BackgroundPhylogeny-based assessments of Holocene vegetation are rare. They are important for understanding eco-evolutionary dynamics of species assembly under environmental changes and ever-increasing anthropogenic pressure.AimsTo reveal any spatio-temporal variation in the phylogenetic dispersion (PD, mean phylogenetic distance of co-occurring taxa) in angiosperm pollen assemblages in mainland Europe and North America and their relationship with regional climate and anthropogenic influence.MethodsUsing 12,250 and 14,898 fossil pollen assemblages from Europe and North America, respectively, we analysed family level spatio-temporal variation in Holocene PD by hierarchical generalised linear models and tested its concordance with Holocene climate and anthropogenic influence by Procrustes randomisation tests.ResultsHolocene PD exhibited a reverse-humped pattern along latitudinal gradients in both continents. A longitudinal pattern in Holocene PD in Europe was not pronounced. However, in North America, it declined irregularly along the gradient from west to east. PD in both continents varied significantly during the early- and late-Holocene in concordance with Holocene climate and anthropogenic influences. Complex fine-scale spatio-temporal variations in PD were also pronounced.ConclusionProfound and complex Holocene eco-evolutionary changes in angiosperm assemblages in Europe and North America correspond largely to changes in extrinsic and intrinsic drivers and mechanisms of ecological changes. Future environmental changes of similar or a greater magnitude may drive further changes in the phylogenetic structure of the assemblages. A more detailed study of their eco-evolutionary dynamics requires detailed spatio-temporal assemblage data with precise taxonomy and census, and a detailed and robust species-level phylogeny of the species pool.

Abstract Spatio-temporal assessment of phylogenetic diversity gradients during the Holocene (past 12,000 years) provides an opportunity for a deeper understanding of the dynamics of species co-occurrence patterns under environmental fluctuations. Using two robust metrics of phylogenetic dispersion (PD) and 99 fossil pollen sequences containing 6557 samples/assemblages, we analyse spatio-temporal variation in PD of angiosperms and its relationship with Holocene climate in central Asia. Overall, PD throughout the Holocene decreases linearly with increasing latitude, except for a rise in mean nearest taxon distance from ca. 25 to 35° N. This indicates that phylogenetically divergent taxa decrease progressively with increasing latitude, leaving more phylogenetically closely related taxa in the assemblages, thereby increasing phylogenetic relatedness among the co-occurring taxa. The latitudinal gradient of PD has not been consistent during the Holocene, and this temporal variation is concordant with the Holocene climate dynamics. In general, profound temporal changes in the latitudinal PD toward higher latitudes implies that the major environmental changes during the Holocene have driven considerable spatio-temporal changes in the phylogenetic assembly of high-latitude angiosperm assemblages. Our results suggest that environmental filtering and the tendency of taxa and lineages to retain ancestral ecological features and geographic distributions (phylogenetic niche conservatism) are the main mechanisms underlying the phylogenetic assembly of angiosperms along the climate-latitudinal gradient. Ongoing environmental changes may pose future profound phylogenetic changes in high-latitude plant assemblages, which are adapted to harsh environmental conditions, and therefore are phylogenetically less dispersed (more conservative or clustered).

Controversies exist regarding the extent of past human influence on terrestrial ecosystems and the relative importance of human versus climatic factors in shaping Holocene vegetation. However, there has been no systematic examination of these issues at a global scale. Here we integrate palaeoecological, archaeological, and palaeoclimate data to assess the influence of humans and climate in driving patterns of past vegetation during the early and middle Holocene (8500 - 2000 years before present) as recorded by pollen-assemblage properties. We quantify and summarise the patterns of change in different properties from individual records to a global scale and assess the relative importance of humans and/or climate in influencing them. Additionally, we assess whether the internal relationships among these properties changed through time. While we find evidence that humans have high localized impact on vegetation dynamics in various regions and times periods, when considered globally, humans appear to be a secondary factor, during the early-to-mid Holocene. Our results underscore the value of merging multidisciplinary palaeodata to provide a holistic understanding of millennia-spanning relationships between humans, climate, and vegetation across different spatial scales.

