A method for reconstructing temporal changes in vegetation functional trait composition using Holocene pollen assemblages

Abstract

Methods of reconstructing changes in plant traits over long time scales are needed to understand the impact of changing environmental conditions on ecosystem processes and services. Although Holocene pollen have been extensively used to provide records of vegetation history, few studies have adopted a functional trait approach that is pertinent to changes in ecosystem processes. Here, for woody and herbaceous fen peatland communities, we use modern pollen and vegetation data combined with pollen records from Holocene deposits to reconstruct vegetation functional dynamics. The six traits chosen (measures of leaf area-to-mass ratio and leaf nutrient content) are known to modulate species’ fitness and to vary with changes in ecosystem processes. We fitted linear mixed effects models between community weighted mean (CWM) trait values of the modern pollen and vegetation to determine whether traits assigned to pollen types could be used to reconstruct traits found in the vegetation from pollen assemblages. We used relative pollen productivity (RPP) correction factors in an attempt to improve this relationship. For traits showing the best fit between modern pollen and vegetation, we applied the model to dated Holocene pollen sequences from Fenland and Romney Marsh in eastern and southern England and reconstructed temporal changes in trait composition. RPP adjustment did not improve the linear relationship between modern pollen and vegetation. Leaf nutrient traits (leaf C and N) were generally more predictable from pollen data than mass-area traits. We show that inferences about biomass accumulation and decomposition rates can be made using Holocene trait reconstructions. While it is possible to reconstruct community-level trends for some leaf traits from pollen assemblages preserved in sedimentary archives in wetlands, we show the importance of testing methods in modern systems first and encourage further development of this approach to address issues concerning the pollen-plant abundance relationship and pollen source area.

What drives biodiversity patterns? Using long‐term multidisciplinary data to discern centennial‐scale change

“…The specific combinations of taxa driving diversity change and traits that condition 'success' or 'failure' to persist also require exploration alongside diversity, as interpreting diversity indices alone may mask the decline or loss of key taxa or functional types (e.g. Carvalho et al, 2019;Davies, 2016;Reitalu et al, 2015). More detailed analysis of species characteristics or traits is needed, which will be addressed in future work on the combined analyses of pollen and archaeobotanical data, which provide information about the scale and intensity of land use (Treasure et al, 2019) This has potential to provide answers to questions about the way in which these factors shaped plant assemblages, which can facilitate more efficient communication across palaeo-and neo-ecology and conservation.…”

Coastal peat‐beds and peatlands of the southern North Sea: their past, present and future

“…Here, palaeoecological evidence has the potential to provide information about how different plant traits affect the rates of delivery of ecosystem processes through time. Numerical techniques are being developed that link plant functional information to pollen data (Reitalu et al ., 2015) so that inferences about ecosystem properties such as biomass accumulation and decomposition rates can be made using Holocene pollen‐based trait reconstructions from fen deposits (Carvalho et al ., 2019 b ).…”

Changes in functional, phylogenetic and taxonomic diversities of lowland fens under different vegetation and disturbance levels

“…Cuttings were collected and removed from sites under mechanised mowing. See Carvalho et al (2019a;2019b) and Waller et al (2017) for further details of the sites.…”