Exploring Holocene Changes in Palynological Richness in Northern Europe – Did Postglacial Immigration Matter?

In mid to high latitudes glacial and interglacial cycles have repeatedly changed the area available for plant growth. The speed at which plants are able to colonize areas at the onset of an interglacial is hypothesized to limit their distribution ranges even today (migrational lag). If the spread of plants would have been generally slow then plant diversity in previously glaciated areas would be expected to increase over time. We explore this hypothesis using results from six palynological investigations from two previously glaciated regions: central Sweden and north-eastern Germany. Rarefaction, slope of rank order abundance, and taxa accumulation plots were used to evaluate richness and evenness in pollen data in an attempt to separate richness from evenness. These analyses show little change in palynological richness for the northern sites throughout the Holocene. In contrast, the southern sites show an increase in richness and evenness during the early Holocene; this may be explained by the different initial conditions at the onset of the Holocene. A strong rise in palynological richness around 6000 and 1000 years ago at the southern sites can be attributed to the regional initiation of agriculture and major opening of the forest, respectively. For the northern sites there is no evidence for increased taxonomic diversity through time that could be due to delayed immigration of species.     

Fossil pollen as a record of past biodiversity

Quaternary pollen records may contribute uniquely to the understanding of present plant diversity. Pollen assemblages can reflect diversity at community and landscape scales but the time resolution of most studies does not match that of modern ecological studies. Because of the complicating effects of differential pollen productivity and dispersal, pollen records do not directly reflect equitability aspects of vegetation diversity. Vegetation diversity indices other than S (the total number of taxa) are therefore not appropriate for pollen assemblages. As a measure of the species richness palynological richness is biased by the lack of taxonomic precision, by a possible interference on pollen dispersal from vegetation structure and by pollen representation. The nonlinear relationship between species richness and pollen-taxa richness may be used in attempts to estimate past floristic richness from fossil pollen assemblages. Using a hypothetical example the strong effect of cover shifts in the vegetation affecting taxa with different representation (R_rel) values on observed palynological richness is demonstrated. It is suggested that estimates of relative pollen productivity should be used to guide the pollen sum on which pollen-type richness is estimated by rarefaction techniques and this approach is illustrated using a paired site study of late Holocene diversity dynamics. The need for a modern training set relating pollen-type richness to species richness, pollen productivity and vegetation structure is emphasized.     

Challenges in estimating past plant diversity from fossil pollen data: statistical assessment, problems, and possible solutions

Fossil pollen data from sediment cores may be used as a measure for past plant diversity. According to the theory of probability, palynological richness is positively related to the pollen count. In a low pollen count, only common taxa are detected, whereas rare taxa are only detected by chance. The detection of all pollen taxa requires a very high pollen count, which is time-consuming. In regular palynological investigations, the detected richness in pollen spectra varies with the pollen count. Rarefaction analysis estimates palynological richness in an exactly equal-sum count for all samples, so that comparison between samples is meaningful. However, the over-representation of some taxa suppresses the detection probability of rare taxa; low total pollen abundance in a sample enhances the detection probability of rare taxa and long-distance transported pollen grains. These factors bias the observed palynological richness and distort comparisons. Palynological richness in a pollen count proportional to its pollen influx may be one proxy for reconstructing diversity trends through time. The use of this proxy overcomes most problems encountered in rarefaction analysis, but is constrained by inaccuracy in estimating pollen influx due to the imprecise time control of sediment cores. Estimating palynological richness by mathematical methods may be another way of reconstructing pollen diversity. Pollen data tend to reflect diversity on a regional scale. Sites from small basins have the advantage of recording diversity at both local and regional scales, if the detection of each taxon is independent. By associating one site from a large basin with a series of sites from very small basins (e.g. forest-hollows), information about both regional and local diversity may be obtained. Entomophilous pollen taxa may have to be measured using a different strategy than anemophilous taxa.     

