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.
Highlights
Recent studies have highlighted the importance of gaining a long-term perspective on the response of ecosystems to environmental change [1, 2]
The community weighted mean (CWM) of leaf traits calculated from the modern vegetation in the 136 plots showed higher variability (y axis in Figs 2 and 3) than the CWMs calculated from the contemporary pollen taxa (x axis in Figs 2 and 3)
Understanding temporal changes in leaf traits with links to ecosystem processes and the competitive ability of species allows for the interpretation of changes in ecosystem functioning and community structure over time
Summary
Recent studies have highlighted the importance of gaining a long-term perspective on the response of ecosystems to environmental change [1, 2]. Such a perspective is crucial to help parameterise numerical models, which would improve ecological predictions and help develop better-informed conservation strategies. Key plant traits (e.g., leaf structure and nutrient content) influence species’ fitness and performance [14] and affect ecosystem processes [15, 16] and services [17, 18]. The implications for ecosystem processes (e.g., biogeochemical cycling) are evident as leaf construction and nutrient content will regulate the amount of recalcitrant compounds (e.g., lignin) of dead litter decomposing in the soil [21,22,23], influencing microbial activity and organic matter mineralisation and accumulation rates [24, 25]
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