Vivian A. Felde

Modern pollen–plant richness and diversity relationships exist along a vegetational gradient in southern Norway

The relationships between modern pollen and floristic plant richness, diversity and evenness are assessed using pollen assemblages and associated vegetation data from 52 lakes along an elevational and vegetational gradient in the Setesdal valley of south-central Norway. Various data transformations were applied to minimise bias in the vegetation and pollen datasets. Plant species were transformed to their pollen or spore equivalents to reduce taxonomic biases. Pollen counts were transformed using Andersen’s general pollen-representation values for northern European trees and shrubs and the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model with pollen-productivity estimates (PPEs) appropriate for Setesdal to minimise pollen-representation bias. Pollen count-size bias (before or after transformation) was eliminated by rarefaction analysis based on bootstrap resampling. Richness and diversity were quantified using Hill numbers (N0, N1, N2), and evenness was estimated as the ratios of N0, N1 and N2. Diversity partitioning was used to estimate β diversity. The strongest correlations between pollen and plant richness and diversity are with pollen counts transformed using Andersen’s representation values and rarefied to a common count size and with plants transformed to their pollen equivalents. However, if sites from the low-alpine zone are excluded where there are high values of far-transported tree pollen, the richness and diversity relationships are also statistically significant for untransformed pollen data and plants transformed into their pollen equivalents. The effects of data transformation on diversity partitioning and estimates of β diversity are explored. We demonstrate that there are statistically significant positive relationships between pollen and plant richness and diversity along the entire elevational gradient after transforming the datasets to minimise biases due to taxonomic differences, differential pollen representation, and pollen-count size, and similar significant positive relationships along the forested parts of the gradient (nemoral, boreonemoral, southern boreal, middle boreal) after transforming the datasets to minimise biases due to taxonomic differences and pollen-count size.

The relationship between vegetation composition, vegetation zones and modern pollen assemblages in Setesdal, southern Norway

Reconstructing and interpreting past vegetation composition can be enhanced by studying modern pollen samples and contemporary vegetation. Here, we compare pollen in surface sediments from 52 medium-sized lakes with the surrounding vegetation along an elevational gradient covering six major vegetation zones in south-central Norway. The aims are to detect how well the vegetational composition and terrestrial pollen assemblages distinguish the major vegetation zones, whether the pollen composition in surface-sediment samples reflects the composition of the surrounding vegetation and whether aquatic pollen and spores reflect the major vegetation zones. We use multivariate classification trees, ordination and co-correspondence analysis to address these questions. We show that it is possible to separate the major zones using terrestrial pollen assemblages and using plant species in the vegetation reasonably well, whereas aquatic pollen and spores poorly reflect the zones. Surprisingly, the terrestrial pollen assemblages separate the zones better than vegetational composition does. The compositional match between the pollen assemblages and surrounding vegetation is consistent for sites along the elevational gradient within the forested zones, but deteriorates in increasingly open vegetation zones. Our results are consistent with other investigations of modern pollen–vegetation relationships. Careful interpretation of past vegetation from pollen assemblages is needed when the vegetation is treeless because of a larger potential pollen-source area and hence a higher proportion of long-distance dispersed pollen in open areas.

Biodiversity trends within the Holocene

There is a rapidly emerging interest in detecting and understanding biodiversity trends during the ‘Anthropocene’ in response to human stressors and climate change. Surprisingly few studies have, however, considered trends in biodiversity during the preceding Holocene. Here, we present general trends in terrestrial alpha- and beta-diversity and biomass for the four main ecological phases (protocratic, mesocratic, Homo sapiens, oligocratic) of the Holocene in north-west Europe based on palynological data at the meta-community scale. Alpha- and beta-diversity decreased in the protocratic, showed little change in the mesocratic, decreased in the oligocratic, and increased markedly in the Homo sapiens phase. Biomass was maximal in the mesocratic. Biodiversity changes in the last 200 years (‘Anthropocene’), as detected from palynological data, are small compared with the changes over the Holocene. There are minor decreases in α-diversity, spatial β-diversity and biomass and a slight increase in temporal β-diversity at sites on fertile soils. This analysis is designed to encourage ecologists and biogeographers interested in the ‘Anthropocene’ to extend the time-scale of their analyses and to consider whether ‘Anthropocene’ biodiversity trends are a simple continuation of trends in the late Holocene or whether recent ‘Anthropocene’ trends deviate from the long-term Holocene trends. Hopefully, it will also stimulate palaeoecologists to consider Holocene biodiversity trends in different geographical areas and different organism groups and ecological systems.

Long-term vegetation stability in northern Europe as assessed by changes in species co-occurrences

Background: The effect of the anticipated climate change on the stability of vegetation and the factors underlying this stability are not well understood. Aims: Our objective was to quantify long-term vegetation changes in a range of habitats in northern Europe by exploring species co-occurrences and their links to diversity and productivity gradients. Methods: We re-sampled vegetation in 16 arctic, mountain and mire sites 20 to 90 years after the original inventories. A site-specific change in species assemblages (stability) was quantified using species co-occurrences. Using a randomisation test we tested whether the changes observed were significantly greater than those expected by chance. Relationships between patterns in vegetation stability and time between surveys, numbers of plots, or species diversity and proxies for productivity, were tested using regression analysis. Results: At most sites the changes in species co-occurrences of vascular plants and bryophytes were greater than those expected by chance. The changes observed were found to be unrelated to gradients in productivity or diversity. Conclusions: Changes in species co-occurrences are not strongly linked to diversity or productivity gradients in vegetation, suggesting that other gradients or site-specific factors (e.g. land use or species interactions) may be more important in controlling recent compositional shifts in vegetation in northern Europe.

Are diversity trends in western Scandinavia influenced by post-glacial dispersal limitation?

Co-ordinating Editor: Thomas Giesecke Abstract Questions: What are the latitudinal diversity patterns in Scandinavia over the last 8 ka? Have they been consistent over time? What are the longterm diversity trends at different sites? Is there a consistent rateofchange between sites? Location: Thirty sites in Norway, two sites in northwest Sweden. Methods: Pollen 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 Hill′s effective species numbers N0, N1 and N2. Diversity relationships in time and along latitude are assessed using ANCOVA. Linear regression is used to investigate siteindependent longterm trends. Patterns in the regression slopes are investigated between vegetation zones and along the latitudinal gradient. Results: The latitudinal pattern of decreasing diversity with increasing latitude existed over the last 8 ka, although for the number of effectively common (N1) and abundant (N2) pollen taxa the relationship was slightly weaker between 8–6 ka. Longterm trends show that diversity increases at most sites over time. However, the magnitude and rateofchange vary between sites. Highest rateofchange in N0 over time is observed in southern sites, although the spatial relationship of rateofchange is not statistically significant. Conclusions: The 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 rateofchange, and the general patterns of increasing diversity over time are consistent with the hypothesis of postglacial (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 2–1 ka BP diversity patterns have probably been increasingly affected by human land use.