The role of landscape structure in determining palynological and floristic richness

The associations between floristic and palynological richness and landscape structure were studied based on modern pollen?Cvegetation data from a patchy cultural landscape in southern Estonia (northern temperate vegetation zone). Nine study sites (small lakes and their surrounding vegetation) represent land cover gradient from closed forest to semi-open vegetation. Floristic richness (number of species) and floristic richness of pollen types (number of pollen-equivalent taxa) were used to describe the vegetation within the radius of 250?m from the pollen sampling sites. Palynological richness was calculated to describe the modern pollen samples diversity. Landscape structure was estimated on the basis of landscape openness and three landscape diversity measures: richness of community patches, Simpson evenness of community patches and Simpson diversity of community patches. To study the effect of the spatial scale of landscapes on the vegetation?Clandscape and pollen?Clandscape associations, landscape structure was estimated within eight radii (250?C2,000?m) around each lake. The results showed that landscape openness was the most important determinant of both floristic richness and palynological richness in southern Estonia and that landscape diversity estimated by Simpson diversity index was also significantly associated with the richness estimates. Floristic and palynological richness were significantly positively correlated with landscape structure within the radii greater than 1,000?m from the pollen sampling sites, which is similar to the estimated Relevant Source Area of Pollen in southern Estonia. We conclude that within one floristic or climatic region, palynological richness gives reliable estimates about the variation in floristic richness and landscape structure; however, caution must be taken when comparing pollen-inferred vegetation diversities from different regions or when interpreting fossil pollen records from times with highly different vegetation associations.     

Prehistoric human impact on rainforest biodiversity in highland New Guinea

In the highlands of New Guinea, the development of agriculture as an indigenous innovation during the Early Holocene is considered to have resulted in rapid loss of forest cover, a decrease in forest biodiversity and increased land degradation over thousands of years. But how important is human activity in shaping the diversity of vegetation communities over millennial time-scales? An evaluation of the change in biodiversity of forest habitats through the Late Glacial transition to the present in five palaeoecological sites from highland valleys, where intensive agriculture is practised today, is presented. A detailed analysis of the longest and most continuous record from Papua New Guinea is also presented using available biodiversity indices (palynological richness and biodiversity indicator taxa) as a means of identifying changes in diversity. The analysis shows that the collapse of key forest habitats in the highland valleys is evident during the Mid–Late Holocene. These changes are best explained by the adoption of new land management practices and altered disturbance regimes associated with agricultural activity, though climate change may also play a role. The implications of these findings for ecosystem conservation and sustainability of agriculture in New Guinea are discussed.     

A survey of modern pollen and vegetation along an altitudinal transect in southern Georgia, Caucasus region

This paper describes the pollen representation of vegetation patterns along an altitudinal transect in the South Caucasus region. Surface sediments from eight small- to medium-sized lakes and wetlands were analysed for modern pollen, and the results analysed numerically using detrended correspondence analysis (DCA) and dichotomised ordination (TWINSPAN). Pollen spectra from the semidesert region have a clear palynological signal characterised by an abundance of Chenopodiaceae. Differentiation of oak forest, upper tree-line and subalpine communities is more difficult: all are dominated by arboreal pollen (AP) types. The authors propose a number of indicator pollen types and pollen threshold values that may assist in detecting tree-line variations and deforestation events in Holocene pollen diagrams.     

Pollen-vegetation richness and diversity relationships in the tropics

Tracking changes in biodiversity through time requires an understanding of the relationship between modern diversity and how this diversity is preserved in the fossil record. Fossil pollen is one way in which past vegetation diversity can be reconstructed. However, there is limited understanding of modern pollen-vegetation diversity relationships from biodiverse tropical ecosystems. Here, pollen (palynological) richness and diversity (Hill N₁) are compared with vegetation richness and diversity from forest and savannah ecosystems in the New World and Old World tropics (Neotropics and Palaeotropics). Modern pollen data were obtained from artificial pollen traps deployed in 1-ha vegetation study plots from which vegetation inventories had been completed in Bolivia and Ghana. Pollen counts were obtained from 15 to 22 traps per plot, and aggregated pollen sums for each plot were >?2,500. The palynological richness/diversity values from the Neotropics were moist evergreen forest?=?86/6.8, semi-deciduous dry forest?=?111/21.9, wooded savannah?=?138/31.5, and from the Palaeotropics wet evergreen forest?=?144/28.3, semi-deciduous moist forest?=?104/4.4, forest-savannah transition?=?121/14.1; the corresponding vegetation richness/diversity was 100/36.7, 80/38.7 and 71/39.4 (Neotropics), and 101/54.8, 87/45.5 and 71/34.5 (Palaeotropics). No consistent relationship was found between palynological richness/diversity, and plot vegetation richness/diversity, due to the differential influence of other factors such as landscape diversity, pollination strategy, and pollen source area. Palynological richness exceeded vegetation richness, while pollen diversity was lower than vegetation diversity. The relatively high global diversity of tropical vegetation was found to be reflected in the pollen rain.     