Fossil pollen data are valuable for understanding past spatio-temporal variations in plant diversity. However, deducing robust patterns of fossil pollen-assemblage properties is challenging due to factors related to pollen production, dispersal, and fossilisation; sediment sampling; and nomenclature and taxonomy of the fossil pollen grains reflecting the vegetation that produced them. If the composition pattern of the most recent fossil pollen assemblage concords with those in modern or surface pollen assemblages from the same location(s), the pattern can be regarded as robust. Using recent (50-500 years) fossil pollen and surface pollen assemblages of angiosperms compiled from the same geographic area of Central Asia, we analyse spatial patterns in compositional turnover and phylogenetic dispersion. These are widely used to quantify different aspects of plant diversity. Despite differences in the data regarding spatial coverage, number of pollen records, and number of pollen taxa, the spatial pattern in the modern and fossil pollen-assemblage properties across climate zones is broadly similar. Especially, the latitudinal patterns of pollen-assemblage properties are strikingly similar between both data types. However, the degree of concordance varies according to the diversity metric being analysed, and the magnitudes of the metric may differ between both data types. When the data are compiled, processed, and standardised following consistent criteria and analysed using appropriate metrics and methods, spatial patterns in pollen-assemblage properties of fossil pollen data are as robust as those in surface pollen data (similar to modern vegetation). Therefore, regional patterns of compositional turnover and phylogenetic dispersion can be confidently inferred from older fossil assemblages through the Holocene.

Historical legacies influence present-day ecosystem composition and dynamics. It is therefore important to understand the long-term dynamics of ecosystems and their properties. Analysis of ecosystem properties during the Holocene using fossil pollen assemblages provides valuable insights into past ecosystem dynamics by summarising so-called pollen-assemblage properties (PAPs). Using 205 fossil pollen data-sets (records), we quantify eight PAPs [pollen-taxonomic richness, diversity, evenness, pollen-compositional turnover, pollen-compositional change, and rate of pollen-compositional change (RoC)] for the Asian continent at different spatial scales (in individual records, within and across climate-zones, and within the continent) and time (temporal patterns over the past 12,000 years). Regression tree (RT) partitioning of the PAP-estimates using sample-age as a sole predictor revealed the "change-point(s)" (time or sample-age of major change in a PAP). We estimated the density of RT and multivariate regression tree (MRT) change-points in 1,000-year time bins during the Holocene. Pollen-compositional turnover (range of sample scores along the first DCCA axis) and change (number of MRT partitions) in each record reveal gradual spatial variation across latitude and a decline with longitude eastward. Temporally, compositional turnover declines linearly throughout the Holocene at all spatial scales. Other PAPs are heterogeneous across and within spatial scales, being more detectable at coarser scales. RT and MRT change-point density is broadly consistent in climate-zones and the continent, increasing from the early- to mid-Holocene, and mostly decrease from the mid-Holocene to the present for all PAPs. The heterogenous patterns in PAPs across the scales of study most likely reflect responses to variations in regional environmental conditions, anthropogenic land-use, and their interactions over space and time. Patterns at the climate-zone and continental scales indicate a gradual but congruent decline in major PAPs such as compositional turnover, rate of compositional change, and major temporal compositional changes (MRT) during the Holocene, especially during recent millennia, suggesting that vegetation in Asia has become progressively more homogenous. Data properties (e.g., spatial distribution of the records, distribution of samples within the records, and data-standardisation and analytical approaches) may also have partly influenced the results. It is critically important to evaluate the data properties and the approaches to data standardisation and summarisation.

