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.

Study area: 

Pollen and plant data were collected from 34 calcareous spring fens in Estonia. Of the 34 sites, seven open and seven forested sites are located in southern Estonia (South region), with ten open and eight forested sites located in Saaremaa Island (West region). The sites distributed between the two regions were located at least 2.5 km apart but the open and forested fens were sampled relatively close to each other (60 to 300 m apart).

Modern pollen data:

Moss polster samples (size of 5 cm in radius) were collected to determine the modern pollen assemblage from each of the fen sites (n=34). The moss samples consisted of a relatively wide range of species, most abundant being Calliergonella cuspidata, Plagiomnium ellipticum, Scorpidium cossonii, Campylium stellatum, Sphagnum subnitens. In the majority of sites, the mosses did not form tense tussocks but the structure was relatively loose. For pollen analysis, only the green (living) upper part of the mosses was collected. Moss sample collection was synchronized with vegetation inventories. All the sampling and preservation of moss polsters followed the Crackles Bequest Project protocol (Bunting et al., 2013). samples were treated with HCl and 10 % KOH followed by standard acetolysis method (Berglund and Ralska-Jasiewiczowa, 1986; Fægri and Iversen, 1989). Samples were examined under a light microscope at magnifications of 250, 400 and 1000x. Approximately 1000 terrestrial and aquatic pollen grains per moss polster and sediment pollen sample were aimed (min = 920; max = 1115). Detailed information on site vegetation type and geographical loaction is provided in data file.

Vegetation data:

Vegetation survey around each moss sample was carried out at the end of the flowering season during the second half of July and August  (2017 and 2018). Survey timing and vegetation recording methodology followed Crackles Bequest Project protocol (Bunting et al., 2013), which is designed to produce vegetation abundance estimates in different distance classes in concentric areas around the pollen sample. Although vegetation mapping was conducted relatively late, only a few spring-flowering ephemerals (e.g., Anemone) might have been overlooked. At each site, vegetation was recorded within a 100 m radius around the moss sample (Figure 1). Within a 10 m radius, the vegetation was described in detail in five concentric areas at radii of 0.5 m, 1.5 m, 3 m, 6 m, and 10 m. In each 10 m area, twenty-one 1 × 1 m quadrats were systematically placed: one quadrat on top of the moss sample, four quadrats positioned at each cardinal direction at 1 m, 2.25 m and 4.5 m from the central moss polster, and eight quadrats at 8 m distance from the centre (Figure 1). In each 1 x 1 m quadrat, the percentage cover of all vascular plants was recorded. Additionally, species not occurring in the quadrats but within the circles were recorded. Between 10 – 100 m, vegetation types were mapped by using orthophoto maps (incl. infrared orthophoto maps) and field-work observations. The vegetation types were delimited keeping in mind the pollen perspective – for example, single trees and shrubs in open fen areas were mapped as separate entities because their role in pollen signal is potentially high (Bunting et al., 2013). Species composition of each vegetation type in 100 m radius was characterized in the field.  For woody taxa, the percentage cover of each species was estimated. For herbaceous taxa, the Braun-Blanquet cover-abundance scale was used (Braun-Blanquet, 1964). The abundances were then translated to cover estimates within each vegetation type as follows: ± 0.01 %; 1 – 5 %; 2 – 10 %; 3 – 25 %; 4 – 50 %; 5 – 75 %.

Data files under these names  “Fen_modern_pollen_&_vegetation_data.xlsx” contain: 1) Modern pollen data (counts) from 34 spring fens. Study reagion South (Karula regioon) and West (Saaremaa Island), and site vegetation type open vs forested 2) geographical coordinates of site location. 3) Modern vegetation data collected from 34 spring fens in nine different scales (radii) of vegetation estimate.