Integrated palaeoecological evidence for biodiversity at the floodplain-forest margin

This paper presents the results of a combined palynological and palaeoentomological investigation into the changing diversity of Holocene floodplain forest biota at Bole Ings in the lower reaches of the River Trent. The aim in combining the two techniques represents an attempt to overcome some of the inherent differences of scale and resolution which characterize different types of fossil species data. The two lines of ecofactual evidence, pollen and beetle remains indicate changes in the biodiversity of the floodplain, both in terms of the diversity and abundance of individual species, habitats and ecosystem structure. The results of the study demonstrate the potential of this approach in tracing the decline in plant and entomofaunal diversity at the floodplain forest margin. Although there are recognized limitations imposed by taphonomic uncertainties, taxonomic resolution and restricted ecological data, the combined results provide added details of variations in both species composition and structural diversity within the landscape. The results emphasize the need for multidisciplinary research design in palaeoecological investigations of biodiversity.     

Multitaxonomic diversity patterns along a desert riparian-upland gradient

Riparian areas are noted for their high biodiversity, but this has rarely been tested across a wide range of taxonomic groups. We set out to describe species richness, species abundance, and community similarity patterns for 11 taxonomic groups (forbs & grasses, shrubs, trees, solpugids, spiders, scarab beetles, butterflies, lizards, birds, rodents, and mammalian carnivores) individually and for all groups combined along a riparian-upland gradient in semiarid southeastern Arizona, USA. Additionally, we assessed whether biological characteristics could explain variation in diversity along the gradient using five traits (trophic level, body size, life span, thermoregulatory mechanism, and taxonomic affiliation). At the level of individual groups diversity patterns varied along the gradient, with some having greater richness and/or abundance in riparian zones whereas others were more diverse and/or abundant in upland zones. Across all taxa combined, riparian zones contained significantly more species than the uplands. Community similarity between riparian and upland zones was low, and beta diversity was significantly greater than expected for most taxonomic groups, though biological traits explained little variance in diversity along the gradient. These results indicate heterogeneity amongst taxa in how they respond to the factors that structure ecological communities in riparian landscapes. Nevertheless, across taxonomic groups the overall pattern is one of greater species richness and abundance in riparian zones, coupled with a distinct suite of species.     

鹤庆深钻孢粉记录揭示的气候变化与西南季风演化

本文在鹤庆深钻孢粉分析的基础上,把各孢粉类型划分成不同的孢粉生态组,结合孢粉多样性指数,系统重建云南鹤庆地区2.78 Ma以来的占气候演化所经历的8个大的阶段,与西南季风在滇西北地区8次大的变化相对应:即在2.729-2.608Ma和0.118Ma-11.83ka BP期间,气候整体湿润,冬、夏季降水的季节性较强,反映西南季风相对较强盛;1.447-0.342Ma期间,气候整体逐渐变湿,冷暖、干湿变化幅度逐渐变大,气候组合特征逐渐变复杂,反映西南季风逐渐增强,其波动幅度也逐渐变大,并于0.991-0.342Ma期间达到最强盛,其波动幅度也最大;而在2.780-2.729Ma、2.608-1.447Ma和0.342-0.118Ma期间,气候普遍相对温暖干旱,西南季风相对较弱.     

