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12 results for “modern pollen”
Climate reconstructions for the SMPDSv1 modern pollen data set
<p>The dataset contains estimates of three bioclimatic variables at modern pollen sites from the SMPDSv1 modern pollen data set (Harrison, 2019). The bioclimatic variables are mean temperature of the coldest month (MTCO), growing degree days above 0°C (GDD0), and an annual Moisture Index, defined as the ratio of annual precipitation to annual potential evapotranspiration (MI). Estimates of these bioclimatic variables were derived using geographically-weighted regression of gridded climate data in order to correct for elevation differences between each pollen site and the corresponding grid cell. The climatological data (mean monthly temperature, precipitation, and fractional sunshine hours) were derived from the CRU CL v2.0 gridded dataset of modern (1961-1990) surface climate at 10 arc minute resolution (~18 km) (New et al., 2002).Geographically- weighted regression (GWR) was carried out in ArcGIS (v10.3, ESRI, 2014). A fixed bandwidth kernel of 1.06 ° (~140km) was used in the GWR because this optimized model diagnostics and reduced spatial clustering of residuals relative to other bandwidths. The climate of each pollen site was then estimated based on its longitude, latitude, and elevation. MTCO was taken directly from the GWR regression. GDD0 were estimated from daily data using a mean-conserving interpolation of the monthly mean temperatures. MI was calculated for each pollen site using code modified from SPLASH v1.0 (Davis et al., 2017) based on daily values of precipitation, temperature and sunshine hours again obtained using a mean-conserving interpolation of the monthly values of each.</p>
Modern pollen data from the East Asian Pollen Database (EAPD): pollen, vegetation and climate relationship
<p>This is a modern pollen dataset of eastern Asia, in which a total of 1756 sample sites is selected from the original database EAPD (East Asian Pollen Database) which consists of 2858 samples. The sample types are mainly surface soil, moss, sediment top (lake, delta, peatland, river basin, reservoir and so on), and dust capture. The pollen data are mostly count numbers, but a few was originally given in percentage (marked with TRUE for proportion or percentage). We have checked pollen taxonomic nomenclature and combined some synonym pollen types from different original sources.</p> <p>This dataset includes only the samples collected in the areas under natural vegetation or land cover with low human disturbance, that the sites located in the agriculture areas or strong human intervention have been excluded. This screening procedure makes the pollen data readily available for biome and climate reconstructions. The contributors' original research concerning pollen-climate relationship from EAPD sources have been published in Zheng, et al. (2014 and 2008), which have revealed that pollen taxa in the dataset have significant relationship with climate variables. This dataset is potentially useful for multiscale paleovegetation and paleoclimate reconstruction studies in Asia. </p> <p>EAPD is developed and maintained by the Laboratory of Quaternary Science and Palynology in the School of Earth Sciences and Engineering, Sun Yat-sen University, Zhuhai, China.</p>
Data from: Modern pollen assemblages of the Neotropics
<p><strong>Aim:</strong> To provide a database of modern pollen abundances from a diversity of Neotropical locations.</p> <p><strong>Location:</strong> The Neotropics, especially western Amazonia, the Andes, The Galápagos, Central America, Puerto Rico, and Mexico.</p> <p><strong>Methods:</strong> Over a 30-year period, mud-water interface samples, moss polsters, soils, and pollen traps were used to assay modern pollen rain. Standard extraction methods were used and a minimum of 300 terrestrial pollen grains counted and identified per sample. Bioclimatic data were assigned to each location, and sexual traits and pollination syndromes are provided for some genera. A detrended correspondence analysis (DCA) shows the structuring of the data relative to mean annual temperatures (MAT), mean annual precipitation (MAP), and precipitation of the driest quarter (PDQ). Probability density functions of distances among samples are calculated within and between Holdridge Life Zones, based on sample DCA scores.</p> <p><strong>Results:</strong> The modern pollen of 636 locations are documented, with >500 pollen types identified. The dataset spans settings with MAT < 5oC to >25oC, and with MAP ranging from c. 500-5000 mm, and PDQ from 80 - 1500 mm. Ordination of the dataset provides evidence that assemblages differ according to temperature and precipitation, although historical biogeography also shapes pollen rains. The pollen grains of zoophilous species contribute important information to habitat descriptions, but they are under-represented in the dataset.</p> <p><strong>Main conclusions:</strong> The dataset covers a broad environmental range and can help inform biogeographic and paleoenvironmental interpretation of paleoecological records. Some caution in using the data is needed as the field of tropical palynology is maturing and the data gathered 30 years ago are less detailed than those gathered recently. Although anemophilous taxa tend to be over-represented in neotropical pollen spectra, the majority of pollen identified in each sample are from zoophilous species.</p>