Pollen taxonomic harmonisation involves the standardisation of the nomenclature of pollen and fern spores with similar morphotypes at the determination level that is common to all grains or spores with that morphotype within the pollen sequence(s) of interest. Such harmonisation is required prior to subsequent investigations such as numerical analysis, comparing, mapping, synthesis, and environmental reconstruction involving several pollen sequences. Here we present two approaches to harmonisation. These are a ‘top-down’ and a ‘bottom-up’ approach. The bottom-up approach is preferred. It is based on the concept of the regional pollen flora for the sequence(s) in the spatial area(s) of study. We present bottom-up harmonisation tables for the continental or sub-continental scales developed for the Humans on Planet Earth (HOPE) project. The tables are for North America, Latin America, Europe, Asia (three parts), and Indo-Pacific. These harmonisations are project-specific and sequence-specific, relating to the geographical area and to the sequences in the area under consideration, both of which are linked to the research questions being addressed. A new bottom-up harmonisation with a consistent taxonomic level and nomenclature is needed when additional sequences or areas are added. However, the HOPE tables can serve as a starting point for further research involving multi-sequence analyses or syntheses.

AimPalaeoecological data are crucial for comprehending large-scale biodiversity patterns and the natural and anthropogenic drivers that influence them over time. Over the last decade, the availability of open-access research databases of palaeoecological proxies has substantially increased. These databases open the door to research questions needing advanced numerical analyses and modelling based on big-data compilations. However, compiling and analysing palaeoecological data pose unique challenges that require a guide for producing standardized and reproducible compilations. InnovationWe present a step-by-step guide of how to process fossil pollen data into a standardized dataset compilation ready for macroecological and palaeoecological analyses. We describe successive criteria that will enhance the quality of the compilations. Though these criteria are project and research question-dependent, we discuss the most important assumptions that should be considered and adjusted accordingly. Our guide is accompanied by an R-workflow-called FOSSILPOL-and corresponding R-package-called R-Fossilpol-that provide a detailed protocol ready for interdisciplinary users. We illustrate the workflow by sourcing and processing Scandinavian fossil pollen datasets and show the reproducibility of continental-scale data processing. Main ConclusionsThe study of biodiversity and macroecological patterns through time and space requires large-scale syntheses of palaeoecological datasets. The data preparation for such syntheses must be transparent and reproducible. With our FOSSILPOL workflow and R-package, we provide a protocol for optimal handling of large compilations of fossil pollen datasets and workflow reproducibility. Our workflow is also relevant for the compilation and synthesis of other palaeoecological proxies and as such offers a guide for synthetic and cross-disciplinary analyses with macroecological, biogeographical and palaeoecological perspectives. However, we emphasize that expertise and informed decisions based on palaeoecological knowledge remain crucial for high-quality data syntheses and should be strongly embedded in studies that rely on the increasing amount of open-access palaeoecological data.

Biological diversity is inextricably linked to community stability and ecosystem functioning, but our understanding of these relationships in freshwater ecosystems is largely based on short-term observational, experimental, and modelling approaches. Using a multidecadal diatom record for the past ca. 16 000 years from Lake Baikal, we investigate how diversity and palaeoproductivity have responded to climate change during periods of both rapid climate fluctuation and relative climate stability. We show dynamic changes in diatom communities during the past 16 000 years, with decadal shifts in species dominance punctuating millennial-scale seasonal trends. We describe for the first time in Lake Baikal a gradual shift from spring to autumnal diatom communities that started during the Younger Dryas and peaked during the Late Holocene, which likely represents orbitally driven ecosystem responses to long-term changes in seasonality. Using a multivariate classification tree, we show that trends in planktonic and tychoplanktonic diatoms broadly reflect both long-term climatic changes associated with the demise of Northern Hemisphere ice sheets and abrupt climatic changes associated with, for example, the Younger Dryas stadial. Indeed, diatom communities are most different before and after the boundary between the Early and Middle Holocene periods of ca. 8.2 cal kyr BP, associated with the presence and demise of Northern Hemisphere ice sheets respectively. Diatom richness and diversity, estimated using Hill's species numbers, are also shown to be very responsive to periods characterized by abrupt climate change, and using knowledge of diatom autecologies in Lake Baikal, diversity trends are interpreted in terms of resource availability. Using diatom biovolume accumulation rates (BVARs; µm3 cm−2 yr−1), we show that spring diatom crops dominate palaeoproductivity for nearly all of our record, apart from a short period during the Late Holocene, when autumnal productivity dominated between 1.8–1.4 cal kyr BP. Palaeoproductivity was especially unstable during the Younger Dryas, reaching peak rates of 18.3 × 103 µm3 cm−2 yr−1 at ca. 12.3 cal kyr BP. Generalized additive models (GAMs), which explore productivity–diversity relationships (PDRs) during pre-defined climate periods, reveal complex relationships. The strongest statistical evidence for GAMs were found during the Younger Dryas, the Early Holocene, and the Late Holocene, i.e. periods of rapid climate change. We account for these differences in terms of climate-mediated resource availability, and the ability of endemic diatom species in Lake Baikal to adapt to extreme forms of living in this unique ecosystem. Our analyses offer insight into how productivity–diversity relationships may develop in the future under a warming climate.