Comparison of lepidopteran larval communities among tree species in a temperate deciduous forest, Japan

Abstract.  1. The enormous diversity of phytophagous insects in forest canopies is hypothesised to be supported by the number of herbivorous species per host tree species or host specificity. It is therefore necessary to examine the effect of host plant species on compositional changes in the herbivore communities.
2. The lepidopteran larval communities were examined in the canopies of 10 tree species in a temperate deciduous forest of Japan. The phylogeny and leaf flush phenology of host plant species were taken into account as factors affecting the herbivore community assembly.
3. Examination of seasonal changes in the larval community structures on each tree species showed that larval species richness, abundance, and evenness decreased significantly from spring to summer. Larval species richness and abundance were characterised by family-level phylogenetic differences among tree species, whereas evenness was determined at a higher taxonomic level.
4. Compositional changes in the larval communities among tree species showed a remarkable pattern, with a phylogenetic effect at a high taxonomic level in spring, similar to evenness, but a phenological effect in summer. This suggests that host specificity could support the lepidopteran larval diversity in spring.
5. These results suggest that the differences in host utilisation of the herbivore, which reflects the phylogenetic effect of the host plants, can be important as a factor affecting the diversity of lepidopteran larval communities in temperate forests.     

Bat and bird diversity along independent gradients of latitude and tree composition in European forests

Species assemblages are shaped by local and continental-scale processes that are seldom investigated together, due to the lack of surveys along independent gradients of latitude and habitat types. Our study investigated changes in the effects of forest composition and structure on bat and bird diversity across Europe. We compared the taxonomic and functional diversity of bat and bird assemblages in 209 mature forest plots spread along gradients of forest composition and vertical structure, replicated in 6 regions spanning from the Mediterranean to the boreal biomes. Species richness and functional evenness of both bat and bird communities were affected by the interactions between latitude and forest composition and structure. Bat and bird species richness increased with broadleaved tree cover in temperate and especially in boreal regions but not in the Mediterranean where they increased with conifer abundance. Bat species richness was lower in forests with smaller trees and denser understorey only in northern regions. Bird species richness was not affected by forest structure. Bird functional evenness increased in younger and denser forests. Bat functional evenness was also influenced by interactions between latitude and understorey structure, increasing in temperate forests but decreasing in the Mediterranean. Covariation between bat and bird abundances also shifted across Europe, from negative in southern forests to positive in northern forests. Our results suggest that community assembly processes in bats and birds of European forests are predominantly driven by abundance and accessibility of feeding resources, i.e., insect prey, and their changes across both forest types and latitudes.     

Floristic diversity in the transition from traditional to modern land-use in southern Sweden a.d. 1800–2008

We aim to provide a long-term ecological analysis of land-use and floristic diversity in the transition from traditional to modern land-use management in the time a.d. 1800–2008 in southern Sweden. We use the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model to quantify land-cover changes on a regional scale at 20-year intervals, based on the fossil pollen record. Floristic richness and evenness are estimated using palynological richness and the Shannon index applied to the REVEALS output, respectively. We identified a transition period of 60?years between 1880 and 1940 when the total tree cover increased and the tree composition changed from deciduous to coniferous dominance. Within the shrinking area of open land, arable land taxa expanded, while the number and coverage of herbs in the remaining grasslands decreased. The succession from open grasslands to more tree-covered habitats initially favoured palynological richness, which reached its highest values during the first 40?years of the transition period. The highest REVEALS-based evenness was recorded in the time of traditional land-use and at the beginning of the transition period, reflecting higher habitat diversity at these time intervals. Our results support a more dynamic ecosystem management that changes between traditional land-use and phases of succession (<40?years) to promote floristic diversity. We have developed and applied a palaeoecological methodology that contributes realistic estimates to be used in ecosystem management.     

Taxonomic and functional diversity covary in rock pool microalgal communities despite their different drivers

Local biodiversity has traditionally been estimated with taxonomic diversity metrics such as species richness. Recently, the concept of biodiversity has been extended beyond species identity by ecological traits determining the functional role of a species in a community. This interspecific functional diversity typically responds more strongly to local environmental variation compared with taxonomic diversity, while taxonomic diversity may mirror more strongly dispersal processes compared with functional metrics. Several trait‐based indices have been developed to measure functional diversity for various organisms and habitat types, but studies of their applicability on aquatic microbial communities have been underrepresented. We examined the drivers and covariance of taxonomic and functional diversity among diatom rock pool communities on the Baltic Sea coast. We quantified three taxonomic (species richness, Shannon''s diversity, and Pielou''s evenness) and three functional (functional richness, evenness, and divergence) diversity indices and determined abiotic factors best explaining variation in these indices by generalized linear mixed models. The six diversity indices were highly collinear except functional evenness, which merely correlated significantly with taxonomic evenness. All diversity indices were always explained by water conductivity and temperature–sampling month interaction. Taxonomic diversity was further consistently explained by pool distance to the sea, and functional richness and divergence by pool location. The explained variance in regression models did not markedly differ between taxonomic and functional metrics. Our findings do not clearly support the superiority of neither set of diversity indices in explaining coastal microbial diversity, but rather highlight the general overlap among the indices. However, as individual metrics may be driven by different factors, the greatest advantage in assessing biodiversity is nevertheless probably achieved with a simultaneous application of the taxonomic and functional diversity metrics.     

