Modern Pollen–Plant Diversity Relationships Inform Palaeoecological Reconstructions of Functional and Phylogenetic Diversity in Calcareous Fens

Triin Reitalu,Ansis Blaus,Pille Gerhold,Inga Hiiesalu,Siim Veski,Jhonny Capichoni Massante

doi:10.3389/fevo.2020.00207

Abstract

Predicting the trajectory of ongoing diversity loss requires knowledge of historical development of community assemblages. Long-term data from palaeoecological 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.

Highlights

Identifying the drivers underlying biodiversity changes is among the key research questions both in ecology (Vellend et al, 2017) and palaeoecology (Birks et al, 2016b)
Results of Phylogenetic diversity (PD) reconstruction in Kanna fen exhibited significant clustering of woody taxa throughout the 9.2 ka when gymnosperms were excluded from the PD calculation but overdispersion was evident when gymnosperms were included in the reconstruction (Figure 7)
In a modern pollen-plant study from Estonian calcareous fens, our results suggest that while pollen of herbaceous taxa in fens reflects vegetation at local fen scale, the pollen of woody taxa is likely to reflect larger landscape scale forest vegetation

Summary

Introduction

Identifying the drivers underlying biodiversity changes is among the key research questions both in ecology (Vellend et al, 2017) and palaeoecology (Birks et al, 2016b). Biodiversity can be measured at different organizational levels – from genetic diversity to taxonomic (species) diversity, to landscape diversity Coupling these measures with community functional diversity (FD), which reflects the type, scope, and abundance of functional traits in communities provides a link between species diversity and ecosystem functioning (Tilman, 2001; Lavorel and Garnier, 2002; Díaz et al, 2007). The more detailed studies of functional and phylogenetic aspects of palaeo communities are relatively rare (e.g., Lacourse, 2009; Reitalu et al, 2015; Brussel et al, 2018; Carvalho et al, 2019; Jabłonska et al, 2019) and have demonstrated the great potential of functional and phylogenetic palaeodiversity to contribute to a better understanding of processes underlying long-term patterns of community assembly. Brussel et al (2018) showed that long-term fire frequency variations may drive directional selection for fire– adapted plant community attributes

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