Global vegetation over the past 18,000 years has been transformed first by the climate changes that accompanied the last deglaciation and again by increasing human pressures; however, the magnitude and patterns of rates of vegetation change are poorly understood globally. Using a compilation of 1181 fossil pollen sequences and newly developed statistical methods, we detect a worldwide acceleration in the rates of vegetation compositional change beginning between 4.6 and 2.9 thousand years ago that is globally unprecedented over the past 18,000 years in both magnitude and extent. Late Holocene rates of change equal or exceed the deglacial rates for all continents, which suggests that the scale of human effects on terrestrial ecosystems exceeds even the climate-driven transformations of the last deglaciation. The acceleration of biodiversity change demonstrated in ecological datasets from the past century began millennia ago.

Past vegetation and biodiversity dynamics, reconstructed using palaeoecological methods, can contribute to assessing the magnitude of the current biodiversity crisis and anticipating future risks and challenges. Among the different palaeoecological techniques, pollen analysis is probably the most widely used to reconstruct vegetation and plant diversity changes through time. Such reconstructions demand robust and comprehensive calibration studies addressing the pollen representation of extant vegetation to be sound. However, calibration studies are rare in the Mediterranean biodiversity hotspot, particularly regarding plant diversity. Here, we contribute to filling this gap by investigating the modern pollen signature of Mediterranean vegetation across a large environmental gradient in northern Greece. At each sampling site ( n = 61), we quantitatively compared the composition and diversity of plant (vegetation surveys) and pollen assemblages (moss/topsoil samples) using numerical techniques. Further, we compared these terrestrial pollen assemblages with those from lake sediment surface samples of the same region. We found an overall good match between plant and pollen assemblages, with maquis and mixed deciduous forest displaying particularly distinct pollen signatures. In contrast, the high regional importance of pines and oaks and their large pollen production blurred the pollen representation of other forested vegetation types and of shrublands and grasslands. Plant and pollen richness and their evenness showed similar declining trends with increasing altitude, but plant and pollen evenness bore a better match than richness. A more detailed vegetation-specific view on the data suggests that pine pollen seriously affected pollen richness and evenness in most of the pine-dominated stands. Lastly, our results suggest a rather straightforward application of vegetation-pollen relationships from moss/topsoil samples to interpret pollen assemblages from lakes in Mediterranean settings.

Terrestrial palaeo-temperature data are of great value in improving our understanding of past climate and they provide a basis for evaluating climate simulations. Such data are, however, poorly constrained for long time scales. In addition to the scarcity of high-quality continuous time-series, finding proxies with a clear response to past temperature changes and developing appropriate reconstruction methods are major challenges. We present a new and robust method ? Locally-weighted Weighted-average partial least squares (LW-WAPLS) to reconstruct quantitative temperature changes based on a high-resolution 1.74-Ma pollen record from the Zoige Basin on the eastern Tibetan Plateau, where the vegetation today is mainly controlled by temperature. The reconstructed mean annual (MAT) and warmest month (MTWM) temperatures reveal a general cooling trend with two major shifts at-1.54 and 0.62 Ma BP, and regular glacial-interglacial variability ranging from4 to 2 ?C and from 8 to 16 ?C, respectively. They indicate-4?5 ?C (MAT) and 5?6 ?C (MTWM) magnitudes of glacial-interglacial temperatures. Both statistical and ecological evaluations validate the reliability of the reconstructions. The reconstructions provide important insights into the spatial aspects of long-term terrestrial temperature change. LW-WAPLS shows advantages over both the traditional modern analogue technique and non-linear transfer-function methodologies such as WAPLS for reconstructing the broad-scale climate changes for the Zoige Basin, by combining the strength of both methods. The LW-WAPLS approach potentially provides a robust tool to develop pollen-based climate reconstructions over long time-scales. Superscript/Subscript Available

AbstractDynamics in the rate of compositional change (rate-of-change; RoC) of biotic or abiotic assemblages preserved in palaeoecological sequences, are thought to reflect changes due to exogenous drivers such as climate and human forcing as well as endogenous factors linked to local dynamics and biotic interactions. However, changes in sedimentation rates and sampling strategies can result in an uneven distribution of time intervals and are known to affect RoC estimates. Furthermore, there has been relatively little exploration of the implications of these challenges in quantifying RoC in palaeoecology.Here, we introduce R-Ratepol – an easy-to-use R package – that provides a robust numerical technique for detecting and summarising RoC patterns in complex multivariate time-ordered stratigraphical sequences. First, we compare the performance of common methods of estimating RoC and detecting periods of high RoC (peak-point) using simulated pollen-stratigraphical data with known patterns of compositional change and temporal resolution. In addition, we propose a new method of binning with a moving window, which shows a more than 5-fold increase in the correct detection of peak-points compared to the more traditional way of using individual levels.Next, we apply our new methodology to four representative European pollen sequences and show that our approach also performs well in detecting periods of significant compositional change during known onsets of human activity, early land-use transformation, and changes in fire frequency.Expanding the approach using R-Ratepol to open-access paleoecological datasets in global databases, such as Neotoma, will allow future palaeoecological and macroecological studies to quantify major changes in biotic composition or in sets of abiotic variables across broad spatio-temporal scales.

Islands are among the last regions on Earth settled and transformed by human activities, and they provide replicated model systems for analysis of how people affect ecological functions. By analyzing 27 representative fossil pollen sequences encompassing the past 5000 years from islands globally, we quantified the rates of vegetation compositional change before and after human arrival. After human arrival, rates of turnover accelerate by a median factor of 11, with faster rates on islands colonized in the past 1500 years than for those colonized earlier. This global anthropogenic acceleration in turnover suggests that islands are on trajectories of continuing change. Strategies for biodiversity conservation and ecosystem restoration must acknowledge the long duration of human impacts and the degree to which ecological changes today differ from prehuman dynamics.

Low- and high-latitude influences have shaped the evolution of the Tibetan Plateau climate over the past 1.74 million years.

Abstract. Biological diversity is inextricably linked to community stability and ecosystem functioning, but our understanding of these relationships in freshwater ecosystems are largely based on short-term observational, experimental, and modelling approaches. Using a multidecadal diatom record for the past 15,800 years from Lake Baikal, we investigate how three ecosystem components – diversity, productivity, and stability – have responded to climate changes on long-timescales. In addition, we investigate how the relationships between diversity, productivity and stability have changed through time in response to these changes. We show that abrupt changes in diatom stability and diversity during the late glacial and early Holocene are part of a network of responses across southern Siberia as a result of extrinsically-forced climate instability. Productivity – diversity relationships were strongly coupled during the late glacial, which we suggest is linked to resource availability, but showed little relationship during the Holocene, perhaps due to few resources being limiting for extended periods of time. For example, periods of low diatom diversity are associated with peak palaeoproductivity, and coincide with climate disturbance events. Such strong negative relationships may reflect resources becoming limiting during palaeoproductivity, leading to monospecific diatom blooms. While species fluctuations respond rapidly to changing resources during much of the Holocene, the ecosystem function of primary production appears to be relatively resilient. Our study provides important perspectives on lake community stability and ecosystem function in relation to rapid periods of climate change.

Aim We aim to use species attributes such as distributions and indicator values to reconstruct past biomes, environment, and temperatures from detailed plant-macrofossil data covering the late glacial to the early Holocene (ca. 14-9 ka). Location Krakenes, western Norway. Methods We applied attributes for present-day geographical distribution, optimal July and January temperatures, and Ellenberg indicator values for plants in the macrofossil data-set. We used assemblage weighted means (AWM) to reconstruct past biomes, changes in light (L), nitrogen (N), moisture (F), and soil reaction (R), and temperatures. We compared the temperature reconstructions with previous chironomid-inferred temperatures. Results After the start of the Holocene around 11.5 ka, the Arctic-montane biome, which was stable during the late-glacial period, shifted successively into the Boreo-arctic montane, Wide-boreal, Boreo-montane, Boreo-temperate, and Wide-temperate biomes by ca. 9.0 ka. Circumpolar and Eurasian floristic elements characteristic of the late-glacial decreased and the Eurosiberian element became prominent. Light demand (L), soil moisture (F), nitrogen (N), and soil reaction (R) show different, but complementary responses. Light-demanding plants decreased with time. Soil moisture was relatively stable until it increased during organic soil development during the early Holocene. Soil nitrogen increased during the early Holocene. Soil reaction (pH) decreased during the Allerod, but increased during the Younger Dryas. It decreased markedly after the start of the Holocene, reaching low but stable levels in the early Holocene. Mean July and January temperatures show similar patterns to the chironomid-inferred mean July temperature trends at Krakenes, but chironomids show larger fluctuations and interesting differences in timing. Conclusion Assigning attributes to macrofossil species is a useful new approach in palaeoecology. It can demonstrate changes in biomes, ecological conditions, and temperatures. The late-glacial to early-Holocene transition may form an analogue for changes observed in the modern arctic and in mountains, with melting glaciers, permafrost thaw, and shrub encroachment into tundra.

The Eemian interglacial represents a natural experiment on how past vegetation with negligible human impact responded to amplified temperature changes compared to the Holocene. Here, we assemble 47 carefully selected Eemian pollen sequences from Europe to explore geographical patterns of (1) total compositional turnover and total variation for each sequence and (2) stratigraphical turnover between samples within each sequence using detrended canonical correspondence analysis, multivariate regression trees, and principal curves. Our synthesis shows that turnover and variation are highest in central Europe (47–55°N), low in southern Europe (south of 45°N), and lowest in the north (above 60°N). These results provide a basis for developing hypotheses about causes of vegetation change during the Eemian and their possible drivers.

QuestionsWhat are the latitudinal diversity patterns in Scandinavia over the last 8ka? Have they been consistent over time? What are the long-term diversity trends at different sites? Is there a consistent rate-of-change between sites? LocationThirty sites in Norway, two sites in north-west Sweden. MethodsPollen data from these 32 lakes. The sites lie within six of the vegetation zones of Moen (1998). The data are used to estimate pollen diversity using Hills effective species numbers N0, N1 and N2. Diversity relationships in time and along latitude are assessed using ANCOVA. Linear regression is used to investigate site-independent long-term trends. Patterns in the regression slopes are investigated between vegetation zones and along the latitudinal gradient. ResultsThe latitudinal pattern of decreasing diversity with increasing latitude existed over the last 8ka, although for the number of effectively common (N1) and abundant (N2) pollen taxa the relationship was slightly weaker between 8-6ka. Long-term trends show that diversity increases at most sites over time. However, the magnitude and rate-of-change vary between sites. Highest rate-of-change in N0 over time is observed in southern sites, although the spatial relationship of rate-of-change is not statistically significant. ConclusionsThe constant increase in diversity over time may reflect additional taxa arriving and changes in abundances. Most sites change in the same direction, but at different rates and magnitudes. There is no clear spatial pattern in rate-of-change, and the general patterns of increasing diversity over time are consistent with the hypothesis of post-glacial (Holocene) dispersal limitation. Drivers of these changes have not been rigorously investigated, but our results suggest that environmental and historical processes are not mutually exclusive. During the last 2-1ka BP diversity patterns have probably been increasingly affected by human land use.