Co-variation and indicators of species diversity: Can richness of forest-dwelling species be predicted in northern boreal forests?

Design and establishment of ecologically good networks of conservation areas often requires quick assessments of their biodiversity. Reliable indicators would be useful when doing such assessments. In order to explore the potential indicators for species richness in boreal forests, we studied (1) the co-variation of species richness and composition of species assemblages among beetles, polypores, birds and vascular plants, (2) the relationships between species richness and four boreal forest site types, (3) the relationship between species richness and forest physical structure and (4) the suitability of potential indicator groups within the four taxa to predict the species richness generally. The data show that there are probably not a single taxonomic or forest structural characteristic to be used as a general biodiversity indicator or surrogate for all the species. The correlations in species richness among the four taxa studied were low. However, group-specific indicators were obvious: forest site type was a good surrogate for vascular plant richness, and quantity and quality of dead wood predicted the species richness of polypores. The results support the view that different indicators shall be used for different forest types and taxonomic groups. These indicators should facilitate relatively rapid methods to assess biodiversity patterns at the forest stand level.     

Variation in the diversity of ducks along a gradient of environmental variability

Tramer (1969) proposed that communities regulated by competition in benign, predictable environments were characterized by (i) damped variation in evenness relative to variation in richness over time, and (ii) high evenness relative to communities regulated by variation in the abundance and diversity of resources in rigorous, unpredictable environments. To test whether patterns of variation in diversity could reflect the mechanisms proposed to regulate community structure, temporal and spatial changes in the diversity, richness and evenness of breeding duck communities were examined along a gradient of variability in wetland conditions using thirty-three years of duck census and climate data from the Canadian prairie and boreal forest regions. Temporal variation in evenness was independent of wetland habitat variability. Changes in richness were more parsimoniously explained by the appearance of ducks displaced (by drought) from rigorous, variable, wetland habitats into relatively benign ones, than by competition in benign areas. Evenness was not significantly higher for duck guilds in more constant wetland habitats, as predicted. Variation in richness, evenness and diversity, predicted by Tramer, do not provide a basis for distinguishing the factors that regulate duck community structure.     

Breeding Birds in Riparian and Upland Dry Forests of the Cascade Range

ABSTRACT We quantified breeding bird abundance, diversity, and indicator species in riparian and upland dry forests along 6 third- to fourth-order streams on the east slope of the Cascade Range, Washington, USA. Upland dry forest on southerly aspects was dominated by open ponderosa pine (Pinus ponderosa) and dry Douglas-fir (Pseudotsuga menziesii) plant associations. Upland mesic forest on northerly aspects was dominated by closed-canopy Douglas-fir or dry grand fir (Abies grandis) plant associations. Riparian overstory vegetation was dominated by black cottonwood (Populus trichocarpa) plant associations with a prominent hardwood tree and shrub component. We quantified bird assemblages, diversity, and abundance from parallel point transects on riparian and adjacent dry and mesic upslope forests. We detected 80 bird species from >12,000 point-transect observations during 1998–1999. Eighteen species accounted for 75% of all detections. Species richness and evenness were similar in all 3 forest types, with approximately 35 species and high evenness (0.85) in each forest type. Bird species assemblages differed among dry, mesic, and riparian forest types, with the greatest differences between riparian and both dry and mesic upland forests. Riparian forest had the greatest number (9) of strong characteristic, or indictor, species among the 3 forest types. Upland mesic forest was characterized by 7 indicator species. Upland dry forest had 4 indicator species. Our results indicate that current standards and guidelines for riparian buffers zones would allow for avian refuge and corridor functions along these streams. Forest managers could use our indicator species to predict and monitor shifts in upland forest species composition from thinning and prescribed burning practices that are used to reduce fuels in uplands and to reduce continuity of fire effects between riparian and upland zones.     