A modern pollen dataset from lake surface sediments on the central-western Tibetan Plateau
<p>This is a modern pollen dataset on the central and western Tibetan Plateaubased on lake surface sediments of 90 lakes. The dataset includes pollen counts and pollen percentages for each lake sediment sample together with their locations (latitude, longitude and altitude) and climatic data. </p>
Data from: Modern pollen from small hollows reflects Athrotaxis cupressoides density across a wildfire gradient in subalpine forests of the Central Plateau, Tasmania, Australia
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Data from: Modern pollen assemblages of the Neotropics
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Modern pollen–plant diversity relationships inform palaeoecological reconstructions of functional and phylogenetic diversity in calcareous fens
<p>Predicting the trajectory of ongoing diversity loss requires knowledge of historical development of community assemblages. Long-term data from paleoecological 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.</p>
Data from: Patterns of modern pollen and plant richness across northern Europe
1. 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. 2. 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. 3. 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. 4. 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. 5. 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. 5. 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 timescales and under changing climatic and habitat conditions.
Fossilized pollen malformations as indicators of past environmental stress and meiotic disruption: insights from modern conifers
<p>Pollen malformations have been proposed as a paleoenvironmental stress proxy. However, the frequency and variability of pollen malformations under near-optimal conditions and environmental stress, as well as their developmental origins, remain unclear. To bridge these gaps, we compared pollen malformation frequencies and assemblages of 14 extant conifer genera of Pinaceae and Podocarpaceae producing saccate (winged) grains grown under near-optimal conditions. These baseline pollen yields were compared with those produced by <i>Pinus mugo</i> 'Columnaris' cultured under an abiotic stress—three experimentally heightened UV-B regimes proposed for the end-Permian crisis. We additionally reviewed previous cytological literature of abnormal microsporogenesis in conifers. Under near-optimal conditions, malformations comprise <3% of pollen yields in 12 out of 13 bisaccate genera and >10% of yields in the naturally trisaccate <i>Dacrycarpus dacrydioides</i>. We detected no phylogenetic pattern in malformation assemblages of the baseline comparisons. UV-B irradiated <i>P. mugo</i> produced significantly higher malformation frequencies and different assemblage compositions when compared with baseline bisaccate lineages. We propose that pollen malformations originate during the meiotic and tetrad stages of microsporogenesis and present a framework for the ontogeny of different malformation types seen in the fossil record. Malformations comprising >3% of bisaccate pollen yields can be used as a paleoenvironmental stress proxy, but rare, naturally trisaccate lineages are not suitable for such assessments. Furthermore, heightened UV-B not only increases pollen malformation production, but also alters the types of abnormalities trees produce. Different environmental stresses may therefore leave behind distinct fingerprints in the fossil record.</p>
Fossilized pollen malformations as indicators of past environmental stress and meiotic disruption: insights from modern conifers
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Data from: Patterns of modern pollen and plant richness across northern Europe
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Modern pollen–plant diversity relationships inform palaeoecological reconstructions of functional and phylogenetic diversity in calcareous fens
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