub parasvöötmest tundrani. Soontaimede liigirikkuse hindamiseks kasutame andmeid kahest Euroopa taimede levikuatlasest. Võrdleme õietolmu ja taimede liigirikkust erinevates taimerühmades (tuultolmlejad vs. mitte tuultolmlejad, puud ja põõsad vs. rohttaimed) ja testime liigirikkuste seoseid kliimat ja maastiku struktuuri iseloomustavate tunnustega.
Leidsime, et õietolmu liigirikkus ja soontaimede liigirikkus on positiivselt korreleerunud (r = 0.53). Õietolmu ja taimede liigirikkuse korrelatsioon paraneb (r = 0.63) kui korrigeerime õietolmu andmestikku, vähendades suurte õietolmutootjate (näiteks kask ja mänd) osatähtsust. Siit järeldub, et kasutades õietolmu liigirikkuse hinnanguid mineviku andmetes, tuleks arvesse võtta liikidevahelised õielmu tootlikkuse erinevused.
Kõige tugevamad korrelatsioonid taimede ja õietolmu liigirikkuste vahel on puudel ja põõsastel (r = 0.83) ja tuultolmlejatel (r = 0.75). Meie tulemuste põhjal on just nende taimerühmade õietolmu liigirikkused sobivaimad taimede regionaalse liigirikkuse muutuste tuvastamiseks.
Nii õitolmu kui taimede liigirikkus on tugevasti seotud aasta keskmise õhutemperatuuriga. Maastiku avatus on positiivselt seotud õietolmu liigirikkusega, aga mitte taimede liigirikkusega. Täiesti avatud maastikes ja/või külma kliimaga aladel, kus kohalik õietolmu tootlikkus on väga madal, mõjutab õietolmu liigirikkuse hinnanguid regiooni välise õietolmu suur osatähtsus.
Kokkuvõtteks. Meie tulemused kinnitavad, et õietolmu andmed võimaldavad uurida taimede liigirikkuse muutusi Põhja‐Euroopas. Võttes arvesse õietolmu tootlikkuse erinevusi ja ruumilist skaalat, mida andmestik peegeldab, võimaldavad õietolmu andmed uurida taimede liigirikkuse pikaajalisi muutusi ja liigirikkuse seoseid mineviku kliima ja keskkonnatingimustega.
The hemispheric-scale climatic fluctuations during the Holocene have probably influenced the large Siberian rivers. However, detailed studies of the West Siberian Plain postglacial environmental ...change are scarce and the records of millennial-scale palaeohydrology are nearly absent. This paper presents the Holocene palaeoecological reconstruction based on the sedimentary record of Lake Svetlenkoye, located near the confluence of major Siberian rivers Ob and Irtysh. Postglacial history of flooding, dynamics of regional and local vegetation, sedimentation regime, geochemical changes and lake water pH were reconstructed based on multi-proxy studies. We used palaeobotanical (plant macrofossils, pollen, diatoms), geochemical (organic matter, total organic carbon and nitrogen content, carbon/nitrogen ratio) and chronological (14C dates, spheroidal fly-ash particle counts) methods. The studied sediment section started to accumulate ~11,400 cal. yr BP. The initial shallow water body was flooded by Ob River waters ~8100–8000 cal. yr BP as confirmed by a remarkable increase in the sedimentation rate and the accumulation rate of the aquatic vegetation proxies. The period of flooding coincides with the high humidity periods reconstructed from regional palaeobotanical records. About 6800–6700 cal. yr BP, the study site became isolated from the Ob River floodplain and remained a small lake until present. The diatom-based lake water pH estimates suggest fluctuations in the pH values during the Holocene, the recent decrease since 1960s being the most notable. The vegetation record revealed constant postglacial presence of tree taxa – Betula, Pinus and Picea – although in different pollen ratios and accumulation rates through time. The paludification of the surroundings occurred since ca. 8500 cal. yr BP.
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