Factors influencing fish distribution and community structure in a small coastal river in southwestern Costa Rica

We evaluated the relative importance of habitat size and diversity and distance from the ocean in explaining longitudinal patterns of fish distribution and community structure (species richness, evenness, and diversity) in the lower 5 km of the Rio Claro. The Rio Claro is a small coastal river in Corcovado National Park, southwestern Costa Rica, with a depauperate freshwater fish fauna. We observed 22 species in pools, 19 of which occured during quantitative sampling. Most of these species probably spent part of their lives in the Pacific Ocean. We observed no species in riffles, although these habitats were common and several taxa (e.g., Gobiesocidae, Gobiidae) were adapted for life in fast turbulent water. Fish abundance, and species richness, evenness, and diversity were highest near the ocean, where high tides influenced river levels and salinity. Eight species were not observed further than 2900 m from the ocean, whereas 6 species were not encountered in samples nearest the ocean; the remaining 8 species were present throughout the study area. Distance from the ocean was a better predictor of fish abundance and community structure than were pool width, pool depth, pool surface area, pool volume, amount of cover present, substrate diversity, or depth diversity. Based in qualitative comparisons of our data with previously published data from 1980–1986, the fish assemblage of the Rio Claro is persistent in both species composition and relative abundance.     

Changes in the relative abundance of Polyarthra vulgaris and P. dolichoptera,following the elimination of fish

In the last decade palynological investigations of the sediments of large lakes in the USSR (Ladoga, Onega, Kubenskoye, Vozhe, Lacha, Beloye) and the Baltic Sea have been carried out. Limnic and marine sediments are notable for their high pollen and spore concentrations and pollen diagrams from these deposits have a regional significance. The diagrams from Lakes Onega and Ladoga belong to the Kola-Karelian type while the sediments of Lacha, Vozhe, Kubenskoye and Beloye belong to the North-Russian type (Neustadt 1957). Three types of Holocene pollen diagrams are registered for the Baltic Sea. Modern and fossil pollen spectra reflect the composition of the zonal vegetation. Late-glacial sediments are found in several profiles of lake and sea deposits. Holocene deposits are divided into eight stratigraphic zones: Late-glacial sediments (DR₂-Al-DR₃) and Post-glacial sediments (PB, BO, AT, SB, SA). The zonations of lake and sea sediments can be clearly correlated.     

Coastal dune vegetation and pollen representation in south Buenos Aires Province, Argentina

Aim To establish the relationship between coastal dune vegetation and its pollen representation as an aid to interpret Holocene vegetation dynamics and environmental changes from pollen assemblages. Location The study area is situated on the temperate Atlantic coast of south Buenos Aires Province, Argentina (c. 39° S and 61°20′ W). Methods The vegetation of the active dune area adjacent to the beach was described on the basis of its floristic composition from 25 plots. Classification of the vegetation into distinct zones was carried out by cluster analysis. Surface samples were collected from each vegetation stand and analysed for their pollen composition. Pollen percentage data were analysed using principal components analysis in order to investigate the degree to which the different vegetation units can be distinguished by their pollen spectra. Pollen–vegetation relationships for selected taxa were explored using simple scatter plots and indices of association, under‐ and over‐representation. Indices of floristic diversity and palynological richness were used to assess the representation of the vegetation in the pollen spectra. Results and conclusions Five vegetation zones are defined on the basis of species composition and their quantitative variation: back shore, mobile dunes, slacks, semi‐fixed and fixed dunes. Pollen assemblages from back shore, mobile dunes and slacks are clearly differentiated from semi‐fixed and fixed dunes. Pollen assemblages differ considerably from the associated vegetation composition. Major discrepancies are caused by large differences in pollen and vegetation proportion of Hyalis argentea and Discaria americana. There is a considerable proportion of non‐local pollen in every spectrum. Pollen representation in the coastal dunes at Monte Hermoso is influenced by differences in pollen production, dispersal and preservation of individual taxa as well as by the spatial distribution of the vegetation, the topography of the dune system and the wind pattern. The pollen–vegetation relationship established in this study has important implication for understanding and interpreting fossil pollen records from coastal